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Cancer Patent Abstract
Methods and compositions for the treatment of anti-estrogen resistant
breast cancer using retinoid compounds which are modulators of Retinoid
X Receptors.
Cancer Patent Claims
We claim:
1. A method for treating a host having anti-estrogen resistant
breast cancer, comprising administering to said host tamoxifen and
a selective Retinoid X Receptor (RXR) modulator, wherein the tamoxifen
and the selective RXR modulator are administered in amounts that
together are pharmaceutically effective, and thereby treating a
host having anti-estrogen resistant breast cancer.
2. The method of claim 1, wherein said selective RXR modulator
is selected from the group consisting of LGD1069, LGD100268 and
LGD100324.
3. The method of claim 1, wherein said selective RXR modulator
selectively activates one or more RXRs in preference to each of
RAR isoforms .alpha., .beta. and .gamma..
4. The method of claim 1, wherein the tamoxifen and the selective
RXR modulator are administered at the same time.
5. The method of claim 1, wherein the host having anti-estrogen
resistant breast cancer has previously been treated with an anti-estrogen
compound.
6. The method of claim 1, wherein the host having anti-estrogen
resistant breast cancer has previously been treated with tamoxifen.
7. The method of claim 1, wherein the anti-estrogen resistant breast
cancer is capable of growing in the presence of at least one anti-estrogen
compound.
8. A method for treating a host having tamoxifen resistant breast
cancer, comprising administering to said host tamoxifen and a selective
RXR modulator, wherein the tamoxifen and the selective RXR modulator
are administered in amounts that together are pharmaceutically effective.
9. The method of claim 8, wherein said selective RXR modulator
is selected from the group consisting of LGD1069, LGD100268, and
LGD100324.
10. The method of claim 8, wherein said selective RXR modulator
selectively activates one or more RXRs in preference to each of
RAR isoforms .alpha., .beta., and .gamma..
11. The method of claim 8, wherein the tamoxifen and the selective
RXR modulator are administered at the same time.
12. The method of claim 8, wherein the host having tamoxifen resistant
breast cancer has previously been treated with an anti-estrogen
compound.
13. The method of claim 8, wherein the host having tamoxifen resistant
breast cancer has previously been treated with tamoxifen.
14. The method of claim 8, wherein the tamoxifen resistant breast
cancer is capable of growing in the presence of at least one anti-estrogen
compound.
15. A method for treating a host having anti-estrogen resistant
breast cancer, comprising administering to said host a pharmaceutically
effective amount of a composition comprising tamoxifen and a selective
RXR modulator.
16. A method for treating a host having tamoxifen resistant breast
cancer, comprising administering to said host a pharmaceutically
effective amount of a composition comprising tamoxifen and a selective
RXR modulator.
17. A method for improving the efficacy of treating a host having
anti-estrogen resistant breast cancer with tamoxifen, comprising
administering to said host a pharmaceutically effective amount of
a selective RXR modulator.
18. A method for improving the efficacy of treating a host having
tamoxifen resistant breast cancer with tamoxifen, comprising administering
to said host a pharmaceutically effective amount of a selective
RXR modulator.
Cancer Patent Description
FIELD OF THE INVENTION
The present invention relates generally to methods and pharmaceutical
compositions for treating breast cancer. More particularly, the
invention relates to methods and pharmaceutical compositions for
treating anti-estrogen resistant breast cancers using retinoid compounds
which are RXR modulators.
BACKGROUND OF THE INVENTION
The vitamin A metabolite, retinoic acid, has long been recognized
to induce a broad spectrum of biological effects. For example, retinoic
acid-containing products, such as Retin-A.RTM. and Accutane.RTM.,
have found utility as therapeutic agents for the treatment of various
pathological conditions. In addition, a variety of structural analogues
of retinoic acid (i.e., retinoids), have been synthesized that also
have been found to be bioactive. Many of these synthetic retinoids
have been found to mimic many of the pharmacological actions of
retinoic acid, and thus have therapeutic potential for the treatment
of numerous disease states.
Medical professionals have become very interested in the therapeutic
applications of retinoids. Among their uses approved by the FDA
is the treatment of severe forms of acne and psoriasis. A large
body of evidence also exists that these compounds can be used to
arrest and, to an extent, reverse the effects of skin damage arising
from prolonged exposure to the sun. Other evidence exists that these
compounds have clear effects on cellular proliferation, differentiation
and programmed cell death (apoptosis), and thus, may be useful in
the treatment and prevention of a variety of cancerous and pre-cancerous
conditions, such as acute promyleocytic leukemia (APL), epithelial
cancers, squamous cell carcinomas, including cervical and skin cancers
and renal cell carcinoma. Furthermore, retinoids may have beneficial
activity in treating and preventing diseases of the eye, cardiovascular
disease and other skin disorders. Major insight into the molecular
mechanism of retinoic acid signal transduction was gained in 1988,
when a member of the steroid/thyroid hormone intracellular receptor
superfamily was shown to transduce a retinoic acid signal. Giguere
et al., Nature, 330:624-29 (1987); Petkovich et al., Nature, 330:
444-50 (1987); for review, see Evans, Science, 240:889-95 (1988).
