U.S. patent application number 10/590445 was filed with the patent office on 2008-04-17 for methods and materials for assessing prostate cancer therapies and compounds.
Invention is credited to Charlie Chen, Michael Jung, Samedy Ouk, Charles Sawyers, Derek Welsbie.
Application Number | 20080090888 10/590445 |
Document ID | / |
Family ID | 35150490 |
Filed Date | 2008-04-17 |
United States Patent
Application |
20080090888 |
Kind Code |
A2 |
Jung; Michael ; et
al. |
April 17, 2008 |
METHODS AND MATERIALS FOR ASSESSING PROSTATE CANCER THERAPIES AND
COMPOUNDS
Abstract
A modest (2-5 fold) increase in androgen receptor (AR) mRNA is
the only expression change consistently associated with developing
resistance to antiandrogen therapy. Increased levels of AR confer
resistance to anti-androgens by amplifying signal output from low
levels of residual ligand and altering the normal response to
antagonists. This invention provides cell based assays for use in
the examination of new therapeutic modalities and provides for the
design of novel antiandrogen compounds.
Inventors: |
Jung; Michael; (Los Angeles,
CA) ; Ouk; Samedy; (Los Angeles, CA) ;
Sawyers; Charles; (New York, NY) ; Chen; Charlie;
(Los Angeles, CA) ; Welsbie; Derek; (Los Angeles,
CA) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
202-344-4000
ksfeatherston@venable.com
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20070191443 A1 |
August 16, 2007 |
|
|
Family ID: |
35150490 |
Appl. No.: |
10/590445 |
Filed: |
August 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60/547,101 |
Feb 24, 2004 |
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Current U.S.
Class: |
514/385 ;
548/100; 548/320.1 |
Current CPC
Class: |
A61K 31/426
20130101 |
Class at
Publication: |
514/385 ;
548/100; 548/320.1 |
International
Class: |
A61K 31/4166 20060101
A61K031/4166; C07D 233/84 20060101 C07D233/84 |
Goverment Interests
[0001] This invention was made with United States Government
support under Department of Defense Grant DAMD17-98-1-8569. The
Government may have certain rights to the invention.
Claims
1. A composition of matter comprising a compound having the formula
##STR5## wherein R is (CH.sub.2).sub.nN.sub.3 or N.sub.3CH.sub.4
and where n is from 3 to 8.
2. A pharmaceutical composition comprising a compound according to
claim 1 and a pharmaceutically acceptable carrier for said
compound.
3. A method of inhibiting prostate specific antigen production in a
mammalian prostate cancer cell, the method comprising contacting
said mammalian prostate cancer cell with a sufficient amount of a
compound according to claim 1, such that prostate specific antigen
production in said mammalian prostate cancer cell is inhibited.
4. A method of inhibiting the growth of a human prostate cancer
cell, the method comprising contacting said human prostate cancer
cell with a therapeutically effective amount of a compound
according to claim 1, such that growth of said human prostate
cancer cell is inhibited.
5. A method of antagonizing the function of the ligand binding
domain of the androgen receptor polypeptide in a prostate cancer
cell, said method comprising the step of contacting said prostate
cancer cell with a sufficient amount of a compound according to
claim 1, such that the function of the ligand binding domain of the
androgen receptor is antagonized.
6. A method of antagonizing the effect of an androgen on a function
of the ligand binding domain of the androgen receptor polypeptide
in a prostate cancer cell, the method comprising the step of
contacting said prostate cancer cell with a sufficient amount of a
compound according to claim 1, such that the effect of an androgen
on a function of the ligand binding domain of the androgen receptor
polypeptide is antagonized.
7. A composition of matter comprising a compound that inhibits the
growth of hormone refractory prostate cancer cells, wherein said
compound has been previously subjected to a method of examining the
physiological effect of said compound on a mammalian prostate
cancer cell wherein said prostate cancer cell expresses an
exogenous wild type androgen receptor polynucleotide that encodes
an androgen receptor polypeptide or an androgen receptor
polypeptide variant, said cell further comprising an abnormal level
of mRNA that encodes said androgen receptor polypeptide or said
androgen receptor polypeptide variant when compared to the level of
mRNA that encodes said androgen receptor polypeptide or said
androgen receptor polypeptide variant in a normal prostate cell,
said method comprising: (a) determining that said abnormal level of
mRNA in said prostate cancer cell is at least two fold higher than
the level of mRNA in said normal prostate cell; (b) contacting said
compound with said prostate cancer cell to provide a treated
prostate cancer cell; and (c) examining one or more physiological
characteristics of said treated prostate cancer cell.
8. A composition of matter comprising a compound that inhibits the
growth of hormone refractory prostate cancer cells, wherein said
compound has been previously subjected to a method of examining the
physiological effect of said compound on a mammalian prostate
cancer cell wherein said prostate cancer cell expresses an
exogenous wild type androgen receptor polynucleotide that encodes
an abnormal level of androgen receptor polypeptide or an abnormal
level of androgen receptor polypeptide variant when compared to the
level of androgen receptor polypeptide or androgen receptor
polypeptide variant encoded by a normal prostate cell, said method
comprising: (a) determining that said abnormal level of androgen
receptor polypeptide or said abnormal level of androgen receptor
polypeptide variant is at least two fold higher than the level of
androgen receptor polypeptide or androgen receptor polypeptide
variant in said normal prostate cell; (b) contacting said compound
with said prostate cancer cell to provide a treated prostate cancer
cell; and (c) examining one or more physiological characteristics
of said treated prostate cancer cell.
9. A composition of matter according to claim 7 wherein said
compound has the formula ##STR6## wherein R is
(CH.sub.2).sub.nN.sub.3 or N.sub.3C.sub.6H.sub.4 and where n is
from 3 to 8.
10. A composition of matter according to claim 8 wherein said
compound has the formula ##STR7## wherein R is
(CH.sub.2).sub.nN.sub.3 or N.sub.3C.sub.6H.sub.4 and where n is
from 3 to 8.
11. A method for making a composition of matter comprising a
compound that inhibits the growth of hormone refractory prostate
cancer cells, wherein said method comprises the initial step of
examining the physiological effect of said compound on a mammalian
prostate cancer cell wherein said prostate cancer cell expresses an
exogenous wild type androgen receptor polynucleotide that encodes
an androgen receptor polypeptide or an androgen receptor
polypeptide variant, said cell further comprising an abnormal level
of mRNA that encodes said androgen receptor polypeptide or said
androgen receptor polypeptide variant when compared to the level of
mRNA that encodes said androgen receptor polypeptide or said
androgen receptor polypeptide variant in a normal prostate cell,
said initial step comprising: (a) determining that said abnormal
level of mRNA in said prostate cancer cell is at least two fold
higher than the level of mRNA in said normal prostate cell; (b)
contacting said compound with said prostate cancer cell to provide
a treated prostate cancer cell; and (c) examining one or more
physiological characteristics of said treated prostate cancer
cell.
12. A method for making a composition of matter comprising a
compound that inhibits the growth of hormone refractoy prostate
cancer cells, wherein said method comprises the initial step of
examining the physiological effect of said compound on a mammalian
prostate cancer cell wherein said prostate cancer cell expresses an
exogenous wild type androgen receptor polynucleotide that encodes
an abnormal level of androgen receptor polypeptide or an abnormal
level of androgen receptor polypeptide variant when compared to the
level of androgen receptor polypeptide or androgen receptor
polypeptide variant encoded by a normal prostate cell said initial
step comprising: (a) determining that said abnormal level of
androgen receptor polypeptide or said abnormal level of androgen
receptor polypeptide variant is at least two fold higher than the
level of androgen receptor polypeptide or androgen receptor
polypeptide variant in said normal prostate cell; (b) contacting
said compound with said prostate cancer cell to provide a treated
prostate cancer cell; and (c) examining one or more physiological
characteristics of said treated prostate cancer cell.
13. A method for making a composition of matter according to claim
11 wherein said compound has the formula ##STR8## wherein R is
(CH.sub.2).sub.nN.sub.3 or N.sub.3C.sub.6H.sub.4 and where n is
from 3 to 8.
14. A method for making a composition of matter according to claim
12 wherein said compound has the formula ##STR9## wherein R is
(CH.sub.2).sub.nN.sub.3 or N.sub.3C.sub.6H.sub.4 and where n is
from 3 to 8.
Description
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to methods and materials for
assessing prostate cancer therapies, as well as novel prostate
cancer compositions and methods for making and using said
compositions.
[0004] 2. Description of Related Art
[0005] Cancer is the second leading cause of human death next to
coronary disease. Worldwide, millions of people die from cancer
every year. In the United States alone, as reported by the American
Cancer Society, cancer causes the death of well over a half-million
people annually, with over 1.2 million new cases diagnosed per
year. While deaths from heart disease have been declining
significantly, those resulting from cancer generally are on the
rise. In this century, cancer is predicted to become the leading
cause of death.
