DOXORUBICIN SENSITIZES HUMAN BLADDER-CARCINOMA CELLS TO FAS-MEDIATED CYTOTOXICITY

BACKGROUND. The resistance of bladder carcinoma to anticancer chemothe rapeutic agents remains a major problem. Hence, several immunotherapeu tic approaches have been developed to treat the drug-resistant cancer cells. Fas antigen (Fas) and Fas Ligand participate in cytotoxicity me diated by T lymphocytes and natural killer cells. Like Fas ligand, ant i-Fas monoclonal antibody (MoAb) induces apoptosis of the cells expres sing Fas. This study examined whether bladder carcinoma cells are sens itive to cytotoxicity mediated hp anti-Fas MoAb and whether anticancer agents synergize with anti-Fas MoAb in cytotoxicity. METHODS. Cytotox icity was determined by a 1-day microculture tetrazolium dye assay. Sy nergy was assessed by isobolographic analysis. RESULTS. The T24 human bladder carcinoma cell line constitutively expressed the Fas on the ce ll surface; however, T24 Line was resistant to anti-Fas MoAb. Treatmen t of T24 cells with anti-Fas MoAb in combination with mitomycin C, met hotrexate, or S-fluorouracil did not overcome their resistance to thes e agents, However, treatment of T24 cells with a combination of anti-F as MoAb and doxorubicin resulted in a synergistic cytotoxic effect. In addition, the doxorubicin-resistant T24 cells were sensitive to treat ment with a combination of anti-Fas MoAb and doxorubicin. Synergy was also achieved in three other bladder carcinoma cell lines and four fre shly derived human bladder carcinoma cells. Treatment with anti-Fas Mo Ab in combination with epirubicin or pirarubicin also resulted in a sy nergistic cytotoxic effect on T24 cells. The mechanisms of synergy wer e examined. Anti-Fas MoAb did not affect the intracellular accumulatio n of doxorubicin, the expression of P-glycoprotein, or the expression of the antioxidant glutathione S-transferase-pi mRNA. However, treatme nt with doxorubicin enhanced the expression of Fas on T24 cells. CONCL USIONS. This study demonstrated that treatment of bladder carcinoma ce lls with doxorubicin sensitized the cells to lysis by anti-Fas MoAb. T he synergistic effect obtained with established doxorubicin-resistant bladder carcinoma cells and freshly isolated bladder carcinoma cells s uggests that drug-resistant bladder carcinoma cells can be sensitized by doxorubicin to Fas- and Fas ligant-mediated cytotoxicity by lymphoc ytes. Furthermore, the sensitization required low concentrations of do xorubicin, thus supporting the in vivo application of a combination of chemotherapy and immunotherapy in the treatment of drug-resistant and /or immunotherapy-resistant bladder carcinoma. (C) 1997 American Cance r Society.