In vitro and in vivo effects of the PPAR-alpha agonists fenofibrate and retinoic acid in endometrial cancer

Regulation of URG4/URGCP and PPARα gene expressions after retinoic acid treatment in neuroblastoma cells

Neuroblastoma (NB), originating from neural crest cells, is the most common extracranial tumor of childhood. Retinoic acid (RA) which is the biological active form of vitamin A regulates differentiation of NB cells, and RA derivatives have been used for NB treatment. PPARα (peroxisome proliferator-activated receptor) plays an important role in the oxidation of fatty acids, carcinogenesis, and differentiation. URG4/URGCP gene is a proto-oncogene and that overexpression of URG4/URGCP is associated with metastasis and tumor recurrence in osteosarcoma. It has been known that URG4/URGCP gene is an overexpressed gene in hepatocellular carcinoma and gastric cancers. This study aims to detect gene expression patterns of PPARα and URG4/URGCP genes in SH-SY5Y NB cell line after RA treatment. Expressions levels of PPARα and URG4/URGCP genes were analyzed after RA treatment for reducing differentiation in SH-SY5Y NB cell line. To induce differentiation, the cells were treated with 10 μM RA in the dark for 3-10 days. Gene expression of URG4/URGCP and PPARα genes were presented as the yield of polymerase chain reaction (PCR) products from target genes compared with the yield of PCR products from the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. SH-SY5Y cells possess small processes in an undifferentiated state, and after treatment with RA, the cells developed long neurites, resembling a neuronal phenotype. PPARα gene expression increased in RA-treated groups; URG4/URGCP gene expression decreased in SH-SY5Y cells after RA treatment compared with that in the control cells. NB cell differentiation might associate with PPARα and URG4/URGCP gene expression profile after RA treatment.

Novel MEK inhibitor trametinib and other retinoblastoma gene (RB)-reactivating agents enhance efficacy of 5-fluorouracil on human colon cancer cells

Chemotherapy for colorectal cancer has become more complicated and diversified with the appearance of molecular-targeting agents. 5-Fluorouracil (5-FU) has been a mainstay of chemotherapy for colorectal cancer, but it is still unknown whether the combining of 5-FU with novel molecular-targeting agents is effective. Thymidylate synthase (TS) is a direct target of 5-FU, and the low TS level has been generally supposed to sensitize 5-FU's efficacy. We therefore hypothesized that RB-reactivating agents could enhance the efficacy of 5-FU, because the RB-reactivating agents could suppress the function of transcription factor E2F of TS gene promoter. We used three RB-reactivating agents, trametinib/GSK1120212 (MEK inhibitor), fenofibrate (PPARα agonist), and LY294002 (PI3K inhibitor), with 5-FU against human colon cancer HT-29 and HCT15 cells. Trametinib induced p15 and p27 expression and reduced cyclin D1 levels in HT-29 cells. Fenofibrate also dephosphorlated ERK1/2 and reduced cyclin D1 levels in HT-29 cells. LY294002 induced p27 expression in HCT15 cells. All three agents caused dephosphorylation of RB protein and G1-phase arrest with a reduction of TS expression. As a consequence, the combination of 5-FU with each of the agents resulted in a significant decrease of colony numbers in HT-29 or HCT15 cells. These results suggest "RB-reactivation therapy" using molecular-targeting agents to be a new strategy for 5-FU-based chemotherapy. In particular, we strongly expect trametinib, which was discovered in Japan and was recently submitted to FDA for approval, to be used together with established regimens for colorectal cancer.

Differential Effects of MicroRNAs on Glioblastoma Growth and Migration

Glioblastoma multiforme is characterized by rapid proliferation, aggressive metastatic potential, and resistance to radio- and chemotherapy. The matricellular protein CYR61 regulates cellular proliferation and migration and is highly expressed in Glioblastomas. MicroRNAs are 22-nucleotides long RNAs that regulate gene expression post-transcriptionally. Here, we utilized the LN229 glioblastoma cell line and found that CYR61 is a target of miR-136, miR-155, and miR-634. Over-expression of miR-136 and miR-634 miRNAs negatively affected proliferation, but not migration, while expression of miR-155 reduced migration but did not affect the proliferation of LN229 cells. Investigation of the molecular mechanisms affected by expression of miR-634 revealed an increased phosphorylation of p70S6 kinase, suggesting an induction of the mammalian target of rapamycin (mTOR) complex 1 pathway. Additionally, in miR-634 overexpressing cells, TSC2, a negative regulator of mTOR signaling, was found to be decreased. Altogether, our study provides insights on the differential roles of miRs-136, -155, and -634 in regulating glioblastoma cell growth and migration, and how microRNAs could be manipulated to decrease the aggressiveness and metastatic potential of tumor cells.

