3.3 P450 enzymes responsible for M1 production and inhibition kinetics by gefitinib.
Previous study in our laboratory showed that among the 15 kinds of P450 enzymes examined, CYP1A1, CYP1B1, CYP2C9 and CYP3A4 could catalyze the metabolism of ningetinib into M1. According to the CLintvalues shown in Table 2, CYP1A1 played a predominant role in M1 formation, whereas CYP1B1, CYP2C9 and CYP3A4 had a minor catalytic effect. The inhibition kinetics of gefitinib on HLMs and the four P450 enzymes was further studied. As shown in Fig. 4, gefitinib demonstrated an inhibitive effect on M1 formation in HLMs, CYP1A1, CYP1B1 and CYP2C9 incubations. The inhibition type was determined to be a mixed-type competitive inhibitory nature with Ki of 16.4, 0.095, 1.83 and 9.23 μM. However, the production of M1 in the CYP3A4 incubation was not inhibited by gefitinib.