INNO-406 is a substrate for P-gp. (A) Growth-inhibitory effects of INNO-406 (○) and imatinib mesylate (•) on K562 cells, (B) growth-inhibitory effects of INNO-406 (○) and imatinib mesylate (•) on P-gp–overexpressing K562/D1-9 cells. (C) K562/D1-9 cells were treated with a combination of INNO-406 and 0 μM (•), 1 μM (▴), 2 μM (▪), 5 μM (○), or 10 μM (△) CsA. (D) K562/D1-9 cells were treated with a combination of INNO-406 and 0 μM (•), 1 μM (▴), 2 μM (▪), 5 μM (○), or 10 μM (△) verapamil. Leukemic cell lines were treated with serial dilutions of either drug for 3 days, and the growth-inhibitory effect of the drugs was assessed by MTT assay. Intracellular concentrations of [¹⁴C]INNO-406 in LLC-PK₁ cells (•) and P-gp–overexpressing LLC-GA5-COL150 cells (○) in the absence of CsA (E), or in the presence of 10 μM CsA (F). Error bars indicate standard deviation.