Fenofibrate down-regulates the expressions of androgen receptor (AR) and AR target genes and induces oxidative stress in the prostate cancer cell line LNCaP

Fenofibrate, a peroxisome proliferator-androgen receptor-alpha agonist, is widely used in treating different forms of hyperlipidemia and hypercholesterolemia. Recent reports have indicated that fenofibrate exerts anti-proliferative and pro-apoptotic properties. This study aims to investigate the effects of fenofibrate on the prostate cancer (PCa) cell line LNCaP. The effects of fenofibrate on LNCaP cells were evaluated by flow cytometry, reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assays, Western blot analysis, and dual-luciferase reporter assay. Fenofibrate induces cell cycle arrest in G1 phase and apoptosis in LNCaP cells, reduces the expressions of androgen receptor (AR) and AR target genes (prostate-specific antigen and TMPRSS2), and inhibits Akt phosphorylation. Fenofibrate can induce the accumulation of intracellular reactive oxygen species and malondialdehyde, and decrease the activities of total anti-oxidant and superoxide dismutase in LNCaP cells. Fenofibrate exerts an anti-proliferative property by inhibiting the expression of AR and induces apoptosis by causing oxidative stress. Therefore, our data suggest fenofibrate may have beneficial effects in fenofibrate users by preventing prostate cancer growth through inhibition of androgen activation and expression.

Molecular bases of endometrial cancer: new roles for new actors in the diagnosis and the therapy of the disease

Endometrial carcinoma (EC) is the most commonly diagnosed gynecologic malignancy in the western world. The majority of these cancers are curable, but a subset about 15-20% of endometrial tumors exhibits an aggressive phenotype. Based on clinic-pathological and molecular characteristics, EC has been classified into two groups: Type I estrogen-dependent adenocarcinomas, which have a good prognosis and an endometrioid histology, and Type II or non-estrogen-dependent EC associated with poor prognosis and non-endometrioid histology. EC develops as a result of a stepwise accumulation of alterations that seem to be specific of each histological type. However, more knowledge is needed to better understand the differences in the biology and the clinical outcome of EC. We would like to highlight the need to explore new potential biomarkers of EC as a tool for the detection and monitoring of aggressive endometrial tumors that, at the same time, will allow us to develop novel and more selective molecular targeted therapies against EC.

Fenofibrate-induced nuclear translocation of FoxO3A triggers Bim-mediated apoptosis in glioblastoma cells in vitro

Anti-neoplastic potential of calorie restriction or ligand-induced activation of peroxisome proliferator activated receptors (PPARs) has been demonstrated in multiple studies; however, mechanism(s) by which tumor cells respond to these stimuli remain to be elucidated. One of the potent agonists of PPARα, fenofibrate, is a commonly used lipid-lowering drug with low systemic toxicity. Fenofibrate-induced PPARα transcriptional activity is expected to shift energy metabolism from glycolysis to fatty acid β-oxidation, which in the long-term, could target weak metabolic points of glycolysis-dependent glioblastoma cells. The results of this study demonstrate that 25 μM fenofibrate can effectively repress malignant growth of primary glial tumor cells and glioblastoma cell lines. This cytostatic action involves G(1) arrest accompanied by only a marginal level of apoptotic cell death. Although the cells treated with 25 μM fenofibrate remain arrested, the cells treated with 50 μM fenofibrate undergo massive apoptosis, which starts after 72 h of the treatment. This delayed apoptotic event was preceded by FoxO3A nuclear accumulation, FoxO3A phosphorylation on serine residue 413, its elevated transcriptional activity and expression of FoxO-dependent apoptotic protein, Bim. siRNA-mediated inhibition of FoxO3A attenuated fenofibrate-induced apoptosis, indicating a direct involvement of this transcription factor in the fenofibrate action against glioblastoma. These properties of fenofibrate, coupled with its low systemic toxicity, make it a good candidate in support of conventional therapies against glial tumors.