It is now known that retinoids modulate the activity of two distinct
intracellular receptor subfamilies; the Retinoic Acid Receptors
(RARs) and the Retinoid X Receptors (RXRs), including their subtypes,
RAR.alpha., .beta., .gamma. and RXR.alpha., .beta., .gamma.. Different
retinoid compounds exhibit different activities with the retinoid
reactor subtypes. For example, all-trans-retinoic acid (ATRA) is
an endogenous low-molecular-weight ligand which specifically modulates
the transcriptional activity of the RARs, while 9-cis retinoic acid
(9-cis) is the endogenous ligand for the RXRs, and activates both
the RARs and RXRs. Heyman et al., Cell, 68:397-406 (1992); Levin
et al., Nature, 355:359-61 (1992).
Although both the RARs and RXRs respond to ATRA in vivo due to
the in vivo conversion of some of the ATRA to 9-cis, the receptors
differ in several important aspects. First, the RARs and RXRs are
significantly divergent in primary structure (e.g., the ligand binding
domains of RAR.alpha. and RXR.alpha. have only approximately 30%
amino acid identity). These structural differences are reflected
in the different relative degrees of responsiveness of RARs and
RXRs to various vitamin A metabolites and synthetic retinoids. In
addition, distinctly different patterns of tissue distribution are
seen for RARs and RXRs. For example, RXR.alpha. mRNA is expressed
at high levels in the visceral tissues, e.g., liver, kidney, lung,
muscle and intestine, while RAR.alpha. mRNA is not. Finally, the
RARs and RXRs have different target gene specificity. In this regard,
RARs and RXRs regulate transcription by binding to response elements
in target genes that generally consist of two direct repeat half-sites
of the consensus sequence AGGTCA. RAR:RXR heterodimers activate
transcription by binding to direct repeats spaced by five base pairs
(a DR5) or by two base pairs (a DR2). However, RXR:RXR homodimers
bind to a direct repeat with a spacing of one nucleotide (a DR1).
See Mangelsdorf et al., "The Retinoid Receptors" in The
Retinoids: Biology, Chemistry and Medicine, M. B. Sporn, A. B. Roberts
and D. S. Goodman, Eds., Raven Press, New York, N.Y., 2.sup.nd ed.
(1994). For example, response elements have been identified in the
cellular retinal binding protein type II (CRBPII), which consists
of a DR1, and Apolipoprotein AI genes which confer responsiveness
to RXR, but not RAR. Further, RAR has also been recently shown to
repress RXR-mediated activation through the CRBPII RXR response
element (Mangelsdorf et al., Cell, 66:555-61 (1991)). Also, RAR
specific target genes have recently been identified, including target
genes specific for RAR.beta. (e.g., .beta.RE), which consists of
a DR5. These data indicate that the two retinoic acid responsive
pathways are not simply redundant, but instead manifest a complex
interplay and control distinct biological processes. For example,
it has been demonstrated in leukemic cells, activation of RAR pathways
regulates cell proliferation and differentiation, whereas activation
of RXR pathways leads to the induction of apoptosis.
Retinoid compounds which are RAR and RXR modulators, including
both RAR specific and RXR specific modulators, have been previously
described. See, e.g., U.S. Pat. Nos. 4,193,931, 4,801,733, 4,831,052,
4,833,240, 4,874,747, 4,877,805, 4,879,284, 4,888,342, 4,889,847,
4,898,864, 4,925,979, 5,004,730, 5,124,473, 5,198,567, 5,391,569,
5,455,265, 5,466,861, 5,552,271, 5,801,253, 5,824,484, 5,837,725
and Re 33,533, and U.S. application Ser. Nos. 08/029,801, 872,707,
944,783, 08/003,223, 08/027,747 and 08/052,050; 60/004,897, 60/007,884,
60/018,318, 60/021,839. See also, WO93/03944, WO93/10094, WO94/20093,
WO95/0436, WO97/12853, EP 0718285, Kagechika et al., J. Med. Chem.,
32:834 (1989); Kagechika et al., J. Med. Chem., 32:1098 (1989);
Kagechika et al., J. Med. Chem., 32:2292 (1989); Boehm et al., J.
Med. Chem., 37:2930 (1994); Boehm et al., J. Med. Chem., 38:3146
(1995); Allegretto et al., J. of Biol. Chem., 270:23906 (1995);
Bissonnette et al., Mol. & Cellular Bio., 15:5576 (1995); Beard
et al., J. Med. Chem., 38:2820 (1995); Dawson et al., J. Med. Chem.,
32:1504 (1989).
