The data are reported as the mean ± S.D. of three incubations.
IC50-shift assays on CYP2J2 and CYP3A4
To comprehensively explore the inhibitory effects of the TKIs on the two P450 isoforms, their mechanism-dependent inhibition was investigated. IC50 shift assays of CYP2J2 and CYP3A4 were performed. Compared with direct inhibition (IC50: 5.23 and 3.71 μM for imatinib and gefitinib, respectively), the 30-min pre-incubation with NADPH in the CYP2J2 incubation did not significantly change the inhibitory effect of imatinib and gefitinib (Figure 6A, C, and Table 4), while the inhibitory effect of sunitinib was slightly increased after the 30-min pre-incubation with NADPH in the CYP2J2 incubation with the IC50 decreasing 1.27-fold (Figure 6B and Table 4). Although the 30-min pre-incubation slightly increased its inhibitory activity, the inhibition of CYP2J2 by sunitinib was still weaker than by imatinib and gefitinib, with an IC50 of 312.90 μM (Table 4). In brief, the 30-min pre-incubation did not significantly affect the inhibition of CYP2J2 by the three TKIs, with all IC50shifts being less than 1.5-fold. Additionally, all IC50values for the inhibition of CYP3A4 by the TKIs decreased by more than 1.5-fold, which indicated that time-dependent inactivation of CYP3A4 by all three TKIs had occurred (Table 5.). Notably, sunitinib showed the largest change in IC50 shift (Figure 6E), with an IC50 value following the 30 min pre-incubation of 2.73 μM.