Advances in drug resistance of triple negative breast cancer caused by pregnane X receptor

Breast cancer is the most common malignancy in women worldwide.Triplenegative breast cancer(TNBC),refers breast cancer negative for estrogen receptor,progesterone receptor and human epidermal growth factor receptor 2,characterized by high drug resistance,high metastasis and high recurrence,treatment of which is a difficult problem in the clinical treatment of breast cancer.In order to better treat TNBC clinically,it is a very urgent task to explore the mechanism of TNBC resistance in basic breast cancer research.Pregnane X receptor(PXR)is a nuclear receptor whose main biological function is to participate in the metabolism,transport and clearance of allobiological agents in PXR.PXR plays an important role in drug metabolism and clearance,and PXR is highly expressed in tumor tissues of TNBC patients,which is related to the prognosis of breast cancer patients.This reviews synthesized the important role of PXR in the process of high drug resistance to TNBC chemotherapeutic drugs and related research progress.

pregnane X receptor and constitutive androstane receptor modulate differently CYp3A-mediated metabolism in earlyand late-stage cholestasis

AIM To ascertain whether cholestasis affects the expression of two CYP3 A isoforms(CYP3 A1 and CYP3 A2) and of pregnane X receptor(PXR) and constitutive androstane receptor(CAR).METHODS Cholestasis was induced by bile duct ligation in 16 male Wistar rats; whereas 8 sham-operated rats were used as controls. Severity of cholestasis was assessed on histological examination of liver sections, and serum concentrations of albumin, AST, ALT, GGT, ALPK and bilirubin. Gene and protein expressions of PXR, CAR, CYP3 A1 and CYP3 A2 were assessed by means of q RT-PCR and Western blot, respectively. Alterations in CYP3 A activity were measured by calculating the kinetic parameters of 4-OH and 1'-OH-midazolam hydroxylation, marker reactions for CYP3 A enzymes.RESULTS The m RNA and protein expression of CYP3 A1 increased significantly in mild cholestasis(P < 0.01). At variance, m RNA and protein expression of CYP3 A2 didn't change in mild cholestasis, whereas the expression and activity of both CYP3 A1 and CYP3 A2 decreased dramatically when cholestasis became severe. Consistently with these observations, the nuclear expression of both PXR and CAR, which was measured because they both translocate into the cell nucleus after their activation, virtually disappeared in the late stage of cholestatic injury, after an initial increase. These results indicate that early-and late-stage cholestasis affects CYP3 Amediated drug metabolism differently, probably as consequence of the different activation of PXR and CAR.CONCLUSION Early-and late-stage cholestasis affects CYP3 Amediated drug metabolism differently. PXR and CAR might be targeted therapeutically to promote CYP3 Amediated liver detoxification.

Pregnane X receptor： a double-edged sword

During the last decade, much progress has been made in exploring the mechanisms of alterations elicited by foreign compounds in xeno- and endobiotic metabolism regulated by the human nuclear pregnane X receptor （PXR）. PXR, identified as a human nuclear receptor in 1998 and generally regarded as a sensor activated by exogenous and endogenous chemicals, regulates a large number of enzymes and transporters involved in the response of mammals to their chemical environment.

Pregnane X receptor in drug-induced liver injury: Friend or foe?

The pregnane X receptor(PXR)is a ligand activated nuclear receptor that is highly expressed in the liver and regulates many cellular functions including drug metabolism,endobiotic metabolism,oxidative stress response,apoptosis,inflammation,cell proliferation and regeneration.PXR activation promotes drug-induced liver injury(DILI)through its ability to increase the expression of phaseⅠand phaseⅡdrug metabolizing enzymes.The PXR also increases lipid synthesis and fatty acid uptake into the liver,leading to lipid accumulation and steatosis.In recent years,PXR has been explored as an important target in DILI and liver diseases.This review will highlight the roles of PXR in modulating DILI.PXR polymorphisms that have been associated with DILI will also be discussed.

Chemical basis of pregnane X receptor activators in the herbal supplement Gancao (licorice)

Background and aims:The herbal supplement Gancao,also known as licorice,belongs to the genus Glycyrrhiza and has been used worldwide for its hepatoprotective effect.Recent studies have raised concerns about potential herb-drug interactions associated with Gancao via pregnane X receptor(PXR)-mediated induction of hepatic cytochrome P4503A4(CYP3A4).The current work aimed to determine the phytochemicals in Gancao that activate PXR and induce CYP3A4.Methods:DPX2 cells were used for cell-based PXR reporter assays.The phytochemicals in Gancao extract were identified using a metabolomics approach.The effects of PXR activators identified from in vitro studies were further investigated in PXR-and CYP3A4-humanized mouse models.Results:Gancao was verified to be a PXR-activating herb.Two major phytochemicals in Gancao,gly-cyrrhizin(GZ)and glycyrrhetinic acid(GA),did not activate PXR in the cell-based reporter assays.However,glabridin was shown to activate PXR in a dose-dependent manner.In vivo studies confirmed that GZ is not a PXR activator and glabridin is a weak PXR activator.Although GA did not active PXR in vitro,it induced CYP3A4 expression in a PXR-dependent manner in the PXR-and CYP3A4-humanized mice.

