Mouse Pancreatic Ductal Adenocarcinoma Research Articles

Stromal reprogramming overcomes resistance to RAS-MAPK inhibition to improve pancreas cancer responses to cytotoxic and immune therapy.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy that is often resistant to therapy. An immune suppressive tumor microenvironment (TME) and oncogenic mutations in KRAS have both been implicated as drivers of resistance to therapy. Mitogen-activated protein kinase (MAPK) inhibition has not yet shown clinical efficacy, likely because of rapid acquisition of tumor-intrinsic resistance. However, the unique PDAC TME may also be a driver of resistance. We found that long-term focal adhesion kinase (FAK) inhibitor treatment led to hyperactivation of the RAS/MAPK pathway in PDAC cells in mouse models and tissues from patients with PDAC. Concomitant inhibition of both FAK (with VS-4718) and rapidly accelerated fibrosarcoma and MAPK kinase (RAF-MEK) (with avutometinib) induced tumor growth inhibition and increased survival across multiple PDAC mouse models. In the TME, cancer-associated fibroblasts (CAFs) impaired the down-regulation of MYC by RAF-MEK inhibition in PDAC cells, resulting in resistance. By contrast, FAK inhibition reprogramed CAFs to suppress the production of FGF1, which can drive resistance to RAF-MEK inhibition. The addition of chemotherapy to combined FAK and RAF-MEK inhibition led to tumor regression, a decrease in liver metastasis, and improved survival in KRAS-driven PDAC mouse models. Combination of FAK and RAF-MEK inhibition alone improved antitumor immunity and priming of T cell responses in response to chemotherapy. These findings provided the rationale for an ongoing clinical trial evaluating the efficacy of avutometinib and defactinib in combination with gemcitabine and nab-paclitaxel in patients with PDAC and may suggest further paths for combined stromal and tumor-targeting therapies.

Reprograming immunosuppressive microenvironment by eIF4G1 targeting to eradicate pancreatic ductal adenocarcinoma

Current therapies against pancreatic ductal adenocarcinoma (PDAC) have limited clinical benefits owing to tumor heterogeneity and their unique immunosuppressive microenvironments. The eukaryotic initiation factor (eIF) 4F complex is involved in regulating translation and various downstream carcinogenic signaling pathways. We report that eIF4G1, one of the subunits of eIF4F, is overexpressed in cancer cells and cancer-associated fibroblasts, and this correlates with poor prognosis in patients with PDAC. In PDAC mice, eIF4G1 inhibition limits tumor progression and prolongs overall survival, especially when combined with PD1/PDL1 antagonists and gemcitabine. Mechanistically, eIF4G1 inhibition hinders the production of cytokines and chemokines that promote fibrosis and inhibit cytotoxic Tcell chemotaxis. Moreover, eIF4G1 inhibition impairs integrinβ1 protein translation and exerts tumor suppression effects through the FAK-ERK/AKT signaling pathway. These findings highlight the effects of eIF4G1 on tumor immune dependence and independence and identify eIF4G1 as a promising therapeutic target for PDAC.

Combined Autophagy Inhibition and Dendritic Cell Recruitment Induces Antitumor Immunity and Enhances Immune Checkpoint Blockade Sensitivity in Pancreatic Cancer.

The effect of immune checkpoint inhibitors is extremely limited in patients with pancreatic ductal adenocarcinoma (PDAC) due to the suppressive tumor immune microenvironment (TIME). Autophagy, which has been shown to play a role in anti-tumor immunity, has been proposed as a therapeutic target for PDAC. Here, single-cell RNA-sequencing of autophagy-deficient murine PDAC tumors revealed that autophagy inhibition in cancer cells induced dendritic cell (DC) activation. Analysis of human PDAC tumors substantiated a negative correlation between autophagy and DC activation signatures. Mechanistically, autophagy inhibition increased intracellular accumulation of tumor antigens, which could activate DCs. Administration of chloroquine (CQ), an autophagy inhibitor, in combination with Flt3 ligand (Flt3L)-induced DC infiltration inhibited tumor growth and increased tumor-infiltrating T lymphocytes. However, autophagy inhibition in cancer cells also induced CD8+ T cell exhaustion with high expression of immune checkpoint LAG3. A triple therapy comprising CQ, Flt3L, and an anti-LAG3 antibody markedly reduced tumor growth in orthotopic syngeneic PDAC mouse models. Thus, targeting autophagy in cancer cells and activating DCs sensitizes PDAC tumors to immune checkpoint inhibitor therapy, warranting further development of this treatment approach to overcome immunosuppression in pancreatic cancer.

Abstract B006: The role of tumor specific IGFBP-3 in the onset and progression of skeletal muscle wasting in a murine model of pancreatic cancer

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer- related death and is highly associated with skeletal muscle wasting (SMW) that leads to treatment intolerance and reduced survival. Research substantiates the role of increased levels of Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) in PDAC-related SMW. Canonically, supraphysiological levels of IGFBP-3 block insulin-like growth factor-1 (IGF-1) binding, thus downregulating the activation of its downstream targets Akt and mTOR. Non-canonical signaling via TGF-βRI results in aberrant FoxO1 signaling, which upregulates the ubiquitin proteasome pathway (UPP) and induces autophagy. Dysregulated UPP and autophagy activation have been shown to promote muscle degradation. Recent findings from our lab implicate canonical and non-canonical signaling of tumor associated IGFBP-3 in increased protein catabolism and decreased anabolism, resulting in SMW in a syngeneic murine model of PDAC. We tested the hypothesis that genetic ablation of IGFBP-3 in PDAC tumor cells attenuates SMW via regulation of Akt and FoxO1, leading to decreases in UPP and autophagy in skeletal muscle.Methods: C57BL/6J female mice (6-8 weeks) were randomized to one of three groups: 1) no tumor control (NTC) (n=10), 2) KCKO-Luc parental cells (PDAC) (n=14), or 3) IGFBP-3-/- KCKO-Luc (n=14). Tumor cells were injected orthotopically. Tumor and lean mass were assessed longitudinally via dual energy x-ray absorptiometry (DEXA). At sacrifice, quadriceps muscles were collected for protein and transcriptional analysis, Tibialis Anterior (TA) muscles for histology and serum for ELISA. TA frozen sections were stained with Oil Red O (ORO) to highlight intramuscular adipogenesis.Results: PDAC mice experience significantly reduced survival (T1/2=56 days) compared to IGFBP-3-/- mice that maintained 100% survival at day 100 (p<0.0001). IGFBP-3-/- mice lost significantly less lean mass from baseline to day 56 compared to PDAC mice (p<0.0001). PDAC mice exhibited 3-fold elevated serum levels of IGFBP-3 compared to NTC and IGFBP-3-/- mice (p<0.01). Transcriptionally, PDAC mice displayed increased expression of igfbp3, tgfbr1, and UPP associated genes fbxo32, and trim63 compared to NTC and IGFBP-3-/- mice. Further, the ratio of pAkt (Ser473), pS6 (Ser235/236), and pFoxO1 (Ser253) to total protein levels were significantly reduced in PDAC mice (p<0.05 vs NTC and IGFBP-3-/-). Additionally, protein levels of ULK1 and the ratio of LC3bII over LC3bI, markers of autophagy, are elevated in PDAC mice compared to NTC and IGFBP-3-/- mice (p<0.05). Lastly, there is a significant increase in ORO positive staining in PDAC mice compared to NTC and IGFBP-3-/- mice (p<0.0001).Conclusion: These findings suggest that PDAC-related SMW is driven by tumor derived IGFBP-3, which acts as an endocrine factor on skeletal muscle cells to inhibit protein synthesis and activate FoxO1 signaling to upregulate the UPP and autophagy. Lastly, we identify skeletal muscle adipogenesis as a biomarker for autophagy upregulation and SMW. Citation Format: Zachary R Sechrist, Calvin L Cole. The role of tumor specific IGFBP-3 in the onset and progression of skeletal muscle wasting in a murine model of pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B006.

