Inhibition of human lung cancer cell growth by the peroxisome proliferator-activated receptor-gamma agonists through induction of apoptosis

Ruthenium biochanin-A complex ameliorates lung carcinoma through the downregulation of the TGF-β/PPARγ/PI3K/TNF-α pathway in association with caspase-3-mediated apoptosis

Lung cancer is the most often reported cancer with a terrible prognosis worldwide. Flavonoid metal complexes have exhibited potential chemotherapeutic effects with substantially low adverse effects. This study investigated the chemotherapeutic effect of the ruthenium biochanin-A complex on lung carcinoma in both in vitro and in vivo model systems. The synthesized organometallic complex was characterized via UV‒visible spectroscopy, FTIR, mass spectrometry, and scanning electron microscopy. Moreover, the DNA binding activity of the complex was determined. The in vitro chemotherapeutic assessment was performed on the A549 cell line through MTT assay, flow cytometry, and western blot analysis. An in vivo toxicity study was performed to determine the chemotherapeutic dose of the complex, and subsequently, chemotherapeutic activity was assessed in benzo-α-pyrene-induced lung cancer mouse model by evaluating the histopathology, immunohistochemistry, and TUNEL assays. The IC50 value of the complex in A549 cells was found to be 20 µM. The complex demonstrated significant apoptosis induction, enhanced caspase-3 expression and cell cycle arrest with downregulated PI3K, PPARγ, TGF-β, and TNF-α expression in A549 cells. The in vivo study suggested that ruthenium biochanin-A therapy restored the morphological architecture of lung tissue in a benzo-α-pyrene-induced lung cancer model and inhibited the expression of Bcl2. Additionally, increased apoptotic events were identified with upregulation of caspase-3 and p53 expression. In conclusion, the ruthenium biochanin-A complex successfully amelioratedlung cancer incidence in both in vitro and in vivo models through the alteration of the TGF-β/PPARγ/PI3K/TNF-α axis with the induction of the p53/caspase-3-mediated apoptotic pathway.

Effect of isorhamnetin on carbonic anhydrase IX expression and tumorigenesis of bladder cancer by activating PPARγ/PTEN/AKT pathway

BACKGROUND

To clarify the research prospect and mechanism analysis of isorhamnetin as a therapeutic drug for bladder cancer.

METHODS

Firstly, the effects of different concentrations of isorhamnetin on the expression of PPARγ/PTEN/Akt pathway protein, CA9, PPARγ, PTEN and AKT protein were discussed by western blot. The effects of isorhamnetin on the growth of bladder cells were also analyzed. Secondly, we verified whether the effect of isorhamnetin on CA9 was related to PPARγ/PTEN/Akt pathway by western blot, and the mechanism of isorhamnetin on the growth of bladder cells is related to this pathway by CCK8, cell cycle and ball formation experiment. Further, nude mouse model of subcutaneous tumor transplantation was constructed to analyze the effects of isorhamnetin, PPAR and PTEN on 5637 cell tumorigenesis and the effects of isorhamnetin on tumorigenesis and CA9 expression through PPARγ/PTEN/Akt pathway.

RESULTS

Isorhamnetin inhibited the development of bladder cancer, and regulated the expression of PPAR, PTEN, AKT, CA9. Isorhamnetin inhibits cell proliferation and the transition of cells from G0/G1 phase to S phase, and tumor sphere formation. Carbonic anhydrase IX is a potential downstream molecule of PPARγ/PTEN/AKT pathway. Overexpression of PPARγ and PTEN inhibited expression of CA9 in bladder cancer cells and tumor tissues. Isorhamnetin reduced CA9 expression in bladder cancer via PPARγ/PTEN/AKT pathway, thereby inhibiting bladder cancer tumorigenicity.

CONCLUSION

Isorhamnetin has the potential to become a therapeutic drug for bladder cancer, whose antitumor mechanism is related to PPARγ/PTEN/AKT pathway. Isorhamnetin reduced CA9 expression in bladder cancer via PPARγ/PTEN/AKT pathway, thereby inhibiting bladder cancer tumorigenicity.

TRIB3 Modulates PPARγ-Mediated Growth Inhibition by Interfering with the MLL Complex in Breast Cancer Cells

Aberrant expression or activity of proteins are amongst the best understood mechanisms that can drive cancer initiation and progression, as well as therapy resistance. TRIB3, a member of the Tribbles family of pseudokinases, is often dysregulated in cancer and has been associated with breast cancer initiation and metastasis formation. However, the underlying mechanisms by which TRIB3 contributes to these events are unclear. In this study, we demonstrate that TRIB3 regulates the expression of PPARγ, a transcription factor that has gained attention as a potential drug target in breast cancer for its antiproliferative actions. Proteomics and phosphoproteomics analyses together with classical biochemical assays indicate that TRIB3 interferes with the MLL complex and reduces MLL-mediated H3K4 trimethylation of the PPARG locus, thereby reducing PPARγ mRNA expression. Consequently, the overexpression of TRIB3 blunts the antiproliferative effect of PPARγ ligands in breast cancer cells, while reduced TRIB3 expression gives the opposite effect. In conclusion, our data implicate TRIB3 in epigenetic gene regulation and suggest that expression levels of this pseudokinase may serve as a predictor of successful experimental treatments with PPARγ ligands in breast cancer.

Peroxisome Proliferator-Activated Receptors and the Hallmarks of Cancer

Peroxisome proliferator-activated receptors (PPARs) function as nuclear transcription factors upon the binding of physiological or pharmacological ligands and heterodimerization with retinoic X receptors. Physiological ligands include fatty acids and fatty-acid-derived compounds with low specificity for the different PPAR subtypes (alpha, beta/delta, and gamma). For each of the PPAR subtypes, specific pharmacological agonists and antagonists, as well as pan-agonists, are available. In agreement with their natural ligands, PPARs are mainly focused on as targets for the treatment of metabolic syndrome and its associated complications. Nevertheless, many publications are available that implicate PPARs in malignancies. In several instances, they are controversial for very similar models. Thus, to better predict the potential use of PPAR modulators for personalized medicine in therapies against malignancies, it seems necessary and timely to review the three PPARs in relation to the didactic concept of cancer hallmark capabilities. We previously described the functions of PPAR beta/delta with respect to the cancer hallmarks and reviewed the implications of all PPARs in angiogenesis. Thus, the current review updates our knowledge on PPAR beta and the hallmarks of cancer and extends the concept to PPAR alpha and PPAR gamma.

Fatty acids and their lipid mediators in the induction of cellular apoptosis in cancer cells

The oxygenation of polyunsaturated fatty acids such as arachidonic and linoleic acid through enzymes like lipoxygenases (LOXs) are common and often leads to the production of various bioactive lipids that are important both in acute inflammation and its resolution and thus in disease progression. Amongst the several isoforms of LOX that are expressed in mammals, 15-lipoxygenase (15-LOX) has shown to be crucial in the context of inflammation. Moreover, being expressed in cells of the immune system, as well as in epithelial cells; the enzyme has been shown to crosstalk with a number of important signalling pathways. Mounting evidences from recent reports suggest that 15-LOX has anti-cancer activities which are dependent or independent of its metabolites, and is executed through several downstream pathways like cGMP, PPAR, p53, p21 and NAG-1. However, it is still unclear whether the up-regulation of 15-LOX is associated with cancer cell apoptosis. Monoamine oxidase A (MAO-A), on the other hand, is a mitochondrial flavoenzyme which is believed to be involved in the pathogenesis of atherosclerosis and inflammation and in many other neurological disorders. MAO-A has also been reported as a potential therapeutic target in different types of cancers like prostate cancer, lung cancer etc. In this review, we discussed about the role of fatty acids and their lipid mediators in cancer cell apoptosis. Here we particularly focused on the contribution of oxidative enzymes like 15-LOX and MAO-A in mediating apoptosis in lung cancer cell after fatty acid induction.

