Expression of peroxisome proliferator-activated receptor (PPAR)gamma in gastric cancer and inhibitory effects of PPARgamma agonists

PPAR γ Networks in Cell Signaling: Update and Impact of Cyclic Phosphatidic Acid

Lysophospholipid (LPL) has long been recognized as a membrane phospholipid metabolite. Recently, however, the LPL has emerged as a candidate for diagnostic and pharmacological interest. LPLs include lysophosphatidic acid (LPA), alkyl glycerol phosphate (AGP), cyclic phosphatidic acid (cPA), and sphingosine-1-phosphate (S1P). These biologically active lipid mediators serve to promote a variety of responses that include cell proliferation, migration, and survival. These LPL-related responses are mediated by cell surface G-protein-coupled receptors and also intracellular receptor peroxisome proliferator-activated receptor gamma (PPARγ). In this paper, we focus mainly on the most recent findings regarding the biological function of nuclear receptor-mediated lysophospholipid signaling in mammalian systems, specifically as they relate to health and diseases. Also, we will briefly review the biology of PPARγ and then provide an update of lysophospholipids PPARγ ligands that are under investigation as a therapeutic compound and which are targets of PPARγ relevant to diseases.

Tumor apoptosis in prostate cancer by PGD(2) and its metabolite 15d-PGJ(2) in murine model

Fifteen-deoxy-Δ(12,14)-PGJ(2) (15d-PGJ(2)) is one of non-enzymatically converted metabolite from prostaglandin D(2) (PGD(2)). Anti-tumor effects of 15d-PGJ(2) in various tumors are partially known, but the detail of in vivo mechanisms of action is still unclear. In this study, we investigated the effects of 15d-PGJ(2) and PGD(2) on murine prostate cancer in vitro and in vivo. Murine prostate cancer cells RM9 were transfected with murine prostaglandin D(2) synthase (mPGDS) gene by using defective retrovirus vector, designated as RM9-mPGDS. In addition, RM9 was also transfected with only defective retrovirus vector, designated as RM9-EV and used as control in this study. The expression and production of the gene were confirmed by RT-PCR and ELISA, respectively. For in vivo study, RM9-mPGDS was injected into the back of C57BL/6 mice, then resulted tumor was used for pathological analysis 14days after the inoculation. Tumor cell apoptosis in the tissue was detected by TUNEL staining. Retrovirally transfected mPGDS in RM9 significantly induced apoptosis in vivo but not in vitro, by TUNEL staining and cell death ELISA, respectively. Our results strongly suggested that the apoptosis induced in RM9-mPGDS in vivo was probably achieved in tumor environment such as hypoxic condition. The introduction of PGDS gene into cancer cells might be a novel therapy against cancer.

Targeting PPARγ Signaling Cascade for the Prevention and Treatment of Prostate Cancer

The peroxisome proliferator-activated receptor-gamma (PPARγ) is a member of the hormone-activated nuclear receptor superfamily. PPARγ can be activated by a diverse group of agents, such as endogenous polyunsaturated fatty acids, 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), and thiazolidinedione (TZD) drugs. PPARγ induces antiproliferative, antiangiogenic, and prodifferentiation pathways in several tissue types, thus making it a highly useful target for downregulation of carcinogenesis. These TZD-derived novel therapeutic agents, alone or in combination with other anticancer drugs, have translational relevance in fostering effective strategies for cancer treatment. TZDs have been proven for antitumor activity in a wide variety of experimental cancer models, both in vitro and in vivo, by affecting the cell cycle, inducing cell differentiation and apoptosis, as well as by inhibiting tumor angiogenesis. Angiogenesis inhibition mechanisms of TZDs include direct inhibition of endothelial cell proliferation and migration, as well as reduction in tumor cell vascular endothelial growth factor production. In prostate cancer, PPARγ ligands such as troglitazone and 15d-PGJ₂ have also shown to inhibit tumor growth. This paper will focus on current discoveries in PPARγ activation, targeting prostate carcinogenesis as well as the role of PPARγ as a possible anticancer therapeutic option. Here, we review PPARγ as an antitumor agent and summarize the antineoplastic effects of PPARγ agonists in prostate cancer.

A phase 1 study of efatutazone, an oral peroxisome proliferator-activated receptor gamma agonist, administered to patients with advanced malignancies

BACKGROUND

Efatutazone (CS-7017), a novel peroxisome proliferator-activated receptor gamma (PPARγ) agonist, exerts anticancer activity in preclinical models. The authors conducted a phase 1 study to determine the recommended phase 2 dose, safety, tolerability, and pharmacokinetics of efatutazone.

METHODS

Patients with advanced solid malignancies and no curative therapeutic options were enrolled to receive a given dose of efatutazone, administered orally (PO) twice daily for 6 weeks, in a 3 + 3 intercohort dose-escalation trial. After the third patient, patients with diabetes mellitus were excluded. Efatutazone dosing continued until disease progression or unacceptable toxicity, with measurement of efatutazone pharmacokinetics and plasma adiponectin levels.

RESULTS

Thirty-one patients received efatutazone at doses ranging from 0.10 to 1.15 mg PO twice daily. Dose escalation stopped when maximal impact on PPARγ-related biomarkers had been reached before any protocol-defined maximum-tolerated dose level. On the basis of a population pharmacokinetic/pharmacodynamic analysis, the recommended phase 2 dose was 0.5 mg PO twice daily. A majority of patients experienced peripheral edema (53.3%), often requiring diuretics. Three episodes of dose-limiting toxicities, related to fluid retention, were noted in the 0.10-, 0.25-, and 1.15-mg cohorts. Of 31 treated patients, 27 were evaluable for response. A sustained partial response (PR; 690 days on therapy) was observed in a patient with myxoid liposarcoma. Ten additional patients had stable disease (SD) for ≥60 days. Exposures were approximately dose proportional, and adiponectin levels increased after 4 weeks of treatment at all dose levels. Immunohistochemistry of archived specimens demonstrated that PPARγ and retinoid X receptor expression levels were significantly greater in patients with SD for ≥60 days or PR (P = .0079), suggesting a predictive biomarker.

CONCLUSIONS

Efatutazone demonstrates acceptable tolerability with evidence of disease control in patients with advanced malignancies.

DNA copy number alterations and PPARG amplification in a patient with multifocal bladder urothelial carcinoma

Background

Bladder cancer is the seventh most common cancer worldwide and over 90% are transitional cell carcinoma (TCC). At the first time of diagnosis at least 70% of TCC present as superficial bladder cancer. Because the clinical outcome of superficial bladder tumors is relatively unpredictable, there is a pressing need to identify markers that may predict tumor recurrence and progression and new treatment strategies.

