Adar1 deletion causes degeneration of the exocrine pancreas via Mavs-dependent interferon signaling

Adenosine deaminase acting on RNA 1 (ADAR1) is an RNA-binding protein that deaminates adenosine (A) to inosine (I). A-to-I editing alters post-transcriptional RNA processing, making ADAR1 a crucial regulator of gene expression. Consequently, Adar1 has been implicated in organogenesis. To determine the role of Adar1 in pancreatic development and homeostasis, we conditionally deleted Adar1 from the murine pancreas (Ptf1aCre/+; Adar1Fl/Fl). The resulting mice had stunted growth, likely due to malabsorption associated with exocrine pancreatic insufficiency. Analyses of pancreata revealed ductal cell expansion, heightened interferon-stimulated gene expression and an increased influx of immune cells. Concurrent deletion of Adar1 and Mavs, a signaling protein implicated in the innate immune pathway, rescued the degenerative phenotype and resulted in normal pancreatic development. Taken together, our work suggests that the primary function of Adar1 in the pancreas is to prevent aberrant activation of the Mavs-mediated innate immune pathway, thereby maintaining pancreatic homeostasis.

A Programmable In Vivo CRISPR Activation Model Elucidates the Oncogenic and Immunosuppressive Functions of MYC in Lung Adenocarcinoma

Conventional genetically engineered mouse models (GEMM) are time-consuming, laborious, and offer limited spatiotemporal control. Here, we describe the development of a streamlined platform for in vivo gene activation using CRISPR activation (CRISPRa) technology. Unlike conventional GEMMs, this model system allows for flexible, sustained, and timed activation of one or more target genes using single or pooled lentiviral guides. Myc and Yap1 were used as model oncogenes to demonstrate gene activation in primary pancreatic organoid cultures in vitro and enhanced tumorigenic potential in Myc-activated organoids when transplanted orthotopically in vivo. Implementation of this model as an autochthonous lung cancer model showed that transduction-mediated activation of Myc led to accelerated tumor progression and significantly reduced overall survival relative to nontargeted tumor controls. Furthermore, Myc activation led to the acquisition of an immune suppressive, "cold" tumor microenvironment. Cross-species validation of these results using publicly available RNA/DNA-seq datasets linked MYC to a previously described immunosuppressive molecular subtype in patient tumors, thus identifying a patient cohort that may benefit from combined MYC- and immune-targeted therapies. Overall, this work demonstrates how CRISPRa can be used for rapid functional validation of putative oncogenes and may allow for the identification and evaluation of potential metastatic and oncogenic drivers through competitive screening.

SIGNIFICANCE

A streamlined platform for programmable CRISPR gene activation enables rapid evaluation and functional validation of putative oncogenes in vivo.

Abstract 918: Development of a platform for programmable in vivo oncogene activation and screening using CRISPRa technology

Conventional genetically engineered mouse models (GEMMs) are time consuming, laborious and offer limited spatio-temporal control. We have developed a streamlined platform for in vivo gene activation using CRISPR activation (CRISPRa) technology. Our model system allows for flexible, sustained and timed activation of one or more target genes, in vitro or in vivo, using single or pooled lentiviral guides. Using Myc and Yap1 as model oncogenes, we implemented this platform to study the effect of oncogene activation on the tumorigenic potential of primary pancreatic organoids, as well as in an autochthonous model of lung adenocarcinoma. We found that Myc-activation in pancreatic organoids increased their tumorigenic potential and resulted in significantly shorter survival relative to controls when transplanted orthotopically. In vivo Myc activation in the lung accelerated tumor progression and resulted in significantly shorter overall survival relative to non-targeted tumor controls. Furthermore, we found that Myc-activation drives the acquisition of an immune suppressive “cold” tumor microenvironment. Through cross-species validation of our results, we were able to link MYC to a previously described, immunosuppressive transcriptomic subtype in patient tumors, thus identifying a patient cohort that may benefit from combined MYC/immune-targeted therapies. Our work demonstrates how CRISPRa can be used for rapid functional validation of putative oncogenes and may allow for the identification and evaluation of potential metastatic and oncogenic drivers through competitive screening.

Citation Format: Fredrik Ivar Thege, Dhwani N. Rupani, Bhargavi B. Barathi, Anirban Maitra, Andrew D. Rhim, Sonja M. Wörmann. Development of a platform for programmable in vivo oncogene activation and screening using CRISPRa technology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 918.

Abstract 1506: APOBEC3A a causative agent in cancer-related chromosomal instability and STING driven metastasis

Chromosomal instability (CIN), a hallmark of cancer, has been associated with a highly metastatic phenotype in numerous cancers. Mechanisms by which these genomic events occur during the lifespan of a neoplasm have yet to be fully delineated. In our study we identified a novel function for APOBEC3A (A3A), a primate-specific cytidine deaminase upregulated in multiple cancers including Pancreatic ductal adenocarcinoma (PDAC), in the initiation of CIN.We demonstrate that A3A is not routinely detected in non-diseased pancreata; however, expression was detected in the epithelial and stromal compartments from patients with chronic pancreatitis and in precursor lesions of PDAC and is further significantly increased in invasive neoplasia. Strikingly, we found that A3A expression but not A3A-induced mutagenesis, was associated with a significantly reduced overall survival in PDAC. By employing a variety of genetic tools, we identified a novel function for A3A in initiating CIN, underscoring its potential role in driving the observed early metastatic propensity in PDAC. Using a series of in vivo and in vitro models, we demonstrate that A3A-induced CIN leads to aggressive cancer, featuring enhanced, STING-dependent, distant organ seeding and metastatic growth. As a consequence of aberrant A3A function and CIN-mediated upregulation of STING, NfkB and Stat3 pathways were activated. More importantly, all these effects were independent of the deaminase domain, underscoring a novel role of A3A beyond its established canonical function. Remarkably, in a novel autochthonous murine model of PDA expressing human A3A, we identified numerous copy number changes, homologous to those altered in A3A overexpressing patient tumors, including deletions in DNA repair pathway genes. While we showed that A3A-expressing PDAC cells do not fully phenocopy a BRCA mutation-like phenotype, A3A-expressing PDAC cells are exceptionally sensitive to PARP inhibition and DNA cross linking agents, recapitulating a state of “chemical BRCAness”. The combined effect of deletions in these genes has yet to be ascertained, and we hypothesize that these losses further add to ongoing DNA damage overall in PDAC. In summary, our study shows, that A3A drives metastasis and specific deletions through a deaminase-independent initiation of CIN, with potential implications for targeted treatment strategies in pancreatic cancer.

Citation Format: Sonja Maria Woermann, Amy Zhang, Fredrik I. Thege, Chris Gates, Reuben S. Harris, Susan R. Ross, Faiyaz Notta, Anirban Maitra, Andrew D. Rhim. APOBEC3A a causative agent in cancer-related chromosomal instability and STING driven metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1506.

A clinical prediction model to assess risk for pancreatic cancer among patients with prediabetes

BACKGROUND

Early detection of pancreatic ductal adenocarcinoma (PDA) may improve survival. We previously developed a clinical prediction model among patients with new-onset diabetes to help identify PDAs 6 months prior to the clinical diagnosis of the cancer. We developed and internally validated a new model to predict PDA risk among those newly diagnosed with impaired fasting glucose (IFG).

METHODS

We conducted a retrospective cohort study in The Health Improvement Network (THIN) (1995-2013) from the UK. Eligible study patients had newly diagnosed IFG during follow-up in THIN. The outcome was incident PDA diagnosed within 3 years of IFG diagnosis. Candidate predictors were factors associated with PDA, glucose metabolism or both.

RESULTS

Among the 138 232 eligible patients with initial IFG diagnosis, 245 (0.2%) were diagnosed with PDA within 3 years. The median time from IFG diagnosis to clinical PDA diagnosis was 326 days (IQR 120-588). The final prediction model included age, BMI, proton pump inhibitor use, total cholesterol, low-density lipoprotein, alanine aminotransferase and alkaline phosphatase. The model achieved good discrimination [area under the curve 0.71 (95% CI, 0.67-0.75)] and calibration (Hosmer and Lemeshow goodness-of-fit test P > 0.05 in 17 of the 20 imputed data sets) with optimism of 0.0012662 (95% CI, -0.00932 to 0.0108771).

CONCLUSIONS

We developed and internally validated a sequential PDA prediction model based on clinical information routinely available at the initial appearance of IFG. If externally validated, this model could significantly extend our ability to detect PDAs at an earlier stage.

APOBEC3A drives deaminase domain-independent chromosomal instability to promote pancreatic cancer metastasis

Despite efforts in understanding its underlying mechanisms, the etiology of chromosomal instability (CIN) remains unclear for many tumor types. Here, we identify CIN initiation as a previously undescribed function for APOBEC3A (A3A), a cytidine deaminase upregulated across cancer types. Using genetic mouse models of pancreatic ductal adenocarcinoma (PDA) and genomics analyses in human tumor cells we show that A3A-induced CIN leads to aggressive tumors characterized by enhanced early dissemination and metastasis in a STING-dependent manner and independently of the canonical deaminase functions of A3A. We show that A3A upregulation recapitulates numerous copy number alterations commonly observed in patients with PDA, including co-deletions in DNA repair pathway genes, which in turn render these tumors susceptible to poly (ADP-ribose) polymerase inhibition. Overall, our results demonstrate that A3A plays an unexpected role in PDA as a specific driver of CIN, with significant effects on disease progression and treatment.

Pancreatic Cancer-Related Mutational Burden Is Not Increased in a Patient Cohort With Clinically Severe Chronic Pancreatitis

INTRODUCTION

Chronic pancreatitis is associated with an increased risk of developing pancreatic cancer, and patients with inherited forms of pancreatitis are at greatest risk. We investigated whether clinical severity of pancreatitis could also be an indicator of cancer risk independent of etiology by performing targeted DNA sequencing to assess the mutational burden in 55 cancer-associated genes.

METHODS

Using picodroplet digital polymerase chain reaction and next-generation sequencing, we reported the genomic profiles of pancreases from severe clinical cases of chronic pancreatitis that necessitated palliative total pancreatectomy with islet autotransplantation.

RESULTS

We assessed 57 tissue samples from 39 patients with genetic and idiopathic etiologies and found that despite the clinical severity of disease, there was no corresponding increase in mutational burden. The average allele frequency of somatic variants was 1.19% (range 1.00%-5.97%), and distinct regions from the same patient displayed genomic heterogeneity, suggesting that these variants are subclonal. Few oncogenic KRAS mutations were discovered (7% of all samples), although we detected evidence of frequent cancer-related variants in other genes such as TP53, CDKN2A, and SMAD4. Of note, tissue samples with oncogenic KRAS mutations and samples from patients with PRSS1 mutations harbored an increased total number of somatic variants, suggesting that these patients may have increased genomic instability and could be at an increased risk of developing pancreatic cancer.

