ENANTIOSELECTIVE, MECHANISM-BASED INACTIVATION OF GUINEA-PIG HEPATIC CYTOCHROME-P450 BY N-(ALPHA-METHYLBENZYL)-1-AMINOBENZOTRIAZOLE

N-Aralkylated derivatives of 1-aminobenzotriazole are well-established , mechanism-based inhibitors of cytochrome P450 (CYP or P450), In this study, the kinetics of inactivation of CYP2B-dependent 7-pentoxyresor ufin O-depentylation (PROD) and CYP1A-dependent 7-ethoxyresorufin O-de ethylation (EROD) activities by enantiomers of N-(alpha-methylbenzyl)- 1-aminobenzotriazole (alpha MB) were compared, The racemic mixture (+/ -)-alpha MB, as well as the enantiomers (-)-alpha MB and (+)-alpha MB, produced a time-, concentration-, and NADPH-dependent loss of PROD an d EROD activity in hepatic microsomes from phenobarbital-treated guine a pigs. The rates of PROD inactivation by (-)-alpha MB were significan tly faster than for (+)-alpha MB. Consistent with this, the derived ma ximal k(inact) was also significantly greater for (-)-alpha MB than fo r (+)-alpha MB (0.49 vs. 0.35 min(-1)). In contrast, the concentration s required for the half-maximal rate of inactivation (K-i) were equiva lent for (-)-alpha MB and (+)-alpha MB, whereas the degree of competit ive inhibition of PROD activity was greater for (+)-alpha MB. No signi ficant differences were found among (-)-alpha MB, (+)-alpha MB, and (/-)-alpha MB with respect to mechanism-based inactivation (k(inact) = 0.18, 0.16, and 0.17 min(-1), respectively) or competitive inhibition of EROD activity, No differences were found for the maximal extent of PROD or EROD inhibition or the loss of spectral P450 after an extended 30-min incubation with the inhibitors. We conclude that mechanism-bas ed inactivation of guinea pig CYP2B, but not CYP1A, isozymes by alpha MB occurs in a stereoselective manner, most likely as a result of a di fference in the balance between metabolic activation and deactivation for the alpha MB enantiomers.