Enantioselective, mechanism-based inactivation of guinea pig hepatic cytochrome P450 by N-(α-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-pentoxyresorufin O- depentylation (PROD) and CYP1A-dependent 7-ethoxyresorufin O-deethylation (EROD) activities by enantiomers of N-(α-methylbenzyl)-1-aminobenzotriazole (αMB) were compared. The racemic mixture (±)-αMB, as well as the enantiomers (-)-αMB and (+)-αMB, produced a time-, concentration-, and NADPH-dependent loss of PROD and. EROD activity in hepatic microsomes from phenobarbital-treated guinea pigs. The rates of PROD inactivation by (-)- αMB were significantly faster than for (+)-αMB. Consistent with this, the derived maximal k(inact) was also significantly greater for (-)-αMB than for (+)-αMB (0.49 vs. 0.35 min^-1). In contrast, the concentrations required for the half-maximal rate of inactivation (K(j)) were equivalent for (-)- αMB and (+)-αMB, whereas the degree of competitive inhibition of PROD activity was greater for (+)-αMB. No significant differences were found among (-)-αMB, (+)-αMB, and (±)-αMB 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-based inactivation of guinea pig CYP2B, but not CYP1A, isozymes by αMB occurs in a stereoselective manner, most likely as a result of a difference in the balance between metabolic activation and deactivation for the αMB enantiomers.