DISCUSSION

Overall, we showed that even in those patients with chronic pancreatitis severe enough to warrant total pancreatectomy with islet autotransplantation, pancreatic cancer-related mutational burden is not appreciably increased.

Epithelial memory of inflammation limits tissue damage while promoting pancreatic tumorigenesis

Inflammation is a major risk factor for pancreatic ductal adenocarcinoma (PDAC). When occurring in the context of pancreatitis, KRAS mutations accelerate tumor development in mouse models. We report that long after its complete resolution, a transient inflammatory event primes pancreatic epithelial cells to subsequent transformation by oncogenic KRAS. Upon recovery from acute inflammation, pancreatic epithelial cells display an enduring adaptive response associated with sustained transcriptional and epigenetic reprogramming. Such adaptation enables the reactivation of acinar-to-ductal metaplasia (ADM) upon subsequent inflammatory events, thereby limiting tissue damage through a rapid decrease of zymogen production. We propose that because activating mutations of KRAS maintain an irreversible ADM, they may be beneficial and under strong positive selection in the context of recurrent pancreatitis.

Stabilized epithelial phenotype of cancer cells in primary tumors leads to increased colonization of liver metastasis in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is therapeutically recalcitrant and metastatic. Partial epithelial to mesenchymal transition (EMT) is associated with metastasis; however, a causal connection needs further unraveling. Here, we use single-cell RNA sequencing and genetic mouse models to identify the functional roles of partial EMT and epithelial stabilization in PDAC growth and metastasis. A global EMT expression signature identifies ∼50 cancer cell clusters spanning the epithelial-mesenchymal continuum in both human and murine PDACs. The combined genetic suppression of Snail and Twist results in PDAC epithelial stabilization and increased liver metastasis. Genetic deletion of Zeb1 in PDAC cells also leads to liver metastasis associated with cancer cell epithelial stabilization. We demonstrate that epithelial stabilization leads to the enhanced collective migration of cancer cells and modulation of the immune microenvironment, which likely contribute to efficient liver colonization. Our study provides insights into the diverse mechanisms of metastasis in pancreatic cancer and potential therapeutic targets.

Abstract A45: Loss of Adar1 in pancreatic acinar cells leads to cell apoptosis and inflammation

While genetic mutations have been shown to drive pancreatic ductal adenocarcinoma (PDAC), epigenomic alterations in cancer cells may also contribute to tumor initiation and progression. Adenosine-to-inosine (A-to-I) editing is the most common type of RNA editing in the cell and is mediated by the adenosine deaminase acting on RNA (ADAR) enzyme. ADAR has been shown to be upregulated in various tumor types, it improves tumor cell viability and loss of Adar1 in melanoma cells increases efficacy of checkpoint blockade therapy in vivo. However, its function in PDAC is currently not well understood. In order to investigate the role of Adar1 in PDAC we developed a mouse model with a conditional knockout of Adar1 in the pancreas using the pancreas specific ptf1a Cre. However, the CYA (ptf1a [cre/wt], Rosa26 [LSL-YFP/LSL-YFP], Adar [F/F]) mice are born runted compared to littermate controls and die preweaning. We find that a conditional loss of Adar1 in the pancreas induces acinar cell death and the pancreatic tissue degenerates over a period of fifteen days. Adar1 inhibits interferon (IFN) responses that are activated by cellular double-stranded RNA (dsRNA) sensors through mitochondrial antiviral signaling protein (Mavs). To rescue the apoptotic and inflammatory phenotype of the CYA mice, we developed a CYAM mouse (ptf1a [cre/wt], Rosa26 [LSL-YFP/LSL-YFP], Adar [F/F], Mavs [-/-]). We find that these mice develop normally and their pancreas is devoid of apoptotic cells. Furthermore, to understand the function of Adar1 in pancreas homeostasis of adult mice, we developed an inducible model wherein in adult CiYA (ptf1aCre-ERTM [cre/wt], Rosa26 [LSL-YFP/LSL-YFP], Adar [F/F]) Adar1 loss was induced with intraperitoneal tamoxifen injections. We find that loss of Adar1 in the CiYA adult pancreas induces cell death and inflammation and the mice decline rapidly. We tested expression of a panel of 5 ISGs (Mx1, Isg15, IfnB1, Ifit1, Ifit2) by RT-qPCR and show that there is an elevated expression of ISGs in the pancreas of CiYA mice compared to WT controls. In conclusion, we show that pancreatic acinar cells are extremely sensitive to Adar1 loss both during developmental stages and in adult mice. Current in vivo models to study the function of Adar1 in development and cancer are limited by the lethal phenotype caused by upregulation of interferon stimulated genes (ISGs) and cell death in tissues where Adar1 is knocked out. Our work establishes a mouse model wherein pancreas-specific role of Adar1 in development and cancer can be studied without activation of Mavs-mediated inflammation. We are currently exploring how the CYAM mouse model can be utilized to advance our understanding of Adar1’s role in pancreas development and cancer.

Citation Format: Dhwani N. Rupani, Robert W. Cowan, Andrew D. Rhim. Loss of Adar1 in pancreatic acinar cells leads to cell apoptosis and inflammation [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A45.

ATDC is required for the initiation of KRAS-induced pancreatic tumorigenesis

Pancreatic adenocarcinoma (PDA) is an aggressive disease driven by oncogenic KRAS and characterized by late diagnosis and therapeutic resistance. Here we show that deletion of the ataxia-telangiectasia group D-complementing (Atdc) gene, whose human homolog is up-regulated in the majority of pancreatic adenocarcinoma, completely prevents PDA development in the context of oncogenic KRAS. ATDC is required for KRAS-driven acinar-ductal metaplasia (ADM) and its progression to pancreatic intraepithelial neoplasia (PanIN). As a result, mice lacking ATDC are protected from developing PDA. Mechanistically, we show ATDC promotes ADM progression to PanIN through activation of β-catenin signaling and subsequent SOX9 up-regulation. These results provide new insight into PDA initiation and reveal ATDC as a potential target for preventing early tumor-initiating events.

Effects of exercise on circulating tumor cells among patients with resected stage I-III colon cancer

BACKGROUND

Physical activity is associated with a lower risk of disease recurrence among colon cancer patients. Circulating tumor cells (CTC) are prognostic of disease recurrence among stage I-III colon cancer patients. The pathways through which physical activity may alter disease outcomes are unknown, but may be mediated by changes in CTCs.

METHODS

Participants included 23 stage I-III colon cancer patients randomized into one of three groups: usual-care control, 150 min∙wk-1 of aerobic exercise (low-dose), and 300 min∙wk-1 of aerobic exercise (high-dose) for six months. CTCs from venous blood were quantified in a blinded fashion using an established microfluidic antibody-mediated capture device. Poisson regression models estimated the logarithmic counts of CTCs.

RESULTS

At baseline, 78% (18/23) of patients had ≥1 CTC. At baseline, older age (-0.12±0.06; P = 0.04), lymphovascular invasion (0.63±0.25; P = 0.012), moderate/poor histology (1.09±0.34; P = 0.001), body mass index (0.07±0.02; P = 0.001), visceral adipose tissue (0.08±0.04; P = 0.036), insulin (0.06±0.02; P = 0.011), sICAM-1 (0.04±0.02; P = 0.037), and sVCAM-1 (0.06±0.03; P = 0.045) were associated with CTCs. Over six months, significant decreases in CTCs were observed in the low-dose (-1.34±0.34; P<0.001) and high-dose (-1.18±0.40; P = 0.004) exercise groups, whereas no significant change was observed in the control group (-0.59±0.56; P = 0.292). Over six months, reductions in body mass index (-0.07±0.02; P = 0.007), insulin (-0.08±0.03; P = 0.014), and sICAM-1 (-0.07±0.03; P = 0.005) were associated with reductions in CTCs. The main limitations of this proof-of-concept study are the small sample size, heterogenous population, and per-protocol statistical analysis.

CONCLUSION

Exercise may reduce CTCs among stage I-III colon cancer patients. Changes in host factors correlated with changes in CTCs. Exercise may have a direct effect on CTCs and indirect effects through alterations in host factors. This hypothesis-generating observation derived from a small pilot study warrants further investigation and replication.

Regulation of Epithelial Plasticity Determines Metastatic Organotropism in Pancreatic Cancer

The regulation of metastatic organotropism in pancreatic ductal a denocarcinoma (PDAC) remains poorly understood. We demonstrate, using multiple mouse models, that liver and lung metastatic organotropism is dependent upon p120catenin (p120ctn)-mediated epithelial identity. Mono-allelic p120ctn loss accelerates Kras^G12D-driven pancreatic cancer formation and liver metastasis. Importantly, one p120ctn allele is sufficient for E-CADHERIN-mediated cell adhesion. By contrast, cells with bi-allelic p120ctn loss demonstrate marked lung organotropism; however, rescue with p120ctn isoform 1A restores liver metastasis. In a p120ctn-independent PDAC model, mosaic loss of E-CADHERIN expression reveals selective pressure for E-CADHERIN-positive liver metastasis and E-CADHERIN-negative lung metastasis. Furthermore, human PDAC and liver metastases support the premise that liver metastases exhibit predominantly epithelial characteristics. RNA-seq demonstrates differential induction of pathways associated with metastasis and epithelial-to-mesenchymal transition in p120ctn-deficient versus p120ctn-wild-type cells. Taken together, P120CTN and E-CADHERIN mediated epithelial plasticity is an addition to the conceptual framework underlying metastatic organotropism in pancreatic cancer.

Abstract 4751: APOBEC3A inhibits tumor immune response independent of deamination in a novel genetic model of pancreatic cancer

Introduction: Apolipoprotein B mRNA Editing enzyme, Catalytic polypeptide 3A (A3A) is a C to U cytidine deaminase, preferentially deaminating the lagging strand of double-stranded DNA at specific sequence motifs. A3A is overexpressed across multiple tumor types, and in pancreatic ductal adenocarcinoma (PDA), high expression is associated with significantly decreased survival in early stage patients. Large scale sequencing studies of various human tumors (TCGA and ICGC), including PDA, have implicated A3A as a potential driver of tumor mutagenesis. However, the biological relevance of the deamination function of A3A has not yet been shown. Here, we utilize a novel genetically engineered mouse model to show that A3A supports the development of aggressive PDA independent of mutagenic capabilities.

