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The colonic and intestinal epithelium are renewed every 3 days. In the intestine there are at least two principal stem cell pools. The first contains rapid cycling crypt based columnar (CBC) Lgr5+ cells, while the second is comprised of slower cycling Bmi1-expressing cells at the +4 position above the crypt base. In the colon, however, the identification of Lgr5-negative stem cell pools has proven more challenging. Here, we demonstrate that the intermediate filament, keratin-19 (Krt19), marks long-lived, radiation resistant cells above the crypt base that generate Lgr5+ CBCs in the colon and intestine. In colorectal cancer models, Krt19+ cancer initiating cells are also radioresistant while Lgr5+ stem cells are radiosensitive. Moreover, Lgr5+ stem cells are dispensable in both the normal and neoplastic colonic epithelium, as ablation of Lgr5+ stem cells results in their regeneration from Krt19 expressing cells. Thus, Krt19+ stem cells are a discrete target relevant for cancer therapy.

Pancreatic exocrine cell plasticity can be observed during development, pancreatitis with subsequent regeneration, and also transformation. For example, acinar-ductal metaplasia (ADM) occurs during acute pancreatitis and might be viewed as a prelude to pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDAC) development. To elucidate regulatory processes that overlap ductal development, ADM, and the progression of normal cells to PanIN lesions, we undertook a systematic approach to identify the Prrx1 paired homeodomain Prrx1 transcriptional factor as a highly regulated gene in these processes. Prrx1 annotates a subset of pancreatic ductal epithelial cells in Prrx1creER T2 -IRES-GFP mice. Furthermore, sorted Prrx1 + cells have the capacity to self-renew and expand during chronic pancreatitis. The two isoforms, Prrx1a and Prrx1b, regulate migration and invasion, respectively, in pancreatic cancer cells. In addition, Prrx1b is enriched in circulating pancreatic cells (Pdx1cre;LSL-Kras G12D/+ ;p53 fl/+ ;R26YFP). Intriguingly, the Prrx1b isoform, which is also induced in ADM, binds the Sox9 promoter and positively regulates Sox9 expression. This suggests a new hierarchical scheme whereby a Prrx1-Sox9 axis may influence the emergence of acinar-ductal metaplasia and regeneration. Furthermore, our data provide a possible explanation of why pancreatic cancer is skewed toward a ductal fate.

Pancreatic cancer is a serious disease with poor patient outcome, often as a consequence of late diagnosis in advanced stages. This is in large part due to the lack of diagnostic tools for early detection. To address this deficiency, we have investigated novel molecular near-infrared fluorescent (NIRF) in vivo imaging techniques in clinically relevant mouse models of pancreatic cancer. Genome wide gene expression profiling was used to identify cathepsin cystein proteases and matrix metalloproteinases (MMP) as targets for NIRF imaging. Appropriate protease activatable probes were evaluated for detection of early-stage pancreatic cancer in mice with orthotopically implanted pancreatic cancer cell lines. Mice with pancreatitis served as controls. Whole body in vivo NIRF imaging using activatable cathepsin sensitive probes specifically detected pancreatic tumors as small as 1-2 mm diameter. Imaging of MMP activity demonstrated high specificity for MMP positive tumors. Intravital flexible confocal fluorescence lasermicroscopy of protease activity enabled specific detection of pancreatic tumors at the cellular level. Importantly, topical application of NIRFprobes markedly reduced background without altering signal intensity. Taken together, macroscopic and confocal lasermicroscopic molecular in vivo imaging of protease activity is highly sensitive, specific and allows discrimination between normal pancreatic tissue, inflammation and pancreatic cancer. Translation of this approach to the clinic could significantly improve endoscopic and laparoscopic detection of early-stage pancreatic cancer. ' 2008 Wiley-Liss, Inc.Key words: pancreatic cancer; matrix metalloproteinases; nearinfrared fluorescence; bioluminescence imaging; detection Pancreatic cancer is one of the most deadly human malignancies with an extremely poor 5-year survival rate, below 5%. 1 This is mainly due to absence of early clinical symptoms and a lack of appropriate diagnostic tools for early-stage detection. Early detection of pancreatic cancer is crucial because curative surgical therapy can be initiated only in stages without locally advanced disease or metastasis. At present, surgical resection can be performed in only 10-15% of cases. 1 Current diagnostic concepts involve abdominal ultrasound, computed tomography (CT) and endoscopic ultrasound (EUS). 2-8 Abdominal ultrasound is a valuable tool for the detection of pancreatic masses. However, sensitivity and accuracy of this method in assessing early pancreatic lesions is very limited. CT based approaches are the standard imaging modality in diagnosing pancreatic cancer, but are limited by their low sensitivity of 53% 2 and failure to detect early-stage pancreatic cancer. 8-10 EUS provides the option of fine needle aspiration and provides sensitivity of up to 93%. 7 However, clinical differentiation between chronic pancreatitis and pancreatic cancer is difficult and detection of precursor lesions, so called pancreatic intraepithelial neoplasia is impossible. 9,11 Furthermore, EUS is strongly depende...