Proc. Natl. Acad. Sci. USA
Vol. 96, pp. 3951–3956, March 1999
Induction of solid tumor differentiation by the peroxisome
proliferator-activated receptor-? ligand troglitazone in
patients with liposarcoma
(nuclear receptors?sarcoma?drug development?oncology?antineoplastic)
GEORGE D. DEMETRI*†, CHRISTOPHER D. M. FLETCHER‡, ELISABETTA MUELLER§, PASHA SARRAF§,
RYAN NAUJOKS*, NATALEE CAMPBELL¶, BRUCE M. SPIEGELMAN§, AND SAMUEL SINGER¶
Departments of *Adult Oncology and§Cell Biology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA 02115; and Departments of
‡Pathology and¶Surgery, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA 02115
Communicated by Pedro M. Cuatrecasas, University of California School of Medicine, San Diego, CA, January 19, 1999 (received for review
October 29, 1998)
oxisome proliferator-activated receptor-? have been shown to
induce terminal differentiation of normal preadipocytes and
human liposarcoma cells in vitro. Because the differentiation
status of liposarcoma is predictive of clinical outcomes, mod-
ulation of the differentiation status of a tumor may favorably
treatment of patients with advanced liposarcoma by using the
peroxisome proliferator-activated receptor-? ligand troglita-
zone, in which extensive correlative laboratory studies of
tumor differentiation were performed. We report here the
results of three patients with intermediate to high-grade
liposarcomas in whom troglitazone administration induced
histologic and biochemical differentiation in vivo. Biopsies of
tumors from each of these patients while on troglitazone
demonstrated histologic evidence of extensive lipid accumu-
lation by tumor cells and substantial increases in NMR-
detectable tumor triglycerides compared with pretreatment
biopsies. In addition, expression of several mRNA transcripts
characteristic of differentiation in the adipocyte lineage was
induced. There was also a marked reduction in immunohis-
tochemical expression of Ki-67, a marker of cell proliferation.
Together, these data indicate that terminal adipocytic differ-
entiation was induced in these malignant tumors by troglita-
zone. These results indicate that lineage-appropriate differ-
entiation can be induced pharmacologically in a human solid
Agonist ligands for the nuclear receptor per-
The process of neoplastic cell growth represents a dysfunc-
tional balance between control of cell proliferation, apoptosis,
and terminal differentiation. In normal cells, activation of
specific pathways leads to cellular differentiation, which typ-
ically is accompanied by cessation of proliferation. Treating
attractive concept, but clinical development of differentiation-
inducing agents to treat cancer has been limited to date. The
most successful example of differentiation therapy for a ma-
lignant disease is the use of all-trans retinoic acid, a ligand for
the retinoic acid receptor, to differentiate the malignant cells
of acute promyelocytic leukemia (1, 2). Other nuclear recep-
tors that regulate cellular differentiation and proliferation
pathways also may represent promising targets for novel
therapeutic strategies in cancer treatment.
The differentiation of adipocytes has been used as an
experimental model of lineage-specific differentiation and
for the adipocytic lineage is a nuclear receptor known as
peroxisome proliferator-activated receptor-? (PPAR?) (3–9).
PPAR? forms a heterodimeric complex with the retinoid X
receptor (RXR). This complex of PPAR? and RXR binds to
specific recognition sites on DNA and, upon binding of ligands
for either receptor, regulates transcription of adipocyte-
specific genes. Ectopic expression and activation of PPAR? in
fibroblastic cells stimulates adipocyte-specific gene expression
and induces a complete adipocytic phenotype (4, 9). Several
natural and synthetic ligands for PPAR? have been identified.
Troglitazone is a member of the thiazolidinedione class of
drugs, which have been identified as agonist ligands for
PPAR? (10–12). These drugs have been developed clinically
and currently are used primarily as insulin-sensitizing antidi-
abetic agents (13, 14).
