Previous studies have demonstrated that cisplatin (CDDP) sensitizes bladder cancer cells to Fas-mediated cytotoxicity and that CDDP also enhances the cytotoxic effect of 5-fluorouracil (5-FU). These agents mediate apoptosis and may share common intracellular pathways leading to cell killing. We reasoned that combination treatment with CDDP, 5-FU and anti-Fas monoclonal antibody (mAb) might overcome the drug-resistance. We investigated whether CDDP, 5-FU and anti-Fas mAb synergize in cytotoxicity and apoptosis against the T24 bladder cancer line. Cytotoxicity was monitored by a one day microculture tetrazolium dye assay. Treatment of T24 cells with anti-Fas mAb in combination with CDDP or 5-FU resulted in a synergistic cytotoxic effect. In addition, combination treatment of T24 cells with CDDP, 5-FU and anti-Fas mAb further enhanced the synergistic cytotoxicity achieved by two agents. The synergy achieved in cytotoxicity with CDDP, 5-FU and anti-Fas mAb was also achieved in apoptosis. The current study demonstrates that combination treatment of bladder cancer cells with CDDP, 5-FU and anti-Fas mAb overcomes their resistance. In addition, the sensitization required low concentrations of CDDP and 5-FU, and thus supporting the potential in vivo application of combination of CDDP, 5-FU and immunotherapy in the treatment of drug-resistant bladder cancer.

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