Abstract LB-130: Reporter genes for a rapid in vivo screen of PDA therapeutics are required for energy homeostasis in pancreatic cancer-associated malnutrition
Authors: Ocal Ozhan , Zolghadri Yalda , Swift Galvin H. , Brekken Rolf A. , Wilkie Thomas M. 
Published: August 2015

Pancreatic ductal adenocarcinoma (PDA) is the 4th leading cause of cancer related deaths. Limited progress in developing effective therapy for PDA is partially due to the lack of a robust in vivo screen for effective drug combinations. Kras mutations (e.g. KrasG12D) are found in over 90% of human PDA and occur early in tumor progression. G Protein Coupled Receptor (GPCR) and protein kinase signaling can initiate Ras activation. Regulators of G-protein Signaling (RGS) proteins are coincidence detectors of Ras activation that feedback regulate, by virtue of their GTPase Activating Protein (GAP) activity, the intensity and duration of Gi- and Gq-coupled GPCR signaling. RGS-resistant mutations in Gq have been associated with PDA. We show a Rgs16::GFP transgene is a KrasG12D-dependent marker of all stages of neoplasia in the LSL-KrasG12D; Cdkn2af/f; p48Cre (KIC) mice. GFP is proportional to and coincident with tumor burden. Although KrasG12D is expressed in embryonic pancreas progenitor cells and in all mature acinar cells, Rgs16::GFP expression in tumors first emerges in ductal PanINs as early as 12 days post birth. The receptor tyrosine kinase Axl is highly expressed in PDA progenitor cells. The Gas6 ligand evokes Axl signaling in epithelial progenitor cells and contributes to activation of KrasG12D, PDA initiation and progression. In a proof-of-principle for drug screens, we determined that warfarin, which blocks maturation of Gas6, an Axl agonist, combined with the standard of care Gemcitabine and Abraxane (GA), significantly reduced PDA progression.

In humans, partial pancreatic deficiency often precedes pancreatic cancer. Pancreatic insufficiency develops by 5 weeks in KC (LSL-KrasG12D;p48Cre) mice that express KrasG12D in all pancreas cells. KrasG12D, in the context of wild type Cdkn2a, causes dedifferentiation of acinar cells and a drastic reduction in digestive enzymes secreted by the pancreas. KC mice become malnourished but can survive over one year before succumbing to PDA. We find Intraductal Papillary Mucinous Neoplasm (IPMN) in KC mice express Rgs16::GFP by 2 weeks of age. We crossed the Rgs8-16 double knockout into KC (KC-R) mice to test if Rgs8-16 are tumor suppressor genes. Most KC-R mice die before 4 months of age because they can not maintain energy homeostasis - Rgs8-16 are required in liver to conserve energy utilization in malnourished mice. The effects of Rgs8-16 deficiency on exocrine pancreas function, acinar-to-ductal metaplasia (ADM), apoptosis and tumor progression in KC-R mice are under investigation. As a reporter gene, Rgs16::GFP faithfully tracks PDA progression and sensitivity to new drug regimens that inhibit KrasG12D mediated oncogenesis. Supported by NCI CA161624.

Citation Format: Ozhan Ocal, Yalda Zolghadri, Galvin H. Swift, Rolf A. Brekken, Thomas M. Wilkie. Reporter genes for a rapid in vivo screen of PDA therapeutics are required for energy homeostasis in pancreatic cancer-associated malnutrition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-130. doi:10.1158/1538-7445.AM2015-LB-130