Lipid profiles and the risk of endometrial cancer in the Swedish AMORIS study

BACKGROUND

While the association between obesity and endometrial cancer (EC) is well established, the underlying mechanisms require further study. We assessed possible links between lipid profiles and EC risk, while also taking into account BMI, parity, and menopausal status at baseline.

METHODS

Using the information available from the Swedish Apolipoprotein MOrtality RISk (AMORIS) study we created a cohort of 225,432 women with baseline values for glucose, triglycerides (TG), and total cholesterol (TC). Two subgroups of 31,792 and 26,317 had, in addition, baseline measurements of HDL, LDL, apolipoprotein A-I and apoB and BMI, respectively. We used Multivariate Cox proportional hazards models to analyze quartiles and dichotomized values of these lipid components for a link to EC risk.

RESULTS

During mean follow-up of 12 years (SD: 4.15), 1,144 persons developed endometrial cancer. A statistically significant association was found between TG and EC risk when using both quartiles and a clinical cut-off (Hazard Ratio (HR): 1.10 (95%CI: 0.88-1.37), 1.34 (1.09-1.63), and 1.57 (1.28-1.92)) for the 2(nd), 3(rd), and 4(th) quartile, compared to the 1(st), with P-value for trend: <0.001). The association remained after exclusion of the first three years of follow-up. Also total cholesterol and TG/HDL ratio were positively associated with EC risk, but no link was found for the other lipid components studied.

CONCLUSION

This detailed analysis of lipid components showed a consistent relation between TG levels and EC risk. Future research should continue to analyze the metabolic pathway and its relation to EC risk, as a pathway to further understand the relation of obesity and disease.

Generation and characterization of orthotopic murine models for endometrial cancer

We describe the generation of two orthotopic murine models for endometrial cancer (EC).The first model is generated from endometrial Hec-1A cancer cells transfected with luciferase and injected directly into the uterus of female mice. This model allows a follow-up with bioluminescence imaging (BLI) along the experiment and generates abdominal dissemination and lymphatic and hematogenous metastases in high percentages, also detectables with BLI. The dissemination pattern of this model imitates the advanced stages of EC in patients, and its molecular profile corresponds to aggressive type 2 EC (p53 positive, hormone receptors negative, high percentage of Ki67 positive cells). The second model is derived from endometrioid human tissue collected from surgical pieces. By injecting this tissue inside the uterine cavity of a mouse we obtain orthotopic growth with pelvic dissemination and lymph node metastasis. The molecular pattern observed in human type 1 endometrioid EC (p53 negative, low Ki67 index, presence of hormone receptors) is conserved after the murine growth in orthotopic tumor and metastases. This model supposes a singular pre-clinical tool to study therapeutic agents, though it mimics clinical and molecular behavior of endometrioid EC, which is the most common histology in the patient.

A Comparative Study of Mouse Hepatic and Intestinal Gene Expression Profiles under PPARα Knockout by Gene Set Enrichment Analysis

Gene expression profiling of PPARα has been used in several studies, but fewer studies went further to identify the tissue-specific pathways or genes involved in PPARα activation in genome-wide. Here, we employed and applied gene set enrichment analysis to two microarray datasets both PPARα related respectively in mouse liver and intestine. We suggested that the regulatory mechanism of PPARα activation by WY14643 in mouse small intestine is more complicated than in liver due to more involved pathways. Several pathways were cancer-related such as pancreatic cancer and small cell lung cancer, which indicated that PPARα may have an important role in prevention of cancer development. 12 PPARα dependent pathways and 4 PPARα independent pathways were identified highly common in both liver and intestine of mice. Most of them were metabolism related, such as fatty acid metabolism, tryptophan metabolism, pyruvate metabolism with regard to PPARα regulation but gluconeogenesis and propanoate metabolism independent of PPARα regulation. Keratan sulfate biosynthesis, the pathway of regulation of actin cytoskeleton, the pathways associated with prostate cancer and small cell lung cancer were not identified as hepatic PPARα independent but as WY14643 dependent ones in intestinal study. We also provided some novel hepatic tissue-specific marker genes.

