TLR3 activation enhances antitumor effects of sorafenib in hepatocellular carcinoma by activating NK cell functions through ERK and NF-κB pathways.

Background Sorafenib is a standard therapeutic agent for advanced hepatocellular carcinoma (HCC). However, its efficacy is moderate, as the survival of patients is prolonged for only a few months, and the response rate is low. The mechanism of low efficacy remains unclear. In this study, we investigated the effect of Toll-like receptor 3 (TLR3) on the effects of sorafenib on HCC. Methods Polyinosinic-polycytidylic acid [poly(I: C)] was used as a double-stranded RNA analog and TLR3 agonist in subsequent experiments. After orthotopic implantation of HCC tumors in BALBc nu/nu or C57BL/6 mice, survival time, tumor growth, and metastasis in the abdomen and lungs were analyzed. Flow cytometry and cytotoxicity assays were used to analyze NK cells isolated from the spleen or peripheral blood. ELISA was used to detect the expression of plasma interferon (IFN)-γ and monocyte chemoattractant protein (MCP)-1. In addition, the expression of phosphorylated-extracellular regulated kinase 1/2 (pERK1/2), phosphorylated-protein kinase B (pAKT), ERK1/2 and AKT was analyzed by Western blotting. Results Sorafenib reduced the number and activity of NK cells in tumor-bearing mice and simultaneously decreased the levels of MCP-1 and IFN-γ in the plasma. The combination of sorafenib and poly(I: C) synergistically inhibited tumor growth and metastasis in tumor xenograft mice and prolonged survival. Poly(I: C) not only exerts a direct inhibitory effect on tumor growth and metastasis by targeting the TLR3 receptor on tumor cells but also facilitates the proliferation and activation of NK cells, indirectly impeding tumor progression. Mechanistically, poly(I: C) decreased the sorafenib-induced inhibition of ERK phosphorylation and increased the phosphorylation of IκB in NK cells, thereby enhancing NK cell function. Conclusion Activation of TLR3 can enhance the antitumor effect of sorafenib on HCC. The combination of a TLR3 activator and sorafenib may be a new strategy for the treatment of HCC.