Can PPARγ Ligands Be Used in Cancer Therapy?

Saroglitazar suppresses the hepatocellular carcinoma induced by intraperitoneal injection of diethylnitrosamine in C57BL/6 mice fed on choline deficient, l-amino acid- defined, high-fat diet

BACKGROUND

Saroglitazar is a novel PPAR-α/γ agonist with predominant PPAR-α activity. In various preclinical models, saroglitazar has been shown to prevent & reverse symptoms of NASH. In view of these observations, and the fact that NASH is a progressive disease leading to HCC, we hypothesized that saroglitazar may prevent the development of HCC in rodents.

METHODS

HCC was induced in C57BL/6 mice by a single intraperitoneal injection of 25 mg/kg diethylnitrosamine (DEN) at the age of 4 weeks and then feeding the animal a choline-deficient, L-amino acid- defined, high-fat diet (CDAHFD) for the entire study duration. Eight weeks after initiation of CDAHFD, saroglitazar (1 and 3 mg/kg) treatment was started and continued for another 27 weeks.

RESULTS

Saroglitazar treatment significantly reduced the liver injury markers (serum ALT and AST), reversed hepatic steatosis and decreased the levels of pro-inflammatory cytokines like TNF-α in liver. It also resulted in a marked increase in serum adiponectin and osteopontin levels. All disease control animals showed hepatic tumors, which was absent in saroglitazar (3 mg/kg)- treatment group indicating 100% prevention of hepatic tumorigenesis. This is the first study demonstrating a potent PPARα agonist causing suppression of liver tumors in rodents, perhaps due to a strong anti-NASH activity of Saroglitazar that overrides its rodent-specific peroxisome proliferation activity.

CONCLUSION

The data reveals potential of saroglitazar for chemoprevention of hepatocellular carcinoma in patients with NAFLD/NASH.

Peroxisome Proliferator-Activated Receptors (PPAR)γ Agonists as Master Modulators of Tumor Tissue

In most clinical trials, thiazolidinediones do not show any relevant anti-cancer activity when used as mono-therapy. Clinical inefficacy contrasts ambiguous pre-clinical data either favoring anti-tumor activity or tumor promotion. However, if thiazolidinediones are combined with additional regulatory active drugs, so-called ‘master modulators’ of tumors, i.e., transcriptional modulators, metronomic low-dose chemotherapy, epigenetically modifying agents, protein binding pro-anakoinotic drugs, such as COX-2 inhibitors, IMiDs, etc., the results indicate clinically relevant communicative reprogramming of tumor tissues, i.e., anakoinosis, meaning ‘communication’ in ancient Greek. The concerted activity of master modulators may multifaceted diversify palliative care or even induce continuous complete remission in refractory metastatic tumor disease and hematologic neoplasia by establishing novel communicative behavior of tumor tissue, the hosting organ, and organism. Re-modulation of gene expression, for example, the up-regulation of tumor suppressor genes, may recover differentiation, apoptosis competence, and leads to cancer control—in contrast to an immediate, ‘poisoning’ with maximal tolerable doses of targeted/cytotoxic therapies. The key for uncovering the therapeutic potential of Peroxisome proliferator-activated receptor γ (PPARγ) agonists is selecting the appropriate combination of master modulators for inducing anakoinosis: Now, anakoinosis is trend setting by establishing a novel therapeutic pillar while overcoming classic obstacles of targeted therapies, such as therapy resistance and (molecular-)genetic tumor heterogeneity.

Inhibition of ERK activity enhances the cytotoxic effect of peroxisome proliferator-activated receptor γ (PPARγ) agonists in HeLa cells

In this study, we examined whether the peroxisome proliferator-activated receptor γ (PPARγ) agonists, ciglitazone (CGZ) and troglitazone (TGZ), induce cell death in human cervical cancer HeLa cells. The cells were treated with a range of CGZ or TGZ doses for 24 or 48 h. Low concentrations of CGZ (≤10 μM) or TGZ (≤20 μM) had no effect on cell viability whereas higher doses induced cell death in a time- and dose-dependent manner as evidenced by the detection of activated caspase-3 and PARP cleavage. Treatment with the PPARγ antagonist GW9662 followed by PPARγ agonists did not increase CGZ- or TGZ-induced cell death, indicating that PPARγ agonists induced HeLa cell death independently of PPARγ. Moreover, ERK1/2 activation was observed at a CGZ concentration of 25 μM and a TGZ concentration of 35 μM, both of which induced cell death. To elucidate the role of ERK1/2 activated by the two PPARγ agonists, the effect of U0126, an inhibitor of ERK1/2, on PPARγ-agonist-induced cell death was examined. Treatment with 10 or 20 μM U0126 followed by CGZ or TGZ induced the down-regulation of ERK1/2 activity and a decrease in Bcl-2 expression accompanied by the collapse of mitochondrial membrane potential, which in turn significantly enhanced CGZ- or TGZ-induced apoptotic cell death. Our results suggest that PPARγ agonists are capable of inducing apoptotic cell death in HeLa cells independently of PPARγ and that inhibition of ERK1/2 activity offers a strategy to enhance the cytotoxicity of PPARγ agonists in the treatment of cervical cancer.

Functions of Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) in Gynecologic Disorders

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of a class of nuclear hormone receptors intimately involved in the regulation of expression of myriad genes that regulate energy metabolism, cell differentiation, apoptosis, and inflammation. Although originally discovered as a pivotal regulator of adipocyte differentiation, the roles that PPARγ plays in gynecological disorders are still unknown. There are a number of studies on the functions of PPARγ and its agonists in gynecological disorders. In this mini-review, we provide a brief summary of the advances in recent years.

Genistein exerts growth inhibition on human osteosarcoma MG-63 cells via PPARγ pathway

The peroxisome proliferator-activated receptor γ (PPARγ) is emerging as an important regulator in various metabolic processes of cancer. Genistein, as a major isoflavonoid isolated from dietary soybean, possesses a wide variety of biological activities, particularly, in cancer prevention. However, the mechanisms by which genistein elicits its growth inhibiting effects in osteosarcoma (OS) MG-63 cells have not been extensively elucidated. MG-63 cells were treated for 2 days with various concentrations of genistein and/or GW9662 (a selective antagonist of PPARγ). The effect of different drugs on cell viability was determined by Cell Counting Kit-8 (CCK-8). The assay of cell proliferation was performed using 5-ethynyl-2'-deoxyuridine (EdU). The changes of apoptosis and cell cycle progression were detected by flow cytometry experiments. The protein expression of PPARγ pathway (PPARγ, PTEN, BCL-2, Survivin, P21WAF1/CIP1 and Cyclin B1) was determined by western blot analysis. The expression of PPARγ and PTEN mRNA was detected by real-time quantitative RT-PCR analysis. We report that genistein caused OS cell growth inhibition. We found that the PPARγ expression in OS cells increased after genistein treatment. Further studies on the mechanisms of genistein revealed a series of cell growth changes related to the PPARγ pathway; while cell cycle changes can be reversed by GW9662. Genistein plays an important role in preventing OS cell growth, which can impede the OS cell cycle as a non-toxic activator of PPARγ, providing novel insights into the mechanisms of the therapeutic activities of genistein.

