Pregnane X receptor is associated with unfavorable survival and induces chemotherapeutic resistance by transcriptional activating multidrug resistance-related protein 3 in colorectal cancer

Advances in drug resistance of osteosarcoma caused by pregnane X receptor

Osteosarcoma (OS) is a prevalent malignancy among adolescents, commonly manifesting during childhood and adolescence. It exhibits a high degree of malignancy, propensity for metastasis, rapid progression, and poses challenges in clinical management. Chemotherapy represents an efficacious therapeutic modality for OS treatment. However, chemotherapy resistance of OS is a major problem in clinical treatment. In order to treat OS effectively, it is particularly important to explore the mechanism of chemotherapy resistance in OS.The Pregnane X receptor (PXR) is a nuclear receptor primarily involved in the metabolism, transport, and elimination of xenobiotics, including chemotherapeutic agents. PXR involves three stages of drug metabolism: stage I: drug metabolism enzymes; stage II: drug binding enzyme; stage III: drug transporter.PXR has been confirmed to be involved in the process of chemotherapy resistance in malignant tumors. The expression of PXR is increased in OS, which may be related to drug resistance of OS. Therefore, wereviewed in detail the role of PXR in chemotherapy drug resistance in OS.

Aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) play both distinct and common roles in the regulation of colon homeostasis and intestinal carcinogenesis

Both aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) belong among key regulators of xenobiotic metabolism in the intestinal tissue. AhR in particular is activated by a wide range of environmental and dietary carcinogens. The data accumulated over the last two decades suggest that both of these transcriptional regulators play a much wider role in the maintenance of gut homeostasis, and that both transcription factors may affect processes linked with intestinal tumorigenesis. Intestinal epithelium is continuously exposed to a wide range of AhR, PXR and dual AhR/PXR ligands formed by intestinal microbiota or originating from diet. Current evidence suggests that specific ligands of both AhR and PXR can protect intestinal epithelium against inflammation and assist in the maintenance of epithelial barrier integrity. AhR, and to a lesser extent also PXR, have been shown to play a protective role against inflammation-induced colon cancer, or, in mouse models employing overactivation of Wnt/β-catenin signaling. In contrast, other evidence suggests that both receptors may contribute to modulation of transformed colon cell behavior, with a potential to promote cancer progression and/or chemoresistance. The review focuses on both overlapping and separate roles of the two receptors in these processes, and on possible implications of their activity within the context of intestinal tissue.

Expression of Chemoresistance-Associated ABC Proteins in Hepatobiliary, Pancreatic and Gastrointestinal Cancers

Simple Summary

One-third of the approximately 10 million deaths yearly caused by cancer worldwide are due to hepatobiliary, pancreatic, and gastrointestinal tumors. One primary reason for this high mortality is the lack of response of these cancers to pharmacological treatment. More than 100 genes have been identified as responsible for seven mechanisms of chemoresistance, but only a few of them play a critical role. These include ABC proteins (mainly MDR1, MRP1-6, and BCRP), whose expression pattern greatly determines the individual sensitivity of each tumor to pharmacotherapy.

Abstract

Hepatobiliary, pancreatic, and gastrointestinal cancers account for 36% of the ten million deaths caused by cancer worldwide every year. The two main reasons for this high mortality are their late diagnosis and their high refractoriness to pharmacological treatments, regardless of whether these are based on classical chemotherapeutic agents, targeted drugs, or newer immunomodulators. Mechanisms of chemoresistance (MOC) defining the multidrug resistance (MDR) phenotype of each tumor depend on the synergic function of proteins encoded by more than one hundred genes classified into seven groups (MOC1-7). Among them, the efflux of active agents from cancer cells across the plasma membrane caused by members of the superfamily of ATP-binding cassette (ABC) proteins (MOC-1b) plays a crucial role in determining tumor MDR. Although seven families of human ABC proteins are known, only a few pumps (mainly MDR1, MRP1-6, and BCRP) have been associated with reducing drug content and hence inducing chemoresistance in hepatobiliary, pancreatic, and gastrointestinal cancer cells. The present descriptive review, which compiles the updated information on the expression of these ABC proteins, will be helpful because there is still some confusion on the actual relevance of these pumps in response to pharmacological regimens currently used in treating these cancers. Moreover, we aim to define the MOC pattern on a tumor-by-tumor basis, even in a dynamic way, because it can vary during tumor progression and in response to chemotherapy. This information is indispensable for developing novel strategies for sensitization.

