Ligands for peroxisome proliferator-activated receptorgamma and retinoic acid receptor inhibit growth and induce apoptosis of human breast cancer cells in vitro and in BNX mice

Pioglitazone enhances cisplatin's impact on triple-negative breast cancer: Role of PPARγ in cell apoptosis

Peroxisome proliferator-activated receptor-gamma (PPARγ) has been recently shown to play a role in many cancers. The breast tissue of triple-negative breast cancer (TNBC) patients were found to have a significantly lower expression of PPARγ than the other subtypes. Furthermore, PPARγ activation was found to exert anti-tumor effects by inhibiting cell proliferation, differentiation, cell growth, cell cycle, and inducing apoptosis. To start with, we performed a bioinformatic analysis of data from OncoDB, which showed a lower expression pattern of PPARγ in different cancer types. In addition, high expression of PPARγ was associated with better breast cancer patient survival. Therefore, we tested the impact of pioglitazone, a PPARγ ligand, on the cytotoxic activity of cisplatin in the TNBC cell line. MDA-MB-231 cells were treated with either cisplatin (40 μM) with or without pioglitazone (30 or 60 μM) for 72 h. The MTT results showed a significant dose-dependent decrease in cell viability as a result of using cisplatin and pioglitazone combination compared with cisplatin alone. In addition, the protein expression of Bcl-2, a known antiapoptotic marker, decreased in the cells treated with cisplatin and pioglitazone combination at doses of 40 and 30 μM, respectively. On the other hand, cleaved- poly-ADP ribose polymerase (PARP) and -caspase-9, which are known as pro-apoptotic markers, were upregulated in the combination group compared with the solo treatments. Taken together, the addition of pioglitazone to cisplatin further reduced the viability of MDA-MB-231 cells and enhanced apoptosis compared with chemotherapy alone.

Development of bile acid activated receptors hybrid molecules for the treatment of inflammatory and metabolic disorders

The farnesoid-x-receptor (FXR) and the G protein bile acid activated receptor (GPBAR)1 are two bile acid activated receptors highly expressed in entero-hepatic, immune, adipose and cardiovascular tissues. FXR and GPBAR1 are clinically validated targets in the treatment of metabolic disorders and FXR agonists are currently trialled in patients with non-alcoholic steato-hepatitis (NASH). Results of these trials, however, have raised concerns over safety and efficacy of selective FXR ligands suggesting that the development of novel agent designed to impact on multiple targets might have utility in the treatment of complex, multigenic, disorders. Harnessing on FXR and GPBAR1 agonists, several novel hybrid molecules have been developed, including dual FXR and GPBAR1 agonists and antagonists, while exploiting the flexibility of FXR agonists toward other nuclear receptors, dual FXR and peroxisome proliferators-activated receptors (PPARs) and liver-X-receptors (LXRs) and Pregnane-X-receptor (PXR) agonists have been reported. In addition, modifications of FXR agonists has led to the discovery of dual FXR agonists and fatty acid binding protein (FABP)1 and Leukotriene B4 hydrolase (LTB4H) inhibitors. The GPBAR1 binding site has also proven flexible to accommodate hybrid molecules functioning as GPBAR1 agonist and cysteinyl leukotriene receptor (CYSLTR)1 antagonists, as well as dual GPBAR1 agonists and retinoid-related orphan receptor (ROR)γt antagonists, dual GPBAR1 agonist and LXR antagonists and dual GPBAR1 agonists endowed with inhibitory activity on dipeptidyl peptidase 4 (DPP4). In this review we have revised the current landscape of FXR and GPBAR1 based hybrid agents focusing on their utility in the treatment of metabolic associated liver disorders.

PPARγ activation modulates the balance of peritoneal macrophage populations to suppress ovarian tumor growth and tumor-induced immunosuppression

BACKGROUND

Ovarian adenocarcinoma (OVAD) frequently metastasizes to the peritoneal cavity and manifests by the formation of ascites, which constitutes a tumor-promoting microenvironment. In the peritoneal cavity, two developmentally, phenotypically and functionally distinct macrophage subsets, immunocompetent large peritoneal macrophages (LPM) and immunosuppressive small peritoneal macrophages (SPM), coexist. Because peroxisome proliferator-activated receptor γ (PPARγ) is a critical factor participating in macrophage differentiation and cooperates with CCAAT/enhancer binding protein β (C/EBPβ), a transcription factor essential for SPM-to-LPM differentiation, PPARγ could be also involved in the regulation of SPM/LPM balance and could be a promising therapeutic target.

METHODS

To evaluate the 15(S)-hydroxyeicosatetraenoic acid (HETE), a PPARγ endogenous ligand, impact on ovarian tumor growth, we intraperitoneally injected 15(S)-HETE into a murine ovarian cancer model. This experimental model consists in the intraperitoneally injection of ID8 cells expressing luciferase into syngeneic C57BL/6 female mice. This ID8 orthotopic mouse model is a well-established experimental model of end-stage epithelial OVAD. Tumor progression was monitored using an in vivo imaging system. Peritoneal immune cells in ascites were analyzed by flow cytometry and cell sorting. To determine whether the impact of 15(S)-HETE in tumor development is mediated through the macrophages, these cells were depleted by injection of liposomal clodronate. To further dissect how 15(S)-HETE mediated its antitumor effect, we assessed the tumor burden in tumor-bearing mice in which the PPARγ gene was selectively disrupted in myeloid-derived cells and in mice deficient of the recombination-activating gene Rag2. Finally, to validate our data in humans, we isolated and treated macrophages from ascites of individuals with OVAD.

RESULTS

Here we show, in the murine experimental model of OVAD, that 15(S)-HETE treatment significantly suppresses the tumor growth, which is associated with the differentiation of SPM into LPM and the LPM residency in the peritoneal cavity. We demonstrate that C/EBPβ and GATA6 play a central role in SPM-to-LPM differentiation and in LPM peritoneal residence through PPARγ activation during OVAD. Moreover, this SPM-to-LPM switch is associated with the increase of the effector/regulatory T-cell ratio. Finally, we report that 15(S)-HETE attenuates immunosuppressive properties of human ovarian tumor-associated macrophages from ascites.

CONCLUSION

Altogether, these results promote PPARγ as a potential therapeutic target to restrain OVAD development and strengthen the use of PPARγ agonists in anticancer therapy.

Endocrine-disrupting chemicals (EDCs) and cancer: new perspectives on an old relationship

PURPOSE

Environmental endocrine-disrupting chemicals (EDCs) are a mixture of chemical compounds capable to interfere with endocrine axis at different levels and to which population is daily exposed. This paper aims to review the relationship between EDCs and breast, prostate, testicle, ovary, and thyroid cancer, discussing carcinogenic activity of known EDCs, while evaluating the impact on public health.

METHODS

A literature review regarding EDCs and cancer was carried out with particular interest on meta-analysis and human studies.

RESULTS

The definition of EDCs has been changed through years, and currently there are no common criteria to test new chemicals to clarify their possible carcinogenic activity. Moreover, it is difficult to assess the full impact of human exposure to EDCs because adverse effects develop latently and manifest at different ages, even if preclinical and clinical evidence suggest that developing fetus and neonates are most vulnerable to endocrine disruption.

CONCLUSION

EDCs represent a major environmental and health issue that has a role in cancer development. There are currently some EDCs that can be considered as carcinogenic, like dioxin and cadmium for breast and thyroid cancer; arsenic, asbestos, and dioxin for prostate cancer; and organochlorines/organohalogens for testicular cancer. New evidence supports the role of other EDCs as possible carcinogenic and pregnant women should avoid risk area and exposure. The relationship between EDCs and cancer supports the need for effective prevention policies increasing public awareness.

Anticancer heterocyclic hybrids: design, synthesis, molecular docking and evaluation of new thiazolidinone-pyrazoles

In order to obtain potential anticancer agents, hybrid compounds have been synthesized by coupling thiazolidinone and pyrazole scaffolds. Among the synthesized compounds, 2-(1,3-diphenyl-1H-pyrazol-4-yl)-3-phenyl thiazolidin-4-one (4a) was found to be the most potent based on a docking (−9.307) and binding scores (−66.46), along with good ADME parameters. In vitro anticancer activity of compound 4a shows a maximum inhibition against lung cancer (NCI-H23) cell lines with a moderate inhibition rate of 31.01%. Molecular docking studies revealed that these hybrid compounds bind well to the active site of peroxisome proliferator-activated receptors-gamma (PPAR-gamma). Doxorubicin was used as a positive control. It can be concluded that 4a having pyrazole-thiazolidinone ring systems has the potential to be developed as an anticancer agent.