Abstract B007: Optimization of an Orthotopic Mouse Model of Pancreatic Cancer to Simulate Liver Metastasis and Cancer Cachexia

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with a poor prognosis due to two key features. The first is metastasis at presentation, occurring in approximately 80% of PDAC patients, with 90% of these metastases occurring in the liver. The second is cachexia, which compromises treatment tolerance and reduces the quality of life for patients. Although various mouse models of PDAC exist, recapitulating both metastatic and cachectic features have been challenging. In this study, we optimized an orthotopic mouse model of PDAC by altering implantation sites, subcloning parental murine PDAC cells, adjusting the number of transplanted cells, and varying the age of recipient mice to study liver metastasis and cancer cachexia. These modifications significantly increased the latency of tumor development and the time course of the disease, concurrently increasing the rate of liver metastasis to approximately 70%. Furthermore, reliable cachexia endpoints were also achieved in both PDAC mice with and without metastases, mirroring the condition in patients. We also found that cachectic muscles from PDAC mice with metastasis exhibit a similar transcriptional profile to muscles derived from mice and patients without metastasis. Together, this model is likely to be advantageous in both advancing our understanding of the mechanisms of PDAC cachexia and in evaluating novel therapeutics. Citation Format: David J Wang, Victoria Spadafora, Benjamin R Pryce, Alexander Oles, Erin E Talbert, Micheal C Ostrowski, Denis C Guttridge. Optimization of an Orthotopic Mouse Model of Pancreatic Cancer to Simulate Liver Metastasis and Cancer Cachexia [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B007.

Abstract PR-11: Altered mRNA splicing mimics chromosome loss and drives pancreatic cancer

Abstract Aiming to identify novel driver mutations that cause pancreatic ductal adenocarcinoma (PDAC), besides p53 mutations, we performed a genetic interaction analysis based on the concept of mutually exclusive mutations, which suggests that mutations exclusive to one another function within the same pathway. Using our unbiased quantitative methods to evaluate the effects of somatic mutations on cancer, we analyzed 3900 human PDAC cases to prioritize mutations among hundreds that appear at low frequencies (5-10%) and are mutually exclusive with p53 mutations. Mutations in RNA splicing factors SF3B1 and RBM10 (∼15% of cases) were among the most significant and mutually exclusive to mutant p53. Thus, we hypothesized that aberrant RNA splicing promoted by mutant SF3B1K700E and truncated RBM10 (RBM10 loss) lead to tumorigenesis and therapy resistance. Through the generation of engineered mouse models to co-express KrasG12D with either Sf3b1K700E or Rbm10 loss in pancreatic cells, we observed that mice harboring KrasG12D and Sf3b1 K700E or Rbm10 loss—like mutant p53—caused PDAC in mice. To identify the RNA splicing mechanism that leads to PDAC formation, we performed deep RNA sequencing and unbiased transcriptome-wide splicing analyses in isolated PDAC cells bearing wild-type SF3B1K700E and RBM10 loss derived from murine and patient PDACs. We established that SF3B1 and RBM10 mutations induce wide splicing changes, primarily affecting exon selection. Since two-thirds of these changes may lead to nonsense-mediated decay (NMD), a mechanism that eliminates aberrant mRNA, we tested whether these changes could trigger this response. Using cycloheximide-dependent NMD inhibition, we confirmed that these mutations cause NMD, resulting in post-transcriptional gene expression loss in mouse chromosomes 2, 7, 11, and 17, also conserved in human models. Intriguingly, recent studies in Nature (2022) have shown that in murine PDACs with loss-of-function p53 mutations, genetic loss of chromosomes 11 and 7 is necessary for PDAC development. These results suggest that mutations in SF3B1 and RBM10, and p53 loss, affect the same chromosomal loci, albeit through different mechanisms, to promote PDAC, supporting the mutual exclusivity findings from patient samples. To determine a personalized therapy for patients with mutant splicing-factor tumors, we found that PDACs with these mutations are more sensitive to Gemcitabine, a component of a PDAC standard-of-care therapy. Moreover, these mutations sensitize cells to small-molecule splicing inhibitor H3B-8800— currently in phase 2 trial for hematologic malignancies. Lastly, we found that combining Gemcitabine and H3B-8800 synergizes to kill mutant splicing cells selectively in vitro and in vivo. We are starting a phase 2 trial for Gemcitabine/Abraxane with escalating doses of H3B-8800 for tumors that have either SF3B1K700E, RBM10 loss, or neomorphic p53, all of which have aberrant RNA splicing. This work has determined novel drivers and mechanisms of PDAC development and a precision therapeutic strategy for treating PDAC patients. Citation Format: Natasha Pinto Medici, Diana Martinez-Saucedo, Danny Lee, Tianyi Chu, Robert Tseng, Vincent Cannataro, Jeffrey Townsend, Christine Iacobuzio-Donahue, Marie Robert, Omar Abdel-Wahab, Steven D. Leach, Luisa Escobar-Hoyos. Altered mRNA splicing mimics chromosome loss and drives pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr PR-11.