Case presentation

We present a unique case of a 67-year old male who underwent total cystectomy after repeated trans-urethral resections of the bladder for multifocal non-muscle invasive bladder cancer. The first and the third tumor were diagnosed as high grade non-infiltrating (HGNI), while the second as carcinoma in situ (CIS). We performed both array comparative genomic hybridization and a targeted chromosomal profile by UroVysion in order to detect copy number variations (CNVs) that may be involved with tumor recurrence and progression. The overall data from this study provide new evidence for the monoclonal origin of urothelial tumor multifocality as several genetic changes were found in different tumors of the same patient. From the analysis of shared CNVs two gained regions emerged at 3p25.2 and 12q23.2, including PPARG and ASCL1 genes, respectively. The copy number level of these genes would seem inversely mutually correlated and highly dependent on histological grade, because the highest level of amplification at 3p25.2 was evidenced in the two HGNI samples, while the highest level of copy number gain at 12q23.2 was reported in the CIS.

Conclusion

We provide new evidence on the role of PPARG in initiation and maintenance of bladder cancer. For the first time we also suggest a possible explanation for the elevated expression of PPARG in this type of tumor through a focal high level amplification at 3p25.2. Furthermore, a new gene, ASCL1, emerged as a potential candidate to assist PPARG in bladder carcinogenesis.

PPARs Signaling and Cancer in the Gastrointestinal System

Nowadays, the study of the peroxisome proliferators activated receptors (PPARs) as potential targets for cancer prevention and therapy has gained a strong interest. From a biological point of view, the overall responsibility of PPARs in cancer development and progression is still controversial since several studies report both antiproliferative and tumor-promoting actions for these signaling molecules in human cancer cells and animal models. In this paper, we discuss PPARs functions in the context of different types of gastrointestinal cancer.

The role of peroxisome proliferator-activated receptors in the esophageal, gastric, and colorectal cancer

Tumors of the gastrointestinal tract are among the most frequent human malignancies and account for approximately 30% of cancer-related deaths worldwide. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that control diverse cellular functions such as proliferation, differentiation, and cell death. Owing to their involvement in so many processes, they play crucial roles also in the development and physiology of the gastrointestinal tract. Consistently, PPARs deregulation has been implicated in several pathophysiological conditions, including chronic inflammation and cancer development. This paper summarizes the current knowledge on the role that the various PPAR isoforms play in the pathogenesis of the esophageal, gastric, and intestinal cancer. Elucidation of the molecular mechanisms underlying PPARs' signaling pathways will provide insights into their possible use as predictive biomarkers in the initial stages of the process. In addition, this understanding will provide the basis for new molecular targets in cancer therapy and chemoprevention.

The Role of PPARγ in Helicobacter pylori Infection and Gastric Carcinogenesis

Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor that is important in many physiological and pathological processes, such as lipid metabolism, insulin sensitivity, inflammation, cell proliferation, and carcinogenesis. Several studies have shown that PPARγ plays an important role in gastric mucosal injury due to Helicobacter pylori (H. pylori). As H. pylori infection is the main etiologic factor in chronic gastritis and gastric cancer, understanding of the potential roles of PPARγ in H. pylori infection may lead to the development of a therapeutic target. In this paper, the authors discuss the current knowledge on the role of PPARγ in H. pylori infection and its related gastric carcinogenesis.

Peroxisome proliferator-activated receptor gamma overexpression suppresses proliferation of human colon cancer cells

Peroxisome proliferator-activated receptor gamma (PPARγ) plays an important role in the differentiation of intestinal cells and tissues. Our previous reports indicate that PPARγ is expressed at considerable levels in human colon cancer cells. This suggests that PPARγ expression may be an important factor for cell growth regulation in colon cancer. In this study, we investigated PPARγ expression in 4 human colon cancer cell lines, HT-29, LOVO, DLD-1, and Caco-2. Real-time polymerase chain reaction (PCR) and Western blot analysis revealed that the relative levels of PPARγ mRNA and protein in these cells were in the order HT-29>LOVO>Caco-2>DLD-1. We also found that PPARγ overexpression promoted cell growth inhibition in PPARγ lower-expressing cell lines (Caco-2 and DLD-1), but not in higher-expressing cells (HT-29 and LOVO). We observed a correlation between the level of PPARγ expression and the cells' sensitivity for proliferation.

Peroxisome proliferator-activated receptors and cancer: challenges and opportunities

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor superfamily, function as transcription factors and modulators of gene expression. These actions allow PPARs to regulate a variety of biological processes and to play a significant role in several diseases and conditions. The current literature describes frequently opposing and paradoxical roles for the three PPAR isotypes, PPARα, PPARβ/δ and PPARγ, in cancer. While some studies have implicated PPARs in the promotion and development of cancer, others, in contrast, have presented evidence for a protective role for these receptors against cancer. In some tissues, the expression level of these receptors and/or their activation correlates with a positive outcome against cancer, while, in other tissue types, their expression and activation have the opposite effect. These disparate findings raise the possibility of (i) PPAR receptor-independent effects, including effects on receptors other than PPARs by the utilized ligands; (ii) cancer stage-specific effect; and/or (iii) differences in essential ligand-related pharmacokinetic considerations. In this review, we highlight the latest available studies on the role of the various PPAR isotypes in cancer in several major organs and present challenges as well as promising opportunities in the field.

Peroxisome proliferator-activated receptors modulate proliferation and angiogenesis in human endometrial carcinoma

Peroxisome proliferator-activated receptors (PPAR) and retinoid X receptors (RXR) are implicated in the development of several obesity-related cancers. Little is known of either the expression or function of PPARs and RXRs in endometrial cancer although this increasingly common disease is highly associated with both obesity and insulin resistance. We investigated the expression of PPAR and RXR subtypes in human endometrial cancers and normal endometrium with immunoblotting and immunohistochemistry and subsequently showed PPAR/RXR binding preferences by coimmunoprecipitation. To determine the functions of PPARs within the endometrium, we investigated proliferation, apoptosis, PTEN expression, and secretion of vascular endothelial growth factor (VEGF) in endometrial cell lines after reducing the expression of PPARα and PPARγ with antisense RNA. The functional effects of PPAR ligands were also investigated in vitro. We identified differential expression of PPAR and RXR subtypes in endometrial cancers and discovered that PPARγ expression correlated with expression of PTEN. PPARα activation influences endometrial cell growth and VEGF secretion. PPARγ activation reduces proliferation of endometrial cells via regulation of PTEN and appears to reduce VEGF secretion. We conclude that the PPAR/RXR pathway contribute to endometrial carcinogenesis by control of PTEN expression and modulation of VEGF secretion. We propose that PPAR ligands should be considered for clinical investigation in early phase studies of women with endometrial cancer.

