The anti-dysenteric drug fraxetin enhances anti-tumor efficacy of gemcitabine and suppresses pancreatic cancer development by antagonizing STAT3 activation

Fraxetin, a natural product isolated and purified from the bark of Fraxinus bungeana A.DC., has anti-inflammatory, analgesic, and anti-dysenteric activities. This study aimed to investigate the anti-tumor effects of fraxetin in pancreatic ductal adenocarcinoma (PDA). The effects of fraxetin on the malignant biological behavior of PDA were evaluated. Besides, the effects of fraxetin on the sensitivity of PCCs to gemcitabine, angiogenesis, the epithelial-mesenchymal transition (EMT), glucose metabolism, reactive oxygen species (ROS), and STAT3 activity were analyzed. By reversing the EMT, fraxetin suppressed proliferation, invasion, and migration, and induced mitochondrial-dependent apoptosis in PCCs. Also, treatment with fraxetin inhibited PDA growth and metastasis in nude mouse models. Furthermore, fraxetin made PCCs more sensitive to the chemotherapy drug gemcitabine. Mechanically, fraxetin treatment suppressed oncogenic KRAS-triggered STAT3 activation in PCCs and PDA tissues. Fraxetin shows significant interactions with STAT3 Src Homology 2 (SH2) domain residues, thereby preventing its homo-dimer formation, which then blocks the activation of downstream signal pathways. The anti-tumor activity of fraxetin in PDA was functionally rescued by a STAT3 activator colivelin. As a result, fraxetin hindered hypoxia-induced angiogenesis by decreasing HIF-1α and VEGFA expression, controlled glucose metabolism by reducing GLUT1 expression, inhibited the EMT by blocking the Slug-E-cadherin axis, and drove ROS-mediated apoptosis by regulating the STAT3-Ref1 axis. In conclusion, fraxetin enhances the anti-tumor activity of gemcitabine and suppresses pancreatic cancer development by antagonizing STAT3 activation.