Research resource: nuclear receptors as transcriptome: discriminant and prognostic value in breast cancer

To identify biologically relevant groupings or clusters of nuclear receptors (NR) that are associated with breast neoplasia, with potentially diagnostic, discriminant or prognostic value, we quantitated mRNA expression levels of all 48 members of the human NR superfamily by TaqMan low-density array analysis in 116 curated breast tissue samples, including pre- and postmenopausal normal breast and both ERα(+) and ERα(-) tumor tissue. In addition, we have determined NR levels in independent cohorts of tamoxifen-treated ERα(+) and ERα(-) tissue samples. There were differences in relative NR mRNA expression between neoplastic and normal breast, and between ER(+) and ER(-) tumors. First, there is overexpression of the NUR77 subgroup and EAR2 in neoplastic breast. Second, we identify a signature of five NR (ERα, EAR2, NUR77, TRα, and RARγ) that classifies breast samples with more than 97% cross-validated accuracy into normal or cancer classes. Third, we find a novel negative association between five NR (TRβ, NUR77, RORγ, COUP-TFII, and LRH1) and histological grade. Finally, four NR (COUP-TFII, TRβ, PPARγ, and MR) are significant predictors of metastasis-free survival in tamoxifen-treated breast cancers, independent of ER expression. The present study highlights the discriminant and prognostic value of NR in breast cancer; identifies novel, clinically relevant, NR signatures; and highlights NR signaling pathways with potential roles in breast cancer pathophysiology and as new therapeutic targets.

Idealized PPARγ-Based Therapies: Lessons from Bench and Bedside

The incidence of type 2 (T2D) diabetes and other chronic conditions associated with insulin resistance is increasing at an alarming rate, underscoring the need for effective and safe therapeutic strategies. Peroxisome-proliferator-activated receptor gamma (PPARγ) has emerged as a critical regulator of glucose homeostasis, lipid homeostasis, and vascular inflammation. Currently marketed drugs targeting this receptor, the thiazolidinediones (TZDs), have proven benefits on insulin resistance and hyperglycemia associated with T2D. Unfortunately, they have been associated with long-term unfavorable effects on health, such as weight gain, plasma volume expansion, bone loss, cardiovascular toxicity, and possibly cancer, and these safety concerns have led to reduced interest for many PPARγ ligands. However, over the last years, data from human genetic studies, animal models, and studies with ligands have increased our understanding of PPARγ's actions and provided important insights into how ligand development strategies could be optimized to increase effectiveness and safety of PPARγ-based therapies.

Effects of rosiglitazone on radioiodine negative and progressive differentiated thyroid carcinoma as assessed by ¹²⁴I PET/CT imaging

AIM

The aim of this study was to evaluate the redifferentiative and antiproliferative effects of rosiglitazone in patients with progressive differentiated thyroid cancer (DTC) without or with negligible overall radioiodine uptake.

MATERIALS AND METHODS

A total of 9 patients with progressive DTC with either no or only negligible radioiodine accumulation were enrolled in this study. Oral rosiglitazone treatment was applied for 6 months (4 mg per day for 2 weeks followed by 8 mg per day). The compatibility of the medication was initially checked twice weekly and then weekly by laboratory tests and clinical evaluation of side effects. The assessments of alterations in the doses absorbed by the tumor and in lesion sizes over the course of rosiglitazone treatment were performed using serial ¹²⁴I positron emission tomography and computed tomography imaging. The assessment time points were before enrollment and 3 and 6 months posttreatment initiation.

RESULTS

Lesion dosimetry indicated that 5 of 9 patients had an improved lesion absorbed dose per administered activity (LDpA), yielding in radioiodine therapy treatment in 4 patients. One third of the patients (3/9) were unchanged with regard to LDpA, and 1 of 9 had deteriorated LDpA. Volumetric analyses revealed that lesion sizes were regredient in 3 of 9 patients, stable in 4 of 9, and was progressive in 1 of 9. The medication was well-tolerated, and no patient developed clinically important toxicity associated with rosiglitazone treatment. In 2 of 9 of the patients, the medication was terminated after 3 months as a precaution due to progressive heart disease in one patient and bone fracture within a known osteolytic bone lesion in another patient. It is not clear that these complications were caused by rosiglitazone.

CONCLUSION

Rosiglitazone appears to be suitable as off-label therapy in radioiodine-negative and progressive DTC that lacks therapy alternatives. In Europe, rosiglitazone was removed for label use because of reported side effects during diabetes treatment. Further investigations of other available glitazone compounds are necessary.

PPARs: Interference with Warburg' Effect and Clinical Anticancer Trials

The metabolic/cell signaling basis of Warburg's effect ("aerobic glycolysis") and the general metabolic phenotype adopted by cancer cells are first reviewed. Several bypasses are adopted to provide a panoramic integrated view of tumoral metabolism, by attributing a central signaling role to hypoxia-induced factor (HIF-1) in the expression of aerobic glycolysis. The cancer metabolic phenotype also results from alterations of other routes involving ras, myc, p53, and Akt signaling and the propensity of cancer cells to develop signaling aberrances (notably aberrant surface receptor expression) which, when present, offer unique opportunities for therapeutic interventions. The rationale for various emerging strategies for cancer treatment is presented along with mechanisms by which PPAR ligands might interfere directly with tumoral metabolism and promote anticancer activity. Clinical trials using PPAR ligands are reviewed and followed by concluding remarks and perspectives for future studies. A therapeutic need to associate PPAR ligands with other anticancer agents is perhaps an important lesson to be learned from the results of the clinical trials conducted to date.