Abstract B075: Functional characterization of TGF-β-dependent cancer-associated fibroblasts in pancreatic cancer using novel in vitro and in vivo models

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDAC) is characterized by abundant cancer- associated fibroblasts (CAFs) which contribute to a tumor-promoting, chemotherapy-resistant and immunosuppressive tumor microenvironment (TME). However, CAF-ablating therapeutic strategies have thus far failed in clinical trials. One potential reason is that PDAC CAFs are heterogeneous and plastic. It was recently discovered that myofibroblastic CAFs (myCAFs) and inflammatory CAFs (iCAFs) can originate from pancreatic stellate cells (PSCs) via TGF-β and IL-1 signaling, respectively. However, their functional heterogeneity remains to be elucidated. We hypothesize that distinct CAF subtypes exhibit different tumor-promoting roles mediated by targetable signaling mechanisms. To this end, we aimed at characterizing the functions of TGF- β-dependent myCAFs in shaping the TME and influencing PDAC progression. Methods: We generated novel myCAF-depleted PDAC mouse models by orthotopically injecting PDAC organoids derived from KPC (Kras LSL-G12D/+ ; Trp53 LSL-R172H/+ ; Pdx1-Cre) mice into Fap-Tgfbr2 knockout (Fap-tTA; Rosa26 LSLtdTom/+ ; tet-O-Cre; Tgfbr2 fl/fl ) mice. The pancreatic tumors were analyzed by flow cytometry, histology and single-cell RNA-sequencing (scRNAseq). In a complementary approach, we generated myCAF-enriched PDAC mouse models by orthotopically co-injecting KPC PDAC organoids and novel TGF-β-driven ‘myCAF-locked’ murine PSCs. In addition, to further dissect myCAF-malignant cell signaling crosstalk, KPC PDAC organoids and myCAF-locked PSCs were co-cultured and then flow-sorted for bulk RNA- sequencing. Results: MyCAF-depleted PDAC tumors from Fap-Tgfbr2 knockout mice had a significant decrease in myCAFs, and a significant expansion of iCAFs, compared to control mice. Additionally, Masson’s trichrome staining indicated significant reduction in collagen content in the TME upon myCAF depletion. Moreover, scRNAseq analysis revealed that myCAF depletion shaped the composition of innate immune cells, including macrophages and neutrophils. Notably, although primary tumor growth was not altered, liver and lung metastases decreased, while diaphragm metastases and ascites increased, in myCAF-depleted PDAC mice. Conversely, liver and lung metastases increased, while diaphragm metastases and ascites decreased in myCAF-enriched PDAC mouse models, suggesting that TGF-β-dependent myCAFs play a role in promoting distant metastases. In line with this, transcriptomic analysis of PDAC organoids co-cultured with myCAF-locked PSCs showed enrichment of pathways in epithelial-mesenchymal transition, hypoxia, VEGF, WNT and cell-matrix interactions. Conclusion: Our study demonstrates that TGF-β-dependent CAFs are not only largely responsible for collagen deposition in PDAC, but also possess immune-modulating properties. Moreover, our study supports a role of TGF-β-dependent CAFs in promoting PDAC metastasis to the liver and the lungs, potentially through upregulating pro-metastatic pathways in the malignant cells. Citation Format: Priscilla S.W. Cheng, Muntadher Jihad, Judhell S. Manansala, Weike Luo, Gianluca Mucciolo, Sara Pinto Teles, Giulia Biffi. Functional characterization of TGF-β-dependent cancer-associated fibroblasts in pancreatic cancer using novel in vitro and in vivo models [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B075.

Abstract C046: Targeting wild-type IDH1 sensitizes homologous recombination proficient pancreatic cancer to PARP inhibition

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer-related mortality in the United States. While Poly (ADP-ribose) polymerase (PARP) inhibitors show promise for PDAC with Homologous Recombination Deficiency (HRD), this mutation is present in less than 10% of cases. Our research focuses on exploiting a vulnerability in the remaining 90% of HR proficient (HRP) tumors. We identified that wild-type isocitrate dehydrogenase 1 (IDH1) plays a critical role in HR repair. By inhibiting IDH1, we discovered suppression of the homologous recombination (HR) pathway, leading to compromised genomic integrity. This renders cancer cells more susceptible to PARP inhibitor therapy, offering a novel therapeutic approach for HRP PDAC. Methods:We assessed the impact of IDH1 inhibition on HR pathway activity using Western blotting to measure HR repair protein levels and HR reporter assays. The effect of IDH1 inhibition (Ivosidenib) combined with PARP inhibition (Olaparib) on in vitro growth inhibition was assessed through drug combination assays. Additionally, we investigated the molecular mechanisms underlying the synergistic effects of the drug combination. To further evaluate the therapeutic potential of IDH1 inhibition in combination with PARP inhibitors, we examined tumor growth in xenograft models of PDAC in athymic nude mice and survival studies were performed in C57BL/6J mice transplanted with orthotopic murine pancreatic cancer. Results:Wild-type IDH1 blockade induces a BRCA-like phenotype by decreasing α-ketoglutarate (αKG) levels and causing histone hypermethylation. This leads to decreased HR repair efficiency in HRP pancreatic cancer cells (MiaPaCa-2 and Panc-1), resulting in a strong synergistic effect when combined with the DNA-damaging agent Olaparib. The combination treatment significantly reduced cell survival in both short and long-term assays. Furthermore, we discovered that these compounds complemented each other in the DNA damage response, leading to increased γ-H2AX (DNA damage marker) and apoptosis. In vivo studies using murine PDAC models demonstrated that the combination of ivosidenib and olaparib synergistically enhanced anti-tumor activity compared to either single agent alone. Conclusion:These data provide novel insight into the mechanisms underlying in the context of HRP cancer susceptibility to a dual treatment approach involving an IDH1 inhibitor and a PARP inhibitor. This approach holds promise for precision medicine in pancreatic cancer treatment, although further pre- clinical studies are needed for validation and refinement. Citation Format: Mehrdad Zarei, Omid Hajihassani, Hallie J. Graor, Soubhi Tahhan, Alexander W. Loftus, Faith Nakazzi, Semmer A. Ali, Parnian Naji, Luke D. Rothermel, Jonothan R. Brody, Jordan M. Winter. Targeting wild-type IDH1 sensitizes homologous recombination proficient pancreatic cancer to PARP inhibition [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C046.

Abstract C017: Targeting KRAS selectively induce metabolic reprogramming in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease largely due to the lack of effective treatments that overcome the tumor drug resistance. Oncogenic KRAS mutation contribute to most PDAC and drive multiple metabolic pathways to promote tumor growth. Despite this overarching role of KRAS, inhibition of KRAS/MAPK pathway often lead to resistance by yet unclear mechanism. Here we find that the pharmacological inhibition of KRAS/MAPK pathway induces distinct responses in various pancreatic cancer cells. Specifically, while KRAS/MAPK inhibition suppressed growth in some cells, the same treatment induced or did not change the growth of other cell lines and also selectively impacted cell migration. In addition, metabolic activities were suppressed in cells where growth was suppressed or not changed but was accelerated where KRAS/MAPK inhibition induced growth. Analysis of gene expression profile of human PDAC and KRAS-driven mouse tumors identified nutrient transporters that are upregulated KRAS induction but also upregulated upon KRAS inhibition. Our study reveals context-dependent response to KRAS inhibition in pancreatic cancer and suggest targeting nutrient transporters to overcome therapeutic resistance. Citation Format: Laiba Shiekh, Matthew Cheung, Linyuhui Zheng, Erica Marlette, Chiamaka J. Ezeh, Don-Gerard Conde, Zeribe C. Nwosu. Targeting KRAS selectively induce metabolic reprogramming in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C017.

