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Pancreatic ductal adenocarcinoma (PDA) and chronic pancreatitis are characterized by a dense collagen-rich desmoplastic reaction. Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagens that can regulate cell proliferation, migration, adhesion, and remodeling of the extracellular matrix. To address the role of DDR1 in PDA, Ddr1-null (Ddr-/-) mice were crossed with the KrasG12D/+; Trp53R172H/+; Ptf1aCre/+ (KPC) model of metastatic PDA. Ddr1-/-; KPC mice progress to differentiated PDA but resist progression to poorly differentiated cancer compared with KPC control mice. Strikingly, severe pancreatic atrophy accompanied tumor progression in Ddr1-/-; KPC mice. To further explore the effects of Ddr1 ablation, Ddr1-/- mice were crossed with the KrasG12D/+; Ptf1aCre/+ neoplasia model and subjected to cerulein-induced experimental pancreatitis. Similar to KPC mice, tissue atrophy was a hallmark of both neoplasia and pancreatitis models in the absence of Ddr1. Compared with controls, Ddr1-/- models had increased acinar cell dropout and reduced proliferation with no difference in apoptotic cell death between control and Ddr1-/- animals. In most models, organ atrophy was accompanied by increased fibrillar collagen deposition, suggesting a compensatory response in the absence of this collagen receptor. Overall, these data suggest that DDR1 regulates tissue homeostasis in the neoplastic and injured pancreas.

Background & Aims Mitogen-activated protein kinase (MAPK) signaling in the exocrine pancreas has been extensively studied in the context of pancreatic cancer, where its potential as a therapeutic target is limited by acquired drug resistance. However, its role in pancreatitis is less understood. We investigated the role of mitogen-activated protein kinase kinase (MEK)-initiated MAPK signaling in pancreatitis to determine the potential for MEK inhibition in treating pancreatitis patients. Methods To examine the role of MEK signaling in pancreatitis, we used both genetic and pharmacologic approaches to inhibit the MAPK signaling pathway in a murine model of cerulein-induced pancreatitis. We generated mice harboring inducible short hairpins targeting the MEK isoforms Map2k1 and/or Map2k2 specifically in the pancreatic epithelium. We also used the MEK inhibitor trametinib to determine the efficacy of systemic inhibition in mice with pancreatitis. Results We demonstrated an essential role for MEK signaling in the initiation of pancreatitis. We showed that both systemic and parenchyma-specific MEK inhibition in established pancreatitis induces epithelial differentiation and stromal remodeling. However, systemic MEK inhibition also leads to a loss of the proliferative capacity of the pancreas, preventing the restoration of organ mass. Conclusions MEK activity is required for the initiation and maintenance of pancreatitis. MEK inhibition may be useful in the treatment of chronic pancreatitis to interrupt the vicious cycle of destruction and repair but at the expense of organ regeneration., Graphical abstract

Aberrant activation of embryonic signaling pathways is frequent in pancreatic ductal adenocarcinoma (PDA), making developmental regulators therapeutically attractive. Here we demonstrate diverse functions for pancreatic and duodenal homeobox 1 (PDX1), a transcription factor indispensable for pancreas development, in the progression from normal exocrine cells to metastatic PDA. We identify a critical role for PDX1 in maintaining acinar cell identity, thus resisting the formation of pancreatic intraepithelial neoplasia (PanIN)-derived PDA. Upon neoplastic transformation, the role of PDX1 changes from tumor-suppressive to oncogenic. Interestingly, subsets of malignant cells lose PDX1 expression while undergoing epithelial-to-mesenchymal transition (EMT), and PDX1 loss is associated with poor outcome. This stage-specific functionality arises from profound shifts in PDX1 chromatin occupancy from acinar cells to PDA. In summary, we report distinct roles of PDX1 at different stages of PDA, suggesting that therapeutic approaches against this potential target need to account for its changing functions at different stages of carcinogenesis. These findings provide insight into the complexity of PDA pathogenesis and advocate a rigorous investigation of therapeutically tractable targets at distinct phases of PDA development and progression.

Immunohistochemical staining for DNA mismatch repair proteins may be affected by various biological and technical factors. Staining variations that could potentially lead to erroneous interpretations have been recognized. A recently recognized staining variation is the significant reduction of staining for MSH6 in some colorectal carcinomas. The frequency and specific characteristics of this aberrant MSH6 staining pattern, however, have not been well analyzed. In this study of 420 colorectal carcinoma samples obtained from patients fulfilling the Revised Bethesda Guidelines, we detected 9 tumors (2%) showing extremely limited staining for MSH6 with positive staining present in5% of the tumor cells. Our analyses showed that these tumors belonged to two distinct categories: (1) MLH1 and/or PMS2 protein-deficient carcinomas (n=5, including 1 with a pathogenic mutation in PMS2); and (2) MLH1, PMS2 and MSH2 normal but with chemotherapy or chemoradiation therapy before surgery (n=4). To test our hypothesis that somatic mutation in the coding region microsatellite of the MSH6 gene might be a potential underlying mechanism for such limited MSH6 staining, we evaluated frameshift mutation in a (C)(8) tract in exon 5 of the MSH6 gene in seven tumors that had sufficient DNA for analysis, and detected mutation in four; all four tumors belonged to the MLH1/PMS2-deficient group. In conclusion, our data outline the main scenarios where significant reduction of MSH6 staining is more likely to occur in colorectal carcinoma, and suggest that somatic mutations of the coding region microsatellites of the MSH6 gene is an underlying mechanism for this staining phenomenon in MLH1/PMS2-deficient carcinomas.