Targeting Nuclear Receptors in Lung Cancer—Novel Therapeutic Prospects

Lung cancer, the second most commonly diagnosed cancer, is the major cause of fatalities worldwide for both men and women, with an estimated 2.2 million new incidences and 1.8 million deaths, according to GLOBOCAN 2020. Although various risk factors for lung cancer pathogenesis have been reported, controlling smoking alone has a significant value as a preventive measure. In spite of decades of extensive research, mechanistic cues and targets need to be profoundly explored to develop potential diagnostics, treatments, and reliable therapies for this disease. Nuclear receptors (NRs) function as transcription factors that control diverse biological processes such as cell growth, differentiation, development, and metabolism. The aberrant expression of NRs has been involved in a variety of disorders, including cancer. Deregulation of distinct NRs in lung cancer has been associated with numerous events, including mutations, epigenetic modifications, and different signaling cascades. Substantial efforts have been made to develop several small molecules as agonists or antagonists directed to target specific NRs for inhibiting tumor cell growth, migration, and invasion and inducing apoptosis in lung cancer, which makes NRs promising candidates for reliable lung cancer therapeutics. The current work focuses on the importance of various NRs in the development and progression of lung cancer and highlights the different small molecules (e.g., agonist or antagonist) that influence NR expression, with the goal of establishing them as viable therapeutics to combat lung cancer.

MicroRNA hsa-miR-657 promotes retinoblastoma malignancy by inhibiting peroxisome proliferator-activated receptor alpha expression

Retinoblastoma is a familial inherited embryonic neuroretinal malignancy with a low survival rate and poor prognosis. Our study aimed to evaluate the potential interaction between microRNA miR-657 and the peroxisome proliferator-activated receptor alpha (PPARA) in retinoblastoma. Expression of miR-657 and PPARA was analyzed in retinoblastoma tissues and cells using RT-qPCR. Cell proliferation, apoptosis, and migration were measured in retinoblastoma cell lines, and xenografting experiments were performed using nude mice. Our study showed that miR-657 expression was markedly increased, whereas that of PPARA was markedly decreased in retinoblastoma. Additionally, PPARA knockdown enhanced the development of retinoblastoma. miR-657 enhanced the retinoblastoma tumorigenesis by directly inhibiting PPARA expression, suggesting that PPARA targeting by miR-657 facilitates retinoblastoma development by enhancing cell growth. This study provides novel insights into the miR-657- and PPARA-mediated mechanisms underlying retinoblastoma progression and suggests that the interaction between miR-657 and PPARA may serve as an effective target for therapeutic intervention.

Overexpression of the PPAR-γ protein in primary Ta/T1 non-muscle-invasive urothelial carcinoma

Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a well-known nuclear receptor that is activated in the nucleus to regulate several transcription factors. Its expression patterns have been examined in various types of cancer. The present study investigated the expression patterns of PPAR-γ in non-muscle-invasive urothelial carcinoma. The expression rates of PPAR-γ, p53 and Ki-67 were compared to determine whether PPAR-γ may be considered as an immunobiomarker for bladder cancer. The intensity and extent of PPAR-γ expression were evaluated in 79 cases of non-muscle-invasive urothelial carcinoma (30 cases of papillary carcinoma low-grade, 30 cases of high-grade and 19 cases of carcinoma in situ) and 30 non-malignant cases. The nuclear overexpression of PPAR-γ was frequently observed in non-muscle-invasive urothelial carcinoma (63/79 cases) but was rarely detected in non-malignant cases (2/30 cases). The histological proliferation types of non-muscle-invasive urothelial carcinoma revealed that PPAR-γ was more frequently overexpressed in papillary carcinoma (54/60 cases) than in carcinoma in situ (9/19 cases). Immunohistochemical staining demonstrated that PPAR-γ was more useful as an immunobiomarker than p53 or Ki-67 (diagnostic odds ratios; 55.13, 16.82 and 11.13, respectively). In summary, this study demonstrated that the expression patterns of PPAR-γ were associated with histological proliferation type and that PPAR-γ was expressed in the nuclei of papillary carcinoma cells. These findings suggested that immunohistochemical staining for PPAR-γ may be used to comprehensively detect non-muscle-invasive urothelial carcinoma.

The Prostaglandin E2 Pathway and Breast Cancer Stem Cells: Evidence of Increased Signaling and Potential Targeting

Culprits of cancer development, metastasis, and drug resistance, cancer stem cells (CSCs) are characterized by specific markers, active developmental signaling pathways, metabolic plasticity, increased motility, invasiveness, and epithelial-mesenchymal transition. In breast cancer, these cells are often more prominent in aggressive disease, are amplified in drug-resistant tumors, and contribute to recurrence. For breast cancer, two distinct CSC populations exist and are typically defined by CD44+/CD24- cell surface marker expression or increased aldehyde dehydrogenase (ALDH) activity. These CSC populations share many of the same properties but also exhibit signaling pathways that are more active in CD44+/CD24- or ALDH+ populations. Understanding these CSC populations and their shared or specific signaling pathways may lead to the development of novel therapeutic strategies that will improve breast cancer patient outcomes. Herein, we review the current evidence and assess published patient tumor datasets of sorted breast CSC populations for evidence of heightened prostaglandin E2 (PGE₂) signaling and activity in these breast CSC populations. PGE₂ is a biologically active lipid mediator and in cancer PGE₂ promotes tumor progression and poor patient prognosis. Overall, the data suggests that PGE₂ signaling is important in propagating breast CSCs by enhancing inherent tumor-initiating capacities. Development of anti-PGE₂ signaling therapeutics may be beneficial in inhibiting tumor growth and limiting breast CSC populations.

The pleiotropic peroxisome proliferator activated receptors: Regulation and therapeutics

The Peroxisome proliferator-activated receptors (PPARs) are key regulators of metabolic events in our body. Owing to their implication in maintenance of homeostasis, both PPAR agonists and antagonists assume therapeutic significance. Understanding the molecular mechanisms of each of the PPAR isotypes in the healthy body and during disease is crucial to exploiting their full therapeutic potential. This article is an attempt to present a rational analysis of the multifaceted therapeutic effects and underlying mechanisms of isotype-specific PPAR agonists, dual PPAR agonists, pan PPAR agonists as well as PPAR antagonists. A holistic understanding of the mechanistic dimensions of these key metabolic regulators will guide future efforts to identify novel molecules in the realm of metabolic, inflammatory and immunotherapeutic diseases.

Glioma Stem-Like Cells and Metabolism: Potential for Novel Therapeutic Strategies

Glioma stem-like cells (GSCs) were first described as a population which may in part be resistant to traditional chemotherapeutic therapies and responsible for tumour regrowth. Knowledge of the underlying metabolic complexity governing GSC growth and function may point to potential differences between GSCs and the tumour bulk which could be harnessed clinically. There is an increasing interest in the direct/indirect targeting or reprogramming of GSC metabolism as a potential novel therapeutic approach in the adjuvant or recurrent setting to help overcome resistance which may be mediated by GSCs. In this review we will discuss stem-like models, interaction between metabolism and GSCs, and potential current and future strategies for overcoming GSC resistance.

