U.S. patent application number 09/964042 was filed with the patent office on 2002-02-14 for treatment of tumors with genetically engineered herpes virus.
This patent application is currently assigned to Arch Development Corporation. Invention is credited to Roizman, Bernard, Weichselbaum, Ralph, Whitley, Richard J..
Application Number | 20020019362 09/964042 |
Document ID | / |
Family ID | 22923971 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019362 |
Kind Code |
A1 |
Weichselbaum, Ralph ; et
al. |
February 14, 2002 |
Treatment of tumors with genetically engineered herpes virus
Abstract
Disclosed are methods for treating cancer by administering an
effective amount of a modified Herpes simplex virus.
Inventors: |
Weichselbaum, Ralph;
(Chicago, IL) ; Roizman, Bernard; (Chicago,
IL) ; Whitley, Richard J.; (Birmingham, AL) |
Correspondence
Address: |
MARSHALL, O'TOOLE, GERSTEIN, MURRAY & BORUN
6300 SEARS TOWER
233 SOUTH WACKER DRIVE
CHICAGO
IL
60606-6402
US
|
Assignee: |
Arch Development
Corporation
|
Family ID: |
22923971 |
Appl. No.: |
09/964042 |
Filed: |
September 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09964042 |
Sep 26, 2001 |
|
|
|
09629021 |
Jul 31, 2000 |
|
|
|
Current U.S.
Class: |
514/44R ;
424/93.21 |
Current CPC
Class: |
C12N 2710/16632
20130101; C12N 2710/16622 20130101; A61P 35/00 20180101; C07K
14/005 20130101; A61K 35/763 20130101 |
Class at
Publication: |
514/44 ;
424/93.21 |
International
Class: |
A61K 048/00 |
Claims
What is claimed is:
1. A method for killing cancer cells comprising the step of
administering to an individual suffering from cancer an amount of a
Herpes simplex virus (HSV) comprising a modified HSV genome wherein
said modification comprises a modification of an inverted repeat
region of said HSV genome such that one .gamma..sub.134.5 gene
remains intact and said amount of HSV being effective to kill
cancer cells.
2. The method of claim 1 wherein the modification of the inverted
repeat region of the genome comprises an alteration of a copy of a
.gamma..sub.134.5 gene which renders that copy of the gene
incapable of expressing an active gene product.
3. The method of claim 2 wherein the alteration of the
.gamma..sub.134.5 gene comprises an insertion of a DNA sequence
comprising one or more nucleotides into the coding region or
regulatory region of the gene.
4. The method of claim 2 wherein the alteration of the
.gamma..sub.134.5 gene comprises a deletion of all or part of the
coding region or regulatory region of the gene.
5. The method of claim 1, 2, 3, or 4 wherein the modified HSV
genome further comprises an alteration in a unique region of the
HSV genome.
6. The method of claims 1, 2, 3, or 4 wherein the cancer is a
noncentral nervous system cancer.
7. The method of claim 1, 2, 3, or 4 wherein the cancer is a
central nervous system cancer.
8. The method of claim 5 wherein the cancer is non-central nervous
system cancer.
9. The method of claim 5 wherein the cancer is a central nervous
system cancer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to use of modified
Herpes simplex viruses as therapeutic treatment for tumors.
BACKGROUND OF THE INVENTION
[0002] The development of viruses as anticancer agents has been an
intriguing yet elusive strategy. The goal of anticancer viral
therapy is to inoculate a small percentage of tumor cells with
replication competent viruses resulting in viral replication in the
targeted tumor cells followed by cellular lysis (oncolysis) and
infection of surrounding tumor cells. A key to viral oncolysis is
genetic modification of the virus such that replication occurs
principally in tumor cells and not in the surrounding normal
tissue. Many strategies have focused on the use of genetically
engineered viruses for oncolysis. For example, in one approach,
attenuated retroviruses, modified to encode herpes simplex virus
(HSV) thymidine kinase, were created to target dividing tumor cells
[Culver, et al., Science 256:1550-1552 (1992); Ram, et al. Nat.
