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Immune expression profile of macrophages isolated from PDAC tumors.

Immune checkpoint characterization of PDAC tumors.

Effect of PI3Kγ inhibitors on PDAC growth and survival.

Effect of PI3Kγ inhibition on immune cell populations.

Intravital imaging of orthotopic PDAC growth and spread.

Effect of macrophage secrete factors on PDAC cell migration in vitro.

Time course of PDAC tumor inflammation.

Supplementary Methods, Figure Legends

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Supplementary Figure 2 from KRas Induces a Src/PEAK1/ErbB2 Kinase Amplification Loop That Drives Metastatic Growth and Therapy Resistance in Pancreatic Cancer

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Early biomarkers and effective therapeutic strategies are desperately needed to treat pancreatic ductal adenocarcinoma (PDAC), which has a dismal 5-year patient survival rate. Here, we report that the novel tyrosine kinase PEAK1 is upregulated in human malignancies, including human PDACs and pancreatic intraepithelial neoplasia (PanIN). Oncogenic KRas induced a PEAK1-dependent kinase amplification loop between Src, PEAK1, and ErbB2 to drive PDAC tumor growth and metastasis in vivo. Surprisingly, blockade of ErbB2 expression increased Src-dependent PEAK1 expression, PEAK1-dependent Src activation, and tumor growth in vivo, suggesting a mechanism for the observed resistance of patients with PDACs to therapeutic intervention. Importantly, PEAK1 inactivation sensitized PDAC cells to trastuzumab and gemcitabine therapy. Our findings, therefore, suggest that PEAK1 is a novel biomarker, critical signaling hub, and new therapeutic target in PDACs. Cancer Res; 72(10); 2554–64. ©2012 AACR.

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Defining drivers of tumour initiation can provide opportunities to control cancer progression. Here we report that lysophosphatidic acid receptor 4 (LPAR4) becomes transiently upregulated on pancreatic cancer cells exposed to environmental stress or chemotherapy where it promotes stress tolerance, drug resistance, self-renewal and tumour initiation. Pancreatic cancer cells gain LPAR4 expression in response to stress by downregulating a tumour suppressor, miR-139-5p. Even in the absence of exogenous lysophosphatidic acid, LPAR4-expressing tumour cells display an enrichment of extracellular matrix genes that are established drivers of cancer stemness. Mechanistically, upregulation of fibronectin via an LPAR4/AKT/CREB axis is indispensable for LPAR4-induced tumour initiation and stress tolerance. Moreover, ligation of this fibronectin-containing matrix via integrins α5β1 or αVβ3 can transfer stress tolerance to LPAR4-negative cells. Therefore, stress- or drug-induced LPAR4 enhances cell-autonomous production of a fibronectin-rich extracellular matrix, allowing cells to survive 'isolation stress' and compensate for the absence of stromal-derived factors by creating their own tumour-initiating niche.

Introduction: Pancreatic cancer is characterized by a desmoplastic, fibroinflammatory stroma. The crosstalk between cancer cells and their surrounding tumor microenvironment (TME) promotes disease progression, metastasis, and chemoresistance. We identified MICAL2 as a super-enhancer associated gene in pancreatic cancer. MICAL2 (molecule interacting with Cas-L) proteins are Flavin monooxygenases that promotes actin depolymerization and indirectly regulate SRF transcription. In other work, we have found that MICAL2 promotes pancreatic cancer growth and progression. In this study, we evaluated how MICAL2 pancreatic cancer cell expression modulates the PDAC tumor microenvironment. Methods: RNA-Seq analysis performed on human pancreas cancer cells (AsPC) before and after MICAL2 knockdown revealed differential regulation of TGF-β and other proinflammatory cytokines. We validated the expression of TGF-β and other potent cytokines in multiple human and mouse pancreas cancer cell lines by q-PCR. We next exposed human and mouse pancreatic stellate cells (PSCs) to conditioned media from cancer cells before and after MICAL2 knockdown and checked the expression of TGF-β responsive genes by qPCR. KrasG12D/+; Trp53R172H/+; Pdx1-cre (KPC) cells with and without MICAL2 were orthotopically injected to assess the in vivo tumor growth and metastasis. We sorted epithelial cells and CAFs from KPC orthotopic tumors with and without MICAL2 by using EPCAM, PDGFR, and PDPN markers. Results: MICAL2 knockdown (KD) resulted in downregulation of TGF-β gene in both human and mouse pancreas cancer cell lines (50% reduction, p Citation Format: Bharti Garg, Shweta Sharma, Sohini Khan, Edgar Esparza, Sarah Sass, Dawn Jacquish, Evangeline Mose, Herve Tiriac, Andrew Lowy. MICAL2 expression in pancreatic cancer cells modulates the tumor microenvironment through the TGF beta pathway [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C044.

