A major problem in pancreatic cancer research is the lack of clinically relevant animal models that can more faithfully replicate human disease. Here we propose to undertake a detailed characterization of co-operating mutations driving a robust animal model for pancreatic islet cell cancer that we have serendipitously created as a result of cell-specifically deleting floxed Rb and p53 loci within the renin-expressing cell compartment of pancreas. Preliminary assessments suggest the model has the hallmarks of a metastatic islet cell carcinoma that expresses high levels of glucagon. It arises with high penetrance and, just like its human equivalent, exhibits profound metastatic spread to clinically relevant sites resulting in death by 4-5 months. We believe it is important to characterize this model further as it exhibits unique features which will foster better understanding of pancreatic islet cell development, the role of the renin-angiotensin system therein, islet cell carcinogenesis, and the associated metastatic process. To characterize co-operating genomic alterations observed in pancreatic tumors, as well as metastases to the liver, a complex cross has been developed where the tumor suppressors p53 and Rb are deleted along with activation of a GFP reporter in renin-expressing cells utilizing the RenCre transgene. In the current proposal we will utilize Next Generation Sequencing (NGS) of the exome and of the methylome to identify co-operating mutations and DNA methylation changes occurring within lineal descendants of the Rb- p53- renin-expressing cells of normal pancreatic islets that are associated with the stochastically arising primary tumors and corresponding liver metastases, with the aim of ultimately identifying genetic signatures for these processes. In addition we will determine the timeline of allelic loss of p53 and Rb from the first expression of renin in alpha islet cell progenitors to development of primary and metastatic pancreatic neuroendocrine tumors. An organizing hypothesis linking the expression of renin to the specific islet cell neoplasia is put forth. Furthermore, the ability to se GFP for lineage tracing of the cells contributing to disease initiation and progression provides a unique opportunity to dissect the timeline of disease pathology in terms of acquisition of DNA copy number changes, mutations, and DNA methylation changes. Overall, these data will result in a newly characterized model of metastatic pancreas cancer that can be used for testing of novel therapeutics and will contribute to a more complete understanding of islet cell cancers.
While endocrine tumors of the pancreas are relatively rare there remains considerable interest in these entities because of the complexity of the tumor spectrum and the uncertain histogenesis underlying their specific origins. Unfortunately, representative animal models that enable a more thorough investigation of the etiology of the disease process are few. Because of the tremendous need for clinically relevant models of various pancreatic cancers, particularly ones that metastasize to clinically relevant locations, we believe it is important to characterize and validate this model further by identifying cooperating mutations that contribute to tumorigenesis and metastasis.
|Glenn, S T; Jones, C A; Sexton, S et al. (2014) Conditional deletion of p53 and Rb in the renin-expressing compartment of the pancreas leads to a highly penetrant metastatic pancreatic neuroendocrine carcinoma. Oncogene 33:5706-15|