Peroxisome proliferator-activated receptors and cancer: challenges and opportunities

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Developing theragnostics for Alzheimer's disease: Insights from cancer treatment

The prevalence of Alzheimer's disease (AD) and its associated economic and societal burdens are on the rise, but there are no curative treatments for AD. Interestingly, this neurodegenerative disease shares several biological and pathophysiological features with cancer, including cell-cycle dysregulation, angiogenesis, mitochondrial dysfunction, protein misfolding, and DNA damage. However, the genetic factors contributing to the overlap in biological processes between cancer and AD have not been actively studied. In this review, we discuss the shared biological features of cancer and AD, the molecular targets of anticancer drugs, and therapeutic approaches. First, we outline the common biological features of cancer and AD. Second, we describe several anticancer drugs, their molecular targets, and their effects on AD pathology. Finally, we discuss how protein-protein interactions (PPIs), receptor inhibition, immunotherapy, and gene therapy can be exploited for the cure and management of both cancer and AD. Collectively, this review provides insights for the development of AD theragnostics based on cancer drugs and molecular targets.

Delineating the role of nuclear receptors in colorectal cancer, a focused review

Colorectal cancer (CRC) stands as one of the most prevalent form of cancer globally, causing a significant number of deaths, surpassing 0.9 million in the year 2020. According to GLOBOCAN 2020, CRC ranks third in incidence and second in mortality in both males and females. Despite extensive studies over the years, there is still a need to establish novel therapeutic targets to enhance the patients' survival rate in CRC. Nuclear receptors (NRs) are ligand-activated transcription factors (TFs) that regulate numerous essential biological processes such as differentiation, development, physiology, reproduction, and cellular metabolism. Dysregulation and anomalous expression of different NRs has led to multiple alterations, such as impaired signaling cascades, mutations, and epigenetic changes, leading to various diseases, including cancer. It has been observed that differential expression of various NRs might lead to the initiation and progression of CRC, and are correlated with poor survival outcomes in CRC patients. Despite numerous studies on the mechanism and role of NRs in this cancer, it remains of significant scientific interest primarily due to the diverse functions that various NRs exhibit in regulating key hallmarks of this cancer. Thus, modulating the expression of NRs with their agonists and antagonists, based on their expression levels, holds an immense prospect in the diagnosis, prognosis, and therapeutical modalities of CRC. In this review, we primarily focus on the role and mechanism of NRs in the pathogenesis of CRC and emphasized the significance of targeting these NRs using a variety of agents, which may represent a novel and effective strategy for the prevention and treatment of this cancer.

Use of drugs for hyperlipidaemia and diabetes and risk of primary and secondary brain tumours: nested case-control studies using the UK Clinical Practice Research Datalink (CPRD)

OBJECTIVES

Previous studies have suggested that fibrates and glitazones may have a role in brain tumour prevention. We examined if there is support for these observations using primary care records from the UK Clinical Practice Research Datalink (CPRD).

DESIGN

We conducted two nested case-control studies using primary and secondary brain tumours identified within CPRD between 2000 and 2016. We selected cases and controls among the population of individuals who had been treated with any anti-diabetic or anti-hyperlipidaemic medication to reduce confounding by indication.

SETTING

Adults older than 18 years registered with a general practitioner in the UK contributing data to CPRD.

RESULTS

We identified 7496 individuals with any brain tumour (4471 primary; 3025 secondary) in total. After restricting cases and controls to those prescribed any anti-diabetic or anti-hyperlipidaemic medication, there were 1950 cases and 7791 controls in the fibrate and 480 cases with 1920 controls in the glitazone analyses. Longer use of glitazones compared with all other anti-diabetic medications was associated with a reduced risk of primary (adjusted OR (aOR) 0.89 per year, 95% CI 0.80 to 0.98), secondary (aOR 0.87 per year, 95% CI 0.77 to 0.99) or combined brain tumours (aOR 0.88 per year, 95% CI 0.81 to 0.95). There was little evidence that fibrate exposure was associated with risk of either primary or secondary brain tumours.

CONCLUSIONS

Longer exposure to glitazones was associated with reduced primary and secondary brain tumour risk. Further basic science and population-based research should explore this finding in greater detail, in terms of replication and mechanistic studies.

Combined In Silico and In Vitro Analyses to Assess the Anticancer Potential of Thiazolidinedione-Thiosemicarbazone Hybrid Molecules

The number of people affected by cancer and antibiotic-resistant bacterial infections has increased, such that both diseases are already seen as current and future leading causes of death globally. To address this issue, based on a combined in silico and in vitro approach, we explored the anticancer potential of known antibacterials with a thiazolidinedione-thiosemicarbazone (TZD-TSC) core structure. A cytotoxicity assessment showed encouraging results for compounds 2-4, with IC50 values against T98G and HepG2 cells in the low micromolar range. TZD-TSC 3 proved to be most toxic to cancer cell lines, with IC50 values of 2.97 ± 0.39 µM against human hepatoma HepG2 cells and IC50 values of 28.34 ± 2.21 µM against human glioblastoma T98G cells. Additionally, compound 3 induced apoptosis and showed no specific hemolytic activity. Furthermore, treatment using 3 on cancer cell lines alters these cells' morphology and further suppresses migratory activity. Molecular docking, in turn, suggests that 3 would have the capacity to simultaneously target HDACs and PPARγ, by the activation of PPARγ and the inhibition of both HDAC4 and HDAC8. Thus, the promising preliminary results obtained with TZD-TSC 3 represent an encouraging starting point for the rational design of novel chemotherapeutics with dual antibacterial and anticancer activities.

Lysine metabolism is a novel metabolic tumor suppressor pathway in breast cancer

The International Agency for Research on Cancer determined that obesity is the primary preventable cause of breast cancer. The nuclear receptor peroxisome proliferator activated receptor γ (PPARγ) binds inflammatory mediators in obesity and its expression is reduced in human breast cancer. We created a new model to better understand how the obese microenvironment alters nuclear receptor function in breast cancer. The obesity related cancer phenotype was PPARγ dependent; deletion of PPARγ in mammary epithelium which is a tumor suppressor in lean mice unexpectedly increased tumor latency, reduced the luminal progenitor (LP) tumor cell fraction, and increased autophagic and senescent cells. Loss of PPARγ expression in mammary epithelium of obese mice increased expression of 2-aminoadipate semialdehyde synthase (AASS) which regulates lysine catabolism to acetoacetate. PPARγ-associated co-repressors and activators regulated AASS expression via a canonical response element. AASS expression was significantly reduced in human breast cancer, and AASS overexpression or acetoacetate treatment inhibited proliferation and induced autophagy and senescence in human breast cancer cell lines. Genetic or pharmacologic HDAC inhibition promoted autophagy and senescence in mammary tumor cells in vitro and in vivo. We concluded that lysine metabolism is a novel metabolic tumor suppressor pathway in breast cancer.

The endocannabinoid system, a new gatekeeper in the pharmacology of human hepatocellular carcinoma

Despite numerous prevention methodologies and treatment options, hepatocellular carcinoma (HCC) still remains as the third leading life-threatening cancer. It is thus pertinent to develop new treatment modality to fight this devastating carcinoma. Ample recent studies have shown the anti-inflammatory and antitumor roles of the endocannabinoid system in various forms of cancers. Preclinical studies have also confirmed that cannabinoid therapy can be an optimal regimen for cancer treatments. The endocannabinoid system is involved in many cancer-related processes, including induction of endoplasmic reticulum (ER) stress-dependent apoptosis, autophagy, PITRK and ERK signaling pathways, cell invasion, epithelial-mesenchymal transition (EMT), and cancer stem cell (CSC) phenotypes. Moreover, changes in signaling transduction of the endocannabinoid system can be a potential diagnostic and prognostic biomarker for HCC. Due to its pivotal role in lipid metabolism, the endocannabinoid system affects metabolic reprogramming as well as lipid content of exosomes. In addition, due to the importance of non-coding RNAs (ncRNAs), several studies have examined the relationship between microRNAs and the endocannabinoid system in HCC. However, HCC is a pathological condition with high heterogeneity, and therefore using the endocannabinoid system for treatment has faced many controversies. While some studies favored a role of the endocannabinoid system in carcinogenesis and tumor induction, others exhibited the anticancer potential of endocannabinoids in HCC. In this review, specific studies delineating the relationship between endocannabinoids and HCC are examined. Based on collected findings, detailed studies of the molecular mechanism of endocannabinoids as well as preclinical studies for investigating therapeutic or carcinogenic impacts in HCC cancer are strongly suggested.

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.