PPAR Ligands for Cancer Chemoprevention

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

Multiple Interactions between Peroxisome Proliferators-Activated Receptors and the Ubiquitin-Proteasome System and Implications for Cancer Pathogenesis

The peroxisome proliferator-activated receptors (PPAR) α, β/δ, and γ are ligand-activated nuclear receptors involved in a number of physiological processes, including lipid and glucose homeostasis, inflammation, cell growth, differentiation, and death. PPAR agonists are used in the treatment of human diseases, like type 2 diabetes and dyslipidemia, and PPARs appear as promising therapeutic targets in other conditions, including cancer. A better understanding of the functions and regulation of PPARs in normal and pathological processes is of primary importance to devise appropriate therapeutic strategies. The ubiquitin-proteasome system (UPS) plays an important role in controlling level and activity of many nuclear receptors and transcription factors. PPARs are subjected to UPS-dependent regulation. Interestingly, the three PPAR isotypes are differentially regulated by the UPS in response to ligand-dependent activation, a phenomenon that may be intrinsically connected to their distinct cellular functions and behaviors. In addition to their effects ongene expression, PPARs appear to affect protein levels and downstream pathways also by modulating the activity of the UPS in target-specific manners. Here we review the current knowledge of the interactions between the UPS and PPARs in light of the potential implications for their effects on cell fate and tumorigenesis.

Role of peroxisome proliferator-activated receptor alpha in the control of cyclooxygenase 2 and vascular endothelial growth factor: involvement in tumor growth

A growing body of evidence indicates that PPAR (peroxisome proliferator-activated receptor) α agonists might have therapeutic usefulness in antitumoral therapy by decreasing abnormal cell growth, and reducing tumoral angiogenesis. Most of the anti-inflammatory and antineoplastic properties of PPAR ligands are due to their inhibitory effects on transcription of a variety of genes involved in inflammation, cell growth and angiogenesis. Cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF) are crucial agents in inflammatory and angiogenic processes. They also have been significantly associated to cell proliferation, tumor growth, and metastasis, promoting tumor-associated angiogenesis. Aberrant expression of VEGF and COX-2 has been observed in a variety of tumors, pointing to these proteins as important therapeutic targets in the treatment of pathological angiogenesis and tumor growth. This review summarizes the current understanding of the role of PPARα and its ligands in the regulation of COX-2 and VEGF gene expression in the context of tumor progression.

Fenofibrate suppresses growth of the human hepatocellular carcinoma cell via PPARα-independent mechanisms

Fenofibrate, a peroxisome proliferator-activated receptor (PPAR) α agonist, is a hypolipidemic drug. Although several studies have explored the fenofibrate-induced antiproliferative effect in cultured human cells, it is not clear which role PPARα plays in this antiproliferative effect. Therefore, we investigated the antiproliferative mechanism of fenofibrate in Huh7 (human hepatoma cell line). Cell viability was measured by the WST-8 assay and cell proliferation was assessed using the BrdU incorporation assay. The cell cycle was analyzed by flow cytometry. The cyclins, tumor suppressor proteins and regulators of the AKT signaling pathway were analyzed by immunoblotting. Using flow cytometry, we showed that fenofibrate blocks entry into the S phase of the cell cycle. We certified that this G1 arrest is caused by the reduction of cyclin A and E2F1 and the accumulation of the cyclin-dependent kinase inhibitor p27. Interestingly, the antiproliferative effect of fenofibrate was not affected by the PPARα antagonist (GW6471) or by PPARα-specific siRNA. These results suggest that fenofibrate suppresses Huh7 cell growth through a PPARα independent mechanism. Furthermore, we showed that treatment of Huh7 cells with fenofibrate leads to suppression of AKT phosphorylation. We also found for the first time that fenofibrate increased the C-terminal modulator protein (CTMP), which inhibits AKT phosphorylation. Our data suggest that fenofibrate inhibits the proliferation of Huh7 cells by blocking Akt activation, and that CTMP is one of the key players for this antiproliferative property of fenofibrate in Huh7 cells.

