The prognosis of muscle-invasive bladder cancer with metastasis is poor. There have been no therapeutic improvements for many years, and an innovative therapy for muscle-invasive bladder cancer has been awaited to replace the conventional cytotoxic chemotherapy. Here, we show a candidate method for the treatment of bladder cancer. The combined treatment with a novel histone deacetylase (HDAC) inhibitor, OBP-801, and celecoxib synergistically inhibited cell growth and markedly induced apoptosis through the caspase-dependent pathway in high-grade bladder cancer cells. Furthermore, the combined treatment induced expression of death receptor 5 (DR5). We identified that knockdown of DR5 by small interfering RNA (siRNA) significantly suppressed apoptosis by the combined treatment. Therefore, we conjectured that the apoptosis induced by OBP-801 and celecoxib is at least partially dependent on DR5. However, it was interesting that the combined treatment drastically suppressed expression of DR5 ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). These data suggest that there is no involvement of TRAIL in the induction of apoptosis by the combination, regardless of the dependence of DR5. Moreover, xenograft studies using human bladder cancer cells showed that the combined therapy suppressed tumor growth by upregulating expressions of DR5 and Bim. The inhibition of tumor growth was significantly more potent than that of each agent alone, without significant weight loss. This combination therapy provided a greater benefit than monotherapy in vitro and in vivo These data show that the combination therapy with OBP-801 and celecoxib is a potential novel therapeutic strategy for patients with muscle-invasive bladder cancer. Mol Cancer Ther; 15(9); 2066-75. ©2016 AACR.
©2016 American Association for Cancer Research.