Breast cancer, like other malignant disease states, is characterized
by a loss of cellular growth control followed by invasion of malignant
cells into surrounding tissue stroma ultimately leading to metastatic
spread of the disease to distant sites within the body. In 1987
over 180,000 new cases of breast cancer were diagnosed in the United
States and there were 44,000 deaths due to breast cancer. Breast
cancer is currently the second leading cause of cancer deaths in
women and the leading cause of cancer deaths in women between the
ages of 40 and 55. Population analysis on the incidence of breast
cancer demonstrates that one-in-eight women in the United States
will develop breast cancer at some point during their life. The
primary therapy for breast cancer is surgery, either a partial or
modified radical mastectomy with or without radiotherapy. This is
typically followed by some form of adjuvant therapy.
The type of adjuvant therapy utilized is often dependant upon the
estrogen receptor status of the tumor. Analysis of the hormone status
of breast cancers demonstrates that 75% of all breast tumors are
estrogen receptor positive and the majority of estrogen receptor
positive tumors are found in postmenopausal women.
The anti-estrogen, tamoxifen, is presently the most commonly used
drug worldwide for the treatment of breast cancer and approximately
66% of estrogen receptor positive breast cancers will respond to
tamoxifen treatment. Tamoxifen is currently the first-line treatment
for postmenopausal, estrogen receptor positive women with advanced
breast cancer. The mechanism of action of tamoxifen in estrogen
receptor positive breast cancer is thought to be due to competitive
antagonism at the estrogen receptor of the estrogen driven growth
of the tumor. Hence tamoxifen is a cytostatic, not a cytotoxic,
agent.
It has previously been shown that as a chemopreventive, the RXR-selective
retinoid LGD1069 (Targretin.RTM.) is as effective as the anti-estrogen
tamoxifen (TAM) at inhibiting mammary carcinoma development in the
NMU-treated rat. Gottardis et al., Can. Res., 56:5566-70 (1996).
Clinical evaluation of the efficacy of tamoxifen shows that a significant
proportion of patients who initially respond to tamoxifen therapy
will acquire resistance, and some on adjuvant tamoxifen therapy
will suffer relapses. All advanced breast cancer patients eventually
tend to develop tamoxifen resistance. The actual mechanisms underlying
the development of tamoxifen resistance are most likely many fold
and may involve decreased intra-tumor drug concentration, development
of tumor cell clones that are now stimulated to grow in the presence
of tamoxifen, and the development of estrogen receptor mutants among
others.
Once a tumor develops tamoxifen resistance it will begin to proliferate
even in the continued presence of tamoxifen. For breast cancer patients
who develop tamoxifen resistance, secondary therapies include second-line
hormonal agents such as progestins, aromatase inhibitors and LHRH
agonists or cytotoxic chemotherapeutic agents. These commonly utilized
second-line agents are at best only effective in approximately 25%
of advanced cases. Hence, acquired tamoxifen resistance is the major
cause of treatment failure in all stages of breast cancer. Accordingly,
a need exists for improved methods and pharmaceutical compositions
for treating anti-estrogen or tamoxifen resistant breast cancers.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that RXR modulators
can be used to treat breast cancer which is resistant to conventional
treatment with anti-estrogen compounds such as tamoxifen. The present
invention provides methods for treating such anti-estrogen resistant
breast cancers through the administration of retinoid compounds
which are modulators of the Retinoid X Receptors (RXRs), including
compounds which are selective modulators of RXRs such as LGD1069
(Targetin.RTM.), LGD100268, and LGD100324. The present invention
also provides pharmaceutical compositions incorporating such RXR
modulators that are effective for treating anti-estrogen resistant
breast cancer.
These and various other advantages and features of novelty which
characterize the invention are pointed out with particularity in
the claims annexed hereto and forming a part hereof. However, for
a better understanding of the invention, its advantages, and objects
obtained by its use, reference should be had to the accompanying
figures and descriptive matter, in which there is illustrated and
described preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE FIGURES
The present invention may be better understood and its advantages
appreciated by those skilled in the art by referring to the accompanying
Figures wherein:
FIG. 1 presents the percentage response of tamoxifen-resistant
primary tumors that were continuously treated with tamoxifen and
of these tamoxifen-resistant tumors treated with LGD1069/tamoxifen,
scored by category.
FIG. 2 presents tumor progression and tumor response of the tamoxifen-resistant
primary tumors treated with tamoxifen and of these tumors treated
with the combination tamoxifen/LGD1069.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to methods and pharmaceutical compositions
for treating a host having breast cancer which is resistant to conventional
treatment with anti-estrogen compounds, such as tamoxifen, by administering
to the host a composition containing a pharmaceutically effective
amount of an RXR modulator. The host may be a human patient or an
animal model of human anti-estrogen resistant breast cancer. The
methods and compositions of this invention are adapted to cure,
improve or prevent one or more symptoms of anti-estrogen resistant
breast cancer in the host. A preferred composition is highly potent
and selective with low toxicity.
The term "RXR modulator" refers to a compound or composition
which, when combined with a Retinoid X Receptor (RXR), modulates
the transcriptional regulation activity of the RXR. RXR modulators
include RXR agonists and partial agonists as well as those, which
increase the transcriptional regulation activity of RXR homodimers
and heterodimers. RXR modulators also include compounds and compositions
that preferentially activate RXRs over RARs. Compounds that preferentially
activate RXRs over RARs may be referred to as "selective RXR
modulators." Compounds and compositions that activate both
RXRs and RARs are referred to as "pan agonists", and compounds
and compositions that activate RXRs in certain cellular contexts,
such as in breast tissue, but not others are referred to as "RXR
partial agonists".