DNA-Protein-Interaction (DPI)-ELISA Assay for PPAR-γ Receptor Binding

Dysregulation of peroxisome proliferator-activated receptor (PPAR)-γ has been described in a plethora of pathological conditions, such as diabetes, obesity, inflammatory-related diseases, and cancer. Therefore, identifying novel drugs that are able to restore PPAR-γ activity is a current challenge, which is however slowed down by the lack of a rapid and reproducible activity assay. To date, only a few methods are able to characterize PPAR-γ activity and most of them are expensive, time-consuming, and not always quantitative.Herein, we presented a sensitive multi-well colorimetric assay, termed DNA-Protein-Interaction enzyme-linked immunosorbent assay (DPI-ELISA). This method is based on the ELISA principle, except that it allows to detect only activated PPAR-γ because, unlike classical ELISA, PPAR-γ is not captured by an antibody but by a double-stranded oligonucleotide probe containing its peroxisome proliferator response elements (PPRE) consensus sequence. Thus, DPI-ELISA represents a useful assay for PPAR-γ studies, as well as for the identification of novel PPAR-γ ligands for the development of innovative therapeutic approaches to human diseases where PPAR-γ signaling is dysregulated.

The Role of PPARs in Breast Cancer

Breast cancer is a malignant tumor with high morbidity and lethality. Its pathogenesis is related to the abnormal expression of many genes. The peroxisome proliferator-activated receptors (PPARs) are a class of ligand-dependent transcription factors in the nuclear receptor superfamily. They can regulate the transcription of a large number of target genes, which are involved in life activities such as cell proliferation, differentiation, metabolism, and apoptosis, and regulate physiological processes such as glucose metabolism, lipid metabolism, inflammation, and wound healing. Further, the changes in its expression are associated with various diseases, including breast cancer. The experimental reports related to "PPAR" and "breast cancer" were retrieved from PubMed since the discovery of PPARs and summarized in this paper. This review (1) analyzed the roles and potential molecular mechanisms of non-coordinated and ligand-activated subtypes of PPARs in breast cancer progression; (2) discussed the correlations between PPARs and estrogen receptors (ERs) as the nuclear receptor superfamily; and (3) investigated the interaction between PPARs and key regulators in several signaling pathways. As a result, this paper identifies PPARs as targets for breast cancer prevention and treatment in order to provide more evidence for the synthesis of new drugs targeting PPARs or the search for new drug combination treatments.

The impact of obesity and adipokines on breast and gynecologic malignancies

The link between obesity and multiple disease comorbidities is well established. In 2003, Calle and colleagues presented the relationship between obesity and several cancer types, including breast, ovarian, and endometrial malignancies. Nearly, 20% of cancer-related deaths in females can be accounted for by obesity. Identifying obesity as a risk factor for cancer led to a focus on the role of fat-secreted cytokines, known as adipokines, on carcinogenesis and tumor progression. Early studies indicated that the adipokine leptin increases cell proliferation, invasion, and inhibition of apoptosis in multiple cancer types. As a greater appreciation of the obesity-cancer link has amassed, we now know that additional adipokines can impact tumorigenesis. A deeper understanding of the adipokine-activated signaling in cancer may identify new treatment strategies irrespective of obesity. Moreover, adipokines may serve as disease biomarkers, harnessing the potential of obesity-associated factors to serve as indicators of treatment response and disease prognosis. As studies investigating obesity and women's cancers continue to expand, it has become evident that breast, ovarian, and uterine cancers are distinctly impacted by adipokines. While complex, these distinct interactions may provide insight into cancer progression in these organs and new opportunities for targeted therapies. This review aims to organize and present the literature from the last 5 years investigating the mechanisms and implications of adipokine signaling in breast, endometrial, and ovarian cancers with a special focus on leptin and adiponectin.

Effects of matcha tea extract on cell viability and peroxisome proliferator-activated receptor γ expression on T47D breast cancer cells

PURPOSE

In the following work, we investigated the nuclear peroxisome proliferator-activated receptor gamma (PPARγ)-dependent proliferation behavior of breast cancer cells after stimulation with matcha green tea extract (MTE).

METHODS

T47D cells were stimulated with MTE at concentrations of 5, 10 and 50 µg/ml. Cell viability was assessed using a WST-1 assay after an incubation time of 72 h. PPARγ expression was quantified at the gene level by real-time polymerase chain reaction (PCR). A western blot (WB) was carried out for the qualitative assessment of the expression behavior of on a protein level.

RESULTS

The WST-1 test showed a significant inhibition of viability in T47D cells after 72 h at 5, 10 and 50 µg/ml. The PCR showed an overexpression of PPARγ in T47D cells in all concentrations. At the concentration of 50 µg/ml the expression was significantly increased (p < 0.05). The WB demonstrated a significant quantitative increase of PPARγ at protein level with MTE concentrations of 10 and 50 µg/ml. In addition, there was a negative correlation between the overexpression of PPAR γ and the inhibition of proliferation.

CONCLUSION

MTE decreases the cell viability of T47D cells and furthermore leads to an overexpression of PPARγ on protein and mRNA level.

The unfolding role of ceramide in coordinating retinoid-based cancer therapy

Sphingolipid-mediated regulation in cancer development and treatment is largely ceramide-centered with the complex sphingolipid metabolic pathways unfolding as attractive targets for anticancer drug discovery. The dynamic interconversion of sphingolipids is tightly controlled at the level of enzymes and cellular compartments in response to endogenous or exogenous stimuli, such as anticancer drugs, including retinoids. Over the past two decades, evidence emerged that retinoids owe part of their potency in cancer therapy to modulation of sphingolipid metabolism and ceramide generation. Ceramide has been proposed as a 'tumor-suppressor lipid' that orchestrates cell growth, cell cycle arrest, cell death, senescence, autophagy, and metastasis. There is accumulating evidence that cancer development is promoted by the dysregulation of tumor-promoting sphingolipids whereas cancer treatments can kill tumor cells by inducing the accumulation of endogenous ceramide levels. Resistance to cancer therapy may develop due to a disrupted equilibrium between the opposing roles of tumor-suppressor and tumor-promoter sphingolipids. Despite the undulating effect and complexity of sphingolipid pathways, there are emerging opportunities for a plethora of enzyme-targeted therapeutic interventions that overcome resistance resulting from perturbed sphingolipid pathways. Here, we have revisited the interconnectivity of sphingolipid metabolism and the instrumental role of ceramide-biosynthetic and degradative enzymes, including bioactive sphingolipid products, how they closely relate to cancer treatment and pathogenesis, and the interplay with retinoid signaling in cancer. We focused on retinoid targeting, alone or in combination, of sphingolipid metabolism nodes in cancer to enhance ceramide-based therapeutics. Retinoid and ceramide-based cancer therapy using novel strategies such as combination treatments, synthetic retinoids, ceramide modulators, and delivery formulations hold promise in the battle against cancer.

Lobeglitazone, A Peroxisome Proliferator-Activated Receptor-Gamma Agonist, Inhibits Papillary Thyroid Cancer Cell Migration and Invasion by Suppressing p38 MAPK Signaling Pathway

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR-γ) ligands have been widely shown to correlate with epithelial-mesenchymal transition (EMT) and cancer progression. Lobeglitazone (LGZ) is a novel ligand of PPAR-γ; and its role in EMT and metastasis in papillary thyroid carcinoma (PTC) is poorly understood. We aimed to investigate the role of LGZ in metastatic behavior of PTC cells.

METHODS

Half maximal inhibitory concentration (IC50) values of LGZ in BRAF-mutated PTC cell lines (BCPAP and K1) were determined using MTT assay. Rosiglitazone (RGZ), the PPAR-γ ligand was used as a positive control. The protein expression of PPAR-γ, cell-surface proteins (E-cadherin, N-cadherin), cytoskeletal protein (Vimentin), transcription factor (Snail), p38 mitogenactivated protein kinase (MAPK), extracellular signal-regulated kinase (ERK) 1/2 pathway, and matrix metalloproteinase (MMP)-2 expression were measured using Western blotting. Changes in E-cadherin expression were also determined using immunocytochemistry. Cell migration and invasion were analyzed using wound healing and Matrigel invasion assays.

RESULTS

Treatment with LGZ or RGZ significantly inhibited transforming growth factor-beta1 (TGF-β1)-induced EMT-associated processes such as fibroblast-like morphological changes, EMT-related protein expression, and increased cell migration and invasion in BCPAP and K1 cells. LGZ restored TGF-β1-induced loss of E-cadherin, as observed using immunocytochemistry. Furthermore, LGZ and RGZ suppressed TGF-β1-induced MMP-2 expression and phosphorylation of p38 MAPK, but not ERK1/2. Although there was no change in PPAR-γ expression after treatment with LGZ or RGZ, the effect of downstream processes mediated by LGZ was hampered by GW9662, a PPAR-γ antagonist.

CONCLUSION

LGZ inhibits TGF-β1-induced EMT, migration, and invasion through the p38 MAPK signaling pathway in a PPAR-γ-dependent manner in PTC cells.

