Synergistic growth inhibition of human hepatocellular carcinoma cells by acyclic retinoid and GW4064, a farnesoid X receptor ligand

GW4064 inhibits migration and invasion through cathepsin B and MMP2 downregulation in human bladder cancer

The ability of bladder cancer to invade and metastasize often leads to poor prognosis in bladder cancer patients. The aim of this study was to evaluate the effect of the farnesoid X receptor (FXR) agonist GW4064 on the migration and invasion of human bladder cancer cells. Long-term exposure to GW4064 decreased the colony formation of RT4 and T24 cells. The wound healing migration assay revealed an inhibitory effect of GW4064 on both of these bladder cancer cell lines. In addition, integrin β3 expression and myosin light chain phosphorylation were decreased after GW4064 treatment. Immunocytochemistry showed an increase in E-cadherin and a decrease in β-catenin in the cell membrane of bladder cancer cells. Total protein expression and membrane fractionation assays also indicated upregulation of E-cadherin and downregulation of β-catenin. Moreover, GW4064 reduced the invasion of muscle-invasive T24 cells. The GW4064-decreased migration and invasion were reversed by the proteasome inhibitor MG132 and the lysosome inhibitor NH4Cl. Furthermore, the GW4064-induced inhibition of matrix metalloproteinase-2 (MMP2) and cathepsin B expression was reversed by NH4Cl. Xenograft animal studies revealed that GW4064 declined MMP2, cathepsin B and lung metastasis of bladder cancer. In conclusion, GW4064 decreases the migration and invasion of human bladder cancer cells, which may provide a new therapeutic strategy for the treatment of human bladder cancer.

Targeting Farnesoid X Receptor in Tumor and the Tumor Microenvironment: Implication for Therapy

The farnesoid-X receptor (FXR), a member of the nuclear hormone receptor superfamily, can be activated by bile acids (BAs). BAs binding to FXR activates BA signaling which is important for maintaining BA homeostasis. FXR is differentially expressed in human organs and exists in immune cells. The dysregulation of FXR is associated with a wide range of diseases including metabolic disorders, inflammatory diseases, immune disorders, and malignant neoplasm. Recent studies have demonstrated that FXR influences tumor cell progression and development through regulating oncogenic and tumor-suppressive pathways, and, moreover, it affects the tumor microenvironment (TME) by modulating TME components. These characteristics provide a new perspective on the FXR-targeted therapeutic strategy in cancer. In this review, we have summarized the recent research data on the functions of FXR in solid tumors and its influence on the TME, and discussed the mechanisms underlying the distinct function of FXR in various types of tumors. Additionally, the impacts on the TME by other BA receptors such as takeda G protein-coupled receptor 5 (TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and muscarinic receptors (CHRM2 and CHRM3), have been depicted. Finally, the effects of FXR agonists/antagonists in a combination therapy with PD1/PD-L1 immune checkpoint inhibitors and other anti-cancer drugs have been addressed.

FXR agonists for colorectal and liver cancers, as a stand-alone or in combination therapy

Farnesoid X receptor (FXR, NR1H4) is generally considered as a tumor suppressor of colorectal and liver cancers. The interaction between FXR, bile acids (BAs) and gut microbiota is closely associated with an increased risk of colorectal and liver cancers. Increasing evidence shows that FXR agonists may be potential therapeutic agents for colorectal and liver cancers. However, FXR agonists alone do not produce the desired results due to the complicated pathogenesis and single therapeutic mechanism, which suggests that effective treatments will require a multimodal approach. Based on the principle of improvingefficacy andreducingside effects, combination therapy is currently receiving considerable attention. In this review, colorectal and liver cancers are grouped together to discuss the effects of FXR agonists alone or in combination for combating the two cancers. We hope that this review will provide a theoretical basis for the clinical application of novel FXR agonists or combination with FXR agonists against colorectal and liver cancers.

