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 K_i = 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 K_m = 6 ± 2 versus 11 ± 2 µM, P=0.04). CYP2C8*3/*3 (pooled HLM) also showed high binding affinity (K_m = 4 µM) and single-enzyme weak autoinhibition (K_i = 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.

• Biotransformation
• CGP74588
• CYP2C8
• CYP3A4
• Gleevec
• microsomes
• pharmacogenetics

Acknowledgements

We thank Dr Yibai Li (Discipline of Pharmacology, School of Medical Sciences, University of Adelaide) for technical assistance with the HPLC analysis and microsome preparation, and Dr Pramod Nair (Department of Clinical Pharmacology, School of Medicine, Flinders University) for technical assistance with quantification of microsomal P450 content.

Declaration of interest

The authors report no declarations of interest. This work was supported by the University of Adelaide, School of Medical Sciences funding, and a University of Adelaide International Post Graduate Research Scholarship.

Supplementary material available online

Supplementary Figures S1–S2