A phase II study of troglitazone, an activator of the PPARgamma receptor, in patients with chemotherapy-resistant metastatic colorectal cancer

PPAR gamma, bioactive lipids, and cancer progression

In this article we review the evolution of cancer research involving PPARgamma, including mechanisms, target genes, and clinical applications. For the last thirteen years, the effects of PPARgamma activity on tumor biology have been studied intensely. Most of this research has focused upon the potential for employing agonists of this nuclear receptor in cancer treatment. As a monotherapy such agonists have shown little success in clinical trials, while they have shown promise as components of combination treatments both in culture and in animal models. Other investigations have explored a possible role for PPARgamma as a tumor suppressor, and as an inducer of differentiation of cancer stem cells. Whereas early studies have yielded variable conclusions regarding the prevalence of PPARgamma mutations in cancer, the protein level of this receptor has been more recently identified as a significant prognostic marker. We predict that indicators of PPARgamma activity may also serve as predictive markers for tailoring treatments.

Paracrine and endocrine effects of adipose tissue on cancer development and progression

The past few years have provided substantial evidence for the vital role of the local tumor microenvironment for various aspects of tumor progression. With obesity and its pathophysiological sequelae still on the rise, the adipocyte is increasingly moving center stage in the context of tumor stroma-related studies. To date, we have limited insight into how the systemic metabolic changes associated with obesity and the concomitant modification of the paracrine and endocrine panel of stromal adipocyte-derived secretory products ("adipokines") influence the incidence and progression of obesity-related cancers. Here, we discuss the role of adipocyte dysfunction associated with obesity and its potential impact on cancer biology.

Peroxisome proliferator-activated receptor δ confers resistance to peroxisome proliferator-activated receptor γ-induced apoptosis in colorectal cancer cells

Peroxisome proliferator-activated receptor γ (PPARγ) may serve as a useful target for drug development in non-diabetic diseases. However, some colorectal cancer cells are resistant to PPARγ agonists by mechanisms that are poorly understood. Here, we provide the first evidence that elevated PPARδ expression and/or activation of PPARδ antagonize the ability of PPARγ to induce colorectal carcinoma cell death. More importantly, the opposing effects of PPARδ and PPARγ in regulating programmed cell death are mediated by survivin and caspase-3. We found that activation of PPARγ results in decreased survivin expression and increased caspase-3 activity, whereas activation of PPARδ counteracts these effects. Our findings suggest that PPARδ and PPARγ coordinately regulate cancer cell fate by controlling the balance between the cell death and survival and demonstrate that inhibition of PPARδ can reprogram PPARγ ligand-resistant cells to respond to PPARγ agonists.

Pathophysiological Roles of PPARgamma in Gastrointestinal Epithelial Cells

Although the highest levels of PPARγ expression in the body have been reported in the gastrointestinal epithelium, little is known about the physiological functions of that receptor in the gut. Moreover, there is considerable controversy concerning the effects of thiazolidinedione PPARγ agonists on the two major diseases of the gastrointestinal track: colorectal cancer and inflammatory bowel disease. We will undertake to review both historical and recently published data with a view toward summarizing what is presently known about the roles of PPARγ in both physiological and pathological processes in the gastrointestinal epithelium.

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents

Peroxisome proliferator-activated receptor-gamma (PPARγ), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARγ was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARγ ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARγ. Overall, PPARγ appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.

To Live or to Die: Prosurvival Activity of PPARgamma in Cancers

The role of PPARγ in tumorigenesis is controversial. In this article, we review and analyze literature from the past decade that highlights the potential proneoplastic activity of PPARγ. We discuss the following five aspects of the nuclear hormone receptor and its agonists: (1) relative expression of PPARγ in human tumor versus normal tissues; (2) receptor-dependent proneoplastic effects; (3) impact of PPARγ and its agonists on tumors in animal models; (4) clinical trials of thiazolidinediones (TZDs) in human malignancies; (5) TZDs as chemopreventive agents in epidemiology studies. The focus is placed on the most relevant in vivo animal models and human data. In vitro cell line studies are included only when the effects are shown to be dependent on the PPARγ receptor.

PPAR Ligands for Cancer Chemoprevention

Peroxisome proliferators-activated receptors (PPARs) that are members of the nuclear receptor superfamily have three different isoforms: PPARalpha, PPARdelta, and PPARgamma. PPARs are ligand-activated transcription factors, and they are implicated in tumor progression, differentiation, and apoptosis. Activation of PPAR isoforms lead to both anticarcinogenesis and anti-inflammatory effect. It has so far identified many PPAR ligands including chemical composition and natural occurring. PPAR ligands are reported to activate PPAR signaling and exert cancer prevention and treatment in vitro and/or in vivo studies. Although the effects depend on the isoforms and the types of ligands, biological modulatory activities of PPARs in carcinogenesis and disease progression are attracted for control or combat cancer development. This short review summarizes currently available data on the role of PPAR ligands in carcinogenesis.

Chondrosarcoma and peroxisome proliferator-activated receptor

Induction of differentiation and apoptosis in cancer cells by ligands of PPARγ is a novel therapeutic approach to malignant tumors. Chondrosarcoma (malignant cartilage tumor) and OUMS-27 cells (cell line established from grade III human chondrosarcoma) express PPARγ. PPARγ ligands inhibited cell proliferation in a dose-dependent manner, and induced apoptosis of OUMS-27. The higher-grade chondrosarcoma expressed a higher amount of antiapoptotic Bcl-xL in vivo. The treatment of OUMS-27 by 15d-PGJ₂, the most potent endogenous ligand for PPARγ, downregulated expression of Bcl-xL and induced transient upregulation of proapoptotic Bax, which could accelerate cytochrome c release from mitochondria to the cytosol, followed by induction of caspase-dependent apoptosis. 15d-PGJ₂ induced the expression of CDK inhibitor p21 protein in human chondrosarcoma cells, which appears to be involved in the mechanism of inhibition of cell proliferation. These findings suggest that targeted therapy with PPARγ ligands could be a novel strategy against chondrosarcoma.

Peroxisome proliferator-activated receptor γ and colorectal cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. PPARγ plays an important role in adipocyte differentiation, lipid storage and energy dissipation in adipose tissue, and is involved in the control of inflammatory reactions as well as in glucose metabolism through the improvement of insulin sensitivity. Growing evidence has demonstrated that activation of PPARγ has an antineoplastic effect in tumors, including colorectal cancer. High expression of PPARγ is detected in human colon cancer cell lines and adenocarcinoma. This review describes the molecular mechanisms by which PPARγ regulates tumorigenesis in colorectal cancer, and examines current clinical trials evaluating PPARγ agonists as therapeutic agents for colorectal cancer.

