Stephanie van Hoppe

32 Chapter 2 /- ;Abcg2 -/- mice compared to WT mice, whereas brain accumulations in the single knockout strains were not significantly different from those in WT (Fig. 4C; Table I). Thus, also at 2 h, either Abcg2 or Abcb1a/1b alone could profoundly restrict the brain accumulation of afatinib, and only a combined deficiency for both transporters resulted in a drastically increased brain penetration of afatinib. As explained above, the liver concentration of drugs often equilibrates relatively quickly with the plasma concentration. The data in Fig. 4D-F and Table 1 support that notion for afatinib. Whereas the liver concentration of afatinib was moderately different between the four strains (Fig. 4D), these differences appeared to entirely reflect the plasma concentrations, as both the liver-to-plasma ratios (Fig. 4E) and liver accumulation data (Fig. 4F) showed virtually equal levels between the four strains. Also measurements of these parameters for kidney and spleen (Supplemental Fig. 6) revealed at most modest differences between the strains. Collectively, these data indicate that the profound difference in brain accumulation of afatinibbetween the strains, especially at 2 h, is a direct consequence of localized activity of Abcg2 and Abcb1a/1b in the blood-brain barrier. Figure 4 - Brain and liver concentration ( A, D ), tissue-to-plasma ratio ( B, E ) and relative tissue accumulation ( C, F ) of afatinib in female WT, Abcg2 -/- , Abcb1a/1b -/- and Abcg2;Abcb1a/1b -/- mice 2 h after oral administration of 10 mg/kg afatinib. *, P < 0.05, **, P < 0.01, ***, P < 0.001 compared to WT mice; + , P < 0.05, ++ , P < 0.01, +++ , P < 0.001 compared to Abcg2;Abcb1a/1b -/- mice. Data are presented as the mean ± SD. Figure 4. Brain and liver concentration ( A, D ), tissue-to-plasma ratio ( B, E ) and relative tissue accumulation ( C, F ) of afatinib in female WT, Abcg2 -/- , Abcb1a/1b -/- and Abcg2;Abcb1a/1b -/- mice 2 h after oral administration of 10 mg/kg afatinib. *, P < 0.05, **, P < 0.01, ***, P < 0.001 compared to WT mice; + , P < 0.05, ++ , P < 0.01, +++ , P < 0.001 compared to Abcg2;Abcb1a/1b -/- mice. Data are presented as the mean ± SD. *** +++ +++ * + WT Abcg2-/- Abcb1a/1b-/- Abcg2;Abcb1a/1b-/- 0 0.2 1 2 3 4 5 0.5 Brainconcentration (µg/g) *** +++ +++ WT Abcg2-/- Abcb1a/1b-/- Abcg2;Abcb1a/1b-/- 0 5 10 15 Brain toplasma ratio *** +++ +++ WT Abcg2-/- Abcb1a/1b-/- Abcg2;Abcb1a/1b-/- 0 2 4 6 8 10 Brainaccumulation (hr -1 ) WT Abcg2-/- Abcb1a/1b-/- Abcg2;Abcb1a/1b-/- 0 10 20 30 40 50 Liver concentration (µg/g) WT Abcg2-/- Abcb1a/1b-/- Abcg2;Abcb1a/1b-/- 0 50 100 150 Liver toplasma ratio WT Abcg2-/- Abcb1a/1b-/- Abcg2;Abcb1a/1b-/- 0 20 40 60 80 100 Liver accumulation (hr -1) A B D C F E 2-hour experiment