Data are reported as μM and were obtained from three independent experiments. All data represent the mean ± S.D.
Reversible inhibition behaviour of TKIs on CYP3A4 and CYP2J2
The reversible inhibition of CYP3A4 and CYP2J2 was investigated with various concentrations of rivaroxaban in the presence and absence of the TKIs (Figures 4, 5). The concentrations of rivaroxaban covered the 1/5Km–5Km range and the TKI concentrations covered the IC50 values. The Ki value of the TKIs was fitted from the kinetic curve and the R2 values and inhibition modes are shown in Tables 2 and 3. As sunitinib did not exert more than 50% inhibition even at 250 μM, the Ki value was not measured. All three TKIs showed non-competitive inhibition on CYP3A4- and CYP2J2-mediated rivaroxaban metabolism with good correlation. This was corroborated by the respective Dixon and Lineweaver–Burk plots, which also showed that the TKIs inhibited rivaroxaban in the non-competitive mode. As with the IC50 results, imatinib showed the strongest inhibition on CYP3A4-mediated rivaroxaban metabolism with a Ki value of 1.92 μM. The Ki values of sunitinib and gefitinib with CYP3A4 were 13.24 and 4.91 μM, respectively, which were similar to their IC50 values. Imatinib and gefitinib showed similar inhibitory effects on CYP2J2, with Ki values of 3.53 and 2.99 μM, respectively. The detailed parameters are given in Tables 1 and 2.