Methods: As opposed to humans, mice only contain one APOBEC3 isoform which has limited to no deaminating activity on genomic DNA. Thus, to dissect the function of A3A on PDA initiation and progression, we made mice with a germline knockin for the coding sequence for human A3A and bred to a well-established GEMM of PDA to yield LSL-KrasG12D; p53fl/+; Pdx1-Cre; RosaLSL-YFP; A3A+/- (KPCY;A3A) mice and compared to KPCY mice. We genotyped tumors from both cohorts using VarScan after exome capture sequencing. Tumor and immune cells were FACS sorted comparative RNAseq performed. The immune contexture of murine and 155 untreated and treated human PDAs was analyzed by performing 7-color multiplex staining and immune cell spatial interaction analysis.

Results: All KPCY;A3A (n=11) mice developed tumors and expired significantly faster compared to KPCY (n=18) controls (3.9 v. 7.0 mo; p&lt;0.01). One third of the KPCY; A3A mice developed macrometastatic disease compared to 3/12 in the KPCY control. Whole exome sequencing of tumors revealed no significant difference in the number of point mutations or neoantigen load between KPCY;A3A and KPCY tumors. However, histologically, KPCY;A3A tumors contained significantly more desmoplasia and altered immune cell infiltrates. Specifically, comparative RNAseq and IHC analyses revealed dramatic differences in the number and distribution of various T-cell and B-cell subsets in KPCY;A3A mice. Moreover, A3A expression led to abrogation of CD8+ T cell activation and proliferation. Concomitantly, a panel of immune checkpoint-related genes were upregulated in A3A high expressing tumors and cell lines compared to non-A3A expressing controls. This was confirmed in a panel of resected human PDA.

Conclusions: Counter to our hypothesis, A3A supports the initiation and growth of PDA in vivo through effects independent of deamination or mutagenesis of cancer cell genomes but rather indirectly through suppression of the tumor immune response. Future studies will address the precise mechanisms underlying A3A-mediated tumor immune evasion.

Citation Format: Sonja Woermann, Robert Cowan, Susan M. Ross, Andrew D. Rhim. APOBEC3A inhibits tumor immune response independent of deamination in a novel genetic model of pancreatic cancer [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 4751.

Loss of Pten and Activation of Kras Synergistically Induce Formation of Intraductal Papillary Mucinous Neoplasia From Pancreatic Ductal Cells in Mice

BACKGROUND & AIMS

Intraductal papillary mucinous neoplasias (IPMNs) are precancerous cystic lesions that can develop into pancreatic ductal adenocarcinomas (PDACs). These large macroscopic lesions are frequently detected during medical imaging, but it is unclear how they form or progress to PDAC. We aimed to identify cells that form IPMNs and mutations that promote IPMN development and progression.

METHODS

We generated mice with disruption of Pten specifically in ductal cells (Sox9CreER^T2;Pten^flox/flox;R26R^YFP or Pten^{ΔDuct/ΔDuct} mice) and used Pten^ΔDuct/+ and Pten^+/+ mice as controls. We also generated Kras^G12D;Pten^{ΔDuct/ΔDuct} and Kras^G12D;Pten^ΔDuct/+ mice. Pancreata were collected when mice were 28 weeks to 14.5 months old and analyzed by histology, immunohistochemistry, and electron microscopy. We performed multiplexed droplet digital polymerase chain reaction to detect spontaneous Kras mutations in Pten^{ΔDuct/ΔDuct} mice and study the effects of Ras pathway activation on initiation and progression of IPMNs. We obtained 2 pancreatic sections from a patient with an invasive pancreatobiliary IPMN and analyzed the regions with and without the invasive IPMN (control tissue) by immunohistochemistry.

RESULTS

Mice with ductal cell-specific disruption of Pten but not control mice developed sporadic, macroscopic, intraductal papillary lesions with histologic and molecular features of human IPMNs. Pten^{ΔDuct/ΔDuct} mice developed IPMNs of several subtypes. In Pten^{ΔDuct/ΔDuct} mice, 31.5% of IPMNs became invasive; invasion was associated with spontaneous mutations in Kras. Kras^G12D;Pten^{ΔDuct/ΔDuct} mice all developed invasive IPMNs within 1 month. In Kras^G12D;Pten^ΔDuct/+ mice, 70% developed IPMN, predominately of the pancreatobiliary subtype, and 63.3% developed PDAC. In all models, IPMNs and PDAC expressed the duct-specific lineage tracing marker yellow fluorescent protein. In immunohistochemical analyses, we found that the invasive human pancreatobiliary IPMN tissue had lower levels of PTEN and increased levels of phosphorylated (activated) ERK compared with healthy pancreatic tissue.

CONCLUSIONS

In analyses of mice with ductal cell-specific disruption of Pten, with or without activated Kras, we found evidence for a ductal cell origin of IPMNs. We also showed that PTEN loss and activated Kras have synergistic effects in promoting development of IPMN and progression to PDAC.

Dose-response Effects of Aerobic Exercise Among Colon Cancer Survivors: A Randomized Phase II Trial

BACKGROUND

Observational studies suggest that higher volumes of physical activity are associated with a lower risk of disease recurrence among survivors of colon cancer. However, the feasibility and safety of prescribing higher volumes of physical activity to survivors of colon cancer are unknown. Furthermore, the pathways through which exercise may reduce disease recurrence are unknown.

PATIENTS AND METHODS

Survivors of stage I to III colon cancer were randomized to usual-care control, 150 minutes per week of aerobic exercise (low-dose), or 300 minutes per week of aerobic exercise (high-dose). Changes in soluble intercellular adhesion molecule-1 and vascular adhesion molecule-1 prognostic biomarkers were examined.

RESULTS

From January 2015 to February 2016, 39 patients were enrolled (n = 13 usual-care control; n = 14 low-dose; n = 12 high-dose), and 38 participants completed the study (97% follow-up). Over 6 months, the low-dose group completed 142 minutes per week (92.8% adherence), and the high-dose group completed 247 minutes per week (89.0% adherence) of exercise. Compared with the control group, changes in soluble intercellular adhesion molecule-1 were -134.9 ng/mL (95% confidence interval, -238.1 to -31.6 ng/mL) in the low-dose group and -114.8 ng/mL (95% confidence interval, -222.5 to -7.1 ng/mL) in the high-dose group (linear Ptrend = .023; nonlinear Ptrend = .044). No changes were observed for soluable vascular adhesion molecule-1 (linear Ptrend = .791; nonlinear Ptrend = .604). Non-serious adverse events occurred at similar rates among randomized groups. No serious adverse events occurred.

CONCLUSION

Higher volumes of moderate-intensity aerobic exercise, up to 300 minutes per week, are feasible, safe, and elicit favorable changes in prognostic biomarkers among patients recently treated for stage I to III colon cancer. These data can be used to guide clinical recommendations for patients, and inform future trials.

A randomized dose-response trial of aerobic exercise and health-related quality of life in colon cancer survivors

OBJECTIVE

To examine the dose-response effects of aerobic exercise on health-related quality of life (HRQoL) among colon cancer survivors.

METHODS

Thirty-nine stage I to III colon cancer survivors were randomized to 1 of 3 groups: usual-care control, 150 min·wk^-1 of aerobic exercise (low-dose) and 300 min·wk^-1 of aerobic exercise (high-dose) for 6 months. HRQoL outcomes included the Short Form (SF)-36 physical and mental component summary, Functional Assessment of Cancer Therapy-Colorectal, Pittsburgh Sleep Quality Index, Fear of Cancer Recurrence Inventory, Fatigue Symptom Inventory, and North Central Cancer Treatment Group bowel function questionnaire, assessed at baseline and post intervention. The primary hypothesis was that exercise would improve HRQoL outcomes in a dose-response fashion, such that high-dose aerobic exercise would yield the largest improvements in HRQoL outcomes.

RESULTS

Over 6 months, the low-dose group completed 141 ± 10 min·wk^-1 of aerobic exercise, and the high-dose group completed 247 ± 11 min·wk^-1 of aerobic exercise. Over 6 months, exercise improved the physical component summary score of the SF-36 (P_trend  = 0.002), the Functional Assessment of Cancer Therapy-Colorectal (P_trend  = 0.025), the Pittsburgh Sleep Quality Index (P_trend  = 0.049), and the Fatigue Symptom Inventory (P_trend  = 0.045) in a dose-response fashion. Between-group standardized mean difference effects sizes for the above-described findings were small to moderate in magnitude (0.35-0.75). No dose-response effects were observed for the mental component summary score of the SF-36, the Fear of Cancer Recurrence Inventory, or bowel function.

CONCLUSION

Higher doses of aerobic exercise, up to 300 min·wk^-1 , improve multiple HRQoL outcomes among stage I to III colon cancer survivors. These findings provide evidence that aerobic exercise may provide multiple health benefits for colon cancer survivors.

Dose-response effects of exercise on insulin among colon cancer survivors

Physical activity is associated with a lower risk of disease recurrence among colon cancer survivors. The pathways through which physical activity may alter disease outcomes are unknown, but may include changes in metabolic growth factors, such as insulin. Between January 2015 and August 2015, 39 stage I-III colon cancer survivors were randomized to one of the three groups: usual care control, 150 min/week of aerobic exercise (low-dose) and 300 min/week of aerobic exercise (high-dose) for six months. The pre-specified key metabolic growth factor outcome was fasting insulin. Insulin resistance was quantified using the homeostatic model assessment. Mean age was 56.5 ± 10.0 years, 51% had stage III disease, 72% were treated with chemotherapy and the mean time since finishing treatment was 10.9 ± 6.1 months. Over six months, the low-dose group completed 141.5 ± 9.9 min/week of aerobic exercise, and the high-dose group completed 247.2 ± 10.7 min/week of aerobic exercise. Fasting insulin concentrations decreased 7.4 ± 9.4 pmol/L in the control group, 28.0 ± 8.3 pmol/L in the low-dose group and 20.7 ± 9.3 pmol/L in the high-dose group (nonlinear P_trend = 0.042). Insulin resistance decreased 0.11 ± 0.20 in the control group, 0.63 ± 0.17 in the low-dose group and 0.43 ± 0.19 in the high-dose group (nonlinear P_trend = 0.012). Aerobic exercise reduces insulin concentrations and insulin resistance among patients with stage I-III colon cancer. Prescribing 150 min/week of aerobic exercise may be sufficient for reducing insulin concentrations and insulin resistance, which may partially mediate the relationship between physical activity and colon cancer prognosis.