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer in large part due to its propensity for early metastasis. We used ChIP-seq to identify differentially tagged super-enhancer associated genes in PDAC and identified MICAL2 as a gene of interest. MICAL (molecule interacting with CasL) proteins are flavin monooyxgenases that induce actin depolymerization. MICAL2 canonically modulates nuclear actin to regulate SRF/MRTF-A (myocardin related transcription factor) mediated transcription to drive EMT (epithelial-mesenchymal transition) and fibrosis. In this study, we sought to determine the impact of MICAL2 on PDAC progression and its dependence on SRF/MRTF-A signaling. Methods: Studies were performed in human and murine PDAC models. MICAL2 and MRTF-A were knocked down with shRNA and gene expression quantitated with qPCR. In vitro cell viability was assessed by MTT colorimetric assay. Cell migration was tested with in vitro wound scratch assays. Cell cycle analysis was done with flow cytometry-based DNA content measurement. Subcutaneous, orthotopic, and intrasplenic injections of PDAC cells were performed to assess in vivo growth and metastasis. Protein expression was measured with Western blotting. Student’s t-test was used to confirm statistical significance of experimental results. Results: In human PDAC cell lines, MICAL2 knockdown decreased cell viability, reduced cell migration and wound healing, and induced cell cycle arrest at G0/G1. MICAL2 inhibition was associated with decreased p-AKT, c-Myc, and increased p27 by Western blot. Orthotopic and subcutaneous injections of KPC46 shMICAL2 cells were performed in syngeneic mice; orthotopic injections of shMICAL2 cells led to decreased tumor growth compared to control (0.26 gm vs. 1 gm, p = 0.008), not observed with shMRTF-A (1.032 gm vs. 1 gm, p = 0.95). Subcutaneous injections of MICAL2 knockdown cells led to no tumor growth; injections of MRTF-A knockdown cells again led to comparable tumor growth as control (3.02 gm vs. 1.72 gm, p = 0.24). GSEA (Gene Set Enrichment Analysis) of RNAseq data demonstrated a correlation between MICAL2 knockdown and downregulation of Hallmark EMT pathways. Intrasplenic injection studies in syngeneic mice revealed grossly decreased liver metastases after intrasplenic injection of shMRTF-A cells, with total abrogation of metastases after injection of shMICAL2 cells. Conclusions: MICAL2 promotes pancreatic cancer cell growth and metastasis. While MICAL2’s effect on metastasis appears largely dependent on SRF/MRTF-A, tumor growth appears to be MRTF-A independent, suggesting putative novel functions of MICAL2. Given its potentially targetable enzymatic domain and important role in promoting cell growth in vitro and tumor progression and metastasis in vivo, MICAL2 holds promise as a novel tractable therapeutic target in pancreatic cancer. Citation Format: Sohini Khan, Shweta Sharma, Divya Sood, Bharti Garg, Dawn Jaquish, Evangeline Mose, Edgar Esparza, Herve Tiriac, Andrew M. Lowy. MICAL2 promotes pancreatic cancer growth and metastasis independent of MRTF-A signaling [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B017.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by marked desmoplasia and drug resistance due, in part, to poor drug delivery to extravascular tumor tissue. Here, we report that carcinoma-associated fibroblasts (CAFs) induce β5 integrin expression in tumor cells in a TGF-β dependent manner, making them an efficient drug delivery target for the tumor-penetrating peptide iRGD. The capacity of iRGD to deliver conjugated and co-injected payloads is markedly suppressed when β5 integrins are knocked out in the tumor cells. Of note, β5 integrin knock-out in tumor cells leads to reduced disease burden and prolonged survival of the mice, demonstrating its contribution to PDAC progression. iRGD significantly potentiates co-injected chemotherapy in KPC mice with high β5 integrin expression and may be a powerful strategy to target an aggressive PDAC subpopulation., The iRGD tumor-penetrating peptide can achieve tumor specific drug delivery but whether and how it can penetrate into desmoplastic tumors is unknown. Here, the authors show that β5 integrin expression on tumor cells, mediated by CAFs-derived TGF-β, is required for iRGD penetration into the desmoplastic PDAC microenvironment and that iRGD-based combination therapy is effective in PDAC mouse models.

The MST1R (RON) kinase is overexpressed in >80% of human pancreatic cancers, but its role in pancreatic carcinogenesis is unknown. In this study, we examined the relevance of Mst1r kinase to Kras driven pancreatic carcinogenesis using genetically engineered mouse models. In the setting of mutant Kras, Mst1r overexpression increased acinar-ductal metaplasia (ADM), accelerated the progression of pancreatic intraepithelial neoplasia (PanIN), and resulted in the accumulation of (mannose receptor C type 1) MRC1+, (arginase 1) Arg+ macrophages in the tumor microenvironment. Conversely, absence of a functional Mst1r kinase slowed PanIN initiation, resulted in smaller tumors, prolonged survival and a reduced tumor-associated macrophage content. Mst1r expression was associated with increased production of its ligand Mst1, and in orthotopic models, suppression of Mst1 expression resulted in reduced tumor size, changes in macrophage polarization and enhanced T cell infiltration. This study demonstrates the functional significance of Mst1r during pancreatic cancer initiation and progression. Further, it provides proof of concept that targeting Mst1r can modulate pancreatic cancer growth and the microenvironment. This study provides further rationale for targeting Mst1r as a therapeutic strategy.

// Jeffery Chakedis 1 , Randall French 1 , Michele Babicky 1 , Dawn Jaquish 1 , Evangeline Mose 1 , Peter Cheng 1 , Patrick Holman 1 , Haleigh Howard 1 , Jaclyn Miyamoto 1 , Paula Porras 1 , Zakk Walterscheid 1 , Carsten Schultz-Fademrecht 2 , Christina Esdar 3 , Oliver Schadt 3 , Jan Eickhoff 2 , Andrew M. Lowy 1 1 Department of Surgery, Division of Surgical Oncology, Moores Cancer Center, University of California, San Diego, La Jolla, CA, USA 2 Lead Discovery Center GmbH, Dortmund, Germany 3 Merck KGaA, Darmstadt, Germany Correspondence to: Andrew M. Lowy, email: alowy@ucsd.edu Keywords: RON, pancreatic cancer, isoform, alternative splicing, tyrosine kinase inhibitor Received: March 03, 2016 Accepted: May 23, 2016 Published: June 14, 2016 ABSTRACT The RON tyrosine kinase receptor is under investigation as a novel target in pancreatic cancer. While RON mutations are uncommon, RON isoforms are produced in cancer cells via a variety of mechanisms. In this study we sought to: 1) characterize RON isoform expression in pancreatic cancer, 2) investigate mechanisms that regulate isoform expression, and 3) determine how various isoforms effect gene expression, oncogenic phenotypes and responses to RON directed therapies. We quantified RON transcripts in human pancreatic cancer and found expression levels 2500 fold that of normal pancreas with RON isoform expression comprising nearly 50% of total transcript. RNA seq studies revealed that the short form (sfRON) and P5P6 isoforms which have ligand independent activity, induce markedly different patterns of gene expression than wild type RON. We found that transcription of RON isoforms is regulated by promoter hypermethylation as the DNA demethylating agent 5-aza-2’-deoxycytidine decreased all RON transcripts in a subset of pancreatic cancer cell lines. The viability of sfRON-expressing HPDE cells was reduced by a RON specific small molecule inhibitor, while a therapeutic monoclonal antibody had no demonstrable effects. In summary, RON isoforms may comprise half of total RON transcript in human pancreatic cancer and their expression is regulated at least in part by promoter hypermethylation. RON isoforms activate distinct patterns of gene expression, have transforming activity and differential responses to RON directed therapies. These findings further our understanding of RON biology in pancreatic cancer and have implications for therapeutic strategies to target RON activity.