STAT3 as a Potential Target for Tumor Suppressive Effects of 15-Deoxy-Δ12,14-prostaglandin J2 in Triple Negative Breast Cancer

STAT3 plays a prominent role in proliferation and survival of tumor cells. Thus, STAT3 has been considered to be a prime target for development of anti-cancer therapeutics. The electrophilic cyclopentenone prostaglandin,15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) has been well recognized for its capability to modulate intracellular signaling pathways involved in cancer cell growth and progression. We previously reported that 15d-PGJ₂ had potent cytotoxicity against harvey-ras transformed human mammary epithelial cells through direct interaction with STAT3. In this study, we have attempted to verify the inhibitory effects of 15d-PGJ₂ on STAT3 signaling in human breast tumor cells. The triple negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468 displaying constitutive phosphorylation of STAT3 on the tyrosine 705 (Tyr705) residue, underwent apoptosis upon inhibition of STAT3 by 15d-PGJ₂. In contrast, estrogen receptor positive MCF-7 breast cancer cells that do not exhibit elevated STAT3 phosphorylation were much less susceptible to 15d-PGJ₂-induced apoptosis as assessed by PARP cleavage. Furthermore, 15d-PGJ₂ inhibited interleukin-6-induced tyrosine phosphorylation of STAT3 in LNCaP cells. According to molecular docking studies, 15d-PGJ₂ may preferentially bind to the cysteine 259 residue (Cys259) present in the coiled-coil domain of STAT3. Site-directed mutagenesis of STAT3 identified Cys259 to be the critical amino acid for the 15d-PGJ₂-induced apoptosis as well as epithelial-to-mesenchymal transition. Taken together, these findings suggest STAT3 inactivation through direct chemical modification of its Cys259 as a potential therapeutic approach for treatment of triple negative breast cancer treatment.

PPARgamma: A Potential Intrinsic and Extrinsic Molecular Target for Breast Cancer Therapy

Over the last decades, the breast tumor microenvironment (TME) has been increasingly recognized as a key player in tumor development and progression and as a promising prognostic and therapeutic target for breast cancer patients. The breast TME, representing a complex network of cellular signaling—deriving from different stromal cell types as well as extracellular matrix components, extracellular vesicles, and soluble growth factors—establishes a crosstalk with cancer cells sustaining tumor progression. A significant emphasis derives from the tumor surrounding inflammation responsible for the failure of the immune system to effectively restrain breast cancer growth. Thus, effective therapeutic strategies require a deeper understanding of the interplay between tumor and stroma, aimed at targeting both the intrinsic neoplastic cells and the extrinsic surrounding stroma. In this scenario, peroxisome proliferator-activated receptor (PPAR) γ, primarily known as a metabolic regulator, emerged as a potential target for breast cancer treatment since it functions in breast cancer cells and several components of the breast TME. In particular, the activation of PPARγ by natural and synthetic ligands inhibits breast cancer cell growth, motility, and invasiveness. Moreover, activated PPARγ may educate altered stromal cells, counteracting the pro-inflammatory milieu that drive breast cancer progression. Interestingly, using Kaplan–Meier survival curves, PPARγ also emerges as a prognostically favorable factor in breast cancer patients. In this perspective, we briefly discuss the mechanisms by which PPARγ is implicated in tumor biology as well as in the complex regulatory networks within the breast TME. This may help to profile approaches that provide a simultaneous inhibition of epithelial cells and TME components, offering a more efficient way to treat breast cancer.

Peroxisome Proliferator-Activated Receptor Gamma Pro12Ala/C161T Genotypes and Risky Haplotype Altering Risk of Breast Cancer: A Turkish Case-Control Study

Breast cancer (BC) has a high incidence rate among women worldwide, and the mechanisms and etiology of this disease are not yet fully understood. The peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear hormone receptor that plays important roles in energy metabolism and cellular differentiation, is also suggested to be effective in cancer development. However, the results of studies investigating the cancer association with PPARgamma are inconsistent, creating a need for further investigation of the effects of this transcription factor on BC risk. We have examined the Pro12Ala-(rs1801282) and C161T-(rs3856806) polymorphisms of the PPARgamma gene in Turkish patients with BC in this case-control study. A total of 95 women diagnosed with BC as cases and 119 controls were genotyped for PPARgamma polymorphisms by polymerase chain reaction and restriction fragment length polymorphism techniques. The ProPro genotype and T161 allele were associated with an increased risk of BC comparing with the Ala12 allele and CC161 genotype, respectively (p < 0.001). The multivariate regression analysis confirmed that the ProPro genotype (p < 0.011), T161 allele (p < 0.001), smoking (p = 0.019), and advanced age (> 60 years) (p = 0.007) are risk factors for breast cancer. We also found that the PPARgamma Pro12Ala and C161T polymorphisms were in linkage disequilibrium (D':0.511, r²:0.099). It was determined that carrying ProPro-T161 risky PPARgamma haplotype was associated with a higher risk of BC compared to protective Ala12-CC161 haplotype (p < 0.01, OR:7.797, 95% CI:3.521-17.263). We concluded that PPARgamma Pro12Ala and C161T polymorphisms are associated with increased BC risk, and ProPro-T161 risky haplotype, which is in linkage disequilibrium, increases this effect.

Peroxisome proliferator-activated receptor γ improves pemetrexed therapeutic efficacy in non-squamous non-small cell lung cancer

OBJECTIVE

The folic acid analog pemetrexed (PMX) is recommended for the first-line chemotherapy for advanced non-squamous non-small cell lung cancer (NSCLC). However, the mechanisms underlying PMX cytotoxicity in NSCLC remain to be fully explored.

METHODS

PMX effect was evaluated in a urethane-induced lung adenocarcinoma mouse model. The interaction between PMX and intracellular proteins, particularly peroxisome proliferator-activated receptor γ (PPARγ), was investigated. The role of PPARγ in mediating pemetrexed cytotoxicity was investigated using NSCLC cell lines, mouse models and clinical specimens.

RESULTS

This study found that PPARγ expression was correlated with prolonged progression-free survival in NSCLC patients. PPARγ downregulated hypoxanthine-guanine phosphoribosyl transferase (HGPRT), a key enzyme for nucleotide salvage synthesis, thereby sensitizing cells to PMX inhibition on nucleotide de novo synthesis. PMX was also a candidate partial agonist of PPARγ, and PMX-activated PPARγ bound to NF-κB and transcriptionally suppressed the NF-κB target gene, c-Myc. PMX inhibited tumor growth by activating PPARγ in a urethane-induced lung cancer model characterized by elevated NF-κB activity.

CONCLUSION

PPARγ improves pemetrexed therapeutic efficacy in non-squamous NSCLC. The cytotoxicity effect of PMX can be synergized by activating PPARγ and thereby inhibiting NF-κB pathway.

Combined COX-2/PPARγ Expression as Independent Negative Prognosticator for Vulvar Cancer Patients

Vulvar cancer incidence numbers have been rising steadily over the past decades. Especially the number of young patients with vulvar cancer increased recently. Therefore, the need to identify new prognostic factors for vulvar carcinoma is more apparent. Cyclooxygenase-2 (COX-2) has long been an object of scientific interest in the context of carcinogenesis. This enzyme is involved in prostaglandin synthesis and the latter binds to nuclear receptors like PPARγ. Therefore, the aim of this study was to investigate COX-2- and PPARγ- expression in tissues of vulvar carcinomas and to analyze their relevance as prognostic factors. The cytoplasmatic expression of COX-2 as well as PPARγ is associated with a significantly reduced survival, whereas nuclear expression of PPARγ results in a better survival. Especially the combined expression of both COX-2 and PPARγ in the cytoplasm is an independent negative prognosticator for vulvar cancer patients.

The Association of Bisphenol A and Phthalates with Risk of Breast Cancer: A Meta-Analysis

Background: Breast cancer is the most common cancer and the second leading cause of cancer-related death amongst American women. Endocrine-disrupting chemicals (EDCs), especially bisphenol A (BPA) and phthalates, have adverse effects on human health. However, the association of BPA and phthalates with breast cancer remains conflicting. This study aims to investigate the association of BPA and phthalates with breast cancer. Methods: Correlative studies were identified by systematically searching three electronic databases, namely, PubMed, Web of Sciences, and Embase, up to November 2020. All data were analyzed using Stata 15.0. Results: A total of nine studies, consisting of 7820 breast cancer cases and controls, were included. The urinary phthalate metabolite mono-benzyl phthalate (MBzP) and mono-2-isobutyl phthalate (MiBP) were negatively associated with breast cancer (OR = 0.73, 95% CI: 0.60–0.90; OR = 0.75, 95% CI: 0.58–0.98, respectively). However, the overall ORs for BPA, mono-ethyl phthalate (MEP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-2-ethylhexyl phthalate (MEHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono-(3-carboxypropyl) phthalate (MCPP), and mono-butyl phthalate (MBP) were 0.85 (95% CI: 0.69–1.05), 0.96 (95% CI: 0.62–1.48), 1.12 (95% CI: 0.88–1.42), 1.13 (95% CI: 0.74–1.73), 1.01 (95% CI: 0.74–1.40), 0.74 (95% CI: 0.48–1.14), and 0.80 (95% CI: 0.55–1.15), respectively, suggesting no significant association. The sensitivity analysis indicated that the results were relatively stable. Conclusion: Phthalate metabolites MBzP and MiBP were passively associated with breast cancer, whereas no associations were found between BPA, MEP, MEHHP, MEHP, MEOHP, MCPP, and MBP and breast cancer. More high-quality case-control studies or persuasive cohort studies are urgently needed to draw the best conclusions.

