U.S. patent number 5,635,533 [Application Number 08/470,229] was granted by the patent office on 1997-06-03 for methods for inducing differentiation of a cell using phenyacetic acid and derivatives.
This patent grant is currently assigned to The United States of America as represented by the Department of Health. Invention is credited to Dvorit Samid.
United States Patent |
5,635,533 |
Samid |
June 3, 1997 |
Methods for inducing differentiation of a cell using phenyacetic
acid and derivatives
Abstract
Compositions and methods of treating anemia, cancer, AIDS, or
severe .beta.-chain hemoglobinopathies by administering a
therapeutically effective amount of phenylacetate or
pharmaceutically acceptable derivatives thereof or derivatives
thereof alone or in combination or in conjunction with other
therapeutic agents. Pharmacologically-acceptable salts alone or in
combinations and methods of preventing AIDS and malignant
conditions, and inducing cell differentiation are also aspects of
this invention.
Inventors: |
Samid; Dvorit (Rockville,
MD) |
Assignee: |
The United States of America as
represented by the Department of Health (Washington,
DC)
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Family
ID: |
26833541 |
Appl.
No.: |
08/470,229 |
Filed: |
June 6, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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135661 |
Oct 12, 1993 |
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779744 |
Oct 21, 1991 |
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Current U.S.
Class: |
514/538; 514/563;
514/567 |
Current CPC
Class: |
A61K
31/20 (20130101); A61K 45/06 (20130101); A61K
31/365 (20130101); A61K 31/70 (20130101); A61K
31/192 (20130101); A61K 31/19 (20130101); A61K
31/35 (20130101); A61K 31/7072 (20130101); A61P
35/00 (20180101); A61K 31/7076 (20130101); A61K
31/365 (20130101); A61K 31/19 (20130101); A61K
31/35 (20130101); A61K 31/19 (20130101); A61K
31/20 (20130101); A61K 31/19 (20130101); A61K
31/19 (20130101); A61K 31/19 (20130101); A61K
31/19 (20130101); A61K 31/17 (20130101); A61K
31/19 (20130101); A61K 31/015 (20130101); A61K
31/19 (20130101); A61K 2300/00 (20130101); A61K
31/20 (20130101); A61K 2300/00 (20130101); A61K
31/35 (20130101); A61K 2300/00 (20130101); A61K
31/365 (20130101); A61K 2300/00 (20130101); A61K
31/70 (20130101); A61K 2300/00 (20130101); A61K
31/7072 (20130101); A61K 2300/00 (20130101); A61K
31/7076 (20130101); A61K 2300/00 (20130101); Y10S
514/886 (20130101); Y10S 514/885 (20130101); Y10S
514/928 (20130101) |
Current International
Class: |
A61K
31/35 (20060101); A61K 31/7042 (20060101); A61K
31/70 (20060101); A61K 31/7072 (20060101); A61K
31/7076 (20060101); A61K 38/22 (20060101); A61K
45/06 (20060101); A61K 38/21 (20060101); A61K
45/00 (20060101); A61K 31/192 (20060101); A61K
31/19 (20060101); A61K 31/185 (20060101); A61K
31/20 (20060101); A61K 31/365 (20060101); A01N
037/12 (); A01N 037/44 (); A61K 031/24 () |
Field of
Search: |
;514/538,563,567 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
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.nu.-globin Synthesis in a Patient with .beta..sup.+ Thalassemia",
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Michael B. Sporn, et al., "Chemoprevention of Cancer with
Retinoids", Federation Proceedings, vol. 38:2528-2534 (Oct. 1979).
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Richard L. Momparler, et al., "Clinical Trial on
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I. Bernard Weinstein, "Cancer Prevention: Recent Progress and
Future Opportunities", Cancer Research, vol. 51:5080s-5085s (1991).
.
Olli Simell, et al, "Waste Nitrogen Excretion Via Amino Acid
Acylation: Benzoate and Phenylacetate in Lysinuric Protein
Intolerance", Pediatr. Res., vol. 20:1117-1121 (1986). .
Neish, et al., "Phenylacetic Acid as a Potential Therapeutic Agent
for the Treatment of Human Cancer", Experentia, vol. 27:860-861
(1971). .
J.A. Stamatoyannopoulos, et al., "Therapeutic Approaches to
Hemoglobin Switching in Treatment of Hemoglobinopathies", Annu.
Rev. Med., vol. 43:497-521 (1992). .
Dvorit Samid, et al., "Selective Growth Arrest and Phenotypic
Reversion of Prostate Cancer Cells In Vitro by NonToxic
Pharmacological Concentrations of Phenylacetate", The Journal of
Clinical Investigation, vol. 91: 2288-2295 (1993). .
Dvorit Samid, et al., "Induction of Erythroid Differentiation and
Fetal Hemoglobin Production in Human Leukemic Cells Treated with
Phenylacetate", Journal of the Amiercan Society of Hematology, vol.
80:1576-1581 (1992). .
Dvorit Samid, et al., "Phenylacetate: A Novel Nontoxic Inducer of
Tumor Cell Differentiation", Cancer Research, vol. 52:1988-1992
(1992). .
George J. Dover, et al., "Increased Fetal Hemoglobin in Patients
Receiving Sodium 4-Phenylbutyrate", The New England Journal of
Medicine, vol. 327:569-570 (1992). .
Burzynski, S.R. et al., Preclinical Studies on antineoplaston As2-1
and Antineoplaston AS2-5, Drugs Exptl. Clin. Res., Supplemental 1,
XII:11-16 (1986). .
Leary, Cancer Drug Also Helps in Treating Sickle Cell Anemia,
Researchers Say, Atlanta Journal-Constitution, Thursday, Aug. 20,
1992. .
Smigel, K., "Non-toxic drug being tested to treat cancer and
anemias [news]", J. Natl. Cancer Inst., 84(18):1398 (Sep. 16,
1992). .
Ross, Philip D. and Subramanian, S., Inhibition of sickle cell
hemoglobin gelation by some aromatic compounds, Biochem. Biophys.
Res. Commun., 77:1217-1223 (1977). .
Jones, G.L., Anti sickling effects of Betw Di
Ethylaminoethylidiphenylpropyl acetate SFK-525-A, Pharmacologist,
20(3):204 (1978). .
Erhum, Wilson O., Acetonyl esters of hydroxybenzoic acids as
potential antisickling agents, Niger. J. Pharm., 12:285-287 (1981).
.
Abemayor, E. et al., Effects of retinoic acid on the in vivo growth
of human neuroblastoma cells, Cancer Lett. (Netherlands),
70(1-2):15-24 (Jun. 15, 1993). .
Cinatl, J. et al., In vitro differentiation of human neuroblastoma
cells induced by sodium phenylacetate, Cancer Lett. (Netherlands),
70(1-2):15-24 (Jun. 15, 1993). .
Gorski, G.K. et al., Synergistic inhibition of human
rhabdomyosarcoma cells by sodium phenylacetate and tretinoin, In
Vitro Cell. Dev. Biol., 29A:189-191 (Mar. 1993)..
|
Primary Examiner: Nutter; Nathan M.
Attorney, Agent or Firm: Needle & Rosenberg, P.C.
Parent Case Text
This application is a division of application Ser. No. 08/135,661,
filed on Oct. 12, 1993 which is, in turn, is a Continuation-In-Part
of Applicant's copending U.S. Ser. No. 07/779,744, filed Oct. 21,
1991, the contents of which are hereby incorporated by reference.
Claims
I claim:
1. A method of inducing the differentiation of a cell comprising
administering to the cell a differentiation inducing amount of a
compound of the formula I: ##STR3## wherein R.sub.0 is aryl,
phenoxy, substituted aryl or substituted phenoxy;
R.sub.1 and R.sub.2 are, independently, H, hydroxy, lower alkoxy,
lower straight or branched chain alkyl or halogen;
R.sub.3 and R.sub.4 are, independently, H, lower alkoxy, lower
straight or branched chain alkyl or halogen; and
n is an integer from 0 to 2;
pharmaceutically-acceptable salt thereof or a mixture thereof.
2. The method of claim 1, wherein the compound is sodium
phenylacetate.
3. The method of claim 1, wherein the compound is sodium
phenylbutyrate.
4. The method of claim 1, wherein the differentiation inducing
amount is from 50 to 1000 mg/kg/day.
5. The method of claim 1, wherein the differentiation inducing
amount is from 300 to 500 mg/kg/day.
6. The method of claim 1, wherein the differentiation inducing
amount is from 150 to 250 mg/kg/day.
7. The method of claim 1, wherein R.sub.0 is aryl or phenoxy, the
aryl and phenoxy being unsubstituted or substituted with,
independently, one or more halogen, hydroxy or lower alkyl;
R.sub.1 and R.sub.2 are independently H, lower alkoxy, hydroxy,
lower alkyl or halogen; and
R.sub.3 and R.sub.4 are independently H, lower alkyl, lower alkoxy
or halogen;
a pharmaceutically-acceptable salt thereof, or a mixture
thereof.
8. The method of claim 1, wherein
R.sub.0 is phenyl, naphthyl, or phenoxy, the phenyl, naphthyl and
phenoxy being unsubstituted or substituted with, independently, one
or more moieties of halogen, hydroxy or lower alkyl.
9. The method of claim 1, wherein
R.sub.0 is phenyl, naphthyl, or phenoxy, the phenyl, naphthyl and
phenoxy being unsubstituted or substituted with, independently,
from 1 to 4 moieties of halogen, hydroxy or lower alkyl of from 1
to 4 carbon atoms;
R.sub.1 and R.sub.2 are, independently, H, hydroxy, lower alkoxy of
from 1 to 2 carbon atoms, lower straight or branched chain alkyl of
from 1 to 4 carbon atoms or halogen; and
R.sub.3 and R.sub.4 are, independently, H, lower alkoxy of from 1
to 2 carbon atoms, lower straight or branched chain alkyl of from 1
to 4 carbon atoms or halogen.
10. The method of claim 1, wherein n is 0; R.sub.0 is aryl or
substituted aryl; R.sub.1 and R.sub.2 are H, lower alkoxy, or lower
alkyl; pharmaceutically-acceptable salts thereof, or mixtures
thereof.
11. The method of claim 1, wherein the compound is
.alpha.-methylphenylacetic acid, .alpha.-ethylphenylacetic acid,
.alpha.-hydroxyphenylacetic acid, .alpha.-methoxyphenylacetic acid,
1-naphthylacetic acid, 4-chlorophenylacetic acid,
4-iodophenylacetic acid, 4-fluorophenylacetic acid,
3-chlorophenylacetic acid, 2-chlorophenylacetic acid,
2,6-dichlorophenylacetic acid, 2-methylphenylacetic acid,
3-methylphenylacetic acid, 4-methylphenylacetic acid,
phenoxypropionic acid, 4-chlorophenylbutyric acid,
4-iodophenylbutyric acid, 4-fluorophenylbutyric acid,
3-chlorophenylbutyric acid, or 2-chlorophenylbutyric acid.
12. The method of claim 1, wherein the compound is administered
topically.
13. The method of claim 1, wherein the compound is applied at a
concentration of from about 0.1 mM to about 10 mM.
14. The method of claim 1, wherein the compound is administered
ocularly.
15. The method of claim 1, wherein the compound is administered
orally.
16. The method of claim 1, wherein the compound is administered in
the form of a suppository.
17. The method of claim 1, wherein the compound is administered
parenterally.
18. The method of claim 1, wherein the compound is administered
intermittently.
19. The method of claim 1, wherein the compound is administered
continuously.
20. The method of claim 1, wherein the cell is a prostatic
carcinoma cell, a glioma cell, an astrocytoma cell, an
adenocarcinoma cell, a melanoma cell, a lymphoma cell, a leukemia
cell, a breast cancer cell, an osteosarcoma cell, a fibrosarcoma
cell, a squamous cancer cell, a neuroblastoma cell, a non-small
cell lung cancer cell, a mesothelioma cell, a multiple myeloma
cell, a renal carcinoma cell, a Kaposi's sarcoma cell, or a
Lennert's T-Cell lymphoma cell.
21. The method of claim 1, wherein the cell is a benign
hyperplastic prostatic cell, a papilloma cell, or a myelodisplasic
cell.
Description
FIELD OF THE INVENTION
This invention relates to methods of using phenylacetic acid and
its pharmaceutically acceptable derivatives to treat and prevent
pathologies and to modulate cellular activities. In particular,
this invention relates to A) phenylacetate and its derivatives in
cancer prevention and maintenance therapy, B) phenylacetate and its
derivatives in the treatment and prevention of AIDS, C) induction
of fetal hemoglobin synthesis in .beta.-chain hemoglobinopathy by
phenylacetate and its derivatives, D) use of phenylacetic acid and
its derivatives in wound healing, E) use of phenylacetic acid and
its derivatives in treatment of diseases associated with
interleukin-6, F) use of phenylacetic acid and its derivatives in
the treatment of AIDS-associated CNS dysfunction, G) use of
phenylacetic acid and its derivatives to enhance
immunosurveillance, H) methods of monitoring the dosage level of
phenylacetic acid and its derivatives in a patient and/or the
patient response to these drugs, I) the activation of the PPAR by
phenylacetic acid and its derivatives, J) use of phenylacetic acid
and its derivatives in treatment of cancers having a multiple-drug
resistant phenotype, and K) phenylacetic acid and its derivatives,
correlation between potency and lipophilicity.
BACKGROUND OF THE INVENTION
Phenylacetic acid (PAA) is a protein decomposition product found
throughout the phylogenetic spectrum, ranging from bacteria to man.
Highly conserved in evolution, PAA may play a fundamental role in
growth control and differentiation. In plants, PAA serves as a
growth hormone (auxin) promoting cell proliferation and enlargement
at low doses (10.sup.-5 -10.sup.-7 M), while inhibiting growth at
higher concentrations. The effect on animal and human cells is less
well characterized. In humans, PAA is known to conjugate glutamine
with subsequent renal excretion of phenylacetylglutamine (PAG). The
latter, leading to waste nitrogen excretion, has been the basis for
using PAA or preferably its salt sodium phenylacetate (NaPA, also
referenced herein as that active anionic meoity, phenylacetate or
"PA") in the treatment of hyperammonemia associated with inborn
errors of ureagenesis. Clinical experience indicates that acute or
long-term treatment with high NaPA doses is well tolerated,
essentially free of adverse effects, and effective in removing
excess glutamine. [Brusilow, S. W., Horwich, A. L. Urea cycle
enzymes. Metabolic Basis of Inherited Diseases, Vol. 6:629-633
(1989)]. These characteristics should be of value in treatments of
cancer and prevention of cancer, treatments which inhibit virus
replication and treatments of severe beta-chain
hemoglobinopathies.
Glutamine is the major nitrogen source for nucleic acid and protein
synthesis, and a substrate for energy in rapidly dividing normal
and tumor cells. Compared with normal tissues, most tumors, due to
decreased synthesis of glutamine along with accelerated utilization
and catabolism, operate at limiting levels of glutamine
availability, and consequently are sensitive to further glutamine
depletion. Considering the imbalance in glutamine metabolism in
tumor cells and the ability of PAA to remove glutamine, PAA has
been proposed as a potential antitumor agent; however, no data has
previously been provided to substantiate this proposal. [Neish, W.
J. P. "Phenylacetic Acid as a Potential Therapeutic Agent for the
Treatment of Human Cancer", Experentia, Vol. 27, pp. 860-861
(1971)].
Despite these efforts to fight cancer, many malignant diseases that
are of interest in this application continue to present major
challenges to clinical oncology. Prostate cancer, for example, is
the second most common cause of cancer deaths in men. Current
treatment protocols rely primarily on hormonal manipulations.
However, in spite of initial high response rates, patients often
develop hormone-refractory tumors, leading to rapid disease
progression with poor prognosis. Overall, the results of cytotoxic
chemotherapy have been disappointing, indicating a long felt need
for new approaches to treatment of advanced prostatic cancer. Other
diseases resulting from abnormal cell replication, for example
metastatic melanomas, brain tumors of glial origin (e.g.,
astrocytomas), and lung adenocarcinoma, are also highly aggressive
malignancies with poor prognosis. The incidence of melanoma and
lung adenocarcinoma has been increasing significantly in recent
years. Surgical treatments of brain tumors often fail to remove all
tumor tissues, resulting in recurrences. Systemic chemotherapy is
hindered by blood barriers. Therefore, there is an urgent need for
new approaches to the treatment of human malignancies including
advanced prostatic cancer, melanoma, brain tumors.
The development of the methods and pharmaceuticals of the present
invention was guided by the hypothesis that metabolic traits that
distinguish tumors from normal cells could potentially serve as
targets for therapeutic intervention. For instance, tumor cells
show unique requirements for specific amino acids such as
glutamine. Thus, glutamine may be a desired choice because of its
major contribution to energy metabolism and to synthesis of
purines, pyrimidines, and proteins. Along this line, promising
antineoplastic activities have been demonstrated with
glutamine-depleting enzymes such as glutaminase, and various
glutamine antimetabolites. Unfortunately, the clinical usefulness
of these drugs has been limited by unacceptable toxicities.
Consequently, the present invention focuses on PAA, a plasma
component known to conjugate glutamine in vivo, and the
pharmaceutically acceptable derivatives of PAA.
In addition to its ability to bind gluatamine to form glutamine
phenylacetate, PAA can induce tumor cells to undergo
differentiation. (See examples 1-5, 7-9, 11-13, and 16 herein).
Differentiation therapy is a known, desirable approach for cancer
intervention. The underlying hypothesis is that neoplastic
transformation results from defects in cellular differentiation.
Inducing tumor cells to differentiate would prevent tumor
progression and bring about reversal of malignancy. Several
differentiation agents are known, but their clinical applications
have been hindered by unacceptable toxicities and/or deleterious
side effects.
Accordingly, the present invention provides methods and
compositions for treating various pathologies with PAA and its
pharmaceutically acceptable salts, derivatives, and analogs.
BRIEF SUMMARY OF THE INVENTION
The invention provides a method of treating various pathologies in
a subject. The invention also provides for the modulation of
various cellular activities in a subject. The pathologies and
cellular activities are treated and modulated utilizing a compound
having the formula: ##STR1## ; wherein R.sub.0 =aryl, phenoxy,
substituted aryl or substituted phenoxy;
R.sub.1 and R.sub.2 =H, lower alkoxy, lower straight and branched
chain alkyl or halogen;
R.sub.3 and R.sub.4 =H, lower alkoxy, lower straight and branched
chain alkyl or halogen; and
n=an integer from 0 to 2.
Specifically, the invention provides a method of treating or
preventing various neoplastic conditions. Relatedly, a method of
inducing differentiation of a cell is provided. The invention also
provides a method of inducing the production of fetal hemoglobin
and treating pathologies associated with abnormal hemoglobin
activity or production.
The invention also provides a method of treating or preventing a
viral infection in a subject. Relatedly, the invention provides a
method of treating an AIDS-associated dysfunction of the central
nervous system in a subject.
Also provided is a method of modulating the production of IL-6 or
TGF.alpha. and TGF-.beta.2 both in vitro and in vivo. Typically,
IL-6 and TGF-.beta.2 are inhibited while TGF.alpha. is induced.
The invention also provides a method of enhancing
immunosurveillance and promoting wound healing in a subject.
Also provided is a method of monitoring the bioavailability of a
compound for treatment of a pathology not associated with
hemoglobin. The method comprises administering to a subject the
compound and measuring the level of fetal hemoglobin TGF-.beta.2,
IL-6 or TGF.alpha..
Finally, a method of treating a neoplastic condition in cells
resistant to radiation and chemotherapy is provided. Specifically,
multiple drug resistant cells are particularly sensitive to the
compounds of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the inhibition of HL-60 leukemia and premalignant
10T1/2 cell proliferation by NaPA.
FIG. 2 shows the induction of HL-60 cell differentiation. The
number of NBT positive cells was determined after 4 [solid bars] or
7 days [hatched bars] of treatment. NaPA (h), 1.6 mg/ml; NaPA (1),
0.8 mg./ml. 4-hydroxyphenylacetate and PAG were used at 1.6 mg./ml.
Potentiation by RA 10 nM was comparable to that by IFN gamma 300
IU/ml, and the effect of acivicin 3 .mu.g/ml similar to DON 30
.mu.g/ml. Glutamine Starvation (Gln, <0.06 mM) was as described.
Cell viability was over 95% in all cases, except for DON and
acivicin (75% and 63%, respectively).
FIG. 3A shows adipocyte conversion in 10T1/2 cultures.
FIG. 4 shows NaPA's ability to invoke growth arrest of human
glioblastoma cells. Dose-dependent inhibition of human glioblastoma
cell proliferation by sodium phenylacetate. Growth rates were
determined, after 4-5 days of continuous treatment, by an enzymatic
assay using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltertrazolium
bromide and confirmed by cell enumeration with a hemocytometer.
Reduction in cell number paralleled changes in de novo DNA
synthesis (not shown).
FIG. 5 shows selective cytostasis induced by phenylacetate (5 mM)
combined with glutamine starvation (0.2 mM glutamine, i.e., 2-3
fold below the normal plasma levels). The results indicate
increased vulnerability of glioblastoma A172 when compared to
actively replicating normal human umbilical vein endothelial cells
(HUVC). Cell viability was over 95% in all cases.
FIG. 6 shows that phenylacetate inhibits the mevalonate pathway of
cholesterol synthesis in glioblastoma cells. FIG. 6 shows key steps
of the MVA pathway discussed in text.
FIG. 7 shows the selective inhibition of cholesterol synthesis from
mevalonate in phenylacetate-treated glioblastoma U87 cells, and
enzymatic inhibition of mevalonate decarboxylation in cell
homogenates. For analysis of steroid synthesis, logarithmically
growing cells were labeled with tritiated MVA in the presence or
absence of 5 mM phenylacetate, and their steroids were separated by
silica thin layer chromatography. MVA decarboxylation was measured
in cell homogenates. The effect of phenylacetate on cholesterol
synthesis and MVA decarboxylation was selective as, under the
experimental conditions used, total protein and DNA synthesis
levels were unaffected.
FIG. 8 shows the effects of phenylacetate on rate of proliferation
after in vitro exposure of 9L tumor cells to various concentrations
of phenylacetate for 5 days. Significant decline in DNA-synthesis
was observed. Data are expressed as means.+-.S.D. counts per minute
(cpm).
FIG. 9 shows the treatment with phenylacetate from the day of
intracerebral tumor inoculation extended survival compared with
treatment with saline (p<0.01; Mantel-Haenzel test).
FIG. 10 shows the treatment of established tumors with
phenylacetate extended survival compared to treatment with saline
(p<0.03; Mantel-Haenzel test).
FIG. 11 shows the effect of NaPA on cell proliferation. PC3; DU145;
LNCaP; and FS4 cultures were treated with NaPA or PAG for four
days.
FIG. 12 shows a chromatogram of phenylacetate (PA) and
phenylacetylglutamine (PAG). The peaks at 9.8 and 17.1 minutes
represent PAG and PA, respectively. Serum concentrations of 250
.mu.g/ml in both instances.
FIG. 13 shows serum concentrations of PA ( ) and PAG ( ) and plasma
concentrations of glutamine ( ) following a 150 mg/kg i.v. bolus of
PA over 2 hours.
FIG. 14 shows declining phenylacetate concentrations over time
during CIVI (250 mg/kg/day) in one patient, suggestive of clearance
induction.
FIG. 15 shows the inhibition of tumor cell invasion by NaPA cells
treated in culture for seven (7) days which were harvested and
assayed for their invasive properties using a modified Boyden
Chamber with a matrigel-coated filter. Results were scored six (6)
to twenty-four (24) hours later.
FIG. 16 shows a simulation of a q 12 hour PA regimen (200
mg/kg/dose, 1 hour infusion) in a pharmacokinetically average
patient. For simplicity, induction of clearance was not factored
in.
FIG. 17 shows the effect of NaPA on cell growth and
differentiation. (.smallcircle.) Total cell number and (.cndot.)
the fraction of benzidine-positive cells were determined after 4
days of continuous treatment. Data represent means.+-.SD (n=4).
Cell viability was greater than 95%.
FIGS. 18A and 18B show the time-dependent changes in cell
proliferation and Hb production. NaPA (5 mM) was added on days 2,
4, 6, and 8 of phase II cultures derived from normal donorsl, and
the cells were analyzed on day 13. Panel 18A: Nubmer of
Hb-containing cells per ml (.times.10.sup.-1), and the amounts of
Hb (pg) per cell (MCH). Panel 18B: Total Hb (pg) per ml culture,
and the proportion of HbF out of total Hb (% HbF). Data points
represent the means of four determinations. The deviation of
results of each determination from the mean did not exceed 10%.
NaPB at 2.5 mM produced comparable effects (not shown). In all
cases, cell viability was over 95%.
FIG. 19 shows the effect of NaPA on the proportions of Hb species
in cultured erythroid precursors derived from a patient with sickle
cell anemia. NaPA was added to 7 day phase II cultures. The cells
were harvested and lysed on day 13, and the proportions of HbF,
HbA.sub.2, and HbS were determined following separation on cation
exchange HPLC.
FIG. 20 shows the increased production of TGF-.alpha. by human
keratinocytes upon treatment with NaPA and NaPB. Epithetial HK5
cells were treated with NaPB (3.0 mM, 1.5 mM, 0.75 mM), NaPB (10
mM, 5.0 mM, 2.5 mM) and PAG (5 mM) continuously for 4 days.
Untreated cells served as a control. The amount of TGF-.alpha.
(ng/ml/10.sup.6 cells) was measured by using anti-TGF-.alpha.
antibodies.
FIG. 21 shows the enhanced expression of the surface antigens W6/32
(MHC class I), DR (MHC class II) and ICAM-1 in melanoma cells
treated with NaPB. Melanoma 1011 cells were treated with 2 mM PB
for 10 days. Treatment was discontinued for 3 days to document the
stability of the effect. FACS analysis revealed markedly increased
expression of the antigens following treatment (shaded area); the
expression of the surface antigens was similar or slightly greater
on day 13 than on day 10, indicating that PB induced terminal
differentiation.
FIG. 22 shows the activation of the Peroxisomal Proliferator
Receptor (PPAR) by PA, PB and various phenylacetic acid analogs.
The activation is measured by the increased production of the
indicator gene for cloramphenicol acetyl transferase (CAT), which
is controlled by the response element for acyl-CoA oxidase,
relative to the control (C). The experimental details this
activation measurement method can be found in Sher et al.,
Biochem., 32(21):5598 (1993)). The concentration (in mM) of a
particular drug is noted next to the following symbols for the
various drugs: CF=clofibrate, PA=phenylacetate,
CP=chlorophenylacetate, PB=phenylbutyrate,
CPB=chlorophenylbutyrate, PAG=phenylacetylglutamine,
IPB=iodophenylbutyrate, B=butyrate, IAA=indole acetic acid,
NA=naphthylacetate, PP=phenoxypropionic acid,
2-4D=2,4-dichlorophenoxy acetate.
FIG. 23 shows the modulation by phenylbutyrate of glutathione
(GSH), gamma-glutamyl transpeptidase (GGT) and catalase activites.
The antioxidant capacity (mM or units/mg protein) of the enzymes
were measured for up to approximately 100 hours following treatment
of prostatic PC3 cells with 2 mM NaPB.
FIG. 24 shows the radiosensitization by PA and PB of human
glioblastoma U87 cells by pretreatment for 72 hours with 1, 3 and 5
mM PA and 2.5 mM PB prior to exposure to ionizing radiation
(Co.sup.60 .gamma.-radiaition).
FIG. 25 shows the inhibition of the growth of breast MCF-7
adriamycin-resistant cancer cells by continuous exposure of up to
10 mM PA for 4 days.
FIG. 26 shows the relationship between lipophilicity and the
cytostasis induced by phenylacetate derivatives in prostate
carcinoma cells and in plants. The log 1/IC.sub.50 values for
prostatic cells (calculated from data presented in Table 21), were
compared with the 1/IC.sub.50 for rapidly developing plant tissues.
Tested compounds, listed in an increasing order of their CLOGPs,
included 4-hydroxy-PA, PA, 4-fluoro-PA, 3-methyl-PA, 4-methyl-PA,
4-chloro-PA, 3-chloro-PA, and 4-iodo-PA.
FIG. 27 the phenotypic reversion induced by phenylacetate and
selected derivatives. The malignant prostatic PC3 cells were
treated as described in "Material and Methods". Data indicates the
relative potency of tested compounds in significantly inhibiting
PC3 anchorage-independence 27(A) and completely blocking matrigel
invasion 27(B). Phenylacetate and analogs are presented in an
increasing order of CLOGP (top to bottom). CLOGP values are
provided in Tables 21 and 22. The effect on anchorage-dependency
was confirmed with U87 cells (not shown).
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term "phenylacetic acid derivative" (or
"phenylacetic acid analog") refers to a compound of the formula:
##STR2## ; wherein R.sub.0 is aryl (e.g., phenyl, napthyl),
phenoxy, substituted aryl (e.g., one or more halogen [e.g., F, Cl,
Br, I], lower alkyl [e.g., methyl, ethyl, propyl, butyl] or hydroxy
substituents) or substituted phenoxy (e.g., one or more halogen
[e.g., F, Cl, Br, I], lower alkyl [e.g., methyl, ethyl, propyl,
butyl] or hydroxy substituents);
R.sub.1 and R.sub.2 are each H, lower alkoxy (e.g., methoxy,
ethoxy), lower straight and branched chain alkyl (e.g., methyl,
ethyl, propyl, butyl) or halogen (e.g., F, Cl, Br, I);
R.sub.3 and R.sub.4 are each H, lower straight and branched chain
alkyl (e.g., methyl, ethyl, propyl, butyl), lower alkoxy (e.g.,
methoxy, ethoxy) or halogen (e.g., F, Cl, Br, I); and
n is an integer from 0 to 2;
salts thereof (e.g., Na.sup.+, K.sup.+ or other pharmaceutically
acceptable salts); stereoisomers thereof; and mixtures thereof.