Abstract B058: Rewiring CD8+ T cell responses to PD-1 immune checkpoint blockade in PDAC via the inhibitory receptor PSGL-1

Abstract Pancreatic ductal adenocarcinoma (PDAC) is an aggressive, poorly immunogenic cancer and non-responsive to all currently available treatments, including immune checkpoint blockade (ICB) therapies. As survival rates remain low (13%), there is an urgent need for new therapeutic options. A hallmark of PDAC is the limited infiltration of anti-tumor cytotoxic CD8+ T cells. Analysis of single-cell RNA-sequencing data of PDAC tumors from treatment naïve patients reveals high expression of P-selectin glycoprotein ligand 1 (PSGL-1) on tumor-infiltrating CD8+ T cells. PSGL-1 is an intrinsic negative regulator of CD8+ T cells that promotes the development of functional exhaustion. We therefore hypothesized that PSGL-1-mediated immune suppression is a critical barrier to effective anti-tumor immunity in PDAC. To test this, we used preclinical models of orthotopic injection PDAC tumor cells into pancreata, recapitulating patient responses to PDAC with limited T cell infiltrates and uncontrolled tumor growth in C57BL/6 (wildtype) control mice and compared anti-tumor immune responses in PSGL-1KO (C57BL/6 background) mice. At 28 days post-injection of KPC.4662 PDAC tumor cells, tumor burden in PSGL-1KO mice was reduced by >50% compared to controls, with 45% of PSGL-1KO animals exhibiting >70% reduction. Total immune infiltration (CD45+) was 2-fold greater in tumors from PSGL-1KO mice, with significant increases in infiltrating CD4+ and CD8+ T cells. Detailed analyses revealed that infiltrating CD8+ T cells from PSGL-1KO mice were less terminally differentiated towards exhaustion. PSGL-1KO PD-1+ CD8+ T cells expressed less TOX expression and fewer cells co-expressed CD38 and CD101 while more expressed CX3CR1 compared to controls. Intratumoral PSGL-1KO CD8+ T cells also retained greater functionality as well as indicated by inflammatory cytokine production (IFNg, TNFa) and Granzyme B expression. Moreover, PSGL-1KO mice showed protection against metastatic disease to the lungs. We find that protection by PSGL-1KO mice is T cell dependent as transient depletion of CD4+ and CD8+ T cells prior to tumor cell implantation results in the loss of PDAC tumor growth inhibition by PSGL-1KO mice. Less-differentiated, proliferation-competent precursors of exhausted CD8+ T cells (TPEX) are essential to PD-1 ICB responsiveness in patients and preclinical models. Given that PSGL-1-deficiency limits terminal differentiation of CD8+ T cells in PDAC, we hypothesized that PSGL-1-deficiency would promote responsiveness to PD-1 ICB, which is ineffective as a monotherapy in PDAC patients and mouse models. While therapeutic treatment with anti-PD-1 had no effect on the tumor growth in the control animals, PD-1 ICB resulted in tumor ablation in 85% of PSGL-1KO animals, demonstrating a profound synergistic effect of PD-1 inhibition in the absence of PSGL-1. From these studies, we conclude that PSGL- 1 is a critical inhibitor anti-tumor T cell immunity in PDAC and represents a novel ICB target with high translational potential for promoting immune responses to PDAC tumors. Citation Format: Jennifer L Hope, Yijuan Zhang, Hannah A. F. Hetrick, Evelyn S. Sanchez Hernandez, Gabriele Romano, Sreeja Roy, Michelle Lin, Ashley B Palete, Swetha Maganti, Dennis C Otero, Katelyn T Byrne, Cosimo Commisso, Linda M Bradley. Rewiring CD8T cell responses to PD-1 immune checkpoint blockade in PDAC via the inhibitory receptor PSGL-1 [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B058.

Abstract IA-08: Syndecan 1 is a therapeutic target for KRAS-driven pancreatic cancer

Abstract KRAS inhibitors targeting G12C mutation have been approved by FDA for the treatment of non-small cell lung cancers and have shown promising clinical responses in pancreatic ductal adenocarcinoma (PDAC). RAS inhibitors targeting additional KRAS mutations or multiple RAS isoforms are under clinical development. Although targeting KRAS exhibits anti-tumor effect in PDAC, majority of tumors inevitably develop resistant disease, as is the case for most targeted therapies. In this new era of targeting KRAS driven cancer, understanding mechanisms driving this resistance to RAS targeted therapies and further devising combination strategies to overcome it have become a necessary, though challenging, task to achieve long term disease control. To tackle this problem, we employed various in vitro and in vivo preclinical model systems to explore the development of resistance to both genetic and pharmacological KRAS blockade. Our previous work identified the membrane proteoglycan Syndecan 1 (SDC1) as a KRAS downstream surrogate whose cell surface localization is tightly controlled by oncogenic KRAS signaling and is critical for KRAS-driven tumor development. Here, our analysis of KRAS driven genetically engineered PDAC mouse model and human pancreatic or colorectal cancer (CRC) cells with KRASG12C mutation discovered that, while cell surface SDC1 is reduced upon acute genetic or pharmacological inhibition of oncogenic KRAS, plasma membrane SDC1 is recovered in tumor cells that become resistant to KRAS inhibition (KRAS-bypass cells). Surface localization of SDC1 leads to the activation of multiple receptor tyrosine kinases (RTKs) and macropinocytosis, resulting in the resistance to KRAS blockade. We further identified that the recovery of plasma membrane SDC1 in KRAS-bypass cells is driven by YAP1 oncogene, which induces the downregulation of ARF6 GAPs, leading to the activation of ARF6, a small GTPase required for SDC1 membrane recycling. To therapeutically targeting SDC1, we have successfully developed a monoclonal antibody (22B mAb), which exhibits remarkable sensitivity and specificity for human SDC1. Our results indicate that 22B mAb exerts substantial inhibition of PDAC cell growth in vitro and desirable tumor inhibitory effects in vivo in murine PDAC tumors and human PDAC cell-derived xenograft tumors. Importantly, our 22B mAb synergizes with KRAS inhibitors, chemotherapy, or immunotherapy, resulting in significantly enhanced therapeutic effects. Taken together, our study identified SDC1 as a functional driver for the bypass of KRAS-dependence and therapeutically targeting SDC1 with a novel mAb will overcome the acquired resistance to KRAS targeted therapy. As such, our research yields important new insights in the fields of cancer biology regarding mechanisms of resistance employed by human cancers, and identifies new actionable therapeutic targets and approaches to overcome resistance to KRAS inhibition. Citation Format: Mitsunobu Takeda, Zecheng Yang, Madeline S Theardy, Alexey Sorokin, Oluwadara Coker, Shuaitong Chen, Long T Vien, Laura Bover, Haoqiang Ying, Scott Kopetz, Wantong Yao. Syndecan 1 is a therapeutic target for KRAS-driven pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr IA-08.

