Enhanced cisplatin-mediated cytotoxicity and apoptosis against bladder cancer cells in vitro and in vivo by the selective cyclooxygenase-2 inhibitor.

5419 Cyclooxygenase-2 ( COX-2 ) is a key inducible enzyme involved in the production of prostaglandins, and its inhibitors have been demonstrated to induce apoptosis in various cancer cells. Several anticancer agents also mediate apoptosis and may share the common intracellular pathways leading to apoptosis. Since enhance\. ment of COX-2 expression has been reported in bladder cancer, we reasoned that combination treatment of bladder cancer cells with COX-2 inhibitors and anticancer agents may result in synergistic apoptosis. This study has examined whether the selective COX-2 inhibitor synergizes with anticancer agents in cytotoxicity and apoptosis against bladder cancer cells. The selective COX-2 inhibitor JTE-522 was gift from Japan Tabacco Co. Ltd. Cytotoxicity was determined by the microculture tetrazolium dye assay. Apoptosis was examined by the TUNEL assay. The mRNA expression of COX-2 was observed in T24, T24/CDDP and J82 bladder cancer cell lines and two primary cultured bladder cancer cells, but not normal bladder cells. Combination treatment of T24 cells with JTE-522 and cisplatin ( CDDP ) resulted in a synergistic cytotoxic effect. Synergy was also achieved in the CDDP-resistant T24 bladder cancer line ( T24/CDDP ), the J82 bladder cancer line and two primary cultured bladder cancer cells, but not normal bladder cells. Although treatment of T24 cells with JTE-522 and carboplatin resulted in synergistic cytotoxicity, combination treatment with JTE-522 and trans-DDP resulted in an additive cytotoxic effect. The synergistic cytotoxicity was obtained irrespective of the sequence of the treatment, and the highest cytotoxicity was obtained when T24 cells were treated with JTE-522 initially. The synergy achieved in cytotoxicity with JTE-522 and CDDP was shown to be due to apoptosis. The mechanisms responsible for the synergistic cytotoxicity and apoptosis was examined. Treatment of T24 cells with JTE-522 reduced the expression of anti-apoptotic molecule Bcl-2, but not Bcl-XL or Bax. Caspase 3 activity in T24 cells was enhanced after combination treatment with JTE-522 and CDDP. The in vivo significant growth inhibitory effect of JTE-522 and CDDP against the T24 line heterotransplanted in SCID mice was also observed. This study has demonstrated that combination treatment of bladder cancer cells with the selective COX-2 inhibitor JTE-522 and CDDP results in synergistic cytotoxicity and apoptosis in vitro and in vivo . The synergy obtained with established CDDP-resistant and primary cultured bladder cancer cells required low subtoxic concentrations of CDDP. These findings support the potential clinical application of a combination of JTE-522 and CDDP in the treatment of bladder cancer as a new form of therapy with more selective cytotoxicity and less collateral side effects.