Retinoic acid inhibits endometrial cancer cell growth via multiple genomic mechanisms

Previous studies have indicated that retinoic acid (RA) may be therapeutic for endometrial cancer. However, the downstream target genes and pathways triggered by ligand-activated RA receptor α (RARα) in endometrial cancer cells are largely unknown. In this study, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and immunoblotting assays were used to assess the roles of RA and the RA agonist (AM580) in the growth of endometrial cancer cells. Illumina-based microarray expression profiling of endometrial Ishikawa cells incubated with and without AM580 for 1, 3, and 6 h was performed. We found that both RA and AM580 markedly inhibited endometrial cancer cell proliferation, while knockdown of RARα could block AM580 inhibition. Knockdown of RARα significantly increased proliferating cell nuclear antigen and BCL2 protein levels. Incubation of Ishikawa cells with or without AM580 followed by microarray expression profiling showed that 12 768 genes out of 47 296 gene probes were differentially expressed with significant P values. We found that 90 genes were the most regulated genes with the most significant P value (P<0.0001) using F-test. We selected four highly regulated genes with diverse functions, namely G0S2, TNFAIP2, SMAD3, and NRIP1. Real-time PCR verified that AM580 highly regulated these genes, whereas chromatin immunoprecipitation-PCR assay demonstrated that ligand-activated RARα interacted with the promoter of these genes in intact endometrial cancer cells. AM580 also significantly altered 18 pathways including those related to cell growth, differentiation, and apoptosis. In conclusion, AM580 treatment of Ishikawa cells causes the differential expression of a number of RARα target genes and activation of signaling pathways. These pathways could, therefore, mediate the carcinogenesis of human endometrial cancer.

Fenofibrate exhibits a high potential to suppress the formation of squamous cell carcinoma in an oral-specific 4-nitroquinoline 1-oxide/arecoline mouse model

The excessive use of areca nut and/or tobacco may induce the production of free radicals and reactive oxygen species, which affect the lipid contents of the cell membrane and are possibly involved in tumorigenic processes in the oral cavity. The aim of this study was to investigate the therapeutic efficacy of fenofibrate (0.1% or 0.3%, w/w), a ligand of the peroxisome proliferator-activated receptor alpha (PPARα), in a 4-nitroquinoline 1-oxide (4-NQO)/arecoline-induced oral cancer mouse model. The carcinogen, 4-NQO/arecoline, was administrated to C57BL/6JNarl mice for 8weeks followed by fenofibrate treatment for 12 or 20weeks. After 28weeks, changes in serum lipids, the multiplicity of tumor lesions, and tumor sizes were determined together with changes in the immunohistochemical expressions of PPARα, acetyl-coenzyme A carboxylase (ACC), the epidermal growth factor receptor (EGFR), and cyclooxygenase-2 (COX2). The results showed that when compared to the 4-NQO/arecoline only group, 0.3% fenofibrate treatment increased serum total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) levels. 0.3% fenofibrate treatment suppressed the incidence rate of tongue lesions, reduced the multiplicity of squamous cell carcinoma (SCC), decreased the tumor size, and increased the immunoreactivity of EGFR and COX2 in oral dysplasia but decreased EGFR and COX2 expressions in SCC. These findings indicated that fenofibrate reduced the tumor incidence rate and suppressed the tumor progression into SCC and that these molecular events might be linked to the EGFR and COX2 regulatory pathways. We suggest that fenofibrate provides a new strategy for preventing oral tumor progression.

ROS accumulation and IGF-IR inhibition contribute to fenofibrate/PPARalpha -mediated inhibition of glioma cell motility in vitro

BACKGROUND

Glioblastomas are characterized by rapid cell growth, aggressive CNS infiltration, and are resistant to all known anticancer regimens. Recent studies indicate that fibrates and statins possess anticancer potential. Fenofibrate is a potent agonist of peroxisome proliferator activated receptor alpha (PPARalpha) that can switch energy metabolism from glycolysis to fatty acid beta-oxidation, and has low systemic toxicity. Fenofibrate also attenuates IGF-I-mediated cellular responses, which could be relevant in the process of glioblastoma cell dispersal.

METHODS

The effects of fenofibrate on Glioma cell motility, IGF-I receptor (IGF-IR) signaling, PPARalpha activity, reactive oxygen species (ROS) metabolism, mitochondrial potential, and ATP production were analyzed in human glioma cell lines.