Liposarcoma represents the most common form of soft-
tissue sarcoma in humans (15). These tumors constitute a
family of mesenchymal malignancies characterized by dysfunc-
tional adipocytic differentiation as well as uncontrolled cellu-
lar proliferation. Several histologic subtypes of liposarcoma
have been well characterized, with differentiation status of the
cells being a major distinguishing feature of these subtypes.
The prognosis of liposarcoma, including risk of developing
metastatic disease and likelihood of long-term survival, cor-
relates well with the histologic subtype, indicating that the
differentiation status of the tumor is one of the most important
prognostic factors for predicting clinical outcomes (15, 16).
The myxoid and round cell subtypes of liposarcoma, compris-
ing approximately 35% of all liposarcomas, represent a histo-
logic continuum that may be grouped together based on the
presence of a characteristic reciprocal translocation between
chromosomes 12 and 16 (15, 17–18). This t(12;16) generates a
chimeric mRNA fusion transcript derived from the CHOP
The contribution of these molecular aberrancies to the process
of malignant transformation remains obscure.
Laboratory analyses of primary tumor tissue have docu-
mented the expression of PPAR? mRNA at levels comparable
to normal fat in each of the histologic subtypes of human
differentiation of human liposarcoma cells in culture can be
induced by exposure to thiazolidinedione drugs (19). Impor-
tantly, the levels of troglitazone that demonstrate differenti-
ating activity in vitro are in the range of 5 ?M (19), and such
levels are consistently achievable and tolerable for prolonged
periods in humans being treated for type II diabetes (13, 14).
Standard therapies for unresectable liposarcomas are purely
The publication costs of this article were defrayed in part by page charge
payment. This article must therefore be hereby marked ‘‘advertisement’’ in
accordance with 18 U.S.C. §1734 solely to indicate this fact.
PNAS is available online at www.pnas.org.
Abbreviations: PPAR?, peroxisome proliferator-activated receptor-?;
MAS, magic angle spinning; TSP, trimethylsilylpropionate.
†To whom reprint requests should be addressed.
palliative, with complete response rates to cytotoxic chemo-
therapy reported in less than 10% of patients (20, 21). Based
on our preclinical data, liposarcoma represents an attractive
clinical model for the therapeutic use of troglitazone to induce
differentiation of malignant tumors in humans. We report here
clear evidence of differentiation in vivo induced by troglita-
zone in three patients with liposarcoma whose tumor tissues
were extensively evaluated.
PATIENTS AND METHODS
Trial Design. An open-label Phase 2 clinical trial was
conducted at the Dana-Farber Cancer Institute with approval
of the Institutional Review Board. Previous surgery, chemo-
therapy, and radiation therapy were not exclusion criteria as
long as patients had measurable disease that had not been
irradiated at the time of study entry. After obtaining informed
consent, all patients were assigned to receive troglitazone
(generously provided by Parke–Davis) at the dose of 800 mg
orally once daily. Patients were monitored with clinical meth-
ods (physical examinations, clinical chemistry and imaging
tests) as well as with serial biopsies of tumor sites before and
approximately 6 weeks after beginning troglitazone dosing. In
tissue was used as a study endpoint to justify further study of
troglitazone in this clinical setting. The study design was
reviewed and approved under an investigator-initiated inves-
tigational new drug permit from the U.S. Food and Drug
Patient Summaries. Patient 1. Patient 1 was a 39-year-old
woman with myxoid liposarcoma (intermediate grade) with
recurrent metastatic disease. Initial management of primary
disease in 1993 consisted of wide resection and postoperative
radiation therapy, with her first metastatic recurrence noted in
August 1997. The patient entered this clinical trial and began
troglitazone dosing in December 1997. She tolerated this
repeat tumor biopsy after 6 weeks of troglitazone administra-
tion in January 1998.
