Sorafenib enhances the chemotherapeutic efficacy of S-1 against hepatocellular carcinoma through downregulation of transcription factor E2F-1

Sorafenib and S-1 (one mixed formulation containing 5-FU prodrug and dihydropyrimidine dehydrogenase inhibitor) were two effective agents against hepatocellular carcinoma (HCC), but whether they had synergistic effects remained unclear. The present study aimed at evaluating their synergistic effects against HCC and its mechanisms. Inhibitory effects of sorafenib, 5-FU and their combination on HCC cells PLC/PRF/5 and SK-HEP-1 were evaluated. Expressions of transcription factor E2F-1 and its downstream thymidylate synthetase (TS) in the treated cells were determined using real-time PCR and Western blot. In vivo anti-tumoral efficacy of S-1 plus sorafenib on HCC was evaluated in NOD/SCID mice. E2F-1 and TS expressions in tumors were determined by immunohistochemical staining. Sorafenib inhibited growth of HCC cells in dose-dependent manner, with IC50 of 5.4 +/- A 0.3 mu mol/L for PLC/PRF/5 and 5.3 +/- A 0.5 mu mol/L for SK-HEP-1. Sorafenib (1 mu mol/L) enhanced inhibitory efficacy of 5-FU on HCC cells in vitro, dropping IC50 of 5-FU from 167.7 +/- A 12.1 to 105.4 +/- A 8.4 mu mol/L for PLC/PRF/5 and 115 +/- A 10.2 to 82 +/- A 7.4 mu mol/L for SK-HEP-1 (both p < 0.01). Sorafenib downregulated E2F-1 and TS expressions on HCC cells, and its combination with 5-FU yielded a synergistic downregulation of TS expression on HCC cells. In NOD/SCID mice with subcutaneously inoculated HCC, sorafenib combined with S-1 yielded greater inhibition on tumor growth and remarkable TS suppression when compared with sorafenib or S-1 alone (all p < 0.05). Sorafenib enhanced therapeutic efficacy of 5-FU/S-1 against HCC through downregulation of E2F-1 and TS expressions. Sorafenib combined with S-1 might represent as valuable therapeutic regimen against HCC.