RESULTS

Fenofibrate treatment attenuated IGF-I signaling responses and repressed cell motility of LN-229 and T98G Glioma cell lines. In the absence of fenofibrate, specific inhibition of the IGF-IR had only modest effects on Glioma cell motility. Further experiments revealed that PPARalpha-dependent accumulation of ROS is a strong contributing factor in Glioma cell lines responses to fenofibrate. The ROS scavenger, N-acetyl-cysteine (NAC), restored cell motility, improved mitochondrial potential, and increased ATP levels in fenofibrate treated Glioma cell lines.

CONCLUSIONS

Our results indicate that although fenofibrate-mediated inhibition of the IGF-IR may not be sufficient in counteracting Glioma cell dispersal, PPARalpha-dependent metabolic switch and the resulting ROS accumulation strongly contribute to the inhibition of these devastating brain tumor cells.

Fenofibrate induces effective apoptosis in mantle cell lymphoma by inhibiting the TNFalpha/NF-kappaB signaling axis

Mantle cell lymphoma (MCL) is a type of aggressive B-cell non-Hodgkin's lymphoma characterized by frequent resistance to conventional chemotherapy. In this study we provided evidence that fenofibrate, which is widely known as an agonist for peroxisome proliferator-activated receptor-alpha (PPARalpha), can induce effective apoptosis in treating MCL cells. Addition of fenofibrate to MCL cell lines significantly decreased the number of viable cells by 50% at approximately 20 microM at 72 h. This decrease in cell growth was due to apoptosis, as evidenced by the cleavage of caspase 3 and poly(ADP-ribose) polymerase. The fenofibrate-mediated effects were not significantly affected by GW6471, a specific PPARalpha antagonist. Using an apoptosis pathway-specific oligonucleotide array, we found that fenofibrate significantly downregulated several pro-survival genes, including tumor necrosis factor-alpha (TNFalpha). Importantly, addition of recombinant TNF-alpha conferred partial protection against fenofibrate-induced apoptosis. Fenofibrate also decreased the nuclear translocation of nuclear factor (NF)-kappaB-p65 and significantly inhibited the DNA binding of NF-kappaB in a dose-dependent manner. To conclude, fenofibrate shows efficacy against MCL, and the mechanism can be attributed to its inhibitory effects on the TNF-alpha/NF-kappaB signaling axis. In view of the documented safety of fenofibrate in humans, it may provide a valuable therapeutic option for MCL patients.

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.

Involvement of PPARα in the growth inhibitory effect of arachidonic acid on breast cancer cells

Epidemiological studies suggest that dietary PUFA may influence breast cancer progression.n-3 PUFA are generally known to exert antitumour effects, whereas reports relative ton-6 PUFA anti-carcinogen effects are controversial. Arachidonic acid (AA; 20 : 4n − 6) and its metabolites have been shown to inhibit the growth of human breast cancer cell lines, even if the downstream mechanisms by which AA may influence carcinogenesis remain unresolved. We explored the molecular basis for AA influence on proliferation, signal transduction and apoptosis in two human breast cancer cell lines, MCF-7 and MDA-MB-231. In both cell lines AA inhibited cell growth in a dose-dependent manner, even if MDA-MB-231 was somewhat more growth-inhibited than MCF-7. AA decreased extracellular signal-regulated protein kinase 1/2 phosphorylation level, and positively modulated PPARγ and PPARα expression, with only a slight effect against PPARβ/δ. In addition, AA increased Bak (an apoptosis-regulating protein) expression and reduced procaspase-3 and -9 levels only in MDA-MB-231 cells, thus indicating that the growth inhibitory effect can be correlated with apoptosis induction. In both cell lines the use of a specific antagonist made it possible to establish a relationship between AA growth inhibitory effect and PPARα involvement. AA decreases cell proliferation most likely by inducing apoptosis in MDA-MB-231 cells, while in the MCF-7 cell line the growth inhibitory activity can be attributed to the inhibition of the signal transduction pathway involved in cell proliferation. In both cases, the results here presented suggest PPARα as a possible contributor to the growth inhibitory effect of AA.

Clinical and biological significance of vascular endothelial growth factor in endometrial cancer

PURPOSE

Vascular endothelial growth factor (VEGF) is critical for angiogenesis and tumor progression; however, its role in endometrial cancer is not fully known. Therefore, we examined the clinical and therapeutic significance of VEGF in endometrial carcinoma using patient samples and an endometrioid orthotopic mouse model.