Mutation screening of the breast and ovarian cancer predisposition genes BRCA1 and BRCA2 is becoming an increasingly important part of clinical practice. Classification of rare non-truncating sequence variants in the BRCA1 and BRCA2 genes is problematic because it is not known whether these subtle changes alter function sufficiently to predispose cells to cancer development. The BRCA1 331G > A substitution mutation, which occurs at the last nucleotide of exon 5, results in an Arg-to-Lys change at codon 71 (R71K). cDNA analysis indicated that the R71K mutation significantly increases the level of a transcript, characterized by a 22 bp deletion in exon 5, which putatively produces a truncated BRCA1 protein of 63 amino acids. The mutation completely abolishes normal splicing as the mutant allele does not generate any normal transcript. Analysis of a tumor specimen indicates loss of heterozygosity. These results support the conclusion that BRCA1 331G > A (R71K) is a deleterious mutation.

Shah MA, Salo-Mullen E, Stadler Z, Ruggeri JM, Mirander M, Pristyazhnyuk Y, Zhang L. De novo CDH1 mutation in a family presenting with early-onset diffuse gastric cancer. In this report, we describe the first concluded case of a de novo germline mutation in CDH1 in a hereditary diffuse gastric cancer (HDGC) kindred. The incident case was a woman with a personal history of Hodgkin's lymphoma and diffuse gastric cancer, who was then confirmed to have a CDH1 mutation (c.1792 C>T (R598X)). The patient's mother was found to have the same CDH1 germline mutation; however, neither maternal grandparent was found to carry the mutation, thus leading to a conclusion that the proband's mother's mutation is of de novo origin. This case highlights the importance of recognition of the HDGC syndrome and of testing for CDH1 germline mutations in young individuals with diffuse gastric cancer without a family history of the disease.

Pancreatic ductal adenocarcinoma (PDA) is an aggressive and devastating cancer often characterized by an intense collagen-rich, fibrotic response. In the presence of an oncogenic Kras mutation, the pancreas undergoes an initial morphological event in which normal acinar cells transdifferentiate into a ductal-like phenotype in a process called acinar-ductal metaplasia (ADM). ADM advances into pre-cancerous lesions, followed by a subsequent replacement of epithelium with a collagen-dense stromal reaction as PDA progresses. Discoidin domain receptors, DDR1 and DDR2, are a unique family of tyrosine receptor kinases that bind to collagen and activate downstream cellular responses that affect cell proliferation, migration, and adhesion. Our preliminary data shows that during Kras-induced ADM in vitro DDR1 is downregulated and is accompanied by an upregulation of DDR2 expression. Immunohistochemistry on human tissue microarrays reveals DDR1 is expressed in normal epithelia and pre-neoplastic lesions, but downregulated during advanced PDA. Conversely, DDR2 is upregulated in metaplastic lesions and advanced carcinoma as well as in the stroma at all stages of progression, suggesting DDRs may play a differential role throughout the PDA. DDR1 is expressed in epithelial cells and associated with disease states such as fibrosis and various cancers, including PDA. To study the role of DDR1 in pancreatitis, a known risk factor of PDA, we used DDR1-null mice (DDR1-/-) with our cerulein-induced pancreatitis protocol. DDR1 ablation induces tissue damage and impairs recovery from extended cerulein treatment. To understand the role of DDR1 in tumorigenesis, we mated DDR1-/- mice in the KrasG12D/+; Ptf1aCre/+ (KC model) of pancreatic neoplasia. The absence of DDR1 in the KC model does not inhibit nor delay tumorigenesis, however, pancreata are smaller with less differentiated morphology than wild-type KC animals. In contrast, DDR2 is expressed in mesenchymal cells and has been implicated in EMT, cell proliferation, tumor invasion, and required for metastasis in breast cancer, however, its significance in PDA remains unknown. Our preliminary data shows DDR2 co-stains with neuroendocrine positive cells within neoplastic lesions that are associated with poor patient survival. To further investigate the role of DDR2 in tumor progression we have successfully mated a conditional, global DDR2 knockout mouse (DDR2fl/fl; β-actinCreERT2) with our novel KrasFSF-G12D/+;p53FRT/+ ;Ptf1a-FlpO/+ (KPF) aggressive PDA mouse model. Collectively, the results from these studies will help determine the role of DDRs throughout the initiation and progression of PDA and help define a potential point of regulation at the interface between the epithelial-stromal interactions. Citation Format: Jeanine Ruggeri, Christopher Halbrook, Anjum Sohail, Rafael Fridman, Howard Crawford. Determining the role of discoidin domain receptors 1 and 2 in the pathogenesis of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4499.