When n is equal to 2, each of the two R.sub.3 substituents and each
of the two R.sub.4 substituents can vary independently within the
above phenylacetic acid derivative definition. It is indended that
this definition includes phenylacetic acid (PAA) and phenylbutyric
acid (PBA). Mixtures according to this definition are intended to
include mixtures of carboxylic acid salts, for instance, a mixture
of sodium phenylacetate and potassium phenylacetate. Because the
carboxylic portion of these compounds is the primarily active
portion, references herein to a carboxylate, such as phenylacetate
(PA) or phenylbutyrate (PB), are intended to refer also to an
appropriate counter cation, such as Na.sup.+, K.sup.+ or another
pharmaceutically acceptable cation such as an organic cation (e.g.,
arginine). Thus, as used herein, a PA or PB derivative or analog
refers to the phenylacetic acid derivatives of this definition.
Some of these derivatives can be interconverted when present in a
biological system. For instance, PA can be enzymatically converted
to PB within an animal and, similarly, PB can be converted to
PA.
Thus, phenylacetic acid derivatives include, without limitation,
phenylacetic acid, phenylpropionic acid, phenylbutyric acid,
1-naphthylacetic acid, phenoxyacetic acid, phenoxypropionic acid,
phenoxybutyric acid, 4-chlorophenylacetic acid,
4-chlorophenylbutyric acid, 4-iodophenylacetic acid,
4-iodophenylbutyric acid, .alpha.-methylphenylacetic acid,
.alpha.-methoxyphenylacetic acid, .alpha.-ethylphenylacetic acid,
.alpha.-hydroxyphenylacetic acid, 4-fluorophenylacetic acid,
4-fluorophenylbutyric acid, 2-methylphenylacetic acid,
3-methylphenylacetic acid, 4-methylphenylacetic acid,
3-chlorophenylacetic acid, 3-chlorophenylbutyric acid,
2-chlorophenylacetic acid, 2-chlorophenylbutyric acid and
2,6-dichlorophenylacetic acid, and the sodium salts of the these
compounds.
The compounds of the present invention can be administered
intravenously, enterally, parenterally, intramuscularly,
intranasally, subcutaneously, topically or orally. The dosage
amounts are based on the effective inhibitory concentrations
observed in vitro and in vivo in antitumorigenicity studies. The
varied and efficacious utility of the compounds of the present
invention is further illustrated by the findings that they may also
be administered concomitantly or in combination with other
antitumor agents (such as hydroxyurea, 5-azacytidine,
5-aza-2'-deoxycytidine, and suramin); retinoids; hormones;
biological response modifiers (such as interferon and hematopoietic
growth factors); and conventional chemo- and radiation therapy or
various combinations thereof.
The present invention also provides methods of inducing tumor cell
differentiation in a host comprising administering to the host a
therapeutically effective amount of PAA or a pharmaceutically
acceptable derivative thereof.
The present invention also provides methods of preventing the
formation of malignancies by administering to a host a
prophylactically effective amount of PAA or a pharmaceutically
acceptable derivative thereof.
The present invention also provides methods of treating malignant
conditions, such as prostatic cancer, melanoma, adult and pediatric
tumors, e.g., brain tumors of glial origin, astrocytoma, Kaposi's
sarcoma, lung adenocarcinoma and leukemias, as well as hyperplastic
lesions, e.g., benign hyperplastic prostate and papillomas by
administering a therapeutically effective amount of PAA or a
pharmaceutically acceptable derivative thereof.
In addition, the present invention provides methods of treating
conditions such as neuroblastoma, promyelocytic leukemia,
myelodisplasia, glioma, prostate cancer, breast cancer, melanoma,
and non-small cell lung cancer.
It is understood that the methods and compositions of this
invention can be used to treat animal subjects, including human
subjects.
According to the present invention, phenylacetic acid derivatives,
and in particular NaPA and NaPB, have been found to be excellent
inhibitors of the growth of specific tumor cells, affecting the
proliferation of the malignant cells while sparing normal tissues.
Also, according to the present invention, NaPA and its analogs have
been found to induce tumor cell differentiation, thus offering a
very desirable approach to cancer prevention and therapy.
Additionally, NaPA and its analogs have been found to be of value
for the treatment of viral indications such as AIDS. NaPA is also
implicated in the treatment of severe beta-chain
hemoglobinopathies. The exact mechanisms by which the compounds
used in the methods of this invention exert their effects are
uncertain. One potential mechanism may involve depletion of plasma
glutamine. Based on the data reported herein, it is believed that
glutamine depletion alone cannot explain the molecular and
phenotypic changes observed in vitro following exposure to NaPA. It
will be understood, however, that the present invention is not to
be limited by any theoretical basis for the observed results.
EXAMPLES
The herein offered examples, including experiments, provide methods
for illustrating, without any implied limitation, the practice of
this invention focusing on phenylacetic acid and its derivatives
directed to A. Cancer therapy and prevention; B. Treatment and
prevention of AIDS; C. Induction of fetal hemoglobin synthesis in
.beta.-chain hemoglobinopathies; D. Use of phenylacetic acid and
its derivatives in wound healing; E. Use of phenylacetic acid and
its derivatives in treatment of diseases associated with
interleukin-6; F. Use of phenylacetic acid and its derivatives in
the treatment of AIDS-associated CNS dysfunction; G. Use of
phenylacetic acid and its derivatives to enhance
immunosurveillance; H. Method of monitoring the dosage level of
phenylacetic acid and its derivatives in a patient and/or the
patient's response to these drugs; I. The activation of the PPAR by
phenylacetic acid and its derivatives; J. Use of phenylacetic acid
and its derivatives in treatment of cancers having a multiple-drug
resistant phenotype; and K. phenylacetic acid and its derivatives,
correlation between potency and lipophilicity.
SECTION A: PHENYLACETATE IN CANCER PREVENTION AND MAINTENANCE
THERAPY
Recent advances in molecular techniques enable the detection of
genetic disorders associated with a predisposition to cancer.
Consequently, it is now possible to identify high-risk individuals
as well as patients in a state of remission but afflicted with a
residual disease. Despite such remarkable capabilities, there is
still no acceptable preventive treatment. Chemopreventive drugs are
also needed for adjuvant therapy, to minimize the carcinogenic
effects of the prevailing anticancer agents and yet maintain tumor
responses.
To qualify for use in chemoprevention, a potential drug should have
antitumor activities, be non-toxic and well tolerated by humans,
easy to administer (e.g., orally or intravenously), and
inexpensive. We suggest that NaPA possesses all of the above
characteristics.
1. Prevention of Neoplastic Transformation--Oncogene Transfer
Studies
NIH 3T3 cells carrying activated Ejras oncogene (originally
isolated from human bladder carcinoma) were used as a model to
study the potential benefit of NaPA treatment to high risk
individuals, in whom predisposition is associated with oncogene
activation. Cell treatment with NaPA was initiated 24-48 hours
after oncogene transfer. Results, scored 14-21 days later, show
dose-dependent reduction in the formation of ras-transformed foci
in cultures treated with NaPA. Molecular analyses indicated that
the drug did not interfere with oncogene uptake and transcription,
but rather prevented the process of neoplastic transformation. The
effect was reversible upon cessation of treatment. In treated
humans, however, the fate of the premalignant cells may be
substantially different due to involvement of humoral and cellular
immunity (see discussion below).
2. Prevention of tumor progression by genotoxic chemotherapy
Current approaches to combat cancer rely primarily on the use of
chemicals and radiation, which are themselves carcinogenic and may
promote recurrences and the development of metastatic disease. One
example is the chemotherapeutic drug 5-aza-2'-deoxycytidine
(5AzadC). While this drug shows promise in treatment of some
leukemias and severe inborn anemias, the clinical applications have
been hindered by concerns regarding toxicity and carcinogenic
effects. However, for the first time the data indicate that NaPA
can prevent tumor progression induced by treatment with 5AzadC.
The experimental model involved nonmalignant 4C8a10 cells
(revertants of Ha-ras-transformed NIH 3T3 fibroblasts). Transient
treatment of the premalignant cells with 5AzadC resulted in
malignant conversion evident within 2 days, as determined by cell
morphology, loss of contact inhibition and anchorage dependent
growth in culture, and acquired invasive properties and
tumorigenicity in recipient athymic mice. Remarkably, NaPA
prevented the development of these malignant phenotypes in the
5AzadC treated cultures (Table 1).
TABLE 1 ______________________________________ Tumor
Formation.sup.a Growth Treatment Incidence Size (mm) on
matrigel.sup.b ______________________________________ None 3/8 1
(0.5-2) - 5AzadC (0.1 uM) 8/8 11.5 (4-19) + NaPA (1.5 mg/ml) 0/8 -
5AzadC + NaPA 0/8 0 - (0.1 uM) (1.5 mg/ml)
______________________________________ .sup.a Cells pretreated in
culture were injected s.c. (5 .times. 10.sup.5 cells per site) into
3 month old female athymic nude mice (Division of Cancer Treatment,
NCI Animal Program, Frederick Cancer Research Facility) Results
indicate the incidence (tumor bearing/injected animals), as well as
tumor size as mean (range), determined after 3 weeks. .sup.b Cells
were plated on top of matrigel (reconstituted basement membrane)
and observed for malignant growth pattern, i.e., active
replication, development of characteristic processes, and
invasion.
3. Activity in Humans.
In terms of cancer prevention, the beneficial effect of NaPA to
humans may be even more dramatic than that observed with the
experimental models. In humans, NaPA is known to deplete
circulating glutamine, an amino acid critical for the development
and progression of cancer. The enzymatic reaction leading to
glutamine depletion takes place in the liver and kidney. It is not
clear whether or not glutamine depletion occurs in the cultured
tumor cells. Moreover, molecular analysis revealed that NaPA
induced the expression of histocompatibility class I antigens,
which are localized on the surface of tumor cells and affect the
immune responses of the host. While the therapeutic benefit of NaPA
observed in cultures is in some cases reversible upon cessation of
treatment, in patients the residual tumor cells would eventually be
eliminated by the immune system. Even if chemoprevention will
require continuous treatment with NaPA, such treatment would be
acceptable considering the lack of toxicity.
Pharmaceutical compositions containing phenylacetate have been
shown to cause reversal of malignancy and to induce differentiation
of tumor cells. To demonstrate the capacity of drugs to induce
differentiation of tumor cells, three in vitro differentiation
model systems and one in vivo phase I clinical trial were used
(further described herein). The first system used a human
promyelocytic leukemia cell line HL-60. This cell line represents
uncommitted precursor cells that can be induced to terminally
differentiate along the myeloid or monocytic lineage. In the second
system, immortalized embryonic mesenchymal C3H 10T1/2 cells were
used which have the capability of differentiating into myocytes,
adipocytes, or chondrocytes. In the third system, human
erythroleukemia K562 cells were used because they can be induced to
produce hemoglobin. Finally, the in vivo experiments demonstrated
the efficacy of NaPA in inducing terminal differentiation in humans
and animals.
NaPA and NaPB have also been shown to affect tumor growth in vitro
and in animal models at pharmacological, non-toxic concentrations.
These aromatic fatty acids induced cytostasis and promoted
maturation of various human malignant cells, including
hormone-refractory prostatic carcinoma, glioblastoma, malignant
melanoma, and lung carcinoma. The marked changes in tumor biologoy
were associated with alterations in the expression of genes
implicated in tumor growth, invasion, anglogenesis, and
immunogenicity. Multiple mechansims of drug action appear to be
involved. These mechanisms include (a) modification of lipid
metabolism, (b) regulation of gene expression through DNA
hypomethylation and transcriptional activation, and (c) inhibition
of protein isoprenylation. Phase I clinical trials confirmed the
efficacy of these novel, nontoxic differentiation inducers (see
Example 15).
EXAMPLE 1
HL-60 and 10T1/2 cells--PAG and NaPA treatment
Referring now to the data obtained using the first system (results
illustrated in FIG. 1), logarithmically growing HL-60 [--.cndot.--]
and 10T1/2 [--.smallcircle.--] cells were treated for four days
with NaPA [solid line] or phenylacetylglutamate (PAG) [dashed
line]. The adherent cells were detached with trypsin/EDTA and the
cell number determined using a hemocytometer. Data points indicate
the mean.+-.S.D. of duplicates from two independent experiments.
The cell lines were obtained from the American Type Culture
Collection and maintained in RPMI 1640 (HL-60) or Dulbecco's
Modified Eagle's Medium (10T1/2) supplemented with 10% heat
inactivated fetal calf serum (Gibco Laboratories), 2 mM
L-Gtutamine, and antibiotics. PAA (Sigma, St. Louis Mo.) and PAG
were each dissolved in distilled water, brought to pH 7.0 by the
addition of NaOH, and stored in -20.degree. C. until used. As
demonstrated in FIG. 1, NaPA treatment of the HL-60 and 10T1/2
cultures was associated with dose dependent inhibition of cell
proliferation.
EXAMPLE 2
HL-60 cells--induction of granulocyte differentiation
To further evaluate the effectiveness of NaPA as an inducer of
tumor cell differentiation, the ability of NaPA to induce
granulocyte differentiation in HL-60 was investigated. The ability
of cells to reduce nitroblue tetrazolium (NBT) is indicative of
oxidase activity characteristic of the more mature forms of human
bone marrow granulocytes. NBT reduction thus serves as an indicator
of granulocyte differentiation. In FIG. 2, the number of NBT
positive cells was determined after 4 days [solid bars] or 7 days
[hatched bar] of treatment. NaPA (h), 1.6 mg/ml; NaPA (1), 0.8
mg/ml. 4-hydroxyphenylacetate (4HPA) and PAG were used at 1.6
mg/ml. Potentiation by retinoic acid (RA) 10 nM was comparable to
that by interferon gamma 300 IU/ml. The direction of
differentiation towards granulocytes in cultures treated with NaPA,
whether used alone or in combination with RA, was confirmed by
microscopic evaluation of cells stained with Wright Stain and the
lack of nonspecific esterase activity. The effect of acivicin (ACV)
1 .mu.g/ml was similar to 6-diazo-5-oxo-L-norleucine (DON) 25
.mu.g/ml. Glutamine starvation (Gln, <0.06 mM) was as described.
Cell viability determined by trypan blue exclusion was over 95% in
all cases, except for DON and ACV which were 75% and 63%,
respectively. DON, ACV and HPA are glutamine antagonists. As
illustrated in FIG. 2, it is clear that NaPA is capable of inducing
granulocyte differentiation in HL-60. As further illustrated in
FIG. 2, differentiation of HL-60, assessed morphologically and
functionally, was sequential and could be further enhanced by the
addition of low doses of retinoic acid [RA, 10 nM) or interferon
gamma (300 IU/ml). After seven days of NaPA treatment, or four
days, when combined with RA, the HL-60 cultures were composed of
early stage myelocytes and metamyelocytes (30-50%), as well as
banded and segmented neutrophils (30-40%) capable of NBT.
Pharmacokinetics studies in children with urea cycle disorders
indicate that infusion of NaPA 300-500 mg/kg/day, a well tolerated
treatment, results in plasma levels of approximately 800 .mu.g/ml.
[Brusilow, S. W. et al. Treatment of episodic hyperammonemia in
children with inborn errors of urea synthesis. The New England
Journal of Medicine. 310:1630-1634 (1984).] This same concentration
was shown to effectively induce tumor cell differentiation in the
present experimental system.
EXAMPLE 3
10T1/2 cells--NaPA induction of adipocyte conversion
FIG. 3 illustrates that NaPA is capable of inducing adipocyte
conversion in 10T1/2 cultures. Confluent cultures were treated with
NaPA for seven days. Lower: Quantitation of adipocytosis. Cells
were fixed with 37% formaldehyde and stained with Oil-Red O. The
stained intracellular lipid was extracted with butanol, and the
optical density was determined using a Titertek Multiskan MC,
manufactured by Flow Laboratories, at a wavelength 510 nm.
Increased lipid accumulation was evident in cells treated with as
little as 0.024 mg/ml of NaPA. The results in FIG. 3 show that
differentiation was dose- and time-dependent, and apparently
irreversible upon cessation of treatment. NaPA at 800 .mu.g/ml was
efficient and totally free of cytotoxic effect. In the 10T1/2
model, adipoocyte conversion involved over 80% of the cell
population. It was noted that higher drug concentrations further
increased the efficiency of differentiation as well as the size of
lipid droplets in each cell.
It is known that glutamine conjugation by NaPA is limited to humans
and higher primates and that in rodents NaPA instead binds glycine.
[James, M. O. et al. The conjugation of phenylacetic acid in man,
sub-human primates and some non-primate species. Proc. R. Soc.
Lond. B. 182:25-35 (1972).] Consequently, the effect of NaPA on the
mouse 10T1/2 cell line could not be explained by an effect on
glutamine. In agreement, neither glutamine starvation nor treatment
with glutamine antagonists such as DON and ACV resulted in
adipocyte conversion.
EXAMPLE 4
Induction of lipid accumulation and adipocyte differentiation
4. Clinical use of phenylacetate and derivatives
TABLE 2 ______________________________________ Phenylacetate and
Derivatives: Induction of cellular differentiation in premalignant
10T1/2 cells Compounds Differentiation at 1 mM DC.sub.50 * (sodium
salts) (%) (mM) ______________________________________
Phenylacetate 65 0.7 1-naphthylacetate >95 <0.1
3-chlorophenylacetate 80 0.5 4-chlorophenylacetate 50 1.0
2,6-dichlorophenylacetate 75 0.5 4-fluorophenylaceatae 65 0.7
______________________________________ *DC.sub.50, concentration of
compound causing 50% differentiation
As shown in Table 2, phenylacetate and its derivatives efficiently
induced lipid accumulation and adipocyte differentiation in
premalignant cells. These and other results indicate that the
tested compounds might be of value in:
A. Cancer prevention. Non-replicating, differentiated tumor cells
are not likely to progress to malignancy.
B. Differentiation therapy of malignant and pathological
nonmalignant conditions.
C. Treatment of lipid disorders, in which patients would benefit
from increased lipid accumulation.
D. Wound healing. This is indicated by the ability of phenylacetate
to induce collagen synthesis in fibroblasts (see Section D
herein).
Studies in plants have revealed that NaPA can interact with
intracellular regulatory proteins and modulate cellular. RNA
levels. In an attempt to explore the possible mechanism of action,
Northern blot analysis of HL-60 and 10T1/2 cells was performed
according to conventional methods. Cytoplasmic RNA was extracted,
separated and analyzed (20 .mu.g/lane) from confluent cultures
treated for 72 hours with NaPA or PAG (mg/ml); C is the untreated
control. The aP2 cDNA probe was labeled with [.sup.32 P]dCTP (New
England Nuclear) using a commercially available random primed DNA
labeling kit. Ethidium bromide-stained 28S rRNA indicates the
relative amounts of total RNA in each lane.
The results of the Northern blot analysis of HL-60 and 10T1/2
cells, showed marked changes in gene expression shortly after NaPA
treatment. Expression of the adipocyte-specific aP2 gene was
induced within 24 hours in treated 10T1/2 confluent cultures
reaching maximal mRNA levels by 72 hours.
EXAMPLE 5
HL-60 cells--myc down regulation
In HL-60, cell transformation has been linked to amplification and
over-expression, and differentiation would typically require down
regulation of myc expression. [Collins, S. J. The HL-60
promyelocytic leukemia cell line: Proliferation, differentiation,
and cellular oncogene expression. Blood. 70:1233-1244 (1987)]. To
demonstrate the kinetics of myc inhibition and HLA-A induction,
Northern blot analysis of cytoplasmic RNA (20 .mu.g/lane) was
carried out on cells treated with NaPA and PAG for specified
durations of time and untreated controls (-). The dose-dependency
and specificity of the effect of NaPA was observed. Two
concentrations of NaPA, 1.6 mg/ml (++) and 0.8 mg/ml (+), and PAG
at 1.6 mg/ml were investigated. The .sup.32 P-labeled probes used
were myc 3rd exon (Oncor) and HLA-A3 Hind III/EcoRI fragment. NaPA
caused a rapid decline in the amounts of myc mRNA. This occurred
within 4 hours of treatment, preceding the phenotypic changes
detectable by 48 hours, approximately two cell cycles, after
treatment. Similar kinetics of myc inhibition have been reported
for other differentiation agents such as dimethyl sulfoxide, sodium
butyrate, bromodeoxyuridine, retinoids, and 1,25-dihydroxyvitamin
D.sub.3. The results observed suggest that down regulation of
oncogene expression by NaPA may be responsible in part for the
growth arrest and induction of terminal differentiation. In
addition, it is evident that NaPA treatment of the leukemic cells
was associated with time- and dose-dependent accumulation of HLA-A
mRNA coding for class I major histocompatibility antigens. This
enhances the immunogenicity of tumors in vivo.
EXAMPLE 6
K562 cells--NaPA promotes hemoglobin biosynthesis
Further support for the use of NaPA as a non-toxic inducer of tumor
cell differentiation is found in the ability of NaPA to promote
hemoglobin biosynthesis in erythroleukemia cells. K562 leukemic
cells have a nonfunctional beta-globin gene and, therefore, do not
normally produce significant amounts hemoglobin. When K562 human
erythroleukemia cells were grown in the presence of NaPA at 0.8 and
1.6 mg/ml concentrations, hemoglobin accumulation, a marker of
differentiation, was found to increase 4 to 9 fold over that of
control cells grown in the absence of NaPA. Hemoglobin accumulation
was determined by Benzidine staining of cells for hemoglobin and
direct quantitation of the protein. The results of this study are
reported in Table 16.
It has been shown that high concentrations of NaPA inhibit DNA
methylation in plants. [Vanjusin, B. J. et al. Biochemia 1,
46:47-53 (1981)]. Alterations in DNA methylation can promote
oncogenesis in the evolution of cells with metastatic capabilities.
[Rimoldi, D. et al. Cancer Research. 51:1-7 (1991)]. These
observations prompted some concerns regarding potential long-term
adverse effects with the use of NaPA. To determine the potential
tumorigenicity of NaPA, a comparative analysis was performed using
NaPA and the known hypomethylating agent 5-aza-2'-deoxycytidine
(5AzadC).
Premalignant cells (3-4.times.10.sup.5) were plated in 75 cm.sup.2
dishes and 5AzadC 0.1 .mu.M was added to the growth medium at 20
and 48 hrs after plating. The cells were then subcultured in the
absence of the nucleoside analog for an additional seven weeks.
Cells treated with NaPA at 1.6 mg/ml were subcultured in the
continuous presence of the drug. For the tumorigenicity assay, 4-5
week-old female athymic nude mice were inoculated s.c. with
1.times.10.sup.6 cells and observed for tumor growth at the site of
injection.
The results set forth in Table 3 show that NaPA, unlike the
cytosine analog, did not cause tumor progression.
TABLE 3 ______________________________________ Tumorigenicity of
C3H 10T1/2 Cells in Athymic Mice Tumors Incidence (positive/
Diameter Time Treatment injected mice) (mm .+-. S.D.) (weeks)
______________________________________ None 0/8 0 13 5AzadC 8/8 5.5
.+-. 2.5 8 NaPA 0/8 0 13 ______________________________________
The transient treatment of actively growing 10T1/2 cells with
5AzadC resulted in the development of foci of neoplastically
transformed cells with a frequency of about 7.times.10.sup.-4.
These foci eventually became capable of tumor formation in athymic
mice. By contrast, actively replicating 10T1/2 cultures treated for
seven weeks with NaPA, 800-1600 .mu.g/ml, differentiated solely
into adipocytes, forming neither neoplastic foci in vitro nor
tumors in vivo in recipient mice.
Furthermore, experiments have demonstrated that NaPA can prevent
spontaneous or 5AzadC-induced neoplastic transformation, thus
demonstrating its novel role in cancer prevention. It is known that
the treatment of premalignant 4C8 and 10T1/2 cells with carcinogens
such as 5AzadC produces malignant conversion of the respective
cells. When 4C8 [Remold: et al., Cancer Research, 51:1-7 (1990)]
and 10T1/2 cells were exposed to 5AzadC, malignant conversion
became evident in two days and two weeks, respectively. NaPA
(0.8-1.6 mg/ml) prevented the appearance of the malignant
phenotype, as determined by cell morphology, contact inhibition and
anchorage dependent growth in culture.
EXAMPLE 7
Growth arrest in malignant gliomas
In addition, Phenylacetate has been implicated in damage to
immature brain in phenylketonuria. Because of similarities in
growth pattern and metabolism between the developing normal brain
and malignant central nervous system tumors, phenylacetate may be
detrimental to some brain cancers. Phenylacetate can induce
cytostasis and reversal of malignant properties of cultured human
glioblastoma cells, when used at pharmacological concentrations
that are well tolerated by children and adults. Interestingly,
treated tumor cells exhibited biochemical alterations similar to
those observed in phenylketonuria-like conditions, including
selective decline in de novo cholesterol synthesis from mevalonate.
Since gliomas, but not mature normal brain cells, are highly
dependent on mevalonate for production of sterols and isoprenoids
vital for cell growth, phenylacetate would be expected to affect
tumor growth in vivo, while sparing normal tissues. Systemic
treatment of rats bearing intracranial gliomas resulted in
significant tumor suppression with no apparent toxicity to the
host. The experimental data, which are consistent with clinical
evidence for selective activity against undifferentiated brain,
suggest that phenylacetate may offer a safe and effective novel
approach to treatment of malignant gliomas.
Clinical experience, obtained during phenylacetate treatment of
children with urea cycle disorders, indicates that millimolar
levels can be achieved without significant adverse effects. The
lack of neurotoxicity in these patients is, however, in marked
contrast to the severe brain damage documented in phenylketonuria
(PKU), an inborn error of phenylalanine metabolism associated with
excessive production of phenylacetate, microcephaly, and mental
retardation. [Scriver, C. R., and C. L. Clow. 1980.
Phenylketonuria: epitome of human biochemical genetics. New Engl.
J. Med. 303: 1394-1400.] The differences in clinical outcome can be
explained by the fact that, although phenylacetate readily crosses
the blood-brain barrier in both prenatal and postnatal life,
neurotoxicity is limited to the immature brain. Compelling evidence
for a developmentally restricted window of susceptibility is
provided by the phenomenon of "maternal PKU syndrome": PKU females
who are diagnosed early and maintained on a
phenylalanine-restricted diet, develop normally and subsequently
tolerate a regular diet. These women often give birth to
genetically normal, yet mentally retarded infants due to the
untreated maternal PKU. The elevated levels of circulating
phenylacetate, while sparing the mature tissues of the mother, are
detrimental to the fetal brain. The primary pathological changes in
PKU involve rapidly developing glial cells and are characterized by
alterations in lipid metabolism and myelination with subsequent
neuronal dysfunction. The vulnerable fetal glial tissues resemble
neoplastic glial cells in numerous molecular and biochemical
aspects, including unique dependence upon mevalonate (MVA)
metabolism for synthesis of sterols and isoprenoids critical to
cell replication [Kandutsch, A. A., and S. E. Saucier. 1969.
Regulation of sterol synthesis in developing brains of normal and
jimpy mice. Arch. Biochem. Biophys. 135: 201-208; Fumagalli, R., E.
Grossi, P. Paoletti, and R. Paoletti. 1964. Studies on lipids in
brain tumors. I. Occurrence and significance of sterol precursors
of cholesterol in human brain tumors. J. Neurochem. 11: 561-565;
Grossi, E., P. Paoletti, and R. Paoletti. 1958. An analysis of
brain cholesterol and fatty acid biosynthesis. Arch. Int. Physiol.
Biochem. 66: 564-572], and on circulating glutamine as the nitrogen
donor for DNA, RNA and protein synthesis [Perry, T. L., S. Hasen,
B. Tischler, R. Bunting, and S. Diamond. 1970. Glutamine depletion
in phenylketonuria, a possible cause of the mental defect. New
Engl. J. Med. 282: 761-766; Weber, G. 1983. Biochemical strategy of
cancer cells and the design of chemotherapy: G. H. A. Clowes
Memorial Lecture. Cancer Res. 43: 3466-3492]. The hypothesis
underlying these studies was that phenylacetate, known to conjugate
and deplete serum glutamine in humans, and to inhibit the MVA
pathway in immature brain [Castillo, M., M. F. Zafra, and E.
Garcia-Peregrin. 1988. Inhibition of brain and liver
3-hydroxy-3-methylglutaryl-CoA reductase and
mevalonate-5-pyrophosphate decarboxylase in experimental
hyperphenylalaninemia. Neurochem. Res. 13: 551-555; Castillo, M.,
J. Iglesias, M. F. Zafra, and E. Garcia-Peregrin. 1991. Inhibition
of chick brain cholesterogenic enzymes by phenyl and phenolic
derivatives of phenylalanine. Neurochem. Int. 18: 171-174;
Castillo, M., M. Martinez-Cayuela, M. F. Zafra, and E.