A systematic and comprehensive analysis of T cell exhaustion related to therapy in lung adenocarcinoma tumor microenvironment

Background: T cell exhaustion (TEX) is an important immune escape mechanism, and an in-depth understanding of it can help improve cancer immunotherapy. However, the prognostic role of TEX in malignant lung adenocarcinoma (LUAD) remains unclear. Methods: Through TCGA and GEO datasets, we enrolled a total of 498 LUAD patients. The patients in TCGA-LUAD were unsupervised clustered into four clusters according to TEX signaling pathway. WGCNA analysis, survival random forest analysis and lasso regression analysis were used to select five differentially expressed genes among different clusters to construct a TEX risk model. The risk model was subsequently validated with GEO31210. By analyzing signaling pathways, immune cells and immune checkpoints using GSEA, GSVA and Cibersortx, the relationship between TEX risk score and these variables was evaluated. In addition, we further analyzed the expression of CCL20 at the level of single-cell RNA-seq and verified it in cell experiments. Results: According to TEX signaling pathway, people with better prognosis can be distinguished. The risk model constructed by CD109, CCL20, DKK1, TNS4, and TRIM29 genes could further accurately identify the population with poor prognosis. Subsequently, it was found that dendritic cells, CD44 and risk score were closely related. The final single-cell sequencing suggested that CCL2O is a potential therapeutic target of TEX, and the interaction between TEX and CD8 + T is closely related. Conclusion: The classification of T cell depletion plays a crucial role in the clinical decision-making of lung adenocarcinoma and needs to be further deepened.

Nuclear receptor modulators inhibit osteosarcoma cell proliferation and tumour growth by regulating the mTOR signaling pathway

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Chemoresistance leads to poor responses to conventional therapy in patients with osteosarcoma. The discovery of novel effective therapeutic targets and drugs is still the main focus of osteosarcoma research. Nuclear receptors (NRs) have shown substantial promise as novel therapeutic targets for various cancers. In the present study, we performed a drug screen using 29 chemicals that specifically target 17 NRs in several different human osteosarcoma and osteoblast cell lines. The retinoic acid receptor beta (RARb) antagonist LE135, peroxisome proliferator activated receptor gamma (PPARg) antagonist T0070907, liver X receptor (LXR) agonist T0901317 and Rev-Erba agonist SR9011 significantly inhibited the proliferation of malignant osteosarcoma cells (U2OS, HOS-MNNG and Saos-2 cells) but did not inhibit the growth of normal osteoblasts. The effects of these NR modulators on osteosarcoma cells occurred in a dose-dependent manner and were not observed in NR-knockout osteosarcoma cells. These NR modulators also significantly inhibited osteosarcoma growth in vivo and enhanced the antitumour effect of doxorubicin (DOX). Transcriptomic and immunoblotting results showed that these NR modulators may inhibit the growth of osteosarcoma cells by regulating the PI3K/AKT/mTOR and ERK/mTOR pathways. DDIT4, which blocks mTOR activation, was identified as one of the common downstream target genes of these NRs. DDIT4 knockout significantly attenuated the inhibitory effects of these NR modulators on osteosarcoma cell growth. Together, our results revealed that modulators of RARb, PPARg, LXRs and Rev-Erba inhibit osteosarcoma growth both in vitro and in vivo through the mTOR signaling pathway, suggesting that treatment with these NR modulators is a novel potential therapeutic strategy.

Association between PPARγ, PPARGC1A, and PPARGC1B genetic variants and susceptibility of gastric cancer in an Eastern Chinese population

PURPOSE

Previous studies showed that peroxisome proliferator-activated receptor gamma (PPARγ) and PPARγ coactivator1 family (PPARGC1A and PPARGC1B) gene single nucleotide variants (SNVs)were strongly associated with cancer susceptibility. The purpose of this study was to investigate the association of PPARγ, PPARGC1A, and PPARGC1B variants with the risk of gastric cancer (GC).

PATIENTS AND METHODS

We performed a case-control study of 490 GC cases and 1,476 healthy controls from eastern China. PPARγ rs1801282 C > G, rs3856806 C > T, PPARGC1A rs2970847 C > T, rs8192678 C > T and PPARGC1B rs7732671 G > C, rs17572019 G > A SNVs were selected to investigate the association between these SNVs and GC susceptibility. Genotypes of the SNVs were assessed by multiplex fluorescent PCR using a custom-by-design 48-Plex SNPscan^tm Kit.

RESULTS

The PPARγ rs1801282 SNV was associated with a decreased risk for GC (GC vs. CC: odds ratio (OR) = 0.62, 95% confidence interval (95%CI) = 0.42-0.93, adjusted P = 0.019; GC + GG vs. GG: OR = 0.63 95%CI = 0.42-0.93, adjusted P = 0.019; respectively). In addition, stratified analysis revealed that the PPARγ rs1801282 SNV was correlated with the risk of GC in subgroups of age ≥ 61, no smoking, and no alcohol consuming. We also confirmed that the PPARγ rs3856806 C > T SNV promoted the risk of GC in women. The PPARGC1A rs8192678 TT genotype decreased the susceptibility of GC in men. The PPARGC1A rs2970847 C > T SNV decreased the susceptibility of GC in the subgroup of BMI ≥ 24 kg/m². The PPARGC1B rs7732671 G > C and rs17572019 G > A SNVs promoted the risk of GC in the subgroup of BMI ≥ 24 kg/m².

CONCLUSION

This study indicates that the PPARγ, PPARGC1A, and PPARGC1B SNVs may be associated with the susceptibility of GC in eastern Chinese population. Future studies with larger populations, detailed H. pylori infection status for subgroup analysis, and functional study are needed to further clarify the relationship between these SNVs and GC risk.

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.

PPARγ signaling in hepatocarcinogenesis: Mechanistic insights for cellular reprogramming and therapeutic implications

Liver cancer or hepatocellular carcinoma (HCC) is leading cause of cancer-related mortalities globally. The therapeutic approaches for chronic liver diseases-associated liver cancers aimed at modulating immune check-points and peroxisome proliferator-activated receptor gamma (PPARγ) signaling pathway during multistep process of hepatocarcinogenesis that played a dispensable role in immunopathogenesis and outcomes of disease. Herein, the review highlights PPARγ-induced effects in balancing inflammatory (tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, IL-1) and anti-inflammatory cytokines (IL-10, transforming growth factor beta (TGF-β), and interplay of PPARγ, hepatic stellate cells and fibrogenic niche in cell-intrinsic and -extrinsic crosstalk of hepatocarcinogenesis. PPARγ-mediated effects in pre-malignant microenvironment promote growth arrest, cell senescence and cell clearance in liver cancer pathophysiology. Furthermore, PPARγ-immune cell axis of liver microenvironment exhibits an immunomodulation strategy of resident immune cells of the liver (macrophages, natural killer cells, and dendritic cells) in concomitance with current clinical guidelines of the European Association for Study of Liver Diseases (EASL) for several liver diseases. Thus, mechanistic insights of PPARγ-associated high value targets and canonical signaling suggest PPARγ as a possible therapeutic target in reprogramming of hepatocarcinogenesis to decrease burden of liver cancers, worldwide.

PPARα at the crossroad of metabolic-immune regulation in cancer

Rewiring metabolism to sustain cell growth, division, and survival is the most prominent feature of cancer cells. In particular, dysregulated lipid metabolism in cancer has received accumulating interest, since lipid molecules serve as cell membrane structure components, secondary signaling messengers, and energy sources. Given the critical role of immune cells in host defense against cancer, recent studies have revealed that immune cells compete for nutrients with cancer cells in the tumor microenvironment and accordingly develop adaptive metabolic strategies for survival at the expense of compromised immune functions. Among these strategies, lipid metabolism reprogramming toward fatty acid oxidation is closely related to the immunosuppressive phenotype of tumor-infiltrated immune cells, including macrophages and dendritic cells. Therefore, it is important to understand the lipid-mediated crosstalk between cancer cells and immune cells in the tumor microenvironment. Peroxisome proliferator-activated receptors (PPARs) consist of a nuclear receptor family for lipid sensing, and one of the family members PPARα is responsible for fatty acid oxidation, energy homeostasis, and regulation of immune cell functions. In this review, we discuss the emerging role of PPARα-associated metabolic-immune regulation in tumor-infiltrated immune cells, and key metabolic events and pathways involved, as well as their influences on antitumor immunity.

