Icotinib Induces Mechanism-Based Inactivation of Recombinant Human CYP3A4/5 Possibly via Heme Destruction by Ketene Intermediate

Icotinib (ICT) is an antitumor drug approved by China National Medical Products Administration and is found to be effective against non-small cell lung cancer. The present study aimed at the interaction of ICT with CYP3A. ICT exhibited time-, concentration-, and NADPH-dependent inhibitory effect on recombinant human CYP3A4/5. About 60% of CYP3A activity was suppressed by ICT at 50 μM after 30 minutes. The observed enzyme inhibition could not be recovered by dialysis. Nifedipine protected CYP3A from the inactivation by ICT. The inhibitory effects of ICT on CYP3A were influenced neither by glutathione/N-acetyl lysine nor by superoxide dismutase/catalase. Incubation of ICT with human hepatic microsomes produced a ketene reactive intermediate trapped by 4-bromobenzylamine. CYP3A4 dominated the metabolic activation of ICT to the ketene intermediate. Ethyl and vinyl analogs of ICT did not induce inactivation of recombinant human CYP3A4/5, which indicates that acetylenic bioactivation of ICT contributed to the enzyme inactivation. Moreover, the metabolic activation of ICT resulted in heme destruction. In conclusion, this study demonstrated that ICT was a mechanism-based inactivator of recombinant human CYP3A4/5, and heme destruction by the ketene metabolite may be responsible for the observed CYP3A inactivation. SIGNIFICANCE STATEMENT: Cytochrome P450 enzymes play an important role in drug-drug interactions. The present study demonstrated that icotinib, an inhibitor of epidermal growth factor receptor used to treat non-small cell lung cancer, is a mechanism-based inactivator of recombinant human CYP3A4/5. The study provided solid evidence for the involvement of acetylene moiety in the metabolic activation as well as the inactivation of the enzyme. Furthermore, the resulting ketene intermediate was found to destroy heme, which is possibly responsible for the observed enzyme inactivation.