Garcia-Peregrin. 1991. Effect of phenylalanine derivatives on the
main regulatory enzymes of hepatic cholestrogenesis. Mol. Cell.
Biochem. 105: 21-25], might attack these critical control points in
malignant gliomas. The efficacy of phenylacetate was demonstrated
using both in vitro and vivo tumor models.
Cell Cultures and Reagents.
Human glioblastoma cell lines were purchased from the American Type
Culture Collection (ATCC, Rockville, Md.), and maintained in RPMI
1640 supplemented with 10% heat inactivated fetal calf serum,
antibiotics and 2 mM L-glutamine, unless otherwise specified. Human
umbilical vein endothelial cells, isolated from freshly obtained
cords, were provided by D. Grant and H. Kleinman (NIH, Bethesda
Md.). Sodium salts of phenylacetic acid and of phenylbutyric acid
were provided by Elan Pharmaceutical Corporation (Gainseville,
Ga.). Phenylacetylglutamine was a gift from S. Brusilow (Johns
Hopkins, Md.).
Evaluation of Cell Replication and Viability. Growth rates were
determined by an enzymatic assay using
3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltertrazolium bromide
(Sigma, St. Louis, Mo.) [Alley, M. C., D. A. Scudiero, A. Monks, M.
L. Hursey, M. J. Czerwinski, D. L. Fine, B. J. Abbott, J. G. Mayo,
R. H. Schoemaker, and M. R. Boyd. 1988. Feasibility of drug
screening with panels of human tumor cell lines using a
microculture tetrazolium assay. Cancer Res. 48: 589-601], cell
enumeration with a hemocytometer following detachment with
trypsin/EDTA, and by thymidine incorporation into DNA. The
different assays produced essentially the same results. Cell
viability was assessed by trypan blue exclusion.
Colony Formation in Semi-Solid Agar.
Tumor cells were detached with trypsin/EDTA, re-suspended in growth
medium containing 0.36% agar, and placed onto a base layer of solid
agar (0.9%) in the presence or absence of drugs. Colonies composed
of 30 or more cells were scored after three weeks.
Immunocytochemistry.
Cells were immunostained with anti-vimentin monoclonal antibodies
using Dako PAP kit K537 (Dako Corporation, California).
Measurement of Cholesterol, Protein and DNA Synthesis.
For studies of steroid synthesis, cells were labeled for 24 hours
with 5.times.10.sup.6 DPM [5-3H]-mevalonate (35 Ci/mmol) (New
England Nuclear, Boston, Mass.) in growth medium containing 3 .mu.M
lovastatin and 0.5 mM unlabeled mevalonate, in the presence or
absence of 5 mM phenylacetate or 2.5 mM phenylbutyrate. Cellular
steroids were extracted with hexane and separated by silica thin
layer chromatography. The R.sub.f of the hexane-soluble radiolabled
product was identical to that of a radiolabled cholesterol standard
in three different solvent systems. Similarly treated cells were
tested for de novo protein and DNA synthesis by metabolic labeling
with [.sup.3 H]-leucine (158 Ci/mmol) or [.sup.3 H]-deoxythymidine
(6.7 Ci/mmol) (New England Nuclear). Measurements of .sup.14
CO.sub.2 released from [1-.sup.14 C]-mevalonate (49.5
mCi/mmol)(Amersham, Chicago, Ill.) in cell homogenates incubated
with phenylacetate/phenylbutyrate were performed with minor
modifications to established procedures.
Analysis of Protein Isoprenylation.
Cell cultures were incubated with 10 mM phenylacetate or 2.5 mM
phenylbutyrate for 24 hours in complete growth medium, and labeled
with RS-[2-.sup.14 C]-mevalonate (16 .mu.Ci/ml, specific activity
15 .mu.Ci/mmol) (American Radiolabeled Chemicals, Inc. St. Louis,
Mo.) during the final 15 hours of treatment. Whole cell proteins
were extracted, resolved on 10% SDS-polyacrylamide gels, and
stained with Commassie Brilliant Blue. Gels were then dried and
exposed to Kodak X-Omat film for 4 days.
Animal Studies.
To determine the effect of phenylacetate on the tumorigenic
phenotype of human glioblastoma cells, cultures were pre-treated
for one week and then harvested, resuspended in medium containing
30% matrigel (Collaborative Biomedical Products, Bedford, Mass.),
and transplanted s.c. (2.5.times.10.sup.6 cells per site) into
5-week old female athymic mice (Division of Cancer Treatment, NCI
Animal Program, Frederick Cancer Research Facility The animals were
then observed for tumor growth at the site of injection. To further
evaluate drug efficacy in vivo, Fisher 344 rats received a
stereotaxic inoculation of syngeneic 9L gliosarcoma cells
(4.times.10.sup.4) into the deep white matter of the right cerebral
hemisphere, as previously described [Weizsaecker, M., D. F., Deen,
M. L. Rosenblum, T. Hoshino, P. H. Gutin, and M. Baker. 1981. The
9L rat brain tumor: description and application of an animal model.
J. Neurol. 224: 183-192; Culver, K. W., Z. Ram, S. Walbridge, H.
Ishii, E. H. Oldfield, and R. M. Blaese. 1992. In vivo gene
transfer with retrovital vector producer cells for treatment of
experimental brain tumors. Science. 256: 1550-1552]. The animals
were then subjected to two weeks of continuous treatment with
sodium phenylacetate (550 mg/kg/day, s.c.), using osmotic minipumps
transplanted subcutaneously. In control rats the minipumps were
filled with saline. Statistical analysis of data employed the
Fisher's Exact Test.
Induction of cytostasis and phenotypic reversion in cultured human
glioblastoma cells. Treatment of glioblastoma cells with
phenylacetate resulted in time- and dose-dependent growth arrest
(FIG. 4), accompanied by similarly diminished DNA synthesis. After
4-6 days of continuous treatment with 4 mM phenylacetate, there was
approximately 50% inhibition of growth in U87, A172, U373, U343,
and HS683 cultures (IC.sub.50 4.4.+-.0.6 mM). Reflecting on the
heterogenous nature of tumor cell responses, glioblastoma U251 and
U138 cells were less sensitive with IC.sub.50 values of 8-10 mM.
Further studies, mimicking pharmacological conditions that are
expected in patients, involved exposure of cells to phenylacetate
in glutamine-depleted medium. These conditions completely blocked
glioblastoma cell growth, but had little effect on the replication
of normal endothelial cells (FIG. 5). Phenylbutyrate, an
intermediate metabolite of phenylacetate formed in the brain by
fatty acid elongation, also inhibited tumor cell replication
(IC.sub.50 2.2.+-.0.2 mM in A172, U87 and U373), while the end
metabolite, phenylacetylglutamine, was inactive. In addition to
inducing selective tumor cytostasis, both phenylacetate and
phenylbutyrate promoted cell maturation and reversion to a
nonmalignant phenotype, manifested by an altered pattern of
cytoskeletal intermediate filaments, loss of
anchorage-independence, and reduced tumorigenicity in athymic mice
(Table 4). Immunocytochemical analysis of vimentin in
phenylacetate-treated human glioblastoma U87 cells showed altered
morphology and cytoskeletal filament pattern. These changes,
confirmed by immunolabeling for glial fibrillary acidic protein are
consistent with cell maturation and correlate with reduced
proliferative capacity and regained contact inhibition of growth.
These profound changes in tumor behavior were accompanied by
alterations in the expression of genes implicated in growth
control, angiogenesis, and immunosuppression (e.g., TGF.alpha.,
HbF, and TGF-.beta.2).
TABLE 4 ______________________________________ Reversal of
Malignancy of Human Glioblastoma Cells Clonogenicity Tumor
Incidence.sup.2 in Soft Agar.sup.1 Positive/Injected Treatment (%)
Sites ______________________________________ None 8.1 9/10
Phenylacetate 2.5 mM 0.5 ND 5 mM >0.01 2/10 Phenylbutyrate 1.25
mM 0.15 ND 2.5 mM >0.01 1/10
______________________________________ .sup.1 U87 cells were
detached with trypsin/EDTA, resuspended in growth medium containing
0.36% agar, and placed onto a base layer of solid agar (0.9%) in
the presence or absence of drugs. Colonies composed of 30 or more
cells were scored after three weeks. .sup.2 U87cells pretreated in
culture for one week, were harvested, resuspended in medium
containing 30% matrigel, and transplanted s.c. into 5week old
female athymic mice (2.5 .times. 10.sup.6 cells per mouse). Dat
were recorded 5 weeks after cell inoculation. ND = not
determined.
Phenylacetate inhibits the mevalonate pathway and protein
isoprenylation. The most consistent biochemical change observed in
glial cells exposed to phenylacetate involved alterations in lipid
metabolism and inhibition of the MVA pathway (FIG. 6). Active de
novo synthesis of cholesterol and isoprenoids from precursors such
as acetyl-CoA and MVA is an important feature of the developing
brain (but not the mature brain), coinciding with myelination. It
is also a hallmark of malignant gliomas [Azarnoff, D. L., G. L.
Curran, and W. P. Williamson. 1958. Incorporation of
acetate-1-.sup.14 C into cholesterol by human intracranial tumors
in vitro. J. Nat. Cancer Inst. 21: 1109-1115; Rudling, M. J., B.
Angelin, C. O. Peterson, and V. P. Collins. 1990. Low density
lipoprotein receptor activity in human intracranial tumors and its
relation to cholesterol requirement. Cancer Res. 50 (suppl):
483-487]. Cholesterol production and protein isoprenylation
diminished within 24 hours of glioblastoma treatment with either
phenylacetate or phenylbutyrate (FIG. 7), preceding changes in DNA
and total protein synthesis, which were detectable after 48 hours.
The reduction in isoprenylation was paralleled by a decrease in MVA
decarboxylation (to less than 50% of control), an effect previously
observed in embryonic brain in PKU-like conditions.
MVA-5-pyrophosphate decarboxylase, a key enzyme regulating
cholesterol synthesis in brain, is inhibited by phenylacetate under
conditions in which MVA kinase and MVA-5-phosphate kinase are only
minimally affected. Phenylacetate might also interfere with MVA
synthesis from acetyl-CoA. Glioblastoma cells could not, however,
be rescued by exogenous MVA (0.3-3 mM), suggesting that MVA
utilization, rather than its synthesis, is the prime target. The
decline in MVA decarboxylation and protein isoprenylation in
phenylacetate-treated cells could be mimicked by using 1-2.5 mM
phenylbutyrate.
Mevalonate is a precursor of several isopentenyl moieties required
for progression through the cell cycle such as sterols, dolichol,
the side chains of ubiquinone and isopentenyladenine, and prenyl
groups that modify a small set of critical proteins [Goldstein, J.
L., and M. S. Brown. 1990. Regulation of the mevalonate pathway.
Nature. 343: 425-430; Marshall, C. J. 1993. Protein prenylation: A
mediator of protein-protein interactions. Science. 259: 1865-1866;
Braun, P. E., D. De Angelis, W. W. Shtybel, and L. Bernier. 1991.
Isoprenoid modification permits 2',3'-cyclic nucleotide
3'-phosphodiesterase to bind to membranes. J. Neurosci. Res. 30:
540-544]. The latter include plasma membrane G and G-like proteins
(e.g., ras) involved in mitogenic signal transduction (molecular
weight 20-26 kDa), the myelination-related enzyme 2',3'-cyclic
nucleotide 3'-phosphodiesterase, and nuclear envelope lamins that
play a key role in mitosis (44-74 kDa). Inhibition of sterol and
isoprenoid synthesis during rapid development of the brain could
lead to the microcephaly and impaired myelination seen in untreated
PKU. Targeting MVA in dedifferentiated malignant gliomas, on the
other hand, would be expected to inhibit tumor growth in vivo
without damaging the surrounding normal tissues, as the MVA pathway
is significantly less active in mature brain.
Activity of phenylacetate in experimental gliomas in rats. To
evaluate the in vivo antitumor effect of phenylacetate, Fisher rats
were inoculated with stereotaxic intracerebral injection of
syngeneic 9L gliosarcoma cells. This tumor model is known for its
aggressive growth pattern that results in nearly 100% mortality of
rats within 3 to 4 weeks. Phenylacetate was continuously
administered by implanted subcutaneous osmotic minipumps to deliver
a clinically-achievable dose of 550 mg/kg/day. Systemic treatment
for two weeks of rats bearing intracranial glioma cells markedly
suppressed tumor growth (p<0.05, Table 5) with no detectable
adverse effects. Further studies in experimental animals indicate
that phenylacetate (plasma and cerebrospinal fluid levels of 2-3
mM) induces tumor cell maturation in vivo and significantly
prolongs survival.
TABLE 5 ______________________________________ Phenylacetate
Activity in Experimental Brain Cancer Brain Tumors.sup.2 No. Macro-
Micro- Tumor Treatment.sup.1 of animals scopic scopic Free
______________________________________ Saline 10 8 1 1
Phenylacetate 15 3 4 8 ______________________________________
.sup.1 Fisher 344 rats received a stereotaxic inoculation of
syngeneic 9L gliosarcoma cells into the deep white matter of the
right cerebral hemisphere, as described in Material and Methods.
Animals were then subjected to two weeks of continuous treatment
with either sodium phenylacetate (550 mg/kg/day, s.c.) or saline,
using osmotic minipumps transplanted subcutaneously. .sup.2 Animals
were sacrificed 23 days after tumor inoculation to determine
antitumor effects. Findings were confirmed by histological
evaluation of the inoculated site.
Summary and Prospective.
Phenylacetate has long been implicated in damage to the developing
fetal brain. As primary CNS tumors are highly reminiscent of
immature fetal brain, malignant gliomas should be equally
vulnerable. Moreover, viewing maternal PKU syndrome as a natural
human model, phenylacetate would be expected to suppress the growth
of brain neoplasms without harming normal tissues. Experimental
data supports this hypothesis. Phenylacetate induced selective
cytostasis and promoted maturation of glioma cells in vitro and in
vivo. Premature growth arrest and differentiation could also
underlie the damage to fetal brain in PKU. Multiple mechanisms of
action are involved, including inhibition of protein isoprenylation
and depletion of plasma glutamine in humans. The demonstrable
antitumor activity, lack of toxicity, and ease of administration
(oral or intravenous), demonstrate the clinical efficacy of
phenylacetate in management of malignant gliomas, and perhaps of
other neoplasms as well. Previously, phenylacetate showed activity
in prostate cancer in vitro. Phase I clinical studies with
phenylacetate in the treatment of adults with cancer confirmed that
therapeutic levels can be achieved in the plasma and cerebrospinal
fluid with no significant toxicities, and provide preliminary
evidence for benefit to prostatic carcinoma and glioblastoma
patients (see Example 18).
Phenylacetate was used to treat human solid tumors, including
prostatic carcinoma, glioblastomas, and malignant melenoma.
Treatment resulted in selective cytostasis and phenotypic
reversion, as indicated by the restored anchorage-dependence,
reduced invasiveness and loss of tumorigenicity in athymic mice.
Molecular analysis of brain and hormone-refractory prostate cancer
cells revealed marked decline in the production and secretion of
TGF.beta., a protein implicated in growth control, angiogenesis,
and immunosuppression. Treated prostatic cells exhibited decreased
proteolytic activity mediated by urokinase-plasminogen activator, a
molecular marker of disease progression in man.
EXAMPLE 8
Growth arrest, tumor maturation, and extended survival in brain
tumors treated with NaPA
In Vitro Studies.
Cell proliferation.
The effect of NaPA on cell proliferation was evaluated using
tritiatedthymidine incorporation assay on cultured 9L gliosarcoma
cells and cell enumeration using a hemocytometer following
detachment with trypsin/EDTA. 9L is a syngeneic malignant glial
tumor derived from Fischer 344 rats and is associated with 100%
mortality within three to four weeks after intracerebral
inoculation [Weizsaecker M, Deen D. F., Rosenblum M. L., et al. The
9L rat brain tumor: description and application of an animal model.
J Neuol. 1981; 224: 183-192]. Tumor cells were plated at
5.times.10.sup.4 tumor cells/well in 24-well plates (Costar,
Cambridge, Mass.) in Dulbecco Modified Eagle's medium (DMEM) with
10% fetal bovine serum (Hyclone Laboratories Inc., Logan, Utah), 2
mM L-glutamine (GIBCO BRL, Gaithersburg, Md.), 50 U/ml penicillin
(GIBCO) and 50 .mu.g/ml streptomycin (GIBCO) and 2.5 .mu.g/ml
Fungizone (ICN Biomedicals Inc., Costa Mesa, Calif.). After 24
hours, the medium was changed and NaPA (Elan Pharmaceutical
Research Corp., Gainesville, Ga.) added to the medium at 0, 2.5, 5,
and 10 mM concentration for 5 days. Six hours before harvest, 0.5
mCi tritiatedthymidine (ICN Radiochemicals, Irvine, Calif.) was
added to each well. Thymidine incorporation was determined by
scintillation counting in triplicates.
Colony formation in semi-solid agar.
Anchorage independent growth (the ability of cells to form colonies
in semi-solid agar) is characteristic of malignant glial cells. 9L
cells were harvested with trypsin/EDTA and resuspended at
1.0.times.10.sup.4 cells/ml in growth medium containing 0.36% agar
(Difco). Two ml of the cell suspension was added to 60 mm plates
(Costar, Cambridge, Mass.) which were precoated with 4 ml of solid
agar (0.9%). Phenylacetate was added to the agar at different
concentrations (0, 1.25, 2.5, and 5 mM). In a second experiment, 9L
cells were grown for 7 days in tissue culture containing 5 mM NaPA.
The cells were then transferred, as described, to agar plates
without NaPA. Colonies composed of 30 or more cells were counted
after 3 weeks.
9L brain tumor inoculation and phenylacetate administration.
Fisher 344 rats (n=50) weighing 230-350 grams were anesthetized
using intraperitoneal (i.p.) Ketamine (90 mg/Kg, Fort Dodge
Laboratories, Inc., Fort Dodge, Iowa) and Xylazine (10 mg/Kg, Mobay
Corporation, Shawnee, Kans.) and placed in a steriotaxic apparatus
(David Kopf Instruments, Tujunga, Calif.). 4.times.10.sup.4
syngeneic 9L gliosarcoma cells in 5 .mu.L (Hank's) balanced salt
solution were injected into the deep white matter (depth of
inoculation -3.5 mm) of the right cerebral hemisphere using a 10
.mu.L Hamilton syringe connected to the manipulating arm of the
sterotaxic apparatus. In 10 rats, phenylacetate was administered by
continuous subcutaneous (s.c.) release of the drug using two 2ML2
osmotic pumps release rate of 5 .mu.l/hr for 14 days (Alza
Corporation, Palo Alto, Calif.). On the day of tumor inoculation
the pumps were implanted in the subcutaneous tissue of both flanks.
The concentration of the drug in the pumps was 650 mg/ml (total of
2600 mg for both pumps) for a daily dose of 550 mg/kg per rat. The
minipumps were replaced after 14 days for a total treatment of 28
days. Fifteen additional rats received NaPA, as described, starting
7 days after intracerebral inoculation of the tumor. In these rats,
an additional daily injection of NaPA (300 mg/kg, i.p.) was given
for 28 days. Control rats (n=25) received continuous saline from
two s.c. 2ML2 osmotic pumps. Perioperative penicillin (100,000
u/kg, i.m.) was given to all rats before implantation of the
minipumps. Survival was recorded in each group. Three rats treated
for established tumors and two control rats were sacrificed 7 days
after initiation of NaPA (14 days after tumor inoculation). These
were used for electron microscopic studies of treated tumors, in
vivo proliferation assays, and measurement of NaPA levels in the
serum and CSF. Peripheral organs (heart, lung, spleen, liver,
kidney, bowel, adrenal, and gonads) were harvested and subjected
for a routine histological examination. Brain specimens were
sectioned and stained for routine hematoxylin and eosin (H&E)
and myelin stains (Luxol-fast blue) for evidence of drug-related
toxicity.
Electron microscopy.
Animals were sacrificed by intracardiac perfusion with 1%
paraformaldehyde and 2.5% gluteraldehyde in 0.1M sodium cacodylate
buffer at pH 7.4. Two hours later the fixed brains were washed in
buffer and sliced into 1 mm thick coronal sections. The areas
containing tumors were further dissected into 1 mm.sup.j cubes,
post-fixed with 2% osmium tetroxide in 0.1M sodium cacodylate
buffer for 2 hours, washed in buffer, mordanted en block with 1%
uranyl acetate at pH 5 overnight, then washed, dehydrated and
embedded in Epon. Thin sections were cut at several levels into
each block to ensure greater sampling. Electron micrographs of
tumor cells were taken at random for morphology.
In vivo proliferation assay.
One NaPA-treated and one saline-treated rat received an i.p.
injection of 9 mg/3 ml of BrdU (Amersham, Ill.) 14 days after tumor
inoculation and 7 days after initiation of treatment. Two hours
later the rats were sacrificed and the brains were removed and
sectioned. Mouse anti-BrdU monoclonal antibodies were used for
immunostaining of the tissues which were then counterstained with
hematoxylin. Tumor cells in 10 high-power fields were enumerated in
each tumor specimen and the percent of positively staining cells
(indicating incorporation of BrdU during active cell division) was
recorded.
Measurement of NaPA levels in serum and CSF.
Three NaPA-treated and 2 saline-treated rats were sacrificed after
7 days of combined s.c. and i.p. NaPA or saline administration.
Blood was drawn from the heart and CSF was aspirated from the
cisterna magna. Due to volume limitations of CSF, pooled serum and
CSF samples were assessed in a similar fashion. Protein extraction
of a 200 .mu.l aliquot of biological fluid was carried out with 100
.mu.l of a 10% perchloric acid solution. 150 .mu.l of supernate was
neutralized with 25 .mu.l of 20% potassium bicarbonate and
centrifuged. 125 .mu.l of supernate was then pipetted into sampling
tubes. Chromatography was performed on a Gilson 715 HPLC system
using a 30 cm Waters C18 column (i.d. 3.9 mm) at 60.degree. C. A 75
.mu.l injectate was eluted with an acetonitrile/water gradient
ranging from 5 to 30% over 20 minutes and flowing at 1 ml/min.
UV-monitoring was performed at a wavelength of 20 nm. Elution time
for phenylacetate was 14.8 minutes.
Statistical analysis.
The Chi-square test was used to compare proportions of
BrdU-positive cells. The Mantel-Haenzel test was used to compare
survival between NaPA-treated and saline-treated rats in the
survival experiments.
In Vitro Results
In vitro Effect of NaPA on cell proliferation and anchorage
dependency. Treatment of 9L cells with NaPA for 5 days resulted in
dose-dependent decrease in cell number with IC.sub.50 at 6.0.+-.0.5
mM. This was accompanied with a decrease in tritiated-thymidine
incorporation (FIG. 8). In addition, phenylacetate induced a
dose-dependent restoration of anchorage dependency, indicating a
reversion of the malignant phenotype (Table 19). 9L cells that were
exposed to NaPA for 7 days before plating in agar (not containing
NaPA) still showed >40% inhibition in colony formation (Table
19).
TABLE 19 ______________________________________ Phenylacetate
Inhibits Anchorage-Independent Growth of 9L Gliosarcoma Cells
Treatment PA in Colony Formation in Culture Agar (mM) # Colonies %
Inhibition ______________________________________ none 0 628 .+-.
50 -- none 5 8 .+-. 4 98.7 2.5 111 .+-. 13 82.4 1.25 326 .+-. 20
48.0 .sup.a Phenylacetate 0 375 .+-. 25 40.3
______________________________________ .sup.a 9L cells were treated
with 5 mM phenylacetate in culture for 7 day before being plated on
soft agar.
In Vivo Studies
In vivo proliferation assay and electron microscopy findings.
Treatment of established brain tumors with NaPA resulted in a
significant decrease in the rate of proliferation. 285 of 1283
treated tumor cells stained for BrdU compared to 429 of 1347
saline-treated tumor cells (mitotic index of 0.22 in NaPA-treated
vs. 0.33 in saline-treated tumors; p<0.0001).
Electron microscopy of these tumors showed a striking abundance of
well-organized rough endoplasmic reticulum in the NaPA-treated
tumor cells, indicating a higher degree of cell differentiation
[Ghadially FN. Endoplasmic reticulum and ribosomes in cell
differentiation and neoplasia. In: eds. Ultrastructural Pathology
of the Cell and Matrix. Third, London:Buttorworths; 1992:450-454].
By contrast, untreated tumors generally had scant rough endoplasmic
reticulum and numerous polyribosomes, which are characteristics of
highly malignant cells.
In addition, mitotic cells were more frequently found in untreated
tumors.
Serum and CSF levels of NaPA.
Assays of pooled serum and CSF from 3 treated and 2 control rats,
obtained after 7 days of combined s.c. and i.p. NaPA (total daily
dose of 850 mg/kg) or saline administration, revealed a mean
phenylacetate level of 2.45 mM in the serum and 3.1 mM in the CSF.
No phenylacetate was detected in the serum of CSF samples from
saline-treated rats.
Survival Experiments
Simultaneous tumor inoculation and administration of NaPA. Seven of
10 NaPA-treated rats survived for >90 days after tumor
inoculation when NaPA was administered for 4 weeks starting on the
day of tumor inoculation. Nine of 10 control rats died within 34
days after tumor inoculation (p<0.01, Mantel-Haenzel test) (FIG.
9).
Treatment of established tumors with NaPA.
Five of 12 rats treated with s.c. and i.p. NaPA for 4 weeks
(starting 7 days after tumor inoculation) are still alive 50 days
after tumor inoculation, while 12 of 13 saline-treated rats died by
day 36 (p<0.03, Mantel-Haenzel test) (FIG. 10).
Toxicity.
No adverse effects of NaPA treatment were detected in any treated
rats. Histological evaluation of the major peripheral organs and
non-tumoral brain showed no abnormalities.
Discussion.
Phenylacetate induced a potent cytostatic and antitumor effect in
the in vitro and in vivo brain tumor models used in these studies.
This effect extended beyond the duration of drug administration,
indicated by the long-term survival and apparent cure of rats which
received NaPA either simultaneously with tumor inoculation or after
tumors were established. This extended effect of NaPA shows that
the malignant phenotype of treated tumor cells reverted, perhaps
irreversibly in some animals, to one that was more benign and
differentiated. Anchorage independence, i.e., the ability of cells
to form colonies in semi-solid agar, is characteristic of malignant
glioma cells. Phenylacetate caused a dose-dependent restoration of
anchorage dependency, indicating reversion of the glioma cells to a
non-malignant phenotype. More than 80% inhibition of colony
formation was achieved at NaPA concentration in the agar plate of
2.5 mM, similar to the serum and CSF levels measured in treated
rats. In addition, after one week of exposure to NaPA, more than
40% of tumor cells maintained a benign growth pattern despite the
absence of NaPA in the agar plates (Table 19). A significant in
vivo indicator of cell differentiation was observed in our study in
the subcellular organelles of treated brain-tumor cells. The
disorganized cytoplasmic polyribosomes in the saline-treated tumor
cells were transformed by NaPA to a hyperplastic, well organized,
rough endoplasmic reticulum. The endoplasmic reticulum is a highly
specialized structure that performs many distinct functions. Hence
a well-developed endoplasmic reticulum represents cell
differentiation and functional activity. An inverse relationship
has been noted between the amount of rough endoplasmic reticulum
and the growth rate and degree of malignancy of tumors [Ghadially
FN. Diagnostic Electron Microscopy of Tumours. eds. 2.
London:Butterworth; 1985]. The numerous polyribosomes in the
untreated tumor cells correlated well with the number of mitoses
seen by light microscopy and were confirmed by the BrdU
proliferation assay. These changes underscore the differentiating
effect of NaPA on the malignant glial cells and correlate with the
in vivo decrease in cell proliferation and extended survival that
occurred in treated animals with brain tumors.
Therapeutic blood and CSF NaPA levels were reached in the treated
rats. The high CSF levels indicate good penetration of NaPA into
the central nervous system and into the developing tumor. The doses
used are well below the known toxic levels of NaPA in children with
inborn errors of urea synthesis (2.5 g/kg/d) or rats (1.6 g/kg/d)
and indicate that NaPA can be given safely at a higher doses,
possibly with enhancement of antitumor efficacy. These data
indicate that phenylacetate, given to rats at a non-toxic dose, has
a profound effect on tumor growth regulation and cell
maturation.
EXAMPLE 9
Suppression of 5-Aza-2'-deoxycytidine induced carcinogenesis
Differentiation inducers selected for their low cytotoxic and
genotoxic potential could be of major value in chemoprevention and
maintenance therapy. Specifically, the ability of phenylacetate to
prevent carcinogenesis by the chemotherapeutic hypomethylating
drug, 5-aza-2'-deoxycytidine (5AzadC), was tested in vitro and in
mice. Transient exposure of immortalized, but non-tumorigenic
ras-transformed 4C8 fibroblasts to 5AzadC resulted in neoplastic
transformation manifested by loss of contact inhibition of growth,
acquired invasiveness, and tumorigenicity in athymic mice. The
latter was associated with increased ras expression and a decline
in collagen biosynthesis. These profound phenotypic and molecular
changes were prevented by a simultaneous treatment with
phenylacetate. Protection from 5AzadC carcinogenesis by
phenylacetate was: (a) highly efficient despite DNA hypomethylation
by both drugs; (b) free of cytotoxic and genotoxic effects; (c)
stable after treatment was discontinued, and; (d) reproducible in
vivo. Whereas athymic mice bearing 4C8 cells developed
fibrosarcomas following a single i.p. injection with 5AzadC, tumor
development was significantly inhibited by systemic treatment with
nontoxic doses of phenylacetate. Phenylacetate and its precursor
suitable for oral administration, phenylbutyrate, may thus
represent a new class of chemopreventive agents, the efficacy and
safety of which should be further evaluated.
