781 Sensitive DNA Marker Panel for Detection of Pancreatic Cancer by Assay in Pancreatic Juice

Abstract

G A A b st ra ct s Ectopic expression of Spdef in tumors caused by treatment with azoxymethane (AOM) and dextran sodium sulfate (DSS), or spontaneously formed in ApcMin/+ mice was sufficient to drive cell cycle exit of tumor cells in both mouse models. Furthermore, loss of Spdef lead to a significant increase in colonic tumor number from both mouse models (AOM+DSS and ApcMin/+ ), defining Spdef as a tumor suppressor in the colon. Importantly, our previous study indicates that SPDEF expression is often silenced in human colon cancer and this SPDEF silencing in colon cancer is tightly correlated to ATOH1 silencing, suggesting SPDEF as a mediator of ATOH1's function in intestinal homeostasis and tumorigenesis. Therefore, we hypothesize that Spdef is a key effector of Notch-Atoh1 effects in intestinal tumors. Here, we assess the requirement of Spdef for Atoh1-directed growth inhibition in colonic tumors, and extend the analysis to elucidate the sufficiency of Spdef to promote cell cycle exit and goblet cell differentiation in Atoh1-null colonic tumors that mimic human colon cancer. Method: All analysis was performed in transgenic mice. The sufficiency of Spdef was tested by re-expressing Spdef in colonic tumors that lack Atoh1. The requirement of Spdef was tested by inducing Atoh1 expression through inhibition of the Notch activity in tumors that lack Spdef. Progenitor cell proliferation, Lgr5+ stem cell population and differentiation were immunohistologically assessed. Results: In Atoh1-null tumors, proliferation and Lgr5+ stem cell population was significantly reduced upon expression of SPDEF without induction of goblet cell markers. In response to Atoh1 induction by Notch inhibitor treatment, cell proliferation was inhibited and goblet cell differentiation was induced in colonic tumors; this response was prevented in Spdef-/mice. In contrast, Lgr5+ stem cell population was similarly reduced in tumors from both control and Spdef-/mice. Conclusions: SPDEF mediates the effect on tumor cell proliferation of Atoh1 induced by Notch inhibitors. The sufficiency and requirement for Spdef in promoting cell cycle exit in intestinal tumors suggest Spdef as a potential therapeutic target for colon cancer. Future studies will investigate the Notch-Atoh1 independent mechanisms to activate expression of SPDEF, which can be utilized as a colon cancer therapy.