PPARδ Agonist Promotes Type II Cartilage Formation in a Rabbit Osteochondral Defect Model

Osteoarthritis (OA) is a chronic degenerative joint disease accompanied by an inflammatory milieu that results in painful joints. The pathogenesis of OA is multifactorial, with genetic predisposition, environmental factors, and traumatic injury resulting in the direct or indirect loss of cartilage. The articular cartilage can also be damaged by direct focal traumatic injury. Articular cartilage provides a smooth, deformable bearing surface with a low coefficient of friction, increased contact area, and reduced contact stress. Articular type II hyaline cartilage lines the synovial joints and, when injured, has a limited ability for repair, except for the most superficial layers via diffusion from the synovial fluid, secondary to no blood supply, a complex structure, and a low metabolic rate. Restoring the articular surface can relieve pain and restore function. Although many strategies have been developed to regenerate type II collagen based on the extent of the lesion, surgical treatments are still evolving. The peroxisome proliferator-activated receptor delta (PPARδ) agonist and collagen treatment of mesenchymal stem cells (MSCs) enhance the chondrogenic capacity in vitro. We present a novel technique for cartilage restoration in a rabbit cartilage osteochondral defect model using a PPARδ agonist (GW0742)-infused 3D collagen scaffold to induce type II cartilage from MSCs.

Identification of a novel interplaying loop of PPARγ and respective lncRNAs are involved in colorectal cancer progress

Long noncoding RNAs (lncRNAs) as regulatory molecules play important roles in early treatment and diagnosis of cancers. Considering the role of PPARγ in colorectal cancer (CRC) as a tumor suppressor, the GEO database was used to identify candidate genes that affect the activation of PPARγ protein in CRC cell lines. Then were selected 5 genes containing PPARγ response element (PPRE) in up to 4000 bp upstream and were affected by PPARγ protein activation in HT-29 colon cancer cell line using UCSC database. Expression meta-analysis was applied to map the expression network between candidate genes and all known lncRNAs through expression correlation and lncRNAs that correlated with a greater number of candidate genes (R > 0.5, P.value < 0.001). Moreover, were selected 3 lncRNAs as lncRNAs affected by PPARγ protein activation. Next, the expression levels of candidate genes and lncRNAs were evaluated using RT-qPCR in HT-29 cell line. Results showed a significant increase (FDR <0.05) in the expression level of 5 candidate genes and lncRNAs LINC01133, MBNL1-AS, LOC100288911 after treatment with pioglitazone as PPARγ ligand compared to the untreated group in HT-29 cells. Although additional tests are needed to confirm bioinformatics predictions, it can be concluded that increased expression of PPARγ may increase genes and lncRNAs expression. In summary, this study could be suggested identifying lncRNAs affected by PPARγ activation could be a new strategy in understanding the function and activity of PPARγ in colon cancer.

Soluble TGFBI aggravates the malignancy of cholangiocarcinoma through activation of the ITGB1 dependent PPARγ signalling pathway

BACKGROUND

Cholangiocarcinoma is a devastating cancer with a poor prognosis. Previous reports have presented conflicting results on the role of transforming growth factor-β-induced protein (TGFBI) in malignant cancers. Currently, our understanding of the role of TGFBI in cholangiocarcinoma is ambiguous. The aim of the present study was to investigate the role of TGFBI in human cholangiocarcinoma.

METHODS

Iterative patient partitioning (IPP) scoring and consecutive elimination methods were used to select prognostic biomarkers. mRNA and protein expression levels were determined using Gene Expression Omnibus (GEO), Western blot and ELISA analyses. Biological activities of selected biomarkers were examined using both in vitro and in vivo assays. Prognostic values were assessed using Kaplan-Meier and Liptak's z score analyses.

RESULTS

TGFBI was selected as a candidate cholangiocarcinoma biomarker. GEO database analysis revealed significantly higher TGFBI mRNA expression levels in cholangiocarcinoma tissues compared to matched normal tissues. TGFBI protein was specifically detected in a soluble form in vitro and in vivo. TGFBI silencing evoked significant anti-cancer effects in vitro. Soluble TGFBI treatment aggravated the malignancy of cholangiocarcinoma cells both in vitro and in vivo through activation of the integrin beta-1 (ITGB1) dependent PPARγ signalling pathway. High TGFBI expression was associated with a poor prognosis in patients with cholangiocarcinoma.

CONCLUSIONS

Our data suggest that TGFBI may serve as a promising prognostic biomarker and therapeutic target for cholangiocarcinoma.

Troglitazone-Induced Autophagic Cytotoxicity in Lung Adenocarcinoma Cell Lines

Lung cancer is the leading cause of cancer-related deaths worldwide. Troglitazone (TGZ), a peroxisome proliferator-activated receptor gamma (PPARγ) ligand, is a potential antitumor agent. However, the action mechanism of TGZ in lung adenocarcinoma cells has not been completely elucidated. To assess this mechanism and the anticancer effects of TGZ in human lung adenocarcinoma cell lines (A549 and H1975), we investigated the involvement of PPARγ, apoptosis, the mitogen-activated protein kinase (MAPK) pathway, protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway, and autophagy. Cell viability was measured using fluorescence-based assays. Apoptotic cells were detected by Hoechst 33342 and Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) double staining; protein expression was detected by Western blotting. TGZ inhibited cell proliferation in a dose-dependent manner in both cell lines, and the effect was not suppressed by a PPARγ inhibitor. Additionally, TGZ increased apoptotic cell number and upregulated p38 and c-Jun N-terminal kinase (JNK) phosphorylation; however, p38 and JNK inhibitors did not block TGZ-mediated inhibition of cell proliferation in either cell line. TGZ also upregulated extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, whereas an ERK1/2 inhibitor enhanced TGZ-mediated cytotoxicity in A549 cells. Additionally, TGZ increased LC3-II expression, and chloroquine (an autophagy inhibitor) attenuated TGZ-mediated inhibition of cell proliferation. These findings suggest that TGZ-induced inhibition of cell proliferation is PPARγ independent. TGZ-mediated inhibition of cell proliferation was accompanied by apoptosis and independent of the MAPK signaling pathway. These results suggest that TGZ inhibits cell proliferation through autophagy-induced cytotoxicity. This study demonstrated that chemotherapy using TGZ may be effective for lung adenocarcinoma.

Identification of a Novel PPAR Signature for Predicting Prognosis, Immune Microenvironment, and Chemotherapy Response in Bladder Cancer

Background

Mounting evidence has confirmed that peroxisome proliferator-activated receptors (PPARs) played a crucial role in the development and progression of bladder cancer (BLCA). The purpose of this study is to comprehensively investigate the function and prognostic value of PPAR-targeted genes in BLCA.

Methods

The RNA sequencing data and clinical information of BLCA patients were acquired from The Cancer Genome Atlas (TCGA). The differentially expressed PPAR-targeted genes were investigated. Cox analysis and least absolute shrinkage and selection operator (LASSO) analysis were performed for screening prognostic PPAR-targeted genes and constructing the prognostic PPAR signature and then validated by GSE13507 cohort and GSE32894 cohort. A nomogram was constructed to predict the outcomes of BLCA patients in combination with PPAR signature and clinical factors. Gene set enrichment analysis (GSEA) and immune cell infiltration were implemented to explore the molecular characteristics of the signature. The Genomics of Drug Sensitivity in Cancer (GDSC) database was used to predict the chemotherapy responses of the prognostic signature. The candidate small molecule drugs targeting PPAR-targeted genes were screened by the CMAP database.

Results

We constructed and validated the prognostic signature comprising of 4 PPAR-targeted genes (CPT1B, CALR, AHNAK, and FADS2), which was an independent prognostic biomarker in BLCA patients. A nomogram based on the signature and clinical factors was established in the TCGA set, and the calibration plots displayed the excellent predictive capacity. GSEA analysis indicated that PPAR signature was implicated in multiple oncogenic signaling pathways and correlated with tumor immune cell infiltration. Patients in the high-risk groups showed greater sensitivity to chemotherapy than those in the low-risk groups. Moreover, 11 candidate small molecule drugs were identified for the treatment of BLCA.

Conclusion

We constructed and validated a novel PPAR signature, which showed the excellent performance in predicting prognosis and chemotherapy sensitivity of BLCA patients.