Med. 3:1354-1361 (1997)]. In this technique, however, viral
infection of tumor cells was limited since only 10 to 15% of tumor
cells were actively progressing through the cell cycle. In another
approach, conditional replication-competent adenoviruses (E1b
deleted) were designed to replicate only in tumor cells lacking
p53, however only 50% of tumors are estimated to contain
nonfunctional p53 [Bischoff, et al., Science 274:373-376 (1996);
Heise, et al. Nat. Med. 3:639-645 (1997); Hollstein, et al.,
Science 253:49-53 (1991)]. The success of these strategies,
therefore has been limited experimentally only to small tumor
xenografts.
[0003] Recently, genetically engineered replication-competent HSV
has been proposed to treat malignant gliomas [Martuza, et al.,
Science 252:854-856 (1991)]. In anti-glioma therapy, HSV-1 mutants
were constructed to preferentially replicate in proliferating tumor
cells thereby eliminating the risk of widespread dissemination of
the virus in the central nervous system, which is observed in rare
cases of HSV encephalitis in human. Initial strategies focused on
deletion of viral genes encoding enzymes required for viral DNA
synthesis (e.g., thymidine kinase, ribonucleotide reductase
[Martuza, et al, Science 252:854-856 (1991); Mineta, et al., Cancer
Res. 54:3963-3966 (1994)]. More recent studies centered on the use
of HSV mutants that lack a newly identified .gamma..sub.134.5 gene
involved in neurovirulence [Chou, et al., Science 250:1262-1266
(1990); Chou, et al., Proc. Natl. Acad. Sci. (USA) 89:3266-3270
(1992); Chou, et al., Proc. Natl. Acad. Sci. (USA) 92:10516-10520
(1995); Andreansky, et al. Cancer Res. 57:1502-1509 (1997)]. The
combination of previous results suggested that a decrease in viral
proliferative potential required for safe intracranial HSV
inoculation, however, correlates with a decrease in the oncolytic
potential of the virus [Advani, et al. Gene Ther. 5:160-165
(1998)]. The potential therapeutic effects of a genetically
engineered HSV, having more potent antitumor efficacy than is
possible for intracranial inoculation, has not been studied in
models of common human tumors.
[0004] HSV offers many advantages as an oncolytic agent. The virus
replicates well in a large variety on cancer cells and it destroys
the cells in which it replicates. The virus can be attenuated by
introducing specific deletions and it tolerates the insertion and
expression of foreign genes [Meignier, et al, J. Infect. Dis.
158:602-614 (1988)]. Moreover, the functions of many HSV viral
genes are known [Shih, et al., Proc. Natl. Acad. Sci. (USA)
81:5867-5870 (1984); Roizman, Proc. Natl. Acad. Sci, (USA)
93:113076-11312 (1996)]. The undesirable properties of HSV,
however, include neuroinvasiveness, the ability to establish
latency, and a capacity for reactivation from latent state.
[0005] Previous work has shown interactive effects of cytolytic
capacity of modified HSV lacking both .gamma..sub.134.5 genes and
ionizing radiation on glioma xenografts [Advani, et al. Gene Ther.
5: 160-165 (1998)]. Ionizing radiation combined with inoculation
with .gamma..sub.134.5-deficient HSV viruses resulted in
supra-additive reduction in tumor xenograft volume and an
enhancement in viral proliferation and intra-tumoral distribution
in glioma xenografts.
[0006] R7020 is one such HSV strain attenuated by genetic
engineering and tested in a variety of rodent, rabbit, and
non-human primate models [Meignier, et al., J Infect. Dis. 158:
602-614 (1988); Meignier, et al., J Infect. Dis. 162:313-321
(1990)] which have shown that viral infectivity is attenuated in
all species tested. A key property of interest in this strain is
the lack of neuroinvasiveness even in the most susceptible species
tested to date. R7020 is a modified HSV strain designed as a
candidate for human immunization against HSV-1 and HSV-2 infections
[Meignier, et al., Infect. Dis. 158: 602-614 (1988)]. Originally
produced to be a live attenuated viral vaccine against HSV
infection, R7020's has been examined for safety and stability in
rodent and primate studies [Meignier, et al., J. Infect. Dis.