Niclosamide induces miR-148a to inhibit PXR and sensitize colon cancer stem cells to chemotherapy

Tumor recurrence is often attributed to cancer stem cells (CSCs). We previously demonstrated that down-regulation of Pregnane X Receptor (PXR) decreases the chemoresistance of CSCs and prevents colorectal cancer recurrence. Currently, no PXR inhibitor is usable in clinic. Here, we identify miR-148a as a targetable element upstream of PXR signaling in CSCs, which when over-expressed decreases PXR expression and impairs tumor relapse after chemotherapy in mouse tumor xenografts. We then develop a fluorescent reporter screen for miR-148a activators and identify the anti-helminthic drug niclosamide as an inducer of miR-148a expression. Consequently, niclosamide decreased PXR expression and CSC numbers in colorectal cancer patient-derived cell lines and synergized with chemotherapeutic agents to prevent CSC chemoresistance and tumor recurrence in vivo. Our study suggests that endogenous miRNA inducers is a viable strategy to down-regulate PXR and illuminates niclosamide as a neoadjuvant repurposing strategy to prevent tumor relapse in colon cancer.

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miR-148a expression is decreased in colon cancer stem cells

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Forced expression of miR-148a inhibits colon cancer stem cell chemoresistance

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High-content screening identified niclosamide as a potent miR-148a inducer

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Niclosamide induces miR-148a expression, inhibits PXR expression in CSCs and prevents tumor

Regulation of PXR Function by Coactivator and Corepressor Proteins: Ligand Binding Is Just the Beginning

The pregnane X receptor (PXR, NR1I2) is a nuclear receptor which exerts its regulatory function by heterodimerization with the retinoid-X-receptor α (RXRα, NR2B1) and binding to the promoter and enhancer regions of diverse target genes. PXR is involved in the regulation of drug metabolism and excretion, metabolic and immunological functions and cancer pathogenesis. PXR activity is strongly regulated by the association with coactivator and corepressor proteins. Coactivator proteins exhibit histone acetyltransferase or histone methyltransferase activity or associate with proteins having one of these activities, thus promoting chromatin decondensation and activation of the gene expression. On the contrary, corepressor proteins promote histone deacetylation and therefore favor chromatin condensation and repression of the gene expression. Several studies pointed to clear cell- and ligand-specific differences in the activation of PXR. In this article, we will review the critical role of coactivator and corepressor proteins as molecular determinants of the specificity of PXR-mediated effects. As already known for other nuclear receptors, understanding the complex mechanism of PXR activation in each cell type and under particular physiological and pathophysiological conditions may lead to the development of selective modulators with therapeutic potential.

The implications of ABCC3 in cancer drug resistance: can we use it as a therapeutic target?

Drug resistance is one of the main causes of chemotherapy failure. Although several factors are involved in cancer drug resistant, the exporter pumps overexpression that mediates the drugs flow to outside the cells and reduces both the drugs intracellular concentration and effectiveness, has been one of the most important challenges. Overexpression of ABCC3, a member of the ABCC subfamily, has been strongly associated to the resistance to multiple drugs. ABCC3 has been found highly expressed in different types of cancers and is associated with poor prognosis and resistance to treatments. In this review, we summarize the molecular mechanisms involved in cancer drug resistance and discuss the current knowledge about the structure, function and role of ABCC3 in drug resistance, as well as, the expression status of ABCC3 in different types of cancer. We also provide evidences that place ABCC3 as a potential therapeutic target for improving the cancer treatment by focusing on the need of developing more effective cancer therapies to target ABCC3 in translational researches.