In Silico Studies of Tumor Targeted Peptide-Conjugated Natural Products for Targeting Over-Expressed Receptors in Breast Cancer Cells Using Molecular Docking, Molecular Dynamics and MMGBSA Calculations

In this work, in silico studies were carried out for the design of diterpene and polyphenol-peptide conjugates to potentially target over-expressed breast tumor cell receptors. Four point mutations were induced into the known tumor-targeting peptide sequence YHWYGYTPQN at positions 1, 2, 8 and 10, resulting in four mutated peptides. Each peptide was separately conjugated with either chlorogenate, carnosate, gallate, or rosmarinate given their known anti-tumor activities, creating dual targeting compounds. Molecular docking studies were conducted with the epidermal growth factor receptor (EGFR), to which the original peptide sequence is known to bind, as well as the estrogen receptor (ERα) and peroxisome proliferator-activated receptor (PPARα) using both Autodock Vina and FireDock. Based on docking results, peptide conjugates and peptides were selected and subjected to molecular dynamics simulations. MMGBSA calculations were used to further probe the binding energies. ADME studies revealed that the compounds were not CYP substrates, though most were Pgp substrates. Additionally, most of the peptides and conjugates showed MDCK permeability. Our results indicated that several of the peptide conjugates enhanced binding interactions with the receptors and resulted in stable receptor-ligand complexes; Furthermore, they may successfully target ERα and PPARα in addition to EGFR and may be further explored for synthesis and biological studies for therapeutic applications.

Glatiramer acetate enhances tumor retention and innate activation of immunostimulants

Cancer immunotherapy aims to stimulate immune cells to recognize and attack tumor tissue. The immunostimulatory polyanions polyI:C and CpG induce potent pro-inflammatory immune responses as TLR3 and TLR9 agonists, respectively. Clinical trials of TLR agonists, however, have been fraught with immune-related adverse events, even when injecting intratumorally in an effort to minimize systemic exposure. We identified Glatiramer Acetate (GA), a positively-charged polypeptide approved for multiple sclerosis, as a delivery agent capable of complexing with polyI:C or CpG and reducing the mobility of these actives. Small nanoparticles termed polyplexes form when mixing positively-charged GA and negatively-charged immunostimulant (polyI:C or CpG). The ratio of GA to immunostimulant directly affected the potency of TLR activation and the mobility of these actives in simulated tumor tissue. Polyplexes of GA and CpG were injected intratumorally in a tumor model of head and neck cancer (HNC) and significantly mitigated tumor growth as compared to the vehicle controls. Intratumoral injections of CpG showed the slowest tumor growth but exhibited dramatically higher systemic proinflammatory cytokine levels compared to polyplexes of GA with CpG. Sequencing of RNA from resected tumors revealed a similar pattern of upregulated proinflammatory cytokines for CpG and polyplexes, a finding supported by histological tumor staining showing similar infiltration of immune cells induced by these treatments. Intratumoral administration of polyplexes of GA with immunostimulant represents a translational approach to enhance local immune responses while mitigating systemic immune-related adverse events.

Thiazolidinedione "Magic Bullets" Simultaneously Targeting PPARγ and HDACs: Design, Synthesis, and Investigations of their In Vitro and In Vivo Antitumor Effects

Monotargeting anticancer agents suffer from resistance and target nonspecificity concerns, which can be tackled with a multitargeting approach. The combined treatment with HDAC inhibitors and PPARγ agonists has displayed potential antitumor effects. Based on these observations, this work involves design and synthesis of molecules that can simultaneously target PPARγ and HDAC. Several out of 25 compounds inhibited HDAC4, and six compounds acted as dual-targeting agents. Compound 7i was the most potent, with activity toward PPARγ EC50 = 0.245 μM and HDAC4 IC50 = 1.1 μM. Additionally, compounds 7c and 7i were cytotoxic to CCRF-CEM cells (CC50 = 2.8 and 9.6 μM, respectively), induced apoptosis, and caused DNA fragmentation. Furthermore, compound 7c modulated the expression of c-Myc, cleaved caspase-3, and caused in vivo tumor regression in CCRF-CEM tumor xenografts. Thus, this study provides a basis for the rational design of dual/multitargeting agents that could be developed further as anticancer therapeutics.

Upregulated PPARG2 facilitates interaction with demethylated AKAP12 gene promoter and suppresses proliferation in prostate cancer

Prostate cancer (PCA) is one of the most common male genitourinary tumors. However, the molecular mechanisms involved in the occurrence and progression of PCA have not been fully clarified. The present study aimed to investigate the biological function and molecular mechanism of the nuclear receptor peroxisome proliferator-activated receptor gamma 2 (PPARG2) in PCA. Our results revealed that PPARG2 was downregulated in PCA, and overexpression of PPARG2 inhibited cell migration, colony formation, invasion and induced cell cycle arrest of PCA cells in vitro. In addition, PPARG2 overexpression modulated the activation of the Akt signaling pathway, as well as inhibited tumor growth in vivo. Moreover, mechanistic analysis revealed that PPARG2 overexpression induced increased expression level of miR-200b-3p, which targeted 3′ UTR of the downstream targets DNMT3A/3B, and facilitated interaction with demethylated AKAP12 gene promoter and suppressed cell proliferation in PCA. Our findings provided the first evidence for a novel PPARG2-AKAP12 axis mediated epigenetic regulatory network. The study identified a molecular mechanism involving an epigenetic modification that could be possibly targeted as an antitumoral strategy against prostate cancer.

Targeting pyruvate dehydrogenase kinase signaling in the development of effective cancer therapy

Pyruvate is irreversibly decarboxylated to acetyl coenzyme A by mitochondrial pyruvate dehydrogenase complex (PDC). Decarboxylation of pyruvate is considered a crucial step in cell metabolism and energetics. The cancer cells prefer aerobic glycolysis rather than mitochondrial oxidation of pyruvate. This attribute of cancer cells allows them to sustain under indefinite proliferation and growth. Pyruvate dehydrogenase kinases (PDKs) play critical roles in many diseases because they regulate PDC activity. Recent findings suggest an altered metabolism of cancer cells is associated with impaired mitochondrial function due to PDC inhibition. PDKs inhibit the PDC activity via phosphorylation of the E1a subunit and subsequently cause a glycolytic shift. Thus, inhibition of PDK is an attractive strategy in anticancer therapy. This review highlights that PDC/PDK axis could be implicated in cancer's therapeutic management by developing potential small-molecule PDK inhibitors. In recent years, a dramatic increase in the targeting of the PDC/PDK axis for cancer treatment gained an attention from the scientific community. We further discuss breakthrough findings in the PDC-PDK axis. In addition, structural features, functional significance, mechanism of activation, involvement in various human pathologies, and expression of different forms of PDKs (PDK1-4) in different types of cancers are discussed in detail. We further emphasized the gene expression profiling of PDKs in cancer patients to prognosis and therapeutic manifestations. Additionally, inhibition of the PDK/PDC axis by small molecule inhibitors and natural compounds at different clinical evaluation stages has also been discussed comprehensively.

PPARs and Tumor Microenvironment: The Emerging Roles of the Metabolic Master Regulators in Tumor Stromal-Epithelial Crosstalk and Carcinogenesis

Peroxisome proliferator-activated receptors (PPARs) have been extensively studied for more than three decades. Consisting of three isotypes, PPARα, γ, and β/δ, these nuclear receptors are regarded as the master metabolic regulators which govern many aspects of the body energy homeostasis and cell fate. Their roles in malignancy are also increasingly recognized. With the growing interest in crosstalk between tumor stroma and epithelium, this review aims to highlight the current knowledge on the implications of PPARs in the tumor microenvironment. PPARγ plays a crucial role in the metabolic reprogramming of cancer-associated fibroblasts and adipocytes, coercing the two stromal cells to become substrate donors for cancer growth. Fibroblast PPARβ/δ can modify the risk of tumor initiation and cancer susceptibility. In endothelial cells, PPARβ/δ and PPARα are pro- and anti-angiogenic, respectively. Although the angiogenic role of PPARγ remains ambiguous, it is a crucial regulator in autocrine and paracrine signaling of cancer-associated fibroblasts and tumor-associated macrophages/immune cells. Of note, angiopoietin-like 4 (ANGPTL4), a secretory protein encoded by a target gene of PPARs, triggers critical oncogenic processes such as inflammatory signaling, extracellular matrix derangement, anoikis resistance and metastasis, making it a potential drug target for cancer treatment. To conclude, PPARs in the tumor microenvironment exhibit oncogenic activities which are highly controversial and dependent on many factors such as stromal cell types, cancer types, and oncogenesis stages. Thus, the success of PPAR-based anticancer treatment potentially relies on innovative strategies to modulate PPAR activity in a cell type-specific manner.

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.

