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Pancreatic cancer is one of the deadliest cancers with poor survival rates and limited therapeutic options. To improve the understanding of this disease's biology, a prerequisite for the generation of novel therapeutics, new platforms for rapid and efficient genetic and therapeutic screening are needed. Therefore, a combined in vitro/in vivo hybrid shRNA assay was developed using isolated murine primary pancreatic ductal cells (PDCs), in which oncogenic KrasG12D could be activated in vitro by genomic recombination through 4OH-tamoxifen–induced nuclear translocation of Cre-ERT2 expressed under control of the ROSA26 promoter. Further genetic manipulation was achieved through selective and stable RNAi against the tumor suppressors p16Ink4a (CDKN2A) or Trp53 (TP53) using lentiviral gene delivery. Treatment of PDCs with 4OH-tamoxifen increased phosphorylation of ERK downstream of KRAS, and subsequent lentiviral transduction resulted in sustained target gene repression. Double-mutant PDCs were then reintroduced into the pancreata of NOD-SCID-gamma (NSG) mice and monitored for tumor growth. Orthotopic implantation of PDCs carrying the activated KrasG12D -allele and shRNA against p16Ink4a or Trp53 resulted in tumor growth, metastasis, and reduced survival of NSG mice. In contrast, KrasG12D alone was not sufficient to induce tumor growth. Implications: The combinatory in vitro / in vivo approach described in this study allows for rapid and efficient identification of genes involved in carcinogenesis and opens new avenues for the development of therapeutic strategies to improve cancer treatment. Mol Cancer Res; 13(5); 863–9. ©2015 AACR . This article is featured in Highlights of This Issue, [p. 807][1] [1]: /lookup/volpage/13/807?iss=5

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 Prrx1creERT2-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-KrasG12D/+;p53fl/+;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.

Introduction: Embryonic development, regeneration and carcinogenesis share regulatory mechanisms in the pancreas. We sought to identify a transcriptional program in the pancreas that regulates these processes within a distinct cell population of pancreatic duct/duct-like cells. We have identified the paired-related homeodomain transcription factor Prrx1 as a potential master transcriptional factor in this context. Methods: Duct cells, acinar-to-ductal metaplastic cells during acute pancreatitis as well as PanIN cells in KrasG12D-driven early carcinogenesis ( Pdx1-cre;Kras G12D/+ ) were isolated using DBA lectin labeling and magnetic beads separation. We purified RNA from DBA lectin positive cells at critical days of pancreatic ductal development (E14.5, E15.5, E16.5, P1), days 0, 1, 3 and 5 of cerulein-induced acute pancreatitis and from mice in which Kras G12D genetically has been targeted to the pancreas at 10 and 20 weeks of age. The RNA samples were subjected to microarrays and bioinformatic analysis. Functional studies were performed. Results: We were particularly interested in genes that are downregulated during embryonic development as differentiation progresses, genes that are transiently upregulated during acute pancreatitis and subsequent regeneration as well as genes that are upregulated during early carcinogenesis (PanIN). This approach left us with 76 genes common to all three processes. Of these, Prrx1 was one the most regulated genes with known transcriptional activity. Initially, we validated Prrx1 expression by immunostaining in mouse/human tissues of pancreatitis and PanIN/PDAC. Interestingly, the Prrx1b transcript variant is strongly upregulated during cerulein-induced acute pancreatitis whereas the Prrx1a variant remains unchanged. In cancer, however, both variants are upregulated in a stepwise fashion depending upon the genetic alterations that have been introduced (wt vs. Kras G12D/+ vs. Kras G12D/+ ;p53 R172H/+ ). Most notably, circulating pancreatic cells express both variants significantly higher than in pancreatic cells still residing within the primary tumor. In order to assess Prrx1’s role in self-renewal we performed pancreato-sphere assays with pancreatic ductal cells derived from Pdx1-cre;Kras G12D/ + animals. Prrx1b overexpression led to significantly more and larger spheres. Prrx1a overexpression had no effect. Conversely, when we knockdown Prrx1b, but not Prrx1a, by RNAi sphere formation is decreased. In order to investigate the role of Prrx1 in an in vivo setting, we utilized the Prrx1CreER T2 GFP mouse model in which Prrx1 expressing cells are GFP positive. We sorted cells according to DBA lectin (D) and GFP (G) status by FACS. Of all four populations (D+G+, D+G, D-G+ and D-G-), it is the D+G+ population that has the greatest capacity to form spheroids. Remarkably, this population expands approximately 10-fold upon mild chronic injury. Finally, ChIP-seq revealed, for Prrx1a, the most enriched genes are related to cancer progression whereas Prrx1b appears to regulate focal adhesion and ErbB signaling. Conclusion: We have identified Prrx1b as a novel transcription factor that regulates pancreatic regeneration/self-renewal whereas both Prrx1a and Prrx1b appear to be important in pancreatic cancer progression and metastasis. Citation Format: Maximilian Reichert, Anil K. Rustgi, Shigetsugu Takano, Johannes A. von Burstin, Steffen Heeg, Gregory P. Botta, Ju-Seog Lee, Gunter Schneider, Andrew D. Rhim, Ben Z. Stanger. The Prrx1 homeodomain transcription factor plays a central role in pancreatic regeneration and carcinogenesis. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr A71.