[0006] Worldwide, several cancers stand out as the leading killers.
In particular, carcinomas of the lung, prostate, breast, colon,
pancreas, and ovary represent the primary causes of cancer death.
These and virtually all other carcinomas share a common lethal
feature. With very few exceptions, metastaic disease from a
carcinoma is fatal. Moreover, even for those cancer patients who
initially survive their primary cancers, common experience has
shown that their lives are dramatically altered
[0007] Adenocarcinoma of the prostate is the most frequently
diagnosed cancer in men in the United States, and is the second
leading cause of male cancer deaths (Karp et al., Cancer Res.
56:5547-5556 (1996)). Therapy for prostate cancer is typically
initiated using hormone drugs that lower serum testosterone, often
given in combination with competitive androgen receptor (AR)
antagonists. Although initially effective at blocking tumor growth,
these therapies eventually fail, leading to a drug resistant stage
called androgen independent or hormone refractory (HR) disease that
is uniformly lethal.
[0008] Postulated mechanisms to explain resistance to hormone
therapy can be separated into three general categories..sup.1-3 The
first includes DNA-based alterations in the AR gene such as
amplification or point mutations, which collectively only occur in
a minority of patients..sup.4-7 A subset of these AR mutations map
to the ligand binding domain (LBD) and are proposed to cause
resistance by altering the response of the receptor such that
noncanonical ligands like estrogen or hydrocortisone, or even AR
antagonists like flutamide, behave as agonists..sup.8,9 Although
their clinical association with antiandrogen resistance is strong,
the overall frequency of AR amplification or mutation cannot
account for most cases of hormone refractory disease.
[0009] The second category applies to the majority of patients
without AR gene mutation or amplification who retain active AR
signaling. Increased mitogen-activated protein kinase signaling
mediated by oncogenes such as ErbB2 or Ras can cause
ligand-independent activation of AR..sup.10,11 The kinases and
substrates responsible for AR activation in this setting are
unknown, but this is presumed to occur through downstream
phosphorylation of AR-associated proteins or AR itself, analogous
to the estrogen receptor (ER)..sup.12-14 Similarly, alteration in
the balance of coactivators or corepressors can affect AR
activation,.sup.15-16 based on similar findings for ER..sup.17 The
relative frequency of these events and their relationship to
clinical drug resistance remain to be define.
[0010] The third category of hormone resistance mechanisms is based
on the concept that the pro-growth and survival functions of AR can
be "bypassed" by alternative signaling pathways, such that AR is no
longer relevant to disease progression One example is upregulation
of the anti-apoptotic gene Bcl-2 in late stage clinical
samples,..sup.18,19 but functional proof of a role in hormone
resistance is lacking. The AR bypass hypothesis is also consistent
with observations of AR gene methylation leading to decreased or
absent AR expression in some HR cancers,.sup.20 as well as reports
that androgen induces growth arrest or apoptosis in certain
contexts..sup.21,22
[0011] Collectively, these data implicate multiple mechanisms by
which prostate cancers acquire resistance to hormone therapy and
highlight the continuing debate about the role of AR in late stage
disease progression. Consequently, there is a need in the art for
models that reproduce clinically significant aspects of this
disease progression, particularly the transition from the initial
stage in the prostate cancer where the cancer cells are sensitive
to hormone antagonists to the subsequent drug resistant stage. In
particular, a well-defined and manipulatable cell based model is
needed to dissect the molecular events associated with the
progression from a drug sensitive to a drug resistant phase. There
is also a need in the art for cell based prostate cancer models
that reproduce the drug sensitive and/or drug resistant phases of
cancers of the prostate that can be used, for example in the
evaluation of new therapeutic modalities. In addition, there is
need for the identification of novel compounds that can be used to
inhibit the growth of prostate cancer cells, particularly hormone
refractory prostate cancers. The present invention disclosed herein
satisfies this need.
SUMMARY OF THE INVENTION
[0012] Using microarray-based profiling of isogenic prostate cancer
xenograft models, we found that a modest (2-5 fold) increase in
androgen receptor (AR) mRNA was the only expression change
consistently associated with developing resistance to antiandrogen
therapy. This increase in AR mRNA and protein was both necessary
and sufficient to convert prostate cancer growth from a hormone
sensitive to hormone refractory stage, and was dependent on a
functional ligand-binding domain. Furthermore, AR antagonists
displayed agonist activity in cells with increased AR levels, and
this antagonist/agonist conversion was associated with alterations
in the pattern of coactivators and corepressors recruited to the
promoter of AR target genes. Increased levels of AR confer
resistance to anti-androgens by amplifying signal output from low
levels of residual ligand and altering the normal response to
antagonists. The disclosure provided herein Fat is based upon these
findings includes assays for examining the effects of therapeutic
compounds on mammalian cells such as androgen independent prostate
cancer cells and further provides insight toward the design of
novel antiandrogens.
[0013] One embodiment of the invention is a method of testing
compounds for an effect on a mammalian prostate cancer cell
comprising contacting the compound to be tested with a mammalian
prostate cancer cell wherein the mammalian cancer cell is selected
for the test because it expresses an exogenous wild type androgen
receptor (AR) polynucleotide that encodes the AR polypeptide such
that the levels of mRNA in the cell that encode the AR polypeptide
or AR polypeptide are at least about 2 fold higher than
normal/endogenous AR mRNA or AR polypeptide levels in a mammalian
prostate cell; and then comparing one or more characteristics of
the mammalian prostate cancer cell to which the compound was
administered with the same one or more characteristics of a control
mammalian prostate cancer cell to which the compound has not been
administered, wherein a difference in one or more of the one or
more characteristics indicates that the compound has an effect on
the mammalian prostate cancer cell.
[0014] Another embodiment of the invention is a method of examining
the physiological effect of a compound on a mammalian prostate
cancer cell, the method comprising contacting the compound to be
tested with a mammalian prostate cancer cell, wherein the mammalian
prostate cancer cell is selected for the method because it
expresses either an exogenous wild type polynucleotide that encodes
the AR polypeptide or a polynucleotide that encodes a variant of
the AR polypeptide, wherein the variant has a deletion, insertion
or substitution of at least one amino acid in the AR polypeptide
amino acid sequence and wherein the total levels of mRNA in the
cell that encode the AR polypeptide variant or the total levels of
AR polypeptide variant are at least 2 fold higher than
normal/endogenous AR mRNA or AR polypeptide in the cell; and then
examining one or more physiological characteristics of the
mammalian prostate cancer cell to which the compound is
administered, so that the physiological effect of the compound on
the mammalian prostate cancer cell is examined.
[0015] A related embodiment of the invention is a method further
comprising examining the physiological effect of a plurality of
compounds on a mammalian prostate cancer cell selected as described
above, wherein an observable difference in one or more
physiological characteristics exerted by a first compound as
compared to one or more physiological characteristics exerted by a
second compound indicates that the first compound has a stronger or
weaker physiological effect than the second compound on the
mammalian prostate cancer cell. Typically the method is performed
in a high throughput format. Alternatively, the method is performed
in a low throughput format Compounds tested in such assays are
typically antagonists or agonists. In practice we define a drug as
an AR antagonist when the drug inhibits or competes for the binding
of a ligand or a stimulus and inhibits the biological function of
the androgen receptor. A drug is defined as an AR agonist when the
drug stimulates or activates the biological function of the
androgen receptor.
[0016] Yet another embodiment of the invention is a method of
testing one or more compounds for an effect on a mammalian cell,
the method comprising contacting at least one compound to be tested
with the mammalian cell, wherein the mammalian cell is selected for
the test because it expresses an exogenous wild type or mutated
protein of interest, such as the estrogen receptor, such that the
total levels of mRNA in the cell that encode the protein of
interest or the total protein levels of the protein of interest are
at least 2 fold higher than normal/endogenous mRNA or polypeptide
of the protein of interest, such as the estrogen receptor, in the
cell, comparing one or more characteristics of the mammalian cell
to which the compound is administered with the same one or more
characteristics of a control mammalian cell to which the compound
has not been administered, wherein a difference in one or more
characteristics indicates that the compound has an effect on the
mammalian cancer cell or mammalian cell. In such methods, the
mammalian cell is typically a cancer cell, for example a breast,
ovarian or prostate cancer cell.
[0017] A related embodiment of the invention is a method further
comprising examining the physiological effect of a plurality of
compounds on a mammalian cell that is selected as described above,
wherein an observable difference in one or more physiological
characteristics exerted by a first compound as compared to one or
more physiological characteristics exerted by a second compound
indicates that the first compound has a stronger or weaker
physiological effect than the second compound on the mammalian
cell.