EXPERIMENTAL DESIGN

Following Institutional Review Board approval, VEGF expression and microvessel density (MVD) counts were evaluated using immunohistochemistry in 111 invasive endometrioid endometrial cancers by two independent investigators. Results were correlated with clinicopathologic characteristics. For the animal model, Ishikawa or Hec-1A cancer cell lines were injected directly into the uterine horn. Therapy experiments with bevacizumab alone or in combination with docetaxel were done and samples were analyzed for markers of angiogenesis and proliferation.

RESULTS

Of 111 endometrial cancers, high expression of VEGF was seen in 56% of tumors. There was a strong correlation between VEGF expression and MVD (P < 0.001). On multivariate analysis, stage (P = 0.04), grade (P = 0.003), VEGF levels (P = 0.03), and MVD (P = 0.037) were independent predictors of shorter disease-specific survival. In the murine model, whereas docetaxel and bevacizumab alone resulted in 61% to 77% tumor growth inhibition over controls, combination therapy had the greatest efficacy (85-97% inhibition over controls; P < 0.01) in both models. In treated tumors, combination therapy significantly reduced MVD counts (50-70% reduction over controls; P < 0.01) and percent proliferation (39% reduction over controls; P < 0.001).

CONCLUSIONS

Increased levels of VEGF and angiogenic markers are associated with poor outcome in endometrioid endometrial cancer patients. Using a novel orthotopic model of endometrioid endometrial cancer, we showed that combination of antivascular therapy with docetaxel is highly efficacious and should be considered for future clinical trials.

PPARalpha agonist fenofibrate suppresses tumor growth through direct and indirect angiogenesis inhibition

Angiogenesis and inflammation are central processes through which the tumor microenvironment influences tumor growth. We have demonstrated recently that peroxisome proliferator-activated receptor (PPAR)alpha deficiency in the host leads to overt inflammation that suppresses angiogenesis via excess production of thrombospondin (TSP)-1 and prevents tumor growth. Hence, we speculated that pharmacologic activation of PPARalpha would promote tumor growth. Surprisingly, the PPARalpha agonist fenofibrate potently suppressed primary tumor growth in mice. This effect was not mediated by cancer-cell-autonomous antiproliferative mechanisms but by the inhibition of angiogenesis and inflammation in the host tissue. Although PPARalpha-deficient tumors were still susceptible to fenofibrate, absence of PPARalpha in the host animal abrogated the potent antitumor effect of fenofibrate. In addition, fenofibrate suppressed endothelial cell proliferation and VEGF production, increased TSP-1 and endostatin, and inhibited corneal neovascularization. Thus, both genetic abrogation of PPARalpha as well as its activation by ligands cause tumor suppression via overlapping antiangiogenic pathways. These findings reveal the potential utility of the well tolerated PPARalpha agonists beyond their use as lipid-lowering drugs in anticancer therapy. Our results provide a mechanistic rationale for evaluating the clinical benefits of PPARalpha agonists in cancer treatment, alone and in combination with other therapies.

Synergistic Effects of PPARgamma Ligands and Retinoids in Cancer Treatment

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

PPARalpha Ligands as Antitumorigenic and Antiangiogenic Agents

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor family of ligand-activated transcription factors. This subfamily is composed of three members-PPARalpha, PPARdelta, and PPARgamma-that differ in their cell and tissue distribution as well as in their target genes. PPARalpha is abundantly expressed in liver, brown adipose tissue, kidney, intestine, heart, and skeletal muscle; and its ligands have been used to treat diseases such as obesity and diabetes. The recent finding that members of the PPAR family, including the PPARalpha, are expressed by tumor and endothelial cells together with the observation that PPAR ligands regulate cell growth, survival, migration, and invasion, suggested that PPARs also play a role in cancer. In this review, we focus on the contribution of PPARalpha to tumor and endothelial cell functions and provide compelling evidence that PPARalpha can be viewed as a new class of ligand activated tumor "suppressor" gene with antiangiogenic and antitumorigenic activities. Given that PPAR ligands are currently used in medicine as hypolipidemic drugs with excellent tolerance and limited toxicity, PPARalpha activation might offer a novel and potentially low-toxic approach for the treatment of tumor-associated angiogenesis and cancer.