Synergistic interactions between heregulin and peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist in breast cancer cells

Here, we demonstrate that troglitazone (Rezulin), a peroxisome proliferator-activated receptor agonist, acted in synergy with heregulin to induce massive cell death in breast cancer cells. Although the combination of heregulin and troglitazone (HRG/TGZ) induced both apoptosis and necrosis, the main mode of cell death was caspase-independent and occurred via necrosis. This combination increased generation of superoxide in mitochondria, which in turn destabilized mitochondria potential. Pretreatment with N-acetyl-l-cysteine and catalase expression ameliorated cell death induced by the combination treatment, indicating a role of oxidative stress in mediating HRG/TGZ-induced cell death. Notably, pretreatment with pyruvate significantly prevented the cell death, suggesting a potential mechanistic link between metabolic stress and HRG/TGZ-induced cell death. The activation of the HRG signaling axis has been considered as a poor prognostic factor in breast cancer and confers resistance to gefitinib (Iressa) and tamoxifen. However, our data presented here paradoxically suggest that HRG expression can actually be beneficial when it comes to treating breast cancer with peroxisome proliferator-activated receptor-γ ligands. Taken together, the combination of HRG and TGZ may provide a basis for the development of a novel strategy in the treatment of apoptosis-resistant and/or hormone-refractory breast cancer.

Mistletoe lectin-I augments antiproliferative effects of the PPARgamma agonist rosiglitazone on human malignant melanoma cells

As malignant melanoma cells are highly resistant to conventional chemotherapy, survival rates after tumor spread remain poor and hence there is an urgent need for new therapeutic options. For both mistletoe lectin-I (ML-I) and the thiazolidinediones as synthetic ligands of the peroxisome proliferator-activated receptor gamma (PPARgamma) an antiproliferative effect on malignant melanoma cells has previously been shown. Hence, the aim of this study was to investigate whether the combination of ML-I and the PPARgamma ligand rosiglitazone is more efficacious in the treatment of malignant melanoma cells than either agent alone. Proliferation of three human melanoma cell lines treated with ML-I, rosiglitazone and the combination of both was measured in a broad concentration range (0.0001-100 microg/mL) using the XTT cell proliferation assay. Combined application tremendously increased the antiproliferative effect on all three melanoma cell lines compared with single agent treatment. In comparison with the single use of rosiglitazone, the combination with ML-I significantly increased the inhibition of cell growth by 51-79% and in comparison with the single use of ML-I by 9-32%, respectively. In conclusion, this study shows that the combination of ML-I with rosiglitazone significantly augments their antiproliferative effect on malignant melanoma cells in comparison with their single agent application, which might be a promising tool for further therapeutic studies.

In vitro and in vivo therapeutic efficacy of the PPAR-γ agonist troglitazone in combination with cisplatin against malignant pleural mesothelioma cell growth

Malignant pleural mesothelioma (MPM), an aggressive and refractory tumor type, is increasing in frequency throughout the world. Peroxisome proliferator activated receptor-γ (PPAR-γ) agonists have anticancer activity against several cancer cell lines in vitro and in vivo. However, there have been no reports that PPAR-γ agonists induce growth inhibition of MPM cell lines. In this study, we investigated the inhibitory effect of a PPAR-γ agonist in combination with an anticancer agent on MPM cell growth in vitro and in vivo. We examined the therapeutic efficacy of the PPAR-γ agonist troglitazone (TGZ) in combination with cisplatin against a human MPM cell line, both in vitro and orthotopically inoculated into severe combined immunodeficient (SCID) mice. Troglitazone (TGZ) alone inhibited MPM cell growth in vitro in a dose-dependent manner via induction of G1 cell cycle arrest and apoptosis. The combination of TGZ and cisplatin showed an additive inhibitory effect on MPM cell growth compared to treatment with either individual drug. Treatment with 500 mg/kg or 1000 mg/kg TGZ effectively inhibited the production of thoracic tumors and pleural effusion in EHMES-10 cell-bearing SCID mice. Moreover, treatment with 500 mg/kg TGZ in combination with 3 mg/kg cisplatin more effectively prolonged survival compared to treatment with either individual drug. These results suggest that TGZ in combination with cisplatin may become a novel therapy for MPM.

PPARgamma Ligand as a Promising Candidate for Colorectal Cancer Chemoprevention: A Pilot Study

Activating synthetic ligands for peroxisome proliferator-activated receptor gamma (PPARγ), such as pioglitazone, are commonly used to treat persons with diabetes mellitus with improvement of insulin resistance. Several reports have clearly demonstrated that PPARγ ligands could inhibit colorectal cancer cell growth and induce apoptosis. Meanwhile, aberrant crypt foci (ACF) have come to be established as a biomarker of the risk of CRC in azoxymethane-treated mice and rats. In humans, ACF can be detected using magnifying colonoscopy. Previously, CRC and adenoma were used as a target for chemopreventive agents, but it needs a long time to evaluate, however, ACF can be a surrogate marker of CRC even for a brief period. In this clinical study, we investigated the chemopreventive effect of pioglitazone on the development of human ACF as a surrogate marker of CRC. Twenty-nine patients were divided into two groups, 20 were in the endoscopically normal control group and 9 were in the pioglitazone (15 mg/day) group, and ACF and adenoma were examined before and after 1-month treatment. The number of ACF was significantly decreased (5.8 ± 1.1 to 3.3 ± 2.3) after 1 month of pioglitazone treatment, however, there was no significant change in the number of crypts/ACF or in the number and size of adenomas. Pioglitazone may have a clinical application as a cancer-preventive drug. This investigation is just a pilot study, therefore, further clinical studies are needed to show that the PPARγ ligand may be a promising candidate as a chemopreventive agent for colorectal carcinogenesis.

Peroxisome proliferator-activated receptor γ and colorectal cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. PPARγ plays an important role in adipocyte differentiation, lipid storage and energy dissipation in adipose tissue, and is involved in the control of inflammatory reactions as well as in glucose metabolism through the improvement of insulin sensitivity. Growing evidence has demonstrated that activation of PPARγ has an antineoplastic effect in tumors, including colorectal cancer. High expression of PPARγ is detected in human colon cancer cell lines and adenocarcinoma. This review describes the molecular mechanisms by which PPARγ regulates tumorigenesis in colorectal cancer, and examines current clinical trials evaluating PPARγ agonists as therapeutic agents for colorectal cancer.

