Stephanie van Hoppe

80 Chapter 4 Ibrutinib-DiOH is substantially more polar than the parent ibrutinib, and this is probably reflected in lower brain-to-plasma ratios and brain accumulation than for ibrutinib (Figure 4A-C). However, the impact of the absence of Abcb1a/1b on altering brain-to- plasma ratios and brain accumulation of ibrutinib-DiOH was even more pronounced than for ibrutinib, with 12- to 15-fold increases relative to wild-type values (Figure 4A-C, Supplemental Table 1). Like for ibrutinib, any contribution of Abcg2 to limiting ibrutinib-DiOH brain accumulation was at best small. At the same time, the relative liver accumulation of ibrutinib-DiOHwas very similar to that of ibrutinib, and not significantly different between the tested mouse strains (Figure 4D-F). Similar parameters for the distribution of both ibrutinib and ibrutinib-DiOH to kidney and spleen also did not yield pronounced differences between the strains, although there may be some impact of Abcb1a/1b deficiency on increasing ibrutinib spleen distribution (Supplemental Figures 5 and 6). Distribution of both ibrutinib and ibrutinib-DiOH to the brain thus appears to be markedly limited by Abcb1a/1b activity, but distribution to most of the other tested organs is not. In spite of the marked changes in brain distribution of ibrutinib, we did not see any indications for toxicity of ibrutinib at the dosages used in the Abcb1a/1b;Abcg2 -/- mice. Figure 4. Brain and liver concentration ( A, D ), tissue-to-plasma ratio ( B, E ) and relative tissue accumulation ( C, F ) of ibrutinib-DiOH (DiOH) in female WT, Abcb1a/1b −/− , Abcg2 −/− and Abcb1a/1b;Abcg2 −/− mice 1 h after oral administration of 10 mg/kg ibrutinib. *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared to WT mice. Data are given as mean ± SD. n = 5−6 mice per group. WT Abcg2 -/- Abcb1a/1b -/- Abcb1a/1b;Abcg2 -/- 0 20 40 60 DiOH brain concentration (ng/g) WT Abcg2 -/- Abcb1a/1b -/- Abcb1a/1b;Abcg2 -/- 0 200 400 600 800 1000 DiOH liver concentration (ng/g) WT Abcg2 -/- Abcb1a/1b -/- Abcb1a/1b;Abcg2 -/- 0.00 0.05 0.10 0.15 DiOH brain to plasma ratio WT Abcg2 -/- Abcb1a/1b -/- Abcb1a/1b;Abcg2 -/- 0.0 0.5 1.0 1.5 2.0 DiOH liver to plasma ratio WT Abcg2 -/- Abcb1a/1b -/- Abcb1a/1b;Abcg2 -/- 0.00 0.02 0.04 0.06 0.08 DiOH brain accumulation (h -1 ) WT Abcg2 -/- Abcb1a/1b -/- Abcb1a/1b;Abcg2 -/- 0.0 0.5 1.0 1.5 DiOH liver accumulation (h -1 ) A B C D E F 1-hour experiment *** **** **** **** **** **** * * Figure 4 - Brain liver concentration ( A, D ), tissue-to-plasma ratio ( B, E ) nd relative tissue accu ulatio ( C, F ) of ibrutinib-DiOH (DiOH) in female WT, Abcb1a/1b −/− , Abcg2 −/− and Abcb1a/1b;Abcg2 −/− mice 1 h after oral administration of 10 mg/kg ibrutinib. *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared to WT mice. Data are given as mean ± SD. n = 5−6 mice per group.