title: Impact of CYP2C8*3 polymorphism on in vitro metabolism of imatinib to N-desmethyl imatinib.
abstract: 1. Imatinib is metabolized to N-desmethyl imatinib by CYPs 3A4 and 2C8. The effect of CYP2C8*3 genotype on N-desmethyl imatinib formation was unknown. 2. We examined imatinib N-demethylation in human liver microsomes (HLMs) genotyped for CYP2C8*3, in CYP2C8*3/*3 pooled HLMs and in recombinant CYP2C8 and CYP3A4 enzymes. Effects of CYP-selective inhibitors on N-demethylation were also determined. 3. A single-enzyme Michaelis-Menten model with autoinhibition best fitted CYP2C8*1/*1 HLM (n = 5) and recombinant CYP2C8 kinetic data (median ± SD Ki = 139 ± 61 µM and 149 µM, respectively). Recombinant CYP3A4 showed two-site enzyme kinetics with no autoinhibition. Three of four CYP2C8*1/*3 HLMs showed single-enzyme kinetics with no autoinhibition. Binding affinity was higher in CYP2C8*1/*3 than CYP2C8*1/*1 HLM (median ± SD Km = 6 ± 2 versus 11 ± 2 µM, P=0.04). CYP2C8*3/*3 (pooled HLM) also showed high binding affinity (Km = 4 µM) and single-enzyme weak autoinhibition (Ki = 449 µM) kinetics. CYP2C8 inhibitors reduced HLM N-demethylation by 47-75%, compared to 0-30% for CYP3A4 inhibitors. 4. In conclusion, CYP2C8*3 is a gain-of-function polymorphism for imatinib N-demethylation, which appears to be mainly mediated by CYP2C8 and not CYP3A4 in vitro in HLM.
authors.affiliation: a Discipline of Pharmacology, School of Medical Sciences, University of Adelaide , Adelaide , Australia and.
authors.forename: Muhammad Suleman
authors.initials: MS
authors.lastname: Khan
authors.affiliation: a Discipline of Pharmacology, School of Medical Sciences, University of Adelaide , Adelaide , Australia and.|b Centre for Personalised Cancer Medicine, University of Adelaide , Adelaide , Australia.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Barratt
authors.affiliation: a Discipline of Pharmacology, School of Medical Sciences, University of Adelaide , Adelaide , Australia and.|b Centre for Personalised Cancer Medicine, University of Adelaide , Adelaide , Australia.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Somogyi
mesh_terms: D000328:Adult; D000368:Aged; D000410:Alanine Transaminase / Q000097:blood; D065727:Cytochrome P-450 CYP2C8 / Q000235:genetics* / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000235:genetics / Q000378:metabolism; D065692:Cytochrome P-450 CYP3A Inhibitors / Q000493:pharmacokinetics*; D005260:Female; D060005:Genotyping Techniques; D006801:Humans; D000068877:Imatinib Mesylate / Q000493:pharmacokinetics*; D007770:L-Lactate Dehydrogenase / Q000097:blood; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D008875:Middle Aged; D011110:Polymorphism, Genetic; D012709:Serum Albumin / Q000378:metabolism; D005723:gamma-Glutamyltransferase / Q000097:blood
chemical_list: D065692:Cytochrome P-450 CYP3A Inhibitors; D012709:Serum Albumin; D000068877:Imatinib Mesylate; D007770:L-Lactate Dehydrogenase; D065727:Cytochrome P-450 CYP2C8; D051544:Cytochrome P-450 CYP3A; D005723:gamma-Glutamyltransferase; D000410:Alanine Transaminase
keywords: Biotransformation; CGP74588; CYP2C8; CYP3A4; Gleevec; microsomes; pharmacogenetics