FB2 is a promising Abl/Src dual tyrosine kinase inhibitor which is designed to overcome imatinib resistance. The present study aims to investigate the role of P-glycoprotein (P-gp) in intestinal absorption of FB2 with an in vitro Caco-2 and MDCK-MDR1 cell model, single-pass intestinal perfusion model and in vivo pharmacokinetics with a selective inhibitor in rats. The results from Caco-2 cells indicated that P_appB-A of FB2 and its metabolites (FB7 and FB10) were much higher than P_appA-B, and the efflux ratio (P_appB-A/P_appA-B) of FB2, FB7 and FB10 were decreased with P-gp inhibitor LSN335984; FB2 was further confirmed to be the substrate of P-gp in MDCK-MDR1 cells. In addition, P_blood of FB2 and the cumulative amount of metabolites in mesenteric blood were elevated in a concentration-dependent manner in rat intestinal perfusion, while both of them were remarkably increased when P-gp inhibitor was added. The F_oral of FB2 was increased to 24.52% when orally coadministrated with verapamil (25 mg/kg), which was significantly higher than that (5.7%) by FB2 (18 mg/kg) alone in rats. The AUC and Cmax of FB2 metabolites (FB7 and FB10) were also increased in the presence of verapamil. In conclusion, the low bioavailability of FB2 is believed to be partially due to the P-gp mediated active efflux and first-pass metabolism in the rat intestine.

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