Combination therapy of niclosamide with gemcitabine inhibited cell proliferation and apoptosis via Wnt/β-catenin/c-Myc signaling pathway by inducing β-catenin ubiquitination in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a type of cancer with high morbidity and mortality rates worldwide. Owing to a lack of therapeutic options, the overall survival rate of patients with pancreatic cancer is low. Gemcitabine has been mainly used to treat patients with pancreatic cancer, but its efficacy is limited by chemoresistance. Therefore, a novel therapeutic agent for PDAC therapy is urgently needed. An anthelminthic drug, niclosamide, has already been researched in breast, lung, colon, and pancreatic cancer as an anti-cancer purpose by re-positioning its original purpose. However, combination therapy of gemcitabine and niclosamide was not informed yet. Here, we found that niclosamide co-administered with gemcitabine significantly inhibited tumorigenesis of pancreatic cancer compared to gemcitabine alone. Further, combining niclosamide and gemcitabine inhibited cell proliferation and induced apoptosis. Niclosamide induced cell cycle arrest at the G(1) phase, and the levels of CDK4/6 and cyclin D1 were lowered after gemcitabine treatment. In addition, the combination of these chemical compounds more effectively increased the binding level of activated β-catenin destruction complex and β-catenin to enable phosphorylation, compared to gemcitabine alone. After phosphorylation, niclosamide – gemcitabine upregulated the ubiquitin level, which caused phosphorylated β-catenin to undergo proteasomal degradation; the combination was more potent than gemcitabine alone. Finally, the combination more effectively suppressed tumor growth in vivo, compared to gemcitabine alone. Altogether, our results indicate that niclosamide synergistically enhances the antitumor effect of gemcitabine in pancreatic cancer, by inducing the degradation of β-catenin with ubiquitination. Therefore, this drug combination can potentially be used in PDAC therapy.