Melatonin overcomes gemcitabine resistance in pancreatic ductal adenocarcinoma by abrogating nuclear factor-κB activation

Constitutive activation and gemcitabine induction of nuclear factor-κB (NF-κB) contribute to the aggressive behavior and chemotherapeutic resistance of pancreatic ductal adenocarcinoma (PDAC). Thus, targeting the NF-κB pathway has proven an insurmountable challenge for PDAC therapy. In this study, we investigated whether the inhibition of NF-κB signaling pathway by melatonin might lead to tumor suppression and overcome gemcitabine resistance in pancreatic tumors. Our results showed that melatonin inhibited activities of NF-κB by suppressing IκBα phosphorylation and decreased the expression of NF-κB response genes in MiaPaCa-2, AsPc-1, Panc-28 cells and gemcitabine resistance MiaPaCa-2/GR cells. Moreover, melatonin not only inhibited cell proliferation and invasion in a receptor-independent manner, but also enhanced gemcitabine cytotoxicity at pharmacologic concentrations in these PDAC cells. In vivo, the mice treated with both agents experienced a larger reduction in tumor burden than the single drug-treated groups in an orthotopic xenograft mouse model. Taken together, these results indicate that melatonin inhibits proliferation and invasion of PDAC cells and overcomes gemcitabine resistance of pancreatic tumors through NF-κB inhibition. Our findings therefore provide novel preclinical knowledge about melatonin inhibition of NF-κB in PDAC and suggest that melatonin should be investigated clinically, alone or in combination with gemcitabine for PDAC treatment.