Anticancer Role of PPARgamma Agonists in Hematological Malignancies Found in the Vasculature, Marrow, and Eyes

The use of targeted cancer therapies in combination with conventional chemotherapeutic agents and/or radiation treatment has increased overall survival of cancer patients. However, longer survival is accompanied by increased incidence of comorbidities due, in part, to drug side effects and toxicities. It is well accepted that inflammation and tumorigenesis are linked. Because peroxisome proliferator-activated receptor (PPAR)-gamma agonists are potent mediators of anti-inflammatory responses, it was a logical extension to examine the role of PPARgamma agonists in the treatment and prevention of cancer. This paper has two objectives: first to highlight the potential uses for PPARgamma agonists in anticancer therapy with special emphasis on their role when used as adjuvant or combined therapy in the treatment of hematological malignancies found in the vasculature, marrow, and eyes, and second, to review the potential role PPARgamma and/or its ligands may have in modulating cancer-associated angiogenesis and tumor-stromal microenvironment crosstalk in bone marrow.

Differential effects of PPARgamma activation by the oral antidiabetic agent pioglitazone in Barrett's carcinoma in vitro and in vivo

BACKGROUND AND PURPOSE

The nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is a key transcription factor regulating genes involved in adipogenesis, glucose homeostasis and cell differentiation. Moreover, PPARgamma has been demonstrated to control proliferation and apoptosis in various cancer cells. We investigated the biological effects of PPARgamma activation by the oral antidiabetic agent pioglitazone in Barrett's adenocarcinoma cells in vitro and in vivo.

RESULTS

PPARgamma mRNA and protein were overexpressed in endoscopic biopsies of Barrett's epithelium and the human Barrett's adenocarcinoma cancer cell line OE33 as compared to normal esophagus and stomach and the esophageal squamous epithelium cancer cell line Kyse-180. PPARgamma activation by pioglitazone in OE33 cells in vitro led to reduced cell growth by induction of apoptosis. Effects of systemic PPARgamma activation by the thiazolidinedione pioglitazone on tumor cell proliferation and apoptosis were then assessed in vivo in nude mice bearing transplantable Barrett's adenocarcinomas derived from OE33 cells. Unexpectedly, enhanced growth of OE33 derived transplantable adenocarcinomas was observed in Balb/c nu/nu mice upon systemic pioglitazone treatment due to increased cell proliferation.

CONCLUSION

These results indicate that PPARgamma is involved in the molecular pathogenesis of Barrett's adenocarcinoma formation and growth. However, activation of PPARgamma exerts differential effects on growth of Barrett's adenocarcinoma cells in vitro and in vivo emphasizing the importance of additional cell context specific factors and systemic metabolic status for the modulation of PPARgamma action in vivo.

In vivo effects of rosiglitazone in a human neuroblastoma xenograft

BACKGROUND

Neuroblastoma (NB) is the most common extra-cranial solid tumour in infants. Unfortunately, most children present with advanced disease and have a poor prognosis. There is in vitro evidence that the peroxisome proliferator-activated receptor gamma (PPARgamma) might be a target for pharmacological intervention in NB. We have previously demonstrated that the PPARgamma agonist rosiglitazone (RGZ) exerts strong anti-tumoural effects in the human NB cell line, SK-N-AS. The aim of this study was to evaluate whether RGZ maintains its anti-tumoural effects against SK-N-AS NB cells in vivo.

METHODS AND RESULTS

For this purpose, tumour cells were subcutaneously implanted in nude mice, and RGZ (150 mg kg(-1)) was administered by gavage daily for 4 weeks. At the end of treatment, a significant tumour weight inhibition (70%) was observed in RGZ-treated mice compared with control mice. The inhibition of tumour growth was supported by a strong anti-angiogenic activity, as assessed by CD-31 immunostaining in tumour samples. The number of apoptotic cells, as determined by cleaved caspase-3 immunostaining, seemed lower in RGZ-treated animals at the end of the treatment period than in control mice, likely because of the large tumour size observed in the latter group.

CONCLUSIONS

To our knowledge, this is the first demonstration that RGZ effectively inhibits tumour growth in a human NB xenograft and our results suggest that PPARgamma agonists may have a role in anti-tumoural strategies against NB.

Drug efficacy testing in mice

The traditional path of drug development passes from in vitro screening and response assessment to validation of drug efficacy in cell line xenografts. While xenografts have their merits, historically, more often than not, they have not served as an accurate predictor of drug efficacy in humans. The refinement and increased availability of genetically engineered mouse models (GEMMs) of cancer has made GEMMs an attractive avenue for the preclinical testing of therapeutic agents. The histopathologic and genetic resemblance of GEMMs to human cancer are an important measure to evaluate their suitability for pre-clinical studies and a number of studies using kinase inhibitors have now been performed in GEMMs. We have highlighted several of the salient advantages and challenges associated with GEMM studies. Well-characterized GEM models of human cancer should aide in the prioritization of both established and novel therapeutics.

KLF4-dependent, PPARgamma-induced expression of GPA33 in colon cancer cell lines

The glycoprotein A33 (GPA33) is a colon cancer antigen. Phase I trials with 131I and 125I monoclonal antibody A33 in colon carcinoma patients showed excellent localization to colorectal cancer and some evidence of tumor response. Using DNA microarrays, we have identified the GPA33 gene as a target of PPARgamma in HT29-Cl.16E colon cancer cells. Treatment of HT29-Cl.16E, Caco2, SW1116 and LS174T colon cancer cells with the PPARgamma agonist GW7845 induced a 2- to 6-fold increase in GPA33 mRNA as determined by real-time PCR. This induction was also found in HT29-Cl.16E cells treated with rosiglitazone and ciglitazone and was prevented by cotreatment with the PPARgamma antagonist GW9662, indicating that this regulation was PPARgamma dependent. No canonical PPAR responsive element was found in the GPA33 promoter. We therefore analyzed the expression of transcription factors involved in GPA33 expression. CDXl, CDX2 and KLF5 expression was not modified by PPARgamma activation. By contrast, a significant increase in KLF4 was seen, both at mRNA and protein levels. Furthermore, chromatin immunoprecipitation studies demonstrated that an increased amount of KLF4 protein was bound to the GPA33 promoter in cells treated with rosiglitazone. Finally, downregulation of KLF4 expression by siRNA reduced rosiglitazone-induced GPA33 expression. This indicates that PPARgamma activation induces KLF4 expression, which in turn increases GPA33 expression. We also demonstrate that PPARgamma activation leads to increased (p21WAF1/Cip1 and keratin 19) or decreased (cyclin D1) expression of known KLF4 targets, suggesting that KLF4 is a nodal player in a network of PPARgamma-regulated genes.

