Sorafenib augments cytotoxic effect of S-1 in vitro and in vivo through TS suppression

Purpose: Sorafenib, a multikinase and tyrosine-kinase inhibitor, has anti-tumor activity in patients with advanced renal cell carcinoma (RCC). Recently, we reported that S-1 was active and well tolerated for the treatment of cytokine-refractory metastatic RCC. Therefore, we hypothesized that S-1 might be a good candidate for combination therapy with molecular targeting agents. In this study, we examined the mechanisms underlying for the synergism between S-1 and Sorafenib for RCC treatment in vitro and in tumor-bearing murine models. Methods: Human RCC cell lines were used for the in vitro cell proliferation assay. ACHN and 786-O tumors were subcutaneously transplanted into NCr-nu/nu-mice. Mice were treated with S-1 and/or Sorafenib, and tumor growth and side effects were monitored. Results: Synergistic anti-proliferative effects of Sorafenib and S-1 were clearly demonstrated in ACHN and 786-O cell lines in vitro due to the suppression of TS and E2F-1 expression. In the NCr-nu/nu model, the synergistic anti-tumor effects of S-1 and Sorafenib were again clearly seen, indicating direct synergistic effects of each drug on tumor growth. Conclusions: Our results demonstrate the synergistic activity of S-1 and Sorafenib and provided the rationale for combination therapy with S-1 and Sorafenib for the treatment of patients with advanced RCC.