Interaction of Hepatitis B Virus X Protein with the Pregnane X Receptor Enhances the Synergistic Effects of Aflatoxin B1 and Hepatitis B Virus on Promoting Hepatocarcinogenesis

Background and Aims:Hepatitis B virus(HBV)infection has been found to increase hepatocellular sensitivity to carcinogenic xenobiotics,by unknown mechanisms,in the generation of hepatocellular carcinoma.The pregnane X receptor(PXR)is a key regulator of the body’s defense against xenobiotics,including xenobiotic carcinogens and clinical drugs.In this study,we aimed to investigate the molecular mechanisms of HBV X protein(HBx)-PXR signaling in the synergistic effects of chemical carcinogens in HBV-associated hepatocarcinogenesis.Methods:The expression profile of PXR-cytochrome p4503A4(CYP3A4)signaling was determined by PCR,western blotting,and tissue microarray.Cell viability and aflatoxin B1(AFB1)cytotoxicity were measured using the cell counting kit-8 assay.Target gene expression was evaluated using transient transfection and real time-PCR.The genotoxicity of AFB1 was assessed in newborn mice with a single dose of AFB1.Results:HBx enhanced the hepatotoxicity of AFB1 by activating CYP3A4 and reducing glutathione Stransferase Mu 1(GSTM1)in cell lines.Activation of PXR by pregnenolone 16α-carbonitrile increased AFB1-induced liver tumor incidence by up-regulating oncogenic KRAS to enhance interleukin(IL)-11:IL-11 receptor subunit alpha-1(IL11RA-1)-mediated inflammation in an HBx transgenic model.Conclusions:Our finding regarding AFB1 toxicity enhancement by an HBx-PXR-CYP3A4/GSTM1-KRASIL11:IL11RA signaling axis provides a rational explanation for the synergistic effects of chemical carcinogens in HBV infection-associated hepatocarcinogenesis.

Pregnenolone 16α-carbonitrile negatively regulates hippocampal cytochrome P450 enzymes and ameliorates phenytoin-induced hippocampal neurotoxicity

The central nervous system is susceptible to the modulation of various neurophysiological processes by the cytochrome P450 enzyme(CYP),which plays a crucial role in the metabolism of neurosteroids.The antiepileptic drug phenytoin(PHT)has been observed to induce neuronal side effects in patients,which could be attributed to its induction of CYP expression and testosterone(TES)metabolism in the hippocampus.While pregnane X receptor(PXR)is widely known for its regulatory function of CYPs in the liver,we have discovered that the treatment of mice with pregnenolone 16α-carbonitrile(PCN),a PXR agonist,has differential effects on CYP expression in the liver and hippocampus.Specifically,the PCN treatment resulted in the induction of cytochrome P450,family 3,subfamily a,polypeptide 11(CYP3A11),and CYP2B10 expression in the liver,while suppressing their expression in the hippocampus.Functionally,the PCN treatment protected mice from PHT-induced hippocampal nerve injury,which was accompanied by the inhibition of TES metabolism in the hippocampus.Mechanistically,we found that the inhibition of hippocampal CYP expression and attenuation of PHT-induced neurotoxicity by PCN were glucocorticoid receptor dependent,rather than PXR independent,as demonstrated by genetic and pharmacological models.In conclusion,our study provides evidence that PCN can negatively regulate hippocampal CYP expression and attenuate PHT-induced hippocampal neurotoxicity independently of PXR.Our findings suggest that glucocorticoids may be a potential therapeutic strategy for managing the neuronal side effects of PHT.

Cisplatin increases carboxylesterases through increasing PXR mediated by the decrease of DEC1