Mice lacking epidermal PPARγ exhibit a marked augmentation in photocarcinogenesis associated with increased UVB-induced apoptosis, inflammation and barrier dysfunction

Recent studies suggest that peroxisome proliferator-activated receptor gamma (PPARγ) agonists may have cancer chemopreventive activity. Other studies have shown that loss of epidermal PPARγ results in enhanced chemical carcinogenesis in mice via unknown mechanisms. However, ultraviolet B (UVB) exposure represents the primary etiological agent for skin cancer formation and the role of PPARγ in photobiology and photocarcinogenesis is unknown. In previous studies, we demonstrated that UVB irradiation of cells results in the formation of oxidized glycerophosphocholines that exhibit PPARγ ligand activity. We therefore hypothesized that PPARγ would prove to be a chemopreventive target in photocarcinogenesis. We first showed that UVB irradiation of mouse skin causes generation of PPARγ agonist species in vivo. We then generated SKH-1 hairless, albino mice deficient in epidermal Pparg (Pparg-/-(epi)) using a cytokeratin 14 driven Cre-LoxP strategy. Using a chronic model of UVB photocarcinogenesis, we next showed that Pparg-/-(epi) mice exhibit an earlier onset of tumor formation, increased tumor burden and tumor progression. Increased tumor burden in Pparg-/-(epi) mice was accompanied by a significant increase in epidermal hyperplasia and p53 positive epidermal cells in surrounding skin lacking tumors. After acute UVB irradiation, Pparg-/-(epi) mice exhibited an augmentation of both UVB-induced Caspase 3/7 activity and inflammation. Increased apoptosis and inflammation was also observed after treatment with the PPARγ antagonist GW9662. With chronic UVB irradiation, Pparg-/-(epi) mice exhibited a sustained increase in erythema and transepidermal water loss relative to wildtype littermates. This suggests that PPARγ agonists could have possible chemopreventive activity in non-melanoma skin cancer.

Altered peroxisome-proliferator activated receptors expression in human endometrial cancer

Peroxisome proliferator-activated receptors (PPARs) belong to a family of nuclear hormone receptors acting as transcriptional factors, recently involved also in carcinogenesis. Present study was undertaken to evaluate the presence and subcellular localization of different PPAR isoforms (α, β, γ) in healthy endometrial tissue (n = 10) and endometrial carcinoma (FIGO I, endometrioides type, G1, n = 35). We sought to analyze PPARs mRNA content as well as protein immunohistochemical expression that was further quantified by Western Blot technique. For both PPARα and PPARβ, protein expression was significantly higher in endometrial cancers compared to normal endometrial mucosa. In opposite, PPARγ protein expression was lower in endometrial cancer cells. In each case, immunohistochemical reaction was confined to the perinuclear and/or nuclear region. At the transcriptional level, the content of mRNA of all PPAR subunits did not follow the protein pattern of changes. These results provide evidence for altered PPAR's protein expression and disregulation of posttranslational processes in endometrial cancers.

The antidiabetic drug ciglitazone induces high grade bladder cancer cells apoptosis through the up-regulation of TRAIL

BACKGROUND

Ciglitazone belongs to the thiazolidinediones class of antidiabetic drug family and is a high-affinity ligand for the Peroxisome Proliferator-Activated Receptor γ (PPARγ). Apart from its antidiabetic activity, this molecule shows antineoplastic effectiveness in numerous cancer cell lines.

METHODOLOGY/PRINCIPAL FINDINGS

Using RT4 (derived from a well differentiated grade I papillary tumor) and T24 (derived from an undifferentiated grade III carcinoma) bladder cancer cells, we investigated the potential of ciglitazone to induce apoptotic cell death and characterized the molecular mechanisms involved. In RT4 cells, the drug induced G2/M cell cycle arrest characterized by an overexpression of p53, p21(waf1/CIP1) and p27(Kip1) in concomitance with a decrease of cyclin B1. On the contrary, in T24 cells, it triggered apoptosis via extrinsic and intrinsic pathways. Cell cycle arrest and induction of apoptosis occurred at high concentrations through PPARγ activation-independent pathways. We show that in vivo treatment of nude mice by ciglitazone inhibits high grade bladder cancer xenograft development. We identified a novel mechanism by which ciglitazone kills cancer cells. Ciglitazone up-regulated soluble and membrane-bound TRAIL and let TRAIL-resistant T24 cells to respond to TRAIL through caspase activation, death receptor signalling pathway and Bid cleavage. We provided evidence that TRAIL-induced apoptosis is partially driven by ciglitazone-mediated down-regulation of c-FLIP and survivin protein levels through a proteasome-dependent degradation mechanism.

CONCLUSIONS/SIGNIFICANCE

Therefore, ciglitazone could be clinically relevant as chemopreventive or therapeutic agent for the treatment of TRAIL-refractory high grade urothelial cancers.

Cell death is induced by ciglitazone, a peroxisome proliferator-activated receptor γ (PPARγ) agonist, independently of PPARγ in human glioma cells

Peroxisome proliferator-activated receptor γ (PPARγ) regulates multiple signaling pathways, and its agonists induce apoptosis in various cancer cells. However, their role in cell death is unclear. In this study, the relationship between ciglitazone (CGZ) and PPARγ in CGZ-induced cell death was examined. At concentrations of greater than 30 μM, CGZ, a synthetic PPARγ agonist, activated caspase-3 and induced apoptosis in T98G cells. Treatment of T98G cells with less than 30 μM CGZ effectively induced cell death after pretreatment with 30 μM of the PPARγ antagonist GW9662, although GW9662 alone did not induce cell death. This cell death was also observed when cells were co-treated with CGZ and GW9662, but was not observed when cells were treated with CGZ prior to GW9662. In cells in which PPARγ was down-regulated cells by siRNA, lower concentrations of CGZ (<30 μM) were sufficient to induce cell death, although higher concentrations of CGZ (≥30 μM) were required to induce cell death in control T98G cells, indicating that CGZ effectively induces cell death in T98G cells independently of PPARγ. Treatment with GW9662 followed by CGZ resulted in a down-regulation of Akt activity and the loss of mitochondrial membrane potential (MMP), which was accompanied by a decrease in Bcl-2 expression and an increase in Bid cleavage. These data suggest that CGZ is capable of inducing apoptotic cell death independently of PPARγ in glioma cells, by down-regulating Akt activity and inducing MMP collapse.