Pancreatic ductal adenocarcinoma (PDAC), constitutes >90% of pancreatic cancers (PC) and is one of the most aggressive human tumors. Standard chemotherapies for PDAC (e.g., gemcitabine, FOLFIRINOX, etc.) has proven to be largely ineffective. Herein, we report a novel molecule (i.e., compound 1) that potently inhibits proliferation and induces apoptosis of PDAC cells. As we observed in other cancer types (i.e., colorectal, breast cancer), the effect of 1 against PDAC cells is also related to microtubule destabilization and DNA damage checkpoint activation. However, in PDAC cells, the inhibitory effect of 1 was mainly controlled by mitochondrial p53-dependent apoptosis. Compound 1 worked with cells of different p53 mutant status and affected p53 activation/phosphorylation not simply by stabilizing p53 protein but through antagonizing anti-apoptotic effects of Bcl-xL and restoring p53 to activate mitochondrial-apoptotic pathways (i.e., cytochrome c release, caspase activation and PARP cleavage). Compound 1 was more efficient than a typical PDAC combination therapy (i.e., gemcitabine with paclitaxel) and showed synergism in inhibiting PDAC cell proliferation with gemcitabine (or gemcitabine with paclitaxel). This synergism varied between different types of PDAC cells and was partially controlled by the phosphorylation of p53 on Serine15 (phospho-Ser15-p53). In vivo studies in an orthotopic syngeneic murine model showed that 1 (20 mg/kg/day, 28 days, i.p.) inhibited tumor growth by 65% compared to vehicle-treated mice. No apparent acute or chronic toxicity was observed. Thus, compound 1 utilizes a distinct mechanism of action to inhibit PC growth in vitro and in vivo and is a novel anti-PDAC compound.

The MST1R gene is overexpressed in pancreatic cancer producing elevated levels of the RON tyrosine kinase receptor protein. While mutations in MST1R are rare, alternative splice variants have been previously reported in epithelial cancers. We report the discovery of a novel RON isoform discovered in human pancreatic cancer. Partial splicing of exons 5 and 6 (P5P6) produces a RON isoform that lacks the first extracellular immunoglobulin-plexin-transcription (IPT) domain. The splice variant is detected in 73% of pancreatic adenocarcinoma patient derived xenografts and 71% of pancreatic cancer cell lines. Peptides specific to RON P5P6 detected in human pancreatic cancer specimens by mass spectrometry confirms translation of the protein isoform. The P5P6 isoform is found to be constitutively phosphorylated, present in the cytoplasm, and it traffics to the plasma membrane. Expression of P5P6 in immortalized human pancreatic duct epithelial (HPDE) cells activates downstream AKT, and in human pancreatic epithelial nestin-expressing (HPNE) cells activates both the AKT and MAPK pathways. Inhibiting RON P5P6 in HPDE cells using a small molecule inhibitor BMS-777607 blocked constitutive activation and decreased AKT signaling. P5P6 transforms NIH3T3 cells and induces tumorigenicity in HPDE cells. Resultant HPDE-P5P6 tumors develop a dense stromal compartment similar to that seen in pancreatic cancer. In summary, we have identified a novel and constitutively active isoform of the RON tyrosine kinase receptor that has transforming activity and is expressed in human pancreatic cancer. These findings provide additional insight into the biology of the RON receptor in pancreatic cancer and are clinically relevant to the study of RON as a potential therapeutic target.

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a low 5-year survival rate, yet new immunotherapeutic modalities may offer hope for this and other intractable cancers. Here, we report that inhibitory targeting of PI3Kγ, a key macrophage lipid kinase, stimulates antitumor immune responses, leading to improved survival and responsiveness to standard-of-care chemotherapy in animal models of PDAC. PI3Kγ selectively drives immunosuppressive transcriptional programming in macrophages that inhibits adaptive immune responses and promotes tumor cell invasion and desmoplasia in PDAC. Blockade of PI3Kγ in PDAC-bearing mice reprograms tumor-associated macrophages to stimulate CD8+ T-cell–mediated tumor suppression and to inhibit tumor cell invasion, metastasis, and desmoplasia. These data indicate the central role that macrophage PI3Kγ plays in PDAC progression and demonstrate that pharmacologic inhibition of PI3Kγ represents a new therapeutic modality for this devastating tumor type. Significance: We report here that PI3Kγ regulates macrophage transcriptional programming, leading to T-cell suppression, desmoplasia, and metastasis in pancreas adenocarcinoma. Genetic or pharmacologic inhibition of PI3Kγ restores antitumor immune responses and improves responsiveness to standard-of-care chemotherapy. PI3Kγ represents a new therapeutic immune target for pancreas cancer. Cancer Discov; 6(8); 870–85. ©2016 AACR. This article is highlighted in the In This Issue feature, p. 803

The recepteur d'origine nantais (RON) receptor tyrosine kinase is overexpressed and stimulates invasive growth in pancreatic cancer cells, yet the mechanisms that underlie RON-mediated phenotypes remain poorly characterized. To better understand RON function in pancreatic cancer cells, we sought to identify novel RON interactants using multidimensional protein identification analysis. These studies revealed plectin, a large protein of the spectrin superfamily, to be a novel RON interactant. Plectin is a multifunctional protein that complexes with integrin-β4 (ITGB4) to form hemidesmosomes, serves as a scaffolding platform crucial to the function of numerous protein signaling pathways and was recently described as an overexpressed protein in pancreatic cancer (Bausch D et al., Clin Cancer Res 2010; Kelly et al., PLoS Med 2008;5:e85). In this study, we demonstrate that on exposure to its ligand, macrophage-stimulating protein, RON binds to plectin and ITGB4, which results in disruption of the plectin-ITGB4 interaction and enhanced cell migration, a phenotype that can be recapitulated by small hairpin ribosomal nucleic acid (shRNA)-mediated suppression of plectin expression. We demonstrate that disruption of plectin-ITGB4 is dependent on RON and phosphoinositide-3 (PI3) kinase, but not mitogen-activated protein kinase (MEK), activity. Thus, in pancreatic cancer cells, plectin and ITGB4 form hemidesmosomes which serve to anchor cells to the extracellular matrix (ECM) and restrain migration. The current study defines a novel interaction between RON and plectin, provides new insight into RON-mediated migration and further supports efforts to target RON kinase activity in pancreatic cancer.

A major problem in the therapeutic management of cancer is the growth of metastases in distant organs, but the genes orchestrating the process need to be identified for the rational design of new treatment. Here, we provide decisive experimental evidence demonstrating the causal involvement of a specific gene, osteopontin (OPN), in the pathogenesis of metastasis by human breast cancer cells and implicating some of its probable partners. Stable long-term depletion, or up-regulation, of OPN gene expression in a matched, isogenic pair of human breast cancer cell lines of differing metastatic proficiency reproducibly changed their ability to colonize distant organs. OPN down-regulation was achieved by transduction of the metastatic line with a DNA construct encoding a small hairpin RNA in a vector labeled with red fluorescent protein and resulted in a marked reduction of metastatic load (P < 0.01). Up-regulation of OPN in the negligibly metastatic line, with a green fluorescent protein-marked retroviral vector containing OPN cDNA driven by a strong promoter, resulted in heavy colonization of the lungs and lymph nodes (P < 0.005). The reciprocal changes in behavior of these matched cell lines cross-corroborate each other. Concomitant changes were seen in the expression of other metastasis-related genes in both modulated lines. The data indicate that therapeutic targeting of tumor OPN molecules could reset metastatically relevant gene networks, resulting in clinical benefit.