The multi-step nature of neoplastic transformation makes this
disease process amendable to chemopreventive intervention. Several
agents have been shown to inhibit carcinogenesis and thereby
prevent the development of primary or secondary cancers [Kelloff,
G. J., C. W. Boone, W. F., Malone, and V. E. Steele. 1992.
Chemoprevention clinical trials. Mutation Res., 267: 291-295;
Weinstein, B. I. 1991. Cancer prevention: Recent progress and
future opportunities. Cancer Res., 51:5080s-5085s; Wattenberg, L.
W. Inhibition of carcinogenesis by naturally occurring and
synthetic compounds. In: Y. Kuroda, D. M. Shankel and M. D. Waters
(eds), Antimutagenesis and Anticarcinogenesis, Mechanisms II,
pp.155-166. New York: Plenum Publishing Corp., 1990; Sporn, M. B.,
and D. L. Newton. 1979. Chemoprevention of cancer and retinoids.
Fed. Proc. 38:2528-2534]. Of major interest are natural products
and their analogs, including vitamins (A, B12, C, D3, and E),
retinoids, and terpenes. These agents can suppress neoplastic
transformation subsequent to a carcinogenic insult by regulating
cell growth and differentiation. One such growth regulator is
phenylacetate.
The efficacy of phenylacetate as a chemopreventive agent was tested
using in vitro and in vivo models of 5AzadC-induced carcinogenesis.
Despite the promise of 5AzadC in the treatment of cancer and of
beta-chain hemoglobinopathies, its clinical applications have been
hindered by concerns regarding carcinogenic potential. The model
used in the present studies involved premalignant murine
fibroblasts (cell lines 4C8 and PR4), which express a
transcriptionally activated c-Ha-ras protooncogene. These
non-tumorigenic cells are highly susceptible to malignant
conversion by pharmacological doses of 5AzadC. However,
Phenylacetate can protect such vulnerable cells from 5AzadC-induced
carcinogenesis both in culture and in mice.
Cell Cultures and Reagents.
The subclones of mouse NIH 3T3 fibroblasts, PR4N and 4C8-A10
(designated here PR4 and 4C8) have been previously described
[Wilson, V. L., R. A. Smith, H. Autrup, H. Krokan, D. E. Musci,
N-N-T. Le, J. Longoria, D. Ziska, and C. C. Harris. 1986. Genomic
5-methylcytosine determination by .sup.32 P-postlabeling analysis.
Anal. Biochem., 152:275-284; Dugaiczyk, A., J. J. Haron, E. M.
Ston, O. E. Dennison, K. N. Rothblum, and R. J. Schwartz. 1983.
Cloning and sequencing of a deoxyribonucleic acid copy of
glyceraldehyde-3-phosphate dehydrogenase messenger ribonucleic acid
isolated from chicken muscle. Biochem. 22:1605-1613]. Both cell
lines are phenotypic revertants isolated from
LTR/c-Ha-ras1-transformed 3T3 cells after long-term treatment with
murine interferon .alpha./.beta.. Cultures were maintained in
Dulbecco's modified Eagle's medium (DMEM) supplemented with 10%
heat inactivated fetal calf serum (Gibco) and antibiotics. The
sodium salts of phenylacetic and phenylbutyric acids (Elan
Pharmaceutical Corporation) were dissolved in distilled water.
5AzadC (Sigma St. Louis Mo.) was dissolved in phosphate buffered
saline (PBS) and stored in aliquots at -20.degree. C. until use.
Exposure of 5AzadC to direct light was avoided at all times to
prevent drug hydrolysis.
Treatments with 5AzadC.
For treatment in culture, cells were plated at 1-2.times.10.sup.5
cells in 100 mm dishes and the drugs added to the growth medium at
20 and 48 hrs later. The cells were subsequently subcultured in the
absence of the nucleoside analogs and observed for phenotypic
alterations. For in vivo treatment with 5AzadC, 6-9 week-old female
athymic nude mice (Division of Cancer Treatment, NCI Animal
Program, Frederick Cancer Research Facility) were inoculated
subcutaneously (s.c.) with 0.5.times.10.sup.6 cells. Twenty four
hours later 400 .mu.g of freshly prepared 5AzadC in 200 .mu.l of
PBS was administered intraperitoneally (i.p.) into each animal
(approximately 20 mg/kg). Systemic treatment with NaPA is described
in the text.
Growth on Matrigel.
The ability of cells to degrade and cross tissue barriers was
assessed by a qualitative vitro invasion assay that utilize
matrigel, a reconstituted basement membrane (Collaborative
Research). Cells were exposed for 48 hrs in T.C. plastic dishes
with 5AzadC alone or in combination with NaPA. NaPA treatment
continued for additional 1-2 weeks. Cells were then replated (at
5.times.10.sup.4 per point) onto 16 mm dishes (Costar, Cambridge,
Mass.), which were previously coated with 250 of matrigel (10
mg/ml). NaPA was either added to the dishes or omitted in order to
determine the reversibility of effect. Net-like formation
characteristic of invasive cells occurred within 12 hours; invasion
into the matrigel was evident after 6-9 days.
Tumor Formation in Athymic Mice.
Cells were injected s.c. (5.times.10.sup.5 cells per site) into 4-6
week old female athymic nude mice (Division of Cancer Treatment,
NCI animal Program, Frederick Cancer Research Facility). The
number, size, and weight of tumors were recorded after 3-4 weeks.
For histological examination, tumors were excised, fixed in Bouin's
solution (picric acid: 37% formaldehyde: glacial acetic acid,
15:5:1 vol/vol), and stained with H&E.
Measurement of DNA Methylation.
To determine the 5-methylcytosine content, samples of cultures were
taken 24 hours after the second 5AzadC treatment. The cell pellets
were lysed in 0.5% SDS, 0.1M NaCl, 10 mM EDTA pH 8.0, added with
400 .mu.g/ml of proteinase K (Boehringer Mannheim), and stored at
-70.degree. C. until DNA isolation and analysis. The content of
methylated/unmethylated cytosine residues in the cellular DNA was
measured by a .sup.32 P-postlabeling technique as previously
described.
Northern Blot Analysis and DNA Probes.
Cytoplasmic RNA was extracted from exponentially growing cells and
separated by electrophoresis in 1.2% agarose-formaldehyde gels. RNA
preparation, blotting onto nylon membranes (Schleicher and
Schuell), hybridization with radiolabeled DNA probes, and
autoradiography were performed as described [Rimoldi, D., V.
Srikantan, V. L. Wilson, R. H. Bassin, and D. Samid. 1991.
Increased sensitivity of nontumorigenic fibroblasts expressing ras
or myc oncogenes to malignant transformation induced by
5-aza-2'-deoxycytidine. Cancer Res., 51:324-330]. The DNA probes
included: 6.2 kb EcoRI fragment of v-Ki-ras, 2.9 kb SacI fragment
of the human c-Ha-ras1 gene, and a BamHI 4.5 kb fragment of the
c-myc gene. Glyceraldehyde phosphate dehydrogenase cDNA [Dugaiczyk,
A., J. J. Haron, E. M. Ston, O. E. Dennison, K. N. Rothblum, and R.
J. Schwartz. 1983. Cloning and sequencing of a deoxyribonucleic
acid copy of glyceraldehyde-3-phosphate dehydrogenase messenger
ribonucleic acid isolated from chicken muscle. Biochem.
22:1605-1613] was provided by M. A. Tainsky (University of Texas,
Houston), and a mouse transin cDNA by G. T. Bowden (University of
Arizona, Tucson). The cDNA probe for mouse histocompatibility class
I antigens was a gift from G. Jay (NIH, Bethesda). Radiolabeled
probes were prepared with [.sup.32 P]dCTP (NEN) using a random
primed DNA labeling kit (Boehringer Mannhelm, Germany).
In Vitro Carcinogenesis Induced by 5AzadC and Its Prevention by
Phenylacetate.
Untreated 4C8 and PR4 formed contact-inhibited monolayers composed
of epithelial-like cells. In agreement with previous observations,
transient exposure of these cultures to 0.1 uM 5AzadC during
logarithmic phase of growth resulted in rapid and massive
neoplastic transformation. Within one week of 5AzadC treatment, the
great majority of the cell population became refractile and spindly
in shape, and formed multilayered cultures with increased
saturation densities (Table 7), indicative of loss of contact
inhibition of growth. These phenotypic changes could be prevented
by the addition of 5-10 mM NaPA (Table 7). Several different
regimens of NaPA treatment were found to be similarly effective.
These included: (a) pre-treatment with NaPA, starting one day prior
to the addition of 5AzadC; (b) simultaneous exposure to both drugs,
and; (c) addition of NaPA one day after 5AzadC. In all cases, cells
were subsequently subjected to continuous treatment with NaPA for
at least one week. Cells cultured under these conditions, like
those treated with NaPA alone, formed contact-inhibited monolayers
resembling untreated controls. These cells maintained the benign
growth pattern for at least three weeks after NaPA treatment was
discontinued.
That NaPA prevents neoplastic transformation was further indicated
by the inability of cells to invade reconstituted basement
membranes (matrigel), and form tumors in athymic mice. When plated
onto matrigel, 5AzadC-transformed 4C8 and PR4 cells developed
net-like structures characteristic of highly malignant cells, and
eventually degraded the extracellular matrix components. In marked
contrast, NaPA-treated cultures formed small, non-invasive colonies
on top of the matrigel, as previously observed with normal
fibroblasts. Untreated parental cells exhibited an intermediate
phenotype, as their colonies were slow growing and non-invasive,
yet irregular in shape possibly due to increased cell motility. The
chemopreventive effect of phenylacetate could be mimicked by its
precursor, phenylbutyrate. Cells exposed to 5AzadC in the presence
of sodium phenylbutyrate (NaPB, 1.5-3 mM) maintained contact
inhibited growth and exhibited a benign phenotype when placed onto
matrigel (Table 7).
TABLE 7 ______________________________________ Effect of 5AzadC and
NaPA on DNA Methylation DNA Methylation Cells Treatment.sup.a %
5mC.sup.b % of Control ______________________________________ 4C8
none 3.49 .+-. 0.06 100 5AzadC 1.52 .+-. 0.27 43 NaPA 2.22 .+-.
0.10 63 5AzadC + NaPA 1.62 .+-. 0.18 46 PR4 none 2.72 .+-. 0.16 100
5AzadC 1.11 .+-. 0.22 41 NaPA 1.25 .+-. 0.08 46 5AzadC + NaPA 1.06
.+-. 0.11 39 ______________________________________ .sup.a Cells
were treated with 0.1 uM 5AzadC and/or 10 mM NaPA and the
percentage of 5 mC was determined as described in "Materials and
Methods" .sup.b Data indicate the mean .+-. S.D. (n = 4) of two
experiments.
The in vitro growth characteristics of cells correlated with their
behavior in athymic mice. 5AzadC-treated 4C8 cells developed
rapidly growing fibrosarcomas within 2 weeks of s.c.
transplantation into mice. Consistent with their behavior in vitro,
the parental cells were far less aggressive, forming small lesions
after 3-4 weeks in three of eight recipient animals. However, no
tumors developed in animals injected with 4C8 cells that had been
pre-treated for one week in culture with the combination of 5AzadC
and NaPA (Table 7). There was also no tumor formation in mice
injected with 4C8 treated with NaPA alone. Therefore it follows
that NaPA induced phenotypic reversion of the premalignant
fibroblasts and prevented their malignant conversion the cytosine
analog.
Modulation of Gene Expression by NaPA.
The NIH 3T3-derived cells lines, 4C8 and PR4, carry an
LTR-activated c-Ha-ras protooncogene. Northern blot analysis of
5AzadC-treated 4C8 revealed a significant increase in ras mRNA
levels and a decline in the differentiation marker, collagen
.alpha. (type I) transcripts. No such changes in gene expression
occurred in cultures to which NaPA was added. Withdrawal of NaPA
after one week of continuous treatment did not cause restoration of
ras expression, confirming that the therapeutic benefit of NaPA is
stable in the absence of further treatment.
Effect of Phenylacetate and 5AzadC on DNA methylation.
5AzadC is a potent inhibitor of DNA methylation, an epigenetic
mechanism implicated in the control of gene expression and cell
phenotype. Hypomethylation may underlay the therapeutic effect of
5AzadC in cancer and in severe inborn anemias [Momparler, R. L., G.
E. Rivard, and M. Gyger. 1985. Clinical trial on
5-aza-2'-deoxycytidine in patients with acute leukemia. Pharmac.
Ther., 30:277-286; Stamatoyannopoulos, J. A., and A. W. Nienhuis.
1992. Therapeutic approaches to hemoglobin switching in treatment
of hemoglobinopathies. Annu. Rev. Med., 43:497-521; Ley, T. J., J.
DeSimone, N. P. Anagnou, G. H. Keller, R. K. Humphries, P. H.
Turner, P. H., N. S. Young, P. Heller, and A. W. Nienhuis. 1982.
5-Azacytidine selectively increases gamma-globin synthesis in a
patient with beta.sup.+ thalassemia. N. Engl. J. Med.
307:1469-1475]. However, changes in DNA methylation could also be
responsible for its carcinogenic potential. It was of interest
therefore to determine the degree of DNA methylation in cells
protected by phenylacetate. As would be expected, 5AzadC caused a
significant decrease in the content of 5-methylcytosine (5mC)
(Table 6). There was, however, a comparable decline in 5mC in cells
treated with 5AzadC in combination with NaPA, as well as in those
treated with NaPA alone (Table 6).
TABLE 6
__________________________________________________________________________
In vitro Prevention by Phenylacetate of 5AzadC-Induced
Carcinogenesis Cell Saturation Density.sup.a Invas- Tumorigenicity
in mice.sup.c Treatment (cells/cm.sup.2 .times. 10.sup.-5)
iveness.sup.b Incidence Tumor Size (mm)
__________________________________________________________________________
None 3.9 - 3/8 1.0 (0.5-2) 5AzadC 7.0 + 8/8 11.5 (4-19) 5AzadC +
NaPA 1.6 - 0/8 0 5AzadC + NaPB 1.1 - ND NaPA ND - 0/8 0 NaPB 1.3 -
ND
__________________________________________________________________________
.sup.a Cell were treated simultaneously with the indicated drugs
and kept in culture for 5 days post confluency at which time they
were detached an counted. Exposure to 5AzadC was transient as
described in Materials and Methods, while treatment with NaPA and
NaPB continued throughout the experiment. Similar results were
obtained when NaPA treatment was initiated one day prior or after
cell exposure to 5AzadC (data not shown) .sup.b Cells were plated
on top of a matrigel layer and observed for malignant growth
pattern, i.e., development of characteristic processes and
degradation of the reconstituted basement membrane and invasion
towards the plastic surface below. .sup.c Cells pretreated in
culture were injected s.c (5 .times. 10.sup.5 cells per site) into
2 month old female athymic nude mice. Results determined after 3
weeks indicate tumor incidence (tumor bearing, injecte animals) and
size. The values of tumor size are mean (range). ND = not
determined.
In Vivo Chemoprevention by NaPA.
To determine the efficacy of NaPA in vivo, studies were extended to
include an animal model involving athymic mice bearing the
non-tumorigenic 4C8 cells transplanted subcutaneously. A single
i.p. injection of mice with 5AzadC (20 mg/kg) resulted in tumor
development at the site of 4C8 cell inoculation. However, when mice
were pre-treated with NaPA 1.5 hr prior to 5AzadC injection, and
NaPA treatment continued for 22 days thereafter, the incidence of
tumor formation was significantly decreased (Table 8). There were
no adverse effects associated with NaPA treatment as indicated by
animal weight and behavior. Further more, despite causing DNA
hypomethylation NaPA did not induce neoplastic transformation of
transplanted 4C8 cells. Animals protected by NaPA either failed to
develop tumors or formed slow-growing lesions at the site of 4C8
inoculation. The animal data is consistent with the in vitro
findings, indicating that NaPA can prevent 5AzadC-induced
neoplastic transformation without producing significant
toxicities.
TABLE 8 ______________________________________ In vivo
Chemoprevention by Phenylacetate Animal Tumor Incidence.sup.b Tumor
Size.sup.c Group Treatment.sup.a positive/total mean (range)
______________________________________ A PBS 0/4 0 B NaPA 0/4 0 C
5AzadC + PBS 9/9 12 (2-29) D 5AzadC + NaPA 4/10 3 (0-10)
______________________________________ .sup.a 4C8 cells (5 .times.
10.sup.5 per site) were transplanted s.c. int athymic mice. The
next day, the animals in were treated i.p. with 400 mg/kg NaPA, and
1.5 hr later with 20 mg/kg 5AzadC. NaPA treatment was repeated at
4.5 hours following 5AzadC injection. Subsequent treatments
involved NaPA injections twice daily for 8 days, and once a day for
additional 2 weeks. PBS was used as a control. .sup.b Data
indicates tumor growth at 4 weeks after 5AzadC treatment.
Spontaneous tumors developed thereafter in control animals
receiving PBS, and subsequently in those treated with NaPA. .sup.c
Tumor diameter in millimeters.
There is considerable interest in the use of non-toxic
differentiation inducers in cancer chemoprevention. Drug toxicity
is particularly important considering the overall health condition
and variable life-span of candidate populations, i.e., high-risk
individuals and patients in remission. The differentiation inducer
phenylacetate can prevent 5AzadC-induced carcinogenesis both in
vitro and in vivo when used at nontoxic doses.
Chemoprevention can be accomplished by either blocking the
"initiation" step of carcinogenesis (i.e., mutagenesis), or by
suppressing "promotion" and progression to malignancy. The current
studies, using premalignant cells with an activated ras oncogene as
a model, examined the efficacy of phenylacetate as an
anti-promotional drug. Other well characterized chemopreventive
agents that block promotion include vitamin A and its synthetic
retinoids; like phenylacetate, these compounds are also regulators
of cell growth and differentiation.
The current studies exploited in vitro and in vivo models involving
fibroblasts (designated 4C8 and PR4) that are highly vulnerable to
malignant conversion by the DNA hypomethylating agents 5AzadC and
5AzaC (16, 17). Transient exposure of these cells to 5AzadC, either
in culture or in recipient athymic mice, caused rapid neoplastic
transformation. Malignant conversion was associated with an
increase in ras mRNA levels and down-regulation of collagen type I
expression, indicating loss of cell differentiation. These profound
biological and molecular changes brought about by 5AzadC are
prevented by a simultaneous treatment with non-cytotoxic
concentrations of phenylacetate and its precursor, phenylbutyrate.
Phenylacetate's antitumor activity and lack of toxicity were
confirmed in athymic mice. In the in vivo model, mice bearing the
susceptible 4C8 cells transplanted s.c. were injected i.p. with
5AzadC. All mice so treated developed rapidly growing
fibrosarcomas; however, the incidence of tumor formation was
markedly reduced by systemic treatment with NaPA.
The mechanism by which NaPA prevented the 5AzadC induced malignant
conversion is unclear. Like other chemopreventive agents that block
promotion, phenylacetate may act by inducing cytostasis and tumor
maturation. There is a growing body of evidence indicating that
phenylacetate can cause selective growth arrest and tumor
differentiation in vitro and in rodent models. In some cases, e.g.,
promyelocytic leukemia, differentiation induced by phenylacetate
was linked to a decline in myc oncogene expression. In NaPA-treated
4C8, protection from de-differentiation (evidenced by growth
characteristics and collagen expression), was associated with
inhibition of ras overexpression. Down-regulation of oncogene
expression may thus be responsible in part for the chemopreventive
activity of NaPA. In addition to affecting ras at the mRNA levels,
phenylacetate, an inhibitor of the mevalonate pathway of
cholesterol synthesis [Castillo, M., J. Iglesias, M. F. Zafra, and
E. Garcia-Peregrin. 1991. Inhibition of chick brain
cholesterolgenic enzymes by phenyl and phenolic derivatives of
phenylalanine. Neurochem. Int., 18: 171-174], could also block the
post-translational modification of the ras-encoded protein, p21.
Limonene, an inhibitor of p21 prenylation, is a chemopreventive
agent as well.
Phenylacetate blocked carcinogenesis by 5AzadC despite the decline
in 5mC content. In fact, NaPA itself was found to inhibit DNA
methylation; yet, in contrast to 5AzadC, NaPA was not carcinogenic.
Correlations between carcinogenic potential and DNA hypomethylating
activities of chemical agents have been previously documented in
tissue culture models, and alterations in DNA 5mC patterns were
proposed to contribute and enhance the initiation of
carcinogenesis. However, the present data indicate that
quantitative changes in DNA methylation alone are not sufficient to
affect cell phenotype and thus, hypomethylating activity is not
sufficient to induce the tumorigenic phenotype in these in vitro
and animal models.
The selective induction of specific genes by intracellular factors
and chemical agents subsequent to demethylation has been reported
by several laboratories. For example, an increase in human
gamma-globin gene expression in vitro was found to require
activation by hexamethylenebisacetamide following treatment with
5AzaC [Ley J. T., Y. L. Chiang, D. Haidaris, N. P. Anagnou V. L.
Wilson, and W. F. Anderson. 1984. DNA methylation and regulation of
the human .beta.-globin like genes in mouse erythroleukemia cells
containing human chromosome 11. Proc. Natl. Acad. Sci. USA.
81:6618-6622]; demethylation of the gene by 5AzaC was not
sufficient for gene expression. By contrast, phenylacetate and
phenylbutyrate induced gamma-globin gene expression with subsequent
accumulation of fetal hemoglobin in cultured erythroid progenitors
and in humans. In addition to affecting DNA methylation, NaPA and
NaPB also activate a nuclear receptor that functions as a
transcriptional factor (the peroxisome proliferator receptor is
discussed herein). Thus, one possible explanation for the
differences in carcinogenic opposing activities between NaPA/NaPB
and 5AzadC seen here may be the ability of the aromatic fatty acids
to induce the expression of genes critical to growth control.
Phenylacetate and related compounds can possibly reverse the
methylation-mediated state of repression of silent anti-oncogenes.
The finding of DNA hypomethylation by NaPA in mammalian cells does
not come as a surprise in view of previous studies demonstrating
that, at millimolar concentrations, phenylacetate inhibits DNA
methylation in plant. Interestingly, at such high concentrations,
phenylacetate also inhibits plant tumor cell proliferation.
Therefore, the effect of phenylacetate on DNA methylation and its
role in regulating growth and differentiation have been conserved
in evolution.
The outcome of combining NaPA with 5AzadC (or 5AzaC) is of
particular interest. The cytosine analogs have been shown to
benefit patients with severe blood disorders such as leukemia,
sickle cell anemia, and .beta.-thalassemia. There is now
experimental data suggesting that 5AzadC may be active also in some
solid tumors, including malignant melanoma (Weber et al, submitted)
and prostate carcinoma. Unfortunately, the clinical application of
5AzadC has been limited by concerns regarding carcinogenesis. The
data indicate that NaPA can minimize the carcinogenic risk, while
both preserving and potentiating the therapeutic effects of 5AzadC.
Studies with human leukemic cells and with erythroid progenitors
derived from patients with .beta.-hemoglobinopathies revealed that
NaPA can enhance the efficacy of 5AzadC, causing superinduction
fetal hemoglobin production. Moreover, the addition of NaPA/NaPB to
nontoxic, yet sub-optimal concentrations of 5AzadC, induced
complete growth arrest and promoted apoptosis in cultured
hormone-refractory prostatic carcinoma cells (unpublished
data).
It appears therefore that phenylacetate, a common amino acid
derivative, may be of value as an antitumor and chemopreventive
agent. NaPA, which has an unpleasant odor, can be substituted by
its precursor, NaPB (or a derivative or analog of NaPB), for oral
administration. Upon ingestion by humans, phenylbutyrate undergoes
.beta.-oxidation to phenylacetate. Like NaPA, NaPB exhibits
antitumor and chemopreventive activities in experimental models,
and both drugs already proved safe for long-term oral treatment of
children with urea cycle disorders. More recent clinical studies
involving adults with cancer have confirmed that millimolar plasma
levels of phenylacetate and phenylbutyrate can be achieved with no
significant adverse effects. NaPB/NaPA will benefit high risk
individuals predisposed to cancer development, be applied in
combination with other anticancer therapeutics to enhance efficacy
and minimize adverse effects, and perhaps be used in maintenance
therapy to prevent disease relapse.
EXAMPLE 10
HbF induction in K562 cells by NaPA and derivatives
The K562 erythroleukemia line serves as a model for inherited
anemias that are associated with a genetic defect in the beta
globin gene leading to severe .beta.-chain hemoglobinopathies.
The results reported in Table 9 also show that there is a
synergistic affect when leukemia cells are exposed NaPA in
combination with interferon alpha, a known biological response
modifier or with the chemotherapeutic drug hydroxyurea (HU).
TABLE 9 ______________________________________ Induction of
Hemoglobulin Synthesis in Erythroleukemia K562 cells* POSITIVE CELL
CELLS VIABILITY TREATMENT BENZIDINE (%) (%)
______________________________________ Control 1.8 >95 NaPA 0.8
mg/ml 6.0 1.6 mg/ml 17.1 Interferon 500 13.5 IU/ml HU 100 uM 17.2
NaPA (0.8 mg/ml) 40-42 + HU or IFN
______________________________________ *Results at seven days of
treatment.
Analysis of gene transcripts showed accumulation of mRNA coding for
gamma globin, the fetal form of globin. This was confirmed at the
protein level.
Using the erythroleukemia K562 cell line described above it was
found that 4-hydroxyphenylacetate was as effective as NaPA in
inducing fetal hemoglobin accumulation, but was less inhibitory to
cell proliferation. In contrast, some other analogs such as 2,4- or
3,5-dihydroxyphenylacetate were found to be highly toxic.
EXAMPLE 11
PC3 and DU145 cells--NaPA as an antitumor agent
The effectiveness of NaPA as an antitumor agent was further
evaluated in a variety of experimental models. Studies in depth
were performed with two androgen-independent human prostate
adenocarcinoma cell lines, PC3 and DU145, established from bone and
brain metastases, respectively, as well as hormone responsive LNCaP
cultures. NaPA treatment of the prostatic cells resulted in
concentration-dependent growth arrest, accompanied by cellular
swelling and accumulation of lipid that stained positive with
Oil-Red O. The results of this study are shown in FIG. 11. As
illustrated therein, an IC.sub.50 for NaPA occurred at 600-800
.mu.g/ml. Significantly higher doses were needed to affect the
growth of actively replicating normal human FS4 skin fibroblasts or
normal endothelial cells (IC.sub.50 from 12-15 .mu.M), indicating a
selective cytostatic effect of the drug.
EXAMPLE 12
PC3 cells--non-invasiveness after NaPA treatment
It is known that PC3 cells are invasive in vitro and metastatic in
recipient athymic mice. [Albini, A. et al. A rapid in vitro assay
for quantitating the invasive potential of tumor cells. Cancer Res.
47:3239-3245 (1987)]. The invasiveness of PC3 cells which is
indicative of their malignant phenotype can be assessed by their
ability to degrade and cross tissue barriers such as matrigel, a
reconstituted basement membrane. Untreated PC3 cells and PC3 cells
treated with NaPA for 4 days in culture were quantitatively
analyzed in a modified Boyden chamber containing a matrigel-coated
filter with FS4 conditioned medium as a chemoattractant. After 4
days of treatment with 800 .mu.g/ml of NaPA in T.C. plastic dishes,
5.times.10.sup.4 cells were replated onto 16 mm dishes (Costar,
Cambdrige, Mass.) coated with 250 .mu.l of matrigel 10 mg/ml.
Control showed the characteristic growth pattern of untreated
cells, i.e, formation of net-like structures composed of actively
replicating cells which eventually degraded the matrigel and formed
monolayers on the plastic surface beneath. In contrast to the
controls, the NaPA treated cells formed isolated small colonies
which resembled normal human FS4 cells 8 days after plating. The
NaPA treated cells failed to degrade the matrigel barrier. The
formation of small noninvasive colonies on top of the matrigel is
indicative of loss of malignant properties following treatment.
Results of the in vitro invasion assays correlate highly with the
biological behavior of cells in vivo.
EXAMPLE 13
PC3 cells--PAG treatment did not hinder invasiveness
PC3 cells treated with NaPA for one week in culture, in contrast to
untreated cells or those treated with PAG, failed to form tumors
when transplanted s.c. into athymic mice. These results are shown
in Table 10.
TABLE 10 ______________________________________ Tumorigenicity of
Prostatic PC3 Cells in Nude Mice TREATMENT Diameter Weight (mg/ml)
Incidence (mm .+-. S.D.) (mg .+-. S.D.)
______________________________________ None 7/7 9 .+-. 3 285 .+-.
60 NaPA 0.8 1/7 2 50 PAG 0.8 3/4 8 .+-. 2 245 .+-. 35
______________________________________
PC3 cells were pretreated for 1 week in culture and then injected
(2.times.10.sup.5 cells/animal) s.c. into 4-5 week-old female
athymic nude mice. The results in Table 10 indicate the incidence
of tumor bearing animals/injected animals as well as tumor size
measured as mean diameter.+-.S.D. 8 weeks later.
