title: 2-Diethylaminoethyl-2,2-diphenylvalerate-HCl (SKF525A) revisited: comparative cytochrome P450 inhibition in human liver microsomes by SKF525A, its metabolites, and SKF-acid and SKF-alcohol.
abstract: When incubated with human liver microsomes, 2-diethylaminoethyl-2,2-diphenylvalerate-HCl (SKF525A) undergoes cytochrome P450 (P450)-dependent oxidative N-deethylation to the secondary amine metabolite 2-ethylaminoethyl-2,2-diphenylvalerate (SKF8742). P450-selective inhibitors indicated CYP3As catalyzed this reaction, and the deethylation rate correlated best with the CYP3A activity across a range of human liver microsomes. SKF525A and its metabolite and primary amine analog all inhibited CYP2B6-, CYP2C9-, CYP2C19-, CYP2D6-, and CYP3A-selective reactions to varying degrees but had little effect on CYP1A2, CYP2A6, and CYP2E1 reactions. Only the inhibition of CYP3A showed major enhancement when the inhibitors were preincubated with NADPH-fortified microsomes, and the extent of metabolic intermediate (MI) complex formation approximated typical CYP3A content. Two "lost with time" SKF525A derivatives devoid of the ethylamine moiety, 2,2-diphenylpropylethanol (SKF-Alcohol) and 2,2-diphenylpropylacetic acid (SKF-Acid) did not form an MI complex and were identified as selective inhibitors of CYP2C9. Although without detectable metabolism, their CYP2C9 inhibition fitted best with a competitive mechanism. Thus, not all the human P450s are inhibited by SKF525A and related compounds, and the mechanisms contributing to those that are inhibited vary with the isoform. P450 MI-complex formation only seems to play a role with CYP3As.
authors.affiliation: University of Utah, Department of Pharmacology and Toxicology, 30S, 2000 East, Room 201, Salt Lake City, UT 84112-5820, USA. michael.franklin@pharm.utah.edu
authors.forename: Michael R
authors.initials: MR
authors.lastname: Franklin
authors.forename: Laura B
authors.initials: LB
authors.lastname: Hathaway
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D002384:Catalysis / Q000187:drug effects; D065729:Cytochrome P-450 CYP2C9; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000378:metabolism; D004008:Diclofenac / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D011335:Proadifen / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D014631:Valerates / Q000378:metabolism / Q000494:pharmacology
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D014631:Valerates; C027135:SK&F 8742A; D004008:Diclofenac; C006287:aminoethyl diphenylpropylacetate; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D011335:Proadifen; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A