Patient 2. Patient 2 was a 43-year-old woman with high-grade
myxoid and round cell liposarcoma, primary disease resected
in 1987, with progressive metastatic disease at multiple sites
since 1988, including lung metastases, bony sites, as well as
diffuse soft tissue metastatic sites. She previously had been
treated extensively with multiple courses of radiation therapy
as well as cytotoxic chemotherapy. Patient began troglitazone
dosing per protocol in March 1998, underwent re-evaluation
with repeat biopsy approximately 6 weeks later, and continued
on study 4 months when progression of a paraspinal metastasis
impinged on the spinal cord.
Patient 3. Patient 3 was a 56-year-old woman with high-grade
pleomorphic liposarcoma with massive retroperitoneal dis-
ease, initially resected in 1996. Since 1996, she had received
multiple courses of radiation therapy and cytotoxic chemo-
therapy for recurrent disease with no effect. She entered this
clinical trial in February 1998, repeat biopsies were performed
after 6 weeks, and the patient remains on study as of October
Tumor Tissue. Biopsies of tumor sites were obtained im-
mediately before study entry and MRI scans of measurable
sites of disease also were obtained at baseline; these biopsies
and imaging studies were repeated approximately 6 weeks
after initiation of troglitazone therapy. Tissue samples from
homogenous and viable portions of the liposarcoma were
obtained from either open incisional biopsy or computed
tomography-guided core biopsy. Conventional classification of
histologic subtype, morphology, and grade was determined by
a single sarcoma specialty pathologist (C.D.M.F.). Histologic
classification was performed on tissue immediately adjacent to
that used for NMR analysis and was correlated with the
diagnosis rendered on the main surgical specimen.
Histological Analysis. Routine histologic staining with he-
matoxylin and eosin was performed on all tumor biopsy
specimens. Immunohistochemistry was performed by using
standard techniques as described. For immunohistochemical
analyses the MIB-1 (1:50 dilution) mAb (Immunotech, Mar-
seille, France) as well as a mAb directed against PPAR? (1:5
dilution) (Santa Cruz Biotechnology) were used. MIB-1 stains
the Ki-67 nuclear proliferation-associated antigen, a standard
marker of cellular proliferation (22), in paraffin sections.
Standard quantification was performed by assessing the per-
centage of cells with positive nuclear staining for this antigen.
RNA Analysis. Northern blot analysis was performed by
using mRNA extracted from tumor biopsy samples, as de-
adipsin, and actin. All signals were standardized against actin
and to mRNA from normal adipose tissue for quantification of
Tumor Sample Preparation for Magic Angle Spinning
(MAS) Proton NMR Spectroscopy. For MAS proton NMR
studies, cylindrical core tissue samples 3 mm in diameter and
12 mm in length were cut from semifrozen tissue by using a
3-mm diameter biopsy punch. These samples were thawed in
3 cc of PBS in deuterium oxide (PBS?D2O, pD 7.4) for 5 min
before rinsing once with fresh PBS?D2O and placement in a
4-mm o.d. zirconium MAS rotor. Ten microliters of 94.1 mM
3-trimethylsilylpropionate-d4 (TSP-d4) in PBS?D2O was
placed in the rotor with the tumor tissue to serve as an internal
spectral intensity reference.
Proton NMR Spectroscopy Measurements. All spectra were
acquired at 20°C and 500 MHz by using a Bruker DRX500
spectrometer equipped with a 4-mm high-resolution1H?13C
MAS probe as described (24, 25). Spin rates of 3.5 KHz were
used, and one-dimensional, fully relaxed
were quantitated for NMR-visible triglycerides and phosphati-
Tumor Cytogenetics. All baseline tumor biopsy samples
were evaluated by cytogenetic testing. Patients 1 and 2 had the
balanced translocation t(12;16)(q13;p11) that is characteristic
of myxoid?round cell liposarcoma (17, 18). Cytogenetic anal-
ysis of tumor biopsy from patient 3 was unsuccessful because
of failure of the cells to proliferate in culture conditions
required for metaphase analysis.