EXAMPLE 14
Phenylacetate in combination with suramin
To further substantiate the phenotypic changes observed in the NaPA
treated prostatic PC3 cells, Northern blot analysis revealed that
NaPA inhibited the expression of collagenase type IV, one of the
major metalloproteases implicated in degradation of basement
membrane components, tumor cell invasion, and metastasis.
Furthermore, it was found that NaPA treated prostatic PC3 cells
showed an increase in the level of HLA-A mRNA which codes for major
histocompatibility class I antigen known to affect tumor
immunogenicity in vivo.
The malignant prostatic cell lines exhibit numerous abnormalities
in gene expression, including increased production of autocrine
tumor growth factor-.beta. (TGF-.beta.) and elevated activity of
urokinase plasminogen activator (uPA). Members of the TGF-.beta.
family have been implicated in tumor growth control, anglogenesis,
and immunosuppression. uPA, in contrast, is a serine protease
involved in degradation of extracellular stroma and basal lamina
structures, with the potential to facilitate tumor invasion and
metastasis. It was of interest, therefore, to examine the effect of
NaPA on TGF-.beta. and uPa expression in the prostatic tumor cells.
Northern blot analysis of PC3 after 72 h treatment revealed a
decrease in TGF-.beta.2 mRNA levels; the effect was specific for
TGF-.beta.2 as there was no change in the expression of
TGF-.beta.1. The decrease in TGF-.beta.2 was accompanied by
approximately a twofold increase in the levels of HLA-A3 mRNA, as
previously observed in treated human leukemic HL-60 cells.
Preliminary analysis of uPA transcript levels showed no significant
change after NaPA treatment. There was, however, a reduction
cell-surface uPA activity. The hormone-refractory malignant PC3 and
DU145 cells, but not the more indolent hormone-responsive LNCaP,
displayed high cell-bound uPA activity. Because the parental PC3
cultures are composed of highly heterogenous cell populations with
respect to uPA production, more homogeneous subclones were
established by limiting dilutions and single-cell cloning. A
subclone designated PC3-1, which resembled the parental PC3 cells
in its invasive capacity and surface-localized uPA activity
(2.2.+-.0.3.times.10.sup.6 Plau units per cell), was chosen for
further studies. After 3 d of treatment of PC3-1 with NaPA 5 mM
there was over 50% reduction in cell-associated uPA activity; the
effect was dose-dependent and reversible upon cessation of
treatment. Similar results were obtained with DU145 cells. Assay
specificity was confirmed by the fact that pretreatment of cells
with neutralizing anti-human uPA monoclonal antibodies, or addition
of antibodies at the time of assay, blocked over 95% of the
plasminogen-dependent proteolytic activity. Plasminogen-independent
proteolysis constituted 30% of the maximal fibronectin degrading
activity, and was similar for both NaPA-treated cells and untreated
controls.
NaPA in Combination with Suramin
TABLE 11 ______________________________________ Malignant Melanoma
A375 Treatment Growth Viability (.mu.g/ml) (% of control) (%)
______________________________________ None 100 >95 NaPA 400
63.3 >95 Suramin 38 78.3 >95 75 56.8 >95 150 38.6 92 300
26.6 82 NaPA (400) + Suramin (38) 45.5 >95 + Suramin (75) 30.1
94 + Suramin (150) 21.8 92
______________________________________
TABLE 12 ______________________________________ Prostate
Adenocarcinoma PC3 Treatment Growth Viability (.mu.g/ml) (% of
control) (%) ______________________________________ None 100 >95
NaPA 800 59.6 >95 Suramin 75 58.5 nd 150 46.5 nd 300 31.0 nd
NaPA (800) + Suramin (75) 24.2 90 + Suramin (150) 10.9 64
______________________________________
NaPA was found to significantly potentlate the therapeutic effect
of suramin, the only experimental drug known to be active against
prostate cancer.
However, drug toxicities have been a major concern. In agreement
with previous in vitro studies, we found that toxic doses of
suramin (300 .mu.g/ml) were needed in order to achieve over 50%
inhibition of prostatic DU145 cell growth. This cellular model was
used to examine whether NaPA could enhance the activity of
suboptimal but less toxic doses of suramin. Results of this
examination show that NaPA and suramin act in an additive manner to
inhibit DU145 cell proliferation. Moreover, suramin was found to be
significantly more active if added to glutamine-depleted medium.
Despite significant differences in tumor sensitivities, there was
complete growth arrest when DU145 and PC3 cells were treated for 6
d with both NaPA and suramin in glutamine-depleted medium, under
conditions in which each treatment alone had only a partial effect.
Similarly, Tables 11 and 12 show the effect of combined NaPA and
suramin treatment of malignant melanoma A375 cells and prostate
adenocarcinoma PC3 cells.
It is known that a disease state characterized by the presence of
benign hyperplastic lesions of the prostate exists as a separate
disease entity and has been identified in many patients that
progress to a diagnosis of prostatic cancer. Based on the above, it
is anticipated that NaPA, in addition to being effective in the
treatment of prostatic cancer, would be effective in treating
patients having benign hyperplastic prostatic lesions.
Further experiments demonstrated that NaPA appears to have broad
antitumor activity affecting a wide spectrum of malignancies. The
experimental data presented in Table 13 indicate that NaPA 0.4-0.8
mg/ml caused about 50% inhibition of growth in treated
adenocarcinoma of the prostate cell lines PC3 and DU145, melanoma
A375 and SK MEL 28, lung adenocarcinoma H596 and H661, and
astrocytoma U87, U373, and 343. Somewhat higher concentrations
(1.0-1.5 mg/ml) were needed to cause a similar inhibition of
squamous cell carcinoma A431, breast tumor MCS-7, osteosarcoma
KRIB, and fibrosarcoma V7T. Typically, NaPA treatment was
associated with growth arrest, induction of differentiation
markers, reduced invasiveness in vitro and loss of tumorigenicity
in nude mice.
TABLE 13 ______________________________________ Responses of
Different Tumor Ceil Lines to NaPA Treatment % Inhibition by #
Tumor Cell Line NaPA 0.8 mg/ml.sup.a
______________________________________ 1 Melanoma A375 .gtoreq.70
SK MEL 28 >50 2 Prostatic Ca.sup.b PC3 .gtoreq.50 DU145
.gtoreq.50 LaNCop >50 3 Astrocytoma U87 .gtoreq.50 U343
.gtoreq.50 U373 .gtoreq.50 4 Kaposi's Sarcoma KS .ltoreq.40 5
Leukemia HL-60 .ltoreq.40 6 Leukemia K562 .ltoreq.30 7 Breast
Cancer MCF-7 .ltoreq.30 8 Osteosarcoma KRIB .ltoreq.30 HOS <20 9
Fibrosarcoma V7T .ltoreq.30 RS485 .ltoreq.30 10 Squamous Cancer of
Head and Neck A431 <30 ______________________________________
.sup.a Pharmacologically attainable concentration .sup.b
Carcinoma
Of major interest in Table 13 are the following:
#1-3 Tumor cells show significant response i.e., .gtoreq.50%
inhibition of proliferation within one week of treatment. Cf. FIG.
15.
#4 KS, an HIV-associated disorder, may be more dramatically
affected by NaPA in humans, due to inhibition of HIV expression and
of essential growth factors released by infected lymphocytes.
#5,6 The treated HL-60 promeyelocytic leukemic cells undergo
terminal differentiation, a desirable outcome of chemotherapy. In
the K562 erythroleukemia, NaPA induced reversible erythroid
differentiation with no significant growth arrest (<30%); thus
the K562 data is of interest with respect to treatment of certain
anemias, not cancer.
Less attractive:
#7-10 For effective responses, the tumors may require much higher
drug concentrations if used alone.
Although some of the malignant cell lines seem more sensitive than
others, all were significantly more affected by NaPA when compared
to normal or benign cells. For example, NaPA inhibited the growth
of malignant osteosarcoma (KRIB) cells more so than benign
osteosarcoma-derived HOS cells. A differential effect was seen also
in ras-transformed fribrosarcoma V7T, when compared to the parental
non-tumorigenic NIH 3T3 cells. As to normal human cells, as much as
2-4 mg/ml of NaPA were needed to cause a significant inhibition of
growth to primary human skin FS4 fibroblasts. It should be noted
that the treatment was not toxic to either the malignant or the
normal cells.
The concentration range found to selectively suppress malignant
growth can be readily obtained in the clinical setting without
causing significant side effects. Intravenous infusion of NaPA into
humans at 250-500 mg/kg/day which results in plasma levels of
600-800 .mu.g/ml has been found to be a well tolerated treatment.
Cytotoxicity in tissue culture was observed when the NaPA
concentration was as high as 3 mg/ml or higher.
EXAMPLE 15
Phase I clinical trials
Patient Population.
Patients were eligible for this study if they had advanced solid
tumors for which conventional therapy had been ineffective, a
Karnofsky performance status greater than 60%, normal hepatic
transaminases and total bilirubin, a serum creatinine less than 1.5
mg/dl, and normal leukocyte and platelet counts. All patients
signed an informed consent document that had been approved by the
National Cancer Institute (NCI) Clinical Research Subpanel.
Seventeen patients, 16 men and 1 woman, with a median age of 57
years (range: 36-75) were enrolled between January and June 1993.
Disease distribution included progressive, metastatic,
hormone-refractory prostate cancer (9 patients), anaplastic
astrocytoma or glioblastoma multiform (6 patients), ganglioglioma
(1 patient) and malignant pleural mesothelioma (1 patient).
Drug Preparation and Administration.
Sodium phenylacetate for injection was prepared from bulk sodium
phenylacetate powder supplied by Elan Pharmaceutical Research Co.
(Gainesville, Ga.). The finished injectable stock solution was
manufactured by the Pharmaceutical Development Service, Pharmacy
Department, Clinical Center, NIH, in vials containing sodium
phenylacetate at a concentration of 500 mg/ml in sterile water for
injection, USP, with sodium hydroxide and/or hydrochloric acid
added to adjust the pH to approximately 8.5. Doses of sodium
phenylacetate to be infused over 30 minutes to 2 hours were
prepared in 150 ml of sterile water for injection, USP. Doses of
phenylacetate to be given over 24 hours were prepared similarly to
yield a total volume of 1,000 ml and were administered using an
infusion pump.
The protocol as originally designed delivered an i.v. bolus dose of
phenylacetate (150 mg/kg over 2 hours) on the first day of therapy,
to allow for the estimation of pharmacokinetic parameters. This was
followed 24 hours later by a CIVI of the drug for the next 14 days.
Cycles of two week drug infusions were repeated every 6 weeks. The
rate of drug infusion was to be increased in sequential cohorts of
at least three patients, and individual patients could escalate
from one dose level to the next with sequential cycles of therapy
provided they had experienced no drug-related toxicity and their
disease was stable or improved.
The protocol underwent several modifications over the 6 month
period. First, the size of the initial bolus dose was reduced from
150 to 60 mg/kg i.v. and the bolus infusion duration from 2 hours
to 30 minutes, after the first three patients were treated. This
change resulted in drug concentrations optimal for estimating the
drug's pharmacokinetics (vide infra) within a six hour time period.
Second, after the non-linear nature of phenylacetate's
pharmacokinetics was recognized (vide infra), the protocol was
changed from a fixed dose escalation (dose levels 1 and 2:150 and
250 mg/kg/day, respectively) to a concentration-guided escalation
trial (dose levels 3 and 4:200 and 400 .mu.g/ml, respectively). In
the latter format each patient was given an i.v. bolus dose of
phenylacetate (60 mg/kg over 30 minutes) one week prior to
beginning a 14 day CIVI of the drug. The patient-specific
pharmacokinetic parameters estimated from the bolus dose were used
to calculate an infusion rate that would maintain the serum
phenylacetate concentration at the targeted level during the 14 day
infusion. Serum drug concentrations were measured weekly, prompting
weekining reestimation of individual pharmacokinetics and dosage
adjustment (adaptive control with feedback).
Sampling Schedule.
With the initial 150 mg/kg i.v. bolus, blood samples were obtained
through a central venous catheter at the following timepoints
calculated from the beginning of the infusion: 0, 60, 115, 125,
135, 150, 165, 180, 240, 360, 480, and 600 minutes. For the 60
mg/kg bolus given over 30 minutes, blood sampling was performed at
0, 30, 60, 75, 90, 105, 120, 150, 180, 270 and 390 minutes from the
beginning of the infusion. At dose levels 1 and 2, blood samples
were obtained daily during the CIVI, while at dose levels 3 and 4,
blood samples were obtained on days 1, 2, 3, 8, 9 and 10 of the
infusion. Twenty-four hour urine collections for the determination
of phenylacetate and phenylacetylglutamine excretion were obtained
on days 1, 7 and 14 of therapy. Sampling of the CSF was performed
only if clinically indicated.
Determination of sodium phenylacetate and phenylacetylglutamine in
serum and urine by high performance liquid chromatography
(HPLC).
Blood was drawn by venipuncture into a Vacutainer.RTM. tube free of
anticoagulant and was then refrigerated. It was centrifuged at
1,200 g for 10 minutes in a Sorvall.RTM. RT 6000D centrifuge
(DuPont Co., Wilmington, Del.) at 4.degree. C. Serum was then
removed and stored in Nunc Cryotubes (Nunc Co., Denmark) at
-70.degree. C. until the day of analysis.
A standard curve was generated by adding known amounts of sodium
phenylacetate (Elan Pharmaceutical Research Co., Gainesville, Ga.)
and phenylacetylglutamine (a gift from Dr. S. W. Brusilow, Johns
Hopkins University, Baltimore) to a commercial preparation of
pooled serum (Baxter Healthcare Corporation, Deerfield, Ill.). The
standard values spanned the expected range of serum concentrations:
0, 5, 10, 20, 50, 100, 250, 500, 750 and 1,500 .mu.g/ml.
Two hundred microliters of serum were pipetted into a 1.7 ml
Eppendorft tube (PGC Scientifics, Gaithersburg, Md.). Protein
extraction was carried out by adding 100 .mu.l of a 10% (v/v)
solution of perchloric acid (Aldrich Chemical Co., Milwaukee,
Wis.). The tube was vortexed and then centrifuged at 4,500 g for 10
minutes. One hundred and fifty microliters of supernatant were
transferred to a new 1.7 ml Eppendorf tube and 25 .mu.l of 20%
KHCO.sub.3 (w/v) was added to neutralize the solution. This was
centrifuged at 4,500 g for 10 minutes and 125 .mu.l of supernatant
were transferred to an autosampler vial and maintained at
10.degree. C. until HPLC injection. Urine samples were processed in
an identical manner after an initial 1:10 dilution with water.
The HPLC system (Gilson Medical Electronics, Middleton, Wis.) was
composed of two pumps (305 and 306), an 805 manometric module, an
811C dynamic mixer, a 117 variable wavelength UV detector and a 231
autosampler fitted with a 20 .mu.l injection loop and cooled with a
Grey Line model 1200 cooling device. The column was a Waters.RTM.
(Millipore Corporation, Milford, Mass.) C18 Nova-Pak, 3.9.times.300
mm, maintained at 60.degree. C. with a Waters.RTM. temperature
control module. The mobile phase solutions consisted of fifty
microliter samples were auto-injected onto a 10 cm cation-ion
exchange column integrated into a Beckman Model 6300 Amino Acid
Analyzer (Beckman Instruments Inc., Palo Alto, Calif.). The solvent
flow rate (2:1 water/ninhydrin) was maintained constant at 0.5
ml/min. Column temperature was raised by 1.5.degree. C. per minute
to elute sarcosine, the internal standard. The column was
regenerated with lithium hydroxide at 70.degree. C. following each
injection. Absorbance was measured at 570 nm and 440 nm following
post-column color development with ninhydrin-RX (Beckman
Instruments Inc., Palo Alto, Calif.) at 131.degree. C. Beckman
System Gold software was used for data acquisition and data
management.
Pharmacokinetic Methods.
Initial estimates of V.sub.max and K.sub.m for phenylacetate were
obtained by generating Lineweaver-Burk plots from concentration
versus time curves following i.v. bolus doses. These initial
parameter estimates were refined by non-linear least squares
fitting, using the Nelder-Mead iterative algorithm, as implemented
in the Abbottbase.RTM. Pharmacokinetic Systems software package
(Abbott Laboratories, Abbott Park, Ill., version 1.0).
Statistical Methods.
The Student's t-test was used to compare estimates of
phenylacette's pharmacokinetic parameters derived from the
Lineweaver-Burk plots with those obtained using non-linear given
set of dosing and concentration data was quantified by calculating
the weighted sum of the errors squared following non-linear
least-squares fitting. The standard deviation of the errors was
modeled as a function of drug concentration multiplied by the
coefficient of variation of the assay. Confidence regions for the
parameters were derived from the weighted sum of squares in the
model incorporating the induction parameters, and approximate
significance levels for testing between the two models were
calculated using the F distribution [Draper, N. R., Smith H.
Applied Regression Analysis. New York, John Wiley and Sons, p. 282,
1966]. The significance levels of individual cycles were analyzed
by the Spearman rank correlation method in an attempt to discern
whether a relationship existed between time-dependent changes in
drug clearance and dose.
Analytical Assay.
The reverse phase HPLC assay allowed both serum phenylacetate and
phenylacetylglutamine concentrations to be determined
simultaneously from the same sample (see FIG. 12). The lower limit
of detection for both compounds in serum and urine was 5 .mu.g/ml,
based upon a signal-to-noise ratio of 5:1. The interassay CV for
serum concentrations was less than 6% within the range of 40 to
1,000 .mu.g/ml. (Table 14). The lower limit of detection for
glutamine was 0.5 .mu.g/ml, with an interassay CV that did not
exceed 7%.
Model Specification and Initial Parameter Estimation.
FIG. 13 shows representative concentration versus time curves for
simultaneously measured serum levels of phenylacetate and
pheylacetylglutamine and plasma levels of glutamine following a 150
mg/kg bolus dose of sodium phenylacetate. The post-infusion decline
in serum phenylacetate concentration over tim eis linear when
plotted on a non-logarithmic scale, consistent with saturable
elimination kinetics. While useful for demonstrating a zero-order
process, the 150 mg/kg bolus was inadequate for parameter
estimation insofar as most of the phenylacetate concentrations
obtained over the six-hour sampling period were above K.sub.m. In
order to generate concentrations both above and below K.sub.m, the
bolus was changed to 60 mg/kg i.v. over 30 minutes. Visual
inspection of the concentration versus time curves following these
boluses revealed no evidence of an initial distributive phase,
suggesting that a single compartment, open non-linear model should
be adequate to describe the drug's pharmacokinetics. Initial
estimates (mean.+-.SD) of K.sub.m (90.+-.30 .mu.g/ml), V.sub.max
(26.0.+-.10 mg/kg/hr) and Vd (22.4.+-.6.8 L) were calculated in 13
patients using the Lineweaver-Burk equation. Refinement of these
initial parameter estimates by non-linear least squares fitting of
the entire concentration versus time profile for each bolus dose
yielded the following estimates: K.sub.m =105.1.+-.44.5 .mu.g/ml,
V.sub.max =24.1.+-.5.2 mg/kg/hr and Vd=19.2.+-.3.3 L. The
differences between the two methods of estimation were not
statistically different, as measured by the Student's t-test
(p=0.89).
Induction of Phenylacetate Clearance.
In some patients treated at dose levels 1 and 2, we observed a
tendency the serum phenylacetate concentration to decrease with
time. An example of this phenomenon is shown in FIG. 14.
Considering the 12 cycles of therapy delivered at these levels, a
comparison of the serum drug concentration measured on day 2 of
CIVI to that observed on day 11 demonstrated a statistically
significant decline in concentration with time (Wilcoxon signed
rank test, p=0.016). At dose levels 3 and 4, attempts at
maintaining targeted serum phenylacetate concentrations using
adaptive control with feedback led to variable rates of drug
infusion over time, which precluded a simple comparison of drug
concentrations at the beginning and end of therapy.
Therefore all cycles of therapy were analyzed at all four dose
levels and compared with the performance of the single compartment
non-linear model described above with the same model modified to
allow V.sub.max to increase with time. The formula used to describe
this increase was:
wherein t is the time elapsed (in hours) since the initiation of
therapy, IF is an induction factor representing the maximum-fold
increase in V.sub.max at infinite time and IR is a first order rate
constant (h.sup.-1) describing the rate at which V.sub.max
increases over time. Each cycle of therapy (n=21) was evaluated by
comparing the difference in the weighted sum of errors squared
generated by non-linear least-squares-fitting with each model. The
significance of the difference was evaluated using the F test (see
statistical methods). In 9 of the 21 cycles, allowing V.sub.max to
increase with time yielded an improved fit (induction parameters,
mean.+-.SD:IF=1.87.+-.0.37, IR=0.0028.+-.0.003 h.sup.-1,
p.ltoreq.0.035). The Spearman rank correlation method did not
demonstrate a correlation between rate of drug administration and
the need to incorporate the two induction parameters into the model
(rank correlation coefficient=0.39, p=0.084). The dose rates
administered ranged from 450 to 1,850 mg/h.
Review of concomitantly administered medications revealed no
association between specific drugs and the occurrence of a
time-dependent increase in phenylacetate clearance. In seven
patients with primary CNS tumors, treatment with anticonvulsants
always antedated the administration of phenylacetate by months to
years.
Mechanisms of Phenylacetate Clearance.
As shown in FIG. 13, phenylacetate underwent rapid conversion to
phenylacetylglutamine. In the three patients who received 150 mg/kg
of phenylacetate over 2 hours, the peak serum concentration of
phenylacetylglutamine (mean.+-.SD) was 224.+-.81 .mu.g/ml,
325.+-.72 minutes post-infusion. After 60 mg/kg boluses, the peak
serum phenylacetylglutamlne concentration was 104.+-.33 .mu.g/ml at
86.+-.33 min. The plasma glutamine concentration prior to bolus
treatment with phenylacetate was 105.+-.29 .mu.g/ml (mean.+-.SD,
n=16), similar to reported values in the literature for normal
volunteers. The largest reduction in circulating plasma glutamine
levels (46%) was observed in a patient receiving a 150 mg/kg
bolus.
The molar excretion of phenylacetylglutamine was determined from 24
hour urine collections. It accounted for 99.+-.23% (n=18) of the
dose of phenylacetate administered over the same period of time.
The recovery of the free, non-metabolized drug was only 1.5.+-.2.4%
of the total administered dose. A strong phenylacetate odor was
detectable on patients' clothes and on examiners' hands after
physical examination. This suggests that phenylacetate may also be
excreted to some extent transdermally.
Distribution of Phenylacetate and Phenylacetylglutamine into the
CSF.
Clinical circumstances required evaluation of the cerebrospinal
fluid in two patients who had metastatic prostate cancer and were
free of CNS metastases. The first had reached steady-state
phenylacetate and phenylacetylglutamine concentrations of 141 and
199 .mu.g/ml, respectively, the corresponding simultaneous CSF
concentrations were 74 and 5 .mu.g/ml, respectively. At the time of
simultaneous serum and CSF sampling, the second patient had been
off therapy for 6 hours after having reached a serum concentration
of phenylacetate of 1044 .mu.g/ml. Measurements in serum and CSF
were 781 versus 863 .mu.g/ml for phenylacetate and 374 versus 46
.mu.g/ml for phenylacetylglutamine, respectively.
Clinical Toxicities.
No toxicity was associated with bolus administration of the drug.
The highest peak serum concentrations were measured after the 150
mg/kg bolus over 2 hours (533.+-.94 .mu.g/ml, mean.+-.SD). Table 15
lists the average serum phenylacetate concentrations per dose
level. Although those achieved at dose levels 3 and 4 are close to
their target, the large standard deviations reflect our inability
to maintain serum phenylacetate concentrations within the desired
range, even when using adaptive control with feedback.
Drug-related toxicity was clearly related to the serum
phenylacetate concentration. Three episodes of CNS toxicity,
limited to confusion and lethargy and often precided by emesis,
occurred in patients treated at dose levels 3 and 4. They were
associated with drug concentrations of 906, 1044 and 1285 .mu.g/ml
(mean: 950.+-.300 .mu.g/ml), respectively. Symptoms were completely
resolved within 18 hours of terminating the drug infusion in all
instances,
Antitumor Activity.
Stabilization of PSA for more than 2 months was noted in 3 of the 9
patients with prostate cancer treated at dose levels 2, 3 and 4
(mean phenylacetate concentration: 234.+-.175 .mu.g/ml). A fourth
patient experienced marked improvement in bone pain and was able to
substitute a non-steroidal anti-inflammatory drug to his morphine
regimen. One patient with glioblastoma multiform has had
improvement in performance status (30% on Karnofsky's scale),
intellectual function and expressive aphasia of greater than 5
months duration. Although no change in the size of the tumor mass
was noted, reduction in peritumoral edema was documented by
MRI.
Discussion.
Previous descriptions of the pharmacokinetics of phenylacetate have
been fragmentary. Simell et al. reported the drug to have first
order elimination kinetics with a half-life of 4.2 hours following
bolus dose administration 9270 mg/kg) children [Simell, O., Sipila,
I., Rajantie, J., Valle, D. L., and Brusilow, S. W. Waste nitrogen
excretion via amino acid acylation: benzoate and phenylacetate in
lysinuric Protein intolerance. Pediatr. Res., 20:1117-1121, 1986].
The failure to recognize the non-linear nature of phenylacetate
pharmacokinetics probably resulted from the smaller total doses
given to these patients compared to those given in our study. The
saturable pharmacokinetics of phenylacetate are consistent with an
enzymatic process and our calculations from the 24 hour urinary
excretion of phenylacetylglutamine confirm that this is the major
route of elimination. Evidence that drug clearance increases with
time was derived from the comparison of drug levels on days 2 and
11 of the CIVI, adding another layer of complexity to the
pharmacokinetics of phenylacetate. To explain this phenomenon, the
potential role of concomitantly administered medications was first
considered, but failed to demonstrate any association. Analysis of
a the relationship between an increase in drug clearance with time
and the rate of drug administration did not reach statistical
significance and suffered from the small number of cycles of
therapy available for analysis. It should also be noted that,
relative to the 14 day period over which it is assessed, V.sub.max
tended to increase slowly, with an average half-time calculated
from the induction rate (IR) of 9.6 days.
As expected for such a small molecule, phenylacetate readily
penetrates into the CSF, which may explain the dose-limiting
side-effects of the drug, i.e., nausea, vomiting, sedation and
confusion.
The results of Table 15 indicate that attempting to maintain serum
phenylacetate concentrations at either 200 or 400 .mu.g/ml using
adaptive control with feedback was problematic, with drug
concentrations that often greatly exceed the level-specific
targets. All patients who exhibited CNS toxicity had serum
phenylacetate concentrations in excess of 900 .mu.g/ml. In the
average patient, the drug must be infused at a rate equal to 75% of
V.sub.max, in order to maintain a constant serum phenylacetate
concentration of 400 .mu.g/ml, which is four times greater than
K.sub.m. Thus, the slightest error in the estimation of individual
pharmacokinetics or in the rate of drug infusion results in large
changes in drug concentration. Phenylacetate was delivered by CIVI
in order to mimic the preclinical conditions that had demonstrated
antitumor activity, namely, continuous exposure to concentrations
above 475 .mu.g/ml for at least two weeks. Unfortunately, such
concentrations cannot be practically maintained.
An alternative strategy is to deliver the drug by repeated short
infusions. Our limited experience with the 150 mg/kg i.v. boluses
suggests that serum phenylacetate concentrations occurring
transiently above 500 .mu.g/ml are well tolerated. In addition, the
time interval between infusions allows some drug washout to occur,
thereby minimizing drug accumulation. A simulated regimen of 200
mg/kg q 12 h (1 hour infusion) is presented in FIG. 16. The
simulation assumes that the pharmacokinetic parameters determined
from our 17 patients are representative of the cancer population at
large and that V.sub.max does not change with time. It predicts
that a wide range of peak drug concentrations will be present.
However, it is possible that these would be sufficiently transient
so as not to produce CNS toxicity and the troughs not so prolonged
as to abrogate the drug's antitumor activity.
TABLE 14 ______________________________________ PA Standard Curve
Assay Variability PA CV PAG CV (.mu.g/ml) (%) (.mu./ml) (%)
______________________________________ 40 2.6 40 4.6 400 1.7 400
4.3 1000 3.4 1000 3.1 ______________________________________
TABLE 15 ______________________________________ PA and PAG
Concentrations Per Dose Level During CIVI PA.sup.a PAG.sup.a Dose
Level PA dose level (.mu.g/ml) (.mu.g/ml)
______________________________________ 1 150 mg/kg/d 49 .+-. 19 90
.+-. 34 2 250 mg/kg/d 104 .+-. 40 150 .+-. 63 3 200 .mu.g/ml 178
.+-. 85 188 .+-. 55 4 400 .mu.g/ml 397 .+-. 244 306 .+-. 51
______________________________________ .sup.a mean .+-. SD
EXAMPLE 16
Effect of NaPA on differentiation of human neuroblastoma cells.