DNA methylation in adipocytes from visceral and subcutaneous adipose tissue influences insulin-signaling gene expression in obese individuals

OBJECTIVE

Both obesity and insulin resistance are characterized by severe long-term changes in the expression of many genes of importance in the regulation of metabolism. Because these changes occur throughout life, as a result of external factors, the disorders of gene expression could be epigenetically regulated.

MATERIALS/METHODS

We analyzed the relationship between obesity and insulin resistance in enrolled patients by means of evaluation of the expression rate of numerous genes involved in the regulation of adipocyte metabolism and energy homeostasis in subcutaneous and visceral adipose tissue depots. We also investigated global and site-specific DNA methylation as one of the main regulators of gene expression. Visceral and subcutaneous adipose tissue biopsies were collected from 45 patients during abdominal surgery in an age range of 40-60 years.

RESULTS

We demonstrated hypermethylation of PPARG, INSR, SLC2A4, and ADIPOQ promoters in obese patients with insulin resistance. Moreover, the methylation rate showed a negative correlation with the expression of the investigated genes. More, we showed a correlation between the expression of PPARG and the expression of numerous genes important for proper insulin action. Given the impact of PPARγ on the regulation of the cell insulin sensitivity through modulation of insulin pathway genes expression, hypermethylation in the PPARG promoter region may constitute one of the epigenetic pathways in the development of insulin resistance in obesity.

CONCLUSIONS

Our research shows that epigenetic regulation through excessive methylation may constitute a link between obesity and subsequent insulin resistance.

Retinoic Acid Synthesis Deficiency Fosters the Generation of Polymorphonuclear Myeloid-Derived Suppressor Cells in Colorectal Cancer

Metabolism is reprogrammed in cancer to fulfill the demands of malignant cells for cancer initiation and progression. Apart from its effects within cancer cells, little is known about whether and how reprogramed metabolism regulates the surrounding tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSC) are key regulators of the TME and greatly affect tumor progression and therapeutic responses. In this study, our results revealed that retinol metabolism-related genes and enzymes were significantly downregulated in human colorectal cancer compared with adjacent colonic tissues, and tumors exhibited a defect in retinoic acid (RA) synthesis. Reduced ADH1-mediated retinol metabolism was associated with attenuated RA signaling and accumulated MDSCs in colorectal cancer tumors. Using an in vitro model, generating MDSCs from CD34+ myeloid precursors, we found that exogenous RA could abrogate the generation of polymorphonuclear MDSCs (PMN-MDSC) with negligible impact on myeloid differentiation. Mechanistically, RA could restrain the glycolytic capacity of myeloid cells, which in turn activated the AMP-activated protein kinase (AMPK) pathway, further impairing the suppressive capacity of myeloid cells. Supplementation with RA could significantly delay tumor growth, with reduced arginase-1-expressing myeloid cells and increased CD8+ and granzyme B+ T cells in both colitis-associated and implanted MC38 mouse colorectal cancer models. Our results indicated that the defect in ADH1-mediated RA synthesis could provide a possible mechanism that fosters the generation of PMN-MDSCs in colorectal cancer and that restoring RA signaling in the TME could serve as a promising therapeutic strategy to abrogate the generation of PMN-MDSCs.

Natural and Synthetic PPARγ Ligands in Tumor Microenvironment: A New Potential Strategy against Breast Cancer

Multiple lines of evidence indicate that activation of the peroxisome proliferator-activated receptor γ (PPARγ) by natural or synthetic ligands exerts tumor suppressive effects in different types of cancer, including breast carcinoma. Over the past decades a new picture of breast cancer as a complex disease consisting of neoplastic epithelial cells and surrounding stroma named the tumor microenvironment (TME) has emerged. Indeed, TME is now recognized as a pivotal element for breast cancer development and progression. Novel strategies targeting both epithelial and stromal components are under development or undergoing clinical trials. In this context, the aim of the present review is to summarize PPARγ activity in breast TME focusing on the role of this receptor on both epithelial/stromal cells and extracellular matrix components of the breast cancer microenvironment. The information provided from the in vitro and in vivo research indicates PPARγ ligands as potential agents with regards to the battle against breast cancer.

Abscisic acid regulates dormancy of prostate cancer disseminated tumor cells in the bone marrow

Prostate cancer (PCa) commonly metastasizes to the bone where the cells frequently undergo dormancy. The escape of disseminated tumor cells from cellular dormancy is a major cause of recurrence in marrow. Abscisic acid (ABA), a phytohormone, is known to regulate dormancy of plant seeds and to regulate other stress responses in plants. Recently, ABA was found to be synthesized by mammals cells and has been linked to human disease. Yet the role of ABA in regulating tumor dormancy or reactivation is unknown. We found that ABA is produced by human marrow cells, and exogenous ABA inhibits PCa cell proliferation while increasing the expression of p27, p21, and p16 and decreasing the expression of the proliferation marker, Ki67. Further, ABA significantly increased the percentage of PCa cells in the G₀ phase of the cell cycle as well as the duration the cells were arrested in G₀. We found that ABA regulates an increase of PPARγ receptor expression and suppressed phosphorylation of mTOR/p70S6K signaling and resulting in the induction of the cellular dormancy. We then confirmed that ABA regulates G₀ cell cycle arrest through PPARγ receptor signaling in vitro and under co-culture conditions with osteoblasts. Finally, we demonstrate that ABA regulates PCa dormancy in vivo following intratibial injection in an animal model. Together these data suggest that the ABA and PPARγ signaling pathways contribute to the establishment of PCa cellular dormancy in the bone marrow microenvironment. These findings may suggest critical pathways for targeting metastatic disease.

Differential Effects of Cancer-Associated Mutations Enriched in Helix H3 of PPARγ

Peroxisome proliferator-activated receptor gamma (PPARγ) has recently been revealed to regulate tumor microenvironments. In particular, genetic alterations of PPARγ found in various cancers have been reported to play important roles in tumorigenesis by affecting PPARγ transactivation. In this study, we found that helix H3 of the PPARγ ligand-binding domain (LBD) has a number of sites that are mutated in cancers. To uncover underlying molecular mechanisms between helix H3 mutations and tumorigenesis, we performed structure‒function studies on the PPARγ LBDs containing helix H3 mutations found in cancers. Interestingly, PPARγ Q286E found in bladder cancer induces a constitutively active conformation of PPARγ LBD and thus abnormal activation of PPARγ/RXRα pathway, which suggests tumorigenic roles of PPARγ in bladder cancer. In contrast, other helix H3 mutations found in various cancers impair ligand binding essential for transcriptional activity of PPARγ. These data indicate that cancer-associated mutations clustered in helix H3 of PPARγ LBD exhibit differential effects in PPARγ-mediated tumorigenesis and provide a basis for the development of new biomarkers targeting tumor microenvironments.

A novel PPARɣ ligand, PPZ023, overcomes radioresistance via ER stress and cell death in human non-small-cell lung cancer cells

Peroxisome proliferator-activated receptor gamma (PPARɣ) agonists exert powerful anticancer effects by suppressing tumor growth. In this study, we developed PPZ023 (1-(2-(ethylthio)benzyl)-4-(2-methoxyphenyl)piperazine), a novel PPAR ligand candidate, and investigated the underlying signaling pathways in both non-small-cell lung cancer (NSCLC) and radio-resistant NSCLC cells. To identify whether PPZ023 has anticancer effects in NSCLC and radioresistant NSCLC cells, we performed WST-1, LDH, Western blot, and caspase-3 and -9 activity assays. Furthermore, we isolated exosomes from PPZ023-treated NSCLC cells and studied cell death signaling. PPZ023 reduces cell viability and increases LDH cytotoxicity and caspase-3 activity in NSCLC cells. PPZ023 induces cell death by generating reactive oxygen species (ROS) and triggering mitochondrial cytochrome c release. PPZ023 treatment causes cell death via the PERK–eIF2α–CHOP axis in both NSCLC cell lysates and exosomes, and PERK and CHOP knockdown significantly blocks ER stress-mediated apoptosis by reducing cleaved caspase-3. Interestingly, diphenyleneiodonium (DPI, a Nox inhibitor) inhibits PPZ023-induced cell death via ER stress, and PPARɣ knockdown inhibits PPZ023-induced ROS, ER stress, and cell death. Moreover, PPZ023, in combination with radiation, causes synergic cell death via exosomal ER stress in radioresistant NSCLC cells, indicating that PPZ023/radiation overcomes radioresistance. Taken together, our results suggest that PPZ023 is a powerful anticancer reagent for overcoming radioresistance.

