Allosteric activation of midazolam CYP3A5 hydroxylase activity by icotinib - Enhancement by ketoconazole

作者：Zhuang, XiaoMei^*; Zhang, TianHong; Yue, SiJia; Wang, Juan; Luo, Huan; Zhang, YunXia; Li, Zheng; Che, JinJing; Yang, HaiYing; Li, Hua; Zhu, MingShe; Lu, Chuang^*

来源：Biochemical Pharmacology, 2016, 121: 67-77.

DOI：10.1016/j.bcp.2016.09.012

• Icotinib
• CYP3A5
• Allosteric activation
• Ketoconazole
• Drug-drug interaction
• Species differences

Icotinib (ICO), a novel small molecule and a tyrosine kinase inhibitor, was developed and approved recently in China for non-small cell lung cancer. During screening for CYP inhibition potential in human liver microsomes (HLM), heterotropic activation toward CYP3A5 was revealed. Activation by icotinib was observed with CYP3A-mediated midazolam hydroxylase activity in HLM (similar to 40% over the baseline) or recombinant human CYP3A5 (rhCYP3A5) (similar to 70% over the baseline), but not in the other major CYPs including rhCYP3A4. When co-incubated with selective CYP3A4 inhibitor CYP3cide or monoclonal human CYP3A4 inhibitory antibody in HLM, the activation was extended to similar to 60%, suggesting CYP3A5 might be the isozyme involved. Further, the relative activation was enhanced to similar to 270% in rhCYP3A5 in the presence of ketoconazole. The activation was substrate and pathway dependent and observed only in the formation of 1 '-OH-midazolam, and not 4-OH-midazolam, 6p-OH-testosterone, or oxidized nifedipine. The activation requires the presence of cytochrome b5 and it is only observed in the liver microsomes of dogs, monkeys, and humans, but not in rats and mice. Kinetic analyses of 1 '-OH-midazolam formation showed that ICO increased the V-max values in HLM and rhCYP3A5 with no significant changes in K-m values. By adding CYP3cide with ICO to the incubation, the V. values increased 2-fold over the CYP3cide control. Addition of ketoconazole with ICO alone or ICO plus CYP3cide resulted in an increase in V-max values and decrease in K-m values compared to their controls. This phenomenon may be attributed to a new mechanism of CYP3A5 heterotropic activation, which warrants further investigation.

• 出版日期2016-12-1
• 单位北京邮电大学