Representative RXR modulator compounds which may be used to treat
anti-estrogen resistant breast cancer according to the present invention
are described in the following U.S. patents and patent applications
which are incorporated by reference herein: U.S. Pat. Nos. 5,399,586,
5,466,861, and 5,801,253; U.S. patent application Ser. Nos. 07/809,980,
08/003,223, 08/027,747, 08/045,807, 08/052,050, 08/052,051, 08/179,750,
08/366,613, 08/480,127, 08/481,877, 08/872,707, and 08/944,783.
See, also, WO93/11755, WO 93/21146, WO 94/15902, WO/94/23068, WO
95/04036, and WO 96/20913. Other RXR modulator compounds are also
known to those skilled in the art, such as those described for example,
in the following articles: Boehm et al. J. Med. Chem. 38:3146 (1994),
Boehm et al. J. Med. Chem. 37:2930 (1994), Antras et al., J. Biol.
Chem. 266:1157-61 (1991), Salazar-Olivo et al., Biochem. Biophys.
Res. Commun. 204:257-263 (1994), and Safanova, Mol. Cell. Endocrin.
104:201 (1994). Such compounds may be prepared according to methods
known in the art as described in the aforementioned references,
as well as in M. I. Dawson and W. H. Okamura, Chemistry and Biology
of Synthetic Retinoids, Chapters 3, 8, 14 and 16, CRC Press, Inc.,
Florida (1990); M. I. Dawson and P. D. Hobbs, The Retinoids, Biology,
Chemistry and Medicine, M. B. Sporn et al., Eds. (2nd ed.), Raven
Press, New York, N.Y., pp. 5-178 (1994); Liu et al., Tetrahedron,
40:1931 (1984); Cancer Res., 43:5268 (1983); Eur. J. Med. Chem.
15:9 (1980); Allegretto et al., J. of Biol. Chem., 270:23906 (1995);
Bissonette et al., Mol. Cell. Bio., 15:5576 (1995); Beard et al.,
J. Med. Chem., 38:2820 (1995), Koch et al., J. Med. Chem., 39:3229
(1996); and U.S. Pat. Nos. 4,326,055 and 4,578,498.
In a preferred embodiment, RXR modulators which preferentially
activate RXRs over RARs, (i.e., selective RXR modulators) are used
to treat anti-estrogen resistant breast cancer according to the
present invention. For example, RXR selective modulators useful
in the present invention include, but are not limited to, the retinoid
compounds LGD1069 (Targretin.RTM.), LGD100268, and LGD100324, and
the congeners, analogs, derivatives and pharmaceutically acceptable
salts thereof. The structures of LGD1069, LGD100268, and LGD100324
are shown below, and the synthesis of these compounds is described
in U.S. patent application Ser. No. 08/141,496. The synthesis of
compounds LGD1069, LGD100268, and LGD100324 is also described in,
e.g., WO 94/15902 and Boehm et al., J. Med. Chem. 38(16):3146 (1994).
##STR00001##
The ability of a compound or composition to modulate the transcriptional
ability of intracellular receptors including RXRs may be measured
by assays known to those of skill in the art, including but not
limited to the co-transfection (cis-trans) assays. Such assays are
described in, e.g., U.S. Pat. Nos. 4,981,784, 5,071,773, 5,298,429,
5,506,102 and U.S. application Ser. Nos. 128,331, 276,536, 426,894,
586,187, 801,562, 865,878, 07/464,837, 07/882,771, 07/939,246, 08/045,807,
08/177,740, and 08/179,750 which are incorporated by reference herein.
See also, WO89/05355, WO91/06677, WO92/05447, WO93/11235, WO93/23431,
WO94/23068, WO95/18380 and CA 2,034,220. For further reference,
also see, Heyman et al., Cell, 68:397-406 (1992). Such assays may
be used to evaluate retinoid compounds to determine activity with
the retinoid receptor subtypes RAR.alpha., RAR.beta., RAR.gamma.,
RXR.alpha., RXR.beta., and RXR.gamma..
Briefly, the co-transfection assay involves the introduction of
two plasmids by transient transfection into a retinoid receptor-negative
mammalian cell background. The first plasmid contains a retinoid
receptor cDNA and directs constitutive expression of the encoded
receptor. The second plasmid contains a cDNA that encodes for a
readily quantifiable protein, e.g., firefly luciferase or chloramphenicol
acetyl transferase (CAT), under control of a promoter containing
a retinoid acid response element, which confers retinoid dependence
on the transcription of the reporter. In this co-transfection assay,
all retinoid receptors respond to all-trans-retinoid acid in a similar
fashion. This assay can be used to accurately measure efficacy and
potency of retinoic acid and synthetic retinoids as ligands that
interact with the individual retinoid receptor subtypes.