[0018] Another embodiment of the invention is a method of treating
a hormone refractory prostate cancer in a patient, the method
comprising administering to the patient an agent that decreases or
affects the biological function of the androgen receptor by
affecting the androgen receptor ligand-binding, nuclear
translocation, or by affecting DNA-binding, or through altering
formation of coactivator or corepressor complexes associated with
the androgen receptor.
[0019] Another embodiment of the invention is a method of treating
a hormone refractory prostate cancer in a patient, the method
comprising administering to the patient and an agent that decreases
or affects the biological function of the androgen receptor through
affecting the androgen receptor DNA levels, androgen mRNA levels,
or androgen protein levels. In such methods, the androgen receptor
protein level can be decreased through modulation of signal
transduction pathways such as targeting EGF receptors that
crosstalk to the androgen receptor. Alternatively, the androgen
receptor protein level is decreased by the induction of cellular
degradation pathways such as proteosome degradation machinery.
Alternatively, the androgen receptor protein level is decreased by
dissociating the androgen receptor from heat shock proteins that
maintain the androgen receptor integrity. Preferably the androgen
receptor protein level is decreased using androgen receptor
antisense or mRNA knockdown technology. We consider that any one of
these above manipulations or combination of any of these
manipulations would affect the biological function of the androgen
receptor. The preferred way of these methods would be to use an
agent to disrupt or reduce the ligand binding of the androgen
receptor.
[0020] Another embodiment of the invention is a method of treating
a hormone refractory prostate cancer in a patient, the method
comprising administering to the patient an agent that decreases or
affects the biological function of the androgen receptor through
modifying the androgen receptor protein. Optionally, the androgen
receptor protein is modified by modifying the polynucleotide or
polypeptide sequence of the androgen receptor or by
posttranslational modifications of the androgen receptor including,
but not restricted to, phosphorylation, acetylation,
ubiquitination, and sumolation.
[0021] Another embodiment of the invention is a method of treating
a disease or condition, which is resistant to a drug, or a
treatment, or combination of a drug and a treatment by increasing
the concentration of the protein that is the target of the drug or
treatment, the method comprising administering one or more agents
or utilizing a technique that affects the biological function of
the protein through means described in the paragraphs above.
Typically the disease or condition is hormone refractory prostate
cancer, in which the androgen receptor DNA, mRNA, or protein levels
is increased in prostate cancer cells after surgical or medical
castration, or treatments with anti-androgen therapy, or the
combination of castration and anti-androgen therapy. In an
illustrative embodiment, the disease or condition is hormone
refractory breast cancer, in which the estrogen receptor DNA, mRNA,
or protein levels is increased in breast cancer cells after hormone
therapy such as treatments with tamoxifen or raloxifene.
[0022] Yet another embodiment of the invention is a method of
inhibiting prostate specific antigen production in a mammalian
prostate cancer cell (e.g. a hormone refractory prostate cancer),
the method comprising contacting the cell with a composition
comprising a compound selected from the group consisting of
compounds 4 and 5 shown in Example 6, so that prostate specific
antigen production in the prostate cancer cell is inhibited. A
related embodiment of the invention is method of inhibiting the
growth of a human prostate cancer cell, the method comprising
contacting the cell with a composition comprising a compound
selected from the group consisting of compounds 4 and 5 shown in
Example 6, such that growth of the prostate cancer cell is
inhibited. Another related embodiment of the invention is a method
of antagonizing the function of the ligand binding domain of the AR
polypeptide in a prostate cancer cell, the method comprising
contacting the cell with a compound selected from the group
consisting of compounds 4 and 5 shown in Example 6, such that the
function of the ligand binding domain of the AR is antagonized.
[0023] Yet another embodiment of the invention is a method of
antagonizing the effect of an androgen on a function of the ligand
binding domain of the AR polypeptide in a prostate cancer cell, the
method comprising contacting the cell with a androgen antagonist
compound selected from the group consisting of compounds 4 and 5
shown in Example 6, such that the effect of an androgen on a
function of the ligand binding domain of the AR polypeptide is
antagonized.
[0024] Another embodiment of the invention is a composition
comprising a compound selected from the group consisting of
compounds 4 and 5 shown in Example 6. A related embodiment is a
pharmaceutical composition comprising a compound selected from the
group consisting of compounds 4 and 5 shown in Example 6. Certain
embodiments of the invention include methods of administering these
compounds, for example to an individual having a prostate cancer.
In view of their similarity with chemical structure of (Casodex),
certain methods used in administering this compound can be used in
the administration of the novel compounds disclosed herein (see,
e.g. U.S. Pat. Nos. 5,985,868, 6,479,063 and 6,506,607 which are
incorporated herein by reference).
[0025] In a further embodiment of the invention, there are provided
articles of manufacture and kits containing materials useful for
examining compounds such as AR agonists or antagonists using the
methods disclosed herein. The article of manufacture comprises a
container with a label. Suitable containers include, for example,
bottles, vials, and test tubes. The containers may be formed from a
variety of materials such as glass or plastic. The label on the
container may indicate directions for either in vivo or in vitro
use, such as those described above. The kit of the invention
comprises the container described above and a second container
comprising a buffer. It may further include other materials
desirable from a commercial and user standpoint, including other
buffers, diluents, filters, needles, syringes, and package inserts
with instructions for use.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 depicts the results of tests showing expression of AR
mRNA in HS And HR Xenografs. Top, normalized microarray values for
AR probe sets one and two (Affymetrix IDs 1577 and 1578,
respectively) are shown for pools of tumors from each of the
fourteen xenografts. Bottom, AR Western blot from one tumor of each
xenografts' pool lysed in 2% SDS. AR protein expression in HS
LUCaP35 was evident upon longer exposures.
[0027] FIG. 2 diagrammatically depicts a model of prostate cancer
progression. Hormone therapy, consisting of androgen-lowering drugs
and competitive AR antagonists, decreases the number of active
receptors leading to a clinical response (HS disease). Failure of
therapy (HR disease) results from increased receptor level which
inverts the response to antagonists and amplifies the response to
all ligands--residual androgens, antagonists and other
steroids.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Unless otherwise defined, all terms of art, notations and
other scientific terms or terminology used herein are intended to
have the meanings commonly understood by those of skill in the art
to which this invention pertains. In some cases, terms with
commonly understood meanings are defined herein for clarity and/or
for ready reference, and the inclusion of such definitions herein
should not necessarily be construed to represent a substantial
difference over what is generally understood in the art Many of the
techniques and procedures described or referenced herein are well
understood and commonly employed using conventional methodology by
those skilled in the art, such as, for example, the widely utilized
molecular cloning methodologies described in see Ausubel et al.,
Current Protocols in Molecular Biology, Wiley Interscience
Publishers, (1995) and Sambrook et al., Molecular Cloning: A
Laboratory Manual 2nd. edition (1989) Cold Spring Harbor Laboratory
Press, Cold Spring Harbor, N.Y. As appropriate, procedures
involving the use of commercially available kits and reagents are
generally carried out in accordance with manufacturer defined
protocols and/or parameters unless otherwise noted.
[0029] As used herein, the term "polynucleotide" means a polymeric
form of nucleotides of at least about 10 bases or base pars in
length, either ribonucleotides or deoxynucleotides or a modified
form of either type of nucleotide, and is meant to include single
and double stranded forms of DNA.
[0030] As used herein, the term "polypeptide" means a polymer of at
least about 6 amino acids. The term "androgen receptor
polynucleotide" means any of the polynucleotides that encode the
androgen receptor polypeptide. Such polynucleotides are known to
those skilled in the art. For example, see Chang et al., Science
240 (4850), 324-326 (1988). Also see
NM.sub.--000044<http://www.ncbi.nlm.nih-gov:80/entrez/viewer.fcgi?cmd=-
Retrieve&
db=nucleotide&list_uids=21322251&dot=GenBank&term=sapiens+AR+and-
rogen+receptor+prostate+cancer&qty=1>gi:21322251). The term
"androgen receptor polypeptide" means any of the known androgen
receptor polypeptides. For example, see Chang et al., Science 240
(4850), 324-326 (1988). Also see
NM.sub.--000044<http://www.ncbi.nlm.nih.gov:80/entrez/viewer.fcgi?cmd=-
Retrieve&
db=nucleotide&list_uids=21322251&dopt=GenBank&term=sapiens+AR+an-
drogen+receptor+prostate+cancer&qty=1>gi:21322251). The term
"androgen receptor polypeptide variant" means a polypeptide that
exhibits AR activity and which has a deletion, insertion or
substitution of at least one amino acid in the AR polypeptide amino
acid sequence as set forth in Chang et al., Science 240 (4850),
324-326 (1988).