158:602-614 (1988); Meignier, et al., J. Infect. Dis. 162:313-321
(1990)]. The construction of R7020 has been previously described
[Meignier, et al., J. Infect. Dis. 158: 602-614 (1988); and
Roizman, U.S. Pat. No: 4,859,587, incorporated herein by
reference]. Briefly, wild-type HSV DNA consists of two regions of
unique double-stranded DNA sequences flanked by inverted repeats
[Roizman, et al., Proc Natl. Acad. Sci. (USA) 93:11307-11312
(1996)]. The inverted repeats regions contain two copies of five
genes designated .alpha.0, .alpha.4, .gamma..sub.134.5, ORF P and
ORF O. R7020 contains an HSV-2 DNA fragment inserted in place of
one set of the repeats and therefore lacks only one of the two
copies of the .gamma..sub.134.5 gene. Previously work has shown
that, in certain cell lines, R7020 replicates more efficiently than
viruses lacking both copies of the .gamma..sub.1 34.5 gene [Advani,
et al. Gene Ther. 5:160-165 (1998)]. To date, R7020 has been
subjected to limited trials in humans.
[0007] One of the causes of failure in cancer therapy is tumor cell
resistance to conventional cytotoxic and/or hormonal treatments
that arises from genetic instability caused by these agents and
inherent instability of tumor cells. For example, p53 gene deletion
or mutation may decrease tumor cell susceptibility to apoptosis
induced by chemotherapy and/or radiation [Houldsworth, et al.,
Oncogene 16:2345-2349 (1998); Aas. et al. Nat. Med. 2: 811-814
(1998); Lowe, et al., Science 266:807-810 (1994); Dalta, et al.,
Cell Growth Differ. 6:363-370 (1995)] and mutations in the androgen
receptor lead to hormone resistance in prostate cancer. Also, "gain
of function" mutations, such as activation of the bc1-2 family of
genes, enhances resistance to a variety of cytotoxic therapies. In
addition to intrinsic genetic instability of tumor cells, commonly
employed anticancer therapies that rely on DNA damage to tumor
cells are mutagenic and a consequence of anticancer treatment is
the selection and evolution of resistance to DNA damaging agents.
One benefit of using viral lysis as an antitumor strategy is that
viral lysis has the potential to overcome tumor resistance to
conventional agents. Since tumor cell infection with replication
component herpes results in cell lysis and is not per se mutagenic,
selective evolution of tumor cells to evade herpes is less likely
to occur within the tumor cell population.
[0008] Thus there exists a need in the art to identify and develop
viral therapeutic agents and effective methods of treatment to
retard and/or reduce tumor growth in patients in need thereof.
SUMMARY OF THE INVENTION
[0009] The present invention provides methods for treating cancer
comprising the steps of administering to an individual in need
thereof an effective amount of a Herpes simplex virus (HSV)
comprising a modified HSV genome wherein said modification
comprises a modification of an inverted repeat region of said HSV
genome. In one embodiment, methods of the invention include use of
HSV strains wherein the modification of the inverted repeat region
of the genome comprises an alteration of a copy of a .gamma.134.5
gene that renders that copy of the gene incapable of expressing an
active gene product. In a preferred embodiment, methods of the
invention comprise use of an HSV strain wherein the alteration of
the .gamma..sub.1134.5 gene comprises (i) an insertion of a DNA
sequence comprising one or more nucleotides into the coding region
or regulatory region of the gene or (ii) a deletion of all or part
of the coding region or regulatory region of the gene. Methods of
the invention include use of HSV strains wherein the modified HSV
genome further comprises an alteration in a unique region of the
HSV genome.
[0010] Methods of the invention include treatment of noncentral
nervous system cancer as well as central nervous system cancer.
DETAILED DESCRIPTION
[0011] The present invention provides materials and methods for
treating a variety of tumors including noncentral nervous system
tumors and tumors of the central nervous system origin. The
treatment methods involve infecting target tumors with genetically
modified herpes simplex virus wherein the modification comprises a
modification of an internal inverted repeat region of the herpes
simplex virus genome. In a preferred embodiment the modification of
the herpes simplex virus genome comprises the deletion of one copy
of the internal repeat sequence of the viral gene which region
comprises one copy each of ICP0, IPC4, ORFO, ORFP and
.gamma..sub.134.5 genes. The herpes simplex viruses useful in the
practice of the invention are attenuated with respect to the
wild-type herpes simplex viruses but are more replication competent
than viruses having both copies of the inverted repeat region
modified (to render the region incapable of expressing an actual
gene product of any one of the various genes) or deleted. Viruses
useful in the practice of the present invention may have additional
alterations in their genome that may include insertion of
expressible non-natural protein encoding sequences under the
control of herpes simplex virus promoters that in turn permits the
sequence to be regulated as an .alpha., .beta.or .gamma. class of
herpes simplex virus genes that are well known in the art. [See,
e.g. Fundamental Virology, Second Edition, Field et al.(eds.)