Activation of FXR and inhibition of EZH2 synergistically inhibit colorectal cancer through cooperatively accelerating FXR nuclear location and upregulating CDX2 expression

Our previous study indicated that colon cancer cells varied in sensitivity to pharmacological farnesoid X receptor (FXR) activation. Herein, we explore the regulatory mechanism of FXR in colorectal cancer (CRC) development and aim to design effective strategies of combined treatment based on the regulatory axis. We found that the expression of FXR was negatively correlated with enhancer of zeste homolog 2 (EZH2) in colon cancer tissues. EZH2 transcriptionally suppressed FXR via H3K27me3. The combination of FXR agonist OCA plus EZH2 inhibitor GSK126 acted in a synergistic manner across four colon cancer cells, efficiently inhibiting clonogenic growth and invasion in vitro, retarding tumor growth in vivo, preventing the G0/G1 to S phase transition, and inducing caspase-dependent apoptosis. Benign control cells FHC were growth-arrested without apoptosis induction, but retained long-term proliferation and invasion capacity. Mechanistically, the drug combination dramatically accelerated FXR nuclear location and cooperatively upregulated caudal-related homeobox transcription factor 2 (CDX2) expression. The depletion of CDX2 antagonized the synergistic effects of the drug combination on tumor inhibition. In conclusion, our study demonstrated histone modification-mediated FXR silencing by EZH2 in colorectal tumorigenesis, which offers useful evidence for the clinical use of FXR agonists combined with EZH2 inhibitors in combating CRC.

Pleiotropic roles of FXR in liver and colorectal cancers

Nuclear receptor farnesoid X receptor (FXR) is generally considered a cell protector of enterohepatic tissues and a suppressor of liver cancer and colorectal carcinoma (CRC). Loss or reduction of FXR expression occurs during carcinogenesis, and the FXR level is inversely associated with the aggressive behaviors of the malignancy. Global deletion of FXR and tissue-specific deletion of FXR display distinct effects on tumorigenesis. Epigenetic silencing and inflammatory context are two main contributors to impaired FXR expression and activity. FXR exerts its antitumorigenic function via the following mechanisms: 1) FXR regulates multiple metabolic processes, notably bile acid homeostasis; 2) FXR antagonizes hepatic and enteric inflammation; 3) FXR impedes aberrant activation of some cancer-related pathways; and 4) FXR downregulates a number of oncogenes while upregulating some tumor suppressor genes. Restoring FXR functions via its agonists provides a therapeutic approach for patients with liver cancer and CRC. However, an in-depth understanding of the species-specific pharmacological effects is a prerequisite for assessing the clinical safety and efficacy of FXR agonists in human cancer treatment.

The Orphan Nuclear Receptor Gene NR0B2 Is a Favorite Prognosis Factor Modulated by Multiple Cellular Signal Pathways in Human Liver Cancers

BACKGROUND

Liver cancer is a leading cause of cancer death worldwide, and novel prognostic factor is needed for early detection and therapeutic responsiveness monitoring. The orphan nuclear receptor NR0B2 was reported to suppress liver cancer development in a mouse model, and its expression levels were reduced in liver cancer tissues and cell lines due to hypermethylation within its promoter region. However, it is not clear if NR0B2 expression is associated with cancer survival or disease progression and how NR0B2 gene expression is regulated at the molecular level.

METHODS

Multiple cancer databases were utilized to explore NR0B2 gene expression profiles crossing a variety of human cancers, including liver cancers, on several publicly assessable bioinformatics platforms. NR0B2 gene expression with or without kinase inhibitor treatment was analyzed using the qPCR technique, and NR0B2 protein expression was assessed in western blot assays. Two human hepatocellular carcinoma cell lines HepG2 and Huh7, were used in these experiments. NR0B2 gene activation was evaluated using NR0B2 promoter-driven luciferase reporter assays.

