RT Journal Article SR Electronic T1 Q172H Replacement Overcomes Effects on the Metabolism of Cyclophosphamide and Efavirenz Caused by CYP2B6 Variant with Arg262 JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 2045 OP 2048 DO 10.1124/dmd.111.039586 VO 39 IS 11 A1 Noritaka Ariyoshi A1 Miyuki Ohara A1 Mayumi Kaneko A1 Sakino Afuso A1 Takuya Kumamoto A1 Hiroyoshi Nakamura A1 Itsuko Ishii A1 Tsutomu Ishikawa A1 Mitsukazu Kitada YR 2011 UL http://dmd.aspetjournals.org/content/39/11/2045.abstract AB There are a number of reports indicating that CYP2B6*6 (c.516G>T and c.785A>G) is responsible for decreased clearance of efavirenz (EFV), although increased disposition of cyclophosphamide (CPA) in individuals with this polymorphism was observed. Thus, we hypothesized that the effects of the two single nucleotide polymorphisms (SNPs) of CYP2B6*6 on the metabolism of drugs might be considerably different between these two agents. To clarify this possibility, we expressed two major variants of this enzyme, CYP2B6.6 (Q172H and K262R) and CYP2B6.4 (K262R), and investigated metabolic activities of these variants toward EFV and CPA. Kinetic analyses clearly indicated that CYP2B6.4 possessed enhanced metabolic activity toward EFV compared with that of the wild-type enzyme (CYP2B6.1), whereas CPA was metabolized less efficiently by CYP2B6.4 than by CYP2B6.1. On the other hand, CYP2B6.6 showed a completely opposite character, suggesting that Q172H gives inverse effects on metabolic activities of CYP2B6 affected by K262R. Although it is recognized that effects of amino acid change in cytochrome P450 on the metabolic activity depend on substrates, this study revealed SNPs giving an opposite effect on the metabolism of two clinically important drugs currently used. Furthermore, this study provides the first evidence that Q172H can reverse the direction of the effect caused by K262R in CYP2B6 on the metabolism of certain drugs.