For example, the synthetic retinoid compound LGD1069 was evaluated
for its ability to regulate gene expression mediated by retinoid
receptors. As shown in Table 1, this compound is capable of activating
members of the RXR subfamily, i.e., RAR.alpha., RAR.beta., and RAR.gamma.,
but clearly has no significant activity for members of the RAR subfamily,
i.e., RAR.alpha., RAR.beta., and RAR.gamma.. Potency and efficacy
were calculated for the LGD1069 compound, as summarized in Table
1. Assays of 9-cis-retinoic acid were run for reference, and the
results shown in Table 1 demonstrate that these retinoic acid isomers
activate members of both the RAR and RXR subfamilies.
TABLE-US-00001 TABLE 1 LDG1069 Potency (nM) Efficacy RXR.alpha.
40 83% RXR.beta. 21 102% RXR.gamma. 34 80% RAR.alpha. >10,000
6% RAR.beta. >10,000 17% RAR.gamma. >10,000 19% 9-cis-retinoic
acid RXR.alpha. 150 140% RXR.beta. 100 140% RXR.gamma. 110 140%
RAR.alpha. 160 100% RAR.beta. 5 82% RAR.gamma. 47 120%
As shown by the data in Table 1, LGD1069 readily and at low concentrations
activates RXRs. Further, LGD1069 is more potent an activator of
RXRs than RARs, and preferentially activates RXRs in comparison
to RARs, in that much higher concentrations of the compound are
required to activate the RARs. In contrast, 9-cis-retionic acid
does not preferentially activate the RXRs, as also shown in Table
1. Rather, 9-cis-retinoic acid activates the RAR.beta. and RAR.gamma.
isoforms at lower concentrations and more readily than the RXR.beta.
and RXR.gamma. isoforms, and has substantially the same, within
the accuracy of the measurement, activity for the RAR.alpha. isoform
in comparison to the RXR.alpha. isoform.
TABLE-US-00002 TABLE 2 Potency (nM) Efficacy LDG100268 RXR.alpha.
4 63% RXR.beta. 4 93% RXR.gamma. 3 49% RAR.alpha. >10,000 <2%
RAR.beta. >10,000 <2% RAR.gamma. >10,000 <2% LDG100324
RXR.alpha. 15 66% RXR.beta. 8 51% RXR.gamma. 12 62% RAR.alpha. >10,000
<3% RAR.beta. >10,000 <3% RAR.gamma. >10,000 <3%
As shown in Table 2 above, LGD100268 and LGD100324 (like LGD1069)
readily and preferentially activate RXRs and are more potent an
activator of RXRs than of RARs.
In a preferred embodiment, the retinoid compounds and compositions
of this invention preferentially activate RXRs in comparison to
RARs, are preferably at least three times and more preferably five
times more potent as activators of RXRs than RARs, and most preferably
ten times more potent as activators of RXRs than RARs, and are more
potent as an activator of an RXR than all of RAR isoforms .alpha.,
.beta., and .gamma..
Anti-estrogen resistant breast cancer has been demonstrated to
be effectively treated using RXR selective modulators such as, e.g.
LGD1069 (Targretin.RTM.), as shown in the following examples.
EXAMPLE 1
Mammary tumorigenesis was induced by administration of 50 mg/kg
of N-nitroso-N-methylurea (NMU) (Sigma, St. Louis, Mo.) to 50 day
old virgin female Sprague-Dawley rats (Harlan-SD, Indianapolis,
Ind.). NMU was formulated as an aqueous solution of 10 mg/ml by
wetting NMU powder with 3% acetic acid and dissolving it in sterile
saline. Fresh solutions of NMU were injected within 30 minutes of
preparation. The animals were injected in the tail vein with 5 mg
NMU/100 g body weight. Rats were housed in a USDA registered facility
in accordance with NIH guidelines for the care and use of laboratory
animals. All animals received food (Harlan Teklad LM485-7012, Indianapolis,
Ind.) and acidified water ad libitum. Beginning five weeks after
tumor induction, animals were examined for tumors twice a week.
Tumors were measured with electronic calipers (Mitushoyo, Japan)
and cross sectional areas were determined by multiplying the longest
length of the tumor by the greatest perpendicular width of the tumor.
When tumors developed (at approximately 6 weeks after initiation)
and reached an area of 75 mm.sup.2, animals were administered tamoxifen
at 800 .mu.g/kg subcutaneously daily for six weeks. After the six
week tamoxifen treatment period, animals bearing mammary tumors
that did not respond to tamoxifen therapy (tamoxifen resistant)
were randomized into two groups. As a control, the first group of
animals remained on tamoxifen, while the second group animals remained
on tamoxifen and in addition were administered the RXR-agonist LGD1069
(Targretin.RTM.) at 100 mg/kg orally daily. Tumor response was monitored
for an additional six weeks of therapy, and the following categories
were used to score the tumor response: progressive disease--the
tumor grew over the course of treatment, and its final area was
at least 40% greater than its initial area; stable disease--the
tumor did not fluctuate more than 40% from its initial area throughout
the course of treatment; partial regression--the tumor regressed
more than 40% from its initial area or showed at least two consecutive
decreases in area of more than 40% each; and complete regression--the
tumor was no longer measurable or no longer palpable.