15-lipoxygenase-1 exerts its tumor suppressive role by inhibiting nuclear factor-kappa B via activation of PPAR gamma

15-Lipoxygenase-1 (15-LOX-1) is an enzyme of the inflammatory eicosanoid pathway whose expression is known to be lost in colorectal cancer (CRC). We have previously shown that reintroduction of the gene in CRC cell lines slows proliferation and induces apoptosis (Cimen et al. [2009] Cancer Sci 100: 2283-2291). We have hypothesized that 15-LOX-1 may be anti-tumorigenic by the inhibition of the anti-apoptotic inflammatory transcription factor nuclear factor kappa B. We show here that ectopic expression of 15-LOX-1 gene in HCT-116 and HT-29 CRC cell lines inhibited the degradation of inhibitor of kappa B (IκBα), decreased nuclear translocation of p65 and p50, decreased DNA binding in the nucleus and decreased transcriptional activity of Nuclear factor kappa B (NF-κB). As the 15-LOX-1 enzymatic product 13(S)-HODE is known to be a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, and NF-κB can be inhibited by PPARγ, we examined whether activation of PPARγ was necessary for the abrogation of NF-κB activity. Our data show that the inhibition of both early and late stages of NF-κB activation could rescued by the PPARγ antagonist GW9662 indicating that the inhibition was most likely mediated via PPARγ.

The Role of PPAR-gamma and Its Interaction with COX-2 in Pancreatic Cancer

In recent years, the study of the peroxisome proliferators activated receptor gamma (PPAR-γ) as a potential target for cancer prevention and therapy has gained a strong interest. However, the overall biological significance of PPAR-γ in cancer development and progression is still controversial. While many reports documented antiproliferative effects in human cancer cell and animal models, several studies demonstrating potential tumor promoting actions of PPAR-γ ligands raised considerable concerns about the role of PPAR-γ in human cancers. Controversy also exists about the role of PPAR-γ in human pancreatic cancers. The current review summarizes the data about PPAR-γ in pancreatic cancer and highlights the biologically relevant interactions between the cyclooxygenase and PPAR system.

The complexities of obesity and diabetes with the development and progression of pancreatic cancer

Pancreatic cancer (PC) is one of the most lethal malignant diseases with the worst prognosis. It is ranked as the fourth leading cause of cancer-related deaths in the United States. Many risk factors have been associated with PC. Interestingly, large numbers of epidemiological studies suggest that obesity and diabetes, especially type-2 diabetes, are positively associated with increased risk of PC. Similarly, these chronic diseases (obesity, diabetes, and cancer) are also a major public health concern. In the U.S. population, 50 percent are overweight, 30 percent are medically obese, and 10 percent have diabetes mellitus (DM). Therefore, obesity and DM have been considered as potential risk factors for cancers; however, the focus of this article is restricted to PC. Although the mechanisms responsible for the development of these chronic diseases leading to the development of PC are not fully understood, the biological importance of the activation of insulin, insulin like growth factor-1 (IGF-1) and its receptor (IGF-1R) signaling pathways in insulin resistance mechanism and subsequent induction of compensatory hyperinsulinemia has been proposed. Therefore, targeting insulin/IGF-1 signaling with anti-diabetic drugs for lowering blood insulin levels and reversal of insulin resistance could be useful strategy for the prevention and/or treatment of PC. A large number of studies have demonstrated that the administration of anti-diabetic drugs such as metformin and thiazolidinediones (TZD) class of PPAR-γ agonists decreases the risk of cancers, suggesting that these agents might be useful anti-tumor agents for the treatment of PC. In this review article, we will discuss the potential roles of metformin and TZD anti-diabetic drugs as anti-tumor agents in the context of PC and will further discuss the complexities and the possible roles of microRNAs (miRNAs) in the pathogenesis of obesity, diabetes, and PC.

Combined treatment with TRAIL and PPARγ ligands overcomes chemoresistance of ovarian cancer cell lines

PURPOSE

Ovarian cancer accounts for the highest mortality among all gynecological cancers, mainly due to the fast developing chemoresistance. The death ligand TRAIL induces apoptosis and is able to sensitize tumor cells to cytostatic drugs without affecting physiological tissue. Combined treatment of TRAIL and the antidiabetic acting PPARγ ligands was shown to induce apoptosis synergistically in different ovarian cancer cell lines.

METHODS

To investigate feasible TRAIL-dependent inhibition of proliferation and induction of apoptosis in chemoresistant ovarian cancer cell lines, the drug- and TRAIL-sensitive HEY cell line was utilized to develop subclones with selective resistance against cisplatin, etoposide, docetaxel, paclitaxel, gemcitabine and pemetrexed, as well as against TRAIL as control cell line. Expression of the key factors of the TRAIL signaling pathway, TRAIL receptors 1-4, caspase-8, FLIP and XIAP, was analyzed before and after TRAIL treatment by immunoblotting.

RESULTS

Cell proliferation experiments showed TRAIL-dependent inhibition that was further increased by combination treatment with the PPARγ ligands. Simultaneous exposure of TRAIL and the PPARγ ligands also resulted in enhanced induction of apoptosis even in partial TRAIL-resistant HEY cell lines. In the parental HEY cell line, additional treatment with the PPARγ ligands led to an increased protein expression of DR5 and a further decline of XIAP expression.

CONCLUSION

Therefore, the combinational treatment with TRAIL and PPARγ ligands might be a promising experimental therapy because the PPARγ ligands, especially d15-PGJ(2), sensitize drug-resistant ovarian cancer cells to TRAIL-induced apoptosis.

Insights on distinct pathways of thiazolidinediones (PPARgamma ligand)-promoted apoptosis in TRAIL-sensitive or -resistant malignant urothelial cells

Thiazolidinediones, including rosiglitazone and troglitazone, are insulin-sensitizing drugs and high-affinity ligands for the peroxisome proliferator-activated receptor gamma (PPARgamma). Apart from their antidiabetic activity, these molecules possess antitumor properties. We investigated their potential apoptotic effects on RT4 (derived from a well-differentiated Grade I papillary tumor) and T24 (derived from an undifferentiated Grade III carcinoma) bladder cancer cells. Rosiglitazone induced G2/M or G0/G1 phase cell cycle arrest in RT4 and T24 cells, respectively. Only troglitazone triggered apoptosis via extrinsic and intrinsic pathways in both cell lines. Interestingly, rosiglitazone amplified TRAIL-induced apoptosis in TRAIL-sensitive RT4 cells or let TRAIL-resistant T24 cells to respond to TRAIL. Thiazolidinediones acted through PPARgamma activation-independent mechanisms. The underlying mechanisms involved for the first time in cancer cells the upregulation of soluble and/or membrane-bound TRAIL. This was associated with increased cell surface death receptor 5 expression and c-FLIP and survivin downregulation, mediated in part through proteasome-dependent degradation in troglitazone-promoted cell death. Therefore, the combination of rosiglitazone and TRAIL could be clinically relevant as chemopreventive or therapeutic agents for the treatment of TRAIL-resistant high-grade urothelial cancers.

