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Purpose:Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease characterized by an extensive fibroinflammatory stroma, which includes abundant cancer-associated fibroblast (CAF) populations. PDAC CAFs are heterogeneous, but the nature of this heterogeneity is incompletely understood. The Hedgehog pathway functions in PDAC in a paracrine manner, with ligands secreted by cancer cells signaling to stromal cells in the microenvironment. Previous reports investigating the role of Hedgehog signaling in PDAC have been contradictory, with Hedgehog signaling alternately proposed to promote or restrict tumor growth. In light of the newly discovered CAF heterogeneity, we investigated how Hedgehog pathway inhibition reprograms the PDAC microenvironment.Experimental Design:We used a combination of pharmacologic inhibition, gain- and loss-of-function genetic experiments, cytometry by time-of-flight, and single-cell RNA sequencing to study the roles of Hedgehog signaling in PDAC.Results:We found that Hedgehog signaling is uniquely activated in fibroblasts and differentially elevated in myofibroblastic CAFs (myCAF) compared with inflammatory CAFs (iCAF). Sonic Hedgehog overexpression promotes tumor growth, while Hedgehog pathway inhibition with the smoothened antagonist, LDE225, impairs tumor growth. Furthermore, Hedgehog pathway inhibition reduces myCAF numbers and increases iCAF numbers, which correlates with a decrease in cytotoxic T cells and an expansion in regulatory T cells, consistent with increased immunosuppression.Conclusions:Hedgehog pathway inhibition alters fibroblast composition and immune infiltration in the pancreatic cancer microenvironment.

Checkpoint blockade immunotherapy has failed in pancreatic cancer and other poorly responsive tumor types in part due to inadequate T cell priming. Naive T cells can receive costimulation not only via CD28 but also through TNF superfamily receptors that signal via NF-κB. Antagonists of the ubiquitin ligases cellular inhibitor of apoptosis protein (cIAP)1/2, also called second mitochondria-derived activator of caspases (SMAC) mimetics, induce degradation of cIAP1/2 proteins, allowing for the accumulation of NIK and constitutive, ligand-independent activation of alternate NF-κB signaling that mimics costimulation in T cells. In tumor cells, cIAP1/2 antagonists can increase TNF production and TNF-mediated apoptosis; however, pancreatic cancer cells are resistant to cytokine-mediated apoptosis, even in the presence of cIAP1/2 antagonism. Dendritic cell activation is enhanced by cIAP1/2 antagonism in vitro, and intratumoral dendritic cells show higher expression of MHC class II in tumors from cIAP1/2 antagonism-treated mice. In this study, we use in vivo mouse models of syngeneic pancreatic cancer that generate endogenous T cell responses ranging from moderate to poor. Across multiple models, cIAP1/2 antagonism has pleiotropic beneficial effects on antitumor immunity, including direct effects on tumor-specific T cells leading to overall increased activation, increased control of tumor growth in vivo, synergy with multiple immunotherapy modalities, and immunologic memory. In contrast to checkpoint blockade, cIAP1/2 antagonism does not increase intratumoral T cell frequencies. Furthermore, we confirm our previous findings that even poorly immunogenic tumors with a paucity of T cells can experience T cell–dependent antitumor immunity, and we provide transcriptional clues into how these rare T cells coordinate downstream immune responses.

Background & Aims Pancreatic ductal adenocarcinoma (PDA) initiation and progression are accompanied by an immunosuppressive inflammatory response. Here, we evaluated the immunomodulatory role of chemosensory signaling in metaplastic tuft cells (MTCs) by analyzing the role of GNAT3, a gustatory pathway G-protein expressed by MTCs, during PDA progression. Methods Gnat3-null (Gnat3-/-) mice were crossbred with animals harboring a Cre-inducible KrasLSL-G12D/+ allele with either Ptf1aCre/+ (KC) or tamoxifen-inducible Ptf1aCreERT/+ (KCERT) mice to drive oncogenic KRAS expression in the pancreas. Ex vivo organoid conditioned medium generated from KC and Gnat3-/-;KC acinar cells was analyzed for cytokine secretion. Experimental pancreatitis was induced in KCERT and Gnat3-/-;KCERT mice to accelerate tumorigenesis, followed by analysis using mass cytometry and single-cell RNA sequencing. To study PDA progression, KC and Gnat3-/-;KC mice were aged to morbidity or 52 weeks. Results Ablation of Gnat3 in KC organoids increased release of tumor-promoting cytokines in conditioned media, including CXCL1 and CXCL2. Analysis of Gnat3-/-;KCