title: Role of cytochrome P450 3A4 in human metabolism of MK-639, a potent human immunodeficiency virus protease inhibitor.
abstract: MK-639 (L-735,524) is a potent human immunodeficiency virus protease inhibitor under investigation in the treatment of acquired immunodeficiency syndrome. Five in vitro approaches have been used to identify the cytochrome P450 isoform(s) responsible for the human microsomal oxidative metabolism of MK-639. These approaches are: 1) chemical inhibition; 2) immunochemical inhibition; 3) metabolism by cDNA-expressed human cytochrome P450 enzymes; 4) a correlation analysis; and 5) competitive inhibition of marker activities. Ketoconazole and troleandomycin, both selective inhibitors for cytochrome P450 3A4 (CYP3A4), markedly inhibited the formation of all oxidative metabolites of MK-639; whereas other inhibitors (furafylline, sulfaphenazole, quinidine, S-mephenytoin, and diethyldithiocarbamate) had little effect on MK-639 metabolism. This suggested the involvement of CYP3A4 in MK-639 metabolism. Consistent with this, an anti-rat CYP3A1 rabbit polyclonal antibody, which shows a cross-reactive inhibition of CYP3A4-dependent testosterone 6beta-hydroxylation in human liver microsomes, completely inhibited MK-639 metabolism. Human recombinant CYP3A4 showed a high metabolic activity to form all MK-639 metabolites found in native human liver microsomes. In addition, the formation of individual MK-639 metabolites correlated well with each other and with testosterone 6beta-hydroxylation in 12 different human liver microsomes, whereas no correlation was observed between MK-639 metabolite formation and bufuralol 1'-hydroxylation (or tolbutamide methyl hydroxylation). Furthermore, MK-639 strongly inhibited testosterone 6beta-hydroxylation in a concentration-dependent manner. Kinetic analysis showed that MK-639 is a very potent competitive inhibitor for testosterone 6beta-hydroxylation, with a Ki value of approximately 0.5 mu M. Collectively, these results consistently indicate that CYP3A4 is the isoform responsible for the oxidative metabolism of MK-639 in human liver microsomes.
authors.affiliation: Department of Drug Metabolism, Merck Research Laboratories, West Point, PA 19486, USA.
authors.forename: M
authors.initials: M
authors.lastname: Chiba
authors.forename: M
authors.initials: M
authors.lastname: Hensleigh
authors.forename: J A
authors.initials: JA
authors.lastname: Nishime
authors.forename: S K
authors.initials: SK
authors.lastname: Balani
authors.forename: J H
authors.initials: JH
authors.lastname: Lin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D017320:HIV Protease Inhibitors / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation / Q000187:drug effects; D019469:Indinavir / Q000378:metabolism*; D007527:Isoenzymes; D007654:Ketoconazole / Q000494:pharmacology; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D014217:Troleandomycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D017320:HIV Protease Inhibitors; D007527:Isoenzymes; D019469:Indinavir; D003577:Cytochrome P-450 Enzyme System; D014217:Troleandomycin; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D007654:Ketoconazole