Phase-1 bioactivation mechanisms of aflatoxin through AhR, CAR and PXR nuclear receptors and the interactions with Nigella sativa seeds and thymoquinone in broilers

Aflatoxins (AFs) are metabolised in two main phases in the liver. Cytochrome p450 enzyme (CYP) 1A1 and CYP2A6 are expressed through AhR, CAR and PXR nuclear receptors in phase-1 biotransformation of AFs. This study is the first to examine phase-1 biotransformation mechanisms of AF and the activity of Nigella sativa seed (NS) and its active ingredient thymoquinone (TQ) on these enzymes and receptors at the molecular level in broilers. Six groups of one day old broiler chicken (20 animals per group) were fed either control feed or a diet containing Aspergillus parasiticus NRRL 2999 culture material (total AFs 2 mg/kg), TQ (300 mg/kg), and NS (5%), either alone or as AF + TQ and AF + NS. Randomly selected from each group, 10 chicks were necropsied, and the livers were removed. Histopathological examination and serum biochemistry results revealed that AF caused hydropic and fatty degenerations, periportal inflammatory infiltrations, acinar arrangement, and biliary duct proliferation in livers and a significant increase at AST, ALT, ALP and GGT levels while significant decreases at serum cholesterol and total protein levels. These aflatoxicosis lesions and deteriorations in biochemistry levels were significantly ameliorated by NS or TQ (p < 0.05). AF was immunohistochemically found to increase strongly the nuclear receptors of AhR, PXR, CAR, and the enzyme activity of CYP1A1 and CYP2A6 responsible for its metabolism, leading to the emergence of toxic effects. Addition of TQ or NS to AF-containing diets improved the negative effects of AF on these receptors and enzymes significantly (p < 0.05). It was concluded that TQ and NS successfully alleviated liver injury by inhibiting or reducing the bioactivation of AF through phase-1 nuclear receptors and CYP-450 enzymes modulation.

Regulation of CAR and PXR Expression in Health and Disease

Pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3) are members of the nuclear receptor superfamily that mainly act as ligand-activated transcription factors. Their functions have long been associated with the regulation of drug metabolism and disposition, and it is now well established that they are implicated in physiological and pathological conditions. Considerable efforts have been made to understand the regulation of their activity by their cognate ligand; however, additional regulatory mechanisms, among which the regulation of their expression, modulate their pleiotropic effects. This review summarizes the current knowledge on CAR and PXR expression during development and adult life; tissue distribution; spatial, temporal, and metabolic regulations; as well as in pathological situations, including chronic diseases and cancers. The expression of CAR and PXR is modulated by complex regulatory mechanisms that involve the interplay of transcription factors and also post-transcriptional and epigenetic modifications. Moreover, many environmental stimuli affect CAR and PXR expression through mechanisms that have not been elucidated.

Xiaoaiping injection enhances paclitaxel efficacy in ovarian cancer via pregnane X receptor and its downstream molecules

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaoaiping injection, a traditional Chinese medical injection extracted from root of Marsdenia tenacissima (Roxb.) Moon, has been exclusively used on curing malignant tumor in China and as adjuvant therapeutic agent for chemotherapeutics, including paclitaxel.

AIM OF THE STUDY

The goal of this study was to investigate the synergistic inhibitory efficacy of Xiaoaiping injection and paclitaxel on ovarian cancer. The mechanism may be associated with nuclear receptor pregnane X receptor (PXR) regulating its downstream molecules.

MATERIALS AND METHODS

In vitro, MTT assay, flow cytometry and Hoechst dyeing were used to evaluate the SK-OV-3 cell proliferation, apoptosis and cell cycle respectively. The mRNA and protein expression of PXR and its downstream CYP450 enzymes, transporters and Bcl-2 families were measured by qRT-PCR and Western blot. Rhodamine 123 efflux experiment was conducted to detect the P-gp efflux ability. PXR plasmid and PXR siRNA were transiently transfected into SK-OV-3 cells respectively to establish PXR-overexpressed or PXR-interfered cells. In vivo, xenograft tumor mice model was established by SK-OV-3 cells to estimate the antitumor effect of Xiaoaiping injection combined with paclitaxel. The expressions of PXR and its downstream molecules in tumor tissues were determined to further clarify the potential mechanism.

