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Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with appallingly poor outcome. Recent years have witnessed the development of a number of combination therapies that have produced modest survival improvement but at the cost of increased adverse effects. A phenomenon that contributes to the dismal prognosis and therapeutic resistance is a unique characteristic of PDAC called desmoplasia. Desmoplasia is initiated by activation of pancreatic stellate cells (PSCs), which through excessive deposition of extracellular matrix components, leads to expansion of tumor stroma that hinders drug penetration. We have recently shown that glutamine mediates communication between PSCs and pancreatic cancer cells (PCCs). Remarkably, a small molecule inhibitor palmatine (PMT) suppresses glutamine-induced PSC-PCC communication and potentiates gemcitabine (GEM) activity in part through downregulation of survivin. Survivin expression is correlated not only with unfavorable overall survival but also therapeutic resistance. In this study we therefore examined the mechanism associated with glutamine-mediated PSC-PCC interaction. We also designed experiments to test the hypothesis that PMT inhibits survivin to disrupt these interactions to potentiate anti-proliferative activity of GEM. Our results indicate that PMT not only interacts with pTyr p705 binding site in the SH2 domain of STAT3 (canonical), but also interacts at the interface of DNA and the linker domain (non-canonical). PMT-STAT3 interaction resulted in decreased phosphorylation with no significant effect on total levels of STAT3 in pancreatic cancer cells following treatment with PMT. Furthermore, PMT treatment attenuated (i) glutamine-mediated increased levels of pSTAT3 and its downstream target survivin; (ii) glutamine-mediated increased survivin reporter activity and (iii) glutamine-mediated enhanced proliferation and clonogenicity in multiple cell lines. Collectively, these data suggest that PMT abrogates glutamine-induced biological outcome through reduced STAT3/survivin signaling. We further tested the preclinical efficacy of PMT in combination with GEM using the syngeneic orthotopic KPC mouse model. Our results show significantly decreased mean log 10 tumor weight in response to treatment with PMT plus GEM (0.08±1.13) relative to controls (1.87±0.21) or single agent treatment (1.48+0.67; p Citation Format: Xiaoyu Yang, Amanda R. Muñoz, Shih-Bo Huang, Martha Hanes, Roble G. Bedolla, Divya Chakravarthy, Angel Su, Varsha Mulamreddy, Dmytro Kovalskyy, Paul Rivas, Joel Michalek, Rita Ghosh, Addanki P Kumar. Targeting glutamine addiction in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 116.

O 6 -methylguanine ( O 6 mG) is a potent mutagenic and procarcinogenic DNA lesion. Organisms have evolved with a DNA repair mechanism that largely ameliorates the deleterious effects of O 6 mG through a direct reversal mechanism by a protein termed O 6 -methylguanine-DNA methyltransferase (MGMT). However, the contribution of O 6 mG to carcinogenesis, in the absence of known exposure to agents that produce it, has not been defined. Nontransgenic C3HeB male mice have a high frequency of spontaneous liver tumors. Transgenic CeHeB/FeJ mice expressing human MGMT (hMGMT) were generated that had elevated hepatic MGMT activity. The spontaneous development of hepatocellular carcinoma was significantly reduced in those mice expressing hMGMT compared with nontransgenic C3HeB/FeJ male mice. No differences were detected in spontaneous mutant frequencies in lacI transgenes in mice carrying hMGMT compared with that without hMGMT but the proportion of GC to AT transition mutations was lower in the transgenic mice carrying hMGMT as well as lacI . Tumors that arose in C3HeB/FeJ transgenic mice were largely deficient in hMGMT protein as determined by immunohistochemistry with a monoclonal antibody directed against hMGMT. Together these data indicate that spontaneous O 6 mG lesions induced hepatocellular carcinogenesis in C3HeB/FeJ male mice. These transgenic mice represent a rare example of reduced spontaneous carcinogenesis.