RESULTS

NR0B2 gene is predominantly expressed in liver tissue crossing human major organs or tissues, but it is significantly downregulated in liver cancers. NR0B2 expression is mostly downregulated in most common cancers but also upregulated in a few intestinal cancers. NR0B2 gene expression significantly correlated with patient overall survival status in multiple human malignancies, including lung, kidney, breast, urinary bladder, thyroid, colon, and head-neck cancers, as well as liposarcoma and B-cell lymphoma. In liver cancer patients, higher NR0B2 expression is associated with favorite relapse-free and progression-free survival, especially in Asian male patients with viral infection history. In addition, NR0B2 expression negatively correlated with immune infiltration and PIK3CA and PIK3CG gene expression in liver cancer tissues. In HepG2 and Huh7 cells, NR0B2 expression at the transcription level was drastically reduced after MAPK inhibition but was significantly enhanced after PI3K inhibition.

CONCLUSION

NR0B2 gene expression is altered mainly in most human malignancies and significantly reduced in liver cancers. NR0B2 is a prognosis factor for patient survival in liver cancers. MAPK and PI3K oppositely modulate NR0B2 expression, and NR0B2 gene upregulation might serve as a therapeutic responsiveness factor in anti-PI3K therapy for liver cancer.

GW4064 enhances the chemosensitivity of colorectal cancer to oxaliplatin by inducing pyroptosis

Repeated and long-term oxaliplatin therapy leads to drug resistance and severe adverse events, which limit its clinical use. These difficulties highlight the importance of identifying potent and specific drug combinations to enhance the antitumor effects of oxaliplatin. The farnesoid X receptor (FXR) deficiency in colorectal cancer (CRC) suggests that restoring FXR function might be a promising strategy for CRC treatment. A drug combination study showed that the GW4064 acted synergistically with oxaliplatin in colon cancer cells. The combination of oxaliplatin plus GW4064 inhibited cell growth and colony formation, induced apoptosis and pyroptosis in vitro, and slowed tumor growth in vivo. Mechanistically, GW4064 enhanced the chemosensitivity of cells to oxaliplatin by inducing BAX/caspase-3/GSDME-mediated pyroptosis. Furthermore, the combination of oxaliplatin and GW4064 synergistically inhibited STAT3 signaling by restoring SHP expression. Our study revealed that GW4064 could enhance the antitumor effects of oxaliplatin against CRC, which provides a novel therapeutic strategy based on a combinational approach for CRC treatment.

Farnesoid X receptor promotes renal ischaemia-reperfusion injury by inducing tubular epithelial cell apoptosis

Purpose

We investigated the role of farnesoid X receptor (FXR), a ligand‐dependent transcription factor, in renal ischaemia‐reperfusion (I/R) injury.

Materials and Methods

We performed unilateral renal I/R model in FXR knockout (Fxr^−/−) and wild‐type (WT) mice in vivo and a hypoxia‐reoxygenation (H/R) model in vitro. The pathways by which FXR induces apoptosis were detected using a proteome profiler array. The effects of FXR on apoptosis were evaluated using immunoblotting, TUNEL assays and flow cytometry.

Results

Compared with WT mice, Fxr^−/− mice showed improved renal function and reduced tubular injury scores and apoptosis. Consistent with the in vivo results, the silencing of FXR decreased the number of apoptotic HK‐2 cells after H/R, while FXR overexpression aggravated apoptosis. Notably, bone marrow transplantation (BMT) and immunohistochemistry experiments revealed the involvement of FXR in the tubular epithelium rather than in inflammatory cells. Furthermore, in vivo and in vitro studies demonstrated that FXR deficiency increased phosphorylated Bcl‐2 agonist of cell death (p‐Bad) expression levels and the ratio of Bcl‐2/Bcl‐xL to Bax expression in the kidney. Treatment with wortmannin, which reduced p‐Bad expression, inhibited the effects of FXR deficiency and eliminated the tolerance of Fxr^−/− mouse kidneys to I/R injury.

Conclusions

These results established the pivotal importance of FXR inactivation in tubular epithelial cells after I/R injury. FXR may promote the apoptosis of renal tubular epithelial cells by inhibiting PI3k/Akt‐mediated Bad phosphorylation to cause renal I/R damage.