Shared PPARα/γ Target Genes Regulate Brown Adipocyte Thermogenic Function

Brown adipose tissue (BAT) generates heat to maintain body temperature and suppress obesity. Agonists for nuclear receptors PPARα and PPARγ both affect brown adipocyte function, yet the interplay between these factors in BAT is uncertain. Here, we report that PPARα shares most genomic binding sites with PPARγ, and these common binding sites are more related to BAT function than PPARγ-selective sites without PPARα. Integrating PPARα and PPARγ genomic occupancy with cold-responsive BAT transcriptomes identifies a subset of 16 genes with potential relevance to BAT function. Among these, we focused on the lysosomal protease cathepsin Z (CTSZ) and showed it is necessary for mitochondrial respiration in both mouse and human brown adipocytes. Thus, CTSZ is a shared PPARα/γ target gene in BAT and a regulator of brown adipocyte thermogenic function.

Downregulation of fatty acid oxidation by involvement of HIF-1α and PPARγ in human gastric adenocarcinoma and related clinical significance

Lipid metabolism rewiring in gastric adenocarcinoma (GA) pathogenesis is still not clearly elucidated. This study aimed to describe the role of lipid catabolism in GA patient outcomes and possible therapeutic targets by analyzing the effect of hypoxia-inducible factor-1α (HIF-1α) on fatty acid oxidation (FAO). AGS cell line was cultured in normoxic and hypoxic conditions, and FAO-related genes were analyzed by real-time-PCR and Western-blot. The study group comprised 108 newly diagnosed GA patients and 152 control cases. Serum concentrations of medium and long-chain acyl-CoA dehydrogenases (MCAD and LCAD) proteins were measured using ELISA, and local expression of HIF-1α, carnitine palmitoyl transferase 1 (CPT1A) and peroxisome proliferator-activated receptor γ (PPARγ) was evaluated by immunohistochemistry. In addition, gene expression of PPARγ, CPT1A, LCAD, and MCAD was assessed by real-time-PCR. In vitro findings indicate HIF-1α upregulation and FAO-related genes and proteins reduction in the hypoxic culture of AGS cells. GA patients had significantly lower circulating levels of LCAD compared to controls. Higher protein expression of HIF-1α and downregulated CPT1A and PPARγ were observed in GA tissues versus controls. Gene expression of CPT1A, PPARγ, LCAD, and MCAD were repressed in GA tissues compared to controls. Moreover, reduced expression of CPT1A, PPARγ, and MCAD were correlated with HIF-1α upregulation in GA. Poor patient outcome was associated with lower PPARγ and LCAD expression in GA. HIF-1α upregulation in human GA patients and AGS cells was paralleled by downregulation of lipid catabolism genes potentially via reduced PPARγ-mediated FAO. This metabolic adaptation to hypoxic condition may play a role in GA pathogenesis and might have clinical and therapeutic value in GA patients.

Identification of a Potential PPAR-Related Multigene Signature Predicting Prognosis of Patients with Hepatocellular Carcinoma

Peroxisome proliferator-activated receptors (PPARs) and part of their target genes have been reported to be related to the progression of hepatocellular carcinoma (HCC). The prognosis of HCC is not optimistic, and more accurate prognostic markers are needed. This study focused on discovering potential prognostic markers from the PPAR-related gene set. The mRNA data and clinical information of HCC were collected from TCGA and GEO platforms. Univariate Cox and lasso Cox regression analyses were used to screen prognostic genes of HCC. Three genes (MMP1, HMGCS2, and SLC27A5) involved in the PPAR signaling pathway were selected as the prognostic signature of HCC. A formula was established based on the expression values and multivariate Cox regression coefficients of selected genes, that was, risk score = 0.1488∗expression value of MMP1 + (−0.0393)∗expression value of HMGCS2 + (−0.0479)∗expression value of SLC27A5. The prognostic ability of the three-gene signature was assessed in the TCGA HCC dataset and verified in three GEO sets (GSE14520, GSE36376, and GSE76427). The results showed that the risk score based on our signature was a risk factor with a HR (hazard ratio) of 2.72 (95%CI (Confidence Interval) = 1.87 ~ 3.95, p < 0.001) for HCC survival. The signature could significantly (p < 0.0001) distinguish high-risk and low-risk patients with poor prognosis for HCC. In addition, we further explored the independence and applicability of the signature with other clinical indicators through multivariate Cox analysis (p < 0.001) and nomogram analysis (C‐index = 0.709). The above results indicate that the combination of MMP1, HMGCS2, and SLC27A5 selected from the PPAR signaling pathway could effectively, independently, and applicatively predict the prognosis of HCC. Our research provided new insights to the prognosis of HCC.

PPARα-Selective Antagonist GW6471 Inhibits Cell Growth in Breast Cancer Stem Cells Inducing Energy Imbalance and Metabolic Stress

Breast cancer is the most frequent cancer and the second leading cause of death among women. Triple-negative breast cancer is the most aggressive subtype of breast cancer and is characterized by the absence of hormone receptors and human epithelial growth factor receptor 2. Cancer stem cells (CSCs) represent a small population of tumor cells showing a crucial role in tumor progression, metastasis, recurrence, and drug resistance. The presence of CSCs can explain the failure of conventional therapies to completely eradicate cancer. Thus, to overcome this limit, targeting CSCs may constitute a promising approach for breast cancer treatment, especially in the triple-negative form. To this purpose, we isolated and characterized breast cancer stem cells from a triple-negative breast cancer cell line, MDA-MB-231. The obtained mammospheres were then treated with the specific PPARα antagonist GW6471, after which, glucose, lipid metabolism, and invasiveness were analyzed. Notably, GW6471 reduced cancer stem cell viability, proliferation, and spheroid formation, leading to apoptosis and metabolic impairment. Overall, our findings suggest that GW6471 may be used as a potent adjuvant for gold standard therapies for triple-negative breast cancer, opening the possibility for preclinical and clinical trials for this class of compounds.

Curcumin promotes AApoAII amyloidosis and peroxisome proliferation in mice by activating the PPARα signaling pathway

Curcumin is a polyphenol compound that exhibits multiple physiological activities. To elucidate the mechanisms by which curcumin affects systemic amyloidosis, we investigated amyloid deposition and molecular changes in a mouse model of amyloid apolipoprotein A-II (AApoAII) amyloidosis, in which mice were fed a curcumin-supplemented diet. Curcumin supplementation for 12 weeks significantly increased AApoAII amyloid deposition relative to controls, especially in the liver and spleen. Liver weights and plasma ApoA-II and high-density lipoprotein concentrations were significantly elevated in curcumin-supplemented groups. RNA-sequence analysis revealed that curcumin intake affected hepatic lipid metabolism via the peroxisome proliferator-activated receptor (PPAR) pathway, especially PPARα activation, resulting in increased Apoa2 mRNA expression. The increase in liver weights was due to activation of PPARα and peroxisome proliferation. Taken together, these results demonstrate that curcumin is a PPARα activator and may affect expression levels of proteins involved in amyloid deposition to influence amyloidosis and metabolism in a complex manner.

Inhibition of the Soluble Epoxide Hydrolase as an Analgesic Strategy: A Review of Preclinical Evidence

Chronic pain is a complicated condition which causes substantial physical, emotional, and financial impacts on individuals and society. However, due to high cost, lack of efficacy and safety problems, current treatments are insufficient. There is a clear unmet medical need for safe, nonaddictive and effective therapies in the management of pain. Epoxy-fatty acids (EpFAs), which are natural signaling molecules, play key roles in mediation of both inflammatory and neuropathic pain sensation. However, their molecular mechanisms of action remain largely unknown. Soluble epoxide hydrolase (sEH) rapidly converts EpFAs into less bioactive fatty acid diols in vivo; therefore, inhibition of sEH is an emerging therapeutic target to enhance the beneficial effect of natural EpFAs. In this review, we will discuss sEH inhibition as an analgesic strategy for pain management and the underlying molecular mechanisms.

Revealing the role of peroxisome proliferator-activated receptor β/δ in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), a form of chronic liver disease that occurs in individuals with no significant alcohol abuse, has become an increasing concern for global health. NAFLD is defined as the presence of lipid deposits in hepatocytes and it ranges from hepatic steatosis (fatty liver) to steatohepatitis. Emerging data from both preclinical studies and clinical trials suggest that the peroxisome proliferator-activated receptor (PPAR)β/δ plays an important role in the control of carbohydrate and lipid metabolism in liver, and its activation might hinder the progression of NAFLD. Here, we review the latest information on the effects of PPARβ/δ on NAFLD, including its capacity to reduce lipogenesis, to alleviate inflammation and endoplasmic reticulum stress, to ameliorate insulin resistance, and to attenuate liver injury. Because of these effects, activation of hepatic PPARβ/δ through synthetic or natural ligands provides a promising therapeutic option for the management of NAFLD.