Tumors are postulated to arise from tissue stem or progenitor cells. In the stomach, keratin 19 (K19) is thought to mark a potential progenitor cell within the gastric isthmus. To examine the contribution of tissue stem cells to the origin of gastric cancer, we generated a new K19-BAC-CreER transgenic line to study the lineage of K19+ cells and determine whether K19+ might mark both normal and cancer initiating gastric progenitors. K19-BAC-CreER mice were crossed to a ROSA26r(LacZ or GFP) reporter line. The offspring were induced with tamoxifen and studied in a MNU model of antral carcinogenesis. In separate experiments, K19CreER/ROSA26r mice were crossed to LSL-Kras mice to examine the contribution of the K19 lineage to a genetic model of gastric dysplasia. Tamoxifen-induced X-gal labeling occurred in ~10-30% of corpus pit and antral glands. The labeling persisted for greater than 52 weeks, consistent with K19 marking long-lived gastric stem cells. In K19CreER/ROSA26r mice treated with MNU there was a dramatic increase in the labeling of contiguous GFP/X-gal positive glands, consistent with K19+ stem cell expansion and crypt fission. To test whether K19+ progenitor cells labeled by tamoxifen during MNU treatment contribute to the origin of gastric tumors, we examined the pattern of X-gal lineage tracing in antral tumors. Interestingly, when K19+ cells were labeled by tamoxifen during MNU carcinogenesis, tumors originated from both K19-Cre recombined and non-recombined cells, suggesting that MNU stimulated the K19+ progenitor cell to give rise to multiple K19+ daughter cells that contribute to the tumor. In a genetic model of cancer, when oncogenic Kras was expressed in K19+ progenitors, gastric dysplasia was detected as early as 3 months following tamoxifen induction. In summary, K19 marks corpus, as well as, antral stem cells located in the isthmus (above the crypt base), and these K19+ cells serve as cancer initiating cells in both carcinogen and genetic models of gastric tumorigenesis. Kras or MNU-induced division of K19+ cells, evidenced by contiguous crypt labeling and suggestive of symmetric cell division, appears to be an initiating event. Gastric tumors are polyclonal with multiple K19+ cancer stem cells contributing to antral tumors. Thus K19+ stem cells appear relevant for normal homeostasis as well as the development of gastric cancer. Citation Format: Samuel Asfaha, Yoku Hayakawa, Dana Lukin, Russell Ericksen, Ashlesha Muley, Rain Yu, Daniel L. Worthley, Christoph B. Westphalen, Sarah Stokes, Johannes von Burstin, Anil K. Rustgi, Timothy C. Wang. Role of keratin-19 positive stem cells in gastric tumorigenesis. [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 LB-267. doi:10.1158/1538-7445.AM2013-LB-267