cis-Diamminedichloroplatinum(CDDP)is widely used for the treatment of various solid cancers.Here we reported that CDDP increased the expression and enzymatic activities of carboxylesterase 1(CES1)and carboxylesterase 2(CES2),along with the upregulation of pregnane X receptor(PXR)and the downregulation of differentiated embryonic chondrocyte-expressed gene 1(DEC1)in human hepatoma cells,primary mouse hepatocytes,mouse liver and intestine.The overexpression or knockdown of PXR alone upregulated or downregulated the CES1 and CES2 expression,respectively.The increases in CES1 and CES2 expression levels induced by CDDP abolished or enhanced by PXR knockdown or overexpression,implying that CDDP induces carboxylesterases through the activation of PXR.Likewise,the overexpression or knockdown of DEC1 alone significantly decreased or increased PXR and its targets.Moreover,the increases of PXR and its targets induced by CDDP were abolished or alleviated by the overexpression or knockdown of DEC1.The overexpression or knockdown of DEC1 affected the response of PXR to CDDP,but not vice versa,suggesting that CDDP increases carboxylesterases by upregulating PXR mediated by the decrease of DEC1.In addition,CDDP did not increase DEC1 mRNA degradation but suppressed DEC1 promoter reporter activity,indicating that it suppresses DEC1 transcriptionally.The combined use of CDDP and irinotecan had a synergistic effect on two cell lines,especially when CDDP was used first.

Effects of flavonoids derived from Taxus yunnanensis on p-glycoprotein and cytochrome P450 3A4

The intestinal uptake of paclitaxel is hampered by trans-membrane efflux transporters such as P-glycoprotein(P-gp),and paclitaxel is mainly metabolized by cytochrome P4503A4(CYP3A4)presented in the liver.Our previous results demonstrated that flavonoids extracted from Taxus yunnanensis could improve the oral absorption of paclitaxel.The current study was purposed to investigate the effects of the flavonoid extracts on P-gp and CYP3A4 in vitro.The expression and activity of P-gp were detected by western blotting and intracellular rhodamine 123 accumulation assay in Caco-2 cells treated with the flavonoids extract.The expression of CYP3A4 was investigated by western blotting in mouse primary hepatocytes and the activity of CYP3A4 was detected by LC-MS/MS method using rat liver microsomes.Our results showed that the flavonoid extracts from T.yunnanensis could inhibit P-gp activity and concurrently decrease the expression and activity of CYP3A4.In conclusion,activity of P-gp and CYP3A4 could be inhibited by flavonoids extracted from T.yunnanensis which might be potential candidates for development of oral formulation of paclitaxel.

In Silico Investigation of Agonist Activity of a Structurally Diverse Set of Drugs to hPXR Using HM-BSM and HM-PNN

The human pregnane X receptor（hPXR） plays a critical role in the metabolism, transport and clearance of xenobiotics in the liver and intestine. The hPXR can be activated by a structurally diverse of drugs to initiate clinically relevant drug-drug interactions. In this article, in silico investigation was performed on a structurally diverse set of drugs to identify critical structural features greatly related to their agonist activity towards h PXR. Heuristic method（HM）-Best Subset Modeling（BSM） and HM-Polynomial Neural Networks（PNN） were utilized to develop the linear and non-linear quantitative structure-activity relationship models. The applicability domain（AD） of the models was assessed by Williams plot. Statistically reliable models with good predictive power and explain were achieved（for HM-BSM, r^2=0.881, q^2_（LOO）=0.797, q^2_（EXT）=0.674; for HM-PNN, r^2=0.882, q^2_（LOO）=0.856, q^2_（EXT）=0.655）. The developed models indicated that molecular aromatic and electric property, molecular weight and complexity may govern agonist activity of a structurally diverse set of drugs to h PXR.

Atypical functions of xenobiotic receptors in lipid and glucose metabolism

Xenobiotic receptors are traditionally defined as xenobiotic chemical-sensing receptors,the activation of which transcriptionally regulates the expression of enzymes and transporters involved in the metabolism and disposition of xenobiotics.Emerging evidence suggests that“xenobiotic receptors”also have diverse endobiotic functions,including their effects on lipid metabolism and energy metabolism.Dyslipidemia is a major risk factor for cardiovascular disease,diabetes,obesity,metabolic syndrome,stroke,nonalcoholic fatty liver disease(NAFLD),and nonalcoholic steatohepatitis(NASH).Understanding the molecular mechanism by which transcriptional factors,including the xenobiotic receptors,regulate lipid homeostasis will help to develop preventive and therapeutic approaches.This review describes recent advances in our understanding the atypical roles of three xenobiotic receptors:aryl hydrocarbon receptor(AhR),pregnane X receptor(PXR),and constitutive androstane receptor(CAR),in metabolic disorders,with a particular focus on their effects on lipid and glucose metabolism.Collectively,the literatures suggest the potential values of AhR,PXR and CAR as therapeutic targets for the treatment of NAFLD,NASH,obesity and diabetes,and cardiovascular diseases.

