Objective: To investigate the mechanism of combination of matrine and tetrandrine for reversal of multidrug resistance of breast carcinoma MCF-7 cells. Method: Human breast carcinoma MCF-7 and doxorubicin-resistant MCF-7/DOX cells were treated with matrine

tetrandrine and doxorubicin. The inhibition of drugs on cell proliferation was detected by MTT assays. The fluorescence intensity of Rho123 was detected by flow cytometry. The expression of P-glycoprotein was examined by Western blot. Result: The IC50value of matrine toward MCF-7/DOX cell lines was similar to that of MCF-7 cells

indicating that the former has non-cross resistance to matrine. Flow cytometry analysis not only showed matrine reverse multi-drug resistance on MCF-7/DOX

but also has synergy effect with tetrandrine. The cell proliferation inhibition of doxorubicin was obviously increased when the combination of matrine with tetrandrine. Furthermore

reduction of P-glycoprotein expression was detected in MCF-7/DOX cells after exposure to matrine or combination with tetrandrine. Conclusion: Matrine has synergy effect with tetrandrine on reversal of multidrug resistance and reduction of P-glycoprotein expression in breast carcinoma MCF-7 cells.