In this pilot study, we report the results of three patients with
advanced unresectable myxoid and pleomorphic liposarcoma
to whom the PPAR-? ligand troglitazone was administered.
Eligibility criteria for this pilot study also allowed troglitazone
dosing to patients with other histologic subtypes of liposar-
coma, including low-grade, well-differentiated disease. How-
ever, because it would be very difficult to detect drug-induced
changes in the differentiation status of tumors with well-
differentiated characteristics at baseline, more poorly differ-
entiated histologic subtypes of liposarcoma were judged likely
to be more informative. Although the clinical status of all
performed detailed histologic, biochemical, and molecular
analyses on a subset of patients with myxoid?round cell or
pleomorphic liposarcoma, histologic subtypes with character-
istically poorly differentiated morphologies.
Histologic Changes in Tumor Biopsies Induced by Trogli-
tazone. To assess the effects of troglitazone on the tumor, we
performed serial biopsies on patients after 6–8 weeks of
treatment, as discussed in Patients and Methods. Fig. 1 shows
the dramatic histologic changes induced by troglitazone ther-
apy in these patients with intermediate to high-grade disease
before study treatment (Fig. 1A ? pre, Fig. 1B ? post).
3952 Medical Sciences: Demetri et al.Proc. Natl. Acad. Sci. USA 96 (1999)
Marked microvesicular cytoplasmic lipid accumulation and
increased individual cell volumes were noted without changes
in nuclear morphology. These changes were consistent be-
tween biopsy specimens taken from multiple different sections
of tumors and were not caused by artifacts of variability in
intratumoral sampling. The baseline expression of PPAR? was
confirmed by immunohistochemical staining of tissues, with
the expected strong nuclear expression confirmed as noted in
Fig. 2; uniformly high levels of staining for PPAR? were seen
in all patients analyzed in this study (data not shown).
We next examined whether troglitazone treatment affected
the proliferation of the tumor cells. Expression of the Ki-67
was assayed by immunohistochemical staining and quantified
by the percentage of cells with positive-staining nuclei. The
proliferative fraction of even these intermediate to high-grade
tumors is relatively low at baseline. However, in all three
patients, the percentage of cells expressing the Ki-67 antigen
dropped 2- to 4-fold while on troglitazone therapy (Fig. 3),
based on a standardized method of counting at least 100 nuclei
within each sample to take into account possible variations
across different microscopic fields.
To assess more fully the extent of differentiation at a
molecular level, we analyzed biopsies obtained before and
after troglitazone treatment. Sufficient material for molecular
2. As shown in Fig. 4, these assays revealed 1.8- to 4.2-fold
increases in the expression of genes specifically linked to
adipocytic differentiation, including aP2, adipsin, and PPAR?
itself. The data are expressed as the percent expression of
mRNA relative to a sample of normal human fat used as an
external control. These results indicate lineage-appropriate
molecular differentiation of the tumors.
Analysis of tumor specimens by MAS1H-NMR spectros-
copy was performed to characterize and quantify the lipid
hematoxylin and eosin-stained biopsies of liposarcoma tissue obtained (A) immediately before study entry and (B) after 6 weeks of daily dosing
with troglitazone. Magnification: ?400.
