Roles of CYP2C9 and its variants (CYP2C9*2 and CYP2C9*3) in the metabolism of 6-methoxy-2-napthylacetic acid, an active metabolite of the prodrug nabumetone

Nabumetone is a prodrug, used as an anti-inflammation agent and having the active metabolite 6-methoxy-2-naphthylacetic acid (6-MNA). The role of the polymorphic enzyme responsible for the 6- O -demethylation of 6-MNA to 6-hydroxy-2-naphtylacetic acid (6-HNA) was studied using recombinant cytochrome CYP2C9 microsomes (CYP2C9.1, CYP2C9.2 and CYP2C9.3) and human liver microsomes of known genotypes of CYP2C9 . Utilizing recombinant CYP2C9.1, V max and V max / K m values of 6.3 ± 3.3 pmol/min/pmol P450 and 12.4 ± 4.7 nL/min/pmol P450, respectively, were obtained for the 6-MNA metabolism, and were almost similar to those in CYP2C9.2. In contrast, the V max / K m value in recombinant CYP2C9.3 was about one-third that of CYP2C9.1. In kinetic studies using liver microsomes of humans genotyped for the CYP2C9 genes, a sample genotyped as * 3 /* 3 revealed about 4- to sixfold lower intrinsic clearance for 6-HNA formation than did samples genotyped as * 1 /* 1 . No appreciable differences were observed in kinetic parameters for 6-HNA formation in * 1 /* 2 and * 1 /* 3 , while * 2 /* 2 microsomes was comparable to wild type microsomes. In addition, S -warfarin 7-hydroxylation by recombinant CYP2C9.1 and CYP2C9.3 was inhibited by 6-MNA in a mixed manner. The apparent K i value of 6-MNA on S -warfarin 7-hydroxylation by CYP2C9.3 was higher than that by CYP2C9.1. These results may provide valuable information for optimizing the anticoagulant activity of warfarin when nabumetone is co-administrated to patients.