[0031] The terms "agonist" and "agonistic" when used herein refer
to a molecule which is capable of, directly or indirectly,
substantially inducing, promoting or enhancing biological activity
or activation of a molecule such as AR. The terms "antagonist" and
"antagonistic" when used herein refer to a molecule which is
capable of; directly or indirectly, substantially inhibiting
biological activity or activation of a molecule such as AR.
[0032] "Treatment" or "therapy" refer to both therapeutic treatment
and prophylactic or preventative measures.
[0033] The term "therapeutically effective amount" refers to an
amount of a drug effective to treat a disease or disorder in a
mammal. In the case of cancer, the therapeutically effective amount
of the drug may reduce the number of cancer cells; reduce the tumor
size; inhibit (i.e., slow to some extent and preferably stop)
cancer cell infiltration into peripheral organs; inhibit (i.e.,
slow to some extent and preferably stop) tumor metastasis; inhibit,
to some extent, tumor growth; and/or relieve to some extent one or
more of the symptoms associated with the disorder. To the extent
the drug may prevent growth and/or kill existing cancer cells, it
may be cytostatic and/or cytotoxic. For cancer therapy, efficacy in
vivo can, for example, be measured by assessing tumor burden or
volume, the time to disease progression (TIP) and/or determining
the response rates (RR).
[0034] "Growth inhibition" when used herein refers to the growth
inhibition of a cell in vitro and/or in vivo. The inhibition of
cell growth can be measured by a wide variety of methods known in
the art including those described herein. A "growth inhibitory
agent" when used herein refers to a compound or composition which
inhibits growth of a cell in vitro and/or in vivo. Thus, the growth
inhibitory agent may be one which significantly reduces the
percentage of cells in S phase. Examples of growth inhibitory
agents include agents that block cell cycle progression (at a place
other than S phase), such as agents that induce G1 arrest and
M-phase arrest Classical M-phase blockers include the vincas
(vincristine and vinblastine), TAXOL.RTM., and topo II inhibitors
such as doxorubicin, epirubicin, daunorubicin, etoposide, and
bleomycin. Those agents that arrest G1 also spill over into S-phase
arrest, for example, DNA alkylating agents such as tamoxifen,
prednisone, dacarbazine, mechlorethaine, cisplatin, methotrexate,
5-fluorouracil, and ara-C. Further information can be found in The
Molecular Basis of Cancer, Mendelsohn and Israel, eds., Chapter 1,
entitled "Cell cycle regulation, oncogenes, and antineoplastic
drugs" by Murakami et al. (WB Saunders: Philadelphia, 1995),
especially p. 13.
[0035] "Mammal" for purposes of treatment or therapy refers to any
animal classified as a mammal, including humans, domestic and farm
animals, and zoo, sports, or pet animals, such as dogs, horses,
cats, cows, etc. Preferably, the mammal is human.
[0036] The terms "cancer", "cancerous", or "malignant" refer to or
describe the physiological condition in mammals that is typically
characterized by unregulated cell growth. Examples of cancer
include but are not limited to, carcinoma, lymphoma, blastoma,
sarcoma, and leukemia. More particular examples of such cancers
include breast cancer, ovarian cancer, colon cancer, colorectal
cancer, rectal cancer, squamous cell cancer, small-cell lung
cancer, non-small cell lung cancer, Hodgkin's and non-Hodgkin's
lymphoma, testicular cancer, esophageal cancer, gastrointestinal
cancer, renal cancer, pancreatic cancer, glioblastoma, cervical
cancer, glioma, liver cancer, bladder cancer, hepatoma, endometrial
carcinoma, salivary gland carcinoma, kidney cancer, liver cancer,
prostate cancer, vulval cancer, thyroid cancer, hepatic carcinoma
and various types of head and neck cancer.
[0037] Compositions of the invention can be combined with a
pharmaceutically acceptable carrier. As used herein the language
"pharmaceutically acceptable carrier" is intended to include any
and all solvents, dispersion media, coatings, antibacterial and
antifungal agents, isotonic and absorption delaying agents, and the
like, compatible with pharmaceutical administration. The use of
such media and agents for pharmaceutically active substances is
well known in the art. Except insofar as any conventional media or
agent is incompatible with the active compound, such media can be
used in the compositions of the invention. Supplementary active
compounds can also be incorporated into the compositions. A
pharmaceutical composition of the, invention is formulated to be
compatible with its intended route of administration.
[0038] Therapeutic compositions of the invention can be prepared by
mixing the desired molecule having the appropriate degree of purity
with optional pharmaceutically acceptable carriers, excipients, or
stabilizers (see, e.g. Remington: The Science and Practice of
Pharmacy, 19.sup.th Edition, Gennaro (ed.) 1995, Mack Publishing
Company, Easton, Pa.) in the form of lyophilized formulations,
aqueous solutions or aqueous suspensions. Acceptable carriers,
excipients, or stabilizers are preferably nontoxic to recipients at
the dosages and concentrations employed, and include buffers such
as Tris, HEPES, PIPES, phosphate, citrate, and other organic acids;
antioxidants including ascorbic acid and methionine; preservatives
(such as octadecyldimethylbenzyl ammonium chloride; hexamethonium
chloride; benzalkonium chloride, benzethonium chloride; phenol,
butyl or beneyl alcohol; alkyl parabens such as methyl or propyl
paraben; catechol; resorcinol; cyclohexanol; 3-pentanol; and
m-cresol); low molecular weight (less than about 10 residues)
polypeptides; proteins, such as serum albumin, gelatin, or
immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone;
amino acids such as glycine, glutamine, aspaagine, histidine,
arginine, or lysine; monosaccharides, disaccharides, and other
carbohydrates including glucose, mannose, or dextrins; sugars such
as sucrose, mannitol, trehalose or sorbitol; salt-forming
counter-ions such as sodium; and/or non-ionic surfactants such as
TWEEN.TM., PLURONICS.TM. or polyethylene glycol (PEG).
[0039] The invention is based on the discoveries disclosed herein
that a modest (2-5 fold) increase in androgen receptor (AR) mRNA in
prostate cancer cells was the only expression change consistently
associated with developing resistance to antiandrogen therapy. This
increase in AR mRNA and protein was both necessary and sufficient
to convert prostate cancer growth from a hormone sensitive to
hormone refractory stage, and was dependent on a functional
ligand-binding domain. Furthermore, AR antagonists displayed
agonist activity in cells with increased AR levels, and this
antagonist/agonist conversion was associated with alterations in
the pattern of coactivators and corepressors recruited to the
promoter of AR target genes. Increased levels of AR confer
resistance to anti-androgens by amplifying signal output from low
levels of residual ligand and altering the normal response to
antagonists. The findings provide insight toward the design of
novel antiandrogens.
[0040] One embodiment of the invention disclosed herein is a method
of testing compounds for an effect on a mammalian prostate cancer
cell comprising contacting the compound to be tested with a the
mammalian prostate cancer cell, wherein the mammalian cancer cell
is selected for the test because it expresses an exogenous wild
type androgen receptor (AR) polynucleotide that encodes the AR
polypeptide such that the levels of mRNA in the cell that encode
the AR polypeptide or the AR polypeptide are at least about 2 fold
higher than normal/endogenous AR mRNA levels in a mammalian
prostate cell; and then comparing one or more characteristics of
the mammalian prostate cancer cell to which the compound was
administered with the same one or more characteristics of a control
mammalian prostate cancer cell to which the compound has not been
administered, wherein a difference in one or more of the one or
more characteristics indicates that the compound has an effect on
the mammalian prostate cancer cell.
[0041] A test compound which binds AR may then be further screened
for the inhibition of a specific physiological activity (e.g.
tyrosine kinase activity). Such an embodiment includes, for example
determining whether said test compound inhibits the signaling of AR
by utilizing molecular biological protocols to create recombinant
contracts whose enzymological and biological properties can be
examined directly. Enzymology is performed for example, by
measuring tyrosine kinase activity in vitro or in ARS expressing
cells using standard assays.
[0042] Certain discoveries and physiological processes associated
with the invention are discussed below. In addition, in the
examples below, certain compounds useful for example in inhibiting
prostate cancer cell growth are described. Methods for making and
using these compounds are further disclosed herein.
[0043] To examine the range of HR mechanisms in a relatively
unbiased manner, we performed global gene expression profiling on
seven "isogenic" hormone sensitive (HIS) and HR human prostate
cancer xenograft pairs (14 total xenografts). All HR sublines were
derived directly from their HS parental lines by passage in
castrated mice and compared with HS tumors with similar passage
numbers in intact mice..sup.23-26 The microarray dataset was
analyzed using a number of bioinformatic strategies, including
unsupervised and supervised learning. First, we asked if any
subgroups of HR prostate cancer could be identified using an
unsupervised hierarchical clustering algorithm. The following
procedure was followed: (a) Seven 0.5 cm.sup.3 tumors from each
xenograft, grown in either intact (HS) or castrated (HR) mice, were
pooled and total RNA was extracted to generate a single sample.