Troglitazone reverses the multiple drug resistance phenotype in cancer cells

A major problem in treating cancer is the development of drug resistance. We previously demonstrated doxorubicin (DOX) resistance in K562 human leukemia cells that was associated with upregulation of glyoxalase 1 (GLO-1) and histone H3 expression. The thiazolidinedione troglitazone (TRG) downregulated GLO-1 expression and further upregulated histone H3 expression and post-translational modifications in these cells, leading to a regained sensitivity to DOX. Given the pleiotropic effects of epigenetic changes in cancer development, we hypothesized that TRG may downregulate the multiple drug resistance (MDR) phenotype in a variety of cancer cells. To test this, MCF7 human breast cancer cells and K562 cells were cultured in the presence of low-dose DOX to establish DOX-resistant cell lines (K562/DOX and MCF7/DOX). The MDR phenotype was confirmed by Western blot analysis of the 170 kDa P-glycoprotein (Pgp) drug efflux pump multiple drug resistance protein 1 (MDR-1), and the breast cancer resistance protein (BCRP). TRG markedly decreased expression of both MDR-1 and BCRP in these cells, resulting in sensitivity to DOX. Silencing of MDR-1 expression also sensitized MCF7/DOX cells to DOX. Use of the specific and irreversible peroxisome proliferator-activated receptor gamma (PPARγ) inhibitor GW9662 in the nanomolar range not only demonstrated that the action of TRG on MCF/DOX was PPARγ-independent, but indicated that PPARγ may play a role in the MDR phenotype, which is antagonized by TRG. We conclude that TRG is potentially a useful adjunct therapy in chemoresistant cancers.

Targeted drugs in metastatic colorectal cancer with special emphasis on guidelines for the use of bevacizumab and cetuximab: an Acta Oncologica expert report

From having been a 'single-drug not very interesting cancer type' from a medical treatment perspective, treatment of colorectal cancer (CRC) has during the past five years become a more complex issue of the appropriate use of several cytotoxic drugs sometimes integrated with advanced metastatic surgery with curative intent. The new drugs have provided significant benefit to the patients, so far mostly in the metastatic setting but also in adjuvant treatment. The significant progress in molecular and tumour biology has produced a great number of new 'targeted' drugs that are now in various stages of clinical development. Two of these drugs, the monoclonal antibodies bevacizumab (Avastin) and cetuximab (Erbitux), directed against VEGF and EGFR, respectively, have recently been approved within the EU for use in metastatic CRC. This Nordic Expert Consensus Report summarizes the current status of chemotherapy in metastatic CRC, overviews the clinical status of targeted drugs in CRC and, finally, provides guidelines for the routine clinical use of bevacizumab and cetuximab based on the most recently available clinical data.

Rosiglitazone reduces cell invasiveness by inducing MKP-1 in human U87MG glioma cells

We sought to investigate the molecular mechanisms by which rosiglitazone (RGZ) inhibits cell invasion in human glioma cells. In this study, we found that RGZ attenuated MMP-2 protein levels, MMP-2 gelatinolytic activity, and cell invasiveness through a PPAR-gamma independent pathway. RGZ increased mitogen activated protein kinase phosphatase-1 (MKP-1) expression. The addition of triptolide (a diterpenoid triepoxide, which blocked MKP-1 induction) abolished the inhibitory effects by RGZ. Furthermore, we demonstrated that the knock down of MKP-1 by MKP-1 specific small interference RNA reversed the reduction of MMP-2 secretion, and of cell invasiveness by RGZ. In contrast, the stable expression of MKP-1 in glioma cell lines decreased MMP-2 activity and cell invasiveness. These results suggest that RGZ may mediate the inhibitory effects through MKP-1 induction. Thus, MKP-1 could be a potential target in glioma therapy.

Peroxisome proliferator-activated receptor gamma agonist pioglitazone prevents the hyperglycemia caused by phosphatidylinositol 3-kinase pathway inhibition by PX-866 without affecting antitumor activity

The phosphatidylinositol 3-kinase (PI3K)/Akt signaling cascade is an important component of the insulin signaling in normal tissues leading to glucose uptake and homeostasis and for cell survival signaling in cancer cells. Hyperglycemia is an on-target side effect of many inhibitors of PI3K/Akt signaling including the specific PI3K inhibitor PX-866. The peroxisome proliferator-activated receptor gamma agonist pioglitazone, used to treat type 2 diabetes, prevents a decrease in glucose tolerance caused by acute administration of PX-866. Our studies have shown that pioglitazone does not inhibit the antitumor activity of PX-866 in A-549 non-small cell lung cancer and HT-29 colon cancer xenografts. In vitro studies also showed that pioglitazone increases 2-[1-(14)C]deoxy-D-glucose uptake in L-6 muscle cells and prevents inhibition of 2-deoxyglucose uptake by PX-866. Neither pioglitazone nor PX-866 had an effect on 2-deoxyglucose uptake in A-549 lung cancer cells. In vivo imaging studies using [18F]2-deoxyglucose (FDG) positron emission tomography showed that pioglitazone increases FDG accumulation by normal tissue but does not significantly alter FDG uptake by A-549 xenografts. Thus, peroxisome proliferator-activated receptor gamma agonists may be useful in overcoming the increase in blood glucose caused by inhibitors of PI3K signaling by preventing the inhibition of normal tissue insulin-mediated glucose uptake without affecting antitumor activity.

Clinical Use of PPARgamma Ligands in Cancer

The role of PPARγ in adipocyte differentiation has fueled intense interest in the function of this steroid nuclear receptor for regulation of malignant cell growth and differentiation. Given the antiproliferative and differentiating effects of PPARγ ligands on liposarcoma cells, investigation of PPARγ expression and ligand activation in other solid tumors such as breast, colon, and prostate cancers ensued. The anticancer effects of PPARγ ligands in cell culture and rodent models of a multitude of tumor types suggest broad applicability of these agents to cancer therapy. This review focuses on the clinical use of PPARγ ligands, specifically the thiazolidinediones, for the treatment and prevention of cancer.