MYC regulates ductal-neuroendocrine lineage plasticity in pancreatic ductal adenocarcinoma associated with poor outcome and chemoresistance

Intratumoral phenotypic heterogeneity has been described in many tumor types, where it can contribute to drug resistance and disease recurrence. We analyzed ductal and neuroendocrine markers in pancreatic ductal adenocarcinoma, revealing heterogeneous expression of the neuroendocrine marker Synaptophysin within ductal lesions. Higher percentages of Cytokeratin-Synaptophysin dual positive tumor cells correlate with shortened disease-free survival. We observe similar lineage marker heterogeneity in mouse models of pancreatic ductal adenocarcinoma, where lineage tracing indicates that Cytokeratin-Synaptophysin dual positive cells arise from the exocrine compartment. Mechanistically, MYC binding is enriched at neuroendocrine genes in mouse tumor cells and loss of MYC reduces ductal-neuroendocrine lineage heterogeneity, while deregulated MYC expression in KRAS mutant mice increases this phenotype. Neuroendocrine marker expression is associated with chemoresistance and reducing MYC levels decreases gemcitabine-induced neuroendocrine marker expression and increases chemosensitivity. Altogether, we demonstrate that MYC facilitates ductal-neuroendocrine lineage plasticity in pancreatic ductal adenocarcinoma, contributing to poor survival and chemoresistance.

Ultrasensitive mutation detection identifies rare residual cells causing acute myelogenous leukemia relapse

Acute myelogenous leukemia (AML) frequently relapses after complete remission (CR), necessitating improved detection and phenotypic characterization of treatment-resistant residual disease. In this work, we have optimized droplet digital PCR to broadly measure mutated alleles of recurrently mutated genes in CR marrows of AML patients at levels as low as 0.002% variant allele frequency. Most gene mutations persisted in CR, albeit at highly variable and gene-dependent levels. The majority of AML cases demonstrated residual aberrant oligoclonal hematopoiesis. Importantly, we detected very rare cells (as few as 1 in 15,000) that were genomically similar to the dominant blast populations at diagnosis and were fully clonally represented at relapse, identifying these rare cells as one common source of AML relapse. Clinically, the mutant allele burden was associated with overall survival in AML, and our findings narrow the repertoire of gene mutations useful in minimal residual disease-based prognostication in AML. Overall, this work delineates rare cell populations that cause AML relapse, with direct implications for AML research directions and strategies to improve AML therapies and outcome.

Abstract 1035: Direct evidence for a pro-tumor role of APOBEC3A in cancer initiation and progression in vivo: enhanced mutagenesis and immune suppression in a novel humanized autochthonous model of pancreatic cancer

Introduction: The apolipoprotein B editing complex 3 (APOBEC3) family of enzymes are possible candidates for inducing mutations across a number of tumors, including pancreatic ductal adenocarcinoma (PDA; Alexandrov et al, 2013; Roberts et al, 2013). APOBEC3A (hA3A) is one of eight identified isoforms in humans and known to deaminate cytidines in genomic ssDNA at a specific sequence motif. Large scale sequencing studies demonstrate significant enrichment of this signature in a number of human cancers. Furthermore, hA3A is overexpressed in a variety of solid tumors, including PDA. Taken together, these data suggest that hA3A may catalyze point mutations in cancer and drive cancer initiation and progression. However, direct evidence to support this hypothesis in vivo are lacking. Here, we utilize a novel genetically engineered mouse model to determine the precise effects of hA3A on PDA initiation and progression.

Methods: As opposed to humans, mice only contain one APOBEC3 isoform which has limited to no deaminating activity on genomic DNA. Thus, to delineate the function of hA3A on PDA initiation and progression, we exchanged the murine APOBEC3 protein coding sequence for hA3A, leaving the murine 5’ and 3’ endogenous regulatory sequences intact to ensure physiologic expression (murine APOBEC3 and hA3A reflect similar expression kinetics during PDA development). We then bred these mice to a well-established GEMM of PC (Rhim et al., Cell 2012) to yield LSL-KrasG12D; p53fl/+; Pdx1-Cre; RosaLSL-YFP; hA3A+/- (KPCY;hA3A) mice. We compared these mice to KPCY mice. We genotyped tumors from both cohorts with Ilumina exome capture sequencing with variant calling by a custom caller based on VarScan.

Results: All KPCY; hA3A (n=11) mice developed tumors and expired significantly faster compared to KPCY (n=18) controls (3.9 v. 7.0 mo; p&lt;0.01). One third of the KPCY; hA3A mice developed macrometastatic disease compared to 3/12 in the KPCY control. Interestingly, KPCY; hA3A tumors contained dramatic desmoplasia, far surpassing the KPCY controls. Moreover, comparative RNAseq and histologic analyses revealed dramatic differences in the number and distribution of various T-cell and B-cell subsets. Finally, we found that KPCY; hA3A mice contained significantly more single nucleotide variants compared to KPCY controls (51.3 v. 8.4; p&lt;0.05).

Conclusions: These data show for the first time that physiologic expression of hA3A in vivo leads to increased mutations, altered immune response and more aggressive cancer. Future studies will address the precise mechanisms by which hA3A catalyzes tumorigenesis using our novel gain of function model. Furthermore, our data suggest that incorporating our humanized A3A germline allele may provide a more genomically recapitulative model of cancer.

Citation Format: Sonja Woermann, Robert Cowan, Susan M. Ross, Andrew D. Rhim. Direct evidence for a pro-tumor role of APOBEC3A in cancer initiation and progression in vivo: enhanced mutagenesis and immune suppression in a novel humanized autochthonous model of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1035. doi:10.1158/1538-7445.AM2017-1035

A Clinical Prediction Model to Assess Risk for Pancreatic Cancer Among Patients With New-Onset Diabetes

BACKGROUND & AIMS

Approximately 50% of all patients with pancreatic ductal adenocarcinoma (PDA) develop diabetes mellitus before their cancer diagnosis. Screening individuals with new-onset diabetes might allow earlier diagnosis of PDA. We sought to develop and validate a PDA risk prediction model to identify high-risk individuals among those with new-onset diabetes.

METHODS

We conducted a retrospective cohort study in a population representative database from the United Kingdom. Individuals with incident diabetes after the age of 35 years and 3 or more years of follow-up after diagnosis of diabetes were eligible for inclusion. Candidate predictors consisted of epidemiologic and clinical characteristics available at the time of diabetes diagnosis. Variables with P values <.25 in the univariable analyses were evaluated using backward stepwise approach. Model discrimination was assessed using receiver operating characteristic curve analysis. Calibration was evaluated using the Hosmer-Lemeshow test. Results were internally validated using a bootstrapping procedure.

RESULTS

We analyzed data from 109,385 patients with new-onset diabetes. Among them, 390 (0.4%) were diagnosed with PDA within 3 years. The final model (area under the curve, 0.82; 95% confidence interval, 0.75-0.89) included age, body mass index, change in body mass index, smoking, use of proton pump inhibitors, and anti-diabetic medications, as well as levels of hemoglobin A1C, cholesterol, hemoglobin, creatinine, and alkaline phosphatase. Bootstrapping validation showed negligible optimism. If the predicted risk threshold for definitive PDA screening was set at 1% over 3 years, only 6.19% of the new-onset diabetes population would undergo definitive screening, which would identify patients with PDA with 44.7% sensitivity, 94.0% specificity, and a positive predictive value of 2.6%.

CONCLUSIONS

We developed a risk model based on widely available clinical parameters to help identify patients with new-onset diabetes who might benefit from PDA screening.

Myeloid cells are required for PD-1/PD-L1 checkpoint activation and the establishment of an immunosuppressive environment in pancreatic cancer

BACKGROUND

Pancreatic cancer is characterised by the accumulation of a fibro-inflammatory stroma. Within this stromal reaction, myeloid cells are a predominant population. Distinct myeloid subsets have been correlated with tumour promotion and unmasking of anti-tumour immunity.

OBJECTIVE

The goal of this study was to determine the effect of myeloid cell depletion on the onset and progression of pancreatic cancer and to understand the relationship between myeloid cells and T cell-mediated immunity within the pancreatic cancer microenvironment.

METHODS

Primary mouse pancreatic cancer cells were transplanted into CD11b-diphtheria toxin receptor (DTR) mice. Alternatively, the iKras* mouse model of pancreatic cancer was crossed into CD11b-DTR mice. CD11b+ cells (mostly myeloid cell population) were depleted by diphtheria toxin treatment during tumour initiation or in established tumours.

RESULTS

Depletion of myeloid cells prevented KrasG12D-driven pancreatic cancer initiation. In pre-established tumours, myeloid cell depletion arrested tumour growth and in some cases, induced tumour regressions that were dependent on CD8+ T cells. We found that myeloid cells inhibited CD8+ T-cell anti-tumour activity by inducing the expression of programmed cell death-ligand 1 (PD-L1) in tumour cells in an epidermal growth factor receptor (EGFR)/mitogen-activated protein kinases (MAPK)-dependent manner.

CONCLUSION

Our results show that myeloid cells support immune evasion in pancreatic cancer through EGFR/MAPK-dependent regulation of PD-L1 expression on tumour cells. Derailing this crosstalk between myeloid cells and tumour cells is sufficient to restore anti-tumour immunity mediated by CD8+ T cells, a finding with implications for the design of immune therapies for pancreatic cancer.

Abstract IA21: Myeloid cells are required for PD-1/PD-L1 checkpoint activation and the establishment of an immune-suppressive environment in pancreatic cancer

Pancreatic cancer is characterized by the accumulation of a fibro-inflammatory stroma. Accumulation of the stroma is already evident surrounding Pancreatic Intraepithelial Neoplasias (PanINs), common precursor lesions to pancreatic cancer (Hezel et al., 2006). The stroma is abundantly infiltrated by immune cells, and myeloid cells are a predominant population (Clark et al., 2007). Different myeloid subsets have been correlated with tumor promotion and unmasking of anti-tumor immunity (Liou et al., 2015; Long et al., 2016; Mitchem et al., 2013; Stromnes et al., 2014). Both PanINs and pancreatic cancer and commonly associated with oncogenic mutations in the Kras gene (Biankin et al., 2012; Jones et al., 2010; Kanda et al., 2012). Expression of oncogenic Kras in the pancreas of genetically engineered mice recapitulates the PanIN to pancreatic cancer progression, including the accumulation of fibrotic stroma (Hingorani et al., 2003). We have described a mouse model that allows inducible and reversible expression of oncogenic Kras in the pancreas, the iKras* mouse. Inactivation of oncogenic Kras during the PanIN stage or in cancer leads to regression of the epithelial lesions as well as to remodeling of the stroma, indicating that the accumulation of the stroma is regulated by signals derived from oncogenic Kras-expressing epithelial cells (Collins et al., 2012a).