Peroxisome proliferator-activated receptor gamma: a novel therapeutic target for cognitive impairment and mood disorders that functions via the regulation of adult neurogenesis

The proliferation, differentiation, and migration of neural precursor cells occur not only during embryonic development but also within distinct regions of the adult brain through the process of adult neurogenesis. As neurogenesis can potentially regulate brain cognition and neuronal plasticity, the factors that enhance neurogenesis can be attractive therapeutic targets for improving cognitive function and regulating neurodegenerative and neuropsychiatric disorders, including affective and mood disorders. Peroxisome proliferator-activated receptors (PPARs) are a class of ligand-activated transcription factors belonging to the nuclear receptor superfamily. PPARγ is a target for insulin sensitizers and plays an essential role in regulating various metabolic processes, including adipogenesis and glucose homeostasis. Interestingly, evidence demonstrates the role of PPARγ activation in regulating neurogenesis. The pharmacological activation of PPARγ using specific ligands increases the proliferation and differentiation of neural stem cells in specific brain regions, including the hippocampus, and prevents neurodegeneration and improves cognition and anxiety/depression-like behaviors in animal models. We summarize here recent reports on the role of PPARγ in adult neurogenesis, as well as the mechanisms involved, and suggest that PPARγ can serve as a potential therapeutic target for neurological and/or neurodegenerative diseases.

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.

PPARgamma in Metabolism, Immunity, and Cancer: Unified and Diverse Mechanisms of Action

The proliferator-activated receptor γ (PPARγ), a member of the nuclear receptor superfamily, is one of the most extensively studied ligand-inducible transcription factors. Since its identification in the early 1990s, PPARγ is best known for its critical role in adipocyte differentiation, maintenance, and function. Emerging evidence indicates that PPARγ is also important for the maturation and function of various immune system-related cell types, such as monocytes/macrophages, dendritic cells, and lymphocytes. Furthermore, PPARγ controls cell proliferation in various other tissues and organs, including colon, breast, prostate, and bladder, and dysregulation of PPARγ signaling is linked to tumor development in these organs. Recent studies have shed new light on PPARγ (dys)function in these three biological settings, showing unified and diverse mechanisms of action. Classical transactivation-where PPARγ activates genes upon binding to PPAR response elements as a heterodimer with RXRα-is important in all three settings, as underscored by natural loss-of-function mutations in FPLD3 and loss- and gain-of-function mutations in tumors. Transrepression-where PPARγ alters gene expression independent of DNA binding-is particularly relevant in immune cells. Interestingly, gene translocations resulting in fusion of PPARγ with other gene products, which are unique to specific carcinomas, present a third mode of action, as they potentially alter PPARγ's target gene profile. Improved understanding of the molecular mechanism underlying PPARγ activity in the complex regulatory networks in metabolism, cancer, and inflammation may help to define novel potential therapeutic strategies for prevention and treatment of obesity, diabetes, or cancer.

Identification of an irreversible PPARγ antagonist with potent anticancer activity

Melanoma is responsible for most skin cancer deaths, and its incidence continues to rise year after year. Different treatment options have been developed for melanoma depending on the stage of the disease. Despite recent advances in immuno- and targeted therapies, advanced melanoma remains incurable and thus an urgent need persists for safe and more effective melanoma therapeutics. In this study, we demonstrate that a novel compound MM902 (3-(3-(bromomethyl)-5-(4-(tert-butyl) phenyl)-1H-1,2,4-triazol-1-yl) phenol) exhibited potent efficacies in inhibiting the growth of different cancer cells, and suppressed tumor growth in a mouse xenograft model of malignant melanoma. Beginning with MM902 instead of specific targets, computational similarity- and docking-based approaches were conducted to search for known anticancer drugs whose structural features match MM902 and whose pharmacological target would accommodate an irreversible inhibitor. Peroxisome proliferator-activated receptor (PPAR) was computationally identified as one of the pharmacological targets and confirmed by in vitro biochemical assays. MM902 was shown to bind to PPARγ in an irreversible mode of action and to function as a selective antagonist for PPARγ over PPARα and PPARδ. It is hoped that MM902 will serve as a valuable research probe to study the functions of PPARγ in tumorigenesis and other pathological processes.

CB13, a novel PPARγ ligand, overcomes radio-resistance via ROS generation and ER stress in human non-small cell lung cancer

Peroxisome proliferator-activated receptor gamma (PPARγ) is a well-known therapeutic target for type 2 diabetes as well as is a potential target for effective anti-cancer drug, since PPARγ ligands such as ciglitazone (Cig) frequently cause cell death in many types of cancer cells and suppress tumor growth. However, many cancer patients acquire chemo-resistance or radio-resistance after chemo or radiotherapy, and it is still unclear. In the difficulty of well-known anti-cancer drugs, we developed a novel PPARγ agonist CB13 (1-benzyl-5-(4-methylphenyl) pyrido [2,3-d]pyrimidine-2,4(1H,3H)-dione) and investigated the anti-cancer effect and cell death mechanism on human non-small cell lung cancer (NSCLC) cells. With anti-cancer effect of Cig, CB13 also causes inhibition of cell growth by decreasing cell viability, increasing the release of LDH, and increasing caspase-3, and caspase-9 activities. CB13 generates reactive oxygen species (ROS) and causes cell death via ER stress in NSCLC and radio-resistant NSCLC cells (A549R and H460R), and a combination of CB13 and radiation induces greater ER stress and cell death when compared to CB13 alone. Taken together, our results suggest that a combination of CB13 and radiation may overcome radio-resistance caused by radiotherapy.

CB11, a novel purine-based PPARɣ ligand, overcomes radio-resistance by regulating ATM signalling and EMT in human non-small-cell lung cancer cells

Background

Peroxisome proliferator-activated receptor γ (PPARγ) agonists frequently induce cell death in human non-small-cell lung cancer (NSCLC) cells. However, majority of NSCLC patients acquire resistance after cancer therapy, and it is still unclear.

Methods

In this study we investigated the apoptotic mechanism and the anti-cancer effects of a novel purine-based PPARγ agonist, CB11 (8-(2-aminophenyl)-3-butyl-1,6,7-trimethyl-1H-imidazo[2,1-f]purine-2,4(3H,8H)-dione), on human NSCLC cells. CB11 mediates PPARγ-dependent cell death, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) collapse, cell cycle arrest, lactate dehydrogenase (LDH) cytotoxicity, and caspase-3 activity in human NSCLC cells.

Results

CB11 causes cell death via ROS-mediated ATM-p53-GADD45α signalling in human NSCLC cells, and diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, decreases cell death by inhibiting CB11-mediated ATM signalling. In a xenograft experiment, CB11 dramatically reduced tumour volume when compared to a control group. Furthermore, CB11 induced cell death by inhibiting epithelial-to-mesenchymal transition (EMT) under radiation exposure in radiation-resistant human NSCLC cells. However, PPARγ deficiency inhibited cell death by blocking the ATM-p53 axis in radiation/CB11-induced radiation-resistant human NSCLC cells.

Conclusions

Taken together, our results suggest that CB11, a novel PPARγ agonist, may be a novel anti-cancer agent, and it could be useful in a therapeutic strategy to overcome radio-resistance in radiation-exposed NSCLC.

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.