The role of the PAX8/PPARgamma fusion oncogene in the pathogenesis of follicular thyroid cancer

When identified at early stages, most well-differentiated thyroid cancers are readily treated and yield excellent outcomes. Follicular thyroid cancer (FTC) however, when diagnosed at a late stage, may be very resistant to treatment, and exhibits 10-year survival rates less than 40%. Despite substantial progress in recent years, we still have limited understanding of the molecular and biological interrelationships between the various subtypes of benign and malignant follicular thyroid neoplasms. In contrast to the wealth of information available regarding papillary thyroid carcinoma (PTC), the triggering mechanisms of FTC development and the major underlying genetic alterations leading to follicular thyroid carcinogenesis remain obscure. Recent studies have focused on a chromosomal translocation, t(2;3) (q13;p25), fusing PAX8, a transcription factor that is essential for normal thyroid gland development, with the peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the steroid/thyroid nuclear receptor family. This chromatin rearrangement results in the expression of a PAX8/PPARgamma fusion protein, designated PPFP, whose incidence is relatively common in FTC and may represent an initiating event in the genesis of FTC. Here we review progress on the studies of PPFP that assess its involvement in FTC tumorigenesis.

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.

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.

Results of rosiglitazone therapy in patients with thyroglobulin-positive and radioiodine-negative advanced differentiated thyroid cancer

BACKGROUND

Rosiglitazone is a peroxisome proliferator-activated receptor (PPAR) gamma agonist that has shown promise as both an antiproliferative and redifferentiating agent for the treatment of thyroid cancer in preclinical studies. We investigated the efficacy and side effects of rosiglitazone therapy in patients with differentiated thyroid cancer of follicular cell origin that fails to take up radioiodine or is unresectable.

METHODS

Twenty patients with differentiated thyroid cancer were enrolled in an open-label, phase II trial of oral rosiglitazone treatment (4 mg daily for 1 week, then 8 mg daily for 7 weeks).

RESULTS

Five of 20 patients had a positive radioiodine scan after rosiglitazone treatment. Four patients had radioiodine uptake in the neck and one patient had uptake in the pelvis. Unstimulated thyroglobulin levels after rosiglitazone treatment increased in five patients, remained stable in 12 patients, and decreased in three patients. Seven patients had progressive disease on follow-up cross-sectional imaging; six patients in the size and number of lung metastasis and two patients in the size of the neck tumors. Overall, five patients had a partial response (decreased thyroglobulin or positive radioiodine uptake), three patients had stable disease (no change in thyroglobulin and radioiodine uptake status), and 12 patients had disease progression (increased thyroglobulin). By RECIST criteria, no patient had a complete or partial response to rosiglitazone treatment at 3 months follow-up. The mean follow-up time after protocol treatment was 12 months (median 12 months).

CONCLUSIONS

Our findings suggest that rosiglitazone therapy may induce radioiodine uptake and reduce serum thyroglobulin levels in some patients with differentiated thyroid cancer but this did not result in clinically significant response on long-term follow-up. Moreover, no patients had response to rosiglitazone therapy by anatomic imaging studies.

Use of thiazolidinediones does not affect prostate-specific antigen levels in men with diabetes

Thiazolidinediones (TZD) have been shown to down-regulate prostate-specific antigen (PSA) levels in prostate cancer cell lines and decrease PSA velocity among prostate cancer patients; however, the effect of TZDs on serum PSA levels among men with diabetes at risk for prostate cancer is unknown. We conducted a retrospective cohort study of veterans receiving care for diabetes between 1999 and 2005 to determine if TZD use affects PSA levels in veterans at risk for prostate cancer. Eligible patients were male, >or=45 years old, taking at least one oral antidiabetic medication, and with two or more recorded PSA values. Patients with a prior history of prostate cancer or prostatectomy were excluded. Of the 13,791 patients included in the adjusted analysis, 2,016 (14.6%) were prescribed a TZD. No effect of cumulative TZD dose on change in PSA was detected (P = 0.26). Increased TZD exposure was not associated with a change in PSA, suggesting that TZD treatment for diabetes is unlikely to affect prostate cancer detection.

Suppression of pancreatic carcinoma growth by activating peroxisome proliferator-activated receptor gamma involves angiogenesis inhibition

AIM

To study the possible actions and mechanisms of peroxisome proliferator-activated receptor gamma (PPARgamma), a ligand-activated transcription factor, in pancreatic carcinogenesis, especially in angiogenesis.

METHODS

Expressions of PPARgamma and retinoid acid receptor (RXRalpha) were examined by reverse-transcription polymerase chain reaction (RT-PCR) with immunocytochemical staining. Pancreatic carcinoma cells, PANC-1, were treated either with 9-cis-RA, a ligand of RXRalpha, or with 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), a ligand of PPARgamma, or both. Antiproliferative effect was evaluated by cell viability using methyltetrazolium (MTT) assay. A pancreatic carcinoma xenograft tumor model of nude mice was established by inoculating PANC-1 cells subcutaneously. Rosiglitazone, a specific ligand of PPARgamma, was administered via water drinking in experimental group of nude mice. After 75 d, all mice were sacrificed. Expression of proliferating cell nuclear antigen (PCNA) in tumor tissue was examined with immunohistochemical staining. Expression of vascular endothelial growth factor (VEGF) mRNA in PANC-1 cells, which were treated with 15d-PGJ(2) or 9-cis-RA at various concentrations or different duration, was detected by semi-quantitative RT-PCR. Effects of Rosiglitazone on changes of microvascular density (MVD) and VEGF expression were investigated in xenograft tumor tissue. Neovasculature was detected with immunohistochemistry staining labeled with anti-IV collagen antibody, and indicated by MVD.

RESULTS

RT-PCR and immunocytochemical staining showed that PPARgamma and RXRalpha were expressed in PANC-1 cells at both transcription level and translation level. MTT assay demonstrated that 15d-PGJ(2), 9-cis-RA and their combination inhibited the growth of PANC-1 cells in a dose-dependent manner. 9-cis-RA had a combined inhibiting action with 15d-PGJ(2) on the growth of pancreatic carcinoma. In vivo studies revealed that Rosiglitazone significantly suppressed the growth of pancreatic carcinoma as compared to control group (0.48+/-0.23 cm(3) vs 2.488+/-0.59 cm(3), P<0.05), and the growth inhibition rate was 80.7%. Immunohistochemistry study showed that PCNA was down regulated in Rosiglitazone-treated group compared to the control group. 15d-PGJ(2), 9-cis-RA and their combination inhibited the expression of VEGF mRNA in PANC-1 cells in a dose- and time-dependent manner. MVD was decreased more significantly in Rosiglitazone-treated mice (10.67+/-3.07) than in the control group (31.44+/-6.06) (P<0.01). VEGF expression in xenograft tumor tissue was also markedly down-regulated in Rosiglitazone-treated mice.