After processing, the cRNA was hybridized to the Affymetrix U95A
chip and the microarray data was analyzed by Microarray Suite.
Background elements which did not significantly vary (standard
deviation<1000 and coefficient of variation<1) or were not
detected in any of the samples (defined as perfect match
hybridization not significantly different than mismatch control
signal intensity) were filtered out The remaining elements,
representing 1,056 genes, were then used by an unsupervised
learning algorithm to generate a hierarchical clustering diagram.
(b) The microarray data, obtained as described in (a), was
reanalyzed using Microarray Suite whereby each pair was condensed
into a single dataset that represents the ratio in expression
between each HS xenograft and its HR counterpart In addition, using
a number of parameters as defined by Microarray Suite software such
as fold-change, absolute signal intensity and the confidence in
each probe set given by perfect match/mismatch ratios, elements
from the condensed dataset were assigned an independent designation
of increase (I), marginal increase (MD, no change (NC), marginal
decrease (MD) or decrease (D). Elements assessed as NC in all of
the xenograft pairs were filtered out to generate a list of 3,774
genes that was then used by an unsupervised learning algorithm to
generate a hierarchical clustering diagram. (c) Each of the
designations described in (b) was assigned a value ranging from +1
(I) to -1 (D) and a score for each element was produced by summing
the values across each of the seven HS/HR xenograft pairs. This
testing showed that each HR xenograft clustered with its HS
counterpart consistent with the fact that these pairs are
isogenic.
[0044] Since xenograft-specific expression signatures are likely to
obscure gene expression changes responsible for the HS-to-HR
transition,.sup.27 we condensed each HS/HR pair into a single
dataset representing fold-change in expression. Again, no closely
related subgroups emerged, suggesting either that different
mechanisms were responsible for the HS-to-HR transition in each
xenograft or that any common mechanism involved too few genes to
influence the clustering pattern. We explored the latter
possibility using an algorithm to identify any elements that
consistently changed during the HS-to-HR transition. Remarkably,
out of 12,559 probe sets, only one--directed against th AR
cDNA--was differentially expressed in all seven HS/HR pairs (FIG.
1, top). Notably, the second highest ranked probe set, upregulated
in five of seven pairs, was also directed against AR. Consistent
with the RNA data, immunoblots showed higher levels of AR protein
in HR tumors than their parental HS counterparts (FIG. 1, bottom).
The fold-change in AR protein (based on analysis of individual
xenograft tumors) did not perfectly correlate with the fold-change
in AR mRNA (based on expression analysis of pools of tumors for
each xenograft), possibly due to sample-to-sample variation
Alternatively, post-transcriptional mechanisms may affect steady
state AR protein levels..sup.28 Nonetheless, these data raise the
possibility of a common final mechanism of resistance to hormone
therapy.
[0045] To determine if increased AR protein concentration plays a
causal role in the HS-to-HR transition, we introduced an
epitope-tagged wildtype AR cDNA by retrovirus infection into HS
LNCaP human prostate cancer cells. A three-fold increase in AR
levels in LNCaP-AR cells mimics the expression difference observed
in the LNCaP HS/HR pair studied in the microarray experiment To
test whether increased AR expression causes the HS-to-HR
transition, we designed two in vitro assays to mimic the clinical
circumstances of HR disease. The first measures the ability to grow
in low androgen concentrations; the second measures growth in the
presence of the antiandrogen bicalutamide. As expected, LNCaP cells
infected with the empty vector failed to grow in steroid-depleted,
charcoal-stripped serum unless supplemented with 100 pM of the
synthetic androgen, R1881. In contrast, LNCaP-AR cells grew in at
least 80% lower concentrations of R1881. LNCaP-AR cells were also
resistant to bicalutamide.
[0046] Next, we asked if increased AR expression was sufficient, in
vivo, to confer resistance to hormone therapy achieved through
surgical castration using two xenograft models, LNCaP and LAPC4. HS
LAPC4 cells were infected with AR lentivirus (demonstrated to
express about three-fold more AR protein than vector-infected
controls) and then implanted into the flanks of intact or castrated
male SCID mice. AR overexpression shortened the latency of tumor
formation by more than 50%/o in castrated animals in the LAPC4 and
LNCaP models.
[0047] We used stable RNA interference to address the reciprocal
question of whether the increase in AR expression observed in HR
xenografts was necessary for developing resistance to hormone
therapy. Knockdown of AR levels in HR LAPC4 cells was achieved
using a lentivirus vector expressing a short hairpin RNA (shRNA)
against AR cis-linked with a GFP-expression cassette. After
implantation into the flanks of castrated male mice, AR
shRNA-infected tumors grew more slowly than vector-infected
controls. Moreover, those tumors that did grow did not express GFP
when compared to vector-infected controls and still expressed AR
protein, indicating selection for cells that escaped AR knockdown.
Parallel studies of AR knockdown in HR LNCaP sublines gave similar
results.
[0048] To determine the mechanism by which increased AR levels
cause HR disease, we considered two possibilities: (1) high levels
of receptor lead to constitutive activation in the absence of
ligand, consistent with a recent study of AR.sup.29 (a
ligand-independent model), or (2) high levels of receptor sensitize
the cell to the residual amounts of ligand remaining after
testosterone lowering therapy (a ligand-dependent mass action
model). To distinguish between these models, we introduced two AR
mutations, N705S and R752Q, independently into the LBD to
selectively impair ligand-binding without interfering with
ligand-independent functions. N705S is associated with complete
androgen insensitivity syndrome, whereas R752Q is found in patients
with partial androgen insensitivity syndrome..sup.30
[0049] Details of the experimental procedure were as follows:
Mutant or wildtype AR constructs were transfected into AR-null
cells (COS7) and androgen-starved for 48 h Cells were then
incubated with increasing amounts of .sup.3H-R1881 in the presence
or absence of 100-fold excess of cold R1881 and bound ligand was
measured by scintillation counting. LNCaP cells expressing the
various AR LBD or genotropic mutants were assayed for HR growth in
vitro using either the low-androgen sensitization or antagonist
resistance assay as previously described above. All experiments
were done in duplicate. 1.times.10.sup.6 LNCaP cells overexpressing
the various AR cDNAs (n=10) or a vector control (n=10) were
implanted into the flanks of castrated male SCID mice and tumor
volume (.+-.SEM) was measured over time. Confocal
immunofluorescence was performed with a FLAG-specific antibody on
LNCaP cells stably expressing FLAG-tagged, triple point mutant,
K618, 632, 633M (.DELTA.NLS) or wildtype AR.
[0050] As expected, both mutations impaired ligand-binding in a
radiolabeled R1881-binding assay. Consistent with disease severity,
R752Q retained low levels of ligand-binding and transcriptional
activity in a reporter assay, and serves as an internal control to
ensure proper folding of at least one LBD mutant Overexpression of
either LBD mutant AR construct in LNCaP cells, even at levels
approximately 10-fold higher than endogenous AR, failed to promote
HR growth at levels beyond the vector control in low androgen
media, in the presence of bicalutamide or in surgically castrated
mice. These data establish t AR must bind ligand to confer HR
growth and imply that a modest increase in receptor concentration
permits AR to utilize the lower levels of androgens present in
castrated patients. This conclusion also suggests that the widely
used term "androgen-independent" may be a misleading description of
HR prostate cancer.
[0051] The availability of these in vitro assays for AR function
offered an opportunity to address the additional question of
whether AR induces the HS-to-HR transition through genotropic or
non-genotropic functions. Deletion of the nuclear localization
signal (NLS) blocked nuclear translocation and abolished HR growth
in low concentrations of androgen or in the presence of
bicalutamide. Similar results were obtained using a second AR
mutant V581F t lacks DNA binding activity..sup.31 Finally, deletion
of the polyproline region of AR reported to bind the SH3 domain of
Src (.DELTA.P AR).sup.32 had no inhibitory effect on AR function in
these assays. Therefore, the previously reported non-genotropic
effects of AR on bone growth and prostate cancer cell
survival.sup.32-34 are unlikely to play a role in resistance to
antiandrogen therapy.