Chapters 33-34, Raven Press Ltd., New York (1991) incorporated
herein by reference.] Viruses lacking internal repeated can be
further attenuated if necessary by the deletion of one or more of
the 47 genes found dispensable for viral replication in culture
[Roizman, Proc. Natl. Acad. Sci. (USA) (1996)]. Among the genes
suitable for deletion to decrease further virulence are the
U.sub.L16, U.sub.L40, U.sub.L41, U.sub.L55, U.sub.L56, .alpha.22,
U.sub.S4, U.sub.S8, and U.sub.s11 genes. Deletion of virtually any
one of the "dispensable" genes will reduce virulence by a factor
ranging from twofold to several logs. In addition, candidate
viruses lacking the internal inverted repeats may be further
altered by the addition of cytokines, as well as enzymes that
activate prodrugs.
[0012] Herpes viruses useful in the practice of the invention may
be prepared using methods well known in the art such as methods
described in U.S. Pat. No. 4,859,587 (incorporated herein by
reference.) and in U.S. Pat. No. 5,288,641 (also incorporated
herein by reference.)
[0013] The examples set out below describe the use of herpes
simplex virus type HSV-1 strain R7020 to reduce tumor size in mice.
The use of mice as models for the treatment of tumorogenic disease
is well known and widely accepted in the art. Example 1 describes
the structure of HSV-1 strain R7020 which virus strain is
illustrative of the kinds of genetically modified viruses that are
useful in the practice of the present invention. Example 2
describes the use of a modified HSV-1 to reduce the tumor volume of
a grafted epidermal carcinoma cell line in mice.
[0014] Example 3 describes the kinetics of viral replication in the
epidermal carcinoma xenografts described in Example 1. The
experiments described in Example 4 establish that epidermal
carcinoma arising from residual tumor cells retain their
susceptibility to infection by HSV-1 R7020.
[0015] The following examples are presented by way of illustration
and are not intended to limit the scope of the invention as
described in the appended claim.
EXAMPLE 1
Structure of HSV Strain R7020
[0016] The structure of R7020 (A.T.C.C. Accession No: VR2123,
deposited Dec. 10, 1985), as described previously [Meignier, et
al., J. Infect. Dis. 158:602614 (1988)] includes an insertion
comprising a HindIII fragment of HSV-2 DNA encompassing gene
sequences encoding several glycoproteins inserted into the joint
region of the parental HSV genome. A detailed analysis of the R7020
structure revealed differences from those reported by Meignier, et
al. as described below.
[0017] First, insertion of the HSV-2 sequence leaves intact the
parental HSV-1 U.sub.L55 gene whereas previous reports showed that
part of the U.sub.L55 gene was deleted. The U.sub.L55 gene, however
has no known function and probably does not affect safety of the
virus. In addition, the U.sub.L55 region is preceded by 300 bp of
"unknown sequence" at the joint region. As previously reported, the
U.sub.L56 region that has been implicated in pathogenesis [Kehm, et
al., Virus Res 40:17-40 (1996)] was not found in the corrected
sequence.
[0018] Second, the U.sub.L56 sequences are duplicated at the joint
region, which probably leads to defective genomes arising in a
predictable and reproducible manner. Defective genomes are known to
arise spontaneously in HSV-1 stocks if passaged at high
multiplicity and defective genomes arise in R7020 more reproducibly
and frequently. However, passage at low multiplicity of infection
as is routine, minimizes the accumulation of defective genomes.
[0019] In another difference, only 5229 bp of the originally
predicted 9629 bp of HSV-2 sequence were found in R7020.
EXAMPLE 2
Volumetric Reduction of Tumor Xenograft
[0020] In a first series of experiments, SQ-206 cells, a
chemotherapy/radiation-resistant epidermal carcinoma cell line that
expresses a nonfunctional p53, or PC-3 cells, a hormone-independent
p53.sup.+ prostate adenocarcinoma cell line, were injected into the
hindlimb of nude mice. SQ-20b is an epidermal cancer cell line
isolated from a patent following radiotherapy as described
elsewhere [Hallahan, et al. Nat. Med. 1:786-791 (1995)]. PC-3 cell
line was obtained from American Type Culture Collection (A.T.T.C.