Cancer cell signaling pathways targeted by spice-derived nutraceuticals

Extensive research within the last half a century has revealed that cancer is caused by dysregulation of as many as 500 different gene products. Most natural products target multiple gene products and thus are ideally suited for prevention and treatment of various chronic diseases, including cancer. Dietary agents such as spices have been used extensively in the Eastern world for a variety of ailments for millennia, and five centuries ago they took a golden journey to the Western world. Various spice-derived nutraceuticals, including 1'-acetoxychavicol acetate, anethole, capsaicin, cardamonin, curcumin, dibenzoylmethane, diosgenin, eugenol, gambogic acid, gingerol, thymoquinone, ursolic acid, xanthohumol, and zerumbone derived from galangal, anise, red chili, black cardamom, turmeric, licorice, fenugreek, clove, kokum, ginger, black cumin, rosemary, hop, and pinecone ginger, respectively, are the focus of this review. The modulation of various transcription factors, growth factors, protein kinases, and inflammatory mediators by these spice-derived nutraceuticals are described. The anticancer potential through the modulation of various targets is also the subject of this review. Although they have always been used to improve taste and color and as a preservative, they are now also used for prevention and treatment of a wide variety of chronic inflammatory diseases, including cancer.

Combination of thiazolidinedione and hydralazine suppresses proliferation and induces apoptosis by PPARγ up-expression in MDA-MB-231 cells

No proven targeted therapy is currently available for the treatment of triple-negative breast cancer (TNBC). Ligand activation of peroxisome-activated receptor (PPAR)γ induces antitumor effects in cancer but not obviously in TNBC. In TNBC cells, combined treatment with thiazolidinedione and demethylation drugs Hydralazine up-regulated protein and mRNA levels of PPARγ. Besides, the combination of two drugs promote antiproliferative and apoptotic effects in TNBC cells and decrease the proliferation index in the tumor xenografts. Taken together, our results suggest that multidrug regimens including a combination of Thiazolidinedione and Hydralazine may provide a therapeutic advantage in TNBC.

Expression of PPARγ and PTEN in human colorectal cancer: An immunohistochemical study using tissue microarray methodology

Although aberrations of peroxisome proliferator-activated receptor γ (PPARγ) and phosphatase and tensin homolog (PTEN) expression have been identified in several other cancer types, certain previous studies have revealed that PPARγ is abundant in normal and malignant tissue in the colon. The question of whether aberrant PTEN is involved in the initial stage or is a later event during colorectal carcinogenesis remains controversial. Relatively few studies have focused on the correlation of expression of PPARγ and PTEN in various tissues. In the present study, paraffin-embedded blocks from 139 patients with CRC, 18 adenomatous polyps and 50 paired paracancerous benign mucosas were selected and analysed in 4 tissue microarray (TMA) blocks comprising 104, 72, 130 and 54 cores, respectively. Expression of PPARγ and PTEN was examined using immunohistochemical staining on TMAs. There were no significant differences in the expression of PPARγ (P=0.055) and PTEN (P=0.100) between the colorectal cancers, adenomas and paracancerous mucosas. However, correlations of PPARγ expression with clinical stage (P=0.004) and PTEN expression with histological grade (P=0.006) and distant metastasis (P=0.015) were demonstrated in the CRC specimens. Although the differences in PPARγ and PTEN protein expression in human colorectal cancer may not be considered as early diagnostic markers, our results indicate that CRCs with a low expression or deletion of PTEN may progress towards invasion and even metastasis; thus, PTEN may have potential as a prognostic marker in human CRC.

Rosiglitazone inhibits cell invasion and metastasis in human gastric cancer cell lines SGC7901 and SGC7901/VCR

AIM: To investigate the effect of rosiglitazone (ROS) on cell invasion and metastasis in human gastric cancer cell lines SGC7901 and SGC7901/VCR and to explore possible mechanisms involved.

METHODS: Wound healing assay and in vitro invasion assay were used to investigate the antimetastatic activities of ROS in SGC7901 and SGC7901/VCR cells. After treating SGC7901 and SGC7901/VCR cells with ROS (40 μmol/L) for 24 h, the mRNA levels of LIMK1 and cofilin-1 were assessed by reverse transcription-polymerase chain reaction (RT-PCR), and the protein levels of LIMK1, cofilin-1 and p-cofilin-1 were assessed by Western blot.

RESULTS: Treatment with ROS at a concentration of 40 μmol/L for 24 h significantly inhibited cellular invasion and metastasis (P < 0.05), down-regulated the expression of LIMK1 mRNA and protein and the level of p-cofilin-1 (all P < 0.05) but showed no significant impact on cofilin-1-1 mRNA level (P > 0.05).

CONCLUSION: ROS elicited a significant inhibition of in vitro cell migration and invasion in human gastric cancer cell lines SGC7901 and SGC7901/VCR possibly by down-regulating the expression of LIMK1 and inhibiting cofilin-1 activation.

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.

The Critical Role of PPARgamma in Human Malignant Melanoma

The past 30 years have only seen slight improvement in melanoma therapy. Despite a wide variety of therapeutic options, current survival for patients with metastatic disease is only 6-8 months. Part of the reason for this treatment failure is the broad chemoresistance of melanoma, which is due to an altered survival capacity and an inactivation of apoptotic pathways. Several targetable pathways, responsible for this survival/apoptosis resistance in melanoma, have been described and current research has focused on mechanism inactivating these pathways. As PPARgamma was shown to be constitutively active in several tumour entities and PPARgamma agonists extent strong anticancer effects, the role of PPARgamma as a possible target for specific anticancer strategy was investigated in numerous studies. However, only a few studies have focused on the effects of PPARgamma agonists in melanoma, showing conflicting results. The use of PPARgamma agonists in melanoma therapy has to be carefully weighted against considerable, undesirable side effects, as their mode of action is not fully understood and even pro-proliferative effects have been described. In the current review, we discuss the role of PPARs, in particular PPARgamma in melanoma and their potential role as a molecular target for melanoma therapy.

Rosiglitazone Suppresses the Growth and Invasiveness of SGC-7901 Gastric Cancer Cells and Angiogenesis In Vitro via PPARgamma Dependent and Independent Mechanisms

Although thiazolidinediones (TZDs) were found to be ligands for peroxisome proliferators-activated receptorγ (PPARγ), the mechanism by which TZDs exert their anticancer effect remains unclear. Furthermore, the effect of TZDs on metastatic and angiogenesis potential of cancer cells is unknown. Our results in this paper show that rosiglitazone inhibited SGC-7901 gastric cancer cells growth, caused G1 cell cycle arrest and induced apoptosis in a dose-dependent manner. The effects of rosiglitazone on SGC-7901 cancer cells were completely reversed by treatment with PPARγ antagonist GW9662. Rosiglitazone inhibited SGC-7901 cell migration, invasiveness, and the expression of MMP-2 in dose-dependent manner via PPARγ-independent manner. Rosiglitazone reduced the VEGF induced angiogenesis of HUVEC in dose-dependent manner through PPARγ-dependent pathway. Moreover, rosiglitazone did not affect the expression of VEGF by SGC-7901 cells. Our results demonstrated that by PPARγ ligand, rosiglitazone inhibited growth and invasiveness of SGC-7901 gastric cancer cells and angiogenesis in vitro via PPARγ-dependent or -independent pathway.