The influence of conjugated linoleic acid on the expression of peroxisome proliferator-activated receptor-γ and selected apoptotic genes in non-small cell lung cancer

In recent years, peroxisome proliferator-activated receptor-γ (PPARγ) has been intensively studied. Because its activation is often associated with changes in the expression level of various apoptotic genes, many studies have emphasized the role of PPARγ as an important anticancer agent. However, in different types of cancer, different genes are influenced by PPARγ action. Previous studies showed that conjugated linoleic acid (CLA) was able to induce apoptosis, upregulate PPARG gene expression and activate PPARγ protein in certain human cancer cell lines. Moreover, some PPARγ agonists inhibited the growth of human lung cancer cells through the induction of apoptosis. Nevertheless, the impact of CLA on PPARγ mRNA and protein levels in non-small cell lung cancer (NSCLC) cell lines has not been investigated thus far. Therefore, in our study, we analysed the influence of the c9,t11 linoleic acid isomer on the expression of PPARG and other genes involved in the apoptotic response (BCL-2, BAX, and CDKN1A) in two NSCLC cell lines of different histological origin (A549 and Calu-1) and in normal human bronchial epithelial Beas-2B cells. Cells were treated with several doses of c9,t11 CLA, followed by RNA and protein isolation, cDNA synthesis, real-time quantitative PCR (RT-qPCR) and Western blot analysis. We showed that the investigated CLA isomer was able to enhance the expression of PPARγ in the examined cell lines and alter the mRNA and protein levels of genes involved in apoptosis. Fluorescent staining and MMT assay revealed the antiproliferative potential of CLA as well as its ability to activate pathways that lead to cell death.

Peroxisome proliferator-activated receptor gamma controls prostate cancer cell growth through AR-dependent and independent mechanisms

BACKGROUND

Prostate cancer (PC) remains a leading cause of cancer mortality and the most successful chemopreventative and treatment strategies for PC come from targeting the androgen receptor (AR). Although AR plays a key role, it is likely that other molecular pathways also contribute to PC, making it essential to identify and develop drugs against novel targets. Recent studies have identified peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor that regulates fatty acid (FA) metabolism, as a novel target in PC, and suggest that inhibitors of PPARγ could be used to treat existing disease. We hypothesized that PPARγ acts through AR-dependent and independent mechanisms to control PC development and growth and that PPARγ inhibition is a viable PC treatment strategy.

METHODS

Immunohistochemistry was used to determine expression of PPARү in a cohort of patients with PC. Standard molecular techniques were used to investigate the PPARү signaling in PC cells as well a xenograft mouse model to test PPARү inhibition in vivo. Kaplan-Meier curves were created using cBioportal.

RESULTS

We confirmed the expression of PPARү in human PC. We then showed that small molecule inhibition of PPARγ decreases the growth of AR-positive and -negative PC cells in vitro and that T0070907, a potent PPARγ antagonist, significantly decreased the growth of human PC xenografts in nude mice. We found that PPARγ antagonists or small interfering RNA (siRNA) do not affect mitochondrial activity nor do they cause apoptosis; instead, they arrest the cell cycle. In AR-positive PC cells, antagonists and siRNAs reduce AR transcript and protein levels, which could contribute to growth inhibition. AR-independent effects on growth appear to be mediated by effects on FA metabolism as the specific FASN inhibitor, Fasnall, inhibited PC cell growth but did not have an additive effect when combined with PPARγ antagonists. Patients with increased PPARү target gene expression, but not alterations in PPARү itself, were found to have significantly worse overall survival.

CONCLUSIONS

Having elucidated the direct cancer cell effects of PPARγ inhibition, our studies have helped to determine the role of PPARγ in PC growth, and support the hypothesis that PPARγ inhibition is an effective strategy for PC treatment.

15-Deoxy-∆-12,14-Prostaglandin J2 (15d-PGJ2), an Endogenous Ligand of PPAR-γ: Function and Mechanism

15-Deoxy-∆-^12,14-prostaglandin J2 (15d-PGJ2), a natural peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist, has been explored in some detail over the last 20 years. By triggering the PPAR-γ signalling pathway, it plays many roles and exerts antitumour, anti-inflammatory, antioxidation, antifibrosis, and antiangiogenesis effects. Although many synthetic PPAR-γ receptor agonists have been developed, as an endogenous product of PPAR-γ receptors, 15d-PGJ2 has beneficial characteristics including rapid expression and the ability to contribute to a natural defence mechanism. In this review, we discuss the latest advances in our knowledge of the biological role of 15d-PGJ2 mediated through PPAR-γ. It is important to understand its structure, synthesis, and functional mechanisms to develop preventive agents and limit the progression of associated diseases.

Docosahexaenoic acid induces PPARγ-dependent preadipocytes apoptosis in grass carp Ctenopharyngodon idella

Our previous study showed that docosahexaenoic acid (DHA) plays an important role in decreasing lipid accumulation by inducing apoptosis of the adipocytes in grass carp. However, the mechanism involved remains unclear. DHA has been reported as the natural ligand of PPARγ. The present study aimed to assess whether PPARγ mediates the pro-apoptotic effects by DHA. Adipocytes of grass carp were cultured until 2 days post-confluence and were treated with DHA at various concentrations-0, 25, 50, 100, 200, and 400 μmol/L for 24 h and at 200 μmol/L for various time periods (0, 12, 24, and 48 h, respectively). Besides, the adipocytes were exposed to 200 μM DHA and PPARγ antagonist or inhibitor of certain key enzymes of apoptosis, following which the expression levels of key genes of the cell apoptotic and mitochondrial apoptotic pathways were detected. We found that DHA induced apoptosis of grass carp adipocytes in a time- and dose-dependent manner (P < 0.05). In addition, DHA treatment significantly increased the protein and gene expression levels of PPARγ (P < 0.05), but the PPARγ antagonist significantly abolished this effect and the DHA pro-apoptotic effect (P < 0.05). Moreover, treatment with caspase 9 inhibitor significantly attenuated the DHA-induced preadipocytes apoptosis effects, while treatment with caspase 8 inhibitor showed no influence. These observations suggest that the DHA-induced apoptosis in adipocytes might be mediated by PPARγ and via the intrinsic apoptotic pathway in grass carp.

PLAGL1 gene function during hepatoma cells proliferation

Hepatocellular carcinoma develops as a multistep process, in which cell cycle deregulation is a central feature, resulting in unscheduled proliferation. The PLAGL1 gene encodes a homonym zinc finger protein that is involved in cell-proliferation control. We determined the genomic profile and the transcription and expression level of PLAGL1, simultaneously with that of its molecular partners p53, PPARγ and p21, in cell-lines derived from patients with liver cancer, during in vitro cell growth. Our investigations revealed that genomic and epigenetic changes of PLAGL1 are also present in hepatoma cell-lines. Transcription of PLAGL1 in tumor cells is significantly lower than in normal fibroblasts, but no significant differences in terms of protein expression were detected between these two cell-types, indicating that there is not a direct relationship between the gene transcriptional activity and protein expression. RT-PCR analyses on normal fibroblasts, used as control, also showed that PLAGL1 and p53 genes transcription occurs as an apparent orchestrated process during normal cells proliferation, which gets disturbed in cancer cells. Furthermore, abnormal trafficking of the PLAGL1 protein may occur in hepatocarcinogenesis.

A Sterol from Soft Coral Induces Apoptosis and Autophagy in MCF-7 Breast Cancer Cells

The peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor that plays a key role in regulating cellular metabolism, and is a therapeutic target for cancer therapy. To search for potential PPARγ activators, a compound library comprising 11 marine compounds was examined. Among them, a sterol, 3β,11-dihydroxy-9,11-secogorgost-5-en-9-one (compound 1), showed the highest PPARγ activity with an IC₅₀ value of 8.3 μM for inhibiting human breast adenocarcinoma cell (MCF-7) growth. Western blotting experiments showed that compound 1 induces caspase activation and PARP cleavage. In addition, compound 1 modulated the expression of various PPARγ-regulated downstream biomarkers including cyclin D1, cyclin-dependent kinase (CDK)6, B-cell lymphoma 2 (Bcl-2), p38, and extracellular-signal-regulated kinase (ERK). Moreover, compound 1 increased reactive oxygen species (ROS) generation, upregulated the phosphorylation and expression of H2AX, and induced autophagy. Interestingly, pre-treatment with the autophagy inhibitor 3-methyladenine rescued cells from compound 1-induced growth inhibition, which indicates that the cytotoxic effect of compound 1 is, in part, attributable to its ability to induce autophagy. In conclusion, these findings suggest the translational potential of compound 1 in breast cancer therapy.

