PT - JOURNAL ARTICLE AU - Zofia Duniec-Dmuchowski AU - Hai-Lin Fang AU - Stephen C. Strom AU - Ewa Ellis AU - Melissa Runge-Morris AU - Thomas A. Kocarek TI - Human Pregnane X Receptor Activation and CYP3A4/CYP2B6 Induction by 2,3-Oxidosqualene:Lanosterol Cyclase Inhibition AID - 10.1124/dmd.108.025130 DP - 2009 Apr 01 TA - Drug Metabolism and Disposition PG - 900--908 VI - 37 IP - 4 4099 - http://dmd.aspetjournals.org/content/37/4/900.short 4100 - http://dmd.aspetjournals.org/content/37/4/900.full SO - Drug Metab Dispos2009 Apr 01; 37 AB - The effects of [4′-(6-allyl-methyl-amino-hexyloxy)-2′-fluoro-phenyl]-(4-bromophenyl)-methanone fumarate (Ro 48-8071), an inhibitor of 2,3-oxidosqualene:lanosterol cyclase (cyclase), were evaluated on CYP3A4 and CYP2B6 mRNA content in primary cultured human hepatocytes. In seven hepatocyte culture preparations, 24-h treatment with 3, 10, or 30 μM Ro 48-8071 produced median increases in CYP3A4 mRNA content that were 2.2-, 7.1-, and 8.5-fold greater than untreated control, respectively, and produced increases in CYP2B6 mRNA content that were 3.0-, 4.6-, and 3.4-fold greater than control, respectively. Increases in CYP3A4 immunoreactive protein content were also measured in Ro 48-8071-treated hepatocytes. To evaluate the effects of cyclase inhibitor treatments further, a pregnane X receptor (PXR)-responsive transactivation assay in HepG2 cells was used. Ro 48-8071, trans-N-(4-chlorobenzoyl)-N-methyl-(4-dimethylaminomethylphenyl)-cyclohexylamine (BIBX 79), and 3β-(2-diethylaminoethoxy)androst-5-en-17-one HCl (U18666A) induced luciferase expression from a PXR-responsive reporter with EC50s of 0.113, 0.916, and 0.294 μM, respectively. Treatment of the HepG2 system with (E)N-ethyl-N-(6,6-dimethyl-2-hepten-4-ynyl)-3-[(3,3′-bithiophen-5-yl)methoxy]benzenemethanamine (NB-598), an inhibitor of squalene monooxygenase, at concentrations sufficient to achieve cholesterol biosynthesis inhibition significantly inhibited cyclase inhibitor-mediated, but not rifampicin-mediated, reporter induction. Direct treatment of the HepG2 system with 1 to 10 μM squalene 2,3:22,23-dioxide, but not squalene 2,3-oxide, significantly activated PXR-responsive reporter expression. Also, squalene 2,3:22,23-dioxide bound to human PXR in vitro with an IC50 of 3.35 μM. These data indicate that cyclase inhibitors are capable of producing CYP3A4 and CYP2B6 induction in primary cultured human hepatocytes, and that an endogenous squalene metabolite is a conserved intracrine activator of PXR. The American Society for Pharmacology and Experimental Therapeutics