In the current study, we have investigated the interaction between epithelial cells and myeloid cells that infiltrate the pancreas. For this purpose, we have used a combination of genetically engineered mice (iKras*p53* mice (Collins et al., 2012b)) and transplantation approaches into CD11b-DTR mice (Duffield et al., 2005), that allow depletion of myeloid cells upon administration of Diphtheria Toxin. Our results show that the infiltration and polarization of macrophages in the pancreas depends on signals derived from oncogenic Kras-expressing epithelial cells, either directly or through activation of a pro-inflammatory subset of stromal fibroblasts. Conversely, myeloid cells infiltration is required for the progression of PanINs and pancreatic cancer. Depletion of myeloid cells prevented KrasG12D driven pancreatic cancer initiation. In pre-established tumors, myeloid cell depletion resulted in arrest of growth or tumor regression. We observed that tumor progression was dependent on myeloid cell-mediated blockade of CD8+ T cell anti-tumor activity. Furthermore, myeloid cells regulate the expression of the Programmed death-ligand 1 (PD-L1) in tumor cells in an EGFR/MAPK dependent manner.

Our results show that myeloid cells regulate a complex network of signals that ensure immune suppression within the pancreatic cancer microenvironment. Moreover, we show that depletion of the myeloid cell population restores anti-tumor immunity mediated by CD8+ T cells, a finding with implications for the design of immune therapies for pancreatic cancer.

References:

Biankin, A. V., Waddell, N., Kassahn, K. S., Gingras, M. C., Muthuswamy, L. B., Johns, A. L., Miller, D. K., Wilson, P. J., Patch, A. M., Wu, J., et al. (2012). Pancreatic cancer genomes reveal aberrations in axon guidance pathway genes. Nature 491, 399-405.

Clark, C. E., Hingorani, S. R., Mick, R., Combs, C., Tuveson, D. A., and Vonderheide, R. H. (2007). Dynamics of the immune reaction to pancreatic cancer from inception to invasion. Cancer Res 67, 9518-9527.

Collins, M. A., Bednar, F., Zhang, Y., Brisset, J. C., Galban, S., Galban, C. J., Rakshit, S., Flannagan, K. S., Adsay, N. V., and Pasca di Magliano, M. (2012a). Oncogenic Kras is required for both the initiation and maintenance of pancreatic cancer in mice. J Clin Invest 122, 639-653.

Collins, M. A., Brisset, J. C., Zhang, Y., Bednar, F., Pierre, J., Heist, K. A., Galban, C. J., Galban, S., and di Magliano, M. P. (2012b). Metastatic pancreatic cancer is dependent on oncogenic Kras in mice. PLoS One 7, e49707.

Duffield, J. S., Forbes, S. J., Constandinou, C. M., Clay, S., Partolina, M., Vuthoori, S., Wu, S., Lang, R., and Iredale, J. P. (2005). Selective depletion of macrophages reveals distinct, opposing roles during liver injury and repair. J Clin Invest 115, 56-65.

Hezel, A. F., Kimmelman, A. C., Stanger, B. Z., Bardeesy, N., and Depinho, R. A. (2006). Genetics and biology of pancreatic ductal adenocarcinoma. Genes Dev 20, 1218-1249.

Hingorani, S. R., Petricoin, E. F., Maitra, A., Rajapakse, V., King, C., Jacobetz, M. A., Ross, S., Conrads, T. P., Veenstra, T. D., Hitt, B. A., et al. (2003). Preinvasive and invasive ductal pancreatic cancer and its early detection in the mouse. Cancer Cell 4, 437-450.

Jones, S., Wang, T. L., Shih Ie, M., Mao, T. L., Nakayama, K., Roden, R., Glas, R., Slamon, D., Diaz, L. A., Jr., Vogelstein, B., et al. (2010). Frequent mutations of chromatin remodeling gene ARID1A in ovarian clear cell carcinoma. Science 330, 228-231.

Kanda, M., Matthaei, H., Wu, J., Hong, S. M., Yu, J., Borges, M., Hruban, R. H., Maitra, A., Kinzler, K., Vogelstein, B., and Goggins, M. (2012). Presence of somatic mutations in most early-stage pancreatic intraepithelial neoplasia. Gastroenterology 142, 730-733 e739.

Liou, G. Y., Doppler, H., Necela, B., Edenfield, B., Zhang, L., Dawson, D. W., and Storz, P. (2015). Mutant KRAS-induced expression of ICAM-1 in pancreatic acinar cells causes attraction of macrophages to expedite the formation of precancerous lesions. Cancer Discov 5, 52-63.

Long, K. B., Gladney, W. L., Tooker, G. M., Graham, K., Fraietta, J. A., and Beatty, G. L. (2016). IFNgamma and CCL2 Cooperate to Redirect Tumor-Infiltrating Monocytes to Degrade Fibrosis and Enhance Chemotherapy Efficacy in Pancreatic Carcinoma. Cancer Discov.

Mitchem, J. B., Brennan, D. J., Knolhoff, B. L., Belt, B. A., Zhu, Y., Sanford, D. E., Belaygorod, L., Carpenter, D., Collins, L., Piwnica-Worms, D., et al. (2013). Targeting tumor-infiltrating macrophages decreases tumor-initiating cells, relieves immunosuppression, and improves chemotherapeutic responses. Cancer Res 73, 1128-1141.

Stromnes, I. M., Brockenbrough, J. S., Izeradjene, K., Carlson, M. A., Cuevas, C., Simmons, R. M., Greenberg, P. D., and Hingorani, S. R. (2014). Targeted depletion of an MDSC subset unmasks pancreatic ductal adenocarcinoma to adaptive immunity. Gut.

Citation Format: Yaqing Zhang, Esha Mathew, Ashley Velez-Delgado, Kristen B. Long, Dongjun Li, Flor M. Mendez, Kevin Flannagan, Andrew D. Rhim, Diane M. Simeone, Gregory L. Beatty, Marina Pasca di Magliano.{Authors}. Myeloid cells are required for PD-1/PD-L1 checkpoint activation and the establishment of an immune-suppressive environment in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr IA21.

Abstract A62: ATDC is required for KRAS-induced pancreatic tumorigenesis

We have recently demonstrated that ATDC, a novel oncogenic protein, serves as an invasive switch in pancreatic cancer (PDA) by activation of beta–catenin signaling and upregulation of CD44, resulting in EMT and an invasive phenotype during PanIN progression. To further explore the tumorigenic function of ATDC, we generated a floxed ATDC mouse (A F/F) to evaluate the impact of conditional knockout of ATDC on oncogenic Kras-induced PDA initiation and progression. Pancreas-specific ATDC knockout did not cause any histologic abnormalities in pancreas, up to 1 year of age (n=8). Through a series of crosses of LSL-KrasG12D (K), p53F/+ (P), RosaYFP (Y), Pdx1-Cre (C) and AF/F mice, KrasG12D; CY (KCY); KrasG12D; p53+/-; CY (KPCY), KCYA-/- KPCYA-/- mice were generated. Knockout of ATDC in KPCY mice completely prevented the development of ADM and PanIN lesions in 3 month old mice (n= 8), and resulted in the formation of very rare ADM and PanIN1 lesions (2 out of 8) in KPCYA-/- mice at 12 months of age (n=8). In contrast, all KPCY mice developed extensive PanIN (low and high grade) at 3 months of age (n= 8), with the subsequent development of invasive and metastatic cancer at frequencies similar to that reported in the literature. To determine the possible mechanisms by which ATDC inhibited KrasG12D-induced acinar-ductal metaplasia (ADM), we isolated acini from 1.5 month old KCY and KCYA-/- pancreata and performed in vitro 3D cultures and ADM assays. ADM lesions readily formed in 3-D cultures of acini from KCY mice at 5 days, and this was significantly inhibited in acini isolated from KCYA-/- mice (duct-like structures: 95.1±3.5% to 28.0±2.2%*, KCY vs KCYA-/-, n=3, *p&lt;0.05). Expression of ATDC specific shRNA in acini from KCY mice also effectively decreased ADM formation in 3D culture, an effect that was completely reversed by ATDC overexpression using an ATDC-shRNA-resistant expression vector. To further evaluate the role of ATDC in ADM and PanIN formation, we induced caerulein-mediated acute pancreatitis in 1.5 month old WT, CYA-/-, KCY, KCYA-/- mice and analyzed pancreatic tissue 1 and 7 days following cerulein treatment. 1 day post-caerulein treatment, KCY, KCYA-/-, CYA-/- and WT mice exhibited widespread ADM, which was replaced by normal acini by 7 days in WT, CYA-/- and KCYA-/- mice. However, in KCY mice 7 days post-cerulein treatment, extensive ADM and PanIN lesions were present, suggesting that ATDC is required for oncogenic KRAS to promote ADM and PanIN formation. Conclusions: Knockout of ATDC markedly reduces KrasG12D-induced ADM and PanIN formation, highlighting a key biologic function for ATDC in this process and its role in driving progression of KRAS-induced tumorigenesis in the pancreas.

Citation Format: Lidong Wang, Huibin Yang, Ethan V. Abel, Phillip L. Palmbos, Christophe Halbrook, Kenneth Takeuchi, Jiaqi Shi, Yaqing Zhang, Sumithra Urs, Meghna Waghray, Marina Pasca di Magliano, Andrew D. Rhim, Howard C. Crawford, Diane M. Simeone.{Authors}. ATDC is required for KRAS-induced pancreatic tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A62.

Can Stopping Nerves, Stop Cancer?

The nervous system is viewed as a tissue affected by cancer and as a conduit for the transmission of cancer pain and perineural invasion. Here, we review recent studies that indicate a more direct role. Several studies have shown that reducing stress or suppressing sympathetic drive correlates with improved outcomes and prolonged survival. Recent studies using animal models of visceral and somatic cancer further support a role for the nervous system in cancer progression. Specifically, nerve ablation had a profound impact on disease progression, including delayed development of precancerous lesions, and decreased tumor growth and metastasis. In this review, we summarize new evidence and discuss how future studies may address the role of neural signaling in the modulation of tumorigenesis.

Abstract A096: Myeloid cells are required for pancreatic carcinogenesis and PD-1/PD-L1 checkpoint activation

Myeloid cells, including both macrophages and immature myeloid cells/myeloid derived suppressor cells (MDSCs), accumulate during the progression of pancreatic cancer. The goal of this study was to determine the effect of myeloid cell depletion on the onset and progression of pancreatic cancer, and to understand the relationship between myeloid cells and T cell-mediated immunity within the pancreatic cancer microenvironment.

Primary mouse pancreatic cancer cells were transplanted into CD11b-DTR mice. Alternatively, the iKras* mouse model of pancreatic cancer was crossed into CD11b-DTR mice. CD11b+ cells were depleted by Diphtheria Toxin treatment during tumor initiation or in established tumors. Depletion of myeloid cells prevented KrasG12D driven pancreatic cancer initiation.