The ability of NaPA to promote the differentiation of human
neuroblastoma cells was studied, both alone and in combination with
retinoic acid (RA), a known inducer of neuroblastoma
differentiation and maturation. In the LA-N-5 cell line,
phenylacetate stimulated the differentiation of human neuroblastoma
cells as evidenced by dose-dependent inhibition of cell
proliferation, neurite outgrowth, increase acetylcholinesterase
activity, and reduction of N-myc protein levels. Furthermore, NaPA
and RA synergized in inducing LA-N-5 differentiation in that
combination treatment resulted in complete cessation of cell growth
along with morphologic and biochemical changes indicative of the
loss of malignant properties. The combined effects represent a
strong differentiation response in neuroblastoma cells, both as to
number of responding cells and maturational level achieved.
Transient transfection of LA-N-5 cells with a variety of CAT
reporter gene plasmids including constructs containing thyroid and
RA responsive regulatory elements have suggested that the pathways
of action of NaPA and RA may intersect at the nuclear level through
activation of common response elements. The synergistic effects,
thus, may be mediated by the ability of NaPA to modulate the RA
differentiation pathway so as to result in altered transactivation
of RA responsive regulatory elements in relevant target genes.
These in vitro antineoplastic effects were observed under drug
concentrations achievable in humans without significant
toxicities.
SECTION B: PHENYLACETATE AND ITS DERIVATIVES IN THE TREATMENT AND
PREVENTION OF AIDS
The etiology of human acquired immunodeficiency syndrome (AIDS) has
been linked to the human immunodeficiency virus (HIV), which is
capable of selective infection and suppression of the host immune
system. This immune defect renders the human body susceptible to
opportunistic infections and cancer development, which are
ultimately fatal. The spread of HIV throughout the world is rapid,
with no effective therapeutics on hand. It is suggested that NaPA,
a nontoxic natural compound capable of glutamine depletion in vivo,
can be used in the treatment and prevention of AIDS.
HIV is a retrovirus. The production of retroviruses is dependent on
transcriptional activation by the long terminal repeat (LTR)
element, and the availability of glutamine (Gln) for translational
control. Experimental data obtained with chronically infected
cultured cells and animal models indicate that virus replication is
specifically inhibited in cells starved for glutamine, but not in
those starved for other amino acids (Gloger and Panet (1986); (J.
Gen. Virol. 67:2207-2213) Roberts and McGregor, (1991), (J. Gen.
Virol 72:2199-305). The results could not be attributed to either
an effect on cell cycle or a general inhibition of protein
synthesis.
The reason why glutamine depletion leads to virus suppression can
be explained as follows. Replication competent murine retroviruses
contain an amber termination codon at the junction of gag and pol
genes, which can be recognized by amber suppressor tRNA.sup.Gln.
Glutamine is thus essential for the readthrough of viral mRNA
transcripts [Yoshinaka et al. (1985); PNAS 82:1618-1622]. Reduction
in glutamine concentrations disrupts viral mRNA translational
readthrough and protein synthesis, with subsequent inhibition of
viral assembly and secondary spread. Although human retroviruses
are somewhat different from the murine viruses studied, it has been
shown that reduction in the levels of amber suppressor tRNA.sup.Gln
in human cells infected with HIV causes a significant reduction in
the synthesis of vital proteins [Muller et al. Air Research and
Human Retroviruses 4:279-286 (1988)]. Such data suggest that agents
which can lower glutamine levels in humans are likely to benefit
patients infected with HIV. NaPA may be such an agent, since it is
known to conjugate to glutamine in humans with subsequent renewed
excretion of phenylacetylglutamine. Since NaPA also possesses
antitumor activities, the drug is likely to affect Kaposi's
sarcomas, the tumors found in as many as 30% of all AIDS patients,
as well as lymphomas associated with AIDS.
EXAMPLE 17
NaPA for treatment of AIDS related disorders
Evidence from experimental model systems in support of the above
hypotheses includes:
(a) Preliminary findings with cultured cells indicate that NaPA can
inhibit expression of genes controlled by the retroviral LTR; (b)
While animal studies have been hindered by the fact that glutamine
depletion by NaPA is limited to humans and higher primates, an
acceptable animal model (other than primates) involves rodents
treated with glutaminase. The expression of retroviral genes is
under the control of the long terminal repeat (LTR) element;
inhibition of LTR would prevent transcription and synthesis of
viral proteins. To examine the effect of NaPA on the retroviral
LTR, V7T fibrosarcoma cells carrying an LTR-dependent Ha-ras
oncogene were used as a model. Results of Northern blot analysis
showed markedly reduced levels of the ras RNA transcription in
cells treated with NaPA compared to RNA transcription levels in
untreated control cells. The results cannot be explained by a
general effect on gene expression, as indicated by the increased
expression of the cellular genes collagen and 2'-5' oligo adenylate
synthetase (2-5 ASyn). The latter are of particular interest since
collagen is a marker of fibroblast differentiation, and 2-5 ASyn is
associated with growth control. Taken together, the data indicate
the NaPA suppressed the activity of the retroviral LTR, while
restoring growth control and differentiation to the host cells.
Similarly desirable changes might occur in HIV-infected monocytes
and T4 lymphocytes following systemic treatment of afflicted
patients with NaPA. Glutaminase is a bacterial enzyme that causes
reduction of extracellular (and presumably intracellular) glutamine
concentrations. Glutaminase treatment of viremic mice infected with
Rouscher murine leukemia virus (RLV) inhibited retroviral
replication and the development of splenomegaly, and significantly
increased animal survival [Roberts and McGregor J. Gen. Virology
72:29-305 (1991)]. The efficacy of glutaminase therapy compared
favorably with AZT, the drug currently used for treatment of AIDS.
The results are of particular interest since the RLV serves as a
model in the search for anti-HIV drugs (Ruprecht et al., 1986).
Unfortunately, however, glutamine depletion by glutaminase in vivo
is only transient due to development of neutralizing antibodies to
the enzyme. Once this occurs, vital replication can resume,
eventually killing the host. NaPA, unlike the bacterial
glutaminase, is a natural component of the human body, and thus is
less likely to induce the production of neutralizing antibodies;
(c) There is clinical evidence for sustained reduction by NaPA of
plasma glutamine concentrations. NaPA is currently being used for
treatment of hyperammonemia associated with inborn disorders of
urea metabolism. Clinical experience indicates that long-term
treatment with NaPA effectively reduces glutamine levels. Such
treatment is nontoxic and well tolerated even by newborns. In
conclusion, NaPA might benefit patients with HIV infection. NaPA
could inhibit viral replication through (among other mechanisms)
inhibition of LTR and depletion of glutamine, the amino acid
required for appropriate processing of vital proteins. If NaPA
proves to have anti-HIV activities in humans, it could be used to
prevent disease progression in asymptomatic HIV-positive
individuals. The lack of toxicity, easy oral administration and
relatively low cost uniquely qualify NaPA as a chemopreventive
drug. In fact, the drug is so well tolerated by humans that
treatment can start just a few hours after birth. In addition, NaPA
could be used (alone or in combination with other drugs) in
treatment of AIDS-associated disorders including opportunistic
infections, HIV encephalopathy, and neoplasia.
SECTION C: INDUCTION OF FETAL HEMOGLOBIN SYNTHESIS IN .beta.-CHAIN
HEMOGLOBINOPATHY BY PHENYLACETATE AND ITS DERIVATIVES
There is considerable interest in identifying nontoxic therapeutic
agents for treatment of severe .beta.-chain hemoglobinopathies.
Employing the human leukemic K562 cell line as a model, we have
explored the cellular responses to NaPA, an amino acid derivative
essentially nontoxic to humans. Treatment of cultures with
pharmacologically attainable concentrations of NaPA resulted in
time- and dose-dependent inhibition of cell proliferation and
caused an increase in hemoglobin production. Molecular analysis
revealed accumulation of the fetal form of hemoglobin (HbF), which
was associated with elevated steady-state levels of gamma globin
mRNA. All NaPA effects reversed upon cessation of treatment.
Interestingly, addition of NaPA to other antitumor agents of
clinical interest, i.e., 5-azacytidine and hydroxyurea, resulted in
superinduction of HbF biosynthesis. The results suggest that NaPA,
an agent known to be well tolerated by newborns, could be used
alone or in combination with other drugs for long-term treatment of
some inborn blood disorders.
The pathophysiology of inherited blood disorders such as sickle
cell anemia and severe .beta.-thalassemias is based on genetic
abnormalities in the .beta.-globin gene which result in deficient
or absent .beta.-globin synthesis. The latter prevents the
production of hemoglobin and results in ineffective red blood cell
production and circulation. Recent data indicate that
pharmacological manipulation of the kinetics of cell growth and
differentiation might have a beneficial effect in patients with the
.beta.-chain hemoglobinopathies, due to the induction of fetal
hemoglobin (HbF) synthesis. To date, several antitumor drugs
including 5-azacytidine (5AzaC), 5-aza-2'-deoxycytidine (5AzadC),
hydroxyurea (HU), vinblastine, and arabinosylcytosine (ara-C) have
been shown to increase the production of HbF in experimental models
[Dover, Ann NY Acad. Sci. 612:184-190 (199)]. Moreover, there is
clinical evidence for 5AzaC and HU activity in severe
.beta.-thalassemia and sickle cell anemia, respectively. However,
concerns regarding toxic and potential carcinogenic effects of the
prevailing antitumor drugs raise the need to identify safe
alternatives for long-term treatment of the inborn nonmalignant
diseases. The accumulation of fetal hemoglobin in adults is thought
to be due to changes in the kinetics of erythroid differentiation
rather than a direct effect on the fetal globin genes. According to
this hypothesis, other agents that can induce differentiation would
also be expected to affect HbF production. The focus here is on the
efficacy of a novel nontoxic differentiating agent, NaPA.
As discussed in Section A, Applicant's laboratory has found that
NaPA can also affect the maturation (i.e., differentiated state) of
various animal and human cell types. The drug caused growth arrest
and reversal of malignant properties in a variety of in vitro tumor
models including cell lines established from adenocarcinomas of the
prostate and lung, malignant melanomas, and astrocytomas. Moreover,
NaPA treatment was associated with adipocyte conversion in
premalignant mesenchymal C3H 10T1/2 cells, and granulocyte
differentiation in promyelocytic leukemia HL-60 cultures. Studies
indicated that NaPA, in contrast to the chemotherapeutic
differentiating drugs 5AzaC and 5AzadC, may be free of adverse
effects such as cytotoxicity and tumor progression.
Indeed, NaPA is well tolerated by humans as indicated by the vast
clinical experience with NaPA in the treatment of hyperammonemia in
infants with inborn errors of ureagenesis. The clinical experience
indicates that acute or long-term treatment with high doses of NaPA
is essentially free of adverse effects. The lack of toxicity and
the ability to induced cellular differentiation prompted Applicant
to examine the effect of NaPA on HbF expression.
EXAMPLE 18
K562 cells--induction of HbF by treatment with NaPA
The experimental system involved the human leukemic K562 cells,
which carry a nonfunctional .beta.-globin gene, but produce low
levels of the fetal gamma globin and of HbF. The K562 cell line was
originally established from a patient with chronic myelogenous
leukemia in the blast cells transformation, and has since been
extensively utilized as a model in studies of erythroid
differentiation and regulation of the gamma globin gene expression.
Applicant has shown that pharmacologically attainable
concentrations of NaPA can promote HbF biosynthesis in the human
leukemic cells, and can cause superinduction when combined with the
other chemotherapeutic agents of interest, 5AzaC and Cell Culture
and reagents.
The human leukemia K562 cells were maintained in RPMI 1640 medium
supplemented with 10% heat-inactivated fetal calf serum (Gibco), 50
U/ml penicillin, 50 .mu.g/ml streptomycin, and 2 mM L-glutamine
unless otherwise indicated. The suspension cultures were kept in
exponential growth phase by diluting every 3-5 days with fresh
medium, and cell viability was determined by trypan blue exclusion.
Phenylacetic acid, 4-hydroxyphenylacetic acid,
3,4-dihydroxyphenylacetic acid, 2,5-dihydroxyphenylacetic acid
(Sigma, St. Louis, Mo.) and PAG (a gift from L. Trombetta, Houston,
Tex.) were dissolved in distilled water, and brought to pH 7.0 by
the addition of NaOH, DON, adivicin, 5AzadC, 5AzaC, and HU (Sigma)
were also dissolved in distilled water. All drug stock solutions
were stored in aliquots at -20.degree. C. until used.
Determination of Hemoglobin Production.
K562 cells were seeded at 1.times.10.sup.5 cells/ml and treated
with the drugs for four to seven days prior to assay. Qualitative
estimation of hemoglobin production was determined by benzidine
staining of intact cells in suspension. The hemoglobin
concentration within cells was determined by the protein absorption
at 414 nm. Briefly, 1.times.10.sup.7 cells were lysed in 1 ml of
lysing buffer (0.12% Tris pH 7.4, 0.8% NaCl, 0.03% Mg-acetate, and
0.5% Np-40), vortexed and incubated on ice for 15 minutes. The
lysates were then centrifuged for 15 minutes at 1500 rpm at
4.degree. C., and the absorption of the supernatant monitored
between 350 nm and 650 nm using Beckman Du-7 scanning
spectrophotometer. The hemoglobin was quantitated using the
relationship of 1.0 optical density (OD) at 414 nm corresponding to
0.13 mg/ml hemoglobin as described before.
Northern Blot Analysis and DNA probes.
Cytoplasmic RNA was prepared from cultures at logarithmic phase of
growth and separated on 1% agarose-formaldehyde gels. Gel
electrophoresis, transfer of RNA onto nytran membranes (Schleicher
& Schuell), hybridization with radiolabeled DNA probes, and
autoradiography (Kodak X-ray film XAR5) were according to
established procedures. The probe for gamma globin was a 0.6 Kb
EcoRI/HindIII fragment of the human gamma globin gene. Probes were
labeled with [.sup.32 P]dCTP (New England Nuclear, Boston, Mass.)
using random primed DNA labeling kit (Boehringer Mannheim, West
Germany).
Analysis of HbF Protein Synthesis.
Newly synthesized proteins were labeled with .sup.35 S-methionine
and the HbF immunoprecipitated and analyzed as previously
described. Briefly, cells (1.times.10.sup.6 per point in 1 ml) were
first subjected to 1 hr starvation in methionine-free medium, then
incubated in the presence of 100 uCi/ml of .sup.35 S-methionine for
2 hrs. The labeled cells were harvested, washed and lysed in a
lysing buffer containing 10 mM phosphate buffer pH 7.4, 1%
Triton.times.100, 0.1% SDS, 0.5% deoxycholate, 100 mM NaCl, 0>1%
NAN3, 2 mM PMSF, and 10 .mu.g/ml lenpeptin. 1.times.10.sup.7 cpm of
TCA precipitable count of cytoektract was incubated with rabbit
anti-human HbF (Pharmacia) and protein A Sepharose at 4.degree. C.,
and the immunoprecipitates were separated by electrophoresis on 12%
SDS-polyacrylamide gels.
The Effect of NaPA and Analogues on Cell Growth and
Differentiation.
Treatment of the K562 cultures with NaPA resulted in dose dependent
inhibition of cell proliferation, with 1.4 mg/ml causing 50%
reduction in cell number after four days of treatment (FIG. 17). No
toxicity was observed with doses as high as 2.0 mg/ml. In addition
to the cytostatic effect, NaPA also induced erythroid
differentiation, as indicated by an increase in the number of
benzidine-positive cells (FIG. 17) and confirmed by quantitative
analysis of hemoglobin production (Table 16). Similar treatment
with PAG, which is the glutamine conjugated form of NaPA, had no
significant effect on either cell proliferation or hemoglobin
accumulation, suggesting that the changes associated with NaPA
treatment are specific and not due to alterations in culture
conditions.
The effect of NaPA on cell growth and differentiation could be
mimicked by the use of 4-hydroxyphenylacetate (Table 16). This was
in marked contrast to the analogues 3,4-dihydroxyphenylacetate and
2,5-dihydroxyphenylacetate, which were highly toxic to the cells
(LD50 of 60 and 100 .mu.g/ml, respectively), and did not induce
differentiation.
Regulation of Fetal Hemoglobin Production by NaPA.
K562 cells normally express low but detectable levels of HbF.
Protein analysis employing anti-HbF antibodies revealed
significantly increased amounts of HbF in cells treated with NaPA
compared to untreated controls, this was associated with elevated
steady-state levels of the fetal gamma globin mRNA. The effect of
NaPA on HbF production was time and dose dependent, and apparently
reversible upon cessation of treatment.
Glutamine Starvation and HbF Production.
NaPA treatment of humans can lead to depletion of circulating
glutamine due to conjugation to glutamine and formation of PAG, an
enzymatic reaction known to take place in the liver and kidney. The
in vivo reduction in plasma glutamine was mimicked in vitro by
culturing the K562 cells in the presence of lowered glutamine
concentrations. Results presented in Table 17 show, in agreement
with previous reports, that glutamine starvation alone can affect
the growth rate as well as HbF production in the K562 cells.
Addition of NaPA to the glutamine-depleted growth medium further
augmented the cytostatic and differentiating effects observed.
Therefore, the effect of NaPA on erythroid differentiation and HbF
production in humans may be even more dramatic than that observed
with the in vitro model, due to depletion of circulating glutamine
and a direct effect on the erythroid progenitor cells.
Potentiation by NaPA of Erythroid Differentiation induced by Other
Chemotherapeutic Drugs.
There is considerable interest in the use of 5AzaC, 5AzadC and HU
for treatment of sickle cell anemia and .beta.-thalassemia;
however, the clinical use of these drugs is often limited by
unacceptable toxicities. Combination treatments with nontoxic
differentiating agents like NaPA could enhance hemoglobin
production while minimizing the adverse effects. Therefore the
efficacy of various combinations of NaPA with the other drugs of
clinical interest was tested. Results, summarized in Table 18, show
that addition of NaPA 800 .mu.g/ml, to low doses of 5AzadC or HU
act synergistically to further augment HbF production with no toxic
effect to cells. The concentration of HU used in these experiments
is comparable to the plasma HU levels measured in sickle cell
anemia patients following an oral administration of 25 mg/kg
[(Goldberg et al. New England J Med 323:366-372 (1990)]. As to
NaPA, pharmacokinetics studies in children with urea cycle
disorders indicate that plasma levels of approximately 800 .mu.g/ml
can be obtained by infusion with 300-500 mg/kg/day, a treatment
well tolerated even by newborns.
Discussion.
Chemotherapeutic agents selected for their low cytotoxic/mutagenic
potential can be used for induction of fetal hemoglobin in patients
with congenital severe anemias such as sickle cell and
.beta.-thalassemia. Drug toxicity is an important consideration in
view of overall health condition and the variable life-span of
patients with these nonmalignant blood disorders. Unfortunately,
recombinant human erythropoietin, which has proved to be both
nontoxic and effective therapy for anemias associated with chronic
renal disease, is apparently ineffective in the treatment of sickle
cell anemia. The application of other active drugs such as 5AzadC,
HU, vinblastine and ara-C has been hindered by concerns regarding
their carcinogenic effects. HU is also difficult to use because of
the narrow margin between toxicity and the desired effect on
increased HbF production [Dover, et al., Blood 67:735-738 (1986)].
In contrast, NaPA, shown here to affect HbF production, is so well
tolerated by humans that treatment can be initiated just a few
hours after birth.
Using an in vitro model involving human leukemic K562 cells, it is
shown that NaPA can promote the maturation of early erythroid
progenitor cells that have an active HbF program. Addition of NaPA
to other therapeutic agents currently in clinical use, i.e., 5AzaC,
5AzadC, or HU resulted in superinduction of HbF synthesis. 5AzaC
has been shown to be less toxic and more effective than HU in
stimulating HbF production. Moreover, 5AzaC, unlike HU, is
effective in treatment of both sickle cell anemia and
.beta.-thalassemia. Such data are consistent with the
interpretation that 5AzaC acts by both perturbation of
erythropoiesis and by its effect on DNA methylation. However, while
hypomethylation can lead to gene activation and cell
differentiation, it can also promote oncogenesis and the evolution
of cells with metastatic capabilities. Results obtained with the
K562 erythroid progenitor cells indicate that the therapeutic
effects of NaPA compare favorably with those of 5AzadC, yet NaPA
(unlike the cytosine analog) did not cause tumor progression.
Moreover, NaPA was shown to prevent tumor progression induced by
5AzadC.
The data show that NaPA, used alone or in combination with other
drugs,is of value in treatment of leukemias are .beta.-chain
hemoglobinopathies. In addition to promoting the production of red
blood cells expressing HbF through nontoxic mechanisms, NaPA may
also minimize the adverse effects of other antitumor drugs
currently in clinical use.
TABLE 16 ______________________________________ HbF Accumulation in
Treated K562 Cells Benzidine Positive Cells HbF production
Treatment fold fold (mg/ml) (%) increase (pg/cell) increase
______________________________________ None 2.2 .+-. 0.8 1 0.35
.+-. 0.06 1 NaPA 0.4 2.7 .+-. 0.2 1.2 0.49 .+-. 0.02 1.4 0.8 7.0
.+-. 0.3 3.2 1.15 .+-. 0.20 3.3 1.6 14.6 .+-. 0.2 6.6 2.40 .+-.
0.16 6.8 4HP 1.6 14.2 .+-. 0.5 6.45 ND PAG 2.6 2.1 .+-. 0.5 0.95
0.37 .+-. 0.03 1.06 ______________________________________
TABLE 17 ______________________________________ Glutamine
Starvation and HbF Production HbF (g/cell) Gln starvation Gln (mM)
alone Plus NaPA (0.8 mg/ml) ______________________________________
2.0 0.39 .+-. 0.04 1.0 .+-. 0.06 0.5 0.56 .+-. 0.01 1.15 .+-. 0.01
0.2.sup.a 1.17 .+-. 0.12 1.75 .+-. 0.22 0.1.sup.a 1.86 .+-. 0.40
2.22 .+-. 0.20 ______________________________________ .sup.a The
concentration of NaPA used in this study (0.8 mg/ml) is
pharmacologically attainable without toxicity. In children such a
treatment is expected to cause a drop in circulating glutamine
plasma levels to 0.1-0.2 mm. The results presented above indicate
that under suc conditions HbF production increases 4.5-5.7 fold
compared to controls. We propose therefore that the effect of NaPA
in children might be more dramatic than that seen under routine
culture conditions (i.e., cell growth in medium with 2 mM Gln).
TABLE 18 ______________________________________ Potentiation by
NaPA of HU's Therapeutic Effect Treatment HbF (pg/cell)
______________________________________ None 0.39 .+-. 0.04 NaPA
(0.8 mg/ml) 1.64 .+-. 0.07 HU (50 uM) 1.00 .+-. 0.03 HU (50 uM) +
NaPA 5.91 .+-. 0.6.sup.b HU (100 uM) 2.12 .+-. 0.04 HU (100 uM) +
NaPA 6.71 .+-. 0.05.sup.b ______________________________________
.sup.a To mimic the effect of NaPA in vivo, treatments involving
NaPA wer performed in medium supplemented with 0.2 mM Gln (see
explanation to Tabl 17). Control untreated cells and those treated
with HU or 5AzadC alone were maintained in growth medium with 2 mM
Gln. .sup.b The results indicate that NaPA and HU act
synergistically to induc HbF Production int he erythroid progenitor
cells Note: Similar results have been obtained for the combination
NaPA 0.8 mg/ml and 5AzadC 0.3 uM.
EXAMPLE 19
HbF induction in nonmalignant and malignant cells
General ability of NaPA and its derivatives to induce production of
HbF.
The ability of oral administration of sodium 4-phenylbutyrate to
increase fetal hemoglobin production was assayed. To do so, the
percentage of red cells containing fetal hemoglobin (F cells) was
measured by flow-cytometric single-cell immunofluorescent assays in
15 patients (7 females and 8 males) with hereditary urea-cycle
disorders who had received sodium 4-phenylbutyrate therapy for 5 to
65 months. In determining the differences in low levels of fetal
hemoglobin in persons without anemia, the measurement of the
percentage of F cells is more precise than conventional
measurements of fetal hemoglobin as a percentage of total
hemoglobin. The mean percentage of F cells was significantly higher
in the patients than in normal subjects:
______________________________________ Dose of Patient Age
Phenylbutyrate F Cells* No. yr g/kg/day %
______________________________________ 1 29 0.30 9.4 2 11 0.67 20.4
3 6 0.62 0.5 4 5 0.48 6.5 5 2 0.58 22.7 6 13 0.46 7.7 7 2 0.38 11.8
8 11 0.41 1.9 9 6 0.27 1.9 10 5 0.62 2.3 11 6 0.65 21.1 12 21 0.29
1.7 13 3 0.47 7.6 14 6 0.64 40.5 15 2 0.63 29.7 Patients, -- 12.4
.+-. 3.1** mean .+-. SE Normal subjects, -- 3.1 .+-. 0.2 mean .+-.
SE ______________________________________ *F cells were measured
with a flowcytometric technique that counts the percentage of F
cells in a total of 10,000 red cells. The difference between
repeated measurements was less than 10 percent. **P = 0.005 by the
KolmogorovSmirnov twosample test for the comparison of the Fcell
values in the 15 patients with ureacycle disorders and the values
in 293 normal adults. The percentage of F cells reaches the range
of values found in normal adults at about two years of age.
EXAMPLE 20
In vitro study of sickle cell and beta-thalassemia responses to
NaPA/NaPB
An in vitro study was conducted on cells derived from patients with
homozygous sickle cell disease or B-thalassemia who had been
admitted to the Clinical Center of the National Institutes of
Health (NIH) for routine evaluation, or normal blood donors from
the Department of Transfusion Medicine (NIH). Approximately 20-25
ml of blood was obtained for erythroid cell cultures. Diagnosis of
SS or B-thal was made on the basis of: (1) hemoglobin
electrophoresis on alkaline cellulose acetate and on acid citrate
sugar; (2) peripheral blood examination; and occasionally (3) DNA
and RNA analysis of bone marrow aspirates. When possible, diagnosis
was confirmed by family studies. Routine hematologic profiles were
performed on a Coulter Model S.
Peripheral blood mononuclear cells were isolated by centrifugation
on a gradient of Ficoll-Hypaque and cultured for 7 days (phase I)
in alpha-minimal essential medium supplemented with 10% fetal calf
serum (FCS) (both from GIBCO, Grand Island, N.Y.), 1 .mu.g/ml
cyclosporin A (Sandoz, Basel, Switzerland) and 10% conditioned
medium collected from bladder carcinoma 5637 cultures (Myers C. D.,
Katz F. E., Joshi G, Millar J. L.: A cell line secreting
stimulating factors for CFU-GEMM culture. Blood 64:152, 1984). In
phase II, the non-adherent cells were recultured in alpha-medium
supplemented with 30% FCS, 1% deionized bovine serum albumin,
1.times.10.sup.5 M 2-mercaptoethanol, 1.5 mM glutamine (unless
otherwise indicated), 1.times.10.sup.6 M dexamethasone, and 1 U/ml
human recombinant Epo (Ortho Pharmaceutical Co., Raritan, N.J.).
These cultures yielded up to 10.sup.6 erythroid cells per
milliliter of blood. Cell viability was determined by Trypan Blue
exclusion. Phenylacetic acid, 4-phenylbutyric acid,
p-hydroxyphenylcetic acid, p-chlorophenylacetic acid, and butyric
acid (Sigma, St. Louis, Mo.) were dissolved in distilled water and
brought to pH 7.0 by the addition of NaOH. 5-Azacytidine and
hydroxyurease was obtained from Sigma, and PAG was obtained from S.
Brusilow (Johns Hopkins, Baltimore, Md.).
Differentiation was assessed morphologically by preparing
cytocentrifuge slides stained with alkaline benzidine and Giemsa.
The number of Hb-containing cells was determined using the
benzidine-HCl procedure (Orkin S. H., Harosi F. L., Leder P.:
Differentiation of erythroleukemic cells and their somatic hybrids.
Proc Natl. Acad. Sci U.S.A. 72:98, 1975). Hbs were characterized
and quantitated by cation exchange high performance liquid
chromatography (HPLC) of cell lysates as previously described
(Huisman TH: Separation of hemoglobins and hemoglobin chains by
high performance liquid chromatography. J Chromatography 418:277,
1987). Total Hb in lysates prepared from a known number of
Hb-containing (benzidine-positive) cells was measured using either
the tetramethylbenzidine procedure (Sigma kit, Catalog No. 527) or
by cation exchange HPLC (measuring total area under chromatogram).
Standard Hb solutions (Isolab, Inc., Akron, Ohio) were used for
reference. Mean cellular Hb (MCH) was calculated by dividing the
total Hb content of the lysate by the number of benzidine-positive
cells.
Cytoplasmic RNA was separated on 1% agarose-formaldehyde gels. RNA
isolation, gel electrophoresis, transfer onto Nytran membranes
(Schleicher & Schuell, Inc., Keene, N.H.), hybridization with
radiolabeled DNA probes, and autoradiography (Kodak X-ray film
XARS) were described [Samid D., Yeh A., Presanna P.: Induction of
erythroid differntiation and fetal hemoglobin production in human
leukemic cells treated with phenylacetate. Blood, 80:1576, 1992].
