Abstract 5008: A morphologically distinct cancer initiating cell in human and murine PanIN and pancreatic cancer.
Authors: Jennifer M. Bailey, Janivette Alsina, Zeshaan Rasheed, Ya-Yuan Fu, Florencia McAllister, Pankaj Pasricha, William Matsui, Anirban Maitra, Steven Leach
Journal: Cancer Research (2013)

Abstract Pancreatic ductal adenocarcinoma (PDAC) is highly lethal with a survival rate of less than 6 months for the majority of patients. In order to better understand its development we hypothesized that there is cellular heterogeneity in murine and human PDAC precursor lesions (PanINs). We utilized two independent models of murine PanIN (mPanIN) formation to drive oncogenic KrasG12D expression in the murine pancreas during development (KCPdx1) or specifically in adult acinar cells (KCiMist1). The mice were crossed to the mTmG reporter mouse to map the fate of cells expressing Kras (KCiMist1G) that are marked by expression of GFP. We used transmission electron microscopy on mPanIN-containing tissue to identify a morphologically distinct rare cell type present in both models of mPanIN. These cells morphologically resemble tuft cells, which are characterized by their brush-like morphology, including apically projecting microvillae and the expression of DCLK1 and AcTub. Using Flourescence Activated Cell Sorting Techniques (FACS), we were able to isolate DCLK1HI/GFP+ murine PanIN tuft cells expressed in the KCiMist1G model. We discovered that these cells have an increased ability to form PanIN spheres in vitro relative to GFP+ cells alone, indicative of a progenitor PanIN stem cell function. Using immunofluorescent labeling on a human PanIN (n=23) and metastatic PDAC (n=10) tissue arrays, we determined that in 15% of PanIN lesions, 13-30% of the cells have detectable levels of AcTub, with a primarily apical pattern of labeling. In contrast, over 80% of metastatic PDAC cells are AcTub+, but they no longer exhibit an apical pattern of labeling. Applying our cell surface FACS strategy to four different human pancreatic cancer cell lines and three early passage human xenografts, we determined that 2-5% of human pancreatic cancer cells have detectable levels of cell-surface AcTub and DCLK1. We have functionally analyzed the tumor-initiating capacity of cell surface AcTubHI cells using in vitro tumor sphere experiments. In this assay, cell surface AcTubHI cells show a statistically significant 100-fold increase in tumor sphere-forming capacity relative to cell surface AcTubLOW cells. We further evaluated the functional significance of cell surface AcTub by analyzing the in vivo tumor initiating capacities of cell surface AcTubHI and AcTubLOW cells from a human PDAC xenograft. Cell surface AcTubHI cells exhibited significantly increased tumor initiating frequency relative to the AcTubLOW population (**p&amp;lt;0.0000539). These data provide important new information regarding cellular heterogeneity in murine PanIN and human pancreatic cancer, and suggest that novel strategies targeting DCLK1 and AcTub may have potential therapeutic utility. Citation Format: Jennifer M. Bailey, Janivette Alsina, Zeshaan Rasheed, Ya-Yuan Fu, Florencia McAllister, Pankaj Pasricha, William Matsui, Anirban Maitra, Steven Leach. A morphologically distinct cancer initiating cell in human and murine PanIN and pancreatic cancer. [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 5008. doi:10.1158/1538-7445.AM2013-5008