CONCLUSION

Activation of PPARgamma inhibits the growth of pancreatic carcinoma both in vitro and in vivo. Suppression of tumor angiogenesis by down-regulating the expression of VEGF may be one of the mechanisms by which PPARgamma activation inhibits the growth of pancreatic carcinoma.

Rat Urinary Bladder Carcinogenesis by Dual-Acting PPARalpha + gamma Agonists

Despite clinical promise, dual-acting activators of PPARalpha and gamma (here termed PPARalpha+gamma agonists) have experienced high attrition rates in preclinical and early clinical development, due to toxicity. In some cases, discontinuation was due to carcinogenic effect in the rat urothelium, the epithelial layer lining the urinary bladder, ureters, and kidney pelvis. Chronic pharmacological activation of PPARalpha is invariably associated with cancer in rats and mice. Chronic pharmacological activation of PPARgamma can in some cases also cause cancer in rats and mice. Urothelial cells coexpress PPARalpha as well as PPARgamma, making it plausible that the urothelial carcinogenicity of PPARalpha+gamma agonists may be caused by receptor-mediated effects (exaggerated pharmacology). Based on previously published mode of action data for the PPARalpha+gamma agonist ragaglitazar, and the available literature about the role of PPARalpha and gamma in rodent carcinogenesis, we propose a mode of action hypothesis for the carcinogenic effect of PPARalpha+gamma agonists in the rat urothelium, which combines receptor-mediated and off-target cytotoxic effects. The proposed mode of action hypothesis is being explored in our laboratories, towards understanding the human relevance of the rat cancer findings, and developing rapid in vitro or short-term in vivo screening approaches to faciliate development of new dual-acting PPAR agonist compounds.

The pathophysiology of hypertension in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disorder that predominantly affects women during their reproductive years. Although SLE can affect any organ system, the kidneys are prominently involved in the form of immune complex glomerulonephritis. In addition, in women with SLE, risk for the development of cardiovascular disease is dramatically increased. Hypertension is a major risk factor for cardiovascular disease and is highly prevalent in women with SLE. Nevertheless, there has been little exploration of the pathophysiological mechanisms that promote SLE hypertension. This review discusses the role of several mechanisms, with an emphasis on the kidney, in SLE hypertension. These mechanisms include the renin-angiotensin system, endothelin, oxidative stress, sex steroids, metabolic changes, peroxisome proliferator-activated receptor-gamma, and, perhaps most importantly, chronic inflammation and cytokines. Growing evidence suggests a link between chronic inflammation and hypertension. Therefore, elucidation of mechanisms that promote SLE hypertension may be of significant value not only for patients with SLE, but also for a better understanding of the basis for essential hypertension.

The Role of PPARs in the Endothelium: Implications for Cancer Therapy

The growth and metastasis of cancers intimately involve the vasculature and in particular the endothelial cell layer. Tumours require new blood vessel formation via angiogenesis to support growth. In addition, inflammation, coagulation, and platelet activation are common signals in the growth and metastasis of tumour cells. The endothelium plays a central role in the homeostatic control of inflammatory cell recruitment, regulating platelet activation and coagulation pathways. PPARalpha, -beta/delta, and -gamma are all expressed in endothelial cells. This review will discuss the roles of PPARs in endothelial cells in relation to angiogenesis, inflammation, coagulation, and platelet control pathways. In particular, we will discuss the recent evidence that supports the hypothesis that PPARalpha and PPARgamma are antiangiogenic receptors, while PPARbeta/delta is proangiogenic.

Peroxisome proliferator-activated receptor gamma expression in urothelial carcinomas of the bladder: association with differentiation, proliferation and clinical outcome

AIMS

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcriptional factor that regulates the transcription of various target genes. Our purpose is to investigate the clinicopathologic and prognostic significance of PPARgamma expression in human urothelial bladder cancer (BUC).

METHODS

Immunohistochemistry was applied in 117 paraffin-embedded specimens of human BUC to detect the proteins PPARgamma and Ki67. The image analysis method was used for the evaluation of the immunohistochemical staining.

RESULTS

PPARgamma protein was localized in the nuclei of the malignant cells. Its expression was inversely associated with the stage of BUCs (p<0.001), tumor grade (p=0.007) and the expression of the proliferation marker Ki67 (p=0.015) while it was found to exert a favorable effect on patients' overall survival (p=0.001).

CONCLUSION

The findings of the present study suggest that in BUC, PPARgamma expression can identify patients with a better prognosis who suffer from more differentiated, non-invasive tumors, of a low proliferative potential.

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.

1,1-Bis(3'-indolyl)-1-(p-biphenyl)methane inhibits basal-like breast cancer growth in athymic nude mice

Introduction

1,1-Bis (3'-indolyl)-1-(p-biphenyl) methane (CDIM9) has been identified as a new peroxisome proliferator-activated receptor (PPAR)-γ agonist that exhibits both receptor dependent and independent antitumor activities. CDIM9 has not previously been studied with respect to its effects against basal-like breast cancer. Our goal in the present study was to investigate the anti-basal-like breast tumor activity of CDIM9 in vitro and in vivo.

Methods

The effects of CDIM9 on cell protein and DNA syntheses were determined in basal-like breast cancer MDA-MB231 and BT549 cells in vitro. Maximum tolerated dose and dose-limited toxicity were determined in BalB/c mice, and antitumor growth activities were assessed in MDA-MB231 basal-like breast tumor xenografts in athymic nude mice.

