Reversal Of MRP1-Mediated Multidrug Resistance In Human Promyelocytic Leukemia Cell Lines HL60/ADR And HL60/MRP By Schisandrin B

The over-expression of P-glycoprotein or Multidrug Resistance-associated Protein 1 (MRP1) on the surface of tumor cells causes multidrug resistance (MDR) in caner. The protein acts as energy-dependent drug efflux pump reducing the intracellular concentration of structurally un-related drugs. Modulators of MRP1 function can restore the sensitivity of MDR cells to such drugs. Schisandrin B (Sch B) is a novel agent recently discovered as a potent and specific inhibitor of P-gp from an active Chinese herb, Schisandra. In this study we evaluated the in vitro modulating potency of this compound in MRP1-overexpressing cancer cells.We recently reported that schisandrin B (Sch B) was a novel P-glycoprotein (P-gp) inhibitor. Sch B could effectively bind to P-gp and reverse drug resistance in different cancer cell lines. In this study, we revealed that Sch B was also an effective inhibitor of multidrug resistance-associated protein 1 (MRP1). RT-PCR showed that both HL60/ADR and HL60/MRP expressed mrp1 but not mdr1 or bcrp. FCM showed that both HL60/ADR and HL60/MRP expressed MRP1 but not P-gp or BCRP. Theactivities of Sch B to reverse MRP 1-mediated drug resistance was tested using HL60/ADR and HL60/MRP, the human promyelocytic leukemia cell lines with the overexpression of MRP1 but not P-gp. Sch B resumed daunorubicin and carboxyfluorescein diacetate (CFDA, a specific fluorescent substrate for MRP1) accumulation and retention in HL60/ADR cells in a time and concentration dependent manner. At the equimolar concentration, Sch B demonstrated significantly stronger potency than probenecid, a known MRP1 inhibitor. Fluorescence microscopy showed that the distribution of intracellular daunorubicin was changed, indicating that the MRP1 on cytoplastic membranes could sequester the drug substrate into vesicules.This study demonstrated that Sch B could specifically inhibit multidrug resistance caused by MRP1 in HL60/ADR and HL60/MRP cell lines. Sch B showed high modulating potency and low cytotoxicity compared with known MRP1 inhibitor probenecid. The results demonstrated that Sch B was a dual inhibitor of P-gp and MRP1, a type suggested to be preferable to the use of combination of 2 specific modulators to prevent drug-drug interaction and cumulative toxicities.