Novel FXR agonist nelumal A suppresses colitis and inflammation-related colorectal carcinogenesis

FXR is a member of the nuclear receptor superfamily and bile acids are endogenous ligands of FXR. FXR activation has recently been reported to inhibit intestinal inflammation and tumour development. This study aimed to investigate whether the novel FXR agonist nelumal A, the active compound of the plant Ligularia nelumbifolia, can prevent colitis and colorectal carcinogenesis. In a mouse colitis model, dextran sodium sulfate-induced colonic mucosal ulcer and the inflammation grade in the colon significantly reduced in mice fed diets containing nelumal A. In an azoxymethane/dextran sodium sulfate-induced mouse inflammation-related colorectal carcinogenesis model, the mice showed decreased incidence of colonic mucosal ulcers and adenocarcinomas in nelumal A-treated group. Administration of nelumal A also induced tight junctions, antioxidant enzymes, and FXR target gene expression in the intestine, while it decreased the gene expression of bile acid synthesis in the liver. These findings suggest that nelumal A effectively attenuates colonic inflammation and suppresses colitis-related carcinogenesis, presumably through reduction of bile acid synthesis and oxidative damage. This agent may be potentially useful for treatment of inflammatory bowel diseases as well as their related colorectal cancer chemoprevention.

Synergistic tumor inhibition of colon cancer cells by nitazoxanide and obeticholic acid, a farnesoid X receptor ligand

The tumor-suppressive role of Farnesoid X receptor (FXR) in colorectal tumorigenesis supports restoring FXR expression as a novel therapeutic strategy. However, the complicated signaling network and tumor heterogeneity hinder the effectiveness of FXR agonists in the clinical setting. These difficulties highlight the importance of identifying drug combinations with potency and specificity to enhance the antitumor effects of FXR agonists. In this study, we found that the β-catenin level affected the antitumor effects of the FXR agonist OCA on colon cancer cells. Mechanistic studies identified a novel FXR/β-catenin complex in colon cancer cells. Furthermore, the depletion of β-catenin expedited FXR nuclear localization and enhanced its occupancy of the SHP promoter and thereby sensitized colon cancer cells to OCA. Furthermore, we utilized a drug combination study and identified that the antiparasitic drug nitazoxanide (NTZ) abrogated β-catenin expression and acted synergistically with OCA in colon cancer cells. The combination of OCA plus NTZ exerts synergistic tumor inhibition in CRC both in vitro and in vivo by cooperatively upregulating SHP expression. In conclusion, our study offers useful evidence for the clinical use of FXR agonists combined with β-catenin inhibitors in combating CRC.

Emerging targets and potential therapeutic agents in non-alcoholic fatty liver disease treatment

Nonalcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in the world, which is characterized by liver fat accumulation unrelated to excessive drinking. Indeed, it attracts growing attention and becomes a global health problem. Due to the complexity of the NAFLD pathogenic mechanism, no related drugs were approved by Food and Drug Administration (FDA) till now. However, it is encouraging that a series of candidate drugs have entered the clinical trial stage with expectation to treat NAFLD. In this review, we summarized the main pathways and pathogenic mechanisms of NAFLD, as well as introduced the main potential therapeutic targets and the corresponding compounds involved in metabolism, inflammation and fibrosis. Furthermore, we also discuss the progress of these compounds, such as drug design and optimization, the choice of pharmacological properties and druglikeness, and the analysis of structure-activity relationship. This review offers a medium on future drug design and development, to be beneficial to relevant studies.