Abstract A059: Understanding the events that promote pancreatic cancer metastasis

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy due to overwhelming metastatic burden. PDAC cells migrate and invade by two distinct epithelial-to-mesenchymal transition phenotypes: collective (partial-EMT) or single-cell (complete-EMT). The mechanism(s) by which these invasive phenotypes intravasate is unknown. The Tumor Microenvironment of Metastasis (TMEM) doorway, which is formed by a tumor cell, macrophage and an endothelial cell in direct contact, causes opening of the vasculature in which tumor cells intravasate. Intravasation via TMEM doorway is inhibited by Tie2 blockade. Whether this occurs in PDAC and whether the EMT phenotype affects intravasation is unknown. We hypothesize that PDAC cells intravasate through TMEM-dependent mechanisms regardless of EMT phenotype. Tumor samples from murine models were stained for TMEM doorways using a triple immunohistochemistry (IHC) stain (tumor cells expressing the actin regulatory protein Mena, macrophages expressing CD68, and endothelial cells expressing CD31). TMEM doorway opening was assessed in murine models of PDAC treated with or without Tie-2 inhibitor by analyzing TMEM-mediated extravasation of high-molecular weight dextran (155kD-TMR dextran) by Intravital Imaging, IHC and immunofluorescence (IF) of serial slides and circulating tumor cells. An intravasation trans-endothelial migration assay was also performed to assess the intravasation event by TMEM doorway in vitro. A student t-test was used for the analyses. TMEM doorways were observed in all PDAC murine models. For the first time in PDAC, focal extravasation of dextran events followed by a tumor cell intravasation was visualized by intravital imaging. PDAC tumor bearing mice treated with Tie2 inhibitor had a 2-fold decrease in the number of circulating tumor cells compared to control (958 ± 499.8 vs 534 ± 479.9 cells/mL blood, p=0.0257). The intravasation trans-endothelial migration assay showed that C-EMT cells have a higher migration rate than P-EMT cells (17.8 ± 5.53 vs 10.94 ± 3.84 migrating cells p=0.01), and this ratio increases with the presence of macrophages (23.75 ± 5 vs 15.54 ± 3.09 migrating cells p=0.005). The Tie-2 inhibition decreases the number of C-EMT and P-EMT migrating cells (7.69 ± 1.3 vs 3.67 ± 1.2 migrating cells p=0.01). Orthotopic tumors from C-EMT phenotype grow at a faster rate than the P-EMT (0.49mg ± 0.09 vs 0.12mg ± 0.05 p<0.05). Tumors from C-EMT and P-EMT cells will be analyzed for TMEM doorway score, TMEM activity and stemness signatures around TMEM doorway to determine if TMEM doorway is a niche for stemness in PDAC. TMEM doorways are present in PDAC mouse model. Inhibition of Tie2 leads to decreased TMEM doorway function and circulating tumor cells in PDAC. In addition, regarding the EMT phenotype, TMEM doorways are functional mechanisms of intravasation in vitro. This is a novel mechanism in PDAC and suggests a promising therapeutic target for decreasing intravasation and potential metastasis in PDAC. Citation Format: Erika Pereira Zambalde, Lina Ariyan, Francisco Puerta-Martinez, Yuqin Zhu, John Condeelis, Ben Stanger, John McAuliffe. Understanding the events that promote pancreatic cancer metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A059.

Abstract B053: SUMOylation and TIGIT inhibition: a novel immunotherapy combination for pancreatic cancer

Abstract Introduction: Immune checkpoint inhibitors have shown promise in many other solid tumors but have been disappointing in pancreatic ductal adenocarcinoma (PDAC). Preclinical work demonstrates that the immune checkpoint receptor TIGIT plays a key role in PDAC immune evasion and may be a better therapeutic target than the PD1 or CTLA4 axes. Post-translational small-ubiquitin-like modification (SUMOylation) regulates the activity of numerous proteins involved in cell proliferation. Our laboratory has shown that inhibition of SUMOylation with small molecule TAK-981 favorably modulates the PDAC immune microenvironment and specifically increases the expression of TIGIT binding partners CD226 on immune cells and CD155 on tumor cells. We hypothesized that inhibition of SUMOylation with small molecule TAK-981 would synergize with anti-TIGIT antibody therapy to induce anti-tumor immunity. Methods:All studies utilized a murine PDAC organoid line (KPC46) derived from a liver metastasis in a genetically engineered mouse model (KPC). KPC46 consistently metastasizes to the liver when implanted orthotopically into the tail of the pancreas in immunocompetent mice. Following tumor implantation, mice were surveilled by ultrasound until tumors reached 5-7 mm in diameter, then randomized to one of two treatment groups: TAK-981 + anti-TIGIT or vehicle control (n=10/group). Monotherapies were not included, as each drug alone did not produce significant responses in prior studies using this model. The treatment cohort received 15 mg/kg of TAK-981 and 100 micrograms of anti-TIGIT antibody via intraperitoneal injection every 48 hours starting 14 and 15 days, respectively, post-implantation, for a total of 4 weeks. Complete responders were defined as absence of disease after 2 months of observation. Complete responders and age-matched controls (n=3/group) were rechallenged with subcutaneous tumor injection and monitored for tumor development. Results:Survival of PDAC mice was significantly prolonged in the combination group when compared to the control group (median survival 81 vs 42 days, P<0.05). A total of 4 mice (40%) were deemed complete responders after 2 months of monitoring. The re-challenge experiment produced tumors in all three control mice but none of the treated mice by 4 weeks after implantation. Conclusion:In this study, we explored the combination of two promising immunotherapy agents for PDAC which demonstrated significant additive effects generating durable and complete responses. We were able to confirm the presence of protective immunity. These results are rarely seen in PDAC experiments. Further experiments to better understand and optimize these effects are underway. These drugs are currently in clinical trials for solid tumors and could feasibly be studied in the near future in PDAC. Citation Format: Jorge R de la Torre Medina, Utsav Joshi, Jaynath Shankara Narayanan, Herve Tiriac, Yuan Chen, Rebekah White. SUMOylation and TIGIT inhibition: a novel immunotherapy combination for pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B053.