This study shows that solitary, dormant human cancer cells, retrieved from metastasis-free organs of animals carrying spontaneously metastatic primary tumors, can reactivate their tumorigenic and metastatic potency. The tumors were produced by MDA-MB-435 CL16 breast cancer cells permanently labeled with green fluorescent protein and the neomycin resistance gene. This enabled unequivocal identification of tumor cells emerging from organ explants cultured in neomycin to eliminate nonneoplastic host cells. Rescued cells resumed proliferation and generated lines that were tumorigenic and metastatic in fresh animals. All resulting primary and secondary tumors were uniformly labeled. Cells recovered from bone marrows and spleens, where there were no metastases, were as tumorigenic and metastatic as cells recovered from lungs and lymph nodes, which are the preferred sites of colonization for this tumor line. This evidence that malignant growth of disseminated cancer cells is suspended indefinitely by microenvironmental conditions in metastasis-free organs, although it is still active in others of the same host, shows that neoplastic progression can be arrested and has far-reaching biological and clinical implications. Specifically, it predicts the existence of natural, nonimmune host mechanisms that stimulate or inactivate tumor growth in different anatomical sites, which may be exploitable for therapeutic benefit.

This study used a unique xenogeneic breast cancer model to study the effects of tumor cells and neighboring host cells upon each other in tumor growth and metastasis. It exploited species differences between the interacting components to determine how the host influenced the tumor and vice versa. It was found that the gene expression profiles of highly and poorly metastatic clones from the same human breast carcinoma changed differentially when the cells were transferred from growth in vitro to the mammary gland. We describe novel sets of genes, validated by human-specific probes, which were induced in the 2 isogenic, but phenotypically different, tumor lineages by the mammary environment. Conversely, the tumor cells also induced changes in gene expression in the neighboring host stromal (i.e., mesenchymal) cell lineages, validated by mouse-specific probes. Reciprocal inductive interactions were also demonstrated in the tumor deposits formed preferentially in the lungs and lymph nodes by the highly metastatic tumor cells. Subtraction of the induced gene changes in the primary site from those in the metastases revealed that the number and magnitude of specific gene inductions in colonized organs were moderate. This finding indicates that the gene expression program causing metastasis has only limited flexibility and fits well with clinical observations that tumor cells form metastases preferentially in select organs, although tumor cells are scattered ubiquitously. This dependency on suitable host niches suggests new molecular therapeutic avenues that target genes in the host-support system that is manipulated by the malignant cells.

Author(s): Alakus, Hakan; Babicky, Michele L; Ghosh, Pradipta; Yost, Shawn; Jepsen, Kristen; Dai, Yang; Arias, Angelo; Samuels, Michael L; Mose, Evangeline S; Schwab, Richard B; Peterson, Michael R; Lowy, Andrew M; Frazer, Kelly A; Harismendy, Olivier

Background Gastrointestinal stromal tumor (GIST) is the most common sarcoma and its treatment with imatinib has served as the paradigm for developing targeted anti-cancer therapies. Despite this success, imatinib-resistance has emerged as a major problem and therefore, the clinical efficacy of other drugs has been investigated. Unfortunately, most clinical trials have failed to identify efficacious drugs despite promising in vitro data and pathological responses in subcutaneous xenografts. We hypothesized that it was feasible to develop orthotopic patient-derived xenografts (PDXs) from resected GIST that could recapitulate the genetic heterogeneity and biology of the human disease. Methods Fresh tumor tissue from three patients with pathologically confirmed GISTs was obtained immediately following tumor resection. Tumor fragments (4.2-mm3) were surgically xenografted into the liver, gastric wall, renal capsule, and pancreas of immunodeficient mice. Tumor growth was serially assessed with ultrasonography (US) every 3-4 weeks. Tumors were also evaluated with positron emission tomography (PET). Animals were sacrificed when they became moribund or their tumors reached a threshold size of 2500-mm3. Tumors were subsequently passaged, as well as immunohistochemically and histologically analyzed. Results Herein, we describe the first model for generating orthotopic GIST PDXs. We have successfully xenografted three unique KIT-mutated tumors into a total of 25 mice with an overall success rate of 84% (21/25). We serially followed tumor growth with US to describe the natural history of PDX growth. Successful PDXs resulted in 12 primary xenografts in NOD-scid gamma or NOD-scid mice while subsequent successful passages resulted in 9 tumors. At a median of 7.9 weeks (range 2.9-33.1 weeks), tumor size averaged 473±695-mm3 (median 199-mm3, range 12.6-2682.5-mm3) by US. Furthermore, tumor size on US within 14 days of death correlated with gross tumor size on necropsy. We also demonstrated that these tumors are FDG-avid on PET imaging, while immunohistochemically and histologically the PDXs resembled the primary tumors. Conclusions We report the first orthotopic model of human GIST using patient-derived tumor tissue. This novel, reproducible in vivo model of human GIST may enhance the study of GIST biology, biomarkers, personalized cancer treatments, and provide a preclinical platform to evaluate new therapeutic agents for GIST.

Background Mucinous neoplasms of the appendix (MNA) are rare tumors which may progress from benign to malignant disease with an aggressive biological behavior. MNA is often diagnosed after metastasis to the peritoneal surfaces resulting in mucinous carcinomatosis peritonei (MCP). Genetic alterations in MNA are poorly characterized due to its low incidence, the hypo-cellularity of MCPs, and a lack of relevant pre-clinical models. As such, application of targeted therapies to this disease is limited to those developed for colorectal cancer and not based on molecular rationale. Methods We sequenced the whole exomes of 10 MCPs of appendiceal origin to identify genome-wide somatic mutations and copy number aberrations and validated significant findings in 19 additional cases. Results Our study demonstrates that MNA has a different molecular makeup than colorectal cancer. Most tumors have co-existing oncogenic mutations in KRAS (26/29) and GNAS (20/29) and are characterized by downstream PKA activation. High-grade tumors are GNAS wild-type (5/6), suggesting they do not progress from low-grade tumors. MNAs do share some genetic alterations with colorectal cancer including gain of 1q (5/10), Wnt, and TGFβ pathway alterations. In contrast, mutations in TP53 (1/10) and APC (0/10), common in colorectal cancer, are rare in MNA. Concurrent activation of the KRAS and GNAS mediated signaling pathways appears to be shared with pancreatic intraductal papillary mucinous neoplasm. Conclusions MNA genome-wide mutational analysis reveals genetic alterations distinct from colorectal cancer, in support of its unique pathophysiology and suggests new targeted therapeutic opportunities.

