RT Journal Article SR Electronic T1 Selective Inhibition of Dog Hepatic CYP2B11 and CYP3A12 JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 518 OP 528 DO 10.1124/jpet.104.077651 VO 313 IS 2 A1 Ping Lu A1 Suresh B. Singh A1 Brian A. Carr A1 Yulin Fang A1 Cathie Dong Xiang A1 Thomas H. Rushmore A1 A. David Rodrigues A1 Magang Shou YR 2005 UL http://jpet.aspetjournals.org/content/313/2/518.abstract AB In the present study, N-(α-methylbenzyl-)-1-aminobenzotriazole (MBA) and ketoconazole (KET) were identified as the inhibitors with selectivity toward dog CYP2B11 and CYP3A12, respectively. Their selectivity was evaluated using phenacetin O-deethylation (CYP1A), diazepam (DZ) N1-demethylation (CYP2B11), diclofenac 4′-hydrxylation (CYP2C21), bufuralol 1′-hydroxylation (CYP2D11), and DZ C3-hydroxylation (CYP3A12) activities in dog liver microsomes (DLM). MBA exhibited potent mechanism-based inhibition of DZ N1-demethylase activity catalyzed by both baculovirus-expressed CYP2B11 and DLM. In both cases, inhibition was characterized by a low KI (0.35 and 0.46 μM, respectively) and high kinact (1.5 and 0.56 min–1, respectively). Despite complete loss of DZ N1-demethylase activity in the presence of MBA, there was no significant loss of cytochrome P450 (P450) CO-binding spectrum. These data suggest that the inactivation involved covalent modification of P450 apoprotein, instead of the prosthetic heme moiety. A homology model of CYP2B11 was constructed, based on the crystal structure of rabbit CYP2C5, for docking the substrate (DZ) and the inhibitor (MBA), respectively. The model, within the limits of our approximations, helped explain the substrate specificity and inhibitor selectivity of CYP2B11. In contrast to MBA, KET was identified as a potent and selective reversible (competitive) inhibitor of CYP3A12 (KI = 0.13–0.33 μM). In fact, complete inhibition of CYP3A12-dependent DZ C3-hydroxylation was possible at a low KET concentration (1 μM). Therefore, it is concluded that one can attempt to conduct P450 reaction phenotype studies with DLM using MBA and KET as selective inhibitors of CYP2B11 and CYP3A12, respectively. The American Society for Pharmacology and Experimental Therapeutics