Metformin has recently gained attention as an anti-cancer drug and/or a chemoprevention agent because of its roles in inhibiting mTOR, lowering hyperinsulinemia, modulating inflammatory responses, and selectively killing cancer stem cells. However, the key underlying molecular mechanisms for the inhibitory effects of metformin on pancreatic cancer progression remain largely unknown. RET (REarranged during Transfection), a single-pass transmembrane receptor tyrosine kinase and its ligand, glial cell-derived neurotrophic factor (GDNF), were strongly expressed in pancreatic cancer and correlated to invasion and worse survival after surgical resection. In this study, we investigated the roles of RET in the inhibitory effects of metformin on pancreatic cancer cell growth and migration. Real-time PCR and Western blot were used to determine mRNA and protein levels of molecular markers, respectively. siRNAs were adopted to specifically knockdown target genes. Boyden chamber assay was applied to assess cell migration in vitro. We observed that metformin treatment significantly reduced the mRNA and protein expression of RET in a dose-dependent manner in pancreatic cancer cells PANC-1 and MIA PaCa-2. The inhibitory effects of metformin on RET expression were not diminished when AMPK was knockdown by AMPK siRNA or the specific inhibitor, Compound C, suggesting that metformin may suppress RET in an AMPK-independent manner. Metformin treatment or RET knockdown by RET siRNA significantly decreased the phosphorylation of NF-κB and p70S6K, while modestly reduced the phosphorylation of the ERK, AKT, or STAT3. Furthermore, metformin treatment or RET knockdown significantly inhibited GDNF-induced cell migration. These data indicate that targeting RET with metformin may be an attractive and novel strategy for the prevention and treatment of pancreatic cancer progression and metastasis. Further in vitro and in vivo studies are warranted to investigate how metformin modulates RET signaling to inhibit the progression and metastasis of pancreatic cancer. Citation Format: Huailong Chang, Zhiyong Xiao, Tao Li, Lanjing Zhang, Yong Lin, Darren Carpizo, Xianglin Tan. RET signaling in pancreatic cancer: A novel target by metformin to suppress cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2881.

Abstract Sunlight-induced non-melanoma skin cancer is a major cancer in the United States. How obesity contributes to skin cancer, and the molecular changes induced by obesity that promote skin cancer development remain poorly understood. Our previous study showed that surgical removal of the parametrial fat pads from mice fed a high-fat diet inhibited UVB-induced skin carcinogenesis, but this was not observed in mice fed a low-fat chow diet (PNAS. 109: 9065-9070, 2012). These results indicate that dietary high fat caused the parametrial fat pads to secrete high levels of proinflammatory cytokines that may promote UVB-induced skin carcinogenesis. Female SKH-1 mice were fed a 60% kcal high fat diet for 6 months, and the mice were sacrificed at various time intervals. The parametrial fat pads were removed and dissected into rostral (the loose end proximal to the caudal zone) and caudal portion (attached to the uterus). Half of the fat were fixed in formalin for histopathology, and other half of the fat was homogenized, place into a hanging insert of a dual-chamber and incubated in minimal essential medium for 4 hours at 370C. Proteins that were released from the fat passed through the 0.4 μm pore in the insert to provide fat cell-derived medium that was collected and used for adipokine analysis by an antibody array. Our results showed that among the 38 adipokines measured, treatment of mice with a 60% kcal high fat diet time-dependently increased the level of IL-6 (0.5, 1.0, 10.3 and 27.8 fold) and MCP1 (0, 0, 1.5 and 21.2 fold) at 0.5, 1.5, 3 or 6 months of treatment, respectively. Several other adipokines (ICAM1, IGFBP6, Leptin, SerpinE1 and TIMP1) were also increased. Interestingly, the high fat diet-induced the expression of IL-6 and MCP1 almost exclusively in the rostral, but not in the caudal portion of the parametrial fat pads. IL-6 and MCP1 were not detected in control mice fed a low fat chow diet. In addition, the rostral fat from the mice fed the high fat diet had an increased number of dead adipocytes, macrophages, apoptotic cells, and mast cells when compared to the caudal fat. Surgical removal of the whole parametrial fat pads from mice fed the high fat diet resulted in a marked decrease in the levels of IL-6 and MCP1 in the compensatory fat that returned 6 months after the surgery when compared to that of the sham-operated control. In a separate study, we found that mice fed a 40% kcal high fat diet rich in omega-6 fatty acids for 3 months had a significant increase in IL-6 protein expression in the rostral portion of the parametrial fat pads compared to mice fed the same amount of calories from a high fat diet rich in omega-3 fatty acids. Our results suggest that the high fat diet-induced increases of IL-6 and MCP1 protein expression mainly in the rostral portion of the parametrial fat pads may help explain why removal of the parametrial fat pads from mice fed a high fat diet resulted in a decrease in UVB-induced skin carcinogenesis. Citation Format: Yourong Lou, Jamie J. Bernard, Qinyun Peng, Tao Li, Allan H. Conney, Yaoping Lu. High fat diet induces the expression of IL-6 and MCP1 exclusively in the rostral portion of the parametrial fat pads in SKH-1 mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3689. doi:10.1158/1538-7445.AM2013-3689