[0052] The ligand-binding mutagenesis studies provide evidence for
a mass action model to explain resistance to androgen-lowering
hormone therapy. If this mechanism is the sole cause of resistance,
then suprapharmacologic concentrations of bicalutamide should
overcome the excess levels of AR and block transcriptional
activity. Surprisingly, we observed the opposite phenomenon when we
examined the effects of high-dose bicalutamide on prostate specific
antigen (PSA) expression in cells expressing excess AR Bicalutamide
showed typical antagonist activity in parental LAPC4 cells, as
measured by inhibition of PSA mRNA and protein expression, but
functioned as an agonist in LAPC4 cells expressing increased levels
of AR. The antagonist-to-agonist conversion was not unique to
bicalutamide or to the LAPC4 cell line, since similar results were
observed using other AR antagonists such as cyproterone acetate and
flutamide. Similar results were observed with LNCaP cells. In
addition, increased AR levels conferred responsiveness to
noncanonical ligands such as estrogen, reminiscent of the effects
of the T877A AR LBD mutation in LNCaP cells..sup.8
[0053] Details of the above high-dose testing were as follows:
LAPC4 cells over expressing AR or a GFP control were
androgen-starved for 5 days with charcoal-stripped serum and then
challenged with bicalutamide or cyproterone acetate or flutamide
for 96 hour. PSA and .beta.-actin message was assayed using semi
quantitative RT-PCR. Secreted PSA after 48 hour challenge with
bicalutamide or 17.beta.-estradiol was measured via ELISA. LNCaP
cells stably infected with an AR-expressing or control virus (Neo)
was androgen-starved for 5 days and then challenged for 48 hours
with bicalutamide. PSA and .beta.-actin were then measured. LNCaP
cells stably infected with the AR-expressing virus or the vector
control were starved for 5 days and then challenged with either
vehicle, 10 .mu.M bicalutamide, 100 pM R1881 or 1 nM DHT. After 1
hour, cells were harvested and processed for chromatin
iummunoprecipitation..sup.21
[0054] To determine if the above-described conversion was peculiar
to the PSA gene or was true for other androgen-regulated genes, we
conducted a microarray experiment LNCaP cells infected with an
AR-expressing retrovirus or the empty-vector control were
challenged with increasing doses of R1881 or 10 .mu.M bicalutamide
and then processed for hybridization to the Affymetrix U133A chip.
Bicalutamide induced the expression of 48 probe sets (defined as
2-fold increase, P<0.05, 500 minimum expression) in LNCaP-AR
cells, whereas no elements were significantly upregulated in
control cells. The list was comprised mostly of androgen-regulated
genes including the well known members, PSA and kallikrein 2
(KLK2).sup.35. (See the TABLE at the end of this description for a
complete list of the genes tested). However, bicalutamide induced
only a subset (<10%) of the total nunber of androgen-regulated
genes (>600 probe sets). Upon closer examination, the
bicalutamide-induced genes overlapped, for the most part, with the
most highly induced, androgen-responsive genes. Consistent with
this, unsupervised hierarchical clustering of the samples grouped
the profile of genes induced by 10 .mu.M bicalutamide most closely
with those induced by low doses (10-30 pM) of R1881. Together,
these data suggest that increased AR expression globally converts
antagonists to weak agonists, and therefore leads to the induction
of only the most androgen-sensitive genes.
[0055] To address the mechanism by which bicalutamide gains agonist
properties in the setting of increased AR levels, we performed
chromatin immunoprecipitation experiments to define the components
of the AR transcription complex on the promoters of two genes, PSA
and KLK2, activated by bicalutamide in the microarray experiment
After exposure to the classic agonists R1881 or
dihydrotestosterone, AR and polymerase II were recruited to both
promoters regardless of AR level as expected from prior
work..sup.21,36 AR was also recruited to both templates after
exposure to bicalutamide in vector and AR-overexpressing cells, but
polymerase II was present only in the setting of excess AR However,
in AR-overexpressing cells, the repertoire of coactivators
recruited to these promoters by bicalutamide was more limited (e.g.
SRIC1 and not AIB1) when compared with R1881 or
dihydrotestosterone. We also examined the effect of increased AR
levels on promoter occupancy by corepressors. As expected, NCoR was
recruited to both promoters in parental cells following
bicalutamide treatment without evidence of histone acetylation or
polymerase II recruitment. However, NCoR recruitment was reduced
(PSA promoter) or absent (KLK2 promoter) after bicalutamide
treatment in cells with increased AR protein levels. Therefore, a
modest change in the level of AR protein can shift the relative
abundance of coactivators or corepressors assembled on the
promoters of AR target genes, with resultant effects on
transcriptional activity.
[0056] The surprising result from our expression profiling was the
universal upregulation of AR mRNA in all the HR xenograft models, a
finding likely to have clinical relevance based on surveys of AR
levels in patient material..sup.7,37 AR gene amplification could
clearly result in increased AR levels, but this occurs in a
minority of patients and cannot be invoked as the explanation for
our xenograft findings, since there was no increase in AR copy
number during the HS-to-HR transition..sup.38 Studies of AR gene
regulation have implicated AR itself as a positive acting
transcription factor that binds the AR gene and leads to increased
AR mRNA levels..sup.39 Therefore, other mechanisms postulated to
give increased AR activity, such as increased kinase pathway
signaling (ErbB2, Ras, MAPK) or altered coactivator/corepressor
ratios, may also lead to increased AR mRNA levels, albeit
indirectly. Thus, any one of a number of primary molecular events
that alter AR activity could cause an increase in AR mRNA,
suggesting a final common pathway for escape from standard hormone
therapy.
[0057] One caveat is that our conclusions about AR are based on
studies of HS xenograft models, nearly all of which have been
derived from men with HR disease. The question of how HS growth is
"restored" when such tumors are explanted into intact male mice is
a long-debated paradox in the prostate cancer field, and the
mechanism remains unknown. We previously provided evidence that
such explants contain a mixture of HS and HR clones, and that HR
sublines develop through clonal expansion under the selective
pressure of androgen deprivation..sup.40 The HS clones that evolve
from such explants may be HS only in relative terms, reflecting a
transition state in the continuum between truly hormone-naive
prostate cancer (no prior exposure to antiandrogen therapy) and
fill blown HR disease. It remains to be determined whether AR
upregulation is sufficient to confer HR growth to hormone-naive
cells. Newer transgenic or knockout models of murine prostate
cancer may provide an opportunity to address this question in a
"cleaner" experimental system..sup.41,42
[0058] The simplest model to explain how increased expression of AR
can confer resistance to anti-androgen therapy is mass action.
According to this model, the 3-5 fold increase in receptor levels
observed in our xenograft models can compensate for low ligand
levels and restore AR signaling. However, the fact that increased
receptor levels cause antagonists to function as agonists suggests
another level of complexity. Our comparison of genes induced by
bicalutamide to those induced by a range of androgen doses
indicates that antagonists function as weak agonists in the setting
of increased AR levels. Comparative analysis of the transcription
complex assembled on the promoters of AR target genes revealed a
potential mechanism. Specifically, a more limited repertoire of
coactivators is recruited to AR target genes after stimulation with
bicalutamide, suggesting that suboptimal ligands cannot assemble
the optimal array of cofactors for maximal transcriptional activity
(See FIG. 2). Because steroid receptor-antagonist complexes adopt a
variety of conformations,.sup.43,44 antagonist-bound AR may be
unable to bind the full complement of coactivator machinery.
[0059] The molecular basis for loss of antagonism is less apparent
Previous work has demonstrated that the agonist versus antagonist
response of nuclear receptors like ER is altered by increased
expression of coactivators (increased SRC1) or by decreased
expression of corepressors (decreased NCoR)..sup.45,46 Our data
establish that increased expression of the nuclear receptor itself
causes a similar outcome, perhaps by upsetting the balance of
corepression and coactivation in the cell. Additional experiments
examining each of these components are required to sort through
these or alternative explanations.
[0060] The clinical relevance of antagonist/agonist conversion
should also be considered. About 30% of men whose disease
progresses during treatment with AR antagonists experience a
paradoxical fall in serum PSA levels when the antagonist is
discontinued, called anti-androgen withdrawal syndrome..sup.47 One
proposed mechanism is mutation in the AR gene, based on the fact
that flutamide functions as an agonist in cells expressing the
T877A AR mutation..sup.8 Although compelling, this mechanism cannot
account for all cases because recent estimates of the frequency of
AR mutations in HR patients are too low..sup.5 Our findings suggest
that patients with antiandrogen withdrawal syndrome may be those
with the highest level of AR upregulation.
[0061] Perhaps the most important implication of the present
invention is toward the development of novel antiandrogens. The
fact that an intact LBD is required for AR to cause resistance to
hormone therapy provides compelling rationale for the design of
novel antagonists that exploit existing knowledge of this well
defined binding pocket..sup.48 Because AR action appears to be
mediated exclusively through genotropic mechanisms, one can also
envision drugs that prevent AR nuclear translocation or impair
assembly of AR transcription complexes on target genes. Finally, it
will be important to determine if the mechanisms of antiandrogen
resistance implicated here have relevance for other
hormone-dependent diseases such as breast cancer.