RESULTS

Xiaoaiping injection significantly enhanced the anti-proliferation, pro-apoptosis effect of paclitaxel on SK-OV-3 cells. The synergetic effect was displayed by Xiaoaiping injection inhibiting paclitaxel-induced PXR and CAR expression, which subsequently inhibited CYP450 enzymes CYP2C8 and CYP3A4, transporter P-gp and anti-apoptotic proteins Bcl-2 and Bcl-xl in SK-OV-3 cells. In PXR-overexpressed cells, Xiaoaiping injection down-regulated the expression of PXR and its downstream molecules. The result of xenograft tumor model showed that Xiaoaiping injection combined with paclitaxel enhanced anti-tumor effect on ovarian cancer in vivo.

CONCLUSIONS

Xiaoaiping injection enhances anti-tumor effect of paclitaxel by inhibiting cell proliferation, inducing apoptosis process. The mechanism may be associated with Xiaoaiping injection inhibiting PXR and its downstream metabolic enzymes CYP2C8, CYP3A4, transporter P-gp and anti-apoptosis protein Bcl-2.

ZFP36 Binds With PRC1 to Inhibit Tumor Growth and Increase 5-Fu Chemosensitivity of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth common cause of tumor-related death worldwide. ZFP36, a RNA-binding protein, decreases in many cancers and its role in HCC remains unclear. This study aimed to investigate the underlying mechanisms by which ZFP36 inhibited HCC progression and increased fluorouracil (5-Fu) sensitivity. We found that ZFP36 was downregulated and PRC1 was upregulated in HCC tissues compared with adjacent non-tumor tissues. In vitro investigation presented that ZFP36 acted as a tumor suppressor, while overexpression of PRC1 increased cell proliferation, colony formation and invasion. Further investigations demonstrated that overexpression of ZFP36 inhibited tumor growth and promoted 5-Fu sensitivity in xenograft tumor mice model, which could be reversed when PRC1 overexpressed simultaneously. Luciferase reporter assays and Ribonucleoprotein immunoprecipitation analysis indicated that ZFP36 could bind to adenylate uridylate-rich elements located in PRC1 mRNA 3′UTR to downregulate PRC1 expression. Taken together, our findings identified that ZFP36 regulated PRC1 to exert anti-tumor effect, which suggested a potential therapeutic strategy for treating HCC by exploiting ZFP36/PRC1 axis.

PXR: a center of transcriptional regulation in cancer

Pregnane X receptor (PXR, NR1I2) is a prototypical member of the nuclear receptor superfamily. PXR can be activated by both endobiotics and xenobiotics. As a key xenobiotic receptor, the cellular function of PXR is mostly exerted by its binding to the regulatory gene sequences in a ligand-dependent manner. Classical downstream target genes of PXR participate in xenobiotic responses, such as detoxification, metabolism and inflammation. Emerging evidence also implicates PXR signaling in the processes of apoptosis, cell cycle arrest, proliferation, angiogenesis and oxidative stress, which are closely related to cancer. Here, we discussed, in addition to the characterization of PXR per se, the biological function and regulatory mechanism of PXR signaling in cancer, and its potential for the targeted prevention and therapeutics.

Inflammatory pathway interactions and cancer multidrug resistance regulation

Multidrug resistances against chemotherapeutics are among the major challenges related to cancer treatment. Recent studies have demonstrated that different conditions may tune the expression and activity of MDR transporters. For instance, inflammation occurs through a complex cytological process and chemical reactions in the most tumor microenvironment; it can play a critical role in cancer development and is capable of altering the expression and function of MDR transporters. Cytokines, interleukins, and prostaglandins are potent inflammatory mediators that can modulate the expression of MDRs at transcriptional and post-transcriptional levels in the most human cancer cells and tissues and potentially contribute to balance bioavailability of chemotherapeutic agents. Since cancer cases are usually accompanied by inflammatory responses, glucocorticoids and NSAIDs are the primary useful combination chemotherapies in a variety of cancer treatment protocols. In addition to the anti-inflammatory activities of these agents, they exert diverse modulatory effects on MDR-mediated drug resistance via specific mechanisms. Several factors, including cell and MDR-protein types, pharmacokinetics, and pharmacogenetics, mainly influence the regulatory mechanisms. Uncovering the networks between inflammation and multidrug resistance will be clinically helpful in the treatment of malignant cancers and decreasing the cancer mortality rates.