Opposite Interplay Between the Canonical WNT/β-Catenin Pathway and PPAR Gamma: A Potential Therapeutic Target in Gliomas

In gliomas, the canonical Wingless/Int (WNT)/β-catenin pathway is increased while peroxisome proliferator-activated receptor gamma (PPAR-γ) is downregulated. The two systems act in an opposite manner. This review focuses on the interplay between WNT/β-catenin signaling and PPAR-γ and their metabolic implications as potential therapeutic target in gliomas. Activation of the WNT/β-catenin pathway stimulates the transcription of genes involved in proliferation, invasion, nucleotide synthesis, tumor growth, and angiogenesis. Activation of PPAR-γ agonists inhibits various signaling pathways such as the JAK/STAT, WNT/β-catenin, and PI3K/Akt pathways, which reduces tumor growth, cell proliferation, cell invasiveness, and angiogenesis. Nonsteroidal anti-inflammatory drugs, curcumin, antipsychotic drugs, adiponectin, and sulforaphane downregulate the WNT/β-catenin pathway through the upregulation of PPAR-γ and thus appear to provide an interesting therapeutic approach for gliomas. Temozolomide (TMZ) is an antiangiogenic agent. The downstream action of this opposite interplay may explain the TMZ-resistance often reported in gliomas.

Lipid pathway deregulation in advanced prostate cancer

The link between prostate cancer (PC) development and lipid metabolism is well established, with AR intimately involved in a number of lipogenic processes involving SREBP1, PPARG, FASN, ACC, ACLY and SCD1. Recently, there is growing evidence implicating the role of obesity and peri-prostatic adipose tissue (PPAT) in PC aggressiveness and related mortality, suggesting the importance of lipid pathways in both localised and disseminated disease. A number of promising agents are in development to target the lipogenic axis in PC, and the likelihood is that these agents will form part of combination drug strategies, with targeting of multiple metabolic pathways (e.g. FASN and CPT1), or in combination with AR pathway inhibitors (SCD1 and AR).

The role of peroxisome proliferator-activated receptor gamma in prostate cancer

Despite great progress in the detection and treatment of prostate cancer, this disease remains an incredible health and economic burden. Although androgen receptor (AR) signaling plays a key role in the development and progression of prostate cancer, aberrations in other molecular pathways also contribute to the disease, making it essential to identify and develop drugs against novel targets, both for the prevention and treatment of prostate cancer. One promising target is the peroxisome proliferator-activated receptor gamma (PPARγ) protein. PPARγ was originally thought to act as a tumor suppressor in prostate cells because agonist ligands inhibited the growth of prostate cancer cells; however, additional studies found that PPARγ agonists inhibit cell growth independent of PPARγ. Furthermore, PPARγ expression increases with cancer grade/stage, which would suggest that it is not a tumor suppressor but instead that PPARγ activity may play a role in prostate cancer development and/or progression. Indeed, two new studies, taking vastly different, unbiased approaches, have identified PPARγ as a target in prostate cancer and suggest that PPARγ inhibition might be useful in prostate cancer prevention and treatment. These findings could lead to a new therapeutic weapon in the fight against prostate cancer.

PPARgamma agonists sensitize PTEN-deficient resistant lung cancer cells to EGFR tyrosine kinase inhibitors by inducing autophagy

We aimed to develop novel drug combination strategy to overcome drug resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) in the treatment of non-small cell lung cancer (NSCLC). Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor, which upon activation upregulates phosphatase and tensin homolog (PTEN) to inhibit cell signaling downstream of PI3K to mediate apoptosis. To this end, PTEN loss is a known mechanism contributing to resistance to EGFR TKIs. Therefore, PPARγ agonists are hypothesized to overcome EGFR TKI resistance. Using human NSCLC cell models with PTEN deficiency, the potentiation of EGFR TKI anticancer activity by PPARγ agonists was evaluated. PPARγ agonists were found to upregulate PTEN, subsequently inhibiting the PI3K-Akt signaling pathway, and thus enhancing the anticancer activity of gefitinib (a first generation EGFR TKI). Chemical and genetic inhibition of PPARγ were shown to prevent this potentiation of anticancer activity by PPARγ agonists, thus confirming the crucial role played by PPARγ activation. Interestingly, the tested PPARγ agonists were also found to induce autophagy, as evidenced by the increased expression of an autophagy marker LC3-II and the autophagic degradation of p62/SQSTM1. PPARγ agonists-induced autophagic cell death was believed to contribute to the circumvention of resistance in PTEN-deficient cells because the genetic silencing of ATG5 (an autophagy mediator) was found to eliminate the drug potentiation effect by the PPARγ agonists. Our findings thus provide the basis for the rational and personalized use of PPARγ agonists in combination with EGFR TKIs in lung cancer patients.

Thiazolidinedione drugs in the treatment of type 2 diabetes mellitus: past, present and future

Thiazolidinedione (TZD) drugs used in the treatment of type 2 diabetes mellitus (T2DM) have proven effective in improving insulin sensitivity, hyperglycemia, and lipid metabolism. Though well tolerated by some patients, their mechanism of action as ligands of peroxisome proliferator-activated receptors (PPARs) results in the activation of several pathways in addition to those responsible for glycemic control and lipid homeostasis. These pathways, which include those related to inflammation, bone formation, and cell proliferation, may lead to adverse health outcomes. As treatment with TZDs has been associated with adverse hepatic, cardiovascular, osteological, and carcinogenic events in some studies, the role of TZDs in the treatment of T2DM continues to be debated. At the same time, new therapeutic roles for TZDs are being investigated, with new forms and isoforms currently in the pre-clinical phase for use in the prevention and treatment of some cancers, inflammatory diseases, and other conditions. The aims of this review are to provide an overview of the mechanism(s) of action of TZDs, a review of their safety for use in the treatment of T2DM, and a perspective on their current and future therapeutic roles.

Bioinformatics analyses of the differences between lung adenocarcinoma and squamous cell carcinoma using The Cancer Genome Atlas expression data

The present study aimed to explore gene and microRNA (miRNA) expression differences between lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC). Differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs) were identified by analyzing mRNA and miRNA expression data in normal and cancerous lung tissues that were obtained from The Cancer Genome Atlas database. A total of 778 DEGs and 7 DEMs were identified. Altered gene functions and signaling pathways were investigated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses, which revealed that DEGs were significantly enriched in extracellular matrix organization, cell differentiation, negative regulation of toll signaling pathway, and several other terms and pathways. Transcription factor (TF)-miRNA-gene networks in LUAD and LUSC were predicted using the TargetScan, Miranda, and TRANSFAC databases, which revealed the regulatory links among the TFs, DEMs, and DEGs. The central TFs, i.e., the TFs in the middle of the TF-miRNA-gene network, of LUAD and LUSC were similar. Although LUAD and LUSC shared similar miRNAs in the predicted networks, miR-29b-3p was demonstrated to be upregulated only in LUAD, whereas miR-1, miR-105-5p, and miR-193b-5p were altered in LUSC. These findings may improve our understanding of the different molecular mechanisms in non-small cell lung cancers and may promote new and accurate strategies for prevention, diagnosis, and treatment.

