Chemosensitizing multiple drug resistance of human carcinoma by bicyclol involves attenuated P-glycoprotein, GST-P and Bcl-2

Bicyclol, a second generation of synthetic hepatoprotectant being used in China for anti-hepatitis therapy, shows chemosensitizing effect on reverting multiple drug resistance (MDR) of cytostatic agents in two established MDR carcinoma cell lines, vincristine resistant human stomatic epidermoid carcinoma Vin(R)KB and adriamycin resistant human breast carcinoma Adr(R)MCF-7. The reversal rate of drug resistance was calculated from the changes of the IC50 of cell growth inhibition. Bicyclol at the concentration of 25, 50, 100 mu M induced 2.8 7.3 and 20.7 fold, respectively, reversal of vincristine resistance in VinRKB cell. Bicyclol also reversed the cross-resistance of Vin(R)KB cell to taxol and Adr(R)MCF-7 cell resistance to adriamycin at the similar range of potency. Further, Bicyclol recovered the reduced accumulation of adriamycin in Adr(R)MCF-7 cell partially to the level in drug-sensitive MCF-7 cell, indicate the inhibition of MDR related membrane efflux pump system. Overexpression of membrane p-glycoprotein coded by Mdr-1 genes, the most common efflux pump correlated to MDR, was found in both Vin(R)KB and Adr(R)MCF-7 cells by Western blot and immunocytochemistry as compared with drug-sensitive cells. The p-glycoprotein was decreased to the levels in drug-sensitive cells when Vin(R)KB and Adr(R)MCF-7 cells were treated with Bicyclol for 12-72 hours. Both Vin(R)KB and Adr(R)MCF-7 cells showed increased GSH contents, and Adr(R)MCF-7 cell showed increased GST activity and the overexpression of Bcl-2 protein, by which molecules are tightly related to the MDR formation besides Mdr-1 p-glycoprotein. Bicyclol reduced the GSH contents, GST activities and Bcl-2 expression. All these data demonstrate that, by modifying the expressions of Mdr-1, GSH/GST and Bcl-2, Bicyclol increases the intracellular drug concentration and sensitizes the resistant cells to the anti-carcinoma agents.