Translational Studies of Circulating Pancreatic Epithelial Cells in Cancer Progression

In order for blood-borne metastasis to occur, circulating tumor cells (CTC) must first be released into the bloodstream from the primary site. In humans, CTC have been detected (1-10/10ml blood) in pancreatic ductal adenocarcinoma (PDAC), using fluorescence activated cell sorting (FACS) to identify cells expressing epithelial epitopes. However, the low sensitivity of this assay precludes its use as a diagnostic modality. Since no “gold standard” assay exists to detect CTC, it is impossible to determine whether current methods detect all or a portion of CTC in patients. Thus, to perform a robust analysis of CTC, we developed a lineage-labeled genetic mouse model of PDAC. In this model, all pancreatic epithelial cells express yellow fluorescent protein (YFP). We isolated YFP+ pancreas cells from the bloodstream of PKIY mice with PDAC and younger PKIY mice with only PanIN lesions by FACS. (Controls were devoid of YFP+ cells.) Transcriptional analysis confirmed that these were pancreatic epithelial cells. Finally, ~10% of all CTC expressed a commonly-used epithelial marker to enumerate CTC. Thus, our data suggest that current methods of CTC detection may be inefficient but, if optimized, could diagnose early stage PDAC and PanIN. We hypothesize that circulating pancreatic epithelial cells express a common epitope which can be used for detection in patients with PDAC. In this application, we seek to use our system to identify markers of CTC in an unbiased manner. We propose to perform transcriptional analysis to identify potential markers of CTC that are not present in blood cells. Since all CTC in our model can be identified by YFP, we can then validate potential markers in our system. As our ultimate goal is to translate our data to human samples, we also seek to collect blood samples from patients with PDAC and controls for future studies.