Thermodynamics in cancers: opposing interactions between PPAR gamma and the canonical WNT/beta-catenin pathway

Cancer cells are the site of numerous metabolic and thermodynamic abnormalities. We focus this review on the interactions between the canonical WNT/beta-catenin pathway and peroxisome proliferator-activated receptor gamma (PPAR gamma) in cancers and their implications from an energetic and metabolic point of view. In numerous tissues, PPAR gamma activation induces inhibition of beta-catenin pathway, while the activation of the canonical WNT/beta-catenin pathway inactivates PPAR gamma. In most cancers but not all, PPAR gamma is downregulated while the WNT/beta-catenin pathway is upregulated. In cancer cells, upregulation of the WNT/beta-catenin signaling induces dramatic changes in key metabolic enzymes that modify their thermodynamic behavior. This leads to activation of pyruvate dehydrogenase kinase1 (PDK-1) and monocarboxylate lactate transporter. Consequently, phosphorylation of PDK-1 inhibits the pyruvate dehydrogenase complex (PDH). Thus, a large part of pyruvate cannot be converted into acetyl-coenzyme A (acetyl-CoA) in mitochondria and only a part of acetyl-CoA can enter the tricarboxylic acid cycle. This leads to aerobic glycolysis in spite of the availability of oxygen. This phenomenon is referred to as the Warburg effect. Cytoplasmic pyruvate is converted into lactate. The WNT/beta-catenin pathway induces the transcription of genes involved in cell proliferation, i.e., MYC and CYCLIN D1. This ultimately promotes the nucleotide, protein and lipid synthesis necessary for cell growth and multiplication. In cancer, activation of the PI3K-AKT pathway induces an increase of the aerobic glycolysis. Moreover, prostaglandin E2 by activating the canonical WNT pathway plays also a role in cancer. In addition in many cancer cells, PPAR gamma is downregulated. Moreover, PPAR gamma contributes to regulate some key circadian genes. In cancers, abnormalities in the regulation of circadian rhythms (CRs) are observed. CRs are dissipative structures which play a key-role in far-from-equilibrium thermodynamics. In cancers, metabolism, thermodynamics and CRs are intimately interrelated.

PPAR Agonists for the Prevention and Treatment of Lung Cancer

Lung cancer is the most common and most fatal of all malignancies worldwide. Furthermore, with more than half of all lung cancer patients presenting with distant metastases at the time of initial diagnosis, the overall prognosis for the disease is poor. There is thus a desperate need for new prevention and treatment strategies. Recently, a family of nuclear hormone receptors, the peroxisome proliferator-activated receptors (PPARs), has attracted significant attention for its role in various malignancies including lung cancer. Three PPARs, PPARα, PPARβ/δ, and PPARγ, display distinct biological activities and varied influences on lung cancer biology. PPARα activation generally inhibits tumorigenesis through its antiangiogenic and anti-inflammatory effects. Activated PPARγ is also antitumorigenic and antimetastatic, regulating several functions of cancer cells and controlling the tumor microenvironment. Unlike PPARα and PPARγ, whether PPARβ/δ activation is anti- or protumorigenic or even inconsequential currently remains an open question that requires additional investigation. This review of current literature emphasizes the multifaceted effects of PPAR agonists in lung cancer and discusses how they may be applied as novel therapeutic strategies for the disease.

PPAR-γ Agonists As Antineoplastic Agents in Cancers with Dysregulated IGF Axis

It is now widely accepted that insulin resistance and compensatory hyperinsulinemia are associated to increased cancer incidence and mortality. Moreover, cancer development and progression as well as cancer resistance to traditional anticancer therapies are often linked to a deregulation/overactivation of the insulin-like growth factor (IGF) axis, which involves the autocrine/paracrine production of IGFs (IGF-I and IGF-II) and overexpression of their cognate receptors [IGF-I receptor, IGF-insulin receptor (IR), and IR]. Recently, new drugs targeting various IGF axis components have been developed. However, these drugs have several limitations including the occurrence of insulin resistance and compensatory hyperinsulinemia, which, in turn, may affect cancer cell growth and survival. Therefore, new therapeutic approaches are needed. In this regard, the pleiotropic effects of peroxisome proliferator activated receptor (PPAR)-γ agonists may have promising applications in cancer prevention and therapy. Indeed, activation of PPAR-γ by thiazolidinediones (TZDs) or other agonists may inhibit cell growth and proliferation by lowering circulating insulin and affecting key pathways of the Insulin/IGF axis, such as PI3K/mTOR, MAPK, and GSK3-β/Wnt/β-catenin cascades, which regulate cancer cell survival, cell reprogramming, and differentiation. In light of these evidences, TZDs and other PPAR-γ agonists may be exploited as potential preventive and therapeutic agents in tumors addicted to the activation of IGF axis or occurring in hyperinsulinemic patients. Unfortunately, clinical trials using PPAR-γ agonists as antineoplastic agents have reached conflicting results, possibly because they have not selected tumors with overactivated insulin/IGF-I axis or occurring in hyperinsulinemic patients. In conclusion, the use of PPAR-γ agonists in combined therapies of IGF-driven malignancies looks promising but requires future developments.

Excavatolide B inhibits nonsmall cell lung cancer proliferation by altering peroxisome proliferator activated receptor gamma expression and PTEN/AKT/NF-Kβ expression

Marine organisms are proven to be rich source of secondary metabolites that can be used to treat various diseases. Excavatolide B (Exc.B), the most abundant metabolite was found in the marine coral Briareum excavatum exhibits cytotoxic effects against lung cancer cell. Treatment of the A549 cells with Exc.B significantly reduced its cell viability and induced cell cycle arrest at subG1 phase in a dose- and time-dependent manner, respectively. Apoptosis induction by Exc.B was further confirmed by decreased pro-caspase 3 expressions and increased proteolytic cleavage of poly (ADP-ribose) polymerase (PARP) expression. Furthermore, Exc.B increased reactive oxygen species (ROS) and reactive nitrogen species (RNS) and also decreased the antioxidant enzymes such as, Catalase, GPx, SOD, GST, and GSH. The proteomic analysis data revealed that total thirty six proteins were altered by Exc.B. STRING database showed that most of the altered proteins have no interaction between each other. Based on these data, KSR1, RuVBL2, PPAR-γ, and Tenascin X proteins were chosen to validate the 2DE data by Western blotting. Additional experiments demonstrated that Exc.B induced PTEN expression and inhibited pAKT and NF-kB expression. These results provide a novel insight into mechanisms underlying the inhibition of A549 cells growth by excavatolide B. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 290-301, 2017.

Troglitazone Enhances the Apoptotic Response of DLD-1 Colon Cancer Cells to Photodynamic Therapy

PURPOSE

The aim of this study was to investigate whether the peroxisomal proliferator-activated receptor gamma (PPARγ) ligand troglitazone in combination with photodynamic therapy (PDT) enhances the apoptotic response of DLD-1 colon cancer cells.

MATERIALS AND METHODS

The effects of troglitazone, PDT, and troglitazone in combination with PDT on cell viability and apoptosis were assessed in DLD-1 cells. Cell viability and proliferation were evaluated using the tetrazolium-based MTT assay, and apoptosis was evaluated via cell staining with propidium iodide (PI) and annexin V-FITC. The levels of pro-caspase-3 were measured via Western blot analyses.

RESULTS

Treatment of troglitazone and PDT induced the growth retardation and cell death of DLD-1 cells in a dose-dependent manner, respectively. The combination treatment significantly suppressed cell growth and increased the apoptotic response of DLD-1 and resulted in apoptosis rather than necrosis, as shown by PI/annexin V staining and degradation of procaspase-3.