FIG. 1 and FIG. 2 show the tumor response of the two groups. These
figures show that the addition of LGD1069 to the experimental regimen
significantly reduced the incidence of progressive disease from
44% to only 3%, reduced the incidence of stable,disease, and increased
the incidence of partial and complete regression. As shown in FIG.
1, LGD1069 caused a complete regression of 56% of tumors compared
to 16.7% of tumors remaining on tamoxifen alone (p<0.05). As
shown in FIGS. 1 and 2, LGD1069 caused a combined response of partial
or complete regression in more than 90% of the tumors compared to
a 44% response rate in tumors that remained on tamoxifen alone.
EXAMPLE 2
Mammary tumors were induced in Sprague-Dawley rats as in the previous
example with NMU and then, beginning one week after carcinogen treatment,
animals were treated with low-dose tamoxifen (50 .mu.g/kg, SC) to
prevent formation of tumors. Tumors that grew in the presence of
the low-dose tamoxifen were evaluated for tamoxifen resistance by
increasing the dose of tamoxifen (800 .mu.g/kg, SC), or by adding
in LGD1069 (100 mg/kg, PO) to the therapy. The addition of LGD1069
to the therapy significantly reduced the amount of progressive disease
in this model, as compared to treatment with tamoxifen.
EXAMPLE 3
Mammary tumors were induced in Sprague-Dawley rats as in Example
1. When tumors developed and reached an area of 75 mm.sup.2, animals
were randomly assigned to one of three treatment groups and treated
daily for six weeks with vehicle, LGD1069 (100 mg/kg), or tamoxifen
(800 .mu.g/kg).
After six weeks, in vehicle-treated control animals, 87% of the
tumors continued to grow and progress, 8.7% were static, 4.3% partially
regressed, and 0% completely regressed. In contrast, in LGD1069-treated
animals, 11.1% of tumors continued to progress, 16.7% partially
regressed, and 72.2% completely regressed. In tamoxifen-treated
animals, 28.6% of tumors continued to progress, 4.8% remained static,
33.3% partially regressed, and 33.3% completely regressed. As shown,
treatment with LGD1069 demonstrated significant antitumor efficacy
on established mammary tumors and demonstrated greater efficacy
than treatment with tamoxifen.
EXAMPLE 4
Mammary tumors were induced in Sprague-Dawley rats as in Example
1. Animals treated with LGD1069 at the submaximally efficacious
dose of 10 mg/kg showed that 10.5% of primary mammary tumors regressed.
Animals treated with tamoxifen at the submaximally efficacious dose
of 150 mg/kg showed that 5.6% of primary mammary tumors regressed.
However, when the two compounds where coadministered, a significantly
greater effect was achieved, with 26.3% of the tumors completely
regressing.
As shown by the above examples, the administration of RXR modulators
such as LGD1069 has now been shown to demonstrate anti-tumor efficacy
on mammary tumors that are tamoxifen resistant and that fail tamoxifen
therapy. Accordingly, the use of RXR modulators such as, e.g., LGD1069,
has been demonstrated to be useful as both an adjuvant treatment
for breast cancer as well as a treatment for patients who have failed
tamoxifen therapy.
Hormonal receptor status is a factor in determining whether a tumor
is anti-estrogen resistant. Tamoxifen, an anti-estrogen, is primarily
effective in tumors that have estrogen receptor (ER) positive status.
Tumors that have estrogen receptor negative (ER) status are generally
unresponsive to tamoxifen. The hormonal status of a breast cancer
may be determined by staining the tumor cells for ER receptors,
or by other conventional techniques for detecting the presence of
ER receptors. During disease progression, the tumor cell DNA becomes
increasingly mutated. Highly mutated DNA often exhibits an advanced
rate of tumor cell growth. Abnormal tumor cell DNA and a fast rate
of tumor growth are often present in anti-estrogen resistant cells
indicating that tamoxifen therapy may be ineffective.
Since RXR selective modulators have been shown as effective in
adjuvant treatment of tamoxifen resistant breast tumors, treatment
with RXR selective modulators is therefore useful for treatment
of ER negative breast tumors. This includes those patients who have
either failed tamoxifen therapy or have ER negative status tumors
for which tamoxifen therapy would not be considered.
According to the invention, a host having anti-estrogen resistant
breast cancer is treated with a pharmaceutically effective amount
of an RXR modulator. By pharmaceutically effective amount is meant
an amount of a pharmaceutical compound or composition having a therapeutically
relevant effect on anti-estrogen resistant breast cancer. A therapeutically
relevant effect relieves to some extent one or more symptoms of
anti-estrogen resistant breast cancer in a patient or returns to
normal either partially or completely one or more physiological
or biochemical parameters associated with or causative of anti-estrogen
resistant breast cancer.