Abstract C061: Loss of CaMK2B accelerates tumor formation and enhances metastatic competency in genetically engineered mouse models of PDAC

Abstract Background Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer- related deaths in the United States and is often not diagnosed until it has already metastasized. Our prior work established that calcium signaling pathways facilitate a pro-metastatic phenotype through the induction of an epithelial-to-mesenchymal transition (EMT) program in PDAC tumor cells, but the downstream signaling molecules mediating this phenotype have remained elusive. MethodsUsing a novel genetically engineered model of pancreatic cancer, we demonstrate that loss of Calcium/calmodulin-dependent kinase-II B (CaMK2B), a downstream effector kinase activated by calcium, enhances cellular plasticity, and increases metastasis. To this end, we generated a genetically engineered mouse model where Camk2b was knocked out in tumor cells in a lineage-labeled Kras- and p53-driven PDAC mouse model (herein KPCY-Camk2bcKO). Results Genetic deletion of Camk2b in the KPCY genetically engineered model accelerated tumor formation and dramatically reduced the overall median survival of KPCY- Camk2b cKO mice (78 days) relative to KPCY controls (136 days). Pathological and immunofluorescence analysis of KPCY-Camk2b cKO animals showed an increased number of poorly differentiated tumor regions and a higher metastatic burden, with >85% of KPCY- Camk2b cKO animals presenting with multi-focal metastases. Further analysis of tumor cells in KPCY-Camk2b cKO mice showed enhanced expression of markers of the highly aggressive squamous PDAC subtypes. Strikingly, Camk2b deletion combined with oncogenic Kras G12D (in the absence of p53 alterations), was sufficient to form lethal metastatic PDAC tumors, while age-matched control Kras G12D tumors with intact Camk2b only progressed to the acinar-to-ductal metaplasia (ADM) or Pancreatic Intraepithelial Neoplasia (PanIN) stage. Collectively, these results establish Camk2b loss as a new oncogenic and pro-metastatic mechanism in PDAC Conclusion This work demonstrates that Camk2b loss enhances tumor cell evolution and plasticity within PDAC to promote metastasis. In this context, we speculate that loss of Camk2b rewires calcium signaling to drive an aggressive subtype of PDAC with increased metastasis. Citation Format: Jessica Peura, Nikita Bhalerao, Calvin Johnson, Yamini Ogoti, Faith Keller, Emma Watson, Zhen Zhao, Jason Pitarresi. Loss of CaMK2B accelerates tumor formation and enhances metastatic competency in genetically engineered mouse models of PDAC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C061.

Abstract B059: Modulating the immunosuppressive pancreas tumor microenvironment through intratumoral delivery of cytokine-encoding mRNAs

Abstract Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive cancer, with a mere 13% average 5-year survival rate. The hallmark desmoplastic stromal response in PDAC leads to poor vascularization, drug delivery challenges, and impaired cytotoxic immune cell infiltration, contributing to de novo therapy resistance. Our previous research has shown therapeutic induction of cellular senescence with RAS pathway targeting therapies can induce cytokine and chemokine production through the senescence-associated secretory phenotype (SASP) that can effectively activate anti-tumor T cell immunity and responses to anti-PD-1 immune checkpoint blockade. To build on these findings as well as overcome limitations associated with senescence-inducing therapy toxicity and induction of pro-tumorigenic SASP cytokines, here we leveraged mRNA technology to deliver specific SASP cytokines and chemokines we have found to stimulate immune responses directly into the suppressive PDAC TME as an immune oncology platform. We created an in vitro transcription pipeline for mRNA production and multiplexing, and demonstrate we can intratumorally deliver multiple mRNAs simultaneously into the TME of transplanted and autochthonous PDAC mouse models, stimulating the local production of cytokines normally absent in PDAC. We further characterized a novel combination of five cytokines and chemokines that can effectively recruit and activate both innate and adaptive immune responses against PDAC. Through repeated bi-weekly dosing, this mRNA combination also promotes tumor destruction and improves survival outcomes. Considering the recent success of off-the-shelf neoantigen mRNA vaccines in early human PDAC patient trials, we have now developed mRNAs that encode PDAC-specific antigens. By integrating our cytokine mRNA platform with antigen mRNAs, we observe a significant increase in intratumoral antigen-presenting dendritic cell populations and a substantially enhanced T-cell mediated anti- tumor immune response in orthotopic transplant models of PDAC. Overall, this study not only unveils pivotal insights into the cytokines absent in PDAC that are crucial for promoting anti- tumor immunity, but also pioneers an innovative immunotherapy approach. This platform has the potential to be integrated with existing immunotherapy modalities, addressing the longstanding challenge of therapy resistance in PDAC. Citation Format: Chaitanya Naimesh Parikh, Kelly De Marco, Katherine Murphy, Loretah Chibaya, Lin Zhou, Youwei Qiao, Griffin Kane, Li Li, Wen Xue, Marcus Ruscetti. Modulating the immunosuppressive pancreas tumor microenvironment through intratumoral delivery of cytokine-encoding mRNAs [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B059.

Abstract A047: Fibroblast-specific IL1 receptor inhibition reprograms the inflammatory stroma to overcome the immunosuppressive tumor microenvironment in pancreatic cancer

Abstract OBJECTIVE: KRAS-driven inflammatory signaling in pancreatic ductal adenocarcinoma (PDAC) promotes cancer-associated fibroblast (CAF) polarization and an immunosuppressive tumor microenvironment (iTME), driving therapeutic resistance. IL1α, a downstream product of KRAS signaling, activates the pro-inflammatory CAF (iCAF) phenotype and correlates with worse survival. Using patient and PDAC mouse model single-cell RNA sequencing (scRNAseq) data, we have shown that the IL1 Receptor (IL1R1) is highly enriched in the fibroblast compartment. However, the role of IL1R1 in modulating iCAFs and the iTME remains poorly understood. We hypothesize that CAF-specific disruption of IL1R1 signaling will reprogram cellular components of the PDAC TME to overcome the immunosuppressive milieu and therapeutic resistance. METHODS: The effects of IL1R1 inhibition on iCAF modulation in vivo were determined in Ptf1aCre/+, LSL-KrasG12D/+, Tgfbr2flox/flox (PKT) mice treated with IL1R1 antagonist. To determine if CAF-specific silencing of IL1R1 recapitulates the TME remodeling after IL1R1 inhibition, we generated a fibroblast-specific IL1R1KO mouse model Col1a2Cre/+;Il1r1flox/flox (CAF-Il1r1KO) and orthotopically injected KPC tumor cells for endpoint analysis. Flow cytometry was performed in primary tumors of CAF-Il1r1KO and littermate controls. Functional experiments evaluating myeloid-derived suppressor cell (MDSC) trafficking were performed using ex vivo bone marrow-derived cells (BMDCs) co-cultured with CAF/tumor-conditioned media (CM) with/without IL1R1 inhibition in a transwell system. MDSC contribution to iTME was assessed by co-culturing MDSCs from CAF-Il1r1KO tumors and splenic T cells from naïve C57BL/6 mice. To investigate the effects of IL1R1 deletion in overcoming therapeutic resistance, survival studies in CAF-Il1r1KO mice with chemotherapy were conducted. RESULTS: Treatment of PKT mice with IL1R1 antagonist diminished transcriptional levels of Il6 and Cxcl1, iCAF-associated cytokines, in the CAF compartment. Compared to littermate controls, orthotopic tumors in CAF-Il1r1KO showed significant reduction in tumor weights, increased CD8+ T cell infiltration, and overall reduction in polymorphonuclear (PMN) MDSC trafficking by flow cytometry. Moreover, migration of BMDCs was reduced when co-cultured with CAF/tumor CM and IL1R1 antagonist. In addition, co-culture of MDSCs from CAF-Il1r1KO mice with naïve T cells showed diminished inhibition of T cell functional activity. Chemotherapy treatment of orthotopic tumors in CAF-Il1r1KO mice showed significantly decreased tumor size and improved survival compared to tumors in littermate controls. CONCLUSION: Our findings illustrate a novel mechanism of CAF-specific disruption of IL1R1 signaling inhibiting trafficking of immunosuppressive MDSCs and increased infiltration of cytotoxic CD8+ T cells in the PDAC TME. These data pave the way for novel combinatorial treatment strategies targeting IL1R1 to overcome chemotherapeutic resistance through reprogramming of the stromal compartment in PDAC. Citation Format: Camille Acevedo, Samara Singh, Austin Dosch, Edmond W Box, Iago C Silva, Anna Bianchi, Siddharth Mehra, Haleh Amirian, Andrew Adams, Nagaraj Nagathihalli, Jashodeep Datta, Nipun B Merchant. Fibroblast-specific IL1 receptor inhibition reprograms the inflammatory stroma to overcome the immunosuppressive tumor microenvironment in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A047.