No. CRL 1435, Manassas, Va.). Large tumor xenografts were employed
to approximate the relative mass of clinically evident, locally
advanced human cancers. In contrast to earlier studies carried out
with a tumor mass of approximately 100 mm.sup.3, the experiments in
this series were performed with tumors having a mean initial volume
of 630 mm.sup.3 corresponding roughly to 3% of mouse weight [Ram,
et al. Nat. Med. 3:1354-1361 (1997)].
[0021] Briefly, SQ-20b tumor cells in amounts of 5.times.10.sup.5
cells per mouse were suspended in 100 .mu.l of sterile phosphate
buffered saline (PBS), injected into the right hind limb of 5 to 6
week old athymic nu/nu mice, and grown to a tumor size of 200 to
1000 mm.sup.3. The mouse hindlimb model has been described
elsewhere in detail [Advani, S. J. et al. Gene Ther. 5, 160-165
(1998)]. As previously reported, its major advantage is that it
allows the measurement of the effects on oncolytic agents without
recourse to invasive procedures. The previously described model was
modified to increase the mean size of the xenograft from 100 to 600
mm.sup.3 at the time treatment by virus injection was initiated, to
increase the ratio of cells to virus and approximate more closely
the size of the tumor in clinically relevant situations.
[0022] Mice were randomized into two treatment groups: (a) controls
administered 10 .mu.l of a buffer solution and (b) mice
administered 2.times.10.sup.6 plaque forming units (pfu) of R7020
in 10 .mu.l of buffer with a Hamilton syringe. The genetically
engineered R7020 virus is derived from HSV-1 (F) which is the
prototype HSV-1 virus [Meignier, et al., supra]. R7020 lacks
U.sub.L24, U.sub.L56, and one set of the inverted repeats encoding
one copy of the genes .alpha.0, .alpha.4, .gamma..sub.134.5, ORFP
and ORFO. The deleted region of the internal inverted repeat of
HSV-1 (F) was replaced by a DNA fragment encoding HSV-2
glycoproteins G, J, D, and I [Meignier, et al., J. Infect. Dis.
158:602-614 (1988)]. Virus was titered on Vero cells (American Type
Culture Collection, Manassas, Va.) as described elsewhere [Chou, et
al., Science 250:1262-1266 (1990)]. The tumor mass was measured
biweekly or until tumor volume reached 2000 mm.sup.3. Tumor volumes
were calculated using the formula (length X width X height)/2 which
is derived from the formula of an elipsoid (.delta.d.sup.3)/6.
Animal studies were performed according to a protocol approved by
the Animal Resource Center at the University of Chicago. Fraction
tumor volume was defined as tumor volume at the specific time point
divided by the initial volume (V/V.sub.0). Animals were sacrificed
when tumor volume exceeded 2000 mm.sup.3. Similar experiments were
carried out with PC-3, with the only exception that
2.times.10.sup.7 cells in 100 .mu.l of PBS were injected per
xenograft.
[0023] Result indicated that SQ-20b xenografts treated with R7020
began to regress 13 days after infection and reached a nadir at 41
days post-infection at which time the mean tumor volume reduction
was down to one fifth of the initial tumor volume. Seventy two
percent (8 of 11) of the tumor xenografts regressed to less than
10% of the initial tumor volume by day 41, and 7 of these 8
retained the reduced size for greater than 80 days.
[0024] R7020 was effective in tumor volume regression of PC-3
prostate adenocarcinoma xenografts as well. Fractional tumor volume
achieved a nadir approximately 20 to 30 days after infection. R7020
was also as effective in causing regression of a hepatoma
adenocarcinoma tumor xenograft.
EXAMPLE 3
Kinetics of Viral Replication in SQ-208 Xenografts
[0025] In order to assess the kinetics of viral replication in the
SQ-208 xenografts, the following procedures were carried out. SQ20
xenografts were injected with 2.times.10.sup.6 pfu of R7020 or with
buffered saline. The mice injected with virus were divided into two
groups. One group was sacrificed at specified times. Tumors were
aseptically harvested at specific time points after infection, snap
frozen in liquid nitrogen, and stored at -70.degree. C. Tumors were
homogenized in 1 ml of 199V and 1 ml of sterile skim milk for 20
seconds on ice using a Polytron tissue homogenizer (Kinematics,
Switzerland). The homogenate was sonicated three times for 15
seconds each and virus was titered on Vero cells.