[0062] Host cells, such as prostate cancer cells can be transfected
or transformed with expression or cloning vectors described herein
for the expression of the human AR proteins and cultured in
conventional nutrient media modified as appropriate for inducing
promoters, selecting transformants, or amplifying the genes
encoding the desired sequences. The culture conditions, such as
media, temperature, pH and the like, can be selected by the skilled
artisan without undue experimentation. In general, principles,
protocols, and practical techniques for maximizing the productivity
of cell cultures can be found in Mammalian Cell Biotechnology: a
Practical Approach, M. Butler, ed. (IRL Press, 1991) and Sambrook
et al., supra.
[0063] A wide variety of methods of transducing mammalian cells are
known in the art, for example, using reagents and methods such as
viral vectors (e.g. the retroviral vectors disclosed in the
Examples below), lipids (e.g. lipofection), CaPO.sub.4 and
electroporation etc. Depending on the host cell used,
transformation is performed using standard techniques appropriate
to such cells. The calcium treatment employing calcium chloride, as
described in Sambrook et al., supra or electroporation is generally
used for prokaryotes or other cells that contain substantial
cell-wall barriers. For mammalian cells without such cell walls,
the calcium phosphate precipitation method of Graham and van der
Eb, Virology, 52:456-457 (1978) can be employed. General aspects of
mammalian cell host system transformations have been described in
U.S. Pat. No. 4,399,216. However, other methods for introducing DNA
into cells, such as by nuclear microinjection, electroporation,
bacterial protoplast fusion with intact cells, or polycations,
e.g., polybrene, polyornithine, may also be used. For various
techniques for transforming mammalian cells, see Keown et al.,
Methods in Enzymology. 185:527-537 (1990) and Mansour et al.,
Nature 336:348-352 (1988).
[0064] Suitable host cells for cloning or expressing the AR DNA in
the vectors herein include various prostate cancer cell lines such
as LNCaP lines, DU145 and TsuPr1, other transfectable or
transducible prostate cancer cell lines, primary cells (PrEC), as
well as a number of mammalian cells routinely used for the
expression of recombinant proteins (e.g., OS, CHO, 293, 293T
cells).
[0065] The nucleic acid (e.g., cDNA or genomic DNA) encoding AR may
be inserted into a replicable vector for cloning (amplification of
the DNA) or for expression. Various vectors are publicly available.
The vector may, for example, be in the form of a plasmid, cosmid,
viral particle, or phage. The appropriate nucleic acid sequence may
be inserted into the vector by a variety of procedures. In general,
DNA is inserted into an appropriate restriction endonuclease
site(s) using techniques known in the art. Vector components
generally include, but are not limited to, one or more of a signal
sequence, an origin of replication, one or more marker genes, an
enhancer element, a promoter, and a transcription termination
sequence. Construction of suitable vectors containing one or more
of these components employs standard ligation techniques which are
known to the skilled artisan.
[0066] The AR proteins may be produced recombinantly not only
directly, but also as a fusion polypeptide with a heterologous
polypeptide (e.g., the FLAG tag disclosed herein), which may be a
signal sequence or other polypeptide having a specific cleavage
site at the N-terminus of the mature protein or polypeptide. In
general, the signal sequence may be a component of the vector, or
it may be a part of the AR DNA that is inserted into the vector.
The signal sequence may be a prokaryotic signal sequence selected,
for example, from the group of the alkaline phosphatase,
penicillinase, lpp, or heat-stable enterotoxin II leaders. For
yeast secretion the signal sequence may be, e.g., the yeast
invertase leader, alpha factor leader (including Saccharomyces and
Kluyveromyces .alpha.-factor leaders, the latter described in U.S.
Pat. No. 5,010,182), or acid phosphatase leader, the C. albicans
glucoamylase leader (EP 362,179 published 4 Apr. 1990), or the
signal described in WO 90/13646 published 15 Nov. 1990. In
mammalian cell expression, mammalian signal sequences may be used
to direct secretion of the protein, such as signal sequences from
secreted polypeptides of the same or related species, as well as
viral secretory leaders.
[0067] Both expression and cloning vectors typically contain a
nucleic acid sequence that enables the vector to replicate in one
or more selected host cells. Such sequences are well known for a
variety of bacteria, yeast, and viruses. The origin of replication
from the plasmid pBR322 is suitable for most Gram-negative
bacteria, the 2.mu. plasmid origin is suitable for yeast, and
various viral origins (SV40, polyoma, adenovirus, VSV or BPV) are
useful for cloning vectors in mammalian cells. A wide range of
host-vector systems suitable for the expression of AR are
available, see for example, Sambrook et al., 1989, supra; Current
Protocols in Molecular Biology, 1995, supra). Preferred vectors for
mammalian expression include but are not limited to pcDNA 3.1
myc-His-tag (Invitrogen) and the retroviral vector pSR.alpha.tkneo
(Muller et al., 1991, MCB 11:1785). Using these expression vectors,
AR can be expressed in prostate cancer and non-prostate cell lines,
including for example LNCaP, 293, 293T, rat-1, NIH 313 and TsuPr1.
The host-vector systems of the invention are useful for the
production of an AR protein or fragment thereof Such host-vector
systems can be employed to study the functional properties of AR
and AR mutations or analogs.
[0068] Expression and cloning vectors will typically contain a
selection gene, also termed a selectable marker. Typical selection
genes encode proteins that (a) confer resistance to antibiotics or
other toxins, e.g., ampicillin, neomycin, methotrexate, or
tetracycline, (b) complement auxotrophic deficiencies, or (c)
supply critical nutrients not available from complex media, e.g.,
the gene encoding D-alanine racemase for Bacilli.
[0069] Examples of suitable selectable markers for mammalian cells
are those that enable the identification of cells competent to take
up the AR nucleic acid, such as DHFR or thymidine kinase. An
appropriate host cell when wild-type DHFR is employed is the CHO
cell line deficient in DHFR activity, prepared and propagated as
described by Urlaub et al., Proc. Natl. Acad Sci. USA, 77:4216
(1980). A suitable selection gene for use in yeast is the trp1 gene
present in the yeast plasmid YRp7 (Stinchcomb et al., Nature,
282:39 (1979); Kingsman et al., Gene 7:141 (1979); Tschemper et
al., Gene 10:157 (1980)). The trp1 gene provides a selection marker
for a mutant strain of yeast lacking the ability to grow in
tryptophan, for example, ATCC No. 44076 or PEP41 (Jones, Genetics
85:12 (1977)).
[0070] Additional details regarding the practice of the invention
are as follows: Oligonucleotide U95A and U133A gene arrays were
purchased from Affymetrix. Charcoal-stripped dextran-treated fetal
bovine serum was obtained from Omega Scientific. Bicalutamide was
obtained from the UCLA Investigational Drug Pharmacy and dissolved
in acetone. Cold and .sup.3H-R1881 were obtained from NEN Life
Sciences. AR antibody N-20 (Santa Cruz) and Flag antibody M2
(Sigma) were used in the immunoblot assays. Secreted PSA was
measured by ELISA (American Qualex). Protein extracts were prepared
in high detergent buffer (2% SDS) to ensure total cell lysis.
[0071] Typical DNA constructs were prepared as follows: pCSUACG
(U6-shRNA.alpha.AR;CMV-GFP) shRNA.alpha.AR;CMV-GFP) was constructed
by ligating the BamHI/EcoRI digests of pCSCG and the
U6-shNA.alpha.AR PCR product The U6-shRNA.alpha.AR PCR was
performed using a hU6containing plasmid at a 60.degree. C.
annealing temperature with suitable primers: pCSCA (CMV-AR) was
created by subcloning the XhaI fragment of pSR.alpha.-AR into the
NheI site of pCSCG. AR mutants were made by standard PCR-based
site-directed mutagenesis using the QuikChange Kit (Stratagene).
.quadrature.NLS contains three point mutations (K618M, K632M,
K633M) previously shown to disrupt nuclear import..sup.49
.quadrature.Pro contains a deletion of amino acids 372-381, based
on prior work..sup.32 ARR.sub.2Pb-Luciferase was kindly provided by
Robert Matusik (Vanderbilt). PSA RT-PCR was also performed using
suitable primers.