Screening of molecular targets and construction of a ceRNA network for oxaliplatin resistance in colorectal cancer

Oxaliplatin resistance reduces the efficacy of chemotherapy for colorectal cancer (CRC). This study aimed to screen molecular targets of oxaliplatin resistance in CRC to construct a ceRNA network. The differentially expressed mRNA and lncRNA between the oxaliplatin-resistant and oxaliplatin-sensitive colon cancer cell lines was determined using RNA sequencing data (no. GSE42387) from the NCBI GEO database. Gene Ontology BP (biological process) and KEGG pathway enrichment analyses were used to analyze the function and pathway enrichment of the differentially expressed mRNA and lncRNA. The lnCeDB and starBase v2.0 were used to predict miRNA, and Cytoscape software was used to build a ceRNA network. The top 5 mRNA, miRNAs, and lncRNAs with high degrees of connectivity in the ceRNA network were validated by qPCR. TCGA colon cancer clinical data was used to perform a survival analysis of patients with differential mRNA and lncRNA expression. Between the two groups, 2515 mRNAs and 23 lncRNAs were differentially expressed. We constructed a ceRNA network containing 503 lncRNA–miRNA–mRNA regulatory pairs, 210 lncRNA–miRNA pairs, 382 miRNA–mRNA pairs, and 212 mRNA co-expression pairs. The differentially expressed lncRNA, miRNA and mRNA were verified by qPCR. One lncRNA (HOTAIR) and 14 mRNAs significantly correlated with patient prognosis. The discovery of differentially expressed genes and the construction of ceRNA networks will provide important resources for the search for therapeutic targets of oxaliplatin resistance. Moreover, this resource will aid the discovery of the mechanisms behind this type of drug resistance.

Oxaliplatin resistance reduces the efficacy of chemotherapy for colorectal cancer (CRC).

Clinical Significance of Organic Anion Transporting Polypeptide Gene Expression in High-Grade Serous Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) is considered the most deadly and frequently occurring type of ovarian cancer and is associated with various molecular compositions and growth patterns. Evaluating the mRNA expression pattern of the organic anion transporters (OATPs) encoded by SLCO genes may allow for improved stratification of HGSOC patients for targeted invention. The expression of SLCO mRNA and genes coding for putative functionally related ABC-efflux pumps, enzymes, pregnane-X-receptor, ESR1 and ESR2 (coding for estrogen receptors ERα and ERß) and HER-2 were assessed using RT-qPCR. The expression levels were assessed in a cohort of 135 HGSOC patients to elucidate the independent impact of the expression pattern on the overall survival (OS). For identification of putative regulatory networks, Graphical Gaussian Models were constructed from the expression data with a tuning parameter K varying between meaningful borders (Pils et al., 2012; Auer et al., 2015, 2017; Kurman and Shih Ie, 2016; Karam et al., 2017; Labidi-Galy et al., 2017; Salomon-Perzynski et al., 2017; Sukhbaatar et al., 2017). The final value used (K = 4) was determined by maximizing the proportion of explained variation of the corresponding LASSO Cox regression model for OS. The following two networks of directly correlated genes were identified: (i) SLCO2B1 with ABCC3 implicated in estrogen homeostasis; and (ii) two ABC-efflux pumps in the immune regulation (ABCB2/ABCB3) with ABCC3 and HER-2. Combining LASSO Cox regression and univariate Cox regression analyses, SLCO5A1 coding for OATP5A1, an estrogen metabolite transporter located in the cytoplasm and plasma membranes of ovarian cancer cells, was identified as significant and independent prognostic factor for OS (HR = 0.68, CI 0.49-0.93; p = 0.031). Furthermore, results indicated the benefits of patients with high expression by adding 5.1% to the 12.8% of the proportion of explained variation (PEV) for clinicopathological parameters known for prognostic significance (FIGO stage, age and residual tumor after debulking). Additionally, overlap with previously described signatures that indicated a more favorable prognosis for ovarian cancer patients was shown for SLCO5A1, the network ABCB2/ABCB3/ABCC4/HER2 as well as ESR1. Furthermore, expression of SLCO2A1 and PGDH, which are important for PGE₂ degradation, was associated with the non-miliary peritoneal tumor spreading. In conclusion, the present findings suggested that SLCOs and the related molecules identified as potential biomarkers in HGSOC may be useful for the development of novel therapeutic strategies.