The prince and the pauper. A tale of anticancer targeted agents

Cancer rates are set to increase at an alarming rate, from 10 million new cases globally in 2000 to 15 million in 2020. Regarding the pharmacological treatment of cancer, we currently are in the interphase of two treatment eras. The so-called pregenomic therapy which names the traditional cancer drugs, mainly cytotoxic drug types, and post-genomic era-type drugs referring to rationally-based designed. Although there are successful examples of this newer drug discovery approach, most target-specific agents only provide small gains in symptom control and/or survival, whereas others have consistently failed in the clinical testing. There is however, a characteristic shared by these agents: -their high cost-. This is expected as drug discovery and development is generally carried out within the commercial rather than the academic realm. Given the extraordinarily high therapeutic drug discovery-associated costs and risks, it is highly unlikely that any single public-sector research group will see a novel chemical "probe" become a "drug". An alternative drug development strategy is the exploitation of established drugs that have already been approved for treatment of non-cancerous diseases and whose cancer target has already been discovered. This strategy is also denominated drug repositioning, drug repurposing, or indication switch. Although traditionally development of these drugs was unlikely to be pursued by Big Pharma due to their limited commercial value, biopharmaceutical companies attempting to increase productivity at present are pursuing drug repositioning. More and more companies are scanning the existing pharmacopoeia for repositioning candidates, and the number of repositioning success stories is increasing. Here we provide noteworthy examples of known drugs whose potential anticancer activities have been highlighted, to encourage further research on these known drugs as a means to foster their translation into clinical trials utilizing the more limited public-sector resources. If these drug types eventually result in being effective, it follows that they could be much more affordable for patients with cancer; therefore, their contribution in terms of reducing cancer mortality at the global level would be greater.

Regression of drug-resistant lung cancer by the combination of rosiglitazone and carboplatin

PURPOSE

Current therapy for lung cancer involves multimodality therapies. However, many patients are either refractory to therapy or develop drug resistance. KRAS and epidermal growth factor receptor (EGFR) mutations represent some of the most common mutations in lung cancer, and many studies have shown the importance of these mutations in both carcinogenesis and chemoresistance. Genetically engineered murine models of mutant EGFR and KRAS have been developed that more accurately recapitulate human lung cancer. Recently, using cell-based experiments, we showed that platinum-based drugs and the antidiabetic drug rosiglitazone (PPARgamma ligand) interact synergistically to reduce cancer cell and tumor growth. Here, we directly determined the efficacy of the PPARgamma/carboplatin combination in these more relevant models of drug resistant non-small cell lung cancer.

EXPERIMENTAL DESIGN

Tumorigenesis was induced by activation of either mutant KRAS or EGFR. Mice then received either rosiglitazone or carboplatin monotherapy, or a combination of both drugs. Change in tumor burden, pathology, and evidence of apoptosis and cell growth were assessed.

RESULTS

Tumor burden remained unchanged or increased in the mice after monotherapy with either rosiglitazone or carboplatin. In striking contrast, we observed significant tumor shrinkage in mice treated with these drugs in combination. Immunohistochemical analyses showed that this synergy was mediated via both increased apoptosis and decreased proliferation. Importantly, this synergy between carboplatin and rosiglitazone did not increase systemic toxicity.

CONCLUSIONS

These data show that the PPARgamma ligand/carboplatin combination is a new therapy worthy of clinical investigation in lung cancers, including those cancers that show primary resistance to platinum therapy or acquired resistance to targeted therapy.

Inhibition of peroxisome proliferator-activated receptor gamma activity suppresses pancreatic cancer cell motility

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor that has been implicated in the carcinogenesis and progression of various solid tumors, including pancreatic carcinomas. We aimed to clarify the role of this receptor in pancreatic cell motility in vitro and in metastasis in vivo. Cell motility was examined by assaying transwell migration and wound filling in Capan-1 and Panc-1 pancreatic cancer cells, with or without the PPARgamma-specific inhibitor T0070907. A severe combined immunodeficiency xenograft metastasis model was used to examine the in vivo effect of PPARgamma inhibition on pancreatic cancer metastasis. In both transwell-migration and wound-filling assays, inhibition of PPARgamma activity suppressed pancreatic cell motility without affecting in vitro cell proliferation. Inhibition of PPARgamma also suppressed liver metastasis in vivo in metastatic mice. In PPARgamma-inhibited cells, p120 catenin accumulation was induced predominantly in cell membranes, and the Ras-homologous GTPases Rac1 and Cdc42 were inactive. Inhibition of PPARgamma in pancreatic cancer cells decreased cell motility by altering p120ctn localization and by suppressing the activity of the Ras-homologous GTPases Rac1 and Cdc42. Based on these findings, PPARgamma could function as a novel target for the therapeutic control of cancer cell invasion or metastasis.

The high affinity peroxisome proliferator-activated receptor-gamma agonist RS5444 inhibits both initiation and progression of colon tumors in azoxymethane-treated mice

We evaluated RS5444, a thiazolidinedione high affinity PPARgamma agonist, for the ability to inhibit colon carcinogenesis in azoxymethane (AOM)-treated mice. In our initial experiment, mice were treated with RS5444 during AOM treatment, and the drug was withdrawn 12 weeks after the last injection of AOM. RS5444 significantly inhibited aberrant crypt focus formation under these circumstances. Furthermore, exposure to RS5444 during the course of AOM treatment effectively blocked colon tumor formation after withdrawal of the agonist. PPARgamma expression and nuclear localization were reduced in adenomas. RS5444 did not inhibit DNA synthesis in tumor cells, suggesting that PPARgamma activity was impaired in adenomas. To test this hypothesis, pre-existing adenomas were treated with RS5444 for 16 weeks. We observed a slight, albeit not statistically significant, reduction in tumor incidence in RS5444-treated mice. However, histological examination revealed that tumors from RS5444-treated mice were of significantly lower grade, as evaluated by the extent of dysplasia. Furthermore, carcinoma in situ was observed in about one-third of control tumors, but was never observed in RS5444-treated tumors. We conclude that RS5444 inhibits both initiation and progression of colon tumors in the AOM model of sporadic colon carcinogenesis.

Rosiglitazone and risk of cancer: a meta-analysis of randomized clinical trials

OBJECTIVE

Despite experimental data suggesting a protective effect of peroxisome proliferator-activated receptor-gamma agonists with respect to malignancies, results of available epidemiological studies on the incidence of cancer in rosiglitazone-treated patients are not univocal. The aim of this meta-analysis of randomized clinical trials is to assess the effect of rosiglitazone on the incidence of cancer.