Myeloid cells are required for sustained MAPK signaling in pancreatic epithelial cells during the onset of carcinogenesis, notwithstanding the expression of oncogenic Kras. In pre-established tumors, myeloid cell depletion arrested tumor growth and in some cases, induced tumor regressions that were dependent on CD8+ T cells. We found that myeloid cells inhibited CD8+ T cell anti-tumor activity by inducing the expression of Programmed cell death-ligand 1 (PD-L1) in tumor cells in an EGFR/MAPK dependent manner. Treatment with MEK inhibitors lowers the intratumoral expression of PD-L1 and renders the tumor susceptible to PD-1 blockade.

Our results show that myeloid cells support immune evasion in pancreatic cancer through EGFR/MAPK dependent regulation of PD-L1 expression on tumor cells. Derailing this cross-talk between myeloid cells and tumor cells is sufficient to restore anti-tumor immunity mediated by CD8+ T cells, a finding with implications for the design of immune therapies for pancreatic cancer.

Note: This abstract was not presented at the conference.

Citation Format: Yaqing Zhang, Ashley Velez-Delgado, Esha Mathew, Dongjun Li, Flor M. Mendez, Kevin Flannagan, Andrew D. Rhim, Diane M. Simeone, Gregory L. Beatty, Marina Pasca di Magliano. Myeloid cells are required for pancreatic carcinogenesis and PD-1/PD-L1 checkpoint activation [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A096.

Adipocytes promote pancreatic cancer cell proliferation via glutamine transfer

Adipocytes promote progression of multiple cancers, but their role in pancreatic intraepithelial neoplasia (PanIN) and ductal adenocarcinoma (PDAC) is poorly defined. Nutrient transfer is a mechanism underlying stromal cell-cancer crosstalk. We studied the role of adipocytes in regulating in vitro PanIN and PDAC cell proliferation with a focus on glutamine metabolism. Murine 3T3L1 adipocytes were used to model adipocytes. Cell lines derived from PKCY mice were used to model PanIN and PDAC. Co-culture was used to study the effect of adipocytes on PanIN and PDAC cell proliferation in response to manipulation of glutamine metabolism. Glutamine secretion was measured with a bioanalyzer. Western blotting was used to study the effect of PanIN and PDAC cells on expression of glutamine-related enzymes in adipocytes. Adipocytes promote proliferation of PanIN and PDAC cells, an effect that was amplified in nutrient-poor conditions. Adipocytes secrete glutamine and rescue PanIN and PDAC cell proliferation in the absence of glutamine, an effect that was glutamine synthetase-dependent and involved PDAC cell-induced down-regulation of glutaminase expression in adipocytes. These findings suggest glutamine transfer as a potential mechanism underlying adipocyte-induced PanIN and PDAC cell proliferation.

Ablation of sensory neurons in a genetic model of pancreatic ductal adenocarcinoma slows initiation and progression of cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an exuberant inflammatory desmoplastic response. The PDAC microenvironment is complex, containing both pro- and antitumorigenic elements, and remains to be fully characterized. Here, we show that sensory neurons, an under-studied cohort of the pancreas tumor stroma, play a significant role in the initiation and progression of the early stages of PDAC. Using a well-established autochthonous model of PDAC (PKC), we show that inflammation and neuronal damage in the peripheral and central nervous system (CNS) occurs as early as the pancreatic intraepithelial neoplasia (PanIN) 2 stage. Also at the PanIN2 stage, pancreas acinar-derived cells frequently invade along sensory neurons into the spinal cord and migrate caudally to the lower thoracic and upper lumbar regions. Sensory neuron ablation by neonatal capsaicin injection prevented perineural invasion (PNI), astrocyte activation, and neuronal damage, suggesting that sensory neurons convey inflammatory signals from Kras-induced pancreatic neoplasia to the CNS. Neuron ablation in PKC mice also significantly delayed PanIN formation and ultimately prolonged survival compared with vehicle-treated controls (median survival, 7.8 vs. 4.5 mo; P = 0.001). These data establish a reciprocal signaling loop between the pancreas and nervous system, including the CNS, that supports inflammation associated with oncogenic Kras-induced neoplasia. Thus, pancreatic sensory neurons comprise an important stromal cell population that supports the initiation and progression of PDAC and may represent a potential target for prevention in high-risk populations.

A randomized phase II dose-response exercise trial among colon cancer survivors: Purpose, study design, methods, and recruitment results

BACKGROUND

Observational studies indicate that higher volumes of physical activity are associated with improved disease outcomes among colon cancer survivors. The aim of this report is to describe the purpose, study design, methods, and recruitment results of the courage trial, a National Cancer Institute (NCI) sponsored, phase II, randomized, dose-response exercise trial among colon cancer survivors.

METHODS/RESULTS

The primary objective of the courage trial is to quantify the feasibility, safety, and physiologic effects of low-dose (150 min·week(-1)) and high-dose (300 min·week(-1)) moderate-intensity aerobic exercise compared to usual-care control group over six months. The exercise groups are provided with in-home treadmills and heart rate monitors. Between January and July 2015, 1433 letters were mailed using a population-based state cancer registry; 126 colon cancer survivors inquired about participation, and 39 were randomized onto the study protocol. Age was associated with inquiry about study participation (P<0.001) and randomization onto the study protocol (P<0.001). No other demographic, clinical, or geographic characteristics were associated with study inquiry or randomization. The final trial participant was randomized in August 2015. Six month endpoint data collection was completed in February 2016.

DISCUSSION

The recruitment of colon cancer survivors into an exercise trial is feasible. The findings from this trial will inform key design aspects for future phase 2 and phase 3 randomized controlled trials to examine the efficacy of exercise to improve clinical outcomes among colon cancer survivors.

Orthotopic Injection of Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma is an aggressive disease with a 5-yr survival rate of only 5%. The location of the pancreas in the abdomen, where it is obscured by other organs, makes it a difficult tissue to study and manipulate. This protocol describes in detail how to orthotopically inject cancer cells into the pancreas in mice. This technique is particularly useful when the cells must be manipulated in ways that cannot be modeled genetically.

Isolating Epithelial and Epithelial-to-Mesenchymal Transition Populations from Primary Tumors by Fluorescence-Activated Cell Sorting

Transgenic mice that express conditional reporters allow for the isolation of specific cell lineages. These cells can be further stratified by gene expression and collected by fluorescence-activated cell sorting (FACS) for further analysis. Using Cre-recombinase (Cre) technology we have generated a transgenic mouse line termed PKCY in which all pancreatic epithelial cells and therefore all pancreatic cancer cells are constitutively labeled with yellow fluorescent protein (YFP). We have used immunofluorescent staining for E-cadherin to divide the YFP(+) tumor population into epithelial cells (E-cadherin positive) and cells that have undergone an epithelial-to-mesenchymal transition (EMT; E-cadherin negative). This protocol describes how to prepare a tumor sample for FACS, with an emphasis on separating epithelial and EMT populations. These cells can then be used for a number of applications including, but not limited to, the generation of cell lines, gene-expression analysis by quantitative polymerase chain reaction (qPCR) or RNA sequencing, DNA sequencing, chromatin immunoprecipitation, and western blots.

Whole Genome Sequencing Defines the Genetic Heterogeneity of Familial Pancreatic Cancer

Pancreatic cancer is projected to become the second leading cause of cancer-related death in the United States by 2020. A familial aggregation of pancreatic cancer has been established, but the cause of this aggregation in most families is unknown. To determine the genetic basis of susceptibility in these families, we sequenced the germline genomes of 638 patients with familial pancreatic cancer and the tumor exomes of 39 familial pancreatic adenocarcinomas. Our analyses support the role of previously identified familial pancreatic cancer susceptibility genes such as BRCA2, CDKN2A, and ATM, and identify novel candidate genes harboring rare, deleterious germline variants for further characterization. We also show how somatic point mutations that occur during hematopoiesis can affect the interpretation of genome-wide studies of hereditary traits. Our observations have important implications for the etiology of pancreatic cancer and for the identification of susceptibility genes in other common cancer types.

SIGNIFICANCE

The genetic basis of disease susceptibility in the majority of patients with familial pancreatic cancer is unknown. We whole genome sequenced 638 patients with familial pancreatic cancer and demonstrate that the genetic underpinning of inherited pancreatic cancer is highly heterogeneous. This has significant implications for the management of patients with familial pancreatic cancer.

Abstract 1572: Sensitive and robust targeted sequencing of pancreatic precancer and tumors using microfluidic single-molecule enrichment

Pancreatic ductal adenocarcinoma (PDAC) arises from two precursor lesions, pancreatic intraepithelial neoplasias and pancreatic cysts, such as intraductal papillary mucinous neoplasias (IPMNs). Since cyst lesions are readily detected on cross sectional imaging, early diagnosis of IPMN-associated PDAC and intervention may be feasible. However, clinical guidelines dictating which IPMNs are high-risk and require surgical resection are suboptimal. Recently, the genomic signature of IPMN-associated carcinomas has been described opening the possibility for targeted genomic analysis. Previous groups have sought to achieve this using conventional methods. However, since IPMN tissue and cyst fluid are limited in quantity and contain inhibitors of PCR, we developed a novel microfluidics-based approach to achieve sensitive and specific targeted amplification and Illumina library construction.

We have optimized a novel method to enrich targeted genomic regions for next generation sequencing (NGS) platforms featuring microfluidic partitioning of the sample into uniform picoliter volume droplets containing single molecules of target DNA. All droplets contain all of the primers and PCR reagents, ensuring that every target molecule from the sample is amplified, and after endpoint PCR results in a highly uniform yield that facilitates efficient use of the NGS platform. In addition, the primers contain ‘Illumina tails’ that enable easy sample indexing and loading directly onto a MiSeq without additional library preparation.

Here we detail the successful customization and use of the ThunderBolts Cancer Panel, which targets 230 commonly mutated regions in 50 cancer associated genes, with additional primers for commonly mutated genes in PDAC. Addition of the 37 PDAC-relevant primer pairs to the commercially available core panel was very straightforward and resulted in sequencing metrics similar to those of the core panel alone (100% coverage at 100x depth, mean read depth of 2500). Cyst fluid from 30 patients with IPMN resected under Sendai criteria were analyzed. We describe the mutational signature of cyst fluid and relate the presence and quantity of mutations in KRAS, GNAS and PIK3CA to the presence of invasive carcinoma and high grade dysplasia on pathology. Finally, unbiased and high resolution sequencing was obtained using this protocol with as little as 8ng of input DNA.

