title: Enantioselective, mechanism-based inactivation of guinea pig hepatic cytochrome P450 by N-(alpha-methylbenzyl)-1-aminobenzotriazole.
abstract: 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-(alpha-methylbenzyl)-1-aminobenzotriazole (alphaMB) were compared. The racemic mixture (+/-)-alphaMB, as well as the enantiomers (-)-alphaMB and (+)-alphaMB, 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 (-)-alphaMB were significantly faster than for (+)-alphaMB. Consistent with this, the derived maximal kinact was also significantly greater for (-)-alphaMB than for (+)-alphaMB (0.49 vs. 0.35 min-1). In contrast, the concentrations required for the half-maximal rate of inactivation (Ki) were equivalent for (-)-alphaMB and (+)-alphaMB, whereas the degree of competitive inhibition of PROD activity was greater for (+)-alphaMB. No significant differences were found among (-)-alphaMB, (+)-alphaMB, and (+/-)-alphaMB with respect to mechanism-based inactivation (kinact = 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 alphaMB occurs in a stereoselective manner, most likely as a result of a difference in the balance between metabolic activation and deactivation for the alphaMB enantiomers.
authors.affiliation: Department of Pharmacology and Toxicology, University of Western Ontario, London, Ontario, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Sinal
authors.forename: M
authors.initials: M
authors.lastname: Hirst
authors.forename: C D
authors.initials: CD
authors.lastname: Webb
authors.forename: J R
authors.initials: JR
authors.lastname: Bend
mesh_terms: D000818:Animals; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors*; D019362:Cytochrome P-450 CYP2B1 / Q000037:antagonists & inhibitors*; D006168:Guinea Pigs; D006207:Half-Life; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D008862:Microsomes, Liver / Q000201:enzymology*; D013237:Stereoisomerism; D014230:Triazoles / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D007527:Isoenzymes; D014230:Triazoles; C059849:alpha-methylbenzylaminobenzotriazole; D019363:Cytochrome P-450 CYP1A1; D019362:Cytochrome P-450 CYP2B1