Objectives To develop a mouse model for multispectral fluorescence imaging of the pancreas and pancreatic microenvironment. Methods Cre/loxP technology was used to develop this model. We crossed mT/mG indicator mice, engineered to constitutively express a conditional tdTomato transgene that converts to green fluorescent protein (GFP) expression after exposure to Cre recombinase, with Pdx1-Cre transgenic mice. To characterize this model for studies of pancreas biology, we performed bright light and fluorescence imaging of body cavities and intact organs and confocal microscopy of pancreata from offspring of Pdx1-Cre and mT/mG crosses. Results Pdx1-Cre-mT/mG mice demonstrated bright GFP expression within the pancreas and duodenum and intense tdTomato expression in all other organs. Green fluorescent protein expression was mosaic in Pdx1-Cre-mT/mG pancreata, with most showing extensive conversion from tdTomato to GFP expression within the epithelial-derived elements of the pancreatic parenchyma. Because both GFP and tdTomato are membrane targeted, individual cell borders were clearly outlined in confocal images of mT/mG pancreata. Conclusions This mouse model enables multispectral fluorescence imaging of individual cells and cell processes at the microscopic level of the pancreatic microenvironment; it should prove valuable for a variety of fluorescence imaging studies, ranging from pancreatic development to pancreatic cancer biology.

Introduction: The RON (receptor d'origine nantais) tyrosine kinase is overexpressed in >80% of human pancreatic cancers, but its effect on pancreatic carcinogenesis is largely unknown. Methods: We developed a transgenic mouse that overexpresses RON specifically in the pancreas (Pdx-1-RON). Additionally, we utilized an existing transgenic mouse with a functionally inactive RON tyrosine kinase domain (Pdx-1-RTK-/-). These strains were crossed with the established CK murine model of pancreatic cancer yielding compound strains, RCK and CK/TK-/-. We performed immunofluorescent staining, flow cytometry, and western blot analysis on the tissues from these animals to study the effects of RON overexpression and the loss of RON signaling in the setting of oncogenic Kras. Results: RON overexpression results in increased acinar-ductal metaplasia, accelerates PanIN progression to invasive cancer, and results in an accumulation of alternatively-activated (MRC1+) macrophages in the tumor microenvironment. We found that RON overexpression results in upregulation of its own ligand, macrophage-stimulating protein (MSP), activating a positive autocrine/paracrine signaling loop that effects tumor growth and the differentiation of tumor-associated macrophages. Knockdown of RON expression and/or MSP expression results in decreased tumor growth in vivo. Additionally, loss of RON signaling in CK/TK-/- mice leads to a profound decrease in alternatively-activated (MRC1+) macrophages in the tumor microenvironment. In contrast, these animals demonstrate an accumulation of classically activated (CD11c+) macrophages. RON signaling is also associated with downregulation of the chemokine, monocyte chemoattractant protein-1 (MCP-1), a known driver of CD11c+ macrophage activation. The correlation of RON and MSP and the inverse correlation with MCP-1 expression were validated in a database analysis of human pancreatic tumor specimens. Conclusion: Our studies demonstrate that murine RON overexpression accelerates the development of invasive pancreatic cancer in the setting of oncogenic Kras. Active RON signaling results in upregulation of its own ligand, MSP, initiating a positive autocrine/paracrine feedback loop that promotes tumor growth and alters the differentiation of macrophages in the tumor microenvironment. Citation Format: Michele L. Babicky, Megan M. Harper, Evangeline S. Mose, Dawn J. Jaquish, Randall P. French, Susan E. Waltz. The RON tyrosine kinase accelerates pancreatic duct neoplasia and activates a positive autocrine/paracrine signaling loop that promotes alternative macrophage activation. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A26.

The RON receptor is frequently over-expressed in pancreatic cancer. We developed a mouse model of spontaneous pancreatic carcinogenesis driven by RON overexpression and oncogenic KRAS (RCK). RCK mice demonstrate accelerated PanIN progression to invasive cancer marked by desmoplasia that is highly characteristic of human disease. RON signaling in macrophages induces differentiation towards the alternatively activated (M2) phenotype, which promotes tumorigenesis. We hypothesized that pancreatic RON overexpression in RCK mice may promote changes in the tumor microenvironment, specifically by driving the differentiation of infiltrating macrophages towards the M2 phenotype. Methods: Pancreatic tissues from RCK and CK controls (3-12 months) were analyzed via immunofluorescent (IMF) staining to quantify myeloid infiltration. Single cell suspensions were generated from pancreatic and splenic tissues. CD11b+F4/80+ myeloid cell populations, as well as CD11c+ M1 and MRC1+ M2 subpopulations, were analyzed via FACS. Results: RCK pancreata demonstrated increased CD11b+F4/80+ myeloid infiltration at 6-12 months. In RCK, pancreatic myeloid cells were skewed toward the M2 phenotype compared with CK controls (MRC1+ 39% vs. 10% p

Early biomarkers and effective therapeutic strategies are desperately needed to treat pancreatic ductal adenocarcinoma (PDAC), which has a dismal 5-year patient survival rate. Here, we report that the novel tyrosine kinase PEAK1 is upregulated in human malignancies, including human PDACs and pancreatic intraepithelial neoplasia (PanIN). Oncogenic KRas induced a PEAK1-dependent kinase amplification loop between Src, PEAK1, and ErbB2 to drive PDAC tumor growth and metastasis in vivo. Surprisingly, blockade of ErbB2 expression increased Src-dependent PEAK1 expression, PEAK1-dependent Src activation, and tumor growth in vivo, suggesting a mechanism for the observed resistance of patients with PDACs to therapeutic intervention. Importantly, PEAK1 inactivation sensitized PDAC cells to trastuzumab and gemcitabine therapy. Our findings, therefore, suggest that PEAK1 is a novel biomarker, critical signaling hub, and new therapeutic target in PDACs. Cancer Res; 72(10); 2554–64. ©2012 AACR.