Using picodroplet PCR technology we were able to achieve unprecedented sequencing performance on ultra-low sample inputs. Given the ease of use and customization of the panel, the same platform may be readily adapted to other applications in which samples are limited or are difficult to amplify. Future studies will utilize this platform for an expanded analysis of pancreatic cyst fluid with additional primers.

Citation Format: Angelina I. Londoño-Joshi, Erica Pratt, Robert W. Cowan, Michael L. Samuels, Steve Kotsopoulos, Jeff Olson, Francis Long, Michelle A. Anderson, Diane Simeone, Andrew D. Rhim. Sensitive and robust targeted sequencing of pancreatic precancer and tumors using microfluidic single-molecule enrichment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1572. doi:10.1158/1538-7445.AM2015-1572

Abstract A11: Ets transcription factor Etv5 regulates ductal morphogenesis and differentiation in association with Sox9 in vitro and increases susceptibility and delays recovery from pancreatitis in vivo

Introduction: The exocrine pancreas comprises a branched network of ducts that are connected to acini and lined by a monolayered epithelium that derives from the endoderm and is surrounded by mesenchyme. The formation and maturation of pancreatic ductal cells during branching morphogenesis is controlled by a complex hierarchy of transcription factors, which is not fully understood. The Ets-transcription factor Etv5 has been reported to play an important role during the development of organs that undergo branching morphogenesis such as mammary and salivary glands. We therefore aimed to characterize the functional role of Etv5 in pancreatic ductal development and differentiation.

Methods: Cells were isolated from wild-type mouse pancreata and lentiviral transduction was used to induce Etv5 overexpression. Cells were grown in 3D organotypic culture and analyzed with time lapsed microscopy for morphology and dynamics in the formation of duct-like cystic structures. Differentiation status of cells grown in 3D was analyzed by immunofluorescence-staining (IF) and qPCR. To asses the role of Etv5 in the normal mouse pancreas and its role in inflammation and regeneration in vivo, Pdx1cre;Etv5-/-; RosaYFP mice were generated and aged up to six months and subjected to a cerulein induced acute pancreatitis protocol.

Results: Normal pancreatic ductal cells grown in 3D-organotypic culture form spheroid cysts that resemble pancreatic ductal structures. Etv5 overexpression leads to early and exuberant formation of spheroid cysts within 2 days after seeding. Time-lapse microscopy demonstrated a significantly increased movement of cellular structures along the cyst as well as fusion of cysts into larger tubular structures. mRNA analysis of cysts harvested at day 7 displayed a strong upregulation of Sox9 and Foxa2, important regulators of ductal differentiation. Concurrently, E-cadherin was upregulated significantly whereas N-cadherin was downregulated indicating the terminal differentiation of these cells. IF-staining revealed co-localization of Etv5 and Sox9 in spheroid cysts of Etv5-overexpressing cells. Knockdown of Sox9 in Etv5-overexpressing cells with siRNA partially abrogated the formation of tubular structures and disrupted cyst architecture. Etv5 knockout mice (Pdx1Cre;Etv5-/-) were generated and we performed a cerulein-induced acute pancreatitis model. We found significantly elevated levels of serum amylase in Etv5-/- mice on Days 1 and 3 of the protocol. In a semiquantitative, blinded review of the histology, there was significantly more intense edema, inflammation, vacuolization and necrosis in Etv5-/- mice in all time points, which was also confirmed by quantitative amylase area scoring.

Conclusion: Our data suggest a novel role for Etv5 in pancreatic ductal morphogenesis and lumen formation that is at least in part mediated by Sox9. In addition, our data suggests that the loss of Etv5 expression increases susceptibility to pancreatitis and results in persistent pancreatitis with delayed regeneration.

Citation Format: Koushik K. Das, Steffen Heeg, Maximilian Reichert, Shigetsugu Takano, Basil S. Bakir, Gregory P. Botta, Christopher Hahn, Andrew D. Rhim, Anil K. Rustgi. Ets transcription factor Etv5 regulates ductal morphogenesis and differentiation in association with Sox9 in vitro and increases susceptibility and delays recovery from pancreatitis in vivo. [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 A11.

Abstract PR05: p120 catenin mediated epithelial-to-mesenchymal plasticity determines the metastatic potential of pancreatic ductal adenocarcinoma

Introduction: The majority of pancreatic ductal adenocarcinoma (PDAC) patients present with metastases and nearly all will succumb to disease within 6-12 months of clinical presentation (Hidalgo, 2010). Recently, p120catenin (p120) was identified as a “cancer candidate gene” in sleeping beauty-induced PDAC and p120 loss is associated with poor patient survival (Mann et al, 2012). P120 is critical in stabilizing E-cadherin (E-cad) at the adherens junctions. In this study, we wished to unravel new roles for p120 in the context of PDAC initiation and progression (epithelial-mesenchymal transition or EMT), as well as metastasis.

Results: We have introduced a floxed p120 allele into the Pdx1cre;LSL-KrasG12D;R26YFP (KCY) PDAC mouse model. Mice with homozygous p120 deletion in the context of a LSL-KrasG12D allele (KCYp120fl/fl) are not viable. However, mice with heterozygous p120 loss (KCYp120fl/wt) are born according to Mendelian ratios. At 20 weeks of age, KCYp120fl/wt mice show a remarkable acceleration of the Kras-driven phenotype. KCYp120fl/wt mice (n=21) harbor the entire spectrum of precursor lesions, including PanINs (1-3), mucinous cystic neoplasms (MCN) and intraductal papillary mucinous neoplasms (IPMN) and metastatic PDAC. The phenotype in control KCYp120wt/wt mice (n=12) was restricted to early PanINs. We next asked whether the second allele of p120 is lost during metastatic dissemination. We demonstrated that the remaining p120 allele is expressed in liver metastases, indicating that p120 loss-of-heterozygosity did not occur. Of note, in liver metastases, p120 co-localizes with E-cad, thereby indicating that a single p120 allele is sufficient to stabilize E-cad. This raised the question of whether one p120 allele is required to establish epithelial integrity at the metastatic site. In order to address this mechanistically, and since KCYp120fl/fl are not viable, we performed three-dimensional (3D) culture experiments with pancreatic cells isolated from non-recombined LSL-KrasG12D/+;p120wt/wt;R26YFP (KYp120wt/wt), KYp120fl/wt and KYp120fl/fl mice. Cells were Cre-recombined in vitro. In 3D culture, KYp120wt/wt cells form round multicellular cysts. Monoallelic p120 loss only disrupts the symmetry of cysts while biallelic loss completely prevents cells from forming organized, cyctic structures. We next injected these cell lines orthotopically into the pancreata of immunodeficient mice. KYp120wt/wt cells form PanIN-like structures. Interestingly, KYp120fl/wt establish large cysts reminiscent of IPMN/MCN lesions. In the cysts, p120 is localized at the plasma membrane with E-cad. However, the invasive fronts of tumors show significantly less p120 expression. Finally, KYp120fl/fl cells form poorly differentiated tumors invading into the surrounding stroma. Given the fact that p120 stabilizes E-cad and that E-cad is critical in EMT and MET, we injected the KYp120wt/wt, KYp120fl/wt and KYp120fl/fl cell lines directly into the portal veins of these mice. KYp120fl/wt cells colonize the liver and retain the remaining p120 allele and display membranous E-cad localization. By contrast, although KYp120fl/fl cells are able to generate invasive primary pancreatic tumors when being injected orthotopically, these cells fail to colonize the liver.

Conclusions: Our findings demonstrate that monoallelic loss of p120 accelerates Kras-driven PDAC formation. However, one allele of p120 is required to establish epithelial integrity and metastases. Taken together, these results for the first time underscore the importance of p120-mediated EMT plasticity in order to complete the metastatic cascade in vivo. Furthermore, therapeutic strategies to prevent EMT alone may not be sufficient in light of our results but rather require novel approaches to target EMT plasticity so as to enhance survival in metastatic PDAC.

This abstract is also presented as Poster A63.

Citation Format: Maximilian Reichert, Basil S. Bakir, Christopher M. Hahn, Gregory P. Botta, Andrew D. Rhim, Robert H. Vonderheide, Albert B. Reynolds, Yingtao Bi, Ramana Davuluri, Burcu Saka, N. Volkan Adsay, Anil K. Rustgi. p120 catenin mediated epithelial-to-mesenchymal plasticity determines the metastatic potential of pancreatic ductal adenocarcinoma. [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 PR05.

Abstract A46: The Ets-transcription factor Etv1 induces epithelial-mesenchymal transition (EMT) and invasion as well as expands the stromal compartment in vivo

Introduction: The Ets-transcription factor Etv1 is involved in epithelial-mesenchymal interactions during pancreatic development and shows enhanced expression in PanIN as well as in pancreatic ductal adenocarcinoma (PDAC). Therefore, we aimed to identify the mechanistic roles of Etv1 in EMT and invasion in PanIN and PDAC.

Methods: Cells were isolated from Pdx1Cre;KrasG12D/+-mice (PanIN) and Pdx1Cre;KrasG12D/+;p53R175H/+-mice (PDAC) and lentiviral tranduction was used to induce overexpression or knockdown (shRNA) of Etv1, respectively. Cells were grown in 3D organotypic culture to analyze morphology and growth behavior. Invasion and sphere formation (self-renewal) assays were performed. FACS-sorting was used to isolate CD44+/CD24+ cells as a putative cancer stem cell population in PDAC and analyzed for Etv1 expression. To assess the role of Etv1 in PDAC in vivo, orthotopic pancreatic xenograft transplantation of Etv1 overexpressing PDAC cells was performed.

Results: Etv1 overexpression in PanIN cells grown in 3D-organotypic culture induces a spindle shaped morphology and highly perturbed cyst architecture in contrast to control PanIN cells that form spheroid cysts that resemble normal pancreatic ductal structures. Concurrently and consistently, EMT-related genes (snail, twist, zeb1 and zeb2, as well as vimentin and N-cadherin) were found upregulated by &gt;2-fold in PanIN-mEtv1 cells. Moreover, the expression of Mmp3 and Mmp9 was significantly increased. Functionally, the invasive capacity of PanIN-mEtv1 cells was more than twice that of control cells; knockdown of Etv1 in PDAC-cells significantly abrogated their invasive capacity. In sphere forming assays PanIN-mEtv1 cells revealed an increased self-renewal capacity, whereas sphere formation is reduced by knockdown of Etv1 in PanIN as well as in PDAC cells. FACS-sorting and subsequent expression analysis revealed increased Etv1 levels in the putative cancer stem cell population of CD44+/CD24+ PDAC-cells. Data from orthotopic xenografts showed significantly larger tumors, significantly increased stromal expansion measured by trichrome staining, and increased local tumor invasion in Etv1-overexpressing cells compared to controls. The increased stromal expansion significantly correlated to the increased tumor volume observed in Etv1 over-expressing xenografts.