[0026] The tumor volumes in mice injected with saline and those of
the second group of identically treated mice injected with virus
were tested for tumor volume. As in the experiment described in
Example 2, tumors injected with buffered saline grew exponentially
whereas tumors injected with virus regressed. Viral titers peaked
at seven days after infection with 124.times.10.sup.5 pfu/tumor,
i.e., a 62-fold increase in virus over the amount injected into the
tumors. Significant amounts of virus (greater than 10.sup.5pfu)
were recovered at late as 30 days after infection.
EXAMPLE 4
Tumor cells Resistance to Oncolytic Effects of R7020
[0027] In order to assess the ability of SQ-20b tumor cells to
become resistant to the oncolytic effects of R7020, the following
experiments were performed.
[0028] Tumors were grown as described above. When tumors were
greater than 200 mm.sup.3, they were injected with 2.times.10.sup.6
pfu of R7020 in 10 .mu.l of buffer on day 0. Tumors were measured
biweekly. As tumors regrew to their starting tumor volume (volume
at day 0), they were randomized and re-injected with either 10
.mu.l of buffer, 2.times.10.sup.6 pfu of R7020, or 2.times.10.sup.6
pfu of HSV-1 (F) in the same volume of buffer. Animals with tumor
volume greater than 200 mm.sup.3 were sacrificed following
institutional guidelines.
[0029] Results indicated that all three buffer re-injected tumors
continued to increase the size. Fractional tumor volume decreased
following the second viral injection of either R7020 or HSV-1 (F).
Tumors continued to show sensitivity for viral oncolysis through
two cycles of R7020 injection and did not recur for at least 120
days from the initiation of the experiment. Mice reinjected with
HSV-1 (F) died four to six weeks following wild-type virus
injection whereas mice reinjected with R7020 thrived. Thus, SQ-20b
tumors arising from residual cells in tumors previously treated
with R7020 retain susceptibility to infection.
EXAMPLE 5
R7020 Treatment in Combination with Irradiation
[0030] Earlier studies on glioma xenografts have shown that the
combination of irradiation and administration of an attenuated HSV
result in enhanced tumor cell destruction as well as enhanced viral
replication [Advani, et al. Gene Ther. 5:160-165 (1998)]. To
determine whether irradiation of the radiation-resistant SQ-206
cell lines enhanced the oncolytic effect of R7020, xenografts were
infected as described above and subjected to a fractionated
irradiation protocol as described below.
[0031] Irradiation of xenografts was carried out as described
elsewhere [Advani, et al. Gene Ther. 5:160-165 (1998)]. Briefly,
tumor-bearing hindlimbs were exposed to ionizing radiation using a
GE 250 kv maxitron generator (191 cGy/min, 150 kVp). Irradiation
was administered starting six hours after infection with R7020 in
400 cGy fractions on Monday, Tuesday, Thursday, and Friday for two
weeks up to a maximum dosage of 3200 cGy. Fractionated irradiation
was administered in doses routinely employed in clinically relevant
protocols.
[0032] Results indicate that irradiation alone resulted in a modest
delay in xenograft growth compared to control tumors confirming
radiation resistance of the SQ-206 cell line. While tumor volume
reduction did not occur until 13 days after infection of xenografts
with R7020 as described in Example 2, combining irradiation with
R7020 resulted in tumor volume regression one week earlier than
tumors treated with R7020 alone. In addition, the nadir in tumor
volume occurred significantly earlier in xenografts receiving both
irradiation and R7020 as compared to xenografts receiving R7020
alone (day 20 versus day 30).
[0033] These results demonstrate for the first time dramatic
antitumor efficacy of R7020 in the treatment of experimental human
tumors frequently resistant to common cancer treatments and suggest
that, while R7020 is an effective antitumor agent by itself,
combining irradiation with R7020 also provides more rapid and
complete tumor cell destruction. The combination of irradiation and
attenuated HSV as an anticancer therapy may prove to be especially
beneficial in clinical situations where the tumor burden may be too
large for single agent therapy.
[0034] Numerous modifications and variations in the invention as
set forth in the above illustrative examples are expected to occur
to those skilled in the art. Consequently only such limitations as
appear in the appended claims should be placed on the invention.
References cited herein are incorporated by reference in their
entireties.
* * * * *