Abstract A061: DKK3 in pancreatic cancer – Elucidating the roles of a double-edged sword

Abstract Pancreatic ductal adenocarcinoma (PDAC) remains a highly challenging disease with a poor prognosis due to lack of diagnostic biomarkers and high tumor heterogeneity. Therefore, it is crucial to meticulously examine the intricate molecular mechanisms in PDAC. We previously identified DKK3 (Dickkopf-3) as a novel factor promoting organ regeneration during pancreatitis and established a previously unknown link between DKK3 and the Wnt and Hedgehog signaling. Given that pancreatitis is a significant risk factor for pancreatic cancer, we were motivated to investigate the potential role of DKK3 in PDAC development. We utilized PDAC mouse models driven by LSL-KrasG12D/+; Ptf1aCre/+ with wildtype, homozygous/heterozygous DKK3 deletion in both epithelial and stromal compartment while employing in vitro and ex vivo systems to examine the stage and compartment-specific roles of the same. Through a comprehensive and time-resolved analysis of tumor characteristics, we discovered that the loss of DKK3 led to rapid oncogenic transformation, marked by a significant increase in metaplasia and desmoplasia starting at an early stage (10 weeks). Ex vivo acinar-to-ductal metaplasia assay and rescue experiments with wildtype and DKK3-null acinar cells revealed that secreted DKK3 operates as a tumor suppressive roadblock in PDAC-initiating steps. This advanced preneoplastic stage translated into accelerated progression toward invasive tumors at 36 weeks, a shortened overall survival, and a higher liver metastasis incidence in the DKK3-null animals at the endpoint. Interestingly, transcriptomic analyses further validated our observation and revealed the involvement PI3-AKT signaling pathway as an underlying mechanism. Further characterization of isolated tumor cells confirmed our observations, revealing prominent mesenchymal features and enhanced migratory capacities upon loss of DKK3. Interestingly, DKK3-null PDACs exhibited a pronounced stroma remodeling with a myofibroblastic cancer-associated fibroblast-enriched environment, as well as an immunosuppressive stroma with abundant regulatory T cells and cytotoxic T cell depletion, as substantiated by coculture experiments. Intriguingly, while displaying similar phenotypic features to DKK3-null tumors, Dkk3+/- heterozygotes exhibited the most aggressive outcome. To further dissect this finding, we conducted a set of in silico approaches and immunostainings revealing persistent stromal DKK3 expression in DKK3- proficient PDACs. This suggested a possible dual role of DKK3 that could operate either as a friend or a foe depending on its spatiotemporal expression in PDAC. In line, in vitro systems demonstrated a distinct oncogenic effect of DKK3 on endpoint tumor cells, particularly promoting malignant cell migration. In summary, we propose that epithelial DKK3 exerts cell-autonomous tumor suppressive functions during the onset of PDAC, while stromal DKK3 acts as an oncogenic cue driving cancer progression. These findings highlight DKK3 as a promising biomarker and a novel therapeutic target for PDAC tumors. Citation Format: Dharini Srinivasan, Frank Arnold, Elodie Roger, Anna Härle, Michael K Melzer, Chantal Allgöwer, Patrick C Hermann, Lukas Perkhofer, Johann Gout, Alexander Kleger. DKK3 in pancreatic cancer – Elucidating the roles of a double-edged sword [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A061.

Abstract B080: A porcine model of pancreatic ductal adenocarcinoma for human scale translational cancer research

Abstract Pancreatic ductal adenocarcinoma (PDAC) remains a highly fatal form of cancer, requiring urgent advancements in diagnostic and therapeutic strategies. Although PDAC mouse models have been crucial in advancing our comprehension of the disease, they present some limitations in replicating key human PDAC aspects. In this study, we present the development of the first large animal model of pancreatic cancer via Cre activatable mutations in the endogenous KRAS and TP53 genes 1,2. In order to activate these mutations in the pancreas, two Cre driver pig lines expressing Cre recombinase from PTF1A 3 and PDX1 were created. Crossing both Cre lines with pigs carrying latent KRAS G12D and TP53 R167H alleles produced double (KC) and triple (KPC) genetically modified animals. Pathological analyses revealed the presence of inter- and intralobular fibrosis with multifocal acinar-to-ductal metaplasia (ADM), some low-grade PanINs, dysplasia, inflammation and duct obstruction in most of the KPC pigs between 3 to 6 months of age. Interestingly, the majority of these pigs already exhibited local metastasis in the lymph nodes, suggesting that the metastatic potential is established early in the tumorigenic process. Age-matched KC pigs exhibited mainly ADM with dysplasia. Flow cytometry and RNA expression analyses of the established pancreatic tumour primary cells revealed a pronounced epithelial-to-mesenchymal transition (EMT). Moreover, both bulk tumour samples and primary tumour cells showed high expression of the pancreatic cancer stem cell marker CD44, with differential expression of its isoforms, including the major isoform and variants 6 and 9. In addition, histological and molecular analyses revealed notable similarities between pig and human PDAC, including molecular subtypes, neuronal invasion and loss of acinar identity. These findings highlight the unique advantage of the pig PDAC model, that allows longitudinal and multi-regional tumour sampling in the absence of any therapeutic interventions. This makes it a valuable tool for developing new diagnostic and therapeutic approaches that can greatly improve patient outcomes in the long run.