PPARgamma and Apoptosis in Cancer

Peroxisome proliferator-activated receptors (PPARs) are ligand binding transcription factors which function in many physiological roles including lipid metabolism, cell growth, differentiation, and apoptosis. PPARs and their ligands have been shown to play a role in cancer. In particular, PPARγ ligands including endogenous prostaglandins and the synthetic thiazolidinediones (TZDs) can induce apoptosis of cancer cells with antitumor activity. Thus, PPARγ ligands have a potential in both chemoprevention and therapy of several types of cancer either as single agents or in combination with other antitumor agents. Accordingly, the involvement of PPARγ and its ligands in regulation of apoptosis of cancer cells have been extensively studied. Depending on cell types or ligands, induction of apoptosis in cancer cells by PPARγ ligands can be either PPARγ-dependent or -independent. Through increasing our understanding of the mechanisms of PPARγ ligand-induced apoptosis, we can develop better strategies which may include combining other antitumor agents for PPARγ-targeted cancer chemoprevention and therapy. This review will highlight recent research advances on PPARγ and apoptosis in cancer.

The Role of PPARs in Cancer

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. PPARalpha is mainly expressed in the liver, where it activates fatty acid catabolism. PPARalpha activators have been used to treat dyslipidemia, causing a reduction in plasma triglyceride and elevation of high-density lipoprotein cholesterol. PPARdelta is expressed ubiquitously and is implicated in fatty acid oxidation and keratinocyte differentiation. PPARdelta activators have been proposed for the treatment of metabolic disease. PPARgamma2 is expressed exclusively in adipose tissue and plays a pivotal role in adipocyte differentiation. PPARgamma is involved in glucose metabolism through the improvement of insulin sensitivity and represents a potential therapeutic target of type 2 diabetes. Thus PPARs are molecular targets for the development of drugs treating metabolic syndrome. However, PPARs also play a role in the regulation of cancer cell growth. Here, we review the function of PPARs in tumor growth.

The role of insulin-sensitizing agents in the treatment of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome, which includes dyslipidemia, central obesity, hypertension, and insulin resistance. These diseases collectively and individually increase the risk of cardiovascular disease. Nonalcoholic steatohepatitis (NASH) is a subset of NAFLD that can progress to cirrhosis in up to 30% of patients and lead to decompensated liver disease requiring liver transplantation in many patients. Insulin resistance is the pathophysiological hallmark of NASH and addressing insulin resistance is an important aspect of NASH management. Lifestyle modifications with diet and exercise improve insulin sensitivity and are the cornerstone of therapy, but are often difficult to maintain long term. Not surprisingly, insulin-sensitizing agents have been a focus of pharmacologic investigation in NASH. Insulin sensitizers such as the thiazolidinediones, biguanides, glucagon-like peptide-1 receptor agonists, and the dipeptidyl peptidase IV inhibitors, also known as incretins, will be discussed with respect to their mechanism of action and how these drugs might target aspects of NASH pathophysiology. Finally, we will summarize the available clinical data and review both the risks and benefits of insulin sensitizers in the treatment of NASH.

The Ras inhibitors caveolin-1 and docking protein 1 activate peroxisome proliferator-activated receptor γ through spatial relocalization at helix 7 of its ligand-binding domain

Peroxisome proliferator-activated receptor γ (PPARγ) is a transcription factor that promotes differentiation and cell survival in the stomach. PPARγ upregulates and interacts with caveolin-1 (Cav1), a scaffold protein of Ras/mitogen-activated protein kinases (MAPKs). The cytoplasmic-to-nuclear localization of PPARγ is altered in gastric cancer (GC) patients, suggesting a so-far-unknown role for Cav1 in spatial regulation of PPARγ signaling. We show here that loss of Cav1 accelerated proliferation of normal stomach and GC cells in vitro and in vivo. Downregulation of Cav1 increased Ras/MAPK-dependent phosphorylation of serine 84 in PPARγ and enhanced nuclear translocation and ligand-independent transcription of PPARγ target genes. In contrast, Cav1 overexpression sequestered PPARγ in the cytosol through interaction of the Cav1 scaffolding domain (CSD) with a conserved hydrophobic motif in helix 7 of PPARγ's ligand-binding domain. Cav1 cooperated with the endogenous Ras/MAPK inhibitor docking protein 1 (Dok1) to promote the ligand-dependent transcriptional activity of PPARγ and to inhibit cell proliferation. Ligand-activated PPARγ also reduced tumor growth and upregulated the Ras/MAPK inhibitors Cav1 and Dok1 in a murine model of GC. These results suggest a novel mechanism of PPARγ regulation by which Ras/MAPK inhibitors act as scaffold proteins that sequester and sensitize PPARγ to ligands, limiting proliferation of gastric epithelial cells.

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.

Mechanisms by which thiazolidinediones induce anti-cancer effects in cancers in digestive organs

Increasing evidence suggests that thiazolidinediones (TZDs) could have a therapeutic potential for patients with cancers. Here, the evidence on the mechanisms by which TZDs could contribute to different steps of cancer biology in the digestive system is summarized. According to studies, TZDs induce anti-cancer actions through 3 main pathways: (1) cell growth arrest, (2) induction of apoptosis, and (3) inhibition of cell invasion. Cell growth arrest is induced by an increased level of p27(Kip1). p27(Kip1) accumulation results from the inhibition of the ubiquitin-proteasome system and/or inhibition of MEK-ERK signaling. TZDs induce apoptosis through increased levels of apoptotic molecules, such as p53 and PTEN and/or decreased level of anti-apoptotic molecules, such as Bcl-2 and survivin. Inhibition of MEK-ERK signaling-mediated up-regulation of E-cadherin and claudin-4, and/or decreased expression of matrix metalloproteinases (MMPs) such as MMP-2 and MMP-9, play a role in the TZD-induced inhibition of cancer cell invasion. Thus, TZDs are capable of inducing anti-tumor action in a variety of ways in gastrointestinal cancers.

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.

