title: CINPA1 is an inhibitor of constitutive androstane receptor that does not activate pregnane X receptor.
abstract: Constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are xenobiotic sensors that enhance the detoxification and elimination of xenobiotics and endobiotics by modulating the expression of genes encoding drug-metabolizing enzymes and transporters. Elevated levels of drug-metabolizing enzymes and efflux transporters, resulting from CAR activation in various cancers, promote the elimination of chemotherapeutic agents, leading to reduced therapeutic effectiveness and acquired drug resistance. CAR inhibitors, in combination with existing chemotherapeutics, could therefore be used to attenuate multidrug resistance in cancers. Interestingly, all previously reported CAR inverse-agonists are also activators of PXR, rendering them mechanistically counterproductive in tissues where both these xenobiotic receptors are present and active. We used a directed high-throughput screening approach, followed by subsequent mechanistic studies, to identify novel, potent, and specific small-molecule CAR inhibitors that do not activate PXR. We describe here one such inhibitor, CINPA1 (CAR inhibitor not PXR activator 1), capable of reducing CAR-mediated transcription with an IC50 of ∼70 nM. CINPA1 1) is a specific xenobiotic receptor inhibitor and has no cytotoxic effects up to 30 µM; 2) inhibits CAR-mediated gene expression in primary human hepatocytes, where CAR is endogenously expressed; 3) does not alter the protein levels or subcellular localization of CAR; 4) increases corepressor and reduces coactivator interaction with the CAR ligand-binding domain in mammalian two-hybrid assays; and 5) disrupts CAR binding to the promoter regions of target genes in chromatin immunoprecipitation assays. CINPA1 could be used as a novel molecular tool for understanding CAR function.
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: Milu T
authors.initials: MT
authors.lastname: Cherian
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: Wenwei
authors.initials: W
authors.lastname: Lin
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: Jing
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee taosheng.chen@stjude.org.
authors.forename: Taosheng
authors.initials: T
authors.lastname: Chen
mesh_terms: D002460:Cell Line; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation / Q000379:methods; D000090702:Constitutive Androstane Receptor; D018432:Drug Resistance, Multiple / Q000187:drug effects; D057809:HEK293 Cells; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*; D054852:Small Molecule Libraries / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D020798:Two-Hybrid System Techniques; D015262:Xenobiotics / Q000494:pharmacology
chemical_list: D000090702:Constitutive Androstane Receptor; D026901:Membrane Transport Proteins; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D054852:Small Molecule Libraries; D015262:Xenobiotics