Decreased Susceptibility of the Cytochrome P450 2B6 Variant K262R to Inhibition by Several Clinically Important Drugs.
Drug Metab Dispos. 2008 Dec 12
Talakad JC, Kumar S, Halpert JR. University of California San Diego.
Cytochrome P450 (CYP) 2B6 metabolizes a number of clinically relevant drugs and is one of the most highly polymorphic human P450 enzymes, with the Lys(262)-->Arg substitution being especially common in several genetic variants. Therefore, K262R (2B6*4) was created in the CYP2B6dH background (N-terminal modified and C- terminal His tagged) and expressed in E. coli. The recombinant CYP2B6dH and K262R were purified and studied to investigate the effect of the Lys(262)-- >Arg substitution with six of the most potent drug inhibitors of CYP2B6, namely clopidogrel, clotrimazole, itraconazole, raloxifene, sertraline and ticlopidine. K262R showed a > 3-fold increase in the Ki values with clopidogrel, itraconazole, and raloxifene and ~ 6-fold increase in Ki with sertraline, compared with CYP2B6dH. Similarly, K262R showed 2-, 4-, and > 20-fold higher Ks values than CYP2B6dH with clopidogrel, sertraline, and itraconazole, respectively. In contrast, when tested with several known type II inhibitors of CYP2B enzymes, K262R showed a 10-fold lower IC50 with 4-(phenyl)pyridine and ~2-fold lower IC50 with 4-(4-nitrobenzyl)pyridine or 1-(4-phenyl) benzylimidazole than CYP2B6dH. Subsequent analysis predicted possible in vivo drug-drug interactions between the CYP2B6 substrate efavirenz and drug inhibitors clopidogrel, clotrimazole, itraconazole, sertraline, and ticlopidine. Furthermore, Q172H/K262R (2B6*6), which is the most common genetic variant of CYP2B6 harboring K262R, was created in CYP2B6dH, expressed, purified, and characterized for inhibition. Q172H/K262R showed a > 6-fold increase in Ki with sertraline and clopidogrel compared with CYP2B6dH. The results suggest that individuals, especially homozygotes, with the *4 or *6 allele might be less susceptible to drug interactions resulting from P450 inhibition.