Troglitazone suppresses telomerase activity independently of PPARgamma in estrogen-receptor negative breast cancer cells

Background

Breast cancer is one the highest causes of female cancer death worldwide. Many standard chemotherapeutic agents currently used to treat breast cancer are relatively non-specific and act on all rapidly dividing cells. In recent years, more specific targeted therapies have been introduced. It is known that telomerase is active in over 90% of breast cancer tumors but inactive in adjacent normal tissues. The prevalence of active telomerase in breast cancer patients makes telomerase an attractive therapeutic target. Recent evidence suggests that telomerase activity can be suppressed by peroxisome proliferator activated receptor gamma (PPARγ). However, its effect on telomerase regulation in breast cancer has not been investigated.

Methods

In this study, we investigated the effect of the PPARγ ligand, troglitazone, on telomerase activity in the MDA-MB-231 breast cancer cell line. Real time RT-PCR and telomerase activity assays were used to evaluate the effect of troglitazone. MDA-MB-231 cells had PPARγ expression silenced using shRNA interference.

Results

We demonstrated that troglitazone reduced the mRNA expression of hTERT and telomerase activity in the MDA-MB-231 breast cancer cell line. Troglitazone reduced telomerase activity even in the absence of PPARγ. In agreement with this result, we found no correlation between PPARγ and hTERT mRNA transcript levels in breast cancer patients. Statistical significance was determined using Pearson correlation and the paired Student's t test.

Conclusions

To our knowledge, this is the first time that the effect of troglitazone on telomerase activity in breast cancer cells has been investigated. Our data suggest that troglitazone may be used as an anti-telomerase agent; however, the mechanism underlying this inhibitory effect remains to be determined.

PPARs in Human Neuroepithelial Tumors: PPAR Ligands as Anticancer Therapies for the Most Common Human Neuroepithelial Tumors

Neuroepithelial tumors represent a heterogeneous class of human tumors including benignant and malignant tumors. The incidence of central nervous system neoplasms ranges from 3.8 to 5.1 cases per 100,000 in the population. Among malignant neuroepithelial tumors, with regard to PPAR ligands, the most extensively studied were tumors of astrocytic origin and neuroblastoma. PPARs are expressed in developing and adult neuroepithelial cells, even if with different localization and relative abundance. The majority of malignant neuroepithelial tumors have poor prognosis and do not respond to conventional therapeutic protocols, therefore, new therapeutic approaches are needed. Natural and synthetic PPAR ligands may represent a starting point for the formulation of new therapeutic approaches to be used as coadjuvants to the standard therapeutic protocols. This review will focus on the major studies dealing with PPAR expression in gliomas and neuroblastoma and the therapeutic implications of using PPAR agonists for the treatment of these neoplasms.

The use of Cox-2 and PPARγ signaling in anti-cancer therapies

Increased production of the pro-inflammatory enzyme cyclooxygenase-2 (Cox-2) and altered expression and activity of peroxisome proliferator-activated receptor γ (PPARγ) have been observed in many malignancies. Both the PPARγ ligands and the Cox-2 inhibitors possess anti-inflammatory and anti-neoplastic effects in vitro and have been assessed for their therapeutic potential in several pre-clinical and clinical studies. Recently, multiple interactions between PPARγ and Cox-2 signaling pathways have been revealed. Understanding of the cross-talk between PPARγ and Cox-2 might provide important novel strategies for the effective treatment and/or prevention of cancer. This article summarizes recent achievements involving the functional interactions between the PPARγ and Cox-2 signaling pathways and discusses the implications of such interplay for clinical use.

Significance of LRP and PPAR-gamma Expression in Lipomatous Soft Tissue Tumors

Background:

Molecular mechanism of differentiation in lipogenic tumor is still unknown in detail. Low-density lipoprotein receptor-related protein (LRP) and peroxisome proliferator-activated receptor gamma (PPAR-γ), representative regulatory molecules of lipogenic differentiation, have been reported today as multi-functional molecules and to modulate tumorigenesis in various kind of cancer. To date, diagnostic and therapeutic significance of the expression of these molecules in lipogenic tumors are not defined.

Methods:

The immunohistochemical expression status of LRP and PPAR-γ in various grades of 54 lipogenic tumors was analyzed. Correlation between the expression levels and the differentiation of the tumors was confirmed. For statistical analyses, the Kruskal-Wallis test, the Steel-Dwass test and the Mann–Whitney U test were used.

Results:

LRP and PPAR-γ expression was detected in 50 (92.6%) and 44 (81.5%) cases, respectively. The expression level in LRP was significantly higher in cases with well differentiated liposarcoma, pleomorphic liposarcoma and dedifferentiated liposarcoma than in lipoma. Compared with lipoma or well differentiated liposarcoma, significant elevation in expression level of PPAR-γ was confirmed in myxoid liposarcoma, pleomorphic liposarcoma, dedifferentiated liposarcoma and the differentiated area of dedifferentiated liposarcoma.

Conclusion:

The up-regulation of LRP and PPAR-γ in higher grade cases, i.e. less differentiated tumors than in low grade cases was shown, suggesting the candidate role of these molecules as tumor progression modulators rather than regulatory molecules of differentiation in lipogenic tumors.

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.

Significance of peroxisome proliferator-activated receptors in the cardiovascular system in health and disease

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear transcription factors that belong to the nuclear receptor superfamily. Three isoforms of PPAR have been identified, alpha, delta and gamma, which play distinct roles in the regulation of key metabolic processes, such as glucose and lipid redistribution. PPARalpha is expressed predominantly in the liver, kidney and heart, and is primarily involved in fatty acid oxidation. PPARgamma is mainly associated with adipose tissue, where it controls adipocyte differentiation and insulin sensitivity. PPARdelta is abundantly and ubiquitously expressed, but as yet its function has not been clearly defined. Activators of PPARalpha (fibrates) and gamma (thiazolidinediones) have been used clinically for a number of years in the treatment of hyperlipidaemia and to improve insulin sensitivity in diabetes. More recently, PPAR activation has been found to confer additional benefits on endothelial function, inflammation and thrombosis, suggesting that PPAR agonists may be good candidates for the treatment of cardiovascular disease. In this regard, it has been demonstrated that PPAR activators are capable of reducing blood pressure and attenuating the development of atherosclerosis and cardiac hypertrophy. This review will provide a detailed discussion of the current understanding of basic PPAR physiology, with particular reference to the cardiovascular system. It will also examine the evidence supporting the involvement of the different PPAR isoforms in cardiovascular disease and discuss the current and potential future clinical applications of PPAR activators.

Friend or foe? Role of peroxisome proliferator-activated receptor-gamma in human bladder cancer

The peroxisome proliferator-activated receptor (PPAR) family is an important group of transcription factors that regulates immune surveillance, cell proliferation, fatty acid regulation, and angiogenesis--functions which have all been implicated in the pathogenesis of bladder cancer. One particular subtype, PPARgamma, is expressed at higher levels in bladder cancer specimens than in benign urothelium, and is an attractive molecular target for the development of novel treatment strategies for bladder cancer. In this review, we summarize the data available regarding relevance of PPARgamma in bladder cancer and discuss the potential value of PPAR-targeted treatment of bladder cancer.