Results

CDIM9 exhibited selective cell cytotoxicity and anti-proliferation effects on basal-like breast cancer lines. In MDA-MB231 cell, CDIM9 induced caveolin-1 and p27 expression, which was significantly downregulated by co-treatment with the PPAR-γ antagonist GW9662. Nonsteroidal anti-inflammatory drug-activated gene-1 and activating transcription factor-3 were upregulated by CDIM9 through a PPAR-γ independent pathway. CDIM9 (40 mg/kg daily, intraperitoneally, for 35 days) inhibited the growth of subcutaneous MDA-MB231 tumor xenografts by 87%, and produced a corresponding decrease in proliferation index. Nearly half of the treated mice (46%) had complete durable remissions, confirmed by histology. The growth of an established tumor was inhibited by CDIM9 treatment (64 mg/kg daily, intraperitoneally, for 10 days), with a mean tumor growth inhibition of 67% as compared with controls. CDIM9 induced increases in tumor caveolin-1 and p27 in vivo, which may contribute to its antitumor activity in basal-like breast cancer.

Conclusion

CDIM9 showed potent antiproliferative effects on basal-like breast cancer cell in tissue culture and dramatic growth inhibition in animal models at safe doses. These findings justify further development of this drug for treatment of basal-like breast cancer.

PGC-1alpha induces apoptosis in human epithelial ovarian cancer cells through a PPARgamma-dependent pathway

Peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1 alpha (PGC-1alpha) coactivates multiple transcription factors and regulates several metabolic processes. The current study investigated the role of PGC-1alpha in the induction of apoptosis in human epithelial ovarian cancer cells. The PGC-1alpha mRNA level between human ovaries and human ovarian epithelial tumors was examined by quantitative RT-PCR. Less PGC-1alpha expression was found in the surface epithelium of malignant tumors compared with normal ovaries. Overexpression of PGC-1alpha in human epithelial ovarian cancer cell line Ho-8910 induced cell apoptosis through the coordinated regulation of Bcl-2 and Bax expression. Microarray analyses confirmed that PGC-1alpha dramatically affected the apoptosis-related genes in Ho-8910 cells. Mitochondrial functional assay showed that the induction of apoptosis was through the terminal stage by the release of cytochrome c. Furthermore, PGC-1alpha-induced apoptosis was partially, but not completely, blocked by PPARgamma antagonist (GW9662), and suppression of PPARgamma expression by siRNA also inhibited PGC-1alpha-induced apoptosis in Ho-8910 cells. These data suggested that PGC-1alpha exerted its effect through a PPARgamma-dependent pathway. Our findings indicated that PGC-1alpha was involved in the apoptotic signal transduction pathways and downregulation of PGC-1alpha may be a key point in promoting epithelial ovarian cancer growth and progression.

Peroxisome proliferator-activated receptor gamma: a novel target for cancer therapeutics?

Peroxisome proliferator-activated receptors are ligand-activated intracellular transcription factors that have been implicated in important biological processes such as inflammation, tissue remodeling and atherosclerosis. Emerging information also implicates peroxisome proliferator-activated receptors in oncogenesis. Peroxisome proliferator-activated receptor gamma, the best studied of the peroxisome proliferator-activated receptors, modulates the proliferation and apoptosis of many cancer cell types, and it is expressed in many human tumors including lung, breast, colon, prostate and bladder. Natural and synthetic agents capable of activating peroxisome proliferator-activated receptor gamma have been found to inhibit cancer cell growth in vitro and in animal models. These agents, however, are not specific and both peroxisome proliferator-activated receptor gamma-dependent and peroxisome proliferator-activated receptor gamma-independent pathways involved in their effects have been identified. Together, these studies, coupled with a few clinical trials, suggest that peroxisome proliferator-activated receptor gamma is a novel target for the development of new and effective anticancer therapies.

Mechanisms of Disease: adipokines and breast cancer—endocrine and paracrine mechanisms that connect adiposity and breast cancer

A vast number of epidemiological studies suggest an important, but still controversial, role for obesity and adipose tissue mass in breast cancer risk and an association with tumor phenotype. The main conclusions from these studies raise the possibility that the adipose tissue can act as an effector organ that influences both cancer risk and tumor behavior. Here we also review heterotypic mechanisms in breast-cancer tumorigenesis; these mechanisms involve soluble secreted factors from peritumoral cells, extracellular-matrix components and interactions between stromal cells and tumor cells that create a specific and local peritumoral microenvironment. As a special focus, we discuss the increasing evidence for a role of peritumoral adipose tissue and secreted adipokines (such as adiponectin and leptin) in breast cancer; furthermore, the cellular and molecular basis of the peritumoral 'desmoplastic' tissue reaction observed in breast cancer is reviewed in detail.

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.

A phase II trial of rosiglitazone in patients with thyroglobulin-positive and radioiodine-negative differentiated thyroid cancer

BACKGROUND

Rosiglitazone is a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist that has been shown to induce differentiation, cell cycle arrest, and apoptosis in a variety of human cancers including thyroid cancer.

METHODS

Ten patients with differentiated thyroid cancer were enrolled in an open-label, phase II trial of oral rosiglitazone treatment (4 mg daily for 1 week, then 8 mg daily for 7 weeks). The levels of PPARgamma receptor mRNA and protein expression were determined in the patient's neoplasm.

RESULTS

Of 10 patients, 4 had positive radioiodine scans after rosiglitazone therapy with uptake in the neck in 3 patients and in the pelvis in 1 patient. After treatment, the serum thyroglobulin level decreased in 2 patients, increased in 5 patients, and was stable in 3 patients. No patient developed clinically important toxicity associated with rosiglitazone treatment. We found no relationship in the level of PPARgamma mRNA and protein expression in patients who had radioiodine uptake compared with those who did not.

CONCLUSIONS

Our findings suggest that rosiglitazone treatment may induce radioiodine uptake in some patients with thyroglobulin-positive and radioiodine-negative differentiated thyroid cancer. We found no relationship between the expression level of the PPARgamma mRNA and protein in the neoplasm and radioiodine uptake status after rosiglitazone therapy, questioning the potential pathway of effect.

Arachidonic acid suppresses growth of human lung tumor A549 cells through down-regulation of ALDH3A1 expression

Expression of aldehyde dehydrogenase 3A1 (ALDH3A1) in certain normal and tumor cells is associated with protection against the growth inhibitory effect of reactive aldehydes generated during membrane lipid peroxidation. We found that human lung tumor (A549) cells, which express high levels of ALDH3A1 protein, were significantly less susceptible to the antiproliferative effects of 4-hydroxynonenal compared to human hepatoma HepG2 or SK-HEP-1 cells that lack ALDH3A1 expression. However, A549 cells became susceptible to lipid peroxidation products when they were treated with arachidonic acid. The growth suppression of A549 cells induced by arachidonic acid was associated with increased levels of lipid peroxidation and with reduced ALDH3A1 enzymatic activity, protein, and mRNA levels. Furthermore, arachidonic acid treatment of the A549 cells resulted in an increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma), whereas NF-kappaB binding activity was inhibited. Blocking PPARgamma using a selective antagonist, GW9662, prevented the arachidonic acid-mediated reduction of ALDH3A1 expression as well as the growth inhibition of A549 cells, suggesting the central role of PPARgamma in these phenomena. The increase in PPARgamma and the reduction in ALDH3A1 were also prevented by exposing cells to vitamin E concomitant with arachidonic acid treatment. In conclusion, our data show that the arachidonic acid-induced suppression of A549 cell growth is associated with increased lipid peroxidation and decreased ALDH3A1 expression, which may be due to activation of PPARgamma.

