title: Relative activation of human pregnane X receptor versus constitutive androstane receptor defines distinct classes of CYP2B6 and CYP3A4 inducers.
abstract: Both the human pregnane X receptor (hPXR) and constitutive androstane receptor (hCAR) are capable of regulating CYP3A4 and CYP2B6 gene expression. However, the majority of currently identified CYP3A4 and CYP2B6 inducers are confirmed activators of hPXR but not hCAR. To compare these receptors with respect to their chemical selectivities, 16 drugs known to induce CYP3A4 and/or CYP2B expression were evaluated for relative activation of hPXR versus hCAR. Because of the high basal but low chemical-induced activation of hCAR in immortalized cells, alternative methods were used to evaluate hCAR activation potential. Thirteen of the 16 compounds were classified as moderate to strong hPXR activators. In contrast, carbamazepine (CMZ), efavirenz (EFV), and nevirapine (NVP) were classified as negligible or weak hPXR activators at concentrations associated with efficacious CYP2B6 reporter or endogenous gene induction in primary human hepatocytes, suggesting potential activation of hCAR. Subsequent experiments demonstrated that these three drugs efficiently induced nuclear accumulation of in vivo-transfected enhanced yellow fluorescent protein-hCAR and significantly increased expression of a CYP2B6 reporter gene when hCAR was expressed in CAR-/- mice. In addition, using a recently identified, chemically responsive splice variant of hCAR (hCAR3), the hCAR activation profiles of the 16 compounds were evaluated. By combining results from the hPXR- and hCAR3-based reporter gene assays, these inducers were classified as hPXR, hCAR, or hPXR/hCAR dual activators. Our results demonstrate that CMZ, EFV, and NVP induce CYP2B6 and CYP3A4 preferentially through hCAR and that hCAR3 represents a sensitive tool for in vitro prediction of chemical-mediated human CAR activation.
authors.affiliation: Division of Molecular Pharmaceutics, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Faucette
authors.forename: Tong-Cun
authors.initials: TC
authors.lastname: Zhang
authors.forename: Rick
authors.initials: R
authors.lastname: Moore
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sueyoshi
authors.forename: Curtis J
authors.initials: CJ
authors.lastname: Omiecinski
authors.forename: Edward L
authors.initials: EL
authors.lastname: LeCluyse
authors.forename: Masahiko
authors.initials: M
authors.lastname: Negishi
authors.forename: Hongbing
authors.initials: H
authors.lastname: Wang
mesh_terms: D000480:Alkynes; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D048588:Benzoxazines; D002220:Carbamazepine / Q000494:pharmacology; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D003521:Cyclopropanes; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D022781:Hepatocytes / Q000201:enzymology; D006801:Humans; D051379:Mice; D019829:Nevirapine / Q000494:pharmacology; D010078:Oxazines / Q000494:pharmacology; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics*; D000077297:Pregnane X Receptor; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000502:physiology; D011987:Receptors, Steroid / Q000187:drug effects* / Q000502:physiology; D014157:Transcription Factors / Q000187:drug effects* / Q000502:physiology; D015533:Transcriptional Activation
chemical_list: D000480:Alkynes; D048588:Benzoxazines; D000090702:Constitutive Androstane Receptor; D003521:Cyclopropanes; D010078:Oxazines; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D002220:Carbamazepine; D003577:Cytochrome P-450 Enzyme System; D019829:Nevirapine; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; C098320:efavirenz