Stephanie van Hoppe

56 Chapter 3 for the three strains for brain, liver, kidney, spleen, and testis were all relatively close and not significantly different (Supplemental Table 1 and data not shown). Overall, there is therefore no indication that Cyp3a or CYP3A4 activity has a major impact on the plasma exposure and tissue distribution of osimertinib in mice. Figure 4 - Plasma concentration-time curves of osimertinib in male wild-type (WT) (black), Cyp3a -/- (purple triangles), Cyp3aXAV (red squares) mice, over 90 minutes after oral administration of 10 mg/kg osimertinib. Data are given as mean ± SD. N = 5-6 mice per group. B r a i n a c c umu l a t i on o f t he a c t i ve me t abo l i t e A Z 5104 i s r e s t r i c t ed by Ab c b1a / 1b and Ab c g2 In the final phase of this study an LC-MS/MS assay became available for the pharmacodynamically most active metabolite of osimertinib, AZ5104 (Supplemental Figure 1). Samples still available from the 1.5 h study with ABC transporter knockout strains could then be re-measured for the presence of this compound after oral administration of osimertinib. As shown in Supplemental Figure 4, the plasma concentrations of AZ5104 and the AZ5104-to-osimertinib ratios gradually rose between 0.5 and 1.5 h, with no significant differences between the four tested strains (WT, Abcb1a/1b -/- , Abcg2 -/- , and Abcb1a/1b;Abcg2 -/- ). Themetabolite-to-osimertinib ratiowas about 20-25% at 1.5 h. Whereas the plasma levels of AZ5104 were thus hardly affected by the ABC transporters, its brain concentration, brain-to-plasma ratio, and brain accumulation were dramatically increased in the Abcb1a/1b -/- mice, but especially in the Abcb1a/1b;Abcg2 -/- mice (Figure 5A-C). Abcg2 deficiency did not show a significant difference compared to WT mice, however due to the significant difference between Abcb1a/1b and Abcb1a/1b;Abcg2 -/- mice in the brain (P < 0.001), it does suggest that Figure 4. Plasma concentration-time curves of osimertinib in male wild-type (WT) (black), Cyp3a -/- (purple triangles), Cyp3aXAV (red squares) mice, over 90 minutes after oral administration of 10 mg/kg osimertinib. Data are given as m an ± SD. N = 5-6 mic per group. 0.5 1.0 1.5 0 0 50 100 150 200 time (h) Osimertinib plasma concentration (ng/ml) WT Cyp3a -/- Cyp3aXAV