Chronic activation of FXR-induced liver growth with tissue-specific targeting Cyclin D1

The nuclear receptor (FXR) plays essential roles in maintaining bile acid and lipid homeostasis by regulating diverse target genes. And its agonists were promising agents for treating various liver diseases. Nevertheless, the potential side effect of chronic FXR activation by specific agonists is not fully understood. In this study, we investigated the mechanism of FXR agonist WAY-362450 induced liver enlargement during treating liver diseases. We demonstrated that chronic ingestion of WAY-362450 induced liver hypertrophy instead of hyperplasia in mouse. Global transcriptional pattern was also examined in mouse livers after treatment with WAY-362450 by RNA-seq assay. Through GO and KEGG enrichment analyses, we demonstrated that the expression of Cyclin D1 (Ccnd1) among the cell cycle-regulating genes was notably increased in WAY-362450-treated mouse liver. Activation of FXR-induced Ccnd1 expression in hepatocyte in a time-dependent manner in vivo and in vitro. Through bioinformatics analysis and ChIP assay, we identified FXR as a direct transcriptional activator of Ccnd1 through binding to a potential enhancer, which was specifically active in livers. We also found active histone acetylation was essential for Ccnd1 induction by FXR. Thus, our study indicated that activation of FXR-induced harmless liver hypertrophy with spatiotemporal modulation of Ccnd1. With a better understanding of the mechanism of tissue-specific gene regulation by FXR, it is beneficial for development and appropriate application of its specific agonist in preventing hepatic diseases.

Structural insights into the heterodimeric complex of the nuclear receptors FXR and RXR

Farnesoid X receptor (FXR) is a member of the family of ligand-activated nuclear receptors. FXR plays critical roles in maintaining many metabolic pathways, including bile acid regulation and glucose and lipid homeostasis, and forms a heterodimeric complex with the retinoid X receptor (RXR). Despite the important roles of the FXR/RXR heterodimerization in human physiology, the molecular basis underlying the FXR/RXR interaction is still uncertain in the absence of a complex structure. Here, we report the heterodimeric structure of FXR and RXR in the presence of an FXR agonist (WAY-362450), RXR agonist (9-cis-retinoic acid), and a peptide derived from a steroid receptor coactivator (SRC2), revealing both unique and conserved modes for FXR heterodimerization. We found that the dimerization with RXR induced allosteric conformational changes on the coactivator-binding site of FXR. These changes enhanced the transcriptional activity of FXR by promoting the coactivator binding, thus suggesting a structural basis for the functional permissiveness of the FXR/RXR heterodimer complex. Furthermore, sequence analyses together with functional mutagenesis studies indicated that the helix H10 largely responsible for the dimerization is highly conserved and also critical for the FXR transcriptional activity. Our findings highlight the important roles of RXR heterodimerization in the nuclear receptor signaling, providing a potential framework to develop pharmaceutical agents in treating FXR/RXR-related diseases.

C-terminal truncated hepatitis B virus X protein promotes hepatocellular carcinogenesis through induction of cancer and stem cell-like properties

Tumor relapse after chemotherapy typifies hepatocellular carcinoma (HCC) and is believed to be attributable to residual cancer stem cells (CSCs) that survive initial treatment. Chronic infection with hepatitis B virus (HBV) has long been linked to the development of HCC. Upon infection, random HBV genome integration can lead to truncation of hepatitis B virus X (HBx) protein at the C-terminus. The resulting C-terminal-truncated HBx (HBx-ΔC) was previously shown to confer enhanced invasiveness and diminished apoptotic response in HCC cells. Here, we found HBx-ΔC to promote the appearance of a CD133 liver CSC subset and confer cancer and stem cell-like features in HCC. HBx-ΔC was exclusively detected in HCC cell lines that were raised from patients presented with a HBV background with concomitant CD133 expression. Stable overexpression of the naturally occurring HBx-ΔC mutants, HBx-Δ14 or HBx-Δ35, in HCC cells Huh7 and immortalized normal liver cells MIHA resulted in a significant increase in the cells ability to self-renew, resist chemotherapy and targeted therapy, migrate and induce angiogenesis. MIHA cells with the mutants stably overexpressed also resulted in the induction of CD133, mediated through STAT3 activation. RNA sequencing profiling of MIHA cells with or without HBx-ΔC mutants stably overexpressed identified altered FXR activation. This, together with rescue experiments using a selective FXR inhibitor suggested that C-terminal truncated HBx can mediate cancer stemness via FXR activation. Collectively, we find C-terminal truncated HBx mutants to confer cancer and stem cell-like features in vitro and to play an important role in driving tumor relapse in HCC.