RESEARCH DESIGN AND METHODS

Randomized clinical trials of rosiglitazone with duration of >24 weeks were retrieved through Medline and from the GlaxoSmithKline Web site, which reports main results of all trials sponsored by GlaxoSmithKline; incident malignancies were retrieved from the summary of serious adverse events. Proportions of outcome measures across treatment groups were compared by odds ratios (ORs) and 95% CI. Considering differences in the duration of follow-up among treatment arms in some of the trials, we also calculated the incidence of cancer in rosiglitazone and control groups.

RESULTS

Eighty trials, enrolling 16,332 and 12,522 patients in the rosiglitazone and comparator groups, respectively, were retrieved. Rosiglitazone was not associated with a significant modification of the risk of cancer (OR 0.91 [95% CI 0.71-1.16], P = 0.44). The incidence of malignancies was significantly lower in rosiglitazone-treated patients than in control groups (0.23 [0.19-0.26] vs. 0.44 [0.34-0.58] cases/100 patient-years; P < 0.05).

CONCLUSIONS

The use of rosiglitazone appears to be safe in terms of incidence of cancer, whereas its possible protective effect needs to be further investigated.

Immunostaining for peroxisome proliferator gamma distinguishes dedifferentiated liposarcoma from other retroperitoneal sarcomas

Dedifferentiated liposarcoma can be readily diagnosed by the juxtaposition of a well-differentiated liposarcoma to a nonlipogenic sarcoma. However, if the lipogenic component is not abundant due to surgical sampling or small biopsy, dedifferentiated liposarcoma can be difficult to distinguish from other poorly different sarcomas. Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is a nuclear hormone receptor that plays a critical role in adipocyte differentiation. Prior studies have not only demonstrated PPAR-gamma mRNA in various subtypes of liposarcoma but have also shown that adipocyte differentiation can be induced in some liposarcomas by a PPAR-gamma agonist. In the present study, we investigated whether immunostaining for PPAR-gamma can be used to distinguish dedifferentiated liposarcoma from other retroperitoneal sarcomas. We examined a series of 40 dedifferentiated liposarcoma and compared the staining for PPAR-gamma to a series of 24 retroperitoneal sarcomas that lacked lipogenic differentiation. A monoclonal antibody against PPAR-gamma was used to stain formalin-fixed paraffin-embedded tissue. Specific nuclear immunostaining was present in 37/40 (93%) of the dedifferentiated liposarcoma and 6/24 (25%) of the other sarcomas (two leiomyosarcomas and four undifferentiated sarcomas). Interestingly, immunostaining for CDK4 and/or MDM2 was identified in three of the four PPAR-gamma-positive undifferentiated sarcomas, raising the possibility that these may represent dedifferentiated liposarcoma. This is the first study demonstrating the utility of PPAR-gamma immunohistochemistry in the diagnosis of dedifferentiated liposarcoma in tissue sections. Although not completely specific, the presence of PPAR-gamma staining, in combination with histologic findings and other markers, can aid in the diagnosis of dedifferentiated liposarcoma, particularly on small biopsies that may not sample the well-differentiated component.

[Nuclear receptor PPAR and hepatology: pathophysiological and therapeutical aspects]

In last few years, the topic of nuclear receptor has been developed in the field of hepatology allowing envisaging therapeutic strategies for the most frequent chronic liver diseases. Peroxysome proliferator-activated receptors (PPAR) contribute to wide physiological processes within the liver such as lipid/glucid metabolisms, inflammatory response, cell differenciation and cell cycle. In vitro experiments and animal studies showed that PPARalpha discloses anti-inflammatory property and PPARgamma discloses anti-inflammatory, antifibrogenic and antiproliferative properties in the liver. Main available agonists are fibrates (PPARalpha) used for 20 years in cases of lipid metabolism abnormalities and glitazones (PPARgamma) used since 2000 for type 2 diabetes. In terms of therapy, animal studies and human trials have been conducted in steatopathies. However, clinicians have to be aware of potential specific side effects related to glitazones especially on cardiovascular system.

Peroxisome proliferator activated receptor gamma and oxidized docosahexaenoic acids as new class of ligand

PPARgamma regulates the expression of numerous genes. In addition to their anti-diabetic activity, PPARgamma agonists have been reported to have beneficial effects for cancer, inflammation including inflammatory bowel disease, atherosclerosis and brain inflammation, as well as bone turnover. To investigate a potential new class of ligands for PPARgamma, we designed with reference to the crystal structure of the ligand-binding domain of PPARgamma oxidized docosahexaenoic acid (DHA) derivatives, which have a hydrophilic substituent at the C(4)-position and are putative metabolites of DHA. We synthesized 14 compounds and evaluated their activities in vitro. We found that these DHA derivatives show PPARgamma transactivation higher than, or comparable to, that of pioglitazone, which is a thiazolidinedione derivative used as an antidiabetic agent. Furthermore, one of them showed anti-diabetic activity in animal models. In this paper, we review the potential of PPARgamma as a drug target and oxidized DHA as a new class of ligand for PPARgamma.

Synergistic Effects of PPARgamma Ligands and Retinoids in Cancer Treatment

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily. The activation of PPARs by their specific ligands is regarded as one of the promising strategies to inhibit cancer cell growth. However, recent clinical trials targeting several common cancers showed no beneficial effect when PPAR ligands are used as a monotherapy. Retinoid X receptors (RXRs), which play a critical role in normal cell proliferation as a master regulator for nuclear receptors, preferentially form heterodimers with PPARs. A malfunction of RXRalpha due to phosphorylation by the Ras/MAPK signaling pathway is associated with the development of certain types of human malignancies. The activation of PPARgamma/RXR heterodimer by their respective ligands synergistically inhibits cell growth, while inducing apoptosis in human colon cancer cells when the phosphorylation of RXRalpha was inhibited. We herein review the synergistic antitumor effects produced by the combination of the PPAR, especially PPARgamma, ligands plus other agents, especially retinoids, in a variety of human cancers. We also focus on the phosphorylation of RXRalpha because the inhibition of RXRalpha phosphorylation and the restoration of its physiological function may activate PPAR/RXR heterodimer and, therefore, be a potentially effective and critical strategy for the inhibition of cancer cell growth.

The non-genomic crosstalk between PPAR-gamma ligands and ERK1/2 in cancer cell lines

Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor superfamily acting as transcription factors. PPAR-gamma, one of the three PPAR subtypes, is expressed in many malignant and non-malignant cells and tissues. PPAR-gamma ligands influence cancer biology via both genomic as well as non-genomic events. The non-genomic action of PPAR-gamma ligands, including the activation of MAPK signaling pathways, is under intense investigation. In the presence of PPAR-gamma ligands, a rapid phosphorylation of ERK1/2 is observed in many cancer cell lines. Activated ERK1/2 elicits rapid, non-genomic cellular effects and can directly repress PPAR-gamma transcriptional activity by phosphorylation. This paper reviews the interrelation of PPAR-gamma ligands and activated ERK1/2, in relation to their antineoplastic actions in cancer cell lines, which may offer the potential for improved anticancer therapies.

