Abstract 2268: Metformin prevents progression of pancreatic intraepithelial neoplasia to ductal adenocarcinoma by targeting cancer stem cells and mTOR signaling.
Authors: Mohammed Altaf , Brewer Misty , Ritchie Rebekah L. , Marya Anuj , Lightfoot Stan , Janakiram Naveena B. , Steele Vernon E. , Rao Chinthalapally V. 
Published: August 2014

Abstract
Pancreatic cancer (PC) is one of the most lethal malignancies and a devastating disease almost uniformly lethal with a &lt;6% five year survival. Developing novel strategies to prevent or delay progression of PC is currently of intense interest. Epidemiologic studies show that diabetes mellitus is positively associated with increased risk for PC. Recent meta-analysis showed that metformin, an insulin-lowering agent, reduces risk of PC. Studies have clearly demonstrated that metformin elicits a protective effect by targeting mTOR signaling and tumor-initiating cancer stem cells (TICSC). However, metformin efficacy and systematic analysis of mechanisms have not been evaluated in a preclinical model that recapitulates human PC. We tested the effects of metformin on pancreatic intraepithelial neoplasms (PanINs) and their progression to pancreatic ductal adenocarcinoma (PDAC) in Kras-activated p48Cre/+-LSL-KrasG12D/+ transgenic mice. Six-week old male and female KrasG12D/+ mice (∼35/group) were fed AIN-76A diets containing 0, 1000 and 2000 ppm metformin for 38 weeks. Pancreata were collected, weighed, and evaluated histopathologically for PanINs and PDAC. To evaluate molecular mechanisms, we analyzed modulation of mTOR signaling molecules: mTOR, pAMPK, IRS1, TSC1, TSC2, S6, p70-S6, Rheb, ERK, pERK, ATG2, leptin, IGF1, C-reactive protein and markers of TICSC : ALDH1, CD133, CD24, CD44, EPCAM and DCLK-1 in pancreatic tumors and/or serum by IHC, IHF, Western blotting, and/or real time-PCR. Male and female mice fed control diet had 80 and 62% incidence of PDAC, respectively. Dietary administration of 1000 or 2000 ppm metformin yielded a PDAC incidence of 20 or 26%, respectively, in males (p&lt;0.002-0.0006) and 7 or 0%, respectively, in females (p&lt;0.0004-0.0001).The pancreatic tumor weights were decreased by 34-49% (p&lt;0.03-0.001) with both doses of metformin. Most importantly, metformin caused &gt;95% (p&lt;0.0001) inhibition of carcinoma spread in the pancreas and a significant suppression of PanIN 3 lesions (carcinoma in situ) (28-39%, p&lt;0.002). The pancreatic tissue and/or serum of mice fed metformin showed a significant decrease in mTOR signaling molecules mTOR, S6, p70-S6, Rheb, IGF-1, C-protein, ERK and pERK with an increase in pAMPK, TSC1, TSC2, IRS1 and ATG2. The TICSC markers CD44, CD133, ALDH1 and EPCAM were reduced significantly with an increase in CD24 expression (p&lt;0.04-0.0002). These results suggest that the anti-tumor effects of metformin are mediated through decreased TICSC markers and modulation of the mTOR signaling pathway. These studies with a transgenic mouse model of pancreatic cancer suggest that metformin has significant potential for human chemoprevention trials in individuals at high-risk for pancreatic cancer. {Supported by NCI-CN-N01-53300}.
Citation Format: Altaf Mohammed, Misty Brewer, Rebekah L. Ritchie, Anuj Marya, Stan Lightfoot, Naveena B. Janakiram, Vernon E. Steele, Chinthalapally V. Rao. Metformin prevents progression of pancreatic intraepithelial neoplasia to ductal adenocarcinoma by targeting cancer stem cells and mTOR signaling. [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 2268. doi:10.1158/1538-7445.AM2013-2268