FXR agonists enhance the sensitivity of biliary tract cancer cells to cisplatin via SHP dependent inhibition of Bcl-xL expression

Chemoresistance is common in patients with biliary tract cancer (BTC) including gallbladder cancer (GBC) and cholangiocarcinoma (CC). Therefore, it is necessary to identify effective chemotherapeutic agents for BTC. In the present study, we for the first time tested the effect of farnesoid X receptor (FXR) agonists GW4064 and CDCA (chenodeoxycholic acid) in combination with cisplatin (CDDP) on increasing the chemosensitivity in BTC. Our results show that co-treatment of CDDP with FXR agonists remarkably enhance chemosensitivity of BTC cells. Mechanistically, we found that activation of FXR induced expression of small heterodimer partner (SHP), which in turn inhibited signal transducer and activator of transcription 3 (STAT3) phosphorylation and resulted in down-regulation of Bcl-xL expression in BTC cells, leading to increased susceptibility to CDDP. Moreover, the experiments on tumor-bearing mice showed that GW4064/CDDP co-treatment inhibited the tumor growth in vivo by up-regulating SHP expression and down-regulating STAT3 phosphorylation. These results suggest CDDP in combination with FXR agonists could be a potential new therapeutic strategy for BTC.

Nuclear bile acid signaling through the farnesoid X receptor

Bile acids (BAs) are amphipathic molecules produced from cholesterol by the liver. Expelled from the gallbladder upon meal ingestion, BAs serve as fat solubilizers in the intestine. BAs are reabsorbed in the ileum and return via the portal vein to the liver where, together with nutrients, they provide signals to coordinate metabolic responses. BAs act on energy and metabolic homeostasis through the activation of membrane and nuclear receptors, among which the nuclear receptor farnesoid X receptor (FXR) is an important regulator of several metabolic pathways. Highly expressed in the liver and the small intestine, FXR contributes to BA effects on metabolism, inflammation and cell cycle control. The pharmacological modulation of its activity has emerged as a potential therapeutic strategy for liver and metabolic diseases. This review highlights recent advances regarding the mechanisms by which the BA sensor FXR contributes to global signaling effects of BAs, and how FXR activity may be regulated by nutrient-sensitive signaling pathways.

Metformin suppresses diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BL/KsJ-+Leprdb/+Leprdb mice

Obesity and related metabolic disorders, such as diabetes mellitus, raise the risk of liver carcinogenesis. Metformin, which is widely used in the treatment of diabetes, ameliorates insulin sensitivity. Metformin is also thought to have antineoplastic activities and to reduce cancer risk. The present study examined the preventive effect of metformin on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BL/KsJ-+Lepr^db/+Lepr^db (db/db) obese and diabetic mice. The mice were given a single injection of DEN at 2 weeks of age and subsequently received drinking water containing metformin for 20 weeks. Metformin administration significantly reduced the multiplicity of hepatic premalignant lesions and inhibited liver cell neoplasms. Metformin also markedly decreased serum levels of insulin and reduced insulin resistance, and inhibited phosphorylation of Akt, mammalian target of rapamycin (mTOR), and p70S6 in the liver. Furthermore, serum levels of leptin were decreased, while those of adiponectin were increased by metformin. These findings suggest that metformin prevents liver tumorigenesis by ameliorating insulin sensitivity, inhibiting the activation of Akt/mTOR/p70S6 signaling, and improving adipokine imbalance. Therefore, metformin may be a potent candidate for chemoprevention of liver tumorigenesis in patients with obesity or diabetes.