CONCLUSION

These results document the anti-proliferative and apoptotic activities of PDT in combination with the PPARγ ligand troglitazone and provide a strong rationale for testing the therapeutic potential of combination treatment in colon cancer.

PPARγ as a Novel Therapeutic Target in Lung Cancer

Lung cancer is the leading cause of cancer-related death, with more than half the patients having advanced-stage disease at the time of initial diagnosis and thus facing a poor prognosis. This dire situation poses a need for new approaches in prevention and treatment. Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor belonging to the nuclear hormone receptor superfamily. Its involvement in adipocyte differentiation and glucose and lipid homeostasis is well-recognized, but accumulating evidence now suggests that PPARγ may also function as a tumor suppressor, inhibiting development of primary tumors and metastases in lung cancer and other malignancies. Besides having prodifferentiation, antiproliferative, and proapoptotic effects, PPARγ agonists have been shown to prevent cancer cells from acquiring the migratory and invasive capabilities essential for successful metastasis. Angiogenesis and secretion of certain matrix metalloproteinases and extracellular matrix proteins within the tumor microenvironment are also regulated by PPARγ. This review of the current literature highlights the potential of PPARγ agonists as novel therapeutic modalities in lung cancer, either as monotherapy or in combination with standard cytotoxic chemotherapy.

PGA1-induced apoptosis involves specific activation of H-Ras and N-Ras in cellular endomembranes

The cyclopentenone prostaglandin A₁ (PGA₁) is an inducer of cell death in cancer cells. However, the mechanism that initiates this cytotoxic response remains elusive. Here we report that PGA₁ triggers apoptosis by a process that entails the specific activation of H- and N-Ras isoforms, leading to caspase activation. Cells without H- and N-Ras did not undergo apoptosis upon PGA₁ treatment; in these cells, the cellular demise was rescued by overexpression of either H-Ras or N-Ras. Consistently, the mutant H-Ras-C118S, defective for binding PGA₁, did not produce cell death. Molecular analysis revealed a key role for the RAF-MEK-ERK signaling pathway in the apoptotic process through the induction of calpain activity and caspase-12 cleavage. We propose that PGA₁ evokes a specific physiological cell death program, through H- and N-Ras, but not K-Ras, activation at endomembranes. Our results highlight a novel mechanism that may be of potential interest for tumor treatment.

Breast Cancer Genetic and Molecular Subtype Impacts Response to Omega-3 Fatty Acid Ethyl Esters

Epidemiological studies have correlated frequent omega-3 (n-3) fatty acid consumption with a lower risk for breast cancer; however, recent prospective studies have been less conclusive. Efforts in the preventive setting have focused on the use of n-3 fatty acids, and the pharmaceutical ethyl esters (EE) of these natural compounds, for high-risk patient populations. Limited understanding of specific mechanisms by which these agents function has hampered identification of the cancer subtype(s) that would gain the greatest therapeutic benefit. In this study, we investigated the in vitro effects of n-3 EEs in four distinct breast cancer subtypes and explored how they affect not only breast cancer cell survival but also modulate the nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) and peroxisome proliferator-activated receptor gamma signaling pathways. Similar to the high variance in response observed in human studies, we found that the effectiveness of n-3 EEs depends on the molecular characteristics of the MCF-7, CAMA-1, MDA-MB-231, and SKBR3 breast cancer cell lines and is closely associated with the suppression of NF-κB. These data strongly suggest that the use of n-3 fatty acids and their pharmaceutical ether esters in the prevention and therapeutic setting should be guided by specific tumor characteristics.

Pioglitazone inhibits growth of human retinoblastoma cells via regulation of NF-κB inflammation signals

OBJECTIVES

We aimed to study the antitumor effects of the PPARγ agonist pioglitazone on human retinoblastoma.

METHODS

The effects of pioglitazone on cell proliferation and apoptosis of the human retinoblastoma Y79 cells were investigated by MTT assay and Hoechst 33258 staining assay. The apoptosis related protein levels were detected by western blot. Inflammationary factors analysis was evaluated by western blot and ELISA. The effect of pioglitazone on nuclear factor-kappa B (NF-κB)-dependent reporter gene transcription induced by LPS was analyzed by NF-κB-luciferase assay. Then human retinoblastoma Y79 cells were subcutaneously transplanted in BALB/c nude mice and the animals were treated with pioglitazone to verify its antitumor effect in vivo.

RESULTS

Our data revealed that pioglitazone suppressed the viability of Y79 cells dose- and time-dependently and induced apoptosis in Y79 cells in vitro. Molecular biology analysis found that pioglitazone could affect the apoptosis and inflammation related signal via modulating the activity of NF-κB signal. Also we found that pioglitazone could markedly reduce the growth of Y79 cells transplanted into the mice without causing significant side effects.

CONCLUSIONS

Our results suggested that pioglitazone demonstrated antitumor activity against the human retinoblastoma Y79 cells by inhibiting cell growth, inducing apoptosis and modulating NF-κB pathway, and thus delayed tumor growth in vivo.

Functional activation of PPARγ in human upper aerodigestive cancer cell lines

Upper aerodigestive cancer is an aggressive malignancy with relatively stagnant long-term survival rates over 20 yr. Recent studies have demonstrated that exploitation of PPARγ pathways may be a novel therapy for cancer and its prevention. We tested whether PPARγ is expressed and inducible in aerodigestive carcinoma cells and whether it is present in human upper aerodigestive tumors. Human oral cancer CA-9-22 and NA cell lines were treated with the PPAR activators eicosatetraynoic acid (ETYA), 15-deoxy-δ- 12,14-prostaglandin J2 (PG-J2), and the thiazolidinedione, ciglitazone, and evaluated for their ability to functionally activate PPARγ luciferase reporter gene constructs. Cellular proliferation and clonogenic potential after PPARγ ligand treatment were also evaluated. Aerodigestive cancer specimens and normal tissues were evaluated for PPARγ expression on gene expression profiling and immunoblotting. Functional activation of PPARγ reporter gene constructs and increases in PPARγ protein were confirmed in the nuclear compartment after PPARγ ligand treatment. Significant decreases in cell proliferation and clonogenic potential resulted from treatment. Lipid accumulation was induced by PPARγ activator treatment. 75% of tumor specimens and 100% of normal control tissues expressed PPARγ RNA, and PPARγ protein was confirmed in 66% of tumor specimens analyzed by immunoblotting. We conclude PPARγ can be functionally activated in upper aerodigestive cancer and that its activation downregulates several features of the neoplastic phenotype. PPARγ expression in human upper aerodigestive tract tumors and normal cells potentially legitimizes it as a novel intervention target in this disease. © 2016 Wiley Periodicals, Inc.

Morusin suppresses breast cancer cell growth in vitro and in vivo through C/EBPβ and PPARγ mediated lipoapoptosis

Background

Breast cancer is the most fatal malignant cancer among women, the conventional therapeutic modalities of it are limited. Morusin possesses cytotoxicity against some cancer cells in vitro. The purpose of this study is to test the growth inhibition effect of morusin on human breast cancer growth in vitro and in vivo and to explore the potential mechanism of its action.

Methods

The growth inhibition effect of morusin on human breast cancer cells in vitro and in vivo were tested by cell cytotoxicity, colony formation inhibition, adipogenic differentiation, apoptosis induction, and tumor growth inhibition in vivo assays. The potential molecular mechanisms underlying the growth inhibition effect of morusin on human breast cancer cells in vitro and in vivo were investigated with Western blotting evaluation of expression levels of transcription factors, C/EBPβ and PPARγ, adipogenic and apoptotic proteins in morusin treated breast cancer cells and tumor tissues.