[0072] Details of typical In vitro and In vitro Growth experiments
are as follows: LNCaP (ATCC) and LAPC4 cells were maintained in
Iscove's medium supplemented with 10% fetal bovine serum. LNCaP-AR
and LNCaP-vector were derived by infection with the
pSR.quadrature.-AR or pSR.quadrature. retrovirus, respectively, and
selection in 500 ng/ml of G418. LNCaP-AR, LNCaP-vector, LAPC4AR,
and LAPC4-vector in other experiments were derived by infection
with the pCSCA or pCSC lentivins, respectively, without selection
(>90% infection). For in vitro experiments, LNCaP or LAPC4 cells
stably infected with different constructs were androgen-starved by
growth in charcoal-stripped serum for 3-5 d. 5.times.10.sup.4 cells
were plated per well in media containing 10% charcoal-stripped
serum supplemented with various concentration of R1881 or in media
containing 10% full serum with various concentration of
bicalutamide. Colonies were visualized with crystal violet staining
2 weeks later. In vivo tumorigenicity was measured by injection of
5.times.10.sup.5 LAPC4 or 1.times.10.sup.6 LNCaP cells in 1100
.mu.l of Matrigel (Collaborative Biomedical) subcutaneously into
the flanks of intact or castrated male SCID mice. Tumor size was
measured weekly in three dimensions using caliber as
described..sup.26 AR knockdown was performed by infection of HR
LAPC4 with shRNA AR lentivirus. Tumors which grew in castrated mice
were explanted, and analyzed by flow cytometry for the percentage
of GFP-positive cells. All mouse experiments were performed in
compliance with the guidelines of the Animal Research Committee
(ARC) of the UCLA.
[0073] HS and HR xenograft pairs for the microarray study were
collected from three institutions. LUCaP23, 35, and 41 were
developed at University of Washington; CWR22 was developed by Case
Western Reserve University and kindly provided by University of
North Carolina at Chapel Hill; LAPC4 and 9 were developed at the
University of California at Los Angeles; LNCaP was purchased from
ATCC and implanted into mice. The HS xenografts were either grown
in intact nude mice or SCID male mice, and their HR counterparts
were developed by serial passage in castrated male mice. Microarray
experiments were performed and data analyzed according to
manufacture's instructions (Affymetrix). We extracted total RNA
from a pool of two to eight tumors with comparable sizes and serum
PSA levels for each xenograft using TriReagent Molecular Research
Center) and RNeasy (Qiagen). For each sample, 15 .mu.g of total RNA
was used to generate double stranded cDNA and the cRNA Was
transcribed with biotin-labeled nucleotides (ENZO Diagnostics). The
cRNA was fragmented and hybridized to U95A microarray (Affymetrix).
Scanned images were used for absolute and comparison analysis
(Affymetrix manual). The microarray data were generated through the
Genespring program (Silicon Genetics).
[0074] Details of typical chromatin immunoprecipitation are as
follows: LNCaP-AR or LNCaP-vector were androgen-starved and
challenged with either vehicle, 100 pM of R1881, 1 nM of DHT, or 10
.mu.M of bicalutamide for 1 hour. Soluble chromatin was prepared
after formaldehyde crosslinking and sonication. Specific IgGs
against AR, N--CoR, PolII, Ac-H3/4, SRC1, TIF2, AIB1, and PCAF were
used to immunoprecipitate protein-bound DNA fragments. After
reversing the crosslinking, PCR reactions were performed to amplify
the promoter regions of KLK3/PSA or KLK2..sup.21 Duplicates for
bicalutamide or vehicle treatment were averaged and queried for the
number of probe sets induced 2-fold, P<0.05 with a minimum
expression of 500 in at least one sample. The dataset was analyzed
for the number of probe sets that induced a minimum 2-fold
increase. The data showed that increased AR expression globally
converts antagonists to weak agonists.
[0075] Throughout this application, various publications are
referenced (within parentheses for example). The disclosures of
these publications are hereby incorporated by reference herein in
their entireties. In order to facilitate an understanding of
various typical aspects of the invention, certain aspects of these
incorporated materials are reproduced herein.
[0076] The following examples provide an illustration of how the
screening method of the present invention was used in the testing,
development and identification of new chemical compounds for the
treatment of prostate cantor, especially hormone-refractory
(androgen-independent) prostate cancer).
[0077] There are many compounds which have been reported to be
inhibitors of the ligand binding domain (LBD) androgen receptor
(AR). Several have been used as drugs to treat prostate cancer,
e.g., bicalutamide (Casodex) 1, which is the current drug of choice
for treatment of: ##STR1##
[0078] prostate cancer. Several more potent binders of the AR LBD
have been identified, e.g., the thiohydantoins, RU59063 2 and BTID,
3 (see, e.g. Teutsch et al., J. Steroid Biochem. Molec. Biol. 1994,
48, 111-119 and Van Dort et al., J. Med Chem. 2000, 43, 3344-3347).
We decided to carry out a study using the screening method of the
present invention to identify novel analogues of compounds such as
2 and 3 which would have other alkyl groups with final polar
functionality in place of the 4hydroxybutyl group (R in 2 and 3)
which might form much stronger interactions, and even in some cases
covalent interactions, with the various polar amino acid side
chains of the LBD of the AR. Thus the state of the art was that
some strong binders had been discovered but they had not been yet
developed into prostate cancer drugs. ##STR2##
[0079] We have prepared a series of compounds 4 based on the
general structure 2 and have carried out initial screening using
the method of the present invention and additional biological
testing which shows that these compounds inhibit the growth of a
prostate cancer cell line, including hormone-sensitive and
hormone-refractory variants. The biological data allows us to
measure both agonist and antagonist effects and we find that the
best compounds are pure antagonists, namely they bind strongly to
the LBD of the AR and shut down the natural process of active
cancer growth. In particular the 4-azido-phenyl derivative 5 has
shown the best antagonist effects without any strong agonist
effects. ##STR3##
[0080] The preferred sequence for the chemical synthesis of these
compounds is shown below. The commercially available aniline 6 is
converted in one step into the isothiocyanate 7. Commercially
available acetone cyanohydrin 8 is converted into the two
cyanoamines 10ab by reaction with the amines 9a (n=3-8) and the
aniline 9b. Addition of 10ab to 7 followed by treatment with mild
acid produces the desired thiohydantoins 4 (n=3-8) and 5 in good
yield. ##STR4##
[0081] These compounds 4 and 5 show remarkable anti-prostate cancer
activity. The biological testing was carried out by measurement of
the amount of prostate-specific antigen (PSA) produced by LNCaP
cells. The IC.sub.50 values of 4 and 5 for PSA expression are
ten-fold lower that that for bicalutamide (2-3 times stronger) and
the compounds seem to be fill antagonists. Therefore they offer the
potential for a better drug for the treatment of prostate cancer,
namely they antagonize the effect of androgens on the AR and thus
should greatly slow the progression of prostate cancer.
[0082] As shown above, we have prepared the compounds 4 and 5 and
carried out the initial set of biological assays (including initial
screening using the method of the present invention) that show
their potent binder and antagonist ability. This exciting set of
compounds is relatively simple to synthesize and already have more
potential man the well known heavily used antiprostate cancer drug
Casodex.
[0083] The present invention is not to be limited in scope by the
embodiments disclosed herein, which are intended as single
illustrations of individual aspects of the invention, and any that
are functionally equivalent are within the scope of the invention.
Various modifications to the models and methods of the invention,
in addition to those described herein, will become apparent to
those skilled in the art from the foregoing description and
teachings, and are similarly intended to fall within the scope of
the invention. Such modifications or other embodiments can be
practiced without departing from the true scope and spirit of the
invention. However, the invention is only limited by the scope of
the appended claims. TABLE-US-00001 TABLE Affy ID GenBank ID Affy
ID GenBank ID 212005 AL582808 206205 NM_022782.1 213017 NM_138340
221965 NM_022782 201662 D89053.1 208309 NM_006785.1 216323
XM_054284 214087 NM_002465 211689 AF270487.1 211548 J05594.1 205102
NM_005656 205040 NM_000607.1 215990 S67779.1 205041 NM_000607.1
203356 NM_014296 220954 NM_013440.1 222201 AB037736.1 206178
NM_000929.1 221272 NM_030806.1 214443 NM_006505.1 222121 NM_015595
218782 NM_014109.1 212665 NM_015508 205924 BC005035.1 209389
M15887.1 201975 NM_002956.1 204560 NM_004117.1 201562 NM_003104
210892 BC004472.1 216920 M27331.1 219312 NM_023929.1 215806
M13231.1 219476 NM_024115.1 209813 M16768.1 210339 BC005196.1
211144 M30894.1 209854 NM_005551 201108 NM_003246 204583 U17040.1
222118 AK023669.1 204582 NM_001648 219555 NM_018455 212789
XM_166201 219551 NM_018456.1 205862 NM_014668.1 209053 BE793789
201551 J03263.1 209309 D90427.1
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* * * * *
References