Prevention of spontaneous hepatocarcinogenesis in farnesoid X receptor-null mice by intestinal-specific farnesoid X receptor reactivation

Farnesoid X receptor (FXR) is the master regulator of bile acid (BA) homeostasis because it controls BA synthesis, influx, efflux, and detoxification in the gut/liver axis. Deregulation of BA homeostasis has been linked to hepatocellular carcinoma (HCC), and spontaneous hepatocarcinogenesis has been observed in FXR-null mice. This dreaded liver neoplasm has been associated with both FXR gene deletion and BA-mediated metabolic abnormalities after inactivation of FXR transcriptional activity. In the present study, we addressed the hypothesis that intestinal selective FXR reactivation would be sufficient to restore the fibroblast growth factor 15 (FGF15)/cholesterol-7alpha-hydroxylase (Cyp7a1) enterohepatic axis and eventually provide protection against HCC. To this end, we generated FXR-null mice with re-expression of constitutively active FXR in enterocytes (FXR(-/-)iVP16FXR) and corresponding control mice (FXR(-/-)iVP16). In FXR-null mice, intestinal selective FXR reactivation normalized BA enterohepatic circulation along with up-regulation of intestinal FXR transcriptome and reduction of hepatic BA synthesis. At 16 months of age, intestinal FXR reactivation protected FXR-null mice from spontaneous HCC development that occurred in otherwise FXR-null mice. Activation of intestinal FXR conferred hepatoprotection by restoring hepatic homeostasis, limiting cellular proliferation through reduced cyclinD1 expression, decreasing hepatic inflammation and fibrosis (decreased signal transducer and activator of transcription 3 activation and curtailed collagen deposition).

CONCLUSION

Intestinal FXR is sufficient to restore BA homeostasis through the FGF15 axis and prevent progression of liver damage to HCC even in the absence of hepatic FXR. Intestinal-selective FXR modulators could stand as potential therapeutic intervention to prevent this devastating hepatic malignancy, even if carrying a somatic FXR mutation.

Farnesoid X receptor inhibits LNcaP cell proliferation via the upregulation of PTEN

Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. In the present study, the activation of the farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, was demonstrated to inhibit cell proliferation in LNcaP cells. Using clinical samples, mRNA and protein levels of FXR were found to be significantly decreased by quantitative PCR and western blot analysis in prostate cancer tissues. In vitro studies identified further that activation or overexpression of FXR suppressed prostate cancer cell proliferation as measured by BrdU incorporation assays. At the molecular level, the results further revealed that the expression of the tumor suppressor gene, PTEN, was upregulated by FXR activation. Therefore, the observations indicated that FXR functions as a tumor suppressor in prostate cancer, which may provide a novel method for molecular targeting cancer treatment.

MicroRNA-92 promotes gastric cancer cell proliferation and invasion through targeting FXR

MicroRNAs (miRNAs), a class of small noncoding RNAs, play critical roles in human carcinogenesis through downregulation of various target genes. In the present study, we found that miR-92 is upregulated in gastric cancer tissues compared with adjacent normal tissues. Interestingly, miR-92 expression is significantly associated with clinical characteristics of patients. Gain or loss-of-function in vitro experiments further show that miR-92 mimics significantly promoted, while its antisense oligos inhibited gastric cancer cell proliferation and invasion. Moreover, luciferase reporter assays and western blot indicated that farnesoid X receptor (FXR), is a direct target of miR-92. Therefore, our data suggest that upregulation of miR-92 may represent an important mechanism for the development of gastric cancer.

Pharmaceutical and nutraceutical approaches for preventing liver carcinogenesis: chemoprevention of hepatocellular carcinoma using acyclic retinoid and branched-chain amino acids