Introduction: The clonal origin of tumors is not well understood. Previous studies using chimeric mice have suggested that the origin of tumors in the mammalian small intestine may be polyclonal, with 2 or more progenitor cells contributing to intestinal adenomas. In the intestine, tissue stem cells are believed to be present in small numbers, and either quiescent or actively dividing, as previously shown with Lgr-5+ cells. Cytokeratin 19 (K19) is a potential progenitor marker expressed in the intestinal isthmus. Using the K19 gene promoter to drive Cre recombinase expression, we tracked the lineage of K19+ cells in an inducible fashion. Here, we used K19-CreERT2;ROSA26rLacZ mice to examine whether K19+ cells contribute to colonic tumor formation. Methods: In order to recapitulate the endogenous expression pattern of K19, we used a BAC strategy and generated a transgenic mouse with a Tamoxifen inducible Cre under the control of the K19 promoter (K19-BAC-Cre-ERT2). K19CreERT2 mice were crossed to ROSA26rLacZ (or GFP) reporter mice and treated with tamoxifen (6 mg/ day p.o. for 3 days) to assess K19+ lineage tracing by X-gal or GFP staining. To examine the contribution of the K19+ cells to colonic tumorigenesis, we used the AOM/DSS inflammation-associated model of colonic carcinogenesis. Mice were sacrificed 20 weeks following AOM induction and X-gal staining performed to stain for the K19+ cell lineage. Results: Treatment of control K19CreERT2/Rosa26r mice with tamoxifen resulted in the stochastic labelling of about 20-50% of colonic and intestinal glands, respectively. Consistent with the labeling of stem cells, marked glands stained positive beyond 52 weeks following tamoxifen induction. K19CreERT2/Rosa26r mice treated with AOM or DSS alone following tamoxifen labelling of K19+ glands displayed evidence of K19+ cell expansion and crypt fission, as determined by increased labelling of contiguous X-gal positive glands. K19CreERT2/Rosa26r mice were then treated with a single dose of AOM followed by DSS. When K19+ cells were labelled by tamoxifen administration prior to AOM, we observed that ∼10% tumors were entirely X-gal positive, suggesting derivation from a single K19+ cell. Interestingly, when K19+ cells were labelled by tamoxifen shortly after tumor initiation with AOM, some tumors were derived from both K19 recombined and non-recombined cells in a clonal fashion, suggesting a model whereby a K19+ cell gives rise to multiple K19+ daughter cells that each contribute to the tumor. Conclusions. Using K19CreERT2/Rosa26r mice, we show that K19 marks stem cells within the intestinal isthmus of the small intestine and colon. Using a carcinogen induced model of inflammation-associated carcinogenesis, we demonstrate that K19 expressing cells contribute to tumor formation in a manner consistent with tumor initiation following division of K19+ cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3301. doi:1538-7445.AM2012-3301

Background & Aims Early metastasis is a hallmark of pancreatic ductal adenocarcinoma and responsible for >90% of pancreatic cancer death. Because little is known about the biology and genetics of the metastatic process, we desired to elucidate molecular pathways mediating pancreatic cancer metastasis in vivo by an unbiased forward genetic approach. Methods Highly metastatic pancreatic cancer cell populations were selected by serial in vivo passaging of parental cells with low metastatic potential and characterized by global gene expression profiling, chromatin immunoprecipitation, and in vivo metastatic assay. Results In vivo selection of highly metastatic pancreatic cancer cells induced epithelial-mesenchymal transition (EMT), loss of E-cadherin expression, and up-regulation of mesenchymal genes such as Snail. Genetic inactivation of E-cadherin in parental cells induced EMT and increased metastasis in vivo. Silencing of E-cadherin in highly metastatic cells is mediated by a transcriptional repressor complex containing Snail and histone deacetylase 1 (HDAC1) and HDAC2. In line, mesenchymal pancreatic cancer specimens and primary cell lines from genetically engineered Kras G12D mice showed HDAC-dependent down-regulation of E-cadherin and high metastatic potential. Finally, transforming growth factor β-driven E-cadherin silencing and EMT of human pancreatic cancer cells depends on HDAC activity. Conclusions We provide the first in vivo evidence that HDACs and Snail play an essential role in silencing E-cadherin during the metastatic process of pancreatic cancer cells. These data link the epigenetic HDAC machinery to EMT and metastasis and provide preclinical evidence that HDACs are promising targets for antimetastatic therapy.