Basic evidence of molecular targeted therapy for oral cancer and salivary gland cancer

BACKGROUND

Recently, attention has been focused on molecular targeted cancer therapy in various tumors. Although there is no single consistent molecular target specific for oral squamous cell carcinoma (OSCC) and salivary gland cancer (SGC), there are a number of promising candidate proteins. The aim of this review is to introduce the basic evidences to support the molecular targeting for OSCC and SGC.

METHODS

We focused on the 4 molecules, epidermal growth factor receptor (EGFR), cyclooxygenase-2 (COX-2), peroxisome proliferator-activated receptor gamma (PPARgamma), and progesterone receptor, that are, respectively, associated with the proliferation and the differentiation of OSCC and SGC.

RESULTS

Gefitinib ("Iressa," ZD1839), a small molecule EGFR tyrosine kinase inhibitor, can inhibit the proliferation of OSCC cell lines in a dose- and time-dependent manner and lead to cell cycle arrest with accumulation of cells in the G1 phase, and a decrease of cells in S phase. The agent suppressed tumor metastasis in the animal model. Furthermore, a cooperative antiproliferative effect was obtained when cancer cells were treated with radiation followed by gefitinib. While radiation alone did not significantly affect p38 mitogen-activated protein kinase and MAP kinase kinase (MEK)1/2 autophosphorylation, the combination of gefitinib and radiation completely inhibited the downstream signaling of EGFR. Gefitinib enhanced tumor radioresponsiveness by multiple mechanisms, including the growth inhibition and effects on DNA repair after exposure to radiation. Next, the level of COX-2 expression correlated inversely with increased tumor radiation sensitivity. Treatment with celecoxib, a COX-2 selective inhibitor, enhanced the radioresponsiveness of HSC-2 cells, which constitutively expressed COX-2. Another promising molecular target is the PPARgamma, which is a member of the nuclear receptor superfamily of ligand-activated transcription factors. Recent studies have demonstrated that PPARgamma ligands induce cellular differentiation and inhibit cell growth in carcinomas of various types. These data suggest that synthetic PPARgamma ligands may be useful for molecular targeting of oral cancer. Finally, the possibility of using molecular targeted therapy directed at hormone receptors in the treatment of advanced SGCs was described.

CONCLUSION

The basic data strongly suggested the possibility of tumor suppression by targeting these molecules. Studies of different targeted agents alone or with more conventional treatment modalities are needed to fully determine what role the targeted therapy will play in the management of patients with OSCC and SGC.

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.

MAZ drives tumor-specific expression of PPAR gamma 1 in breast cancer cells

The peroxisome proliferator-activated receptor gamma 1 (PPARgamma1) is a nuclear receptor that plays a pivotal role in breast cancer and is highly over-expressed relative to normal epithelia. We have previously reported that the expression of PPARgamma1 is mediated by at least six distinct promoters and expression in breast cancer is driven by a tumor-specific promoter (pA1). Deletional analysis of this promoter fragment revealed that the GC-rich, 263 bp sequence proximal to the start of exon A1, is sufficient to drive expression in breast cancer cells but not in normal, human mammary epithelial cells (HMEC). By combining the disparate technologies of microarray and computer-based transcription factor binding site analyses on this promoter sequence the myc-associated zinc finger protein (MAZ) was identified as a candidate transcription factor mediating tumor-specific expression. Western blot analysis and chromatin immunoprecipitation assays verify that MAZ is overexpressed in MCF-7 cells and is capable of binding to the 263 bp promoter fragment, respectively. Furthermore, the over-expression of MAZ in HMEC is sufficient to drive the expression of PPARgamma1 and does so by recruiting the tumor-specific promoter. This results in an increase in the amount of PPARgamma1 capable of binding to its DNA response element. These findings help to define the molecular mechanism driving the high expression of PPARgamma1 in breast cancer and raise new questions regarding the role of MAZ in cancer progression.

Herbal isoprenols induce apoptosis in human colon cancer cells through transcriptional activation of PPARgamma

Farnesol (FOH) and geranylgeraniol (GGOH) possess anti-tumor potential, while peroxisome proliferator-activated receptor gamma (PPARgamma) has exhibited modulating effects in colorectal cancers. We investigated the anti-carcinogenic effects of these isoprenols in HT-29 and HCT116 colon cancer cells and PPARgamma involvement. Results indicate that the FOH- and GGOH-induced apoptosis involve caspase 3 activation, PARP cleavage, nuclear chromatin condensation, down-regulation of Bcl-x(L) and survivin expression, with increased PPARgamma promoter activity. Pretreatment of the PPARgamma antagonist GW9662 reduces FOH-induced growth inhibition and the associated PARP cleavage. We conclude that PPARgamma activation is essential to elicit the anti-carcinogenic action of herbal isoprenols in colonic cancer cells.

1,1-bis(3'-indolyl)-1-(p-substituted phenyl)methanes decrease mitochondrial membrane potential and induce apoptosis in endometrial and other cancer cell lines

1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methanes, containing p-t-butyl (DIM-C-pPhtBu) and phenyl (DIM-C-pPhC(6)H(5)) substituents, are peroxisome proliferator-activated receptor gamma (PPARgamma) agonists; however, DIM-C-pPhtBu-induced growth inhibition and cell death in human HEC1A endometrial cancer cells is PPARgamma-independent. DIM-C-pPhtBu decreased mitochondrial membrane potential (MMP) and promoted the release of cytochrome c and caspase activation and nuclear uptake of endonuclease G leading to apoptosis of HEC1A cells. DIM-C-pPhtBu specifically targeted the mitochondrial permeability transition pore complex (PTPC) because the DIM-C-pPhtBu-induced pro-apoptotic responses were inhibited by atractyloside (Atra), a compound that specifically interacts with the inner mitochondrial membrane adenine nucleotide transport (ANT) proteins. At the dose of Atra used in this study (300 microM), this compound alone did not alter the PTPC but inhibited the mitochondriotoxic effects of DIM-C-pPhtBu. DIM-C-pPhtBu/DIM-C-pPhC(6)H(5) and Atra also differentially affected the ability of eosin-5-maleimide (EMA) to alkylate Cys160 in the ANT protein and Atra, but not DIM-C-pPhtBu, inhibited the exchange of ATP/ADP in isolated mitochondria suggesting that these pharmacophores act on different sites on the ANT protein. Results of this study show that the receptor-independent proapoptotic activity of DIM-C-pPhtBu and DIM-C-pPhC(6)H(5) were related to novel mitochondriotoxic activities involving inner mitochondrial ANT proteins.