Functional genomic analysis reveals cross-talk between peroxisome proliferator-activated receptor gamma and calcium signaling in human colorectal cancer cells

Activation of PPARgamma in MOSER cells inhibits anchorage-dependent and anchorage-independent growth and invasion through Matrigel-coated transwell membranes. We carried out a longitudinal two-class microarray analysis in which mRNA abundance was measured as a function of time in cells treated with a thiazolidinedione PPARgamma agonist or vehicle. A statistical machine learning algorithm that employs an empirical Bayesian implementation of the multivariate HotellingT2 score was used to identify differentially regulated genes. HotellingT2 scores, MB statistics, and maximum median differences were used as figures of merit to interrogate genomic ontology of these targets. Three major cohorts of genes were regulated: those involved in metabolism, DNA replication, and migration/motility, reflecting the cellular phenotype that attends activation of PPARgamma. The bioinformatic analysis also inferred that PPARgamma regulates calcium signaling. This response was unanticipated, because calcium signaling has not previously been associated with PPARgamma activation. Ingenuity pathway analysis inferred that the nodal point in this cross-talk was Down syndrome critical region 1 (DSCR1). DSCR1 is an endogenous calcineurin inhibitor that blocks dephosphorylation and activation of members of the cytoplasmic component of nuclear factor of activated T cells transcription factors. Lentiviral short hairpin RNA-mediated knockdown of DSCR1 blocks PPARgamma inhibition of proliferation and invasion, indicating that DSCR1 is required for suppression of transformed properties of early stage colorectal cancer cells by PPARgamma. These data reveal a novel, heretofore unappreciated link between PPARgamma and calcium signaling and indicate that DSCR1, which has previously been thought to function by suppression of the angiogenic response in endothelial cells, may also play a direct role in transformation of epithelial cells.

Present concepts and future outlook: function of peroxisome proliferator-activated receptors (PPARs) for pathogenesis, progression, and therapy of cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily of transcriptional regulators that regulate lipid, glucose, and amino acid metabolism. In recent studies it also has been shown that these receptors are implicated in tumor progression, cellular differentiation, and apoptosis and modulation of their function is therefore considered as a potential target for cancer prevention and treatment. PPAR ligands and other agents influencing PPAR signalling pathways have been shown to reveal chemopreventive potential by mediating tumor suppressive activities in a variety of human cancers and could represent a potential novel strategy to inhibit tumor carcinogenesis and progression. This review summarizes the currently available data on the roles of PPARs in relation to the processes of cell differentiation and carcinogenesis as well as their role as promising future therapeutic targets.

Thiazolidinediones and the risk of lung, prostate, and colon cancer in patients with diabetes

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPARgamma) mediates cell cycle arrest and adipocyte differentiation; has tumor suppressor activity in liposarcoma, lung, and prostate cancers; and suppresses colonic polyp formation in adenomatous polyposis coli (APC)min/+ mice. To assess the influence of thiazolidinediones (TZDs), which are PPAR ligands used to treat diabetes mellitus, a retrospective analysis of a database from 10 Veteran Affairs medical centers was conducted.

PATIENTS AND METHODS

Data on male patients 40 years and older diagnosed to have diabetes mellitus between 1997 and 2003 were obtained from the Veterans Integrated Services Network 16 (VISN 16) data warehouse. Subsequent diagnoses of colorectal, lung, and prostate cancer and use of TZD, other antidiabetic agents, and insulin were identified. Cox regression with time-dependent covariates was used to estimate the association between TZD use and cancer risk. Relative risks were adjusted for confounders (age, race/ethnicity, body mass index, use of insulin, and other oral antidiabetic agents).

RESULTS

Of 87,678 individuals, 1,137 had colorectal cancer, 3,246 had prostate cancer, and 1,371 had lung cancer. We observed a 33% reduction in lung cancer risk among TZD users compared with nonusers after adjusting for confounder interactions (relative risk, 0.67; 95% CI, 0.51 to 0.87). The risk reduction for colorectal and prostate cancers did not reach statistical significance.

CONCLUSION

TZD use was associated with reduced risk of lung cancer. Further studies are warranted to confirm our findings.

Synergy between PPARgamma ligands and platinum-based drugs in cancer

PPARgamma is a member of the nuclear receptor family for which agonist ligands have antigrowth effects. However, clinical studies using PPARgamma ligands as a monotherapy failed to show a beneficial effect. Here we have studied the effects of PPARgamma activation with chemotherapeutic agents in current use for specific cancers. We observed a striking synergy between rosiglitazone and platinum-based drugs in several different cancers both in vitro and using transplantable and chemically induced "spontaneous" tumor models. The effect appears to be due in part to PPARgamma-mediated downregulation of metallothioneins, proteins that have been shown to be involved in resistance to platinum-based therapy. These data strongly suggest combining PPARgamma agonists and platinum-based drugs for the treatment of certain human cancers.

Pilot study of rosiglitazone therapy in women with breast cancer: effects of short-term therapy on tumor tissue and serum markers

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a steroid nuclear receptor that is activated by natural compounds such as specific fatty acids and synthetic drugs such as thiazolidinedione antidiabetic agents. Expressed in normal and malignant mammary epithelial cells, activation of PPARgamma is associated with antiproliferative effects on human breast cancer cells in preclinical studies. The purpose of this study was to test the hypothesis that PPARgamma ligand therapy might inhibit tumor growth and progression in human breast cancer.

EXPERIMENTAL DESIGN

We conducted a pilot trial of short-term (2-6 weeks) treatment with the thiazolidinedione rosiglitazone in 38 women with early-stage (T(is)-T(2), N(0-1), M(0)) breast cancer, administered between the time of diagnostic biopsy and definitive surgery.

RESULTS

Short-term treatment with rosiglitazone (8 mg/d) did not elicit significant effects on breast tumor cell proliferation using Ki67 expression as a measure of cell proliferation and surrogate marker of tumor growth and progression. In pretreatment tumors notable for nuclear expression of PPARgamma by immunohistochemistry, down-regulation of nuclear PPARgamma expression occurred following rosiglitazone administration (P = 0.005). No PPARG mutations were identified, and the incidence of P12A and H446H polymorphisms did not differ relative to U.S. controls (P = 0.5). Treatment with rosiglitazone resulted in increased serum adiponectin (P < 0.001), decreased insulin levels (P = 0.005), and increased insulin sensitivity (P = 0.004). Rosiglitazone was well tolerated without serious adverse events.