Discovery and Structure-Activity Relationships of Novel Template, Truncated 1'-Homologated Adenosine Derivatives as Pure Dual PPARγ/δ Modulators

Following our report that A₃ adenosine receptor (AR) antagonist 1 exhibited a polypharmacological profile as a dual modulator of peroxisome proliferator-activated receptor (PPAR)γ/δ, we discovered a new template, 1'-homologated adenosine analogues 4a-4t, as dual PPARγ/δ modulators without AR binding. Removal of binding affinity to A₃AR was achieved by 1'-homologation, and PPARγ/δ dual modulation was derived from the structural similarity between the target nucleosides and PPAR modulator drug, rosiglitazone. All the final nucleosides were devoid of AR-binding affinity and exhibited high binding affinities to PPARγ/δ but lacked PPARα binding. 2-Cl derivatives exhibited dual receptor-binding affinity to PPARγ/δ, which was absent for the corresponding 2-H derivatives. 2-Propynyl substitution prevented PPARδ-binding affinity but preserved PPARγ affinity, indicating that the C2 position defines a pharmacophore for selective PPARγ ligand designs. PPARγ/δ dual modulators functioning as both PPARγ partial agonists and PPARδ antagonists promoted adiponectin production, suggesting their therapeutic potential against hypoadiponectinemia-associated cancer and metabolic diseases.

Recent Insights on the Role of PPAR-β/δ in Neuroinflammation and Neurodegeneration, and Its Potential Target for Therapy

Peroxisome proliferator-activated receptor (PPAR) β/δ belongs to the family of hormone and lipid-activated nuclear receptors, which are involved in metabolism of long-chain fatty acids, cholesterol, and sphingolipids. Similar to PPAR-α and PPAR-γ, PPAR-β/δ also acts as a transcription factor activated by dietary lipids and endogenous ligands, such as long-chain saturated and polyunsaturated fatty acids, and selected lipid metabolic products, such as eicosanoids, leukotrienes, lipoxins, and hydroxyeicosatetraenoic acids. Together with other PPARs, PPAR-β/δ displays transcriptional activity through interaction with retinoid X receptor (RXR). In general, PPARs have been shown to regulate cell differentiation, proliferation, and development and significantly modulate glucose, lipid metabolism, mitochondrial function, and biogenesis. PPAR-β/δ appears to play a special role in inflammatory processes and due to its proangiogenic and anti-/pro-carcinogenic properties, this receptor has been considered as a therapeutic target for treating metabolic syndrome, dyslipidemia, carcinogenesis, and diabetes. Until now, most studies were carried out in the peripheral organs, and despite of its presence in brain cells and in different brain regions, its role in neurodegeneration and neuroinflammation remains poorly understood. This review is intended to describe recent insights on the impact of PPAR-β/δ and its novel agonists on neuroinflammation and neurodegenerative disorders, including Alzheimer’s and Parkinson’s, Huntington’s diseases, multiple sclerosis, stroke, and traumatic injury. An important goal is to obtain new insights to better understand the dietary and pharmacological regulations of PPAR-β/δ and to find promising therapeutic strategies that could mitigate these neurological disorders.

A New Prognostic Risk Model Based on PPAR Pathway-Related Genes in Kidney Renal Clear Cell Carcinoma

OBJECTIVE

This study is aimed at using genes related to the peroxisome proliferator-activated receptor (PPAR) pathway to establish a prognostic risk model in kidney renal clear cell carcinoma (KIRC).

METHODS

For this study, we first found the PPAR pathway-related genes on the gene set enrichment analysis (GSEA) website and found the KIRC mRNA expression data and clinical data through TCGA database. Subsequently, we used R language and multiple R language expansion packages to analyze the expression, hazard ratio analysis, and coexpression analysis of PPAR pathway-related genes in KIRC. Afterward, using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) website, we established the protein-protein interaction (PPI) network of genes related to the PPAR pathway. After that, we used LASSO regression curve analysis to establish a prognostic survival model in KIRC. Finally, based on the model, we conducted correlation analysis of the clinicopathological characteristics, univariate analysis, and multivariate analysis.

RESULTS

We found that most of the genes related to the PPAR pathway had different degrees of expression differences in KIRC. Among them, the high expression of 27 genes is related to low survival rate of KIRC patients, and the high expression of 13 other genes is related to their high survival rate. Most importantly, we used 13 of these genes successfully to establish a risk model that could accurately predict patients' prognosis. There is a clear correlation between this model and metastasis, tumor, stage, grade, and fustat.

CONCLUSIONS

To the best of our knowledge, this is the first study to analyze the entire PPAR pathway in KIRC in detail and successfully establish a risk model for patient prognosis. We believe that our research can provide valuable data for future researchers and clinicians.

The Role of Peroxisome Proliferator-Activated Receptors (PPARs) in Pan-Cancer

Peroxisome proliferator-activated receptors (PPARs) are members of nuclear transcription factors. The functions of the PPAR family (PPARA, PPARD, and PPARG) and their coactivators (PPARGC1A and PPARGC1B) in maintenance of lipid and glucose homeostasis have been unveiled. However, the roles of PPARs in cancer development remain elusive. In this work, we made use of 11,057 samples across 33 TCGA tumor types to analyze the relationship between PPAR transcriptional expression and tumorigenesis as well as drug sensitivity. We performed multidimensional analyses on PPARA, PPARG, PPARD, PPARGC1A, and PPARGC1B, including differential expression analysis in pan-cancer, immune subtype analysis, clinical analysis, tumor purity analysis, stemness correlation analysis, and drug responses. PPARs and their coactivators expressed differently in different types of cancers, in different immune subtypes. This analysis reveals various expression patterns of the PPAR family at a level of pan-cancer and provides new clues for the therapeutic strategies of cancer.

PPARGC1A gene polymorphism is associated with exercise-induced fat loss

Obesity is a widespread problem within modern society, serving to increase the risk of cardiovascular, metabolic, and neurodegenerative disorders. Peroxisome proliferator-activated receptor gamma (PPARγ) and PPARγ coactivator 1 α (PGC1α) play a key role in the regulation of cellular energy metabolism and is implicated in the pathology of these diseases. This study examined the association between polymorphisms of the PPARG and PPARGC1A genes and individual variability in weight loss in response to physical activity intervention. 39 obese Ukrainian women (44.4 ± 7.5 years, BMI > 30.0 kg/m²) undertook a 3-month fitness program whilst following a hypocaloric diet (~ 1500 cal). Anthropometric and biochemical measurements took place before and after the program. Single nucleotide polymorphisms within or near PPARG (n = 94) and PPARGC1A (n = 138) were identified and expression of PPARG mRNA was measured via reverse transcription and amplification. The association between DNA polymorphisms and exercise-induced weight loss, initial body mass, biochemistry and PPARG expression was determined using one-way analysis of variance (ANOVA). The present intervention induced significant fat loss in all participants (total fat: 40.3 ± 5.3 vs 36.4 ± 5.7%; P < 0.00001). Only one polymorphism (rs17650401 C/T) within the PPARGC1A gene was found to be associated with fat loss efficiency after correction for multiple testing, with T allele carriers showing the greatest reduction in body fat percentage (2.5-fold; P = 0.00013) compared to non-carriers. PPARGC1A (rs17650401) is associated with fat loss efficiency of the fitness program in obese women. Further studies are warranted to test whether this variation is associated with fat oxidation.

The PPARγ Agonist Rosiglitazone Enhances the Radiosensitivity of Human Pancreatic Cancer Cells

Purpose

As radiation therapy is widely used for the management of pancreatic cancer, identifying novel targets to improve the radiosensitivity of cancer cells is beneficial. Rosiglitazone, a specific peroxisome proliferator-activated receptor γ (PPARγ) agonist, has an inhibitory effect on various types of cancer cells. The purpose of this paper is to investigate the effect of rosiglitazone on the radiosensitivity of pancreatic cancer cells and the potential mechanism.

Materials and Methods

PPARγ expression in pancreatic cancer and adjacent tissues was evaluated using immunohistochemistry analysis. The viability, migration and invasion ability of PANC1 and PaTu8988 cells were detected using MTT assay, scratch-wound assay and transwell invasion assay. The effect of rosiglitazone on radiosensitivity of the cells was determined using the clonogenic assay. PANC1 cells were inoculated into BALB/c mice to establish tumors. Microarray was used to investigate changes of genes involved.

Results

Higher PPARγ expression was demonstrated in pancreatic cancer tissues compared with para-carcinoma tissues. Rosiglitazone inhibited the cell viability and enhanced the radiation-induced anti-migration and anti-invasion effect. Rosiglitazone potentiated the radiosensitivity of pancreatic cancer cells and PANC1 xenografts. Microarray analysis revealed that rosiglitazone plus radiation altered the expression of multiple genes and affected multiple pathways.