The poor prognosis for patients with hepatocellular carcinoma (HCC) is associated with its high rate of recurrence in the cirrhotic liver. Therefore, more effective strategies need to be urgently developed for the chemoprevention of this malignancy. The malfunction of retinoid X receptor α, a retinoid receptor, due to phosphorylation by Ras/mitogen-activated protein kinase is closely associated with liver carcinogenesis and may be a promising target for HCC chemoprevention. Acyclic retinoid (ACR), a synthetic retinoid, can prevent HCC development by inhibiting retinoid X receptor α phosphorylation and improve the prognosis for this malignancy. Supplementation with branched-chain amino acids (BCAA), which are used to improve protein malnutrition in patients with liver cirrhosis, can also reduce the risk of HCC in obese cirrhotic patients. In experimental studies, both ACR and BCAA exert suppressive effects on HCC development and the growth of HCC cells. In particular, combined treatment with ACR and BCAA cooperatively inhibits the growth of HCC cells. Furthermore, ACR and BCAA inhibit liver tumorigenesis associated with obesity and diabetes, both of which are critical risk factors for HCC development. These findings suggest that pharmaceutical and nutraceutical approaches using ACR and BCAA may be promising strategies for preventing HCC and improving the prognosis of this malignancy.

Synergistic growth inhibition by acyclic retinoid and phosphatidylinositol 3-kinase inhibitor in human hepatoma cells

BACKGROUND

A malfunction of RXRα due to phosphorylation is associated with liver carcinogenesis, and acyclic retinoid (ACR), which targets RXRα, can prevent the development of hepatocellular carcinoma (HCC). Activation of PI3K/Akt signaling plays a critical role in the proliferation and survival of HCC cells. The present study examined the possible combined effects of ACR and LY294002, a PI3K inhibitor, on the growth of human HCC cells.

METHODS

This study examined the effects of the combination of ACR plus LY294002 on the growth of HLF human HCC cells.

RESULTS

ACR and LY294002 preferentially inhibited the growth of HLF cells in comparison with Hc normal hepatocytes. The combination of 1 μM ACR and 5 μM LY294002, in which the concentrations used are less than the IC₅₀ values of these agents, synergistically inhibited the growth of HLF, Hep3B, and Huh7 human HCC cells. These agents when administered in combination acted cooperatively to induce apoptosis in HLF cells. The phosphorylation of RXRα, Akt, and ERK proteins in HLF cells were markedly inhibited by treatment with ACR plus LY294002. Moreover, this combination also increased RXRE promoter activity and the cellular levels of RARβ and p21(CIP1), while decreasing the levels of cyclin D1.

CONCLUSION

ACR and LY294002 cooperatively increase the expression of RARβ, while inhibiting the phosphorylation of RXRα, and that these effects are associated with the induction of apoptosis and the inhibition of cell growth in human HCC cells. This combination might therefore be effective for the chemoprevention and chemotherapy of HCC.

Inhibition of Leydig tumor growth by farnesoid X receptor activation: the in vitro and in vivo basis for a novel therapeutic strategy

Leydig cell tumors (LCTs) are the most common tumors of the gonadal stroma and represent about 3% of all testicular neoplasms. In most cases, LCTs are benign; however, if the tumor is malignant, no effective treatments are currently available. We have recently reported that farnesoid X receptor (FXR) is expressed in R2C Leydig tumor cells, and it reduces the estrogen-dependent cell proliferation by negatively regulating aromatase expression. Here, we demonstrated that treatment with GW4064, a specific FXR agonist, markedly reduced Leydig tumor growth in vivo by inhibiting proliferation and inducing apoptosis. Indeed, the tumors from GW4064-treated mice exhibited a decrease in the expression of the proliferation marker Ki-67 and aromatase along with an increase in the apoptotic nuclei. FXR activation induced an enhanced poly(ADP-ribose) polymerase cleavage, a marked DNA fragmentation and a strong increase in TUNEL-positive R2C cells also in vitro. Moreover, in both in vivo and in vitro models, FXR ligands upregulated mRNA and protein levels of p53 and of its downstream effector p21(WAF1/Cip1) . Functional experiments showed that FXR ligands upregulated p53 promoter activity and this occurred through an increased binding of FXR/nuclear factor-kB (NF-kB) complex to the NF-kB site located within p53 promoter region as revealed by electrophoretic mobility shift assay and chromatin immunoprecipitation analysis. Taken together, results from our study show, for the first time, that treatment with FXR ligands induces Leydig tumor regression in vivo, suggesting that activation of FXR may represent a promising therapeutic strategy for LCTs.