Histologic changes in liposarcoma tumor tissue with accumulation of intracellular lipid in three separate patients (I, II, III). Shown are
Medical Sciences: Demetri et al. Proc. Natl. Acad. Sci. USA 96 (1999)3953
metabolites within the tumor tissue. Representative quantita-
tive one-dimensional MAS1H-NMR spectra were acquired
from the tumor tissue of patient 1 before therapy (Fig. 5A) and
after 6 weeks of troglitazone therapy (Fig. 5B). The vertical
scale of each spectrum was normalized to the integral of
TSP-d4 (reference location at 0.0 ppm) because the same
resonances in these spectra arise from triglycerides and phos-
pholipids. The presence of NMR-detectable triglyceride with
this technique is confirmed by detection of characteristic
resonances from the glycerol backbone (multiplets centered at
4.1 and 4.3 ppm) and the presence of a triplet resonance
centered at 0.9 ppm, which originates from terminal methyl
protons on fatty acyl chains. The spectra in Fig. 5 demonstrate
that the myxoid liposarcoma tissue after 6 weeks of troglita-
zone administration exhibited a 2.6-fold increase in triglycer-
ide levels compared with prestudy baseline. The vertical scale
of the same spectra in the 3.2–3.3 ppm region was increased
(Fig. 5 A and B, Insets) to allow visualization of nontriglyceride
metabolites such as myo-inositol, the N-methyls of phosphati-
choline (PC), and choline (Cho). The insets for this region in
Fig. 5 are scaled by the same factor relative to TSP-d4and
demonstrate higher levels of the N-methyls of PtdCho, myo-
inositol, and GPC after 6 weeks of troglitazone therapy when
compared with the same resonances in spectra acquired from
tissue at baseline. From the one-dimensional MAS NMR
spectra, an estimate of NMR-visible triglyceride and phos-
phatidylcholine content (nmol per mg tissue) was determined
for samples of tumor tissue before and after troglitazone
therapy in patients 1 and 2 (Table 1).
Clinical Imaging of Tumors. In this pilot study, initial
increases in tumor volumes were expected, because induction
of differentiation of liposarcoma tissues in vitro was accom-
panied by intracellular accumulation of lipid and associated
increases in cellular volume (19). Serial clinical MRI scans in
patients 1 and 2 demonstrated moderate increases in tumor
volume after 6 weeks of troglitazone administration, but no
tissue. Immunohistochemical staining of a biopsy sample of liposar-
coma tissue from patient 2 obtained immediately before study entry.
Comparative hematoxylin and eosin staining of tissue is noted in Fig.
1IIA. Magnification: ?400.
Nuclear expression of PPAR? protein in liposarcoma
sion after 6 weeks of troglitazone treatment. The percentage of cells
with strong nuclear staining for Ki-67 was quantified by immunohis-
tochemical staining with the MIB-1 mAb, as described in Patients and
Decreases in Ki-67 proliferation-associated antigen expres-
linked to adipocytic terminal differentiation. mRNA was prepared
from serial biopsies of liposarcoma tissue from patients 1 and 2 (A and
B, respectively) and subjected to Northern analysis as described in
Patients and Methods. The levels of mRNA for aP2, adipsin, and
PPAR? were quantified and normalized against levels of mRNA for
?–actin. Levels of gene expression then were scaled against normal fat,
which was set as 100% expression for these adipocytic-lineage genes.
Troglitazone-associated increases in expression of genes
NMR spectra acquired from the tumor tissue of patient 1 (A) before
therapy and (B) after 6 weeks of troglitazone therapy, showing
increases in triglycerides standardized to the TSP peak at the right.
(Insets) Where the vertical scale of the same spectra in the 3.2–3.3 ppm
region was increased to allow visualization of nontriglyceride metab-
Representative quantitative one-dimensional MAS1H-
3954 Medical Sciences: Demetri et al. Proc. Natl. Acad. Sci. USA 96 (1999)
new sites of disease were noted. These scans also indicated a
change in magnetic resonance characteristics of the tumors
consistent with the histologic changes described above, with
subtle increases in fat density, as noted in the representative
MRI scans of a pelvic mass in patient 3 (Fig. 6).
Safety and Tolerability of Troglitazone in Patients. No
adverse events were noted to be associated with this treatment,
and all patients tolerated the daily dosing of troglitazone with
no side effect problems. In particular, liver function tests were
thereafter), because rare cases of hepatotoxicity have been
described in diabetic patients (27, 28). No abnormalities of
hepatic function were detected in any patient.
The potential to counteract the uncontrolled proliferation of
malignant cell growth through promotion of cellular differen-
tiation represents an attractive approach to cancer therapy.