A novel small molecule drug candidate known as PPZ023 could be a powerful anti-cancer agent due to its ability to overcome the resistance of tumors to radiation therapy. Sung Hee Hong and colleagues at the Korea Institute of Radiological and Medical Sciences in Seoul, South Korea, investigated the effects of the molecule on lung cancer cells, including cells that that had acquired resistance to radiotherapy. PPZ023 induces the death of cancer cells by binding to a protein in a known signaling pathway, which generates damaging chemicals known as reactive oxygen species. The researchers identified additional molecular details of the anti-cancer activity. They found the radiotherapy resistance of cancer cells is reversed when PPZ023 promotes cell death via a pathway interfering with the folding of newly formed proteins in a cell structure called the endoplasmic reticulum.

The Role of PPARγ Ligands in Breast Cancer: From Basic Research to Clinical Studies

Peroxisome proliferator-activated receptor gamma (PPARγ), belonging to the nuclear receptor superfamily, is a ligand-dependent transcription factor involved in a variety of pathophysiological conditions such as inflammation, metabolic disorders, cardiovascular disease, and cancers. In this latter context, PPARγ is expressed in many tumors including breast cancer, and its function upon binding of ligands has been linked to the tumor development, progression, and metastasis. Over the last decade, much research has focused on the potential of natural agonists for PPARγ including fatty acids and prostanoids that act as weak ligands compared to the strong and synthetic PPARγ agonists such as thiazolidinedione drugs. Both natural and synthetic compounds have been implicated in the negative regulation of breast cancer growth and progression. The aim of the present review is to summarize the role of PPARγ activation in breast cancer focusing on the underlying cellular and molecular mechanisms involved in the regulation of cell proliferation, cell cycle, and cell death, in the modulation of motility and invasion as well as in the cross-talk with other different signaling pathways. Besides, we also provide an overview of the in vivo breast cancer models and clinical studies. The therapeutic effects of natural and synthetic PPARγ ligands, as antineoplastic agents, represent a fascinating and clinically a potential translatable area of research with regards to the battle against cancer.

Effects of PPAR-γ agonists on oral cancer cell lines: Potential horizons for chemopreventives and adjunctive therapies

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR-γ) activators have anti-cancer effects. Our objective was to determine the effect of PPAR-γ ligands 15-deoxy-D^12,14 -Prostaglandin J₂ (15-PGJ₂ ) and ciglitazone on proliferation, apoptosis, and NF-κB in human oral squamous cell carcinoma cell lines.

METHODS

NA and CA9-22 cells were treated in vitro with 15-PGJ₂ and ciglitazone. Proliferation was measured by MTT colorimetric assay and cell cycle analysis performed via flow cytometry, apoptosis by caspase-3 colorimetric assay and poly-(ADP-ribose) polymerase cleavage on Western blot, and NF-κB activation by luciferase assays.

RESULTS

MTT assays demonstrated dose-dependent decreases after 15-PGJ₂ treatment in both cell lines, and S-phase cell cycle arrest was also demonstrated. NF-κB luciferase reporter gene activity decreased seven- and eightfold in NA and CA9-22 cells, respectively. Caspase-3 activity increased two- and eightfold in NA and CA9-22 cells, respectively.

CONCLUSIONS

Our results suggest these agents, in addition to activating PPAR-γ, can downregulate NF-κB and potentiate apoptosis in oral cancer cells.

S. Ferreira KC, Neto JCR. Pharmacological Strategies for Insulin Sensitivity in Obesity and Cancer: Thiazolidinediones and Metformin

Background:

Chronic diseases, such as obesity and cancer, have high prevalence rates. Both diseases have hyperinsulinemia, hyperglycemia, high levels of IGF-1 and inflammatory cytokines in common. Therefore, these can be considered triggers for cancer development and growth. In addition, low-grade inflammation that modulates the activation of immune cells, cellular metabolism, and production of cytokines and chemokines are common in obesity, cancer, and insulin resistance. Pharmacological strategies are necessary when a change in lifestyle does not improve glycemic homeostasis. In this regard, thiazolidinediones (TZD) possess multiple molecular targets and regulate PPARγ in obesity and cancer related to insulin resistance, while metformin acts through the AMPK pathway.

Objective:

The aim of this study was to review TZD and metformin as pharmacological treatments for insulin resistance associated with obesity and cancer.

Conclusions:

Thiazolidinediones restored adiponectin secretion and leptin sensitivity, reduced lipid droplets in hepatocytes and orexigen peptides in the hypothalamus. In cancer cells, TZD reduced proliferation, production of reactive oxygen species, and inflammation by acting through the mTOR and NFκB pathways. Metformin has similar effects, though these are AMPK-dependent. In addition, both drugs can be efficient against certain side effects caused by chemotherapy.

Interaction of epidermal growth factor with COX-2 products and peroxisome proliferator-activated receptor-γ system in experimental rat Barrett's esophagus

Mixed acidic-alkaline refluxate is a major pathogenic factor in chronic esophagitis progressing to Barrett's esophagus (BE). We hypothesized that epidermal growth factor (EGF) can interact with COX-2 and peroxisome proliferator-activated receptor-γ (PPARγ) in rats surgically prepared with esophagogastroduodenal anastomosis (EGDA) with healthy or removed salivary glands to deplete salivary EGF. EGDA rats were treated with 1) vehicle, 2) EGF or PPARγ agonist pioglitazone with or without EGFR kinase inhibitor tyrphostin A46, EGF or PPARγ antagonist GW9662 respectively, 3) ranitidine or pantoprazole, and 4) the selective COX-2 inhibitor celecoxib combined with pioglitazone. At 3 mo, the esophageal damage and the esophageal blood flow (EBF) were determined, the mucosal expression of EGF, EGFR, COX-2, TNFα, and PPARγ mRNA and phospho-EGFR/EGFR protein was analyzed. All EGDA rats developed chronic esophagitis, esophageal ulcerations, and intestinal metaplasia followed by a fall in the EBF, an increase in the plasma of IL-1β, TNFα, and mucosal PGE₂ content, the overexpression of COX-2-, and EGF-EGFR mRNAs, and proteins, and these effects were aggravated by EGF and attenuated by pioglitazone. The rise in EGF and COX-2 mRNA was inhibited by pioglitazone but reversed by pioglitazone cotreated with GW9662. We conclude that 1) EGF can interact with PG/COX-2 and the PPARγ system in the mechanism of chronic esophagitis; 2) the deleterious effect of EGF involves an impairment of EBF and the overexpression of COX-2 and EGFR, and 3) agonists of PPARγ and inhibitors of EGFR may be useful in the treatment of chronic esophagitis progressing to BE.NEW & NOTEWORTHY Rats with EGDA exhibited chronic esophagitis accompanied by a fall in EBF and an increase in mucosal expression of mRNAs for EGF, COX-2, and TNFα, and these effects were exacerbated by exogenous EGF and reduced by removal of a major source of endogenous EGF with salivectomy or concurrent treatment with tyrphostin A46 or pioglitazone combined with EGF. Beneficial effects of salivectomy in an experimental model of BE were counteracted by PPARγ antagonist, whereas selective COX-2 inhibitor celecoxib synergistically with pioglitazone reduced severity of esophageal damage and protected esophageal mucosa from reflux. We propose the cross talk among EGF/EGFR, PG/COX-2, and proinflammatory cytokines with PPARγ pathway in the mechanism of pathogenesis of chronic esophagitis progressing to BE and EAC.

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

Although the use of oral administration of pharmacological all-trans retinoic acid (ATRA) concentration in acute promyelocytic leukaemia (APL) patients was approved for over 20 years and used as standard therapy still to date, the same use in solid cancers is still controversial. In the present review the literature about the top five lethal solid cancers (lung, stomach, liver, breast, and colon cancer), as defined by The Global Cancer Observatory of World Health Organization, and retinoic acids (ATRA, 9-cis retinoic acid, and 13-cis retinoic acid, RA) was compared. The action of retinoic acids in inhibiting the cell proliferation was found in several cell pathways and compartments: from membrane and cytoplasmic signaling, to metabolic enzymes, to gene expression. However, in parallel in the most aggressive phenotypes several escape routes have evolved conferring retinoic acids-resistance. The comparison between different solid cancer types pointed out that for some cancer types several information are still lacking. Moreover, even though some pathways and escape routes are the same between the cancer types, sometimes they can differently respond to retinoic acid therapy, so that generalization cannot be made. Further studies on molecular pathways are needed to perform combinatorial trials that allow overcoming retinoic acids resistance.

