Neferine increases STI571 chemosensitivity via inhibition of P-gp expression in STI571-resistant K562 cells

We investigated the effects of neferine (Nef) on STI571 sensitivity and the possible mechanism in STI571-resistant K562/G01 cells. We observed cell proliferation by the modified MTT (methyl thiazolyl tetrazolium) assay. We determined the intracellular concentration of STI571 in K562/G01 cells by high-performance liquid chromatography (HPLC), the expression of P-glycoprotein (P-gp) by Western blotting, and the expression of MDR-1 mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR). We observed that drug resistance to STI571 for K562/G01 cells was 43.99-fold higher than that for K562 cells. We also observed that a low concentration of Nef (<8 μM) and verapamil hydrochloride (VRP) (<10 μM) showed no direct cytotoxicity but significantly reduced the 50% cell growth inhibitory concentration (IC(50)) values of STI571 in K562/G01 cells. The reverse multiples for 8 μM Nef and 10 μM VRP were approximately two-fold. Both Nef (8 μM) and VRP (10 μM) decreased MDR-1 mRNA and P-gp protein expression and increased intracellular STI57I concentrations significantly in K562/G01 cells. Nef is a candidate chemical that can increase STI571 chemosensitivity in STI571-resistant K562 cells by inhibition of P-gp expression and increasing intracellular STI571 accumulation.