Intrahepatic cholangiocarcinoma (CCA) is an aggressive cancer that lacks an effective targeted therapy. Here, we assessed the therapeutic efficacy of regorafenib in CCA, as well as elucidated its underlying mechanism. We first demonstrated that regorafenib not only inhibited growth but also induced apoptosis in human CCA cells. Subsequently, we used in silico approaches to identify MALT1 (Mucosa-associated lymphoid tissue protein 1), which plays an important role in activating NF-κB, as a potential target of regorafenib. Overexpression of Elk-1, but not Ets-1, in HuCCT1 cells markedly reduced their sensitivity to regorafenib, which might be attributed to a significant increase in MALT1 levels. Our results further demonstrated that this drug drastically inhibited MALT1 expression by suppressing the Raf/Erk/Elk-1 pathway. The efficacy of regorafenib in decreasing in vivo CCA growth was confirmed in animal models. Regorafenib efficacy was observed in two MALT1-positive CCA patients who failed to respond to several other lines of therapy. Finally, MALT1 was also identified as an independent poor prognostic factor for patients with intrahepatic CCA. In conclusion, our study identified MALT1 to be a downstream mediator of the Raf/Erk/Elk-1 pathway and suggested that MALT1 may be a new therapeutic target for successful treatment of CCA by regorafenib.
Keywords: Elk-1; MALT1; MI-2; cholangiocarcinoma; regorafenib.