title: Decreased susceptibility of the cytochrome P450 2B6 variant K262R to inhibition by several clinically important drugs.
abstract: Cytochrome P450 (P450) 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 Escherichia 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 K(i) values with clopidogrel, itraconazole, and raloxifene and approximately 6-fold increase in K(i) with sertraline compared with CYP2B6dH. Likewise, K262R showed 2-, 4-, and >20-fold higher K(s) 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 IC(50) with 4-(phenyl)pyridine and approximately 2-fold lower IC(50) 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 K(i) with sertraline and clopidogrel compared with CYP2B6dH. The results suggest that individuals, especially homozygotes, with the 2B6*4 or 2B6*6 allele might be less susceptible to drug interactions resulting from P450 inhibition.
authors.affiliation: Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California, USA.
authors.forename: Jyothi C
authors.initials: JC
authors.lastname: Talakad
authors.forename: Santosh
authors.initials: S
authors.lastname: Kumar
authors.forename: James R
authors.initials: JR
authors.lastname: Halpert
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D065702:Cytochrome P-450 CYP2B6; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D008958:Models, Molecular; D016296:Mutagenesis; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D010089:Oxidoreductases, N-Demethylating