However, this strategy has been limited by inadequate knowl-
edge of specific systems that regulate differentiation in par-
ticular lineages and by the lack of means to activate such
intracellular pathways. The identification of PPAR? as a
critical regulator of adipocyte differentiation has provided a
novel target for therapeutic drug discovery (3–9). The subse-
quent identification of thiazolidinedione drugs as agonist
ligands for the PPAR? receptor (10–12) has provided an
attractive opportunity to test these hypotheses. Preclinical
work using primary cultures of human liposarcoma showed
that differentiation of human liposarcoma cells could be
induced by stimulation of PPAR? (19), and these in vitro
clinical trial. This report describes the successful induction of
differentiation of human solid tumors in vivo. These observa-
tions support the clinical development of receptor-targeted
therapeutics to induce differentiation as a feasible antineo-
The histologic, biochemical, and molecular evidence of
ing and consistent among these three patients with interme-
diate and high-grade liposarcoma who were subjected to
extensive analysis. Although certain liposarcomas can exhibit
histologic heterogeneity within individual tumors, multiple
troglitazone administration are not caused by artifactual intra-
tumoral sampling variables. Most notably, these patterns of
morphologic differentiation and lipid accumulation noted
after troglitazone exposure are essentially never seen in the
myxoid or pleomorphic subsets of liposarcoma (15). The
changes in gene expression were very consistent in the two
mRNA markers of gene expression (aP2, adipsin, and PPAR?
itself) are increased 2- to 4-fold after troglitazone treatment.
The data in Fig. 4 are presented as the expression of each
mRNA species in tumor relative to expression by a ‘‘normal’’
fat control. This normalized comparison of molecular changes
from homogeneous regions of tumor tissue before and after
exposure to troglitazone is consistent with the histologic
changes and illustrative of adipocytic differentiation. These
observations are particularly relevant for the myxoid?round
cell and pleomorphic subtypes, which tend to be highly cellular
and exhibit little evidence of lipid accumulation in the baseline
state. The NMR biochemical analyses for these patients are
also consistent with lineage-appropriate differentiation, dem-
onstrating marked increases in the levels of both triglyceride
and phosphatidylcholine in tumor tissue. These data therefore
represent a measure of troglitazone responsiveness within
these patients with intermediate to high-grade disease for
whom sufficient tissue was obtained for molecular and NMR
Induction of differentiation would be expected to decrease
the proliferative rates of cancer and thus slow the progression
of disease. In well-differentiated (low-grade) liposarcoma,
5-year survival rates may exceed 90%, and patients often can
live many years even with measurable disease because of the
indolent nature of the disease process. In contrast, patients
with intermediate to high-grade myxoid or pleomorphic lipo-
sarcoma typically have lower 5-year survival rates (25–50%)
because of the more rapid progression of disease (16, 18). The
decreased expression of the Ki-67 proliferation-associated
antigen in tumors after troglitazone exposure is of consider-
able magnitude and consistent in all the patients analyzed. It
is also consistent with the decreases in cell proliferation that
are observed when adipogenesis is induced through PPAR? in
cell culture (9, 19).
From laboratory studies, it is expected that terminal adipo-
cytic differentiation would be accompanied by accumulation
of lipids and increased volume of tumor cells (19). With
differentiation, as adipocytic cells enlarge the net synthesis of
cell membrane components such as phosphatidylcholine must
increase with accumulation of intracellular triglycerides. Such
changes would render typical volumetric assessments of tumor
size potentially misleading, because more differentiated tu-
before and (B) after 6 weeks of troglitazone administration. Note the
subtle change in the fat density signal (whitish stranding) within the
tumor (low T1?high T2 signal characteristics) after troglitazone ex-
Serial MRI images of pelvic liposarcoma in patient 3 (A)
phosphatidylcholine in samples of tumor tissue
Assessments of NMR-visible triglyceride and
Liposarcoma tissue lipid
metabolite levels determined by
Medical Sciences: Demetri et al. Proc. Natl. Acad. Sci. USA 96 (1999)3955
mors might get larger on the basis of increased cell volume Download full-text
rather than by increased cell number. Thus, although the
imaging studies did not show any decrease in the size of bulky
tumors, these data provide encouraging justification for con-
tinuing the development of PPAR? receptor-based differen-
tiation strategies as a novel therapeutic intervention for ma-
lignant diseases that express this receptor.
