Comparisons between in-vitro and in-vivo metabolism of (S)-warfarin:: catalytic activities of cDNA-expressed CYP2C9, its Leu359 variant and their mixture versus unbound clearance in patients with the corresponding CYP2C9 genotypes

To study whether an in-vitro model for three different genotypes of human CYP2C9*3 polymorphism would be useful for predicting the in-vivo kinetics of (S)-warfarin in patients with the corresponding genotypes, the intrinsic clearance (Cl-int or V-max/K-m) for (S)-warfarin 7-hydroxylation obtained hem recombinant human CYP2C9*1 [wild-type (wt)] and CYP2C9*3 (Leu(359)/Leu) expressed in yeast and the mixture of equal amounts of these were compared with the in-vivo unbound oral Cl (Cl-po,Cl-u) of (S)-warfarin obtained from 47 Japanese cardiac patients with the corresponding CYP2C9 genotypes, The in-vitro study revealed that the recombinant CYP2C9*1 (wt/wt), 2C9*3 (Leu(359)/Leu) and their mixture (Ile(359)/Leu) possessed a mean K-m of 2.6, 10.4 and 6.6 mu M and V-max of 280, 67 and 246 pmol/min/nmol P450, respectively. Thus, the mean in-vitro Cl-int obtained from recombinant CYP2C9*3 (Leu(359)/Leu) and the mixture (Ile(359)/Leu) of 2C9*3 and 2C9*1 were 94% and 65% lower than that obtained from CYP2C9*1 (wt/wt) (6.7 versus 38 versus 108 ml/min/mu mol P450, respectively), The in-vivo study showed that the median Cl-po,Cl-u for (S)-warfarin obtained from patients with homozygous (Leu(359)/Leu, n = 1) and heterozygous (Ile(359)/Leu, n = 4) CYP2C9*3 mutations were reduced by 90% (62 ml/min) and 66% (212 ml/min, P < 0.05) compared with that obtained from those with homozygous 2C9*1 (625 ml/min, n = 42). Consequently there was a significant correlation (r = 0.99, P < 0.05) between the in-vitro Cl-int for (S)-warfarin 7-hydroxylation and the in-vivo Cl-po,Cl-u for (S)-warfarin in relation to the CYP2C9*3 polymorphism, Ln conclusion, the in-vitro model for human CYP2C9*3 polymorphism using recombinant cytochrome P450 proteins would serve as a useful means for predicting changes in in-vivo kinetics for (S)-warfarin and possibly other CYP2C9 substrates in relation to CYP2C9*3 polymorphism, Pharmacogenetics 8:365-373 (C) 1998 Lippincott Williams & Wilkins.