Sorafenib/MEK inhibitor combination inhibits tumor growth and the Wnt/p-catenin pathway in xenograft models of hepatocellular carcinoma

Mutations affecting the Wnt/[beta]-catenin pathway have been identified in 26-40% of hepatocellular carcinoma (HCC) cases. Aberrant activation of this pathway leads to uncontrolled cell proliferation and survival. Thus, identifying Wnt/p-catenin pathway inhibitors may benefit a subset of patients with HCC. In the present study, the effects of sorafenib and a MEK inhibitor on tumor growth and Wnt/[beta]-catenin signaling in HCC models were evaluated. A [beta]-catenin mutant and [beta]-catenin wild-type HCC models were treated once daily with i) 10 mg/kg sorafenib, ii) 15 mg/kg refametinib (or 25 mg/kg selumetinib), or iii) sorafenib/refametinib. Western blotting was employed to determine changes in biomarkers relevant to Wnt/[beta]-catenin signaling. Apoptosis, cell proliferation and [beta]-catenin localization were analyzed by immunohistochemistry. Sorafenib/refametinib markedly inhibited tumor growth and cell proliferation, and caused cell death in naive and sorafenib-resistant HCC models. Despite similar total [beta]-catenin levels, significant reductions in phosphorylated (p)-RanBP3 Ser58, p-[beta]-catenin Tyr142, active [beta]-catenin and [beta]-catenin target genes were observed in sorafenib/refametinib-treated tumors. Greater levels of [beta]-catenin in sorafenib/refametinib-treated tumors were accumulated at the membrane, as compared with in the control. In vitro, sorafenib/refametinib inhibited the Wnt/[beta]-catenin pathway and suppressed Wnt-3A-induced p-low-density lipoprotein receptor-related protein 6 Ser1490, p-RanBP3 Ser58 and p-[beta]-catenin Tyr142 in HCC cells. Combination of sorafenib and refametinib inhibits the growth of naive and sorafenib resistant HCC tumors in association with active suppression of [beta]-catenin signaling regardless of [beta]-catenin mutational status. Thus, the sorafenib/MEK inhibitor combination may represent an alternative treatment for patients with HCC whose tumors develop resistance to sorafenib therapy. Key words: Wnt/p-catenin pathway, patient-derived xenograft, hepatocellular carcinoma, sorafenib, MEK inhibitor, refametinib, selumetinib