Abstract A073: Desmoglein-2 is a regulator of pancreatic ductal adenocarcinoma progression

Abstract Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies, with a dismal 5-year survival rate of <13%. We have discovered that desmoglein-2 (DSG2), a cell surface protein, is highly expressed on PDAC cells. In silico data indicate that elevated levels of DSG2 is associated with PDAC progression and poor patient survival. Immunohistochemistry (IHC) analysis of a tissue microarray of 302 patient samples showed that DSG2 was expressed by >90% of PDAC patients. We hypothesized that DSG2 is an under-appreciated contributor to PDAC progression and that DSG2 can be targeted. The main aims of this study were to: 1) investigate the role of DSG2 in PDAC cell function in vitro, 2) investigate the molecular biology underpinning the role of DSG2 in PDAC, and 3) to use murine PDAC tumor models to evaluate the contribution of DSG2 to cancer progression in vivo. Our in vitro data showed that reducing the expression of DSG2 (via small interfering RNA (siRNA)) significantly decreased PDAC cell proliferation, migration, and invasion. Moreover, signaling analysis of PDAC cells with or without DSG2 (via siRNA) using a reverse-phase protein array and cytokine array revealed that DSG2 modulates pro-tumorigenic and pro-metastatic cellular pathways, through reducing the effects of certain proteins. Particular alterations were observed in pathways involving gene regulation (e.g., beta-catenin), migration (e.g., epidermal growth factor receptor and integrin-beta1), and cytokine release (e.g., serpine-1). Next, in an orthotopic xenograft mouse model, BxPC-3 PDAC cells with a stable knockdown of DSG2 (via short-hairpin RNA) were injected into NSG (NOD scid gamma) mice, where we observed a significant reduction in tumor burden and liver metastasis when compared to control mice. IHC staining of tumor sections revealed that the DSG2 knockdown tumors contained reduced levels of collagen, tumor vasculature and cancer associated fibroblasts. Thus, suggesting that DSG2 also has a modulatory effect on the tumor microenvironment (TME). A similar reduction in tumor burden, cancer progression and changes to the TME were observed when a neutralizing anti-DSG2 monoclonal antibody was administered intraperitoneally twice a week at 5mg/kg to BxPC-3 tumor bearing mice. Finally, to investigate the immune cell landscape, we used an orthotopic syngeneic mouse model, whereby Dsg2 was knocked out of KPC (LSL-KrasG12D/+; LSL-Trp53R172H/+; Pdx-1-Cre) mouse PDAC cells via clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9. This mouse model also showed that loss of Dsg2 resulted in a significant reduction in tumor burden, cancer cell metastasis and changes to the TME. In summary, we have identified a potential new target for the treatment of PDAC, namely DSG2, and future experiments are pursuing clinical opportunities to improve PDAC patient survival. Citation Format: Charlie B Ffrench, Kay K Myo Min, Mark DeNichilo, Michaelia P Cockshell, Emma L Dorward, Emma J Thompson, Michael Ortiz, Michael S Samuel, Savio George Barreto, Claudine S Bonder. Desmoglein-2 is a regulator of pancreatic ductal adenocarcinoma progression [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A073.

Abstract PR-08: Reprogramming and selective recruitment of distinct neutrophil subpopulations restrain cancer metastasis

Abstract Neutrophils are integral to the metastatic tumor microenvironment (TME), and discrete subsets of neutrophils have been associated with pro- and anti-tumor responses. However, the composition of neutrophils in the metastatic TME and strategies to harness neutrophils for the treatment of metastatic disease remain poorly understood. Here, we studied the role of neutrophils in metastatic disease using mouse models of metastatic pancreatic ductal adenocarcinoma (PDAC). By utilizing mouse PDAC cells driven by mutant KRAS and p53 with controllable expression of ovalbumin, an immunogenic antigen (“TumorAg ON” or “TumorAg OFF”), we found that TumorAg ON PDAC engendered more than 10-fold higher recruitment of neutrophils into liver metastatic lesions compared to TumorAg OFF PDAC. RNA sequencing analysis of micro-dissected metastatic lesions showed that TumorAg ON PDAC elicited transcription of genes associated with neutrophil chemotaxis, including Cxcr2 and its ligands. Multimodal immune phenotyping and imaging mass cytometry (IMC) analysis further revealed that neutrophils within metastatic lesions consisted of CXCR2high and CXCR2low subpopulations and were spatially associated with distinct subsets of tumor cells, T cells, and myeloid cells. In both mouse models of liver and lung metastasis, small molecule inhibition of CXCR2 using SX-682 led to enrichment of CXCR2low neutrophils and reduced metastatic burden in TumorAg ON PDAC. In contrast, CXCR2 inhibition had no impact on metastatic burden in TumorAg OFF PDAC. To define the subpopulations of neutrophils in further depth, we also performed single-cell spatial transcriptomics using Xenium. Notably, CXCR2 inhibition in TumorAg ON PDAC, but not in TumorAg OFF, led to enrichment of neutrophil subsets that expressed higher levels of Mpo, Nos2, and Ly6g and lower levels of Cxcr2 and Siglecf into metastatic lesions. In this setting, depletion of neutrophils using anti-Ly6G antibodies worsened metastatic burden, highlighting anti-tumor properties of these neutrophil subsets in the presence of antigenic recognition. Indeed, in a highly immune-resistant model of PDAC, 6419c5, the use of tumor-targeting listeria vaccine CRS-207 along with CXCR2 inhibition significantly reduced metastatic burden, whereas CXCR2 inhibitor or CRS-207 alone had no impact. To extend the clinical relevance of these observations, we analyzed serial tissue biopsies collected from patients with metastatic PDAC in the liver treated with immunotherapy regimen incorporating CRS-207 (NCT03190265). Consistent with our mouse model results, IMC analysis revealed increased proportion of MPOhigh NOS2high neutrophils upon treatment, suggesting that induction of tumor antigen response results in an effective remodeling of the neutrophil compartment . Taken together, our results show that neutrophils may acquire anti-tumor properties under appropriate inflammatory conditions and that distinct subpopulations of neutrophils may be leveraged for the treatment of metastatic disease. Citation Format: Jae W Lee, Diana Caroline Vargas Carvajal, Yeonju Cho, Sarah M Shin, Erin M Coyne, Alexei Hernandez, Courtney D Cannon, Xuan Yuan, Zhehao Zhang, Nicole E Gross, Soren Charmsaz, Daniel H Shu, Katherine M Bever, Dung T Le, Luciane T Kagohara, Elizabeth M Jaffee, Won Jin Ho. Reprogramming and selective recruitment of distinct neutrophil subpopulations restrain cancer metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr PR-08.