We report the expression of melanocyte-related genes (MRG) in freshly resected, histopathologically confirmed, human breast cancer specimens and describe experiments illuminating similar observations on a variety of breast cancer cell lines including MDA-MB-435. This finding has implications for research on breast cancer, for clinical investigation of cancer patients presenting with metastases from occult primary tumors and for understanding aberrant differentiation in cancer cells. For example, higher expression of six MRG correlated inversely with propensity for metastatic spread in clones isolated from the human breast cancer cell line MDA-MB-435. Comparisons of MRG expression in cells growing in vitro with those seen in tumors generated by the same lines in vivo showed that the levels of activity of these genes are influenced by the surrounding environment. Also, silencing of expression of the melanocyte-related transcription factor MITF, by transduction of the non-metastatic clone NM2C5 with a construct expressing a specific anti-MITF shRNA, resulted in decreased production of 5 of the melanocyte-related proteins including TYRP1, Pmel 17, MART 1(Melan-A) and TYRP2, but no increase in metastatic capability. Hence MRG expression reproducibly ear-marked, but did not cause, metastatic incompetence. We also report cytogenetic and other data that conflict with the recent suggestion that MDA-MB-435 is of melanocytic origin and are more consistent with its original designation as being of mammary lineage. We conclude that detection of MRG expression profiles in freshly excised breast cancers and in cultured breast cancer cells reflects the operationally important clinical phenomenon of inappropriate gene expression in malignant neoplasms. Concomitantly, we suggest that the evidence we have obtained (i) collectively supports the continued widespread use of the MDA-MB-435 cell line in breast cancer and metastasis research and (ii) advances knowledge of the diversity of aberrant differentiation programs in malignant cells, which is valuable for making accurate diagnoses and treatment decisions in clinical oncology.

Introduction:The RON tyrosine kinase receptor is increasingly overexpressed during progression to Pancreatic Intraepithelial Neoplasia (PanIN) and pancreatic duct adenocarcinoma (PDAC). RON expression in these neoplastic cells is associated with a highly invasive phenotype and resistance to gemcitabine. Mutations in the gene for RON, MST1R, are rare but alternative splicing produces a wide variety of protein isoforms. Exon skipping is the most common and a skipping of exon 11 produces RONΔ165. Alternative transcription start in intron 10 produces short-form RON (sfRON) which promotes metastasis in breast cancer. Eight RON isoforms have previously been reported in different epithelial cancer types (Colon, Breast, Stomach) and we initially sought to characterize their expression in PDAC. Using low passage patient derived xenografts (PDXs), we found that the known RON isoforms Δ165 and sfRON were expressed in the majority of PDX’s. Results: This study revealed a novel RON isoform resulting from partial splicing of exons 5 and 6 (P5P6) to produce a protein that lacks the first extracellular immunoglobulin-plexin-transcription (IPT) domain. Peptides specific to RON P5P6 were detected in pancreatic cancer specimens by mass spectrometry which confirms translation of the protein. Using end point PCR we determined that RON is overexpressed in 90% of PDX and P5P6 expressed in 73%. In PDXs absolute quantification PCR determined RON isoforms P5P6, sfRON, and RONΔ165 make up 15 – 50% of total RON transcripts. This puts total isoform expression at up to 500 times more than the full length protein in normal pancreas. To determine function of these isoforms we overexpressed sfRON, RON P5P6, and RONΔ165 in a Human Pancreatic Ductal Epithelial (HPDE) cell line using a lentiviral vector. We found that all isoforms are constitutively phosphorylated, present in the cytoplasm in a reticular pattern, and RON P5P6 traffics to the plasma membrane. RON P5P6 is spliced into α and β subunits and can bind its ligand Macrophage Stimulating Protein similar to full length RON. Expression of P5P6 in HPDE cells activates downstream AKT and MAPK signaling pathways and increases cell motility, VEGF secretion, and markers of EMT. HPDE cells expressing P5P6 and short form RON were injected orthotopically into NOD SCID Gamma mouse pancreata and are tumorigenic while the parental cell line is not. P5P6 and short form RON tumors induce a denser stroma not characteristically observed in cell line derived xenografts. In HPDE sfRON tumors, host mouse acini adjacent to the tumor undergo acinar to ductal metaplasia. As the tumor invades into the mouse pancreas these newly formed ducts become increasingly dysplastic and begin to express mesenchymal markers. Conclusion: We have identified protein isoforms of the RON tyrosine kinase receptor which are expressed in human pancreatic cancer. A novel isoform RON P5P6 and short form RON transform human pancreatic ductal epithelial cells to become tumorigenic. Expression of short form RON in these tumors causes host mouse pancreas to undergo acinar to ductal metaplasia. Ultimately these findings demonstrate that RON isoform expression by pancreatic cancer cells has significant biologic consequences and promotes interaction with the adjacent normal pancreas. Further work to characterize the soluble factors responsible for RON paracrine signaling is currently underway. Citation Format: Jeffery M. Chakedis, Randall French, Michele Babicky, Dawn Jaquish, Haleigh Howard, Evangeline Mose, Jaclyn Miyamoto, Zakk Walterscheid, Patrick Holman, Andrew M. Lowy. Protein isoforms of the RON tyrosine kinase receptor transform human pancreatic ductal epithelial cells and induce acinar to ductal metaplasia. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A72.

We investigated alpha1-antichymotrypsin (ACT) gene expression in xenograft tumors generated by two isogenic human breast cancer cell lines derived from the same parent, MDA-MB-435, which display opposite metastatic behaviors. Microarray and real-time PCR experiments showed an overexpression of this serine protease inhibitor in the metastatic tumors (M-4A4T) and its derived metastases (M4-Mets) compared with the weakly metastatic tumors (NM-2C5T), and its release into the blood was confirmed by western-blotting. However, functional assays in vivo using genetically engineered tumor cells demonstrated that ACT up-regulation was not, by itself, responsible for the metastatic phenotype. We also made observations that ACT gene regulation was sensitive to tumor-host interactions: inoculation of these lines into the mouse mammary gland greatly increased ACT production and accentuated the intrinsic difference observed when they are cultured in vitro. Sensitivity of tumor cells to their environment was further analyzed by in vitro experiments, which demonstrated that a purified ECM environment and soluble components from normal host mammary cells were both able to significantly promote ACT expression. In addition, we took advantage of the xenogeneic nature of the model to measure ACT expression by the host cells (mouse) and the tumor cells (human) within the neoplasm using species-specific primers in real-time PCR experiments. It was found that the presence of tumor cells, irrespective of their metastatic capabilities, induced local ACT production by host cells at the primary and secondary tumor sites. Thus, this work indicates that there is a specific association of ACT overexpression with the metastatic phenotype in our breast cancer metastasis model. Moreover, because of the xenogeneic nature of our system, we were able to provide evidence of tumor-host reciprocal regulation of ACT production.