CONCLUSION

Our data indicate that short-term rosiglitazone therapy in early-stage breast cancer patients leads to local and systemic effects on PPARgamma signaling that may be relevant to breast cancer.

PPARgamma inhibitors reduce tubulin protein levels by a PPARgamma, PPARdelta and proteasome-independent mechanism, resulting in cell cycle arrest, apoptosis and reduced metastasis of colorectal carcinoma cells

The nuclear transcription factor peroxisome proliferator-activated receptor-gamma (PPARgamma) has been identified as an important therapeutic target in murine models of colorectal cancer (CRC). To examine whether PPARgamma inhibition has therapeutic effects in late-stage CRC, the effects of PPARgamma inhibitors on CRC cell survival were examined in CRC cell lines and a murine CRC model. Low doses (0.1-1 microM) of PPARgamma inhibitors (T0070907, GW9662 and BADGE) did not affect cell survival, while higher doses (10-100 microM) of all 3 PPARgamma inhibitors caused caspase-dependent apoptosis in HT-29, Caco-2 and LoVo CRC cell lines. Apoptosis was preceded by altered cell morphology, and this alteration was not prevented by caspase inhibition. PPARgamma inhibitors also caused dual G and M cell cycle arrest, which was not required for apoptosis or for morphologic alterations. Furthermore, PPARgamma inhibitors triggered loss of the microtubule network. Notably, unlike other standard antimicrotubule agents, PPARgamma inhibitors caused microtubule loss by regulating tubulin post-transcriptionally rather than by altering microtubule polymerization or dynamics. Proteasome inhibition by epoxomicin was unable to prevent tubulin loss. siRNA-mediated reduction of PPARgamma and PPARdelta proteins did not replicate the effects of PPARgamma inhibitors or interfere with the inhibitors' effects on apoptosis, cell cycle or tubulin. PPARgamma inhibitors also reduced CRC cell migration and invasion in assays in vitro and reduced both the number and size of metastases in a HT-29/SCID xenograft metastatic model of CRC. These results suggest that PPARgamma inhibitors are a novel potential antimicrotubule therapy for CRC that acts by directly reducing microtubule precursors.

Antineoplastic effects of rosiglitazone and PPARgamma transactivation in neuroblastoma cells

Neuroblastoma (NB) is the most common extracranial solid tumour in infants. Unfortunately, most children present with advanced disease and have a poor prognosis. In the present study, we evaluated the role of the peroxisome proliferator-activated receptor γ (PPARγ) agonist rosiglitazone (RGZ) in two NB cell lines (SK-N-AS and SH-SY5Y), which express PPARγ. Rosiglitazone decreased cell proliferation and viability to a greater extent in SK-N-AS than in SH-SY5Y. Furthermore, 20 μM RGZ significantly inhibited cell adhesion, invasiveness and apoptosis in SK-N-AS, but not in SH-SY5Y. Because of the different response of SK-N-AS and SH-SY5Y cells to RGZ, the function of PPARγ as a transcriptional activator was assessed. Noticeably, transient transcription experiments with a PPARγ responsive element showed that RGZ induced a three-fold increase of the reporter activity in SK-N-AS, whereas no effect was observed in SH-SY5Y. The different PPARγ activity may be likely due to the markedly lower amount of phopshorylated (i.e. inactive) protein observed in SK-N-AS. To our knowledge, this is the first demonstration that the differential response of NB cells to RGZ may be related to differences in PPARγ transactivation. This finding indicates that PPARγ activity may be useful to select those patients, for whom PPARγ agonists may have a beneficial therapeutic effect.

Inhibition of peroxisome proliferator-activated receptor gamma activity in esophageal carcinoma cells results in a drastic decrease of invasive properties

Esophageal cancer is difficult to treat because of its rapid progression, and more effective therapeutic approaches are needed. The PPARgamma is a nuclear receptor superfamily member that is expressed in many cancers. PPARgamma expression is a feature of esophageal cancer cell lines, and in the present investigation, the PPARgamma antagonists T0070907 and GW9662 could induce loss of invasion but could not induce growth reduction or apoptosis at low concentrations (< 10 mM). A high concentration of antagonists (50 microM) inhibited cell growth and induced apoptosis, but these effects did not explain our result at the low concentration. Morphological change, decreased expression of the cell signaling pathway and inhibition of cancer cell invasion were observed in the low concentration. This suggested that PPARgamma antagonists inhibited esophageal cancer cell invasion as well as cell adherence, most likely due to alteration in the FAK-MAPK pathway, and this was independent of apoptosis. These results suggested that PPARgamma plays an important role in cancer cell invasion and that it might be a novel target for therapy of esophageal cancer.

The mighty mouse: genetically engineered mouse models in cancer drug development

Deficiencies in the standard preclinical methods for evaluating potential anticancer drugs,such as xenograft mouse models, have been highlighted as a key obstacle in the translation of the major advances in basic cancer research into meaningful clinical benefits. In this article, we discuss the established uses and limitations of xenograft mouse models for cancer drug development, and then describe the opportunities and challenges in the application of novel genetically engineered mouse models that more faithfully mimic the genetic and biological evolution of human cancers. Greater use of such models in target validation, assessment of tumour response, investigation of pharmacodynamic markers of drug action, modelling resistance and understanding toxicity has the potential to markedly improve the success of cancer drug development.

Expression of peroxisome proliferator activated receptor gamma and cyclo-oxygenase 2 in primary and recurrent ovarian carcinoma

AIM

Peroxisome proliferator-activated receptor gamma (PPARgamma) has emerged as a potential therapeutic target in several types of cancer. In ovarian carcinomas, limited and conflicting data on PPARgamma protein expression have been reported.

METHODS

The immunoexpression of PPARgamma and its putative target cyclo-oxygenase 2 (COX2) was investigated in tumour tissues from 80 patients with primary and corresponding recurrent ovarian serous carcinomas after conventional platinum-based chemotherapy.

RESULTS

PPARgamma expression was observed in 29% of primary and recurrent carcinomas. In the recurrent tumours, PPARgamma expression inversely correlated with COX2 overexpression in both chemosensitive (p = 0.02) and chemoresistant (p = 0.04) carcinomas.

CONCLUSIONS

The data indicate that PPARgamma may represent a potential target for second-line treatment in ovarian cancers.