title: In vitro studies on the metabolic activation of the furanopyridine L-754,394, a highly potent and selective mechanism-based inhibitor of cytochrome P450 3A4.
abstract: L-754,394, a furanopyridine derivative, is an experimental anti-HIV agent which has been shown to be an unusually potent and selective inhibitor of cytochrome P450 3A enzymes in a number of mammalian species. In the present studies, L-754,394 was demonstrated to undergo NADPH-dependent metabolic activation in hepatic microsomal preparations from rats, dogs, rhesus monkeys, and humans to electrophilic intermediates which became bound covalently to cellular proteins. The extent of binding was species-dependent, the highest levels being observed with liver microsomes from rhesus monkeys. Inclusion in incubation media of the nucleophilic trapping agents glutathione, cysteine, or methoxyamine led to a modest (15-25%) decrease in the covalent binding, while trichloropropylene oxide, an inhibitor of epoxide hydrolase, had no effect. When L-754,394 was incubated with monkey liver microsomes, the corresponding dihydrofurandiol was identified as a metabolite by liquid chromatography-tandem mass spectrometry. In contrast, when incubations were carried out in the presence of methoxyamine, the O-methyloxime derivative of the ring-opened dihydrodiol tautomer was formed, while inclusion of glutathione or N-acetylcysteine led to the formation of S-linked conjugates of a putative furan epoxide. Collectively, these results are taken to indicate that L-754,394 undergoes cytochrome P450-dependent oxidation of the fused furan ring system, leading to the formation of chemically-reactive intermediates. One or more of these electrophilic species may be responsible for the autocatalytic destruction of cytochrome P450 enzymes which accompanies L-754,394 metabolism in vitro and in vivo.
authors.affiliation: Department of Drug Metabolism, Merck Research Laboratories, West Point, Pennsylvania 19486, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Sahali-Sahly
authors.forename: S K
authors.initials: SK
authors.lastname: Balani
authors.forename: J H
authors.initials: JH
authors.lastname: Lin
authors.forename: T A
authors.initials: TA
authors.lastname: Baillie
mesh_terms: D000818:Animals; D001665:Binding Sites; D001711:Biotransformation; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004285:Dogs; D004791:Enzyme Inhibitors / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006898:Hydroxylamines / Q000494:pharmacology; D066298:In Vitro Techniques; D007189:Indans / Q000737:chemistry / Q000378:metabolism*; D008253:Macaca mulatta; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010879:Piperazines / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D014239:Trichloroepoxypropane / Q000494:pharmacology
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D006898:Hydroxylamines; D007189:Indans; C094644:L 754394; D010879:Piperazines; D014239:Trichloroepoxypropane; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; C005214:methoxyamine; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A