Abstract: Objective Multidrug resistance is one of the main causes of treatment failure of chemotherapy.Reversal agents may be used clinically.This study was to evaluate the reverse effect of microwave hyperthermia on drug-resistance of MCF-7/ ADM to adriamycinum(ADM) cells,and to explore its mechanisms.Methods Breast cell line MCF-7 and its ADM- resistance cell line MCF-7/ADM were treated with ADM and microwave hyperthermia.Reverse effect of microwavehyperthermia on drug-resistance of MCF-7/ADM to ADM was tested by MTT assay.The levels of cellular multidrug resistance related protein(MRP) and P-glycoprotein(P-gp) were detected by Real-Time PCR.The intracellular concentration of ADM was measured by high performance liquid chromatography.Results The resistance index of MCF-7/ADM cells to ADM was 45.5.After microwave hyperthermia, the 50%inhibitory concentration(IC_(50)) of ADM to MCF-7/ADM cells reduced by 2.64 folds from(60.56±2.38)ug/ ml to(22.86±2.76)ug/ml.Protein levels of MRP and P-gp were higher in MCF-7/ADM cells than that in MCF-7 cells,and they were markedly decreased in MCF-7/ADM cells after microwave hyperthermia.The concentration of ADM in MCF-7/ADM cells was significantly increased after microwave hyperthermia.Conclusion Microwave hyperthermia may reverse drug-resistance of MCF-7/ADM cells to ADM through down-regulating MRP and P-gp and increasing intracellular cumulation of ADM.

Key words: Microwave hyperthermia, Breast cancer, MCF-7/ADM Cells, Adriamycinum, Drug resistance