Activation of PXR causes drug interactions with Paxlovid in transgenic mice

Paxlovid is a nirmatrelvir(NMV)and ritonavir(RTV)co-packaged medication used for the treatment of coronavirus disease 2019(COVID-19).The active component of Paxlovid is NMV and RTV is a pharmacokinetic booster.Our work aimed to investigate the drug/herb-drug interactions associated with Paxlovid and provide mechanism-based guidance for the clinical use of Paxlovid.By using recombinant human cytochrome P450s(CYPs),we confirmed that CYP3A4 and 3A5 are the major enzymes responsible for NMV metabolism.The role of CYP3A in Paxlovid metabolism were further verified in Cyp3a-null mice,which showed that the deficiency of CYP3A significantly suppressed the metabolism of NMV and RTV.Pregnane X receptor(PXR)is a ligand-dependent transcription factor that upregulates CYP3A4/5 expression.We next explored the impact of drug-and herb-mediated PXR activation on Paxlovid metabolism in a transgenic mouse model expressing human PXR and CYP3A4/5.We found that PXR activation increased CYP3A4/5 expression,accelerated NMV metabolism,and reduced the systemic exposure of NMV.In summary,our work demonstrated that PXR activation can cause drug interactions with Paxlovid,suggesting that PXR-activating drugs and herbs should be used cautiously in COVID-19 patients receiving Paxlovid.

PXR activation impairs hepatic glucose metabolism partly via inhibiting the HNF4α-GLUT2 pathway

Drug-induced hyperglycemia/diabetes is a global issue. Some drugs induce hyperglycemia by activating the pregnane X receptor(PXR), but the mechanism is unclear. Here, we report that PXR activation induces hyperglycemia by impairing hepatic glucose metabolism due to inhibition of the hepatocyte nuclear factor 4-alpha(HNF4 a)-glucose transporter 2(GLUT2) pathway. The PXR agonists atorvastatin and rifampicin significantly downregulated GLUT2 and HNF4 a expression, and impaired glucose uptake and utilization in HepG2 cells. Overexpression of PXR downregulated GLUT2 and HNF4 a expression, while silencing PXR upregulated HNF4 a and GLUT2 expression.Silencing HNF4 a decreased GLUT2 expression, while overexpressing HNF4 a increased GLUT2 expression and glucose uptake. Silencing PXR or overexpressing HNF4 a reversed the atorvastatininduced decrease in GLUT2 expression and glucose uptake. In human primary hepatocytes, atorvastatin downregulated GLUT2 and HNF4 a mRNA expression, which could be attenuated by silencing PXR. Silencing HNF4 a downregulated GLUT2 mRNA expression. These findings were reproduced with mouse primary hepatocytes. Hnf4 a plasmid increased Slc2 a2 promoter activity. Hnf4 a silencing or pregnenolone-16 a-carbonitrile(PCN) suppressed the Slc2 a2 promoter activity by decreasing HNF4 a recruitment to the Slc2 a2 promoter. Liver-specific Hnf4 a deletion and PCN impaired glucose tolerance and hepatic glucose uptake, and decreased the expression of hepatic HNF4 a and GLUT2. In conclusion, PXR activation impaired hepatic glucose metabolism partly by inhibiting the HNF4 aGLUT2 pathway. These results highlight the molecular mechanisms by which PXR activators induce hyperglycemia/diabetes.

Applanoids A—E as the First Examples of C-15/C-20 Michael Adducts in Ganoderma Triterpenoids and Their PXR Agonistic Activity

Ganoderma triterpenoids(GTs),a class of major active constituents of Ganoderma fungi,possess diverse structures and remarkable activities.In the present study,nine new GTs,namely applanoids A—I(1—9),were isolated from the medicinal fungus of Ganoderma applanatum.Their structures including absolute configurations were established by comprehensive spectroscopic analyses and ECD calculation.Applanoids A—E(1—5)represent the first example of GTs with 6/6/5/6/5 pentacyclic system and the formation of the ether ring between C-15 and C-20 involves Michael addition reaction.Furthermore,compounds 1—8 were evaluated for their human pregnane X receptor(hPXR)agonistic activity using dual-luciferase reporter gene assay,and the results showed that compounds 1,2 and 4 can dose-dependently activate hPXR.This investigation further illustrated the structural diversity of GTs and provided new insights for searching PXR agonists from GTs.

Nuclear receptors and non-alcoholic fatty liver disease:An update

Non-alcoholic fatty liver disease(NAFLD)has become the leading cause of chronic liver disease in adults and children worldwide.The symptoms of NAFLD range from simple steatosis and non-alcoholic stea-tohepatitis(NASH)to hepatic fibrosis or cirrhosis,even ultimately develops to hepatocellular carcinoma.Nuclear receptors(NRs)are a superfamily of ligand-activated transcription factors,most of which are ligand-activated that control cellular homeostasis in the liver and other tissues.A growing number of studies demonstrated the important role of NRs in NAFLD.In this review,the current findings on the role of NRs in NAFLD are summarized and future perspectives to target NRs for NAFLD are discussed.