In-vitro metabolism of celecoxib, a cyclooxygenase-2 inhibitor, by allelic variant forms of human liver microsomal cytochrome P450 2C9: correlation with CYP2C9 genotype and in-vivo pharmacokinetics

Abstract

In-vitro studies were conducted to assess the impact of CYP2C9 genotype on the metabolism (methyl hydroxylation) and pharmacokinetics of celecoxib, a novel cyclooxygenase-2 inhibitor and CYP2C9 substrate. When compared to cDNA-expressed wild-type CYP2C9 (CYP2C9*1), the Vmax/Km ratio for celecoxib methyl hydroxylation was reduced by 34% and 90% in the presence of recombinant CYP2C9*2 and CYP2C9*3, respectively. These data indicated that the amino acid substitution at position 359 (Ile to Leu) elicited a more pronounced effect on the metabolism of celecoxib than did a substitution at position 144 (Arg to Cys). The Vmax/Km ratio was also decreased in microsomes of livers genotyped CYP2C9*1/*2 (47% decrease, mean of two livers), or CYP2C9*1/*3 (59% decrease, one liver). In all cases, these changes were largely reflective of a decrease in Vmax, with a minimal change in Km. Based on simulations of the in-vitro data obtained with the recombinant CYP2C9 proteins, it was anticipated that the pharmacokinetics of celecoxib (as a much as a five-fold increase in plasma AUC) would be altered (versus CYP2C9*1/*1 subjects) in subjects genotyped heterozygous or homozygous for the CYP2C9*2 (Cys144) or CYP2C9*3 (Leu359) allele. In a subsequent clinical study, the AUC of celecoxib was increased (versus CYP2C9*1/*1 subjects) approximately 2.2-fold (range, 1.6-3-fold) in two CYP2C9*1/*3 subjects and one CYP2C9*3/*3 subject receiving a single oral dose (200 mg) of the drug. In contrast, there was no significant change in celecoxib AUC in two subjects genotyped CYP2C9*1/*2.

Oxidation of celecoxib by polymorphic cytochrome P450 2C9 and alcohol dehydrogenase

“…This was also evident in a relatively large sample of livers from heterozygous CYP2C9*1/*3-individuals. Tang et al recently reported similar results, but our experiments showed a greater difference in apparent K m between CYP2C9.1 and CYP2C9.3, and could not confirm a lower intrinsic clearance reported previously for CYP2C9.2 [21]. These discrepancies might relate to the different expression systems used for the kinetic analysis.…”

Pharmacogenetics of nonsteroidal anti-inflammatory drugs

“…26 There are conflicting results about whether CYP2C9*2 has a significant decrease in intrinsic clearance. 26,27 The most marked decrease in metabolism of celecoxib was noted in enzymes expressing homozygous polymorphism CYP2C9*3/*3. 26,27 A corresponding increase in celecoxib's AUC would be expected in individuals expressing CYP2C9*3 allele, and this could result in an increase in dose-related adverse reactions due to accumulation of celecoxib.…”

“…28 These conflicting results may be explained by the fact that celecoxib is also metabolized by CYP3A4; individuals with CYP2C9 polymorphisms may experience different pharmacokinetic profiles depending on their CYP2C9/CPY3A4 ratio. 27 Furthermore, in addition to the ratio of enzymes, there might be a corrective shift from one enzymatic pathway to another that might become saturated leading to the compromising mechanism failing to maintain an adequate level of drug elimination. However, it is still patient specific as to whether this would be consistent with greater efficacy or with an increased incidence and severity of the adverse events.…”

“…Although the cardiovascular adverse events were observed in wild-type genotyped subjects who received low or high dose of celecoxib, the events were reported only in variant genotyped subjects who were administered high doses of the drug. 30 A clinical study conducted by Tang et al 27 measured celecoxib concentrations in plasma samples after a single oral dose. CYP2C9*1/*3 and CYP2C9*3/*3 genotypes demonstrated higher values of AUC compared with subjects with wild-type genotypes.…”

Cloning of cytochrome P-450 2C9 cDNA from human liver and its expression in CHL cells

“…The human CYP2C subfamily comprises four members, CYP2C8, CYP2C9, CYP2C18 and CYP2C19 [3] , accounting for 20% of the total CYP in human liver. CYP2C9 is a polymorphic enzyme responsible for the metabolism of a large number of clinically important drugs such as S-warfarin, phenytoin, tolbutamide, torsemide, losartan, fluoxetine, dapsone [4] , cyclooxygenase-2 inhibitor: celecoxib [5,6] , nonpeptide angiotensin II receptor antagonist: irbesartan [7] and numerous nonsteroidal antiinflammatory drugs. It ranks among the most important drug metabolizing enzymes in humans [8] .…”