Identification and functional assessment of a new CYP2C9 allelic variant CYP2C9∗59

Abstract

CYP2C9, one of the most important drug-metabolizing enzymes, is responsible for metabolizing approximately 15% of clinically important drugs, including warfarin, diclofenac, and losartan. Similar to other CYP members, human CYP2C9 exhibits marked genetic polymorphisms among individuals of different ethnicities. In this study, a novel missense mutation (1300A>T) was identified in a warfarin-sensitive patient after a genetic screen of three candidate genes related to high variability in response to warfarin doses. This base transversion leads to an Ile-to- Phe amino acid substitution at codon 434 within the CYP2C9 protein, and this new variant has been named a novel allele, CYP2C9∗59, by the Human CYP Allele Nomenclature Committee (http://www.cypalleles.ki. se/cyp2c9.htm). The exogenous expression of CYP2C9.59 in insect cell microsomes revealed that, despite a similar protein expression level as wild-type CYP2C9, variant CYP2C9.59 exhibited significantly reduced maximal velocity, V max, and/or increased Michaelis constant, K m, values toward three CYP2C9-specific substrates. Our data suggest that the 1300A>T mutation can greatly decrease the enzymatic activity of the CYP2C9 protein both in vitro and in vivo.