Results

Morusin inhibited breast cancer cells growth in vitro and in vivo; it induced adipogenic differentiation, apoptosis and lipoapoptosis of cancer cells.

Conclusions

Morusin has the potential to inhibit human breast cancer cell growth in vitro and in vivo through C/EBPβ and PPARγ mediated lipoapoptosis.

Minireview: Familiar Faces in Unfamiliar Places: The Emerging Role of Nuclear Receptors in Lung Cancer

Nuclear hormone receptors (NRs) are a superfamily of 48 transcription factors that are frequently modulated by ligands and control various cancer-relevant cellular pathways, such as differentiation, proliferation, migration, and metabolism. These properties make them excellent therapeutic targets in cancers dependent upon their activity, and as such, 3 NRs, estrogen receptor-α, androgen receptor, and retinoic acid receptor-α (more specifically, the promyelocytic leukemia-retinoic acid receptor-α translocation), have been targeted clinically in breast cancer, prostate cancer, and acute promyelocytic leukemia, respectively. Recently, a number of studies have highlighted a putative role for NRs in nonsmall cell lung cancer (NSCLC), a highly lethal type of lung cancer with relatively few targeted agents. Here, we review the potential roles of selected NRs in NSCLC and offer insights on how NRs may be leveraged in NSCLC to improve patient outcomes.

Beneficial health effects of Chios Gum Mastic and peroxisome proliferator-activated receptors: indications of common mechanisms

For thousands of years, Chios Gum Mastic (CGM), the resin produced by the trunk of Pistachia lentiscus var Chia, has been used for culinary and medicinal purposes and several therapeutic properties have been attributed to it. CGM has been used in traditional medicine of various nations in the eastern Mediterranean area. This survey was carried out to identify biological mechanisms that could explain traditional usage and recent pharmacological findings. We reviewed the related scientific literature available from the NCBI PUBMED database on CGM studies and on natural products showing peroxisome proliferator-activated receptor (PPAR) agonist effects. We investigated whether CGM qualifies as a PPAR modulator. A large number of studies demonstrate that CGM has antioxidant, anti-inflammatory, hypolipidemic, and anticancer properties. Recently, the first evidence of CGM antidiabetic effect became known. CGM chemical composition has been extensively analyzed and the presence of several compounds, especially triterpenoids is well documented. Some of them, oleanonic acid, oleanolic acid, and gallic acid are considered to act as PPAR modulators. PPARs are nuclear receptors functioning as transcription factors and thereby controlling cellular functions at the level of gene expression. PPARs are involved in the pathways of significant diseases, such as metabolic syndrome, diabetes mellitus, dyslipidemia, inflammation, atheromatosis, and neoplasias, constituting a key target for pharmacological interventions. This article proposes that the synergistic action of some constituents of CGM on PPARs and more precisely on both PPARs isotypes-α and -γ, may be one of the major biological mechanisms via which CGM exerts its multiple effects.

Peroxisome proliferator activated receptor γ protein expression is asymmetrically distributed in primary lung tumor and metastatic to lung osteosarcoma samples and does not correlate with gene methylation

Background

Peroxisome proliferator activated receptor-γ (PPAR-γ) is a ligand-dependent transcription factor that plays important roles in cellular proliferation and differentiation. It has been implicated as a tumor suppressor in many solid tumors including human prostate, breast, colon, and lung cancer. The objective of this study was to determine the tissue distribution of PPAR-γ in normal canine lung, canine lung cancer, and metastatic to lung cancer, as well as determine the role, if any, of DNA methylation in epigenetic control of gene expression. The protein was studied using immunohistochemistry (IHC) and DNA methylation was studied using combined bisulfite restriction analysis (COBRA), and methylation-specific PCR (MSP).

Results

PPAR-γ is expressed in all large conducting airways, particularly in goblet cells and bronchial glands, in the canine lung. The protein is also expressed in interstitial macrophages. PPAR-γ is expressed in 33 % of canine non-small cell lung cancer (NSCLC) cases and 66 % of metastatic osteosarcoma (OSA) cases. There is a significant loss of 5′ PPAR-γ methylation from normal lung to primary lung cancer and metastatic OSA (p = 0.0002), however altered PPAR-γ promoter methylation at the interrogated locus does not appear to be associated with changes in protein expression.

Conclusions

PPAR-γ protein is expressed in normal canine lung tissue, canine primary lung cancer, and metastatic OSA. Confirmation of PPAR-γ protein expression in tumor-bearing dogs supports the investigation of PPAR-γ agonists in this subset of veterinary patients. These results are the first to describe epigenetic marks and protein localization of PPAR-γ among different lung pathologies in the dog.

Increasing doxorubicin activity against breast cancer cells using PPARγ-ligands and by exploiting circadian rhythms

BACKGROUND AND PURPOSE

Doxorubicin is effective against breast cancer, but its major side effect is cardiotoxicity. The aim of this study was to determine whether the efficacy of doxorubicin on cancer cells could be increased in combination with PPARγ agonists or chrono-optimization by exploiting the diurnal cycle.

EXPERIMENTAL APPROACH

We determined cell toxicity using MCF-7 cancer cells, neonatal rat cardiac myocytes and fibroblasts in this study.

KEY RESULTS

Doxorubicin damages the contractile filaments of cardiac myocytes and affects cardiac fibroblasts by significantly inhibiting collagen production and proliferation at the level of the cell cycle. Cyclin D1 protein levels decreased significantly following doxorubicin treatment indicative of a G1/S arrest. PPARγ agonists with doxorubicin increased the toxicity to MCF-7 cancer cells without affecting cardiac cells. Rosiglitazone and ciglitazone both enhanced anti-cancer activity when combined with doxorubicin (e.g. 50% cell death for doxorubicin at 0.1 μM compared to 80% cell death when combined with rosiglitazone). Thus, the therapeutic dose of doxorubicin could be reduced by 20-fold through combination with the PPARγ agonists, thereby reducing adverse effects on the heart. The presence of melatonin also significantly increased doxorubicin toxicity, in cardiac fibroblasts (1 μM melatonin) but not in MCF-7 cells.

CONCLUSIONS AND IMPLICATIONS

Our data show, for the first time, that circadian rhythms play an important role in doxorubicin toxicity in the myocardium; doxorubicin should be administered mid-morning, when circulating levels of melatonin are low, and in combination with rosiglitazone to increase therapeutic efficacy in cancer cells while reducing the toxic effects on the heart.

Anticancer effect of rosiglitazone in rats treated with N-nitrosodiethylamine via inhibition of DNA synthesis: an implication for hepatocellular carcinoma

Rosiglitazone, peroxisome proliferator-activated receptor-γ (PPARγ) ligand, is a clinically tested drug used in the treatment of diabetes.

The Robustness of Pathway Analysis in Identifying Potential Drug Targets in Non-Small Cell Lung Carcinoma

The identification of genes responsible for causing cancers from gene expression data has had varied success. Often the genes identified depend on the methods used for detecting expression patterns, or on the ways that the data had been normalized and filtered. The use of gene set enrichment analysis is one way to introduce biological information in order to improve the detection of differentially expressed genes and pathways. In this paper we show that the use of network models while still subject to the problems of normalization is a more robust method for detecting pathways that are differentially overrepresented in lung cancer data. Such differences may provide opportunities for novel therapeutics. In addition, we present evidence that non-small cell lung carcinoma is not a series of homogeneous diseases; rather that there is a heterogeny within the genotype which defies phenotype classification. This diversity helps to explain the lack of progress in developing therapies against non-small cell carcinoma and suggests that drug development may consider multiple pathways as treatment targets.