evaluated the effect of metformin on four pancreatic cancer PDX tumor lines and, similar to previous cell line xenograft studies, found substantial growth inhibition . in (A) P722 and (B) PT4 PDX tumors after 28 day treatment with 400 mg/kg metformin.(TIF) pone.0147113.s002.tif (9.0M) GUID:?D8CD3185-B7F1-4884-B84D-4EA4FE6692EE Data Availability StatementAll relevant data are within the paper and its Supporting Information files. Abstract There is currently tremendous interest in developing anti-cancer therapeutics targeting cell signaling pathways important for both cancer cell metabolism and growth. Several Mangiferin epidemiological studies have shown that diabetic patients taking metformin have a decreased incidence of pancreatic cancer. This has prompted efforts to evaluate metformin, Mangiferin a drug with negligible toxicity, as a therapeutic modality in pancreatic cancer. Preclinical studies in cell line xenografts and one study in patient-derived xenograft (PDX) models were promising, while recently published clinical trials showed no benefit to adding metformin to combination therapy regimens for locally advanced and metastatic pancreatic cancer. PDX models in which patient tumors are directly engrafted into immunocompromised mice have been shown to be excellent preclinical models for biomarker discovery and therapeutic development. We evaluated the response of four PDX tumor lines to metformin treatment and found that all four of our PDX lines were resistant to metformin. We found that the mechanisms of resistance may occur through lack of sustained activation of adenosine monophosphate-activated protein kinase (AMPK) or downstream reactivation of the mammalian target of rapamycin (mTOR). Moreover, combined treatment with metformin and mTOR inhibitors failed to improve responses in cell lines, which further indicates that metformin alone or in combination with mTOR inhibitors will Mangiferin be ineffective in patients, and that resistance to metformin may occur through multiple pathways. Further studies are required to better understand these mechanisms of resistance and inform potential combination therapies with metformin and existing or novel therapeutics. Introduction Pancreatic cancer is one of the most aggressive and lethal malignancies, with 80% of patients presenting with locally advanced or metastatic disease that portends a 6C12 month median survival and a dismal 6% five-year survival rate . Chemotherapy produces only modest improvements in survival, and novel therapies are desperately needed to improve treatment options for this large patient population . There is currently tremendous interest in developing anti-cancer therapeutics that target cell signaling pathways important in both cell metabolism and cell growth . The 5′ adenosine monophosphate-activated protein kinase (AMPK) pathway has gained increasing interest, as AMPK physiologically inhibits the mammalian target of rapamycin (mTOR) to maintain homeostasis in conditions of decreased available cellular energy sources [4, 5]. Studies have shown that mTOR signaling plays key roles in survival and proliferation of malignant cells [6, 7]. Thus, AMPK activators have generated substantial interest as potential antineoplastic agents that function by altering metabolism and inhibiting the mTOR pathway . Metformin is the first-line agent for treatment of type 2 diabetes mellitus. Metformin inhibits mitochondrial oxidative phosphorylation, thereby increasing the ratio of AMP to ATP [8, 9]. High levels of AMP activate AMPK, which then inhibits energy-consuming pathways such as protein synthesis, in part by downregulating mTOR signaling by direct phosphorylation of the tumor suppressor TSC2 and the mTOR binding partner Raptor [9C13]. The state of energy conservation induced by metformin has been proposed to explain the cytostatic effect of metformin on cancer  and the apparent protective effect observed in diabetic patients treated with metformin who subsequently develop pancreatic cancer . Several epidemiological studies have indicated that patients with diabetes taking metformin have a decreased incidence of pancreatic cancer [14C17]. This has prompted a great deal of excitement to evaluate metformin, a widely used drug with negligible toxicity, as a therapeutic modality in pancreatic cancer. There are currently 3 clinical trials evaluating metformin in combination with various chemotherapies in pancreatic cancer (cancer.gov/clinicaltrials). Preclinical studies in cell line xenografts and one recent study in patient-derived xenograft (PDX) models have shown promise [18C22]. PDX models in which patient tumors are directly engrafted into immunocompromised mice have been shown to recapitulate primary tumor architecture and genetic characteristics, even after passaging and expanding MCM7 the tumors in successive generations of mice [23, 24]. Furthermore, PDX models are superior to traditional cell line xenografts, which are adapted to in vitro growth and lack the heterogeneity of patient tumors, for evaluating responses to therapies and novel biomarkers [23C27]. Until recently, there have been very limited studies of PDX responses to many proposed oncological agents, and results for metabolic therapies like metformin are still severely lacking . Thus, the objective of this study was to evaluate the response of pancreatic cancer PDX models to metformin and to investigate metformins mechanism of action and compensatory resistance pathways. Materials and Methods Drugs and reagents Metformin hydrochloride (Spectrum, New Brunswick, NJ, Mangiferin USA) was dissolved in phosphate-buffered saline (PBS) for both in vitro and in vivo studies. Rapamycin (LC Laboratories, Woburn, MA, USA) and BEZ235.