The human globin cDNA probes included JW101 (alpha), JW102 (beta),
and a 0.6 kb EcoRI/HindIII fragment of the 3' end of human
G-gamma-globin gene. Probes were labeled with [.sup.32 P]dCTP (New
England Nuclear, Boston, Mass.) using a random primed DNA labeling
kit (Boehringer, Mannheim, Germany). Results. Addition of NaPA or
NaPB to phase II erythroid cultures resulted in reduced cell
proliferation with no apparent change in cell viability. Cytostatis
was associated with a decline in total Hb produced per culture;
however, both Hb content per cell (MCH) and the proportion of HbF
(% HbF) increased upon treatment (FIG. 18). The extent of changes
observed was dose- and time-dependent: the earlier the drugs were
added during the second phase of growth, the higher was the
increase in % HbF, however, cell yields were proportionately
decreased. For example, addition of 5 mM NaPA to normal precursors
on day 2 caused approximately 90% decrease in cell number along
with a 12-fold increase in % HbF, a determined on day 13. When
treatment was initiated on day 67, cell number decreased on by 60%
compared to controls, and % HbF increased 3.3-fold. In order to
obtain sufficient cells for further analysis, subsequent
experiments involved the addition of drugs on days 6-7, and cells
were harvested on day 13. Under these conditions, results were
reproduced in cultures derived from 6 normal donors as well as 4
patients with sickle cell anemia and 4 patients with B-thal. NaPA
(5 mM) and NaPB (2.5 mM) caused a significant increase in both
MCH(38-100%) and the proportion of HbF produced. In the case of
homozygous SS patients, % HbF was elevated 2.0-4.1 fold (mean 3.0)
by 4 mM NaPA, and 3.2-5.6 fold (mean 4.0) by 2.5 mM NaPB. The
latter was associated with a 12.+-.3% decrease in HbS levels, with
no change in HbA.sub.2 (FIG. 19).
As in K562 cells, increased HbF production by NaPA or NaPB in
primary cultures of normal or SS cells appears to be due to
pre-translational regulation of gamma-globin expression. Northern
blot analysis showed dose-dependent increase (up to 5 fold) in the
steady-state levels of gamma globin mRNA, accompanied by a slight
decrease (less than two fold) in the amounts of beta globin
transcripts. There was no change in alpha globin expression.
PAG, the end-metabolite of both NaPB and NaPA, is formed by
phenylacetate conjugation to glutamine with subsequent excretion in
the urine. PAG was found to be inactive on erythroid proliferation
and HbF accumulation. Glutamine starvation of the non-malignant
erythroid cells had no effect on either cell growth or HbF
production, nor did it enhance the efficacy of NaPA.
The effect of NaPA with other drugs was also assayed. When used
alone in cultures derived from normal donors (HbF base levels of
0.8-2.0%), NaPA (5 mM) and hydroxyurease (0.05 mM) increase % HbF
by 3.5 and 2.0-fold, respectively; the combination of the two
resulted in a 4.7-fold increase in HbF. NaPA also augmented HbF
stimulation by butyrate (0.5 mM) (from 3.1 to 7.15-fold), and of
5-Azacytidine (2 uM) (from 2.5 to 6.6-fold). These results indicate
that NaPA when added to suboptimal, non-toxic doses of other drugs,
can potentlate HbF production with significant cytostasis and no
signficant change in cell viability.
As exemplified below in Table 20, combination treatment comprising
administration of NaPA (or a pharmaceutically acceptable derivative
of phenylacetic acid) simultaneously with hemin, a known stimulator
of HbF production, synergistically increases the induction of
erythroid differentiation, as indicated by the increase in the
number of benzidine positive cells, and HbF production. In K562
cells, the range of increase in the production of HbF with this
combination treatment varied from 1.5 to 5 times that produced by
treatment with 10 mM PA alone. Further, treatment with NaPB in
combination with hemin also resulted in classical synergism.
Similar results were also obtained with PB in non-malignant
erythroid progenator primary cells. In all cases, treatment with
both drugs was maintained for 4-6 days prior to measurement of
HbF.
TABLE 20 ______________________________________ STIMULATION OF HbF
BY NaPA IN COMBINATION WITH HEMIN - K562 MODEL R.sub.x % Benzidine
pos. Hb pg/cell Viability ______________________________________
CONTROL >0.01 0.26 97 NaPA (10 mM) 1.6-3.1 0.91 96 NaPA (10 mM)
+ H 25.4-32.6 4.03 92 NaPA (5 mM) + H 12.6 2.34 99 NaPA (2.5 mM) +
H 8.1 1.95 94 HEMIN (20 .mu.M) 2.9 1.04 98 CONTROL 2.1 0.65 97 NaPA
(2.5 mM) 2.6 0.91 97 NaPA (5 mM) 7.7 1.04 97 NaPA (10 mM) 14.3 nd
96 HEMIN (20 .mu.M) 13.8 2.34 nd NaPA (5 mM) + H 42.3 5.2 97
______________________________________
SECTION D: USE OF PHENYLACETIC ACID AND ITS DERIVATIVES IN WOUND
HEALING
Growth factors, including TGF-.alpha., play a critical role in
wound healing and repair processes. Wound healing is a localized
process that involves inflammation, wound cell migration and
mitosis, neovascularization, and regeneration of the extracellular
matrix. Recent data suggest the action of wound cells may be
regulated by local production of peptide growth factors which
influence wound cells through autocrine and paracrine mechanisms
(Schultz et al., J. Cell Biochem. 45(4):346 (1991); Schultz et al.,
Acta Ophthalmol. Suppl.(Copenh), 202:60 (1992)). Two peptide growth
factors which may play important roles in normal wound healing in
tissues such as skin, cornea, and the gastrointestinal tract are
the structurally related epidermal growth factor (EGF) and
TGF-.alpha., whose receptors are expressed by many types of cells
including skin keratinocytes, fibroblasts, vascular endothelial
cells, and epithelial cells of the gastrointestinal tract. EGF or
TGF-.alpha. is synthesized by several cells involved in wound
healing, including platelets, keratinocytes, activated macrophages
and corneal epithelial cells. Healing of a variety of wounds in
animals and patients, such as epidermal regeneration of partial
thickness burns, dermatome wounds, gastroduodenal ulcers and
epithelial injuries to the ocular surface, is enhanced by exogenous
treatment with EGF or TGF-.alpha.. TGF-.alpha., which is a potent
inducer of lysyl oxidase mRNA levels in cultures of human scleral
fibroblasts, may be primarily responsible for inducing synthesis of
extracellular matrix components after an injury. Furthermore,
TGF-.alpha. is known to promote anglogenesis.
The lack of adequate stimulation of growth factors contributes to
the nonhealing conditions of many chronic wounds. Poorly healing
conditions could markedly benefit from either addition of exogenous
TGF-.alpha. or stimulation of effector cells to produce TGF-.alpha.
and related growth factors. It has now been discovered that PA and
PB (or a pharmaceutically acceptable derivative) are capable of
stimulating production of TGF-.alpha. in cells of melanocytic
origin; astrocytic lineage (glioblastoma cells); and several normal
human epithelial cell types, including keratinocytes (FIG. 20),
which are involved in wound healing. Further, treatment with PA and
PB enhances collagen-.alpha. type 1 expression. Introduction
TGF-.alpha. mRNA expression upon treatment with NaPA and NaPB in
human melanoma cells was observed; expression of TGF-.alpha. was
confirmed following protein analysis. FIG. 20 shows the increased
production of the TGF-.alpha. protein in human keratinocytes upon
exposure to NaPA and NaPB. This increased production of TGF-.alpha.
is maintained for a few days after which the levels return to
approximately pretreatment levels. As discussed below and in FIG.
21, further support for the use these compounds in treating wounds
may be found in the enhanced expression of ICAM-1, which is a
cellular adhesion molecule/surface antigen, following treatment
with NaPB.
Thus, the instant invention provides a method for stimulating the
production of TGF-.alpha. in cells. Further, wound healing in a
human or animal can be enhanced by treatment with a therapeutic
amount of phenylacetic acid or a derivative of phenylacetic acid
such as NaPA or NaPB, which stimulates the in-situ production of
TGF-.alpha.. For instance, surface wounds can be treated by
topically applying PA, PB or a derivative of either PA or PB to the
skin surface, such as in a cream formulation. Likewise, ocular
injuries can be treated by application of a PA or PB (or PA/PB
derivative) formulation, such as eye drops, to the cornea.
Similarly, internal injuries, such as injuries to the
gastrointestinal tract, can be treated by administration of oral
formulations. Vaginal or anal injuries can also be treated, such as
with a suppository containing pharmaceutically effective amounts of
PAA or a derivative. The PA/PB or derivative formulations can be
administered continuously or, preferably, intermittently, such as
one or more doses in daily, weekly or monthly courses. For example
topical administration once or twice a day of a composition
containing from 0.1 to 10 mM PA, preferably 0.1 to 5.0 mM PA or
from 0.1 to 5 mM PB, preferably 0.1 to 2.5 mM PB over the course of
a week adequately stimulates wound repair. From the information
contained herein, dosage concentrations and amounts for the various
administration vehicles can be easily determined. For instance, a
topical treatment, such as a cream containing PB, typically will
contain approximately 0.5 to 3.0 mM PB or an equipotent (by
equipotent it is meant that dosage may be varied among the
different phenylacetic acid derivatives so as to achieve the
equivalent effect on the subject) dose of a phenylacetic acid
derivative. For instance, and without limitation, approximately
one-half as much PB in a dose is needed to equal the potency of a
similarly indicated PA dose.
SECTION E: USE OF PHENYLACETIC ACID OR ITS DERIVATIVES IN TREATMENT
OF DISEASES ASSOCIATED WITH INTERLEUKIN-6
Interleukin-6 (IL-6), which can be produced by monocytes and
keratinocytes upon stimulation, is a pleiotropic cytokine that
plays a central role in defense mechanisms, including the immune
response, acute phase reaction and hematopoiesis. Activation of
mature B cells can be triggered by antigen in the fluid phase. When
antigen binds to cell membrane IgM in the presence of IL-1 and
IL-6, mature virgin B cells differentiate and switch isotypes to
IgG, IgA or IgE. Abnormal expression of the IL-6 gene has been
suggested to be involved in the pathogenesis and/or symptoms of a
variety of diseases, including (1) non-malignant disorders
associated with abnormal differentiation programs, autoimmunity and
inflammatory processes, e.g., rheumatoid arthritis, Castleman's
disease, mesangial proliferation, glomerulonephritis, uveitis,
sepsis, autoimmune diseases such as lupus, inflammatory bowel, type
I diabetes, vasculitis, and several skin disorders of cell
differentiation such as psoriasis and hyperkeratosis; (2) viral
diseases such as AIDS and associated neoplasms, e.g., Kaposi's
Sarcoma and lymphomas; and (3) other neoplasms, e.g., multiple
myeloma, renal carcinoma, Lennert's T-cell lymphoma and plasma cell
neoplasms. For instance, significantly increased IL-6 mRNA levels
in lesional psoriatic tissue relative to normal tissue and elevated
amounts of IL-6 in sera and peripheral blood mononuclear cells of
psoriatics compared to samples from atopics or healthy controls
have been found (Elder et al., Arch. Dermatol. Res., 284(6):324
(1992); Neuner et al., J. Invest. Dermatol., 97(1):27 (1991)).
It has now been discovered that phenylacetic acid or a derivative
of phenylacetic acid, such as NaPA or NaPB, can inhibit the
expression of IL-6. For instance, PA inhibits IL-1-induced IL-6
expression in colon carcinoma cells. This reduction in RNA is
confirmed by reduction in IL-6 protein. Thus, PA, PB and their
derivatives can be used in the treatment of diseases involved with
the abnormal overexpression of IL-6.
For instance, treatment twice daily by topical application of
either 2 mM NaPB in a mineral oil-based cream or 2 mM
napthylacetate and Vitamin B.sub.1 in a mineral oil-based cream
directly onto the patient's psoriatic lesions resulted in
disappearance of the lesions within a week. Similar treatment of a
patient with a severe case of psoriasis resulted in the psoriatic
lesions resolving in approximately 1-3 weeks. Obviously, the mode
of administration and amount of drug can vary depending upon the
IL-6-related disease being treated in order to target the drug to
the cells in which reduction of IL-6 expression is desired. For
example, injection of a 0.1 mM-5 mM PB solution or an equipotent
solution containing a pharmaceutically acceptable phenylacetic acid
derivative into the joint region may be appropriate for treatment
rheumatoid arthritis whereas other diseases may be more
appropriately treated by topical, intravenous or oral delivery.
Treatment can be by either continuous or discontinuous treatment,
but cessation of the drug, particularly PB, may be accomplished by
ramping down the dosage amounts to prevent an overreaction to the
cessation of treatment with the drug. Additionally, diseases
involving the abnormal overexpression of IL-6 can be treated by
administration of an effective amount of phenylacetic acid or a
phenylacetic acid derivative, particularly PA or PB, in combination
with an effective amount of an anti-inflammatory agent, including
various vitamins such as vitamin B.sub.1, non-steroidal
inflammatory agents and steroidal anti-inflammatory agents. The
anti-inflammatory agent can be combined with the phenylacetic acid
derivative(s) of this invention in the same dosage form or
administered separately by the same or different route as the
derivative. An effective amount of the anti-inflammatory agent
refers to amounts currently in clinical use for the specific
disease state or less.
SECTION F: USE OF PHENYLACETIC ACID OR ITS DERIVATIVES IN THE
TREATMENT OF AIDS-ASSOCIATED CNS DYSFUNCTION
Hallmarks of central nervous system (CNS) disease in AIDS patients
are headaches, fever, subtle cognitive changes, abnormal reflexes
and ataxia. Dementia and severe sensory and motor dysfunction
characterize more severe disease. Autoimmune-like peripheral
neuropathies, cerebrovascular disease and brain tumors are also
observed. In AIDS dementia, macrophages and microglial cells of the
CNS are the predominant cell types infected and producing HIV-1.
However, it has been proposed that, rather than direct infection by
HIV-1, the CNS disease symptoms are mediated through secretion of
viral proteins or viral induction of cytokines that bind to glial
cells and neurons, such as IL-1, TNF-.alpha. and IL-6 (Merrill et
al., FASEB J., 5(10):1291(1991)). TGF-.beta. is a growth factor
which is released by many cell types. Among other effects,
TGF-.beta. is highly chemotactic for macrophages and fibroblasts
and stimulates the release of TNF-.alpha., TGF-.alpha. and,
indirectly, a variety of other modulators from macrophages which
have been implicated in the initiation of the CNS symptoms of
AIDS.
It has now been discovered that phenylacetic acid or a derivative
of phenylacetic acid, such as NaPA or NaPB, can inhibit the
production of TGF-.beta.2. Because TGF-.beta.2 is an
immunosuppresive factor, this inhibition results in a general
improvement of the patient's immune system. Gene expression of
TGF-.beta.2 in glioblastoma cells was inhibited by both PA and PB.
This reduction in RNA leads to reduced TGF-.beta.2 protein
synthesis. Thus, PA, PB or their derivatives can be used to inhibit
the production of TGF-.beta.2 in cells, particularly to control or
alleviate the CNS symptoms resulting from HIV infection. As
discussed above, this treatment also inhibits the production of
IL-6, further allowing for alleviation of the CNS symptoms. Amounts
of drug and/or regimens of administration effective for inhibiting
TGF-.beta.2 correspond to those appropriate for treatment or
prevention of cancer as given herein, such as in SECTION C.
SECTION G: USE OF PHENYLACETIC ACID AND ITS DERIVATIVES TO ENHANCE
IMMUNOSURVEILLANCE
Immunosurveillance in an animal such as a human can be enhanced by
treatment with PA, PB or their derivatives. Tumor cells are thought
to escape attack by the immune system by at least two means. First,
many tumors secrete immune suppressive factors that directly reduce
immune activity. Additionally, some tumor cells do not express, or
have reduced expression of, appropriate surface antigens that allow
the immune system to identify outlaw cells. However, the
compositions of the instant invention can activate otherwise
dormant genes such as fetal globin, perhaps by DNA hypomethylation.
Similarly, activation of cancer suppressor genes, dormant antigens
and other genes, such as (1) cellular major histocompatibility
antigens (MHC Class I and II) or other surface antigens, such as
ICAM-1; (2) tumor antigens such as MAGE-1; and (3) vital latent
proteins such as EBV's latent membrane protein (which is implicated
in numerous diseases such as T-cell neoplasms, Burkitt's lymphoma
nasopharyngeal carcinoma, and Hodgkin's disease), may contribute to
enhanced immunosurveillance. Thus, neoplastic cells can be treated
with PA, PB or their derivatives to provide for expression of cell
surface antigens that increase the effectiveness of the immune
system by allowing for adequate identification and clearance of the
tumor cells by the immune system. Activation of latent viral
proteins could also induce a lytic cycle leading to death of the
infected cell.
Evidence that the instant phenylacetic acid or phenylacetic acid
derivative compositions can activate dormant genes and enhance
expression of surface antigens is given by FIG. 21, which shows
enhanced expression of MHC Class I, MHC Class II and the adhesion
molecule ICAM-1 in melanoma cells that have been treated for 10
days with 2 mM NaPB (e.g., note the shift of the population mean
from approximately 50 to 200 for MHC class I).
Furthermore, it has now been discovered that PB induces expression
of EBV's latent membrane protein (LMP) in Burkitt's lymphoma cells.
Cytoplasmic RNA (20 .mu.g/lane) was isolated from LandisP, RajI and
P3HRI Burkitt's lymphoma cell lines, which had been treated with 2
mM PB for four days, and subjected to Northern blot analysis with a
specific LMP probe. In all three cell lines, a positive reaction
was observed compared to controls (untreated cells), indicating
that PB induces the expression of EBV's latent membrane protein. In
Burkitt's lymphoma cells both PA and PB cause additional molecular
and cellular changes, including cytostasis, decline in myc
expression and enhancement of HLA+1.
Because these surface antigens enhance tumor immunogenicity in
vivo, treatment of the animal (human) with PA, PB or their
derivatives can enhance the effectiveness of the immune system of
the individual. Doses of approximately 0.5-3.0 mM PB or equipotent
doses of pharmaceutically acceptable phenylacetic acid derivatives
may be useful. This treatment can also be combined with
conventional immunotherapy treatments and/or antigen targeted,
antibody-mediated chemotherapy. While treatment usually is
accomplished by a protocol which allows for substantially
continuous treatment, discontinuous or pulsed treatment protocols
are also effective, especially for cells capable of terminally
differentiating upon treatment with PAA or a PAA derivative. For
instance, treatment of the melanoma cells given in FIG. 21 for 10
days was sufficient to allow continued enhanced expression of the
surface antigens past this 10 day period.
SECTION H: METHOD OF MONITORING THE DOSAGE LEVEL OF PHENYIACETIC
ACID OR ITS DERIVATIVES IN A PATIENT AND/OR THE PATIENT RESPONSE TO
THESE DRUGS
As discussed above, administration of phenylacetic acid or a
derivative of phenylacetic acid such as NaPA or NaPB to an animal
(human) in amounts and over treatment courses as described herein
induce a variety of molecular changes. These molecular traits can
be used as biomarkers to either (1) monitor the dosage level of the
drug or its bioavailability in the animal and/or (2) serve as a
biomarker of the patient response to the drug. For instance, as
described above, administration of an effective amount of NaPA or
NaPB (or their derivatives) results in a variety of molecular
effects, including a) increased levels of fetal hemoglobin in
erythrocytes; b) increased production of TGF-.alpha. in various
cells such as those of melanocytic origin, astrocytic lineage or
epithelial cell types; c) inhibition of the production of IL-6; and
d) inhibition of the production of TGF-.beta.2. Thus, absolute or
relative (before/after treatment) concentrations of a particular
biomarker can be determined in an appropriate cell population of
the individual to allow monitoring of the dosage level or
bioavailability of the drug. Further, this concentration can be
correlated or compared with patient responses to develop a patient
response scale for a desired treatment goal based upon that
biomarker. For instance, the increased amount of fetal hemoglobin
can be used to indicate the bioavailability of PA or PB for
treatment or prevention of a neoplastic condition as well as
indicating the degree of patient response to the drug.
SECTION I: THE ACTIVATION OF THE PPAR BY PHENYLACETIC ACID AND ITS
DERIVATIVES
Peroxisomes are cellular organelles that contain enzymes which
control the redox potential of the cell by metabolizing a variety
of substrates such as hydrogen peroxide. Recent advances in this
area reveal that peroxisomes can be proliferated through activation
of a nuclear receptor which regulates the transcription of specific
genes (Gibson, Toxicol. Lett., 68(1-2):193(1993)). This nuclear
receptor has been named the peroxisome proliferator-activated
receptor (PPAR) and belongs to the steroid nuclear receptors family
that have a major effect on gene expression and cell biology.
Binding by peroxisome proliferators such as clofibrate, herbicides,
and leukotriene antagonists with PPAR activates the nuclear
receptor, which acts as a transcriptional factor, and can cause
differentiation, cell growth and proliferation of peroxisomes.
Although these agents are thought to play a role in hyperplasia and
carcinogenesis as well as altering the enzymatic capability of
animal cells, such as rodent cells, these agents appear to have
minimal negative effects in human cells, as exemplfied by the
safety of drugs such as clofibrate (Green, Biochem. Pharm.
43(3):393(1992)).
Peroxisome proliferators typically contain a carboxylic functional
group. Therefore, PA, PB and various phenylacetic acid derivatives
were tested for their ability to activate the PPAR and compared
with known peroxisomal proliferators. As shown in FIG. 22,
Clofibrate, a known activator of peroxisosmal proliferation, caused
a 4- to 5-fold increase in activation as measured by increased
production of the response element for acyl-CoA oxidase, which is
the rate limiting enzyme in betaoxidation and is contained in
peroxisomes (Dreyer et al., Biol. Cell, 77(1):67(1993)). PA and PB
caused mild activation (double baseline activity), naphthyl acetate
was relatively more active (approximately 2.5- to 4-fold increase)
while the halogenated analogs of PB were very potent stimulators.
Interestingly, butyrate was not a significant peroxisomal
proliferation activator.
The peroxisome proliferator-activated receptor has been shown to
belong to the same family of nuclear receptors as the retinoid,
thyroid and steroid receptors and PPAR is known to interact with
RXR, the receptor of 9-cis-retinoic acid (a metabolite of
all-trans-retinoic acid). Because the PPAR signaling pathway
converges with the 9-cis retinoid receptor signal, it can be
anticipated that retinoic acid or the like will significantly
enhance the activity of PA or PB or other phenylacetic acid
derivatives of this invention. Indeed, enhancement of the induction
of HL-60 cell differentiation by NaPA in combination with retinoic
acid is discussed above. Additionally, this synergistic response
has been confirmed in other tumors, such as neuroblastoma, melanoma
and rhabdomyosarcoma cells.
Thus, combination therapy consisting of administration
(simultaneously in the same dosage form or
simultaneously/sequentially in separate dosage forms) of Vitamin A,
Vitamin D, Vitamin C, Vitamin E, B-carotene, of other retinoids and
the like with PA, PB or other phenylacetic acid derivatives is
encompassed by the instant invention for any of the treatment
regimes given herein. Appropriate doses of the phenylacetic acid
derivatives include approximately 0.5-10 mM PA, more preferably
0.5-5 mM PA, doses or equipotent doses of a pharmaceutically
acceptable phenylacetic acid derivitive. Between 0.1 and 1.0 .mu.M
concentrations of the retinoids are expected to be effective. This
combination therapy enhances, for instance, the efficacy of
treatment with PA, PB or other phenylacetic acid derivatives, taken
alone, for cancer, anemia and AIDS treatment, wound healing, and
treatment of nonmalignant disorders of differentiation.
Agents affecting cellular peroxisomes have a major impact on
oxidative stress and the redox state of a cell. Thus, further
evidence that PA, PB or other phenylacetic acid derivatives
activate PPAR can be found by the rapid increase of gamma glutamyl
transpeptidase and catalase following cellular exposure to PA or PB
as shown in FIG. 23. These antioxidant enzymes, whose activities
are increased when peroxisome proliferation has been activated,
were increased by 100% 24 hours after administration of sodium
phenylbutyrate. This effect was reversed by approximately 48 hours
and activity was maintained below control levels through 100 hours.
The intracellular level of glutathione followed a similar biphasic
pattern with an initial increase (20%) followed by a fall to levels
below baseline at 100 h. The rapid induction with subsequent sharp
decline of these antioxidant enzymes was observed in numerous tumor
types from prostatic, breast and colon adenocarcinomas,
osteosarcoma, and brain tumors. Nolecular analysis showed changes
in the rate of gene transcription of the GSH-related and
antioxidant enzymes, which are consistent with activation of PPAR
by PA, PB or their analogs.
Because peroxisomal enzymes are instrumental in defending against
oxidative stress, experiments were undertaken to examine the
effects of treatment with PA or PB on cells which were subjected to
chemical or radiation stress. Pretreatment of glioblastomas (FIG.
42), breast carcinoma and metastatic prostate cells with a
non-toxic dose of PA or PB 72 hours prior to CO.sup.60
.gamma.-radiation or treatment with adriamycin demonstrated a
significant dose-related increase in cell killing by either
modality. The surviving fraction of cells following drug treatment
was nearly one tenth the fraction surviving with no pretreatment,
which suggests that PA, PB or other like analogs could be used to
increase the efficacy of radiation therapy and chemotherapy
substantially. As such, the instant invention encompasses
combination anti-cancer therapy consisting of administration of an
non-toxic effective amount of phenylacetic acid or a
pharmaceutically acceptable phenylacetic acid derivative (according
to any of the dosage concentration protocols given herein) in
combination with radiation therapy, particularly local treatment,
or chemotherapy, particularly targeted to the tumor cells. This
adjuvant therapy can be administered, for instance, after
approximately 24 hours, such as from 24 hours to 120 hours or more,
from the initiation of the administration of the derivative.
These results suggest a further consideration of a variety of
pathogenic disorders. Inflammatory response to tissue injury,
pathogenesis of emphysema, ischemia-associated organ injury
(shock), doxorubicin-induced cardiac injury, drug-induced
hepatotoxicity, atherosclerosis, and hyperoxic lung injuries are
each associated with the production of reactive oxygen species and
a change in the reductive capacity of the cell. Although long-term
exposure to PA or other phenylacetic acid analogs depletes cellular
redox protection systems, short term treatment with PA and the like
may have significant implications for treatment of disorders
associated with increased reactive oxygen species.
SECTION J: USE OF PHENYLACETIC ACID AND ITS DERIVATIVES IN
TREATMENT OF CANCERS HAVING A MULTIPLE-DRUG RESISTANT PHENOTYPE
In treating disseminated cancers, systemic treatment with cytotoxic
agents is frequently considered the most effective treatment.
However, a number of cancers exhibit the ability to resist the
cytotoxic effects of the specific antineoplastic drug administered
as well as other agents to which the patient's system has never
been exposed. In addition, some cancers appear to have multiple
drug resistance even prior to the first exposure of the patient to
an antineoplastic drug. Three mechanisms have been proposed to
explain this phenomenon: P-glycoprotein Multiple Drug Resistance
(MDR), MDR due to Topoisomerase Poisons and MDR due to altered
expression of drug metabolizing enzymes (Holland et al., Cancer
Medicine, Lea and Febiger, Philadelphia, 1993, p. 618-622).
P-glycoprotein MDR resistance appears to be mediated by the
expression of an energy-dependent pump which rapidly removes
cytotoxic agents from the cell. High levels of p-glycoprotein are
associated with amplification of the MDR gene and transcriptional
activation. Increased expression of p-glycoprotein can also be
stimulated by heat shock, heavy metals, other cytotoxic drugs and
liver insults, and ionizing radiation in some cell lines from some
species. The results are not sufficiently consistent to confirm a
causal relationship but are highly suggestive.
Topoisomerases are nuclear enzymes which are responsible for
transient DNA strand breaks during DNA replication, transcription
and recombination. Cytotoxic agents, such as etoposide,
doxorubicin, amsacrine and others are known poisons of
topoisomerase II, and cause lethal DNA strand breakage by the
formation of stable complexes between the DNA, topoisomerase II and
drug. MDR to this type of drug is thought to be caused by changes
in the nature and amount of enzymatic activity, which is thought to
prevent the formation or effect of the DNA-enzyme-drug complex.
Some cytotoxic agents are able to induce increased metabolic
capability which permits rapid elimination of the toxin. Among the
enzymes which have been implicated are glutathione S-transferase
isozymes (GSTs). These enzymes are responsible for the conjugation
of the electrophilic moieties of hydrophobic drugs with
glutathione, which leads to detoxification and elimination of the
drug.
As discussed above, PA and other phenylacetic acid analogs have
been shown to stimulate the proliferation of peroxisomes which
contain some isozymes of GST. Based on that observation, it would
be expected that PA and PB would also stimulate MDR. However, as
shown in FIG. 25 it has now been discovered that the opposite
occurs. Thus, FIG. 25 shows the inhibition by PA of the growth of
cells from a line of breast cancer cells that exhibit the MDR
phenotype. Up to 10 mM PA in cultures, growth of cells is
dramatically inhibited in a dose-dependent manner. Surprisingly, PA
and PB are more highly active against adriamycin-resistant breast
cancer cells than compared to adriamycin-sensitive cells. This
increased sensitivity of the MDR phenotype is reproducible in other
tumor models, including those that are resistant to radiation
therapy.