Transcription profiling of lung adenocarcinomas of c-myc-transgenic mice: identification of the c-myc regulatory gene network

Background

The transcriptional regulator c-Myc is the most frequently deregulated oncogene in human tumors. Targeted overexpression of this gene in mice results in distinct types of lung adenocarcinomas. By using microarray technology, alterations in the expression of genes were captured based on a female transgenic mouse model in which, indeed, c-Myc overexpression in alveolar epithelium results in the development of bronchiolo-alveolar carcinoma (BAC) and papillary adenocarcinoma (PLAC). In this study, we analyzed exclusively the promoters of induced genes by different in silico methods in order to elucidate the c-Myc transcriptional regulatory network.

Results

We analyzed the promoters of 361 transcriptionally induced genes with respect to c-Myc binding sites and found 110 putative binding sites in 94 promoters. Furthermore, we analyzed the flanking sequences (+/- 100 bp) around the 110 c-Myc binding sites and found Ap2, Zf5, Zic3, and E2f binding sites to be overrepresented in these regions. Then, we analyzed the promoters of 361 induced genes with respect to binding sites of other transcription factors (TFs) which were upregulated by c-Myc overexpression. We identified at least one binding site of at least one of these TFs in 220 promoters, thus elucidating a potential transcription factor network. The analysis correlated well with the significant overexpression of the TFs Atf2, Foxf1a, Smad4, Sox4, Sp3 and Stat5a. Finally, we analyzed promoters of regulated genes which where apparently not regulated by c-Myc or other c-Myc targeted TFs and identified overrepresented Oct1, Mzf1, Ppargamma, Plzf, Ets, and HmgIY binding sites when compared against control promoter background.

Conclusion

Our in silico data suggest a model of a transcriptional regulatory network in which different TFs act in concert upon c-Myc overexpression. We determined molecular rules for transcriptional regulation to explain, in part, the carcinogenic effect seen in mice overexpressing the c-Myc oncogene.

Gastric cancer risk and erythrocyte composition of docosahexaenoic acid with anti-inflammatory effects

Infection with Helicobacter pylori is linked to inflammation and is the main cause of peptic ulcer, gastritis, and gastric malignancies. To examine associations between gastric cancer risk and the erythrocyte composition of docosahexaenoic acid (DHA), a fatty acid with anti-inflammatory and apoptosis-inducing effects, here we conducted a case-control study of 179 incident gastric cancer cases and 357 noncancer controls (matched by age, sex, and season of sample collection). Dietary information and blood samples were collected from all subjects, and erythrocyte fatty acid levels were measured using accelerated solvent extraction and gas-liquid chromatography. Gastric cancer risk did not seem to be directly associated with dietary intake of fish and n-3 highly unsaturated fatty acids (HUFAs), such as DHA, derived from fish. However, risk was inversely associated with erythrocyte compositions of n-3 HUFAs [the highest to the lowest tertile, odds ratio (OR), 0.39; 95% confidence interval (95% CI), 0.23-0.68; P(trend)<0.005] and DHA (OR, 0.47; 95% CI, 0.28-0.79; P(trend)<0.01). Particularly strong associations were noted for well-differentiated type lesions and n-3 HUFAs (OR, 0.10; 95% CI, 0.03-0.35; P(trend)=0.0005) as well as DHA (OR, 0.20; 95% CI, 0.07-0.58; P(trend)<0.01) values. In conclusion, the erythrocyte composition of DHA was found to be negatively linked to risk of gastric cancer, especially of well-differentiated adenocarcinoma. Further studies are needed to investigate mechanisms of action of DHA relevant to antitumor effects in the stomach.

Troglitazone, a peroxisome proliferator-activated receptor γ ligand, induces growth inhibition and apoptosis of HepG2 human liver cancer cells

AIM: To examine the effect of troglitazone, a peroxisome proliferator-activated receptor γ (PPARγ) ligand, on the proliferation and apoptosis of human liver cancer cells.

METHODS: Liver cancer cell line HepG2 was cultured and treated with troglitazone. Cell proliferation was detected by 3-(4-,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay; apoptosis was detected by flow cytometry and terminal deoxynucleotidyl transferase-mediated nick end labeling of DNA fragmentation sites (TUNEL) assay; and apoptosis-related protein was detected by immunocytochemistry and Western blotting.

RESULTS: Troglitazone inhibited growth and induced apoptosis of HepG2 cells in a dose-dependent manner, and induced activation of caspase-3 expression. Troglitazone not only drove apoptosis-inhibiting factor survivin to translocate incompletely from the nucleus to the cytoplasm, but also inhibited expression of survivin, while it did not affect expression of apoptosis-promoting factor Bax.

CONCLUSION: PPARγ ligands inhibit growth and induce apoptosis of liver cancer cells, and may have applications for the prevention and treatment of liver cancer.

Alpha-methylacyl-CoA racemase expression is upregulated in gastric adenocarcinoma: a study of 249 cases

Alpha-methylacyl-CoA racemase (AMACR [P504S]) is a mitochondrial and peroxisomal enzyme involved in beta-oxidation of dietary branched-chain fatty acids and their derivatives. Recent studies showed that AMACR is expressed in several neoplasms, including prostate and colon cancer. However, AMACR expression in gastric neoplasms has yet to be thoroughly investigated. Because AMACR overexpression in human solid tumors is a potential target for cancer treatment, we aimed to evaluate the expression of AMACR in a large cohort of patients with gastric adenocarcinoma. The study evaluated 249 primary gastric adenocarcinomas by immunohistochemistry. Nonneoplastic gastric tissue samples from various sites (antrum, body, fundus, and pylorus) were also examined. The immunopositivity of each sample was graded on a scale from 0 to 3 (0, no expression; 1, weak expression, 2, intermediate expression; 3, strong expression). We observed AMACR expression in 141 tumor cases: 44, 47, and 50 cases had weak, intermediate, and strong expression, respectively. Both intestinal and signet ring cell adenocarcinoma cases had overexpression of AMACR, however intestinal adenocarcinoma had significantly higher expression than did signet ring cell adenocarcinoma (p<0.05). Nonneoplastic gastric mucosa did not show AMACR expression. The results of our study demonstrate that AMACR expression is upregulated in gastric cancer, and suggest that further prospective studies to explore the potential role of AMACR as a therapeutic target for gastric cancer are warranted.