Conclusion

Rosiglitazone enhances the radiosensitivity of human pancreatic cancer cells in vitro and in vivo via complex mechanisms.

In silico identification of therapeutic compounds against microRNA targets in drug-resistant pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a major health issue that has been eluding efforts to identify viable therapeutic treatment options. Besides having the lowest survival rate among all types of cancer, almost all conventional methods of treatment are futile against this condition, leaving patients to succumb to this ailment faster than ever. As it is increasingly becoming difficult to come up with new compounds for the treatment of various diseases, alternative solutions are required for tackling these problems. In this study, publically available miRNA and gene expression data were used to identify common elements that were present in gemcitabine-resistant PDAC cell lines. By selecting overexpressed genes involved in pancreatic cancer and cancer pathways in general, potential drug candidates for the treatment of PDAC were identified. In this study, 21 differentially expressed miRNAs were identified from PANC-1 cell line treated with gemcitabine. Pathway analysis revealed that MET and PPARG were overexpressed in cancer-related pathways, including pancreatic cancer, and could be targeted for PDAC treatment. Using CMap, fisetin was identified a likely candidate drug for the treatment of PDAC. Docking studies indicated that fisetin was bound to c-Met and PPARG with an XP G score of -12.819 and -7.021 kcal/mol, respectively. As miRNAs have increasingly been shown to part take in important cancer-related processes and pathways, researching drug development methods based on miRNA targets could be beneficial for pharmaceutical industries. Communicated by Ramaswamy H. Sarma.

A semi-automated workflow for adverse outcome pathway hypothesis generation: The use case of non-genotoxic induced hepatocellular carcinoma

The utility of the Adverse Outcome Pathway (AOP) concept has been largely recognized by scientists, however, the AOP generation is still mainly done manually by screening through evidence and extracting probable associations. To accelerate this process and increase the reliability, we have developed an semi-automated workflow for AOP hypothesis generation. In brief, association mining methods were applied to high-throughput screening, gene expression, in vivo and disease data present in ToxCast and Comparative Toxicogenomics Database. This was supplemented by pathway mapping using Reactome to fill in gaps and identify events occurring at the cellular/tissue levels. Furthermore, in vivo data from TG-Gates was integrated to finally derive a gene, pathway, biochemical, histopathological and disease network from which specific disease sub-networks can be queried. To test the workflow, non-genotoxic-induced hepatocellular carcinoma (HCC) was selected as a case study. The implementation resulted in the identification of several non-genotoxic-specific HCC-connected genes belonging to cell proliferation, endoplasmic reticulum stress and early apoptosis. Biochemical findings revealed non-genotoxic-specific alkaline phosphatase increase. The explored non-genotoxic-specific histopathology was associated with early stages of hepatic steatosis, transforming into cirrhosis. This work illustrates the utility of computationally predicted constructs in supporting development by using pre-existing knowledge in a fast and unbiased manner.

To Probe Full and Partial Activation of Human Peroxisome Proliferator-Activated Receptors by Pan-Agonist Chiglitazar Using Molecular Dynamics Simulations

Chiglitazar is a promising new-generation insulin sensitizer with low reverse effects for the treatment of type II diabetes mellitus (T2DM) and has shown activity as a nonselective pan-agonist to the human peroxisome proliferator-activated receptors (PPARs) (i.e., full activation of PPARγ and a partial activation of PPARα and PPARβ/δ). Yet, it has no high-resolution complex structure with PPARs and its detailed interactions and activation mechanism remain unclear. In this study, we docked chiglitazar into three experimentally resolved crystal structures of hPPAR subtypes, PPARα, PPARβ/δ, and PPARγ, followed by 3 μs molecular dynamics simulations for each system. Our MM-GBSA binding energy calculation revealed that chiglitazar most favorably bound to hPPARγ (-144.6 kcal/mol), followed by hPPARα (-138.0 kcal/mol) and hPPARβ (-135.9 kcal/mol), and the order is consistent with the experimental data. Through the decomposition of the MM-GBSA binding energy by residue and the use of two-dimensional interaction diagrams, key residues involved in the binding of chiglitazar were identified and characterized for each complex system. Additionally, our detailed dynamics analyses support that the conformation and dynamics of helix 12 play a critical role in determining the activities of the different types of ligands (e.g., full agonist vs. partial agonist). Rather than being bent fully in the direction of the agonist versus antagonist conformation, a partial agonist can adopt a more linear conformation and have a lower degree of flexibility. Our finding may aid in further development of this new generation of medication.

NUDT7 Loss Promotes KrasG12D CRC Development

Studies have suggested that dysregulation of peroxisomal lipid metabolism might play an important role in colorectal cancer (CRC) development. Here, we found that Kras^G12D-driven CRC tumors demonstrate dysfunctional peroxisomal β-oxidation and identified Nudt7 (peroxisomal coenzyme A diphosphatase NUDT7) as one of responsible peroxisomal genes. In Kras^G12D-driven CRC tumors, the expression level of Nudt7 was significantly decreased. Treatment of azoxymethane/dextran sulfate sodium (AOM/DSS) into Nudt7 knockout (Nudt7^−/−) mice significantly induced lipid accumulation and the expression levels of CRC-related genes whereas xenografting of Nudt7-overexpressed LS-174T cells into mice significantly reduced lipid accumulation and the expression levels of CRC-related genes. Ingenuity pathway analysis of microarray using the colon of Nudt7^−/− and Nudt7^+/+ mice treated with AOM/DSS suggested Wnt signaling as one of activated signaling pathways in Nudt7^−/− colons. Upregulated levels of β-catenin were observed in the colons of Kras^G12D and AOM/DSS-treated Nudt7^−/− mice and downstream targets of β-catenin such as Myc, Ccdn1, and Nos2, were also significantly increased in the colon of Nudt7^−/− mice. We observed an increased level of palmitic acid in the colon of Nudt7^−/− mice and attachment of palmitic acid-conjugated chitosan patch into the colon of mice induced the expression levels of β-catenin and CRC-related genes. Overall, our data reveal a novel role for peroxisomal NUDT7 in Kras^G12D-driven CRC development.

Cyclin-Dependent Kinase 5 Inhibitor Butyrolactone I Elicits a Partial Agonist Activity of Peroxisome Proliferator-Activated Receptor γ

Adiponectin is an adipocyte-derived cytokine having an insulin-sensitizing activity. During the phenotypic screening of secondary metabolites derived from the marine fungus Aspergillus terreus, a poly cyclin-dependent kinase (CDK) inhibitor butyrolactone I affecting CDK1 and CDK5 was discovered as a potent adiponectin production-enhancing compound in the adipogenesis model of human bone marrow-derived mesenchymal stem cells (hBM-MSCs). CDK5 inhibitors exhibit insulin-sensitizing activities by suppressing the phosphorylation of peroxisome proliferator-activated receptor γ (PPARγ). However, the adiponectin production-enhancing activities of butyrolactone I have not been correlated with the potency of CDK5 inhibitor activities. In a target identification study, butyrolactone I was found to directly bind to PPARγ. In the crystal structure of the human PPARγ, the ligand-binding domain (LBD) in complex with butyrolactone I interacted with the amino acid residues located in the hydrophobic binding pockets of the PPARγ LBD, which is a typical binding mode of the PPARγ partial agonists. Therefore, the adiponectin production-enhancing effect of butyrolactone I was mediated by its polypharmacological dual modulator activities as both a CDK5 inhibitor and a PPARγ partial agonist.

HMGCS2 Mediates Ketone Production and Regulates the Proliferation and Metastasis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common primary malignant tumor worldwide; however, the traditional therapeutic approaches and survival rates are still limited. To improve current therapies, it is necessary to investigate the molecular mechanisms underlying liver cancer and to identify potential therapeutic targets. The aims of this study were to verify the mechanisms and therapeutic potential of the ketogenesis rate-limiting enzyme 3-Hydroxymethylglutaryl-CoA synthase 2 (HMGCS2) in HCC. Immunohistochemical staining of human liver disease tissue arrays showed that HMGCS2 is abundantly expressed in normal liver tissues but is downregulated in cirrhosis and HCC tissues. In HCC patients, lower HMGCS2 expression was correlated with higher pathological grades and clinical stages. In our investigation of the molecular mechanisms of HMGCS2 in HCC, we showed that knockdown of HMGCS2 decreased ketone production, which promoted cell proliferation, cell migration, and xenograft tumorigenesis by enhancing c-Myc/cyclinD1 and EMT signaling and by suppressing the caspase-dependent apoptosis pathway. Ketone body treatment reduced the proliferation- and migration-promoting effects of HMGCS2 knockdown in cells. In contrast, HMGCS2 overexpression increased the intracellular ketone level and inhibited cell proliferation, cell migration, and xenograft tumorigenesis. Finally, ketogenic diet administration significantly inhibited liver cancer cell growth in mice. Our studies highlight the potential therapeutic strategy of targeting HMGCS2-mediated ketogenesis in liver cancer.