Thus, the instant invention provides a method of treating tumor
cell populations in a patient that are resistant or able to survive
current conventional treatments, particularly tumors having a MDR
phenotype, by administration to the patient of non-toxic amounts of
PA (such as amounts that provide up to 10 mM PA or an equipotent
dose of a pharmaceutically acceptable phenylacetic acid derivative)
in the vicinity of the tumor or equivalently effective amounts of
phenylacetic acid or a phenylacetic acid analog. PA or other analog
dosage protocols similar to those described in relation to the
potentiation of differentiation in tumor cells by these
phenylacetic acid-related compounds, inlcuding the various
combination therapies described herein, can be used to treat
patients with resistant tumors such as MDR tumors. Long-term
(weeks, months) or short-term (day(s)) substantially continuous
treatment regimens (including continuous administration or frequent
administration of separate doses) as well as pulsed regimens (days,
weeks or months of substantially continuous administration followed
by a drug-free period) can beneficially be employed to treat
patients with MDR tumors.
SECTION K: PHENYLACETATE AND ITS DERIVATIVES, CORRELATION BETWEEN
POTENCY AND LIPOPHILICITY
One potential problem that could hinder the clinical use of
phenylacetate is related to the large amounts of drug required to
achieve therapeutic concentrations, i.e., over 300 mg/kg/day.
Studies were thus undertaken to develop analogs that are effective
at lower concentrations. Studies in plants revealed that increasing
the lipophilicity of a phenylacetate analogue (as measured by its
octanol-water partition coefficient) enhanced its growth-regulatory
activity [Muir, R. M., Fujita, T., and Hansch, C.
Structure-activity relationship in the auxin activity of
mono-substituted phenylacetic acids. Plant Physiol., 42: 1519-1526,
1967.]. Calculated partition coefficient (CLOGP) was used to
correlate the predicted lipophilicity with the measured antitumor
activity of phenylacetate analogues. For these analogues, enhanced
potency in inducing cytostasis and phenotypic reversion in cultured
prostate carcinoma, glioblastoma, and melanoma cells was correlated
with increased drug lipophilicity.
Cell Cultures.
Studies included the following humans tumor cell lines: (a)
hormone-refractory prostatic carcinoma PC3, DU145, purchased from
the American Type Culture Collection (ATCC, Rockville, Md.); (b)
glioblastoma U87, A172 (ATCC); (c) melanoma A375 and mel 1011,
provided by J. Fidler (M. D. Anderson, Houston Tex.) and J. Weber
(NCI, Bethesda Md.), respectively. Cells were maintained in RPMI
1640 supplemented with 10% heat inactivated fetal calf serum (Gibco
Laboratories), antibiotics, and 2 mM L-glutamine. Diploid human
foreskin FS4 fibroblasts (ATCC), and human umbilical vein
endothelial cells (HUVC) were used for comparison. The HUVC cells,
isolated from freshly obtained cords, were provided by D. Grant and
H. Kleinman (NIH, Bethesda Md.).
Antitumor Agents.
Sodium phenylacetate and phenylbutyrate were from Elan
Pharmaceutical corp, Gainvesville Ga. Iodophenylacetate,
4-iodophenylbutyrate and 4-chlorophenylbutyrate were synthesized by
the Sandmeyer procedure from the corresponding 4-amino-phenyl-fatty
acids. The halogenated products were extracted from the acidic
reaction mixtures with diethyl ether which was then taken to
dryness. The residue was dissolved in boiling hexane and the
crystals that formed on cooling were collected by suction
filtration. The product was recrystallized from hexane until the
reported melting points were obtained. Amides of phenylacetate and
phenylbutyrate were produced by heating the sodium salts with a
small excess of thionylchloride followed by the addition of
ice-cold concentrated ammonia. The amides were purified by
recrystalization from boiling water. The identity of synthesized
compounds was verified by melting point determination and by mass
spectroscopy. All commercially available derivatives were purchased
from Aldrich (Milwaukee, Wis.) or Sigma (St. Louis, Mo.), depending
on availability. Tested compounds were all dissolved in distilled
water, brought to pH 7.0 by the addition of NaOH as needed, and
stored in aliquots at -20.degree. C. till used.
Calculation of Relative Drug Lipophilicities.
Estimation of the contribution of lipophilicity to the biological
activity of a molecule was based on its calculated logarithm of
octanol-water partition coefficient (CLOGP). This was determined
for each compound using the BLOGP program of Bodor et al., (BLOGP
version 1.0, Center for Drug Discovery, University of Florida)
assuming that the degree of ionization is similar for all tested
compounds.
Quantitation of Cell Growth and Viability.
Growth rates were determined by cell enumeration with a
hemocytometer following detachment with trypsin-EDTA, and by an
enzymatic assay using
3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltertrazolium bromide
(MTT). These two assays produced essentially the same results. Cell
viability was assessed by trypan blue exclusion.
Colony Formation in Semi-Solid Agar.
For analysis of anchorage independent growth, cells were harvested
with trypsin-EDTA and resuspended at 1.0.times.10.sup.4 cells per
ml in growth medium containing 0.36% agar (Difco). Two ml of cell
suspension were added to 60 mm plates (Costrar) which were
pre-coated with 4 ml of solid agar (0.9%). Tested drugs were added
at different concentrations, and colonies composed of 30 or more
cells were counted after 3 weeks.
Growth on Matrigel.
Cells were first treated with drugs in T.C. plastic dishes for 4-6
days, and then replated (5.times.10.sup.4 cells per well) onto 16
mm dishes (Costar, Cambridge, Mass.) coated with 250 ul of 10 mg/ml
matrigel, a reconstituted basement membrane (Collaborative
Research). Drugs were either added to the dishes or omitted in
order to determine the reversibility of effect. Net-like formation
characteristic of invasive cells occurred within 12 hours, while
invasion into the matrigel was evident after 6-9 days.
Drug Uptake Studies.
Cells were plated in 6-well T.C. dishes (Costar) at
5.times.10.sup.5 cells per dish. The growth medium was replaced
after 24 hrs with 750 ul of fresh medium containing
4.5.times.10.sup.5 DPM of either .sup.14 C-phenylacetic acid (3.4
mCi/mmol, Sigma) or .sup.14 C-naphthylacetic acid (5.4 mCi/mmol,
Sigma), and the cultures were incubated for 10-180 minutes at
37.degree. C. Labeling was terminated by placing plates on ice.
Cells were then washed twice with 5 ml ice-cold phosphate buffer
saline (PBS), detached by scraping, and the radioactivity retained
by cells determined using liquid scintillation. Blank values were
determined by incubating the radiolabled compounds in an empty
dish.
Correlation Between Drug Lipophilicity and Growth-Inhibitory Effect
of Phenylacetate and its Analogues.
The growth inhibitory effect of these compounds on prostatic
carcinoma, glioblastoma, and melanoma cell lines are expressed as
IC.sub.50 and correlated with drug lipophilicity determined using
the CLOGP program. As seen in Tables 21 and 22, there is a good
correlation between cytostasis and lipophilicity. In agreement with
previous observations with phenylacetate (3), the cytostatic effect
was selective as higher drug concentrations were needed to
significantly affect the proliferation of normal endothelial cells
and skin fibroblasts. No cytotoxicity (i.e., decline in cell
viability) occurred during 4-6 days of continuous treatment with
the tested compounds.
TABLE 21
__________________________________________________________________________
Phenylacetate and analogues containing alkyl- chain substitutions:
Relationship of IC.sub.50 to CLOGP IC.sub.50 (mM) normal Rx CLOGP
prostate ca. glioblastoma melanoma cells
__________________________________________________________________________
.alpha.-methoxy-PA 2.17 6 5.8 6 ND PA 2.05 5 4.3 5 12
.alpha.-methyl-PA 2.42 2.6 3.8 3.5 12 .alpha.-ethyl-PA 2.77 2.1 2.8
2.2 9 PB 2.89 1 1.8 1 ND 4-chloro-PB 3.30 0.75 ND 0.8 ND 4-iodo-PB
3.85 0.36 0.27 0.22 ND
__________________________________________________________________________
ND, not determined
TABLE 22
__________________________________________________________________________
Phenylacetate and analogues containing ring substitutions:
Relationship of IC.sub.50 to CLOGP IC.sub.50 (mM) normal Rx CLOGP
prostate ca. glioblastoma melanoma cells
__________________________________________________________________________
4-Hydroxy-PA 1.78 7.5 10 10 ND PA 2.05 5 4.3 5 12 4-fluoro-PA 2.17
2.8 4 2.5 ND 2-methyl-PA 2.43 2.5 ND ND ND 3-methyl-PA 2.45X 2.1 ND
ND ND 4-methyl-PA 2.47 2.1 ND ND ND 4-chloro-PA 2.48 1 0.9 1.2 3
3-chloro-PA 2.54 1.75 1.7 1.5 7 2-chloro-PA 2.56 2.4 2.1 2.5 ND
2,6-dichloro-PA 2.87 1 0.8 1 ND 4-iodo-PA 3.12 0.6 0.9 1.2 ND
1-naphtylacetate 3.16 0.8 0.9 0.8 2.8
__________________________________________________________________________
ND, not determined
Further analysis of structure-activity relationships was based on
the method of Hansch and Anderson used for the correlation of the
anesthetic and metabolic effects of barbiturates with their
octanol-water partition coefficients [Hansch, C., and Anderson, S.
M. The structure-activity relationship in barbiturates and its
similarity to that in other narcotics. J. Med. Chem 10: 745-753,
1967.]. Adaptation of this method assumes that, if the relationship
is simple, it will follow the equation: log 1/C=slope log P+K.
Plotting the log 1/IC.sub.50 values obtained with prostatic cells
vs drug CLOGP (FIG. 26) shows that the best fit line is described
by the equation: log 1/IC.sub.50 =0.89 CLOGP+0.55. The slope of
this line (0.89) is in the range of values found for the anesthetic
potencies of a series of barbiturate analogues. Hansch and
colleagues also studied the effect of phenylacetate and its
derivatives on plant growth. As shown in FIG. 27, the concentration
range and rank order of inhibition of plant growth by phenylacetate
analogues are comparable to the inhibition of growth of prostatic
cancer cells by this same series of compounds.
While the overall trend of enhanced activity of phenylacetate
derivatives with increased lipophilicity is clear, some small
deviations occur. For both chloro- and methyl-substitutions, the
para position is more potent than the ortho position. In addition,
and despite their nearly equal contributions to lipohilicity, para
chloro-substitution was more potent than methyl. In contrast to
derivatives containing ring or alpha-carbon substitutions, those
with blocked carboxyl groups exhibited a decline in cytostatic
activity. The methyl ester of phenylacetate was about half as
active than the free acid (IC.sub.50 in DU145 prostatic cells 8.8
mM versus 4.1 mM for phenylacetate). The amide forms were also less
active than the parent compounds in this experimental system, with
IC.sub.50 s of 2.0 mM for phenylbutyramide versus 1.2 mM for
phenylbutyrate, and 4.8 mM for phenylacetamide versus 4.1 mM for
phenylacetate.
Drug Uptake.
One possible function of increasing lipophilicity is an increasing
ease with which aromatic fatty acids can enter into, and cross the
plasma membrane as well as the membranes of other organelles. The
rate of phenylacetate uptake by tumor cells was compared that of
the more hydrophobic analog, naphthylacetate (Table 22). After 10
minutes, relative to phenylacetate more than twice as much
naphthylacetate had entered the glioblastoma U87 cells (uptake of
phenylacetic acid was 41% that of naphthylacetic acid) indicating
that its movement through the plasma membrane was more than twice
as fast as phenylacetate. After 20 minutes, the amount of
naphthylacetate taken up by the cells was as only 26% greater than
that of phenylacetate and at 180 minutes the intracellular levels
of both compounds were nearly equal, suggesting that at this time
the more rapid influx of naphthylacetic acid was balanced by an
equally rapid efflux. There was little further uptake and the
concentration of phenylacetate inside and outside the cells was
about equal indicating that these cells do not actively accumulate
much aromatic fatty acid.
Phenotypic Reversion.
In addition to causing selective cytostasis, phenylacetate induces
malignant cells to undergo reversion to a more benign phenotype.
The effect of analogs on tumor biology was tested using as a model
the hormone- refractory prostatic PC3 cells originally derived from
a bone metastasis. PC3 exhibit several growth characteristics in
vitro that correlate with their malignant behavior in vivo,
including anchorage-independent growth (i.e., colony formation in
semi-solid agar), and formation of "net"-like structures when
plated on a reconstituted basement membrane (matrigel). The ability
of phenylacetate and representative analogs to bring about loss of
such properties is summarized in FIG. 27. Similar to the cytostatic
effect, drug ability to induce reversion to a non-malignant
phenotype was highly correlated with the calculated lipophilicity
of the drugs. Of the tested compounds, naphthytacetate, as well as
derivatives of phenylbutyrate and phenylacetate with iodo- and
chlorine substitutions were found to be the most active on a molar
basis. The relative efficacy of the compounds in suppressing
anchorage independent growth was confirmed using U87 glioblastoma
cells (data not shown).
Discussion.
The comparative activity of phenylacetate and its analogues against
a number of tumor cell lines suggest that these compounds may form
a new class of therapeutic agents whose effectiveness varies with
structure. Improved anticancer activity is achieved if factors
controlling their action are understood, and toward this end the
effects of systematic changes in structure with changes in activity
have been compared. The outstanding result is the discovery that:
(a) there is a simple relationship between the lipophilicity of a
phenylacetate derivative and its activity against human tumor
cells, and (b) the relative potency observed with human neoplasms
is similar to that documented in plants, indicating that the role
of the aromatic fatty acids in growth regulation has been conserved
in evolution.
The efficacy of aromatic fatty acids was demonstrated in vitro
using tumor cell lines derived from patients with
hormone-refractory prostatic carcinoma, glioblastomas, and
malignant melanoma. Like phenylacetate, several derivatives
containing alpha-carbon or ring substitutions all induced
cytostasis and phenotypic reversion at non-toxic concentrations.
Changes in tumor biology included reduction in cell proliferation
rate and loss of malignant properties such as invasiveness and
anchorage-independence. There were, however, significant
differences in potency. When compared to phenylacetate, analogs
with naphthyl-, halogen- or alkyl-ring, as well as .alpha.-carbon
alkyl substitutions exhibited increased activity, while those with
.alpha.-methoxy or hydroxyl replacement at the phenyl ring were
less effective. Drug potency was correlated with the degree of
calculated lipophilicity, indicating that differences in efficacy
may be due in part to the ease with which these agents enter into
and cross the lipid bilayer of cell membranes. In agreement, uptake
of the more hydrophobic compound, naphthylacetate, was
significantly faster than that of phenylacetate. At equilibrium
(about 180 minutes for phenylacetate), however, there were no
differences in either the total intracellular concentration of both
compounds, or the levels inside and outside cells. These results
suggest that the rates of drug uptake are balanced by proportional
rates of efflux, and that the overall capacity of the cell to
retain such compounds is not much greater than that of the
extracellular milieu.
Although there is a good correlation between drug potency and
lipophilicity (see FIG. 26), small deviations within the
phenylacetate-related series may give some clues regarding
mechanisms of action. Halogen substitutions para to the
alkylcarboxyl group were found to increase potency more than those
in the ortho position, suggesting that orientation of the
hydrophobic substituent may be important. At the para position,
chlorine had a greater impact on efficacy than a methyl group
despite nearly equal contributions to CLOGP, indicating that
electronegativity may affect growth inhibitory interactions. While
.alpha.-ethylphenylacetic acid, in which the carboxyl group is
crowded by the adjacent ethyl group, was more potent than the
parent compound, the more lipophilic analog
.alpha.-methoxyphenylacetic acid was less active. The
.alpha.-methoxyphenylacetic acid is a significantly stronger acid,
and this greater acidity could be important. Other parameters such
as addition of an aromatic ring to phenylacetate, or an increase in
the distance between the aromatic nucleus and the carboxyl group
did not cause anomalous enhancement or interference in biological
activity (naphthylacetate and phenylbutyrate were about as active
as would be expected on the basis of their lipophilicity). The
importance of a free carboxyl group is unclear. The amide forms of
phenylacetate and phenylbutyrate, in which the carboxylic group is
blocked, were less cytostatic compared to the parental compounds
and failed to induce cell differentiation (unpublished data).
Moreover, phenylacetylglutamine has no detectable effect on cell
growth and maturation. It appears, therefore, that a free carboxyl
group may be essential for some aspects of the antitumor activity
of phenylacetate and derivatives.
The correlation between partition coefficients and bioactivity of
the aromatic fatty acids is reminiscent of that observed for a
large number of other lipophilic agents. A survey by Hansch and
Anderson revealed that, in a variety of animal tissues, the
anesthetic and metabolic effects of barbiturates corresponded well
with their hydrophilicity, having an average slope of about 1
compared to a slope of about 0.67 for lipophilic interaction with
protein. It was concluded that the critical step in initiating
biological activity was entry into the lipid bilayer, probably
followed by interaction with membrane proteins. Some of the
subsequently identified targets of barbiturates are indeed,
membrane proteins and these include the GABA receptor-chloride in
neurons, the ATP-K.sup.+ pump in pancreatic B-cells, and the
G-protein that stimulates PLC activity in leukemic cells. Despite a
wide body of literature implicating phenylacetate and analogs in
growth control throughout phylogeny, little is known regarding
their mode of action. In plants, phenylacetate and naphtylacetate
are endogenous growth hormones (auxins) known to stimulate
proliferation at micromolar concentrations, while inhibiting growth
at millimolar levels. As growth inhibitors (but not stimulators),
the effect of phenylacetate analogues on rapidly developing
embryonic plant tissues, like that on human tumor cells, is a
simple function of their lipophilicities. These similarities in
potency, summarized in FIG. 27, suggest that some of the underlying
mechanisms of negative growth control may be similar as well.
There is accumulating evidence indicating that phenylacetate and
derivatives may act through multiple mechanisms to alter gene
expression and cell biology. At growth inhibitory concentrations,
the aromatic fatty acids could alter the pattern of DNA
methylation, an epigenetic mechanism controlling the transcription
of various eukaryotic genes. Phenylacetate inhibits DNA methylation
in plant and mammalian cells, and both phenylacetate and
phenylbutyrate were shown to activate the expression of otherwise
dormant methylation-dependent genes. DNA hypomethylation per se is
not sufficient to induce gene expression. Preliminary findings
indicate that phenylacetate, phenylbutyrate and several analogs
activate a nuclear receptor that functions as a transcriptional
factor; interestingly, the receptor is a member of a steroid
nuclear receptor superfamily, the ligands of which are carboxylic
acids and include well characterized differentiation inducers such
as retinoids.
In addition to affecting gene transcription, the phenyl-fatty acids
may interfere with protein post-translational processing by
inhibiting the mevalonate (MVA) pathway of cholesterol synthesis.
MVA is a precursor of several isopentenyl moieties required for
progression through the cell cycle, and of prenyl groups that
modify a small set of critical proteins. The latter include plasma
membrane G and G-like proteins (e.g., ras) involved in mitogenic
signal transduction (molecular weight 20-26 kDa), and nuclear
envelope lamins that play a key role in mitosis (44-74 kDa). The
aromatic fatty acids can conjugate with coenzyme-A, enter the
pathway to chain elongation, and interfere with lipid metabolism in
general. Furthermore, compounds such as phenylacetate can assume a
conformation resembling mevalonate pyrophosphate and inhibit MVA
utilization specifically. It was recently demonstrated that
phenylacetate activity against poorly differentiated mammalian
tissues (human glioblastoma cells and the developing fetal brain)
is associated with inhibition of MVA decarboxylation and a decline
in protein isoprenylation. Rapidly developing mammalian and plant
tissues are highly dependent upon MVA for cell replication.
Inhibition of MVA utilization by phenylacetate-related compounds
could thus be responsible in part for their effect documented in
such highly divergent organisms.
In conclusion, phenylacetate and analogs appear to represent a new
class of pleiotropic growth regulators that might alter tumor cell
biology by affecting gene expression at both the transcriptional
and post transcriptional levels. Phenylacetate and phenylbutyrate
have already been established as safe and effective in treatment of
hyperammonemia, and phase I clinical trials in adults with cancer
confirmed that millimolar levels can be achieved in the plasma and
cerebrospinal fluid with no significant toxicities (discussed
herein). However, rather large doses (300 mg/kg/day or more) are
required to achieve potentially therapeutic levels. The identified
relationship between lipophilicity of commercially available
analogs and their antitumor activity in experimental models led us
to predict that analogs with greater CLOGPs, e.g., iodo derivatives
of phenylacetate and phenylbutyrate, would be highly effective.
Indeed, these compounds were found to be the most potent aromatic
fatty acids yet tested. With this approach, it should be possible
to identify highly effective and safe antitumor agents suitable for
clinical application.
Modes of Drug Administration
NaPA (or PAA derivatives) may be administered locally or
systemically. Systemic administration means any mode or route of
administration which results in effective levels of active
ingredient appearing in the blood or at a site remote from the site
of administration of said active ingredient.
The pharmaceutical formulation for systemic administration
according to the invention may be formulated for intravenous,
intramuscular, subcutaneous, oral, nasal, enteral, parenteral or
topical administration. In some cases, a combination of types of
formulations may be used simultaneously to achieve systemic
administration of the active ingredient.
Suitable formulations for oral administration include hard or soft
gelatin capsules, dragees, pills, tablets (including coated
tablets), elixirs, suspensions, and syrups or inhalations.
Solid dosage forms in addition to those formulated for oral
administration include rectal suppositories.
The compounds of the present invention may also be administered in
the form of an implant.
Suitable formulations for topical administration include creams,
gels, jellies, mucilages, pastes and ointments.
Suitable injectable solutions include intravenous, subcutaneous,
and intramuscular injectable solutions. The compounds of the
present invention may also be administered in the form of an
infusion solution or as a nasal inhalation or spray.
The compounds of the present invention may also be used
concomitantly or in combination with selected biological response
modifiers, e.g., interferons, interleukins, tumor necrosis factor,
glutamine antagonists, hormones, vitamins, as well as anti-tumor
agents and hematopoietic growth factors, discussed above.
It has been observed that NaPA is somewhat malodorous. Therefore,
it may be preferable to administer this compound in the presence of
any of the pharmaceutically acceptable odor-masking excipients or
as its precursor phenylbutyrate (or a derivative or analog thereof)
which has no offensive odor.
The PAA and its pharmaceutically acceptable derivatives to be used
as antitumor agents can be prepared easily using pharmaceutical
materials which themselves are available in the art and can be
prepared by established procedures. The following preparations are
illustrative of the preparation of the dosage forms of the present
invention, and are not to be construed as a limitation thereof.
EXAMPLE 21
Parenteral Solution 1
A sterile aqueous solution for parenteral administration containing
200 mg/ml of NaPA for treating a neoplastic disease is prepared by
dissolving 200 g. of sterilized, micronized NaPA in sterilized
Normal Saline Solution, qs to 1000 ml. The resulting sterile
solution is placed into sterile vials and sealed. The above
solution can be used to treat malignant conditions at a dosage
range of from about 100 mg/kg/day to about 1000 mg/kg/day. Infusion
can be continuous over a 24 hour period.
EXAMPLE 22
Parenteral Solution 2
A sterile aqueous solution for parenteral administration containing
50 mg/ml of NaPA is prepared as follows:
______________________________________ Ingredients Amount
______________________________________ NaPA, micronized 50 g.
Benzyl alcohol 0.90% w/v Sodium chloride 0.260% w/v Water for
injection, qs 1000 ml ______________________________________
The above ingredients, except NaPA, are dissolved in water and
sterilized. Sterilized NaPA is then added to the sterile solution
and the resulting solution is placed into sterile vials and sealed.
The above solution can be used to treat a malignant condition by
administering the above solution intravenously at a flow rate to
fall within the dosage range set forth in Example 21.
EXAMPLE 23
Parenteral Solution 3
A sterile aqueous solution for parenteral administration containing
500 mg/ml of sodium phenylbutyrate is prepared as follows:
______________________________________ Ingredients Amount
______________________________________ Sodium phenylbutyrate 500 g.
Dextrose 0.45% w/v Phenylmercuric nitrate 0.002% w/v Water for
injection, qs 1000 ml. ______________________________________
The preparation of the above solution is similar to that described
in Examples 21 and 22.
EXAMPLE 24
Tablet Formulation 1
A tablet for oral administration containing 300 mg of NaPA is
prepared as follows:
______________________________________ Ingredients Amount
______________________________________ NaPA 3000 g.
Polyvinylpyrrolidone 225 g. Lactose 617.5 g Stearic acid 90 g. Talc
135 g. Corn starch 432.5 g. Alcohol 45 L
______________________________________
NaPA, polyvinylpyrrolidone and lactose are blended together and
passed through a 40-mesh screen. The alcohol is added slowly and
the granulation is kneaded well. The wet mass is screened through a
4-mesh screen, dried overnight at 50.degree. C. and screened
through a 20-mesh screen. The stearic acid, talc and corn starch is
bolted through 60-mesh screen prior to mixing by tubing with the
granulation. The resulting granulation is compressed into tablets
using a standard 7/16 inch concave punch.
EXAMPLE 25
Tablet Formulation 2
A tablet for oral administration containing 200 mg of sodium
phenylbutyrate is prepared as follows:
______________________________________ Ingredients Amount
______________________________________ Sodium phenylbutyrate 2240
g. Compressible sugar (Di-Pac) 934 g. Sterotex 78 g. Silica gel
(Syloid) 28 g. ______________________________________
The above ingredients are blended in a twin-shell blender for 15
minutes and compressed on a 13/22 inch concave punch.
EXAMPLE 26
Intranasal Suspension
A 500 ml sterile aqueous suspension is prepared for intranasal
installation as follows:
______________________________________ Ingredients Amount
______________________________________ NaPA, micronized 30.0 g.
Polysorbate 80 2.5 g. Methylparaben 1.25 g. Propylparaben 0.09 g.
Deionized water, qs 500 ml
______________________________________
The above ingredients, with the exception of NaPA, are dissolved in
water and sterilized by filtration. Sterilized NaPA is added to the
sterile solution and the final suspensions are aseptically filled
into sterile containers.
EXAMPLE 27
Ointment
An ointment is prepared from the following ingredients:
______________________________________ Ingredients Amount
______________________________________ NaPA 10 g. Stearyl alcohol 4
g. White wax 8 g. White petrolatum 78 g.
______________________________________
The stearyl alcohol, white wax and white petrolatum are melted over
a steam bath and allowed to cool. The NaPA is added slowly to the
ointment base with stirring.
EXAMPLE 28
Lotion
______________________________________ Ingredient Amount
______________________________________ Sodium phenylbutyrate 1.00
g. Stearyl methylcellulose (4,500) Solution (2%) 25.00 ml
Benzalkonium chloride 0.03 g. Sterile water 250.00 ml
______________________________________
The benzalkonium chloride is dissolved in about 10 ml. of sterile
water. The sodium phenylbutyrate is dispersed into methylcellulose
solution by means of vigorous stirring. The methylcellulose (4,500)
used is a high viscosity grade. The solution of benzalkonium
chloride is then added slowly while stirring is continued. The
lotion is then brought up to the desired volume with the remaining
water. Preparation of the lotion is carried out under aseptic
conditions.
EXAMPLE 29
Dusting Powder
______________________________________ Ingredients Amount
______________________________________ NaPA 25 g. Sterilized
absorbable maize 25 g. starch BP dusting powder
______________________________________
The dusting powder is formulated by gradually adding the sterilized
absorbable dusting powder to NaPA to form a uniform blend. The
powder is then sterilized in conventional manner.
EXAMPLE 30
Suppository, Rectal and Vaginal Pharmaceutical Preparations
Suppositories, each weighing 2.5 g. and containing 100 mg. of NaPA
are prepared as follows:
______________________________________ Ingredients Amount/1000
______________________________________ Suppositories 100 g. NaPA,
micronized Propylene glycol 150 g. Polyethylene glycol 2500 g.
4000, qs ______________________________________
NaPA is finely divided by means of an air micronizer and added to
the propylene glycol and the mixture is passed through a colloid
mill until uniformly dispersed. The polyethylene glycol is melted
and the propylene glycol dispersion added slowly with stirring. The
suspension is poured into unchilled molds at 40.degree. C.
Composition is allowed to cool and solidify and then removed from
the mold and each suppository is foil wrapped.
The foregoing suppositories are inserted rectally or vaginally for
treating neoplastic disease.
It is known that intracellular glutathione plays a major role in
detoxification and repair of cellular injury by chemical and
physical carcinogens. NaPA treatment of normal or tumor cells
markedly induced the activity of intracellular glutathione
approximately 2-10 fold depending on growth conditions. Nontoxic
agents that can induce glutathione are highly desirable since these
are likely to protect cells from damage by a variety of chemical
carcinogens and ionizing radiation.
Taken together, the present invention demonstrates that NaPA, NaPB
and other PAA derivatives have valuable potential in cancer
prevention in case such as high risk individuals, for example,
heavy smokers with familial history of lung cancer, inherited
disorders of concogene abnormalities (Li-Fraumeni syndrome),
individuals exposed to radiation, and patients in remission with
residual disease. Furthermore, these compounds can be used in
combination with other therapeutic agents, such as chemicals and
radiation, to enhance tumor responses and minimize adverse effects
such as cytotoxicity and carcinogenesis. The antitumor activity,
lack of toxicity, and easy administration qualify NaPA as a
preferred chemopreventive drug.
* * * * *