Conclusion: Our novel data indicate that Etv1 induces EMT as well as invasion both in vitro and in vivo and mediates self-renewal capacity of premalignant cells derived from PanIN- as well as PDAC-cells. Our in vivo data suggest a role for Etv1 in expanding the stromal compartment. These striking data suggest that Etv1 is biologically important in EMT. In vivo experiments with conditional knockout of Etv1 in Pdx1Cre;KrasG12D/+;p53R175H/+-mice are ongoing to further elucidate the role of Etv1 in PanIN and PDAC initiation and progression.

Citation Format: Koushik K. Das, Steffen Heeg, Maximilian Reichert, Shigetsugu Takano, Basil S. Bakir, Gregory P. Botta, Christopher Hahn, Andrew D. Rhim, Anil K. Rustgi. The Ets-transcription factor Etv1 induces epithelial-mesenchymal transition (EMT) and invasion as well as expands the stromal compartment in vivo. [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 A46.

Culturing mouse tumor cells

Genetically engineered mouse models (GEMMs) are attractive for the study of cancer; however, they can be time-consuming and expensive to produce and maintain. Thus, in certain contexts, the use of in vitro culture systems of tumor cells may provide an efficient and effective means to test hypotheses before assessment in or to complement discoveries in GEMMs. This introduction will briefly review the issues pertaining to in vitro analyses of primary cancer cells and highlight several "best practice" protocols that can be used when working with diverse types of carcinomas.

Culturing primary mouse pancreatic ductal cells

The most common subtype of pancreatic cancer is pancreatic ductal adenocarcinoma (PDAC). PDAC resembles ductal cells morphologically. To study pancreatic ductal cell (PDC) and pancreatic intraepithelial neoplasia (PanIN)/PDAC biology, it is essential to have reliable in vitro culture conditions. Here we describe a methodology to isolate, culture, and passage PDCs and duct-like cells from the mouse pancreas. It can be used to isolate cells from genetically engineered mouse models (GEMMs), providing a valuable tool to study disease models in vitro to complement in vivo findings. The culture conditions allow epithelial cells to outgrow fibroblast and other "contaminating" cell types within a few passages. However, the resulting cultures, although mostly epithelial, are not completely devoid of fibroblasts. Regardless, this protocol provides guidelines for a robust in vitro culture system to isolate, maintain, and expand primary pancreatic ductal epithelial cells. It can be applied to virtually all GEMMs of pancreatic disease and other diseases and cancers that arise from ductal structures. Because most carcinomas resemble ductal structures, this protocol has utility in the study of other cancers in addition to PDAC, such as breast and prostate cancers.

Creation of primary cell lines from lineage-labeled mouse models of cancer

Frequently, it is necessary to isolate pure populations of cancer cells for downstream assays, such as transcriptional analysis, signaling studies, and the creation of noncontaminated primary cell lines. Genetic lineage labeling with fluorescent reporter alleles allows for the identification of epithelial-derived cells within tumors. This protocol describes a method to isolate lineage-labeled pancreatic epithelial cells for ex vivo analysis, but it can be adapted for any type of lineage-labeled tumor.

Three-dimensional organotypic culture of stratified epithelia

One of the limitations of conventional tissue culture on flat two-dimensional surfaces is the loss of complex interactions between the epithelium and stroma. We have devised a culture system that recreates the salient features of the stratified epithelium using primary cell cultures from mouse models. The protocol described here is applicable to the esophageal epithelium, but stratified epithelial cells from other organs (e.g., skin) can be grown. Once established, the system can be used to interrogate the effect of various pharmacologic and genetic manipulations on epithelial homeostasis and invasion.

ATDC induces an invasive switch in KRAS-induced pancreatic tumorigenesis

The initiation of pancreatic ductal adenocarcinoma (PDA) is linked to activating mutations in KRAS. However, in PDA mouse models, expression of oncogenic mutant KRAS during development gives rise to tumors only after a prolonged latency or following induction of pancreatitis. Here we describe a novel mouse model expressing ataxia telangiectasia group D complementing gene (ATDC, also known as TRIM29 [tripartite motif 29]) that, in the presence of oncogenic KRAS, accelerates pancreatic intraepithelial neoplasia (PanIN) formation and the development of invasive and metastatic cancers. We found that ATDC up-regulates CD44 in mouse and human PanIN lesions via activation of β-catenin signaling, leading to the induction of an epithelial-to-mesenchymal transition (EMT) phenotype characterized by expression of Zeb1 and Snail1. We show that ATDC is up-regulated by oncogenic Kras in a subset of PanIN cells that are capable of invading the surrounding stroma. These results delineate a novel molecular pathway for EMT in pancreatic tumorigenesis, showing that ATDC is a proximal regulator of EMT.

Characterization of microfluidic shear-dependent epithelial cell adhesion molecule immunocapture and enrichment of pancreatic cancer cells from blood cells with dielectrophoresis

Current microfluidic techniques for isolating circulating tumor cells (CTCs) from cancer patient blood are limited by low capture purity, and dielectrophoresis (DEP) has the potential to complement existing immunocapture techniques to improve capture performance. We present a hybrid DEP and immunocapture Hele-Shaw flow cell to characterize DEP's effects on immunocapture of pancreatic cancer cells (Capan-1, PANC-1, and BxPC-3) and peripheral blood mononuclear cells (PBMCs) with an anti-EpCAM (epithelial cell adhesion molecule) antibody. By carefully specifying the applied electric field frequency, we demonstrate that pancreatic cancer cells are attracted to immunocapture surfaces by positive DEP whereas PBMCs are repelled by negative DEP. Using an exponential capture model to interpret our capture data, we show that immunocapture performance is dependent on the applied DEP force sign and magnitude, cell surface EpCAM expression level, and shear stress experienced by cells flowing in the capture device. Our work suggests that DEP can not only repel contaminating blood cells but also enhance capture of cancer cell populations that are less likely to be captured by traditional immunocapture methods. This combination of DEP and immunocapture techniques to potentially increase CTC capture purity can facilitate subsequent biological analyses of captured CTCs and research on cancer metastasis and drug therapies.

Stromal elements act to restrain, rather than support, pancreatic ductal adenocarcinoma

Sonic hedgehog (Shh), a soluble ligand overexpressed by neoplastic cells in pancreatic ductal adenocarcinoma (PDAC), drives formation of a fibroblast-rich desmoplastic stroma. To better understand its role in malignant progression, we deleted Shh in a well-defined mouse model of PDAC. As predicted, Shh-deficient tumors had reduced stromal content. Surprisingly, such tumors were more aggressive and exhibited undifferentiated histology, increased vascularity, and heightened proliferation--features that were fully recapitulated in control mice treated with a Smoothened inhibitor. Furthermore, administration of VEGFR blocking antibody selectively improved survival of Shh-deficient tumors, indicating that Hedgehog-driven stroma suppresses tumor growth in part by restraining tumor angiogenesis. Together, these data demonstrate that some components of the tumor stroma can act to restrain tumor growth.

Microfluidic immunocapture of circulating pancreatic cells using parallel EpCAM and MUC1 capture: characterization, optimization and downstream analysis

We have developed and optimized a microfluidic device platform for the capture and analysis of circulating pancreatic cells (CPCs) and pancreatic circulating tumor cells (CTCs). Our platform uses parallel anti-EpCAM and cancer-specific mucin 1 (MUC1) immunocapture in a silicon microdevice. Using a combination of anti-EpCAM and anti-MUC1 capture in a single device, we are able to achieve efficient capture while extending immunocapture beyond single marker recognition. We also have detected a known oncogenic KRAS mutation in cells spiked in whole blood using immunocapture, RNA extraction, RT-PCR and Sanger sequencing. To allow for downstream single-cell genetic analysis, intact nuclei were released from captured cells by using targeted membrane lysis. We have developed a staining protocol for clinical samples, including standard CTC markers; DAPI, cytokeratin (CK) and CD45, and a novel marker of carcinogenesis in CPCs, mucin 4 (MUC4). We have also demonstrated a semi-automated approach to image analysis and CPC identification, suitable for clinical hypothesis generation. Initial results from immunocapture of a clinical pancreatic cancer patient sample show that parallel capture may capture more of the heterogeneity of the CPC population. With this platform, we aim to develop a diagnostic biomarker for early pancreatic carcinogenesis and patient risk stratification.

Detection of circulating pancreas epithelial cells in patients with pancreatic cystic lesions

Hematogenous dissemination is thought to be a late event in cancer progression. We recently showed in a genetic model of pancreatic ductal adenocarcinoma that pancreas cells can be detected in the bloodstream before tumor formation. To confirm these findings in humans, we used microfluidic geometrically enhanced differential immunocapture to detect circulating pancreas epithelial cells in patient blood samples. We captured more than 3 circulating pancreas epithelial cells/mL in 7 of 21 (33%) patients with cystic lesions and no clinical diagnosis of cancer (Sendai criteria negative), 8 of 11 (73%) with pancreatic ductal adenocarcinoma, and in 0 of 19 patients without cysts or cancer (controls). These findings indicate that cancer cells are present in the circulation of patients before tumors are detected, which might be used in risk assessment.

The effects of long-term therapy with proton pump inhibitors on meal stimulated gastrin

BACKGROUND

Dyspepsia develops in healthy volunteers after withdrawal of proton-pump inhibitors. This phenomenon, attributed to rebound acid hypersecretion, is thought to be mediated by reflex hypergastrinemia.

AIMS

To measure fasting and postprandial gastrin in patients on long-term proton-pump inhibitor treatment and correlate gastrin levels with the duration of treatment and other potential predictors.

METHODS

In this cross sectional study patients, with erosive esophagitis, on long-term proton-pump inhibitor treatment and healthy controls underwent gastrin measurements at baseline and four times following a meal and Helicobacter pylori status was determined.

RESULTS

A total of 100 patients and 50 controls were studied. Pre- and postprandial gastrin levels were higher in patients (p<0.001). No significant correlation was found between the area under the gastrin-curve and the treatment duration. Female patients had significantly higher gastrin levels than males pre- and postprandial, whereas such differences was not found in the control group. Female gender was the only independent predictor of s-gastrin levels (OR 2.50 compared to males, 95% CI: 1.08-5.76, p=0.032) in the patient group.

CONCLUSION

Gastrin values were higher in patients compared to controls. There was no correlation between gastrin levels and treatment duration. Female patients had significantly higher gastrin values than males.