Targeting Glucose Transporters for Breast Cancer Therapy: The Effect of Natural and Synthetic Compounds

Reprogramming of cellular energy metabolism is widely accepted to be a cancer hallmark. The deviant energetic metabolism of cancer cells-known as the Warburg effect-consists in much higher rates of glucose uptake and glycolytic oxidation coupled with the production of lactic acid, even in the presence of oxygen. Consequently, cancer cells have higher glucose needs and thus display a higher sensitivity to glucose deprivation-induced death than normal cells. So, inhibitors of glucose uptake are potential therapeutic targets in cancer. Breast cancer is the most commonly diagnosed cancer and a leading cause of cancer death in women worldwide. Overexpression of facilitative glucose transporters (GLUT), mainly GLUT1, in breast cancer cells is firmly established, and the consequences of GLUT inhibition and/or knockout are under investigation. Herein we review the compounds, both of natural and synthetic origin, found to interfere with uptake of glucose by breast cancer cells, and the consequences of interference with that mechanism on breast cancer cell biology. We will also present data where the interaction with GLUT is exploited in order to increase the efficiency or selectivity of anticancer agents, in breast cancer cells.

PPARγ Agonists in Combination Cancer Therapies

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear receptor acting as a transcription factor involved in the regulation of energy metabolism, cell cycle, cell differentiation, and apoptosis. These unique properties constitute a strong therapeutic potential that place PPARγ agonists as one of the most interesting and widely studied anticancer molecules. Although PPARγ agonists exert significant, antiproliferative and tumoricidal activity in vitro, their anticancer efficacy in animal models is ambiguous, and their effectiveness in clinical trials in monotherapy is unsatisfactory. However, due to pleiotropic effects of PPARγ activation in normal and tumor cells, PPARγ ligands interact with many antitumor treatment modalities and synergistically potentiate their effectiveness. The most spectacular example is a combination of PPARγ ligands with tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML). In this setting, PPARγ activation sensitizes leukemic stem cells, resistant to any previous form of treatment, to targeted therapy. Thus, this combination is believed to be the first pharmacological therapy able to cure CML patients. Within the last decade, a significant body of data confirming the benefits of the addition of PPARγ ligands to various antitumor therapies, including chemotherapy, hormonotherapy, targeted therapy, and immunotherapy, has been published. Although the majority of these studies have been carried out in vitro or animal tumor models, a few successful attempts to introduce PPARγ ligands into anticancer therapy in humans have been recently made. In this review, we aim to summarize shines and shadows of targeting PPARγ in antitumor therapies.

Glitazone loaded fat enhances adiponectin production and inhibits breast cancer cell proliferation

Obesity and diabetes are both associated risk factors for developing breast cancer and poor patient outcomes. Adipose cells are an important endocrine system and are the main producer of adiponectin, with lean patients having higher circulating levels. Patients with diabetes are often treated with thiazolidinediones, glitazones, which also increase adiponectin production. Importantly high circulating levels of adiponectin and treatment with glitazone are associated with increased breast cancer patient survival. This study investigates the potential of using adipose tissue laden with glitazones to act as a drug depot, increase adiponectin levels, and locally release glitazones to inhibit breast cancer cell proliferation. The breast cancer cell lines MCF-7 and MBA-MD-231, and the normal breast epithelial cell line MCF-10A were exposed to media containing a range of concentrations of recombinant adiponectin, pioglitazone, or conditioned media obtained from pioglitazone laden adipose tissue to determine the impact of the different treatments on cell proliferation. The MCF-7 cells demonstrated the greatest reduction in proliferation upon exposure to adiponectin and pioglitazone with lower reductions observed in the MDA-MD-231 and MCF-10a cell lines. All three cell lines exhibited reductions in proliferation in the presence of pioglitazone loaded adipose tissue. Additionally, adiponectin and pioglitazone levels were higher in the media from glitazone loaded adipose tissue. Drug loaded adipose tissue could potentially be used to deliver adiponectin and glitazone to breast cancer cells and inhibit proliferation. Future research will examine the potential efficacy of this treatment approach in vivo.

Cloxiquine, a traditional antituberculosis agent, suppresses the growth and metastasis of melanoma cells through activation of PPARγ

Melanoma is one of the most aggressive skin cancers and 5-year survival rate is only 4.6% for metastatic melanoma patients. Current therapies, especially those involving clinical chemotherapy drugs, have achieved remarkable advances. However, their side effects, such as bone marrow suppression, limit the effectiveness of available pharmacological therapies. Therefore, exploring new antimelanoma drugs with less toxicity is critical for the treatment of melanoma. In the present study, we aimed to identify the antimelanoma drugs with ability to repress the proliferation of melanoma cells by using a high-content screening of FDA-approved drug libraries. We found that cloxiquine (CLQ), a traditional antituberculosic drug, exhibited strong inhibitory effects on the growth and metastasis of melanoma cells both in vivo and in vitro. In contrast, CLQ at the tested doses did not show any apparent toxicity in normal melanocytes and in the liver. At the metabolic level, treatment with CLQ decreased glycolysis, thus potentially inhibiting the “Warburg effect” in B16F10 cells. More importantly, combination of CLQ and 2-deoxyglucose (2-DG), a well-known glycolysis inhibitor, did not show a synergistic effect on the tumor growth and metastasis, indicating that inhibition of glycolysis is potentially involved in mediating CLQ’s antimelanoma function. Bioinformatics analyses revealed that peroxisome proliferator-activated receptor-gamma (PPARγ) served as a potential CLQ target. Mechanistically, CLQ stimulated the transcription and nuclear contents of PPARγ. Furthermore, the specific PPARγ inhibitor GW9662 or PPARγ shRNA partially abolished the effects of CLQ. Collectively, our findings demonstrate that CLQ has a great potential in the treatment of melanoma through activation of PPARγ.

Possible role of Thiazolidinedione in the management of Type-II Endometrial Cancer

Type-II Endometrial Cancer (EMC) is one of the most common types of gynaecological cancer affecting more than 2.7 million people worldwide. Clinical evidence shows that adipokines levels are abnormally altered in Type-II EMC and reported to be one of the major responsible factor for uncontrolled proliferation and metastasis in Type-II EMC. Reversing the altered adipokine levels, therefore, help to control Type-II EMC proliferation and metastasis. In the present hypothesis we focus on the possible role of Thiazolidinediones in favourably altering the adipokine levels to benefit in the management of Type-II EMC.

Possible role of PPAR-γ and COX-2 receptor modulators in the treatment of Non-Small Cell lung carcinoma

Non-Small Cell lung cancer (NSCLC) accounts for 85% of total lung cancers worldwide, affecting more than 1.5 million people every year. Recent studies reported that lung adenocarcinoma express Peroxisome Proliferator Activated Receptor-γ (PPAR-γ) which is believed to be inactivated due to cytoplasmic accumulation or somatic 'loss of function' of the gene. PPAR-γ reported to play an important role in cell proliferation, cell differentiation and apoptosis via inhibition of NF-kβ pathway. Adenocarcinoma also overexpress cyclooxygenase-2 (COX-2), which is reported to promote angiogenesis and metastasis via TX-A2 production. Therefore, we hypothesize that activation of PPAR-γ (through PPAR-γ agonists) and inhibition of COX-2 (through COX-2 inhibitors) will have beneficial effects in the treatment of NSCLC.

Lipocalin-2 abrogates epithelial cell cycle arrest by PPARγ inhibition

Macrophage-epithelial cross-talk regulates cell cycle progression and represents an important factor in rescuing epithelial cells from cell cycle arrest in order to maintain a healthy epithelial phenotype. However, the underlying mechanisms are still not well defined. We provide evidence that macrophage-secreted lipocalin-2 (Lcn-2) plays a key role during this process. In a co-culture setup using cell cycle arrested NRK52e renal epithelial cells and primary bone marrow-derived macrophages, Lcn-2 restores proliferation through inhibition of peroxisome proliferator-activated receptor (PPAR)-γ. Lcn-2 overexpression in macrophages overcomes epithelial cell cycle arrest and enhances epithelial markers via megalin and the downstream activation of PI3K/Akt signalling pathway, whereas a knockdown of Lcn-2 in macrophages prevented this effect. Our results show that macrophage-secreting Lcn-2 is crucial in rescuing epithelial cells from cell cycle arrest and in promoting epithelial proliferation.

PPARγ-Mediated p21 Induction in Aerodigestive Preneoplastic Cell Lines

INTRODUCTION

Oral leukoplakia is defined as a mucous membrane disorder characterized by white patches that cannot be scraped off. Leukoplakia is the most frequent, potentially premalignant oral mucosa disorder and a good candidate for chemopreventive therapies. Pioglitazone activates peroxisome proliferator-activated receptor gamma (PPARγ), which forms a complex with nuclear cofactors and regulates gene expression of a variety of cell-cycle proteins and is currently being tested preclinically and clinically in aerodigestive cancer prevention.

