SENSITIZATION OF HUMAN BLADDER-CANCER CELLS TO FAS-MEDIATED CYTOTOXICITY BY CIS-DIAMMINEDICHLOROPLATINUM(II)

Purpose: The resistance of bladder cancer to anticancer chemotherapeut ic drugs is a major problem. Several immunotherapeutic approaches have been developed to treat drug-resistant tumor cells. The Fas antigen ( Fas)-Fas ligand pathway is involved in cytotoxic T lymphocyte and natu ral killer cell-mediated cytotoxicity. Like the Fas ligand, anti-Fas m onoclonal antibody (mAb) induces apoptosis in tumor cells expressing F as. Several anticancer drugs also mediate apoptosis and may share with Fas common intracellular pathways leading to cell killing. We reasone d that treatment of drug-resistant cancer cells with a combination of anti-Fas mAb and drugs might overcome their resistance. This study has investigated whether anticancer drugs synergize with anti-Fas mAb in cytotoxicity against bladder cancer cells. Materials and Methods: Cyto toxicity was determined by a 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis. Results: Treatment o f the T24 human bladder cancer cell line with anti-Fas mAb in combinat ion with 5-fluorouracil, mitomycin C or methotrexate did not overcome resistance to these agents. However, treatment of T24 tumor cells with a combination of anti-Fas mAb and cis-diamminedichloroplatinum (II) ( CDDP) resulted in a synergistic cytotoxic effect. In addition, the CDD P-resistant T24 line (T24/CDDP) was sensitive to treatment with a comb ination of anti-Fas mAb and CDDP. Synergy by combination of anti-Fas m Ab and CDDP was also achieved in three other bladder cancer lines and four freshly derived human bladder cancer cells. The combination of an ti-Fas mAb and carboplatin also resulted in a synergistic cytotoxic ef fect on T24 cells; however, the combination of anti-Fas mAb and trans- diamminedichloroplatinum (II) resulted in an additive cytotoxic effect . Treatment with CDDP enhanced the expression of Fas on T24 cells. The synergy achieved in cytotoxicity with anti-Pas mAb and CDDP was also achieved in apoptosis. Incubation of T24 cells with anti-Pas mAb incre ased the intracellular accumulation of CDDP. Treatment of freshly isol ated bladder cancer cells with CDDP enhanced their susceptibility to l ysis by autologous lymphocytes. Conclusions: This study demonstrates t hat combination treatment of bladder cancer cells with anti-Fas mAb an d CDDP overcomes their resistance. Synergy was achieved with establish ed CDDP-resistant bladder cancer cells and freshly isolated bladder ca ncer cells. In addition, the sensitization required low concentrations of CDDP, thus supporting the potential in vivo application of combina tion of CDDP and immunotherapy in the treatment of CDDP- and/or immuno therapy-resistant bladder cancer.