PGP and leukemia: Compounds 6g and 6i inhibited rhodamine 123 efflux in the P-gp overexpressed leukemia cells, K562/Dox, at concentrations of 0.19 μM and 0.39 μM, respectively, and increased the intracellular accumulation of doxorubicin at the submicromolar concentration of 0.098 μM.