The findings described in the detailed laboratory studies of
tumor tissue from these patients with intermediate to high-
grade liposarcomas are indicative of a biologically important
effect, which has not previously been possible to induce in
patients. In addition to the patients presented in this report,
three other patients with myxoid?round cell histologies have
been treated with troglitazone on this clinical trial; posttro-
glitazone tumor biopsies from each of these subsequent pa-
tients also exhibit the characteristic histologic changes and
correlative decreases in the expression of Ki-67 illustrated by
the three patients described in this report (data not shown).
These findings suggest that all or nearly all patients with
myxoid?round cell liposarcoma may respond to PPAR? stim-
ulation with induction of cellular differentiation. However, the
clinical relevance of these effects remains under investigation,
and additional clinical trials are planned to define whether
these cellular changes of enhanced differentiation might trans-
late into improved outcomes, such as prolonged time to tumor
progression. The analyses shown here are much more difficult
to assess for changes in the well-differentiated subtypes of
liposarcomas, because they begin with a more fully differen-
tiated adipocytic phenotype. Nonetheless, it remains possible
that prodifferentiation responses occur in those other subtypes
of liposarcomas as well, although our ability to detect histo-
logic changes may be inadequate. Clinical trials are planned to
evaluate appropriate medical endpoints in all types of liposar-
comas, because clinical activity may be noted even in the
absence of detectable changes in histology for the more
well-differentiated subsets. The relatively favorable safety
profile of this orally administered agent (13), confirmed in this
study of cancer patients, also suggest the possible therapeutic
use of troglitazone and other PPAR? ligands as postsurgical
These findings in patients with liposarcomas may have
important relevance for broader groups of patients with neo-
plastic diseases based on the expression of the nuclear receptor
PPAR?. Specifically, it has been shown in preclinical studies
that most colon carcinomas as well as many breast carcinomas
express high levels of PPAR? (29, 30). Additionally, agonist
ligands to the PPAR? receptor can induce changes consistent
with differentiation and lower rates of cellular proliferation in
vitro in both breast cancer and colon cancer cell lines (29, 30).
It is also worth noting that new PPAR? ligands are under
development, and any of these agents that may have increased
potency and efficacy in inducing differentiation may prove
particularly useful in oncology clinical applications. Similarly,
combinations of PPAR? ligands with ligands for retinoid X
receptor or other drugs affecting related pathways may en-
along with the data on the liposarcoma patients presented in
this report, justify additional study of the clinical utility of
PPAR? ligands as novel anticancer therapeutic agents.
We gratefully acknowledge the constructive input and collaboration
of Professor Dave Corey, Dr. Dan Williamson, Dr. Stuart Silverman,
Dr. Jonathan Fletcher, Dr. Robert Maki, Dr. Dan DeAngelo, and Dr.
Myles Brown for helpful discussion. We also thank Drs. Alan Saltiel
and Artemios Vassos of Parke-Davis for their support of this project
and Elizabeth Govoni, Murriam Khambaty, Lucette Robinson, Ruth
Cain, and Leslie Stefanowicz for their contributions. Finally, we
acknowledge with thanks the referral of these patients by Drs. David
Harmon, Dennis Priebat, and William Walsh. This work was sup-
ported in part by unrestricted research grants to G.D.D. and B.M.S.
from Johnson and Johnson, East Brunswick, NJ. B.M.S. is a recipient
of a grant from Novartis. S.S. is a recipient of Grant RO1 CA75720-01
from the National Institutes of Health.
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