METHODS

In the present study, we hypothesized that pioglitazone would decrease proliferation of human leukoplakia cells (MSK Leuk1) and transformed bronchial epithelial cells (BEAS-2B) through regulatory changes of G1 checkpoint protein regulators, p21 and cyclin-D1. MSK Leuk1 and BEAS-2B cells were treated with pioglitazone and assayed for cell proliferation and p21 transcriptional activity.

RESULTS

We discovered pioglitazone significantly inhibited cell proliferation in a dose-dependent fashion. We also observed p21 protein induction after treatment with pioglitazone, which was preceded by measurable increases in p21 mRNA induction.

CONCLUSIONS

We conclude the PPARγ activator, pioglitazone, can activate p21, which is associated with decreased proliferation in 2 aerodigestive preneoplastic cell lines. In addition, the p21 gene may be a potential hypothesis-driven biomarker in translational studies of pioglitazone as a chemoprevention agent for aerodigestive cancer.

Identification of prostate cancer hub genes and therapeutic agents using bioinformatics approach

BACKGROUND

Prostate cancer (PCa) is the most common and the second leading cause of cancer-related death among men in America. As the molecular mechanism of PCa has not yet been completely discovered, identification of hub genes and potential drug of this disease is an important area of research that could provide new insights into exploring the mechanisms underlying PCa.

OBJECTIVE

The aim of this study was to identify potential biomarkers and novel drug for prostate cancer treatment.

METHODS

The differentially expressed genes (DEGs) between prostate cancer and normal cells were screened using microarray data obtained from the Gene Expression Omnibus database. Gene ontology (GO) and pathway enrichment analyses were performed in order to investigate the functions of DEGs, and the protein-protein interaction (PPI) network of the DEGs was constructed using the Cytoscape software. DEGs were then mapped to the connectivity map database to identify molecular agents associated with the underlying mechanisms of PCa.

RESULTS

Totally, 359 genes (155 upregulated and 204 downregulated genes) were found to be differentially expressed between prostate cancer and normal cells. The GO terms significantly enriched by DEGs included cell adhesion, protein binding involved in cell-cell adhesion, response to BMP, extracellular region and extracellular region part. KEGG pathway analysis showed that the most significant pathways included cell adhesion molecules (CAMs) and TGF-beta signaling pathway. The PPI network of up-regulated DEGs and down-regulated DEGs were established, respectively. While CDH1, BMP2, NKX3-1, PPARG and PRKAR2B were identified as the hub genes in the PPI network.

CONCLUSIONS

The BMP2, PPARG and PRKAR2B genes may therefore be potential biomarkers in the treatment of PCa. Additionally, the small molecular agent phenoxybenzamine may be a potential drug for PCa.

Novel mechanism of cannabidiol-induced apoptosis in breast cancer cell lines

Studies have emphasized an antineoplastic effect of the non-psychoactive, phyto-cannabinoid, Cannabidiol (CBD). However, the molecular mechanism underlying its antitumor activity is not fully elucidated. Herein, we have examined the effect of CBD on two different human breast cancer cell lines: the ER-positive, well differentiated, T-47D and the triple negative, poor differentiated, MDA-MB-231 cells. In both cell lines, CBD inhibited cell survival and induced apoptosis in a dose dependent manner as observed by MTT assay, morphological changes, DNA fragmentation and ELISA apoptosis assay. CBD-induced apoptosis was accompanied by down-regulation of mTOR, cyclin D1 and up-regulation and localization of PPARγ protein expression in the nuclei and cytoplasmic of the tested cells. The results suggest that CBD treatment induces an interplay among PPARγ, mTOR and cyclin D1 in favor of apoptosis induction in both ER-positive and triple negative breast cancer cells, proposing CBD as a useful treatment for different breast cancer subtypes.

Troglitazone Inhibits Matrix Metalloproteinase-9 Expression and Invasion of Breast Cancer Cell through a Peroxisome Proliferator-Activated Receptor γ-Dependent Mechanism

Purpose

Peroxisome proliferator-activated receptor γ (PPARγ) is involved in the pathology of numerous diseases including atherosclerosis, diabetes, obesity, and cancer. Matrix metalloproteinases (MMPs) play a significant role in tissue remodeling related to various processes such as morphogenesis, angiogenesis, tissue repair, invasion, and metastasis. We investigated the effects of PPARγ on MMP expression and invasion in breast cancer cells.

Methods

MCF-7 cells were cultured and then cell viability was monitored in an MTT assay. Western blotting, gelatin zymography, real-time polymerase chain reaction, and luciferase assays were performed to investigate the effect of the synthetic PPARγ ligand troglitazone on MMP expression. Transcription factor DNA binding was analyzed by electrophoretic mobility shift assay. A Matrigel invasion assay was used to assess the effects of troglitazone on MCF-7 cells.

Results

Troglitazone did not affect MCF-7 cell viability. 12-O-tetradecanoylphorbol-13-acetate (TPA) induced MMP-9 expression and invasion in MCF-7 cell. However, these effects were decreased by troglitazone. TPA increased nuclear factor κB and activator protein-1 DNA binding, while troglitazone inhibited these effects. The selective PPARγ antagonist GW9662 reversed MMP-9 inhibition by troglitazone in TPA-treated MCF-7 cells.

Conclusion

Troglitazone inhibited nuclear factor κB and activator protein-1-mediated MMP-9 expression and invasion of MCF-7 cells through a PPARγ-dependent mechanism.

PPARγ activation by troglitazone enhances human lung cancer cells to TRAIL-induced apoptosis via autophagy flux

Members of the tumor necrosis factor (TNF) transmembrane cytokine superfamily, such as TNFα and Fas ligand (FasL), play crucial roles in inflammation and immunity. TRAIL is a member of this superfamily with the ability to selectively trigger cancer cell death but does not motive cytotoxicity to most normal cells. Troglitazone are used in the cure of type II diabetes to reduce blood glucose levels and improve the sensitivity of an amount of tissues to insulin. In this study, we revealed that troglitazone could trigger TRAIL-mediated apoptotic cell death in human lung adenocarcinoma cells. Pretreatment of troglitazone induced activation of PPARγ in a dose-dependent manner. In addition conversion of LC3-I to LC3-II and PPARγ was suppressed in the presence of GW9662, a well-characterized PPARγ antagonist. Treatment with troglitazone resulted in a slight increase in conversion rate of LC3-I to LC3-II and significantly decreased p62 expression levels in a dose-dependent manner. This indicates that troglitazone induced autophagy flux activation in human lung cancer cells. Inhibition of autophagy flux applying a specific inhibitor and genetically modified ATG5 siRNA enclosed troglitazone-mediated enhancing effect of TRAIL. These data demonstrated that activation of PPARγ mediated by troglitazone enhances human lung cancer cells to TRAIL-induced apoptosis via autophagy flux and also suggest that troglitazone may be a combination therapeutic target with TRAIL protein in TRAIL-resistant cancer cells.

Peroxisome proliferator-activated receptor-γ agonist-mediated inhibition of cell growth is independent of apoptosis in human epidermoid carcinoma A431 cells

Evidence suggests that peroxisome proliferator activated receptor-γ (PPAR-γ) acts as a tumor suppressor in multiple types of cancer; however, the role of action of PPAR-γ on human epidermoid carcinoma is unclear. The present study investigated the effects of a PPAR-γ agonist, rosiglitazone, on human epidermoid carcinoma cell growth using the A431 cell line. The effects of rosiglitazone on cell viability and proliferation were evaluated with MTS and [³H] thymidine incorporation assays. The effects of rosiglitazone on the cell cycle and apoptosis were analyzed by flow cytometry, and western blotting. It was identified that rosiglitazone inhibited A431 cell proliferation in a dose-dependent manner, increased the proportion of cells in the G1 phase, but did not affect apoptosis. Consistently, there was a significant decrease in the expression of cell proliferation-associated proteins, including cyclin D1, cyclin-dependent kinase (Cdk)2 and Cdk4 in A431 cells treated with rosiglitazone. This decrease was rescued by a selective antagonist of PPAR-γ or specific PPAR-γ small interfering RNAs. However, the ratio of B-cell lymphoma 2 (Bcl-2) to Bcl-2 associated X protein, which is associated with cell apoptosis, was not affected by these treatments. The data of the present study suggest that the PPAR-γ agonist rosiglitazone inhibits human epidermoid carcinoma cell growth through regulating the expression of the cell cycle-associated proteins, and that this effect is independent of apoptosis.

Anti-leukemic effects of PPARγ ligands

The peroxisome proliferator-activated receptor (PPAR) γ, a subtype of PPARs, is a member of the nuclear receptor family. PPARγ and its ligands contribute to various types of diseases including cancer. Given that currently developed therapies against leukemia are not very effective or safe, PPARγ ligands have been shown to be a new class of compounds with the potential to treat hematologic malignancies, particularly leukemia. The capability of PPARγ ligands to induce apoptosis, inhibit proliferation, and promote differentiation of leukemia cells suggests it has significant potential as a drug against leukemia. However, the specific mechanisms and molecules involved are not well-understood, although a number of PPARγ ligands with anti-leukemic effects have been identified. This may explain why PPARγ ligands have not been widely evaluated in clinical trials. To fill the gaps in the lack of understanding of specific anti-leukemic processes of PPARγ ligands and further adapt these molecules as anti-leukemic agents, this review describes previous studies of the anti-leukemic effects of PPARγ ligands.

