Potent and selective inactivation of human liver microsomal cytochrome P-450 isoforms by L-754,394, an investigational human immune deficiency virus protease inhibitor.
L-754,394, N-[2(R)-hydroxy-1(S)-indanyl]-5-[2(S)-(1,1-dimethylethylaminocarbonyl )-4- [(furo[2,3-b]pyridin-5-yl)methyl]piperazin-1-yl]-4(S)-hydroxy-2(R) - phenylmethylpentanamide, is a potent and specific inhibitor of the human immune deficiency virus (HIV) protease. The drug selectively inhibited human liver microsomal CYP 3A4-dependent testosterone 6 beta-hydroxylase and CYP 2D6-dependent bufuralol 1'-hydroxylase activities in a time- and concentration-dependent manner in the presence of an NADPH-generating system. L-754,394 was found to be a very potent inactivator of CYP 3A4. Thus, for testosterone 6 beta-hydroxylase, the inactivation kinetic constants, Kl and kinact, were 7.5 microM and 1.62 min-1, respectively, and the partition ratio (moles product formed per moles enzyme inactivated) was approximately 1.35. To a lesser extent, L-754,394 also was an inactivator of CYP 2D6, for which the corresponding values for Kl, kinact and partition ratio were 32 microM, 0.18 min-1 and 40, respectively. CYP 3A4 inactivation was reduced markedly by ketoconazole, a selective CYP 3A4 inhibitor. Similarly, CYP 2D6 inactivation also was prevented by quinidine, a specific competitive inhibitor of this isoform. However, exogenously added nucleophiles (GSH, semicarbazide and N-acetylcysteine) failed to protect against P-450 inactivation. These results suggest that the inactivation process likely is mediated by a reactive metabolite of L-754,394 that alkylates, and thereby destroys, the enzyme. Furthermore, this electrophilic intermediate may not be released into the medium before the inactivation event.
Department of Drug Metabolism, Merck Research Laboratories, West Point, Pennsylvania, USA.
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D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D017320:HIV Protease Inhibitors / Q000494:pharmacology*; D006801:Humans; D007189:Indans / Q000494:pharmacology*; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors*; D010879:Piperazines / Q000494:pharmacology*; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors
D065607:Cytochrome P-450 Enzyme Inhibitors; D017320:HIV Protease Inhibitors; D007189:Indans; C094644:L 754394; D010879:Piperazines; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C104464:CYP3A protein, human; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C022657:steroid hormone 6-beta-hydroxylase; C043872:bufuralol 1'-hydroxylase