Inhibition of P-gp and BCRP. (A) Effects of JAI-51 on wild-type (S, sensitive) and on P-gp overexpressing (R, resistant) K562 cell lines, with or without daunorubicin (P-gP substrate) and/or cyclosporin (P-gP inhibitor). (B) Effects of JAI-51 on wild-type (S, sensitive) and on BCRP overexpressing (R, resistant) HCT116 cell lines, with or without mitoxantrone (BCRP substrate) and/or cyclosporin (BCRP inhibitor). (C) Percentage of cells in the G2/M phase of the cell cycle after JAI-51 treatment. K562/S and K562/R (A), HCT1162/S and HCT116/R (B) cells were treated with DMSO (vehicle/0.1%) (control) or JAI-51 (10 μM) and analyzed as described in the Methods section. Drug accumulation results are expressed in mean fluorescence intensity (M.F.I.) in arbitrary units. The results are expressed as the mean ± SD from 3 different experiments. * P < 0.05 cyclosporin or JAI-51-treated resistant cells versus their respective control. (C) To test whether JAI-51 was a substrate of P-gp and/or BCRP, multidrug resistant cells and their respective parental cell lines (HCT116/R, HCT116/S, K562/R and K562/S) were incubated in the presence of JAI-51 (10 μM). Phases of the cell cycle were analyzed at 24 h as described in Figure 1B. G2/M is expressed in % of cells. The results are expressed as the mean ± SD from 3 different experiments. * P < 0.05 JAI-51-treated versus control.