Despite recent advances in our understanding of pancreatic ductal adenocarcinoma (PDA), it remains a poorly understood, devastating disease that is largely resistant to all standard treatment modalities. Much effort has been made to identify novel tumor suppressor genes, biomarkers of metastatic behavior, and targets for molecular therapeutics that can improve prognosis and quality of life for PDA patients. Despite the finding that the pro-inflammatory C-X-C family chemokines CXCL1 and CXCL2 are expressed in a significant fraction of human PDA tissues and are known to promote metastasis in bladder and breast cancer, very little is known of its regulation and its role in the progression of PDA. Our laboratory has identified a mechanism by which CXCL1 and CXCL2 expression is regulated in human PDA. CXCL1/2 expression is repressed by the Signal Transducer and Activator of Transcription (STAT)-3 and conversely, the Suppressor of Cytokine Signaling (SOCS)-3, a STAT3 inhibitor, promotes CXCL1/2 gene activation and pro-inflammatory signaling in murine embryonic fibroblasts (MEFs) and human PDA cell lines. Ectopic expression of SOCS3 in the ASPC1 PDA cell line induces CXCL1 and CXCL2 expression and drives resistance to radiation and gemcitibine treatment. Treatment with neutralizing antibodies against CXCL1 or its receptor, CXCR2, sensitizes these cells to ionizing radiation. Further, using an orthotopic xenograft model of human PDA in immunodeficient mice, we demonstrated the in vivo relevance of this pathway. We found that mice injected with human SOCS3-positive human PDA cells have a shorter survival time and develop more aggressive disease compared to mice injected with control cells. We also have shown increased numbers of CD11b-positive granulocytes in the tumor microenvironment of SOCS3+ PDA tumors. We hypothesize that SOCS3 and CXCL1and CXCL2 promote human PDA pathogenesis by two mechanisms: (i) autocrine activation of the CXCR2 receptor expressed on human pancreatic cancer cells and (ii) pro-inflammatory recruitment of neutrophils to the tumor microenvironment. Citation Format: Sisi Jiang, Giovanni Coppola, Evangeline Mose, Andrew Lowy, Christina Jamieson, Nicholas Cacalano. Suppressor of cytokine signaling (SOCS)-3 and the C-X-C chemokines CXCL1 and CXCL2 promote tumor aggressiveness and radiation resistance in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A10.

Mucinous Neoplasm of the Appendix (MNA) is a rare malignancy often diagnosed after metastasis to the peritoneal surfaces resulting in Mucinous Carcinomatosis Peritonei (MCP). Genetic alterations in MNA are poorly characterized due to its low incidence, the hypo-cellularity of MCPs and a lack of relevant pre-clinical models. As such, application of targeted therapies to this disease is limited to those developed for colorectal cancer (CRC) and not based on molecular rationale. We sequenced the whole exomes of 10 MCPs to identify genome-wide somatic mutations and copy number aberrations and validated significant findings in 19 additional cases using deep sequencing and microdroplet PCR. These studies demonstrate that MNA has a different molecular makeup than CRC. Most tumors have co-existing oncogenic mutations in KRAS (26/29) and GNAS (21/29) and are characterized by cAMP-PKA pathway activation. High-grade tumors are GNAS wild-type (5/6), suggesting they do not progress from low-grade tumors. MNAs do share some genetic alterations with CRC including gain of 1q (5/10), Wnt and TGFβ pathway alteration. In contrast, mutations in TP53 (1/10) and APC (0/10), common in CRC, are rare in MNA. Coincident activation of the Ras-Raf-MEK-ERK and cAMP-PKA signaling pathways appears to be shared with pancreatic intraductal papillary mucinous neoplasm. Thus, MNA genome-wide mutational analysis reveals genetic alterations distinct from CRC, in support its unique pathophysiology and suggests MEK and PKA inhibition as new therapeutic opportunities. Citation Format: Hakan Alakus, Michele Babicky, Pradipta Ghosh, Shawn Yost, Kristen Jepsen, Yang Dai, Angelo Arias, Michael Samuels, Evangeline Mose, Michael Peterson, Andrew Lowy, Kelly Frazer, Olivier Harismendy. Genome-wide mutational analysis reveals core signaling pathways in mucinous neoplasms of the appendix. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5191. doi:10.1158/1538-7445.AM2014-5191

Introduction - The RON tyrosine kinase receptor is overexpressed in 80% of Pancreatic Ductal Adenocarcinomas (PDAC) and mediates invasiveness, resistance to apoptosis, and VEGF secretion. Though point mutations are rare a wide variety of RON protein isoforms have been identified, some of which are constitutively active and oncogenic. Previous studies of the DNA methylation patterns of pancreatic cancer specimens identified the gene for RON, MST1R, to be controlled by epigenetic modification. Methylation is one mechanism to regulate expression of RON, and we seek to investigate the effects of hypomethylating therapy on isoform expression and alteration of PDAC biology. Methods - Established pancreatic cancer cell lines (MiaPaca2, BxPC3, AsPC1, HPDE, Panc1) and 2 novel cell lines derived from patient tumor specimens (34E, 79E) were treated with 5-Aza-2′-deoxycytidine (Decitabine, DAC) for 96 hours. Genomic DNA was analyzed using the Methylflash (Epigentek) assay to determine genomic methylation percentage. Reverse Transcriptase PCR and western blot analysis was used to determine treatment effects on RON transcription and expression. Results - Genomic methylation analysis of pancreatic cancer cell lines revealed that compared to the control HPDE line (1.2% methylation) some lines were hypomethylated (ASPC1-1.13%, 34E-1.17%, Panc1-1.17%) while others were hypermethylated (BxPC3-1.6%, MiaPaca2-1.98%, 79E-2.06%). Hypomethylating therapy was effective in decreasing genomic methylation to below normal levels (0.4%-0.9%) in all cell lines and depleted DNA MethylTransferase 1 (DNMT1) protein levels. The effects of demethylating therapy on RON expression were differential. The amount of RON transcripts and protein expression in the RON expressing lines (79E and 34E) was decreased but increased in MiaPaca2 and Panc1. MiaPaca2 does not normally express RON, but demethylation induced RON expression. Transcripts specific for the Δ55 isoform of RON decreased in 34E, 79E, and HPDE cell lines but did not change in the others. Transcription and expression of other RON isoforms which are constitutively active decreased in 34E, 79E, ASPC1, and BxPC3 lines, with less exon 11 skipping and partial splicing of exon 5 and 6. Though RON protein expression was decreased overall in the expressing lines, phosphorylation was still detectable following DAC treatment. Conclusions - Genomic methylation of pancreatic cancer cell lines is variable and RON expression is modulated by the methylation status of its promoter. Demethylating therapy has variable effects on RON expression and is context specific. RON isoform expression was decreased in response to treatment, linking DNA methylation to alternative splicing events. These findings suggest that the consequences of demethylating therapy on PDAC biology are complex and additional studies are required to further elucidate definitive mechanisms. Citation Format: Jeffery Chakedis, Randall French, Dawn Jaquish, Evangeline Mose, Andrew Lowy. Demethylating therapy modulates expression of the RON tyrosine kinase receptor in pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2315. doi:10.1158/1538-7445.AM2014-2315