Polyunsaturated Fatty Acids from Astrocytes Activate PPARγ Signaling in Cancer Cells to Promote Brain Metastasis

Brain metastasis, the most lethal form of melanoma and carcinoma, is the consequence of favorable interactions between the invading cancer cells and the brain cells. Peroxisome proliferator-activated receptor γ (PPARγ) has ambiguous functions in cancer development, and its relevance in advanced brain metastasis remains unclear. Here, we demonstrate that astrocytes, the unique brain glial cells, activate PPARγ in brain metastatic cancer cells. PPARγ activation enhances cell proliferation and metastatic outgrowth in the brain. Mechanistically, astrocytes have a high content of polyunsaturated fatty acids that act as "donors" of PPARγ activators to the invading cancer cells. In clinical samples, PPARγ signaling is significantly higher in brain metastatic lesions. Notably, systemic administration of PPARγ antagonists significantly reduces brain metastatic burden in vivo. Our study clarifies a prometastatic role for PPARγ signaling in cancer metastasis in the lipid-rich brain microenvironment and argues for the use of PPARγ blockade to treat brain metastasis. SIGNIFICANCE: Brain-tropic cancer cells take advantage of the lipid-rich brain microenvironment to facilitate their proliferation by activating PPARγ signaling. This protumor effect of PPARγ in advanced brain metastases is in contrast to its antitumor function in carcinogenesis and early metastatic steps, indicating that PPARγ has diverse functions at different stages of cancer development.This article is highlighted in the In This Issue feature, p. 1631.

Identification of Secreted Phosphoprotein 1 (SPP1) as a Prognostic Factor in Lower-Grade Gliomas

OBJECTIVE

Secreted phosphoprotein 1 (SPP1) is an important extracellular glycoprotein that is associated with immune regulation, tumorigenesis, and cell signaling. However, the prognostic value of SPP1 in patients with glioma has not yet been clarified, especially in lower-grade gliomas. The objective of this study is to evaluate the prognostic merit of SPP1 in lower-grade gliomas.

METHODS

The messenger RNA (mRNA) expression of SPP1 in about 1000 cancer cell lines was explored by using the data from the Cancer Cell Line Encyclopedia database. The Oncomine database was mined to evaluate the mRNA expression of SPP1 in lower-grade glioma, glioblastoma, and normal brain tissues. The correlation between SPP1 mRNA expression and overall survival of patients with glioma from The Cancer Genome Atlas database was analyzed.

RESULTS

SPP1 mRNA expression of glioma was ranked as the eighth highest of all cancer cell lines in the Cancer Cell Line Encyclopedia database. The data from the Oncomine database suggested that SPP1 expression was significantly high in glioblastoma compared with normal brain tissues but was not significantly high in lower-grade glioma compared with normal brain tissue. Analysis of the RNA-Seq data from The Cancer Genome Atlas database showed that the increased SPP1 mRNA expression in lower-grade glioma was significantly associated with poor survival outcomes in patients with lower-grade glioma. Multivariate Cox regression analysis showed that SPP1 might be considered as an independent prognostic factor in lower-grade gliomas.

CONCLUSIONS

The present study showed that SPP1 overexpression is related to worse overall survival in patients with lower-grade glioma. Moreover, SPP1 could be considered as an independent factor in lower-grade gliomas.

Adipose-Derived Stem Cells from Fat Tissue of Breast Cancer Microenvironment Present Altered Adipogenic Differentiation Capabilities

Mesenchymal stem cells (MSCs) are multipotent cells able to differentiate into multiple cell types, including adipocytes, osteoblasts, and chondrocytes. The role of adipose-derived stem cells (ADSCs) in cancers is significantly relevant. They seem to be involved in the promotion of tumour development and progression and relapse processes. For this reason, investigating the effects of breast cancer microenvironment on ADSCs is of high importance in order to understand the relationship between tumour cells and the surrounding stromal cells. With the current study, we aimed to investigate the specific characteristics of human ADSCs isolated from the adipose tissue of breast tumour patients. We compared ADSCs obtained from periumbilical fat (PF) of controls with ADSCs obtained from adipose tissue of breast cancer- (BC-) bearing patients. We analysed the surface antigens and the adipogenic differentiation ability of both ADSC populations. C/EBPδ expression was increased in PF and BC ADSCs induced to differentiate compared to the control while PPARγ and FABP4 expressions were enhanced only in PF ADSCs. Conversely, adiponectin expression was reduced in PF-differentiated ADSCs while it was slightly increased in differentiated BC ADSCs. By means of Oil Red O staining, we further observed an impaired differentiation capability of BC ADSCs. To investigate this aspect more in depth, we evaluated the effect of selective PPARγ activation and nutritional supplementation on the differentiation efficiency of BC ADSCs, noting that it was only with a strong differentiation stimuli that the process took place. Furthermore, we observed no response in BC ADSCs to the PPARγ inhibitor T0070907, showing an impaired activation of this receptor in adipose cells surrounding the breast cancer microenvironment. In conclusion, our study shows an impaired adipogenic differentiation capability in BC ADSCs. This suggests that the tumour microenvironment plays a key role in the modulation of the adipose microenvironment located in the surrounding tissue.

PPAR Receptors Expressed from Vectors Containing CMV Promoter Can Enhance Self-Transcription in the Presence of Fatty Acids from CLA-Enriched Egg Yolks-A Novel Method for Studies of PPAR Ligands

PPAR receptors are ligand-dependent transcription factors activated in response to various small lipophilic ligands controlling the expression of different genes involved in cellular differentiation, development, metabolism, and tumorigenesis. Unexpectedly, our previous studies have shown that single plasmid-based expression of PPARs under the control of CMV promoter/enhancer was significantly elevated in the presence of PPAR agonists. Here we show that the PPAR reporters controlled by the CMV promoter/enhancer, that was shown to contain three internal non-canonical PPRE elements, can be used as a fast screening system for more effective PPAR ligands. This model allowed us to confirm our previous results indicating that fatty acids of CLA-enriched egg yolks (EFA-CLAs) are efficient PPAR ligands that can specifically upregulate the expression of PPARα and PPARγ leading to downregulation of MCF-7 cancer cell proliferation. We also show that synthetic cis9,trans11CLA is more effective in transactivation of PPARγ, while trans10,cis12CLA of PPARα receptor indicating the selectivity of the CLA isomers. This report presents a novel, fast, and reliable strategy for simple testing of PPAR ligands using PPAR expressing plasmids containing the CMV promoter/enhancer that can trigger the positive feedback loop of PPAR self-transcription in the presence of PPAR ligands.

2-Phenyl-8-(1-phenylallyl)-chromenone compounds have a pan-PPAR modulator pharmacophore

Adiponectin is an adipocytokine with insulin-sensitizing, anti-atherogenic, and anti-inflammatory properties. Adiponectin secretion-inducing compounds have therapeutic potential in a variety of metabolic diseases. Phenotypic screening led to the discovery that 5,7-dihydroxy-8-(1-(4-hydroxy-3-methoxyphenyl)allyl)-2-phenyl-4H-chromen-4-one (compound 1) had adiponectin secretion-inducing activity during adipogenesis in human bone marrow mesenchymal stem cells (hBM-MSCs). Compound 1 was originally reported to be an anti-cancer chemical isolated from natural honeybee propolis, and its adiponectin secretion-inducing activity was found in non-cytotoxic concentrations. In a target identification study, compound 1 and its potent synthetic derivative compound 5 were shown to be novel pan-peroxisome proliferator-activator receptor (PPAR) modulators. Molecular docking models with PPARs have indicated that the binding modes of chromenone compounds preferentially interacted with the hydrophobic ligand binding pocket of PPARs. In addition, chromenone compounds have been shown to result in different phenotypic outcomes in the transcriptional regulation of lipid metabolic enzymes than those of selective PPAR mono-agonists for PPARα, PPARγ, and PPARδ. In line with the pharmacology of adiponectin and PPAR pan-modulators, compounds 1 and 5 may have diverse therapeutic potentials to treat cancer and metabolic diseases.