title: Evaluation of 6β-hydroxycortisol, 6β-hydroxycortisone, and a combination of the two as endogenous probes for inhibition of CYP3A4 in vivo.
abstract: An endogenous probe for CYP3A activity would be useful for early identification of in vivo cytochrome P450 (CYP) 3A4 inhibitors. The aim of this study was to determine whether formation clearance (CL(f)) of the sum of 6β-hydroxycortisol and 6β-hydroxycortisone is a useful probe of CYP3A4 inhibition in vivo. In human liver microsomes (HLMs), the formation of 6β-hydroxycortisol and 6β-hydroxycortisone was catalyzed by CYP3A4, and itraconazole inhibited these reactions with half maximal inhibitory concentration (IC(50))(,u) values of 3.1 nmol/l and 3.4 nmol/l, respectively. The in vivo IC(50,u) value of itraconazole for the combined CL(f) of 6β-hydroxycortisone and 6β-hydroxycortisol was 1.6 nmol/l. The greater inhibitory potency in vivo is probably due to circulating inhibitory itraconazole metabolites. The maximum in vivo inhibition was 59%, suggesting that f(m,CYP3A4) for cortisol and cortisone 6β-hydroxylation is ~60%. Given the significant decrease in CL(f) of 6β-hydroxycortisone and 6β-hydroxycortisol after 200-mg and 400-mg single doses of itraconazole, this endogenous probe can be used to detect moderate and potent CYP3A4 inhibition in vivo.
authors.affiliation: Department of Pharmaceutics, University of Washington School of Pharmacy, Seattle, Washington, USA.
authors.forename: C-C
authors.initials: CC
authors.lastname: Peng
authors.forename: I
authors.initials: I
authors.lastname: Templeton
authors.forename: K E
authors.initials: KE
authors.lastname: Thummel
authors.forename: C
authors.initials: C
authors.lastname: Davis
authors.forename: K L
authors.initials: KL
authors.lastname: Kunze
authors.forename: N
authors.initials: N
authors.lastname: Isoherranen
mesh_terms: D003348:Cortisone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis* / Q000378:metabolism; D065692:Cytochrome P-450 CYP3A Inhibitors; D004338:Drug Combinations; D004353:Drug Evaluation, Preclinical / Q000379:methods; D006801:Humans; D006854:Hydrocortisone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D017964:Itraconazole / Q000378:metabolism / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D015335:Molecular Probes / Q000378:metabolism*; D015203:Reproducibility of Results
chemical_list: C485511:6 beta-hydroxycortisone; D065692:Cytochrome P-450 CYP3A Inhibitors; D004338:Drug Combinations; D015335:Molecular Probes; D017964:Itraconazole; C001380:6 beta-hydroxycortisol; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D003348:Cortisone; D006854:Hydrocortisone