Peroxisome proliferator-activated receptor-gamma ligands for the treatment of breast cancer

Pioglitazone and rosiglitazone are thiazolidinediones used for the treatment of Type 2 diabetes mellitus. They modulate glucose and fat metabolism, mainly by binding to the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)-gamma. PPAR-gamma signalling is involved in a number of other disease conditions including cancer. In breast cancer cells, PPAR-gamma ligands inhibit proliferation and induce apoptosis both in vitro and in vivo. PPAR-gamma ligands also inhibit tumour angiogenesis and invasion. The only published clinical trial using a PPAR-gamma ligand in patients with metastatic breast cancer failed to show any clinical benefits. The mechanism of action of the thiazolidinediones in breast cancer cells is not fully understood but involves interactions with other nuclear hormone receptors, transcriptional co-activators and repressors as well as PPAR-gamma-independent effects. A better understanding of these mechanisms will be needed before PPAR-gamma ligands may be useful in the treatment of breast cancer patients.

Comparative effects of RRR-alpha- and RRR-gamma-tocopherol on proliferation and apoptosis in human colon cancer cell lines

Background

Mediterranean societies, with diets rich in vitamin E isoforms, have a lower risk for colon cancer than those of northern Europe and the Americas. Vitamin E rich diets may neutralize free radicals generated by fecal bacteria in the gut and prevent DNA damage, but signal transduction activities can occur independent of the antioxidant function. The term vitamin E represents eight structurally related compounds, each differing in their potency and mechanisms of chemoprevention. The RRR-γ-tocopherol isoform is found primarily in the US diet, while RRR-α-tocopherol is highest in the plasma.

Methods

The effectiveness of RRR-α- and RRR-γ-tocopherol at inhibiting cell growth and inducing apoptosis in colon cancer cell lines with varying molecular characteristics (SW480, HCT-15, HCT-116 and HT-29) and primary colon cells (CCD-112CoN, nontransformed normal phenotype) was studied. Colon cells were treated with and without RRR-α- or RRR-γ-tocopherol using varying tocopherol concentrations and time intervals. Cell proliferation and apoptosis were measured using the trypan blue assay, annexin V staining, DNA laddering and caspase activation.

Results

Treatment with RRR-γ-tocopherol resulted in significant cell death for all cancer cell lines tested, while RRR-α-tocopherol did not. Further, RRR-γ-tocopherol treatment showed no cytotoxicity to normal colon cells CCD-112CoN at the highest concentration and time point tested. RRR-γ-tocopherol treatment resulted in cleavage of PARP, caspase 3, 7, and 8, but not caspase 9. Differences in the percentage cell death and apoptosis were observed in different cell lines suggesting that molecular differences in these cell lines may influence the ability of RRR-γ-tocopherol to induce cell death.

Conclusion

This is the first study to demonstrate that multiple colon cancer cell lines containing varying genetic alterations will under go growth reduction and apoptosis in the presence of RRR-γ-tocopherol without damage to normal colon cells. The amount growth reduction was dependent upon the molecular signatures of the cell lines. Since RRR-γ-tocopherol is effective at inhibition of cell proliferation at both physiological and pharmacological concentrations dietary RRR-γ-tocopherol may be chemopreventive, while pharmacological concentrations of RRR-γ-tocopherol may aid chemotherapy without toxic effects to normal cells demonstrated by most chemotherapeutic agents.

Novel time-dependent vascular actions of Δ9-tetrahydrocannabinol mediated by peroxisome proliferator-activated receptor gamma

Cannabinoids have widespread effects on the cardiovascular system, only some of which are mediated via G-protein-coupled cell surface receptors. The active ingredient of cannabis, Delta9-tetrahydrocannabinol (THC), causes acute vasorelaxation in various arteries. Here we show for the first time that THC also causes slowly developing vasorelaxation through activation of peroxisome proliferator-activated receptors gamma (PPARgamma). In vitro, THC (10 microM) caused time-dependent vasorelaxation of rat isolated arteries. Time-dependent vasorelaxation to THC was similar to that produced by the PPARgamma agonist rosiglitazone and was inhibited by the PPARgamma antagonist GW9662 (1 microM), but not the cannabinoid CB1 receptor antagonist AM251 (1 microM). Time-dependent vasorelaxation to THC requires an intact endothelium, nitric oxide, production of hydrogen peroxide, and de novo protein synthesis. In transactivation assays in cultured HEK293 cells, THC-activated PPARgamma, transiently expressed in combination with retinoid X receptor alpha and a luciferase reporter gene, in a concentration-dependent manner (100 nM-10 microM). In vitro incubation with THC (1 or 10 microM, 8 days) stimulated adipocyte differentiation in cultured 3T3L1 cells, a well-accepted property of PPARgamma ligands. The present results provide strong evidence that THC is a PPARgamma ligand, stimulation of which causes time-dependent vasorelaxation, implying some of the pleiotropic effects of cannabis may be mediated by nuclear receptors.

Receptor-independent actions of PPAR thiazolidinedione agonists: is mitochondrial function the key?

Agonists of the peroxisome proliferator activated receptor gamma (PPAR(gamma)) are currently used for treatment of type 2 diabetes due to their insulin sensitizing and glucose metabolism stabilizing effects. More recently some of these same agonists were shown to exert anti-inflammatory and anti-proliferative effects as well. Although PPAR(gamma) agonists can operate via receptor-mediated events occurring at the genomic level, thereby causing long lasting changes in gene expression patterns, recent studies demonstrate non-genomic as well as genomic actions, and receptor-dependent as well as receptor-independent effects of the thiazolidinedione (TZD) class of PPAR(gamma) agonists. In this review we will summarize data describing some of these novel, receptor independent actions of TZDs, review evidence that TZDs directly influence mitochondrial function, and attempt to reconcile how changes in mitochondrial function could contribute to other receptor-independent actions of these drugs.