A novel peroxisome proliferator-activated receptor alpha/gamma agonist, BPR1H0101, inhibits topoisomerase II catalytic activity in human cancer cells

Peroxisome proliferator-activated receptor (PPAR) gamma agonists are used clinically for treating diabetes mellitus and cancer. 2-Methyl-2[(1-{3-phenyl-7-propylbenzol[d]isoxazol-6-yl}oxy)propyl]-1H-4-indolyl) oxy]propanoic acid (BPR1H0101) is a novel synthetic indole-based compound, discovered through research to identify new PPARgamma agonists, and it acts as a dual agonist for PPARgamma and PPARalpha. Isobologram analysis demonstrated that BPR1H0101 is capable of antagonistic interaction with the topoisomerase (topo) II poison, VP16. A study of its mechanism showed that BPR1H0101 could inhibit the catalytic activity of topo II in vitro, but did not produce detectable topo II-mediated DNA strand breaks in human oral cancer KB cells. Furthermore, BPR1H0101 could inhibit VP16-induced topo II-mediated DNA cleavage and ataxia-telangiectasia-mutated phosphorylation in KB cells. The results suggest that BPR1H0101 can interfere with the topo II reaction by inhibiting catalytic activity before the formation of the intermediate cleavable complex; consequently, it can impede VP16-induced topo II-mediated DNA cleavage and cell death. This is the first identified PPARalpha/gamma agonist that can serve as a topo II catalytic inhibitor, to interfere with VP16-induced cell death. The result might have relevance to the clinical use of the PPARalpha/gamma agonist in combination chemotherapy.

Peroxisome proliferator-activated receptors (PPARs) and the human skin: importance of PPARs in skin physiology and dermatologic diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate lipid, glucose, and amino acid metabolism. More recently, PPARs and corresponding ligands have been shown in skin and other organs to regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. These new functions identify PPARs and corresponding ligands as potential targets for the treatment of various skin diseases and other disorders. It has been shown that in inflammatory skin disorders, including hyperproliferative psoriatic epidermis and the skin of patients with atopic dermatitis, the expression of both PPARalpha and PPARgamma is decreased. This observation suggests the possibility that PPARalpha and PPARgamma activators, or compounds that positively regulate PPAR gene expression, may represent novel NSAIDs for the topical or systemic treatment of common inflammatory skin diseases such as atopic dermatitis, psoriasis, and allergic contact dermatitis. Moreover, recent findings indicate that PPAR-signaling pathways may act as a promising therapeutic target for the treatment of hyperproliferative skin diseases including skin malignancies. Studies in non-diabetic patients suggest that oral thiazolidinediones, which are synthetic ligands of PPARgamma, not only exert an antidiabetic effect but also may be beneficial for moderate chronic plaque psoriasis by suppressing proliferation and inducing differentiation of keratinocytes; furthermore, they may even induce cell growth arrest, apoptosis, and terminal differentiation in various human malignant tumors. It has been reported that PPARalpha immunoreactivity is reduced in human keratinocytes of squamous cell carcinoma (SCC) and actinic keratosis (AK), while PPARdelta appears to be upregulated. Additionally, the microvessel density is significantly higher in AK and SCC that express high levels of PPARdelta. PPARdelta has been demonstrated to have an anti-apoptotic role and to maintain survival and differentiation of epithelial cells, whereas PPARalpha and PPARgamma activators induce differentiation and inhibit proliferation and regulate apoptosis. In melanoma, the growth inhibitory effect of PPARgamma activation is independent of apoptosis and seems to occur primarily through induction of cell cycle arrest in the G1 phase of the cell cycle or induction of re-differentiation. PPARalpha activation causes inhibition of migration of melanoma cells and anchorage-independent growth, whereas primary tumor growth remains unaltered. In clinical trials of gemfibrozil, a PPARalpha ligand, significantly fewer patients treated with this lipid-lowering drug were diagnosed with melanoma as compared to those in the control group. In conclusion, an increasing body of evidence indicates that PPAR signaling pathways may represent interesting therapeutic targets for a broad variety of skin disorders, including inflammatory skin diseases such as psoriasis and atopic dermatitis, and skin malignancies.

Thiazolidinediones as anti-cancer agents

The PPAR-gamma (PPAR-γ) activating thiazolidinedione (TZD) medications are a class of drugs used to improve lipid and glucose metabolism in type-2 diabetes. In addition to their known insulin sensitization action, these drugs have been shown to suppress tumor development in several in vitro and in vivo models. Among the proposed mechanisms for the anti-tumor effects of TZDs, apoptosis induction, cell cycle arrest, and differentiation have been extensively reported. Interestingly, some of the observed anti-tumor effects are independent of PPAR-γ activation. The following review will discuss studies employing TZDs as anti-cancer therapies for the most common types of cancers including, lung, breast, and colon and will explore the principal PPAR-γ-dependent and -independent mechanisms by which TZDs exert their anti-tumor effects.

A Role for PPARgamma in the Regulation of Cytokines in Immune Cells and Cancer

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. PPARgamma and its ligands appear to serve diverse biological functions. In addition to the well-studied effects of PPARgamma on metabolism and cellular differentiation, abundant evidence suggests that PPARgamma is an important regulator of the immune system and cancers. Since cytokines are not only key modulators of inflammation with pro- and anti-inflammatory functions but they also can either stimulate or inhibit tumor growth and progression, this review summarizes the role for PPARgamma in the regulation of cytokine production and cytokine-mediated signal transduction pathways in immune cells and cancer.

Inhibition of estrogen receptor β-mediated human telomerase reverse transcriptase gene transcription via the suppression of mitogen-activated protein kinase signaling plays an important role in 15-deoxy-Δ12,14-prostaglandin J2-induced apoptosis in cancer cells

The nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)-gamma plays a role in cancer development in addition to its role in glucose metabolism. The natural ligand of PPAR-gamma, namely, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), has been shown to possess antineoplastic activity in cancer cells. However, the mechanism underlying its antineoplastic activity remains to be elucidated. Inhibition of the expression of human telomerase reverse transcriptase (hTERT), a major determinant of telomerase activity, reportedly induces rapid apoptosis in cancer cells. In this study, we investigated the effect of 15d-PGJ(2) on hTERT expression. We found that 15d-PGJ(2) induced apoptosis in the MIAPaCa-2 pancreatic cancer cells and dose-dependently decreased hTERT mRNA and protein expression. Down-regulation of hTERT expression by hTERT-specific small inhibitory RNA also induced apoptosis. Furthermore, 15d-PGJ(2) attenuated the DNA binding of estrogen receptor (ER). MIAPaCa-2 expressed only ERbeta, and although its expression did not decrease due to 15d-PGJ(2), its phosphorylation was suppressed. Additionally, a mitogen-activated protein kinase (MAPK) kinase inhibitor decreased ERbeta phosphorylation, and 15d-PGJ(2) attenuated MAPK activity. We conclude that hTERT down-regulation by 15d-PGJ(2) plays an important role in the proapoptotic property of the latter. Furthermore, 15d-PGJ(2) inhibits ERbeta-mediated hTERT gene transcription by suppressing ERbeta phosphorylation via the inhibition of MAP kinase signaling.