In another aspect, this invention features a pharmaceutical composition
specially formulated for treating anti-estrogen resistant breast
cancer containing a pharmaceutically effective amount of a RXR modulator
and a pharmaceutically acceptable carrier adapted for a host, particularly
a human, having anti-estrogen resistant breast cancer. A composition
containing a pharmaceutically effective amount of an RXR modulator
may be administered orally or systemically to a host. In a preferred
embodiment, it is administered orally.
In a preferred embodiment, the composition is held within a container
that includes a label stating to the effect that the composition
is approved by the FDA in the United States (or an equivalent regulatory
agency in a foreign country) for treating anti-estrogen resistant
breast cancer. Such a container provides a therapeutically effective
amount of the active ingredient to be administered to a host.
In pharmaceutical compositions of the present invention, the RXR
modulator is mixed with suitable carriers or excipient(s). In treating
a patient exhibiting anti-estrogen resistant breast cancer, a therapeutically
effective amount of an agent or agents such as these is administered.
A therapeutically effective dose refers to that amount of the compound
that results in amelioration of symptoms or a prolongation of survival
in a patient.
The compounds also can be prepared as pharmaceutically acceptable
salts. Examples of pharmaceutically acceptable salts include acid
addition salts such as those containing hydrochloride, sulfate,
phosphate, sulfamate, acetate, citrate, lactate, tartrate, methanesulfonate,
ethanesulfonate, benzenesulfonate, p-toluenesulfonate, cyclohexylsulfamate
and quinate. See, e.g., U.S. Pat. Nos. 5,409,930, 5,656,643, and
5,710,158. See also, WO 92/20642 and WO 95/15758). Such salts can
be derived using acids such as hydrochloric acid, sulfuric acid,
phosphoric acid, sulfamic acid, acetic acid, citric acid, lactic
acid, tartaric acid, malonic acid, methanesulfonic acid, ethanesulfonic
acid, benzenesulfonic acid, p-toluenesulfonic acid, cyclohexylsulfamic
acid, and quinic acid.
Pharmaceutically acceptable salts can be prepared by standard techniques.
For example, the free base form of the compound is first dissolved
in a suitable solvent such as an aqueous or aqueous-alcohol solution,
containing the appropriate acid. Evaporating the solution then isolates
the salt. In another example, the salt is prepared by a reaction
of the free base and acid in an organic solvent.
Carriers or excipients can be used to facilitate administration
of the compound, for example, to increase the solubility of the
compound. Examples of carriers and excipients include calcium carbonate,
calcium phosphate, various sugars or types of starch, cellulose
derivatives, gelatin, vegetable oils, polyethylene glycols and physiologically
compatible solvents.
Toxicity and therapeutic efficacy of such compounds can be determined
by standard pharmaceutical procedures in cell cultures or experimental
animals, for example, for determining the LD.sup.50 (the dose lethal
to 50% of the population) and the ED.sup.50 (the dose therapeutically
effective in 50% of the population). The dose ratio between toxic
and therapeutic effects, the therapeutic index, can be expressed
as the ratio LD.sup.50/ED.sup.50. Compounds that exhibit large therapeutic
indices are preferred. The data obtained from these cell culture
assays and animal studies can be used in formulating a range of
dosages for use in humans. The dosage of such compounds lies preferably
within a range of circulating concentrations that include the ED.sup.50
with little or no toxicity. The dosage may vary within this range
depending upon the dosage form employed and the route of administration
utilized. Levels in plasma may be measured, for example, by HPLC.
The individual physician in view of the patient's condition can
choose a route of administration, dosage, and exact formulation.
(e.g., Fingl et al., The Pharmacological Basis of Therapeutics Ch.
1, (1975)). It should be noted that the attending physician would
know how to and when to terminate, interrupt, or adjust administration
due to toxicity, or to organ dysfunction. Conversely, the attending
physician would also know to adjust treatment to higher levels if
the clinical response were not adequate (precluding toxicity). The
magnitude of an administrated dose in the management of the disorder
of interest will vary with the severity of the condition to be treated
and to the route of administration. The severity of the condition
may, for example, be evaluated, in part, by standard prognostic
evaluation methods. Further, the dose and perhaps dose frequency,
will also vary according to the age, body weight, and response of
the individual patient. A program comparable to that discussed above
may be used in veterinary medicine.
Depending on the specific conditions being treated, such agents
may be formulated and administered systemically or locally. Techniques
for formulation and administration may be found in Remington's Pharmaceutical
Sciences, 18th ed., Mack Publishing Co., Easton, Pa. (1990). Suitable
routes may include oral, rectal, transdermal, vaginal, transmucosal,
or intestinal administration; parenteral delivery, including intramuscular,
subcutaneous, intramedullary injections, as well as intrathecal,
direct intraventricular, intravenous, intraperitoneal, intranasal,
or intraocular injections.
For injection, the agents of the invention may be formulated in
aqueous solutions, preferably in physiologically compatible buffers
such as Hanks's solution, Ringer's solution, or physiological saline
buffer. For such transmucosal administration, penetrants appropriate
to the barrier to be permeated are used in the formulation. Such
penetrants are generally known in the art.