Despite recent advances in our understanding of pancreatic ductal adenocarcinoma (PDA), it remains a poorly understood, devastating disease that is largely resistant to all standard treatment modalities. Much effort has been made to identify novel tumor suppressor genes, biomarkers of metastatic behavior, and targets for molecular therapeutics that can improve prognosis and quality of life for PDA patients. Despite the finding that the pro-inflammatory C-X-C family chemokines CXCL1 and CXCL2 are expressed in a significant fraction of human PDA tissues and are known to promote metastasis in bladder and breast cancer, very little is known of its regulation and its role in the progression of PDA. Our laboratory has identified a mechanism by which CXCL1 expression is regulated in human PDA. CXCL1/2 expression is repressed by the Signal Transducer and Activator of Transcription (STAT)-3 and conversely, the Suppressor of Cytokine Signaling (SOCS)-3, a STAT3 inhibitor, promotes CXCL1/2 gene activation and pro-inflammatory signaling in murine embryonic fibroblasts (MEFs) and human PDA cell lines. Ectopic expression of SOCS3 in the ASPC1 PDA cell line induces CXCL1 and CXCL2 expression and drives resistance to radiation and gemcitibine treatment. Further, using an orthotopic xenograft model of human PDA in immunodeficient mice, we demonstrated the in vivo relevance of this pathway. We found that mice injected with human SOCS3-positive human PDA cells have a survival time compared and develop more aggressive disease compared to mice injected with control cells. We hypothesize that CXCL1and CXCL2 promote human PDA pathogenesis by two mechanisms: (i) autocrine activation of the CXCR2 receptor expressed on human pancreatic cancer cells and (ii) pro-inflammatory recruitment of neutrophils to the tumor microenvironment. Citation Format: Sisi Jiang, Evangeline Mose, Giovanni Coppola, Andrew Lowy, Christina Jamieson, Nicholas A. Cacalano. Suppressor of Cytokine Signaling (SOCS)-3 and the C-X-C chemokines CXCL1 and CXCL2 promote tumor aggessiveness and radiation resistance in pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4208. doi:10.1158/1538-7445.AM2014-4208

Introduction: The RON tyrosine kinase receptor is overexpressed in the majority of pancreatic duct adenocarcinomas (PDAC) and has been shown to promote pancreatic cancer cell migration, invasion and apoptotic resistance. The RON gene can be alternatively transcribed to produce protein isoforms which have variable activities. RON isoforms have been described previously in colon, breast, gastric, and lung cancer specimens and have been shown to be oncogenic. Several therapies directed against RON are in preclinical and Phase 1 trials, therefore determining biological significance of RON isoforms is of great importance. Here we report their identification in human PDAC and investigate their importance using pancreatic cancer cell lines created to overexpress the isoforms. Methods: Patient derived PDAC xenografts (PDXS) were established in the pancreata of NSG mice. Low passage (P4 or less) xenograft tumors were used to generate RNA and protein lysates for RT-PCR and Western blot analysis. Primers specific for exons 4-6 and 10-12 were created to assess alternative transcription and deletion of these exons. Results: 19 PDX's were analyzed and alternative transcription of the RON gene was identified in all but 1 tumor. Deletions of exons 5, 6, and 11 were common and resulted in transcripts for RONΔ165 (which was as common as the wild type transcript), RONΔ160, RONΔ155, and RONΔ90 isoforms. The RONΔ55 isoform (short-form RON, is created by transcription from an alternative start in exon 11 resulting in a truncated protein where the extra-cellular domain is deleted) was present in 15 of 19 tumors. Western blot analysis and Immunoprecipitation (IP) was used to confirm protein expression and determine RON activity. 7 of 9 fresh tumor samples showed RON phosphorylation. Protein isoforms were purified by IP with RON 8 antibody and then resolved using gel electrophoresis. Mass spectrometry identified the presence of RONΔ165, RON Δ170, and RONe5|6in isoforms with RONΔ165 being the most abundant. We further tested our hypothesis that the RONΔ55 isoform is active by tagging it with green fluorescent protein (GFP) and transfecting the fusion protein into 3 cell lines (Mia-Paca 2, BxPC3, and HPDE6/E7). Analysis of the novel cell lines showed constitutive phosphorylation of Δ55 and increased phosphorylation of ERK and AKT indicating enhanced signaling via the MAPK and PI3K pathways. Conclusions: Our findings show for the first time that RON is alternatively transcribed and produces biologically active isoforms in tissue derived from human pancreatic duct adenocarcinoma. We have confirmed the presence of these isoforms at the protein level and found that RONΔ165 is abundant. Further work to understand the biologic significance of these isoforms is required to guide future drug development and to validate RON as a rational target in the treatment of pancreatic cancer. Citation Format: Jeffery Chakedis, Randall French, Michele Babicky, Megan Harper, Dawn Jaquish, Evangeline Mose, Andrew Lowy. Alternative transcription of the RON tyrosine kinase receptor in human pancreatic adenocarcinoma generates active protein isoforms. [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 3019. doi:10.1158/1538-7445.AM2013-3019

tumor type, and pancreatic cancer is associated with the highest risk. Virchow’s triad describes three factors contributing to Vte: hypercoagulability, stasis, and endothelial injury. Rotational thromboelastography (ROTEM) is a new point of care test that allows rapid quantification of coagulation status, for which there is limited information in cancer. We used ROTEM to compare preoperative clot kinetics/strength in patients undergoing surgery for malignant disease.