ΔFosB regulates rosiglitazone-induced milk fat synthesis and cell survival

Rosiglitazone induces adipogenesis in adipocyte and regulates cell survival and differentiation in number of cell types. However, whether PPARγ regulates the synthesis of milk fat and cell survival in goat mammary gland remains unknown. Rosiglitazone strongly enhanced cellular triacylglycerol content and accumulation of lipid droplet in goat mammary epithelial cells (GMEC). Furthermore, ΔFosB decreased the expression of PPARγ at both mRNA and protein levels, and rosiglitazone-induced milk fat synthesis was abolished by ΔFosB overexpression. ΔFosB reduced milk fat synthesis and enhanced saturated fatty acid concentration. Rosiglitazone increased the number of GMEC in G0/G1 phase and inhibited cell proliferation, and these effects were improved by overexpression of ΔFosB. ΔFosB was found to promote the expression of Bcl-2 and suppress the expression of Bax, and protected GMEC from apoptosis induced by rosiglitazone. Intracellular calcium trafficking assay revealed that rosiglitazone markedly increased intracellular calcium concentration. ΔFosB protected GMEC from apoptosis induced by intracellular Ca²⁺ overload. ΔFosB increased MMP-9 gelatinolytic activity. SB-3CT, an MMP-9 inhibitor, suppressed the expression of Bcl-2, and increased intracellular calcium levels, and this effect was abolished by ΔFosB overexpression. SB-3CT induced GMEC apoptosis and this effect was inhibited by ΔFosB overexpression. These findings suggest that ΔFosB regulates rosiglitazone-induced milk fat synthesis and cell survival. Therefore, ΔFosB may be an important checkpoint to control milk fat synthesis and cell apoptosis.

Pathway-based discovery of genetic interactions in breast cancer

Breast cancer is the second largest cause of cancer death among U.S. women and the leading cause of cancer death among women worldwide. Genome-wide association studies (GWAS) have identified several genetic variants associated with susceptibility to breast cancer, but these still explain less than half of the estimated genetic contribution to the disease. Combinations of variants (i.e. genetic interactions) may play an important role in breast cancer susceptibility. However, due to a lack of statistical power, the current tests for genetic interactions from GWAS data mainly leverage prior knowledge to focus on small sets of genes or SNPs that are known to have an association with breast cancer. Thus, many genetic interactions, particularly among novel variants, remain understudied. Reverse-genetic interaction screens in model organisms have shown that genetic interactions frequently cluster into highly structured motifs, where members of the same pathway share similar patterns of genetic interactions. Based on this key observation, we recently developed a method called BridGE to search for such structured motifs in genetic networks derived from GWAS studies and identify pathway-level genetic interactions in human populations. We applied BridGE to six independent breast cancer cohorts and identified significant pathway-level interactions in five cohorts. Joint analysis across all five cohorts revealed a high confidence consensus set of genetic interactions with support in multiple cohorts. The discovered interactions implicated the glutathione conjugation, vitamin D receptor, purine metabolism, mitotic prometaphase, and steroid hormone biosynthesis pathways as major modifiers of breast cancer risk. Notably, while many of the pathways identified by BridGE show clear relevance to breast cancer, variants in these pathways had not been previously discovered by traditional single variant association tests, or single pathway enrichment analysis that does not consider SNP-SNP interactions.

PPARγ Ligand-induced Annexin A1 Expression Determines Chemotherapy Response via Deubiquitination of Death Domain Kinase RIP in Triple-negative Breast Cancers

Metastatic breast cancer is still incurable so far; new specifically targeted and more effective therapies for triple-negative breast cancer (TNBC) are required in the clinic. In this study, our clinical data have established that basal and claudin-low subtypes of breast cancer (TNBC types) express significantly higher levels of Annexin A1 (ANXA1) with poor survival outcomes. Using human cancer cell lines that model the TNBC subtype, we observed a strong positive correlation between expression of ANXA1 and PPARγ. A similar correlation between these two markers was also established in our clinical breast cancer patients' specimens. To establish a link between these two markers in TNBC, we show de novo expression of ANXA1 is induced by activation of PPARγ both in vitro and in vivo and it has a predictive value in determining chemosensitivity to PPARγ ligands. Mechanistically, we show for the first time PPARγ-induced ANXA1 protein directly interacts with receptor interacting protein-1 (RIP1), promoting its deubiquitination and thereby activating the caspase-8-dependent death pathway. We further identified this underlying mechanism also involved a PPARγ-induced ANXA1-dependent autoubiquitination of cIAP1, the direct E3 ligase of RIP1, shifting cIAP1 toward proteosomal degradation. Collectively, our study provides first insight for the suitability of using drug-induced expression of ANXA1 as a new player in RIP1-induced death machinery in TNBCs, presenting itself both as an inclusion criterion for patient selection and surrogate marker for drug response in future PPARγ chemotherapy trials. Mol Cancer Ther; 16(11); 2528-42. ©2017 AACR.

In vitro and in vivo cytotoxicity of troglitazone in pancreatic cancer

Background

Troglitazone (TGZ) is a peroxisome proliferator-activated receptor gamma (PPARγ) agonist that has been investigated as a potential chemopreventive and chemotherapeutic agent. However, the antitumor efficacy and mechanisms of TGZ in pancreatic cancer have not been extensively investigated. This study was performed to investigate the in vitro and in vivo effects of TGZ against pancreatic cancer cell lines, as well as its action mechanisms in terms of PPARγ dependency and the Akt and mitogen-activated protein kinase (MAPK) pathways. We also evaluated the effects of TGZ on cell invasion and migration.

Methods

MIA Paca2 and PANC-1 human pancreatic cancer cell lines were used. Cell viability and caspase-3 activity were detected using fluorescent reagents, and chromatin condensation was observed after staining the cells with Hoechst 33342. Protein expression levels were detected by western blot analysis. Invasion and migration assays were performed using 24-well chambers. The in vivo antitumor effects of TGZ were investigated in nude mice inoculated with MIA Paca2 cells. Mice were orally administered TGZ (200 mg/kg) every day for 5 weeks, and tumor volumes were measured bi-dimensionally.

Results

TGZ showed dose-dependent cytotoxicity against both cell lines, which was not attenuated by a PPARγ inhibitor. Further, TGZ induced chromatin condensation, elevated caspase-3 activity, and increased Bax/Bcl-2 relative expression in MIA Paca2 cells. TGZ also increased phosphorylation of Akt and MAPK (ERK/p38/JNK) in both cell lines, and a JNK inhibitor significantly increased the viability of MIA Paca2 cells. TGZ moderately inhibited cell migration. Tumor growth in the MIA Paca2 xenograft model was inhibited by TGZ administration, while mouse body weights in the treated group were not different from those of the vehicle administration group.

Conclusion

We demonstrated for the first time the in vivo antitumor effects of TGZ in pancreatic cancer without marked adverse effects. TGZ induced mitochondria-mediated apoptosis in MIA Paca2 cells, and its cytotoxic effects were PPARγ-independent and occurred via the JNK pathway. Our results indicate that TGZ is a potential approach for the treatment of pancreatic cancer and warrants further studies regarding its detailed mechanisms and clinical efficacy.

Retinoic acid directs breast cancer cell state changes through regulation of TET2-PKCζ pathway

The key molecular mechanism governing the cancer cell state (stem cell-like state vs differentiation state) to control the cancer stem cell (CSC) pool remains elusive. This study provides the first evidence showing that all-trans retinoic acid (ATRA) induces the interaction and chromatin recruitment of a novel RARβ-TET2 complex to epigenetically activate a specific cohort of gene targets, including MiR-200c. TET2-activated miR-200c further targets and suppresses PKCζ, a cell polarity protein that has a pivotal role in directing asymmetric division of mammalian stem cells to sustain the stem cell pool. Our data reveal that pharmacological concentration of ATRA effectively downregulates PKCζ through activation of miR-200c, leading to a decrease of the stem cell-like populations from non-tumorigenic mammary epithelial cells and non-aggressive breast cancer cells. However, aggressive breast cancer cells that manifest TET2-miR-200c dysregulation sustain a CSC pool highly resistant to ATRA, where inhibition of PKCζ directs the resistant CSCs to the luminal cell-like state and sensitization to tamoxifen, resulting in abrogation of mammary tumor growth and progression. Together, these findings elucidate a novel RARβ-TET2-miR-200c-PKCζ signaling pathway that directs cancer cell state changes and also provide previously unidentified therapeutic implications for PKCζ inhibitors in diminishment of breast CSCs to eradicate breast cancer.