Use of pharmaceutically acceptable carriers to formulate the compounds
herein disclosed for the practice of the invention into dosages
suitable for systemic administration is within the scope of the
invention. With proper choice of carrier and suitable manufacturing
practice, the compositions of the present invention, in particular,
those formulated as solutions, may be administered parenterally,
such as by intravenous injection. The compounds can be formulated
readily using pharmaceutically acceptable carriers well known in
the art into dosages suitable for oral administration. Such carriers
enable the compounds of the invention to be formulated as tablets,
pills, capsules, liquids, gels, syrups, slurries, suspensions and
the like, for oral ingestion by a patient to be treated.
Agents intended to be administered intracellularly may be administered
using techniques well known to those of ordinary skill in the art.
For example, such agents may be encapsulated into liposomes, then
administered as described above. Liposomes are spherical lipid bilayers
with aqueous interiors. All molecules present in an aqueous solution
at the time of liposome formation are incorporated into the aqueous
interior. The liposomal contents are both protected from the external
microenvironment and, because liposomes fuse with cell membranes,
are efficiently delivered into the cell cytoplasm. Additionally,
due to their hydrophobicity, small organic molecules may be directly
administered intracellularly.
Pharmaceutical compositions suitable for use in the present invention
include compositions wherein the active ingredients are contained
in an effective amount to achieve its intended purpose. Determination
of the effective amounts is well within the capability of those
skilled in the art, especially in light of the disclosure provided
herein. In addition to the active ingredients, these pharmaceutical
compositions may contain suitable pharmaceutically acceptable carriers
comprising excipients and auxiliaries that facilitate processing
of the active compounds into preparations that can be used pharmaceutically.
The preparations formulated for oral administration may be in the
form of tablets, dragees, capsules, or solutions. The pharmaceutical
compositions of the present invention may be manufactured in a manner
that is itself known, for example, by means of conventional mixing,
dissolving, granulating, dragee-making, levitating, emulsifying,
encapsulating, entrapping or lyophilizing processes.
Pharmaceutical formulations for parenteral administration include
aqueous solutions of the active compounds in water-soluble form.
Additionally, suspensions of the active compounds may be prepared
as appropriate oily injection suspensions. Suitable lipophilic solvents
or vehicles include fatty oils such as sesame oil, or synthetic
fatty acid esters, such as ethyl oleate or triglycerides, or liposomes.
Aqueous injection suspensions may contain substances that increase
the viscosity of the suspension, such as sodium carboxymethyl cellulose,
sorbitol, or dextran. Optionally, the suspension may also contain
suitable stabilizers or agents that increase the solubility of the
compounds to allow for the preparation of highly concentrated solutions.
Pharmaceutical preparations for oral use can be obtained by combining
the active compounds with solid excipient, optionally grinding a
resulting mixture, and processing the mixture of granules, after
adding suitable auxiliaries, if desired, to obtain tablets or dragee
cores. Suitable excipients are, in particular, fillers such as sugars,
including lactose, sucrose, mannitol, or sorbitol; cellulose preparations
such as, for example, maize starch, wheat starch, rice starch, potato
starch, gelatin, gum tragacanth, methyl cellulose, hydroxypropylmethyl-cellulose,
sodium carboxymethylcellulose, and/or polyvinylpyrrolidone (PVP).
If desired, disintegrating agents may be added, such as the cross-linked
polyvinyl pyrrolidone, agar, or alginic acid or a salt thereof such
as sodium alginate.
Dragee cores are provided with suitable coatings. For this purpose,
concentrated sugar solutions may be used, which may optionally contain
gum arabic, talc, polyvinyl pyrrolidone, carbopol gel, polyethylene
glycol, and/or titanium dioxide, lacquer solutions, and suitable
organic solvents or solvent mixtures. Dye stuffs or pigments may
be added to the tablets or dragee coatings for identification or
to characterize different combinations of active compound doses.
Pharmaceutical preparations that can be used orally include push-fit
capsules made of gelatin, as well as soft, sealed capsules made
of gelatin and a plasticizer, such as glycerol or sorbitol. The
push-fit capsules can contain the active ingredients in admixture
with filler such as lactose, binders such as starches, and/or lubricants
such as talc or magnesium stearate and, optionally, stabilizers.
In soft capsules, the active compounds may be dissolved or suspended
in suitable liquids, such as fatty oils, liquid paraffin, or liquid
polyethylene glycols. In addition, stabilizers may be added. Liposomes
may be used for encapsulated delivery.
Pharmaceutical formulations disclosed or described in Boehm et
al., U.S. application Ser. Nos. 08/003,223; 08/027,747; 08/052,051,
incorporated by reference herein. See also, WO94/15902 for further
reference.
All publications referenced are incorporated by reference herein,
including the nucleic acid sequences and amino acid sequences listed
in each publication. All the compounds disclosed and referred to
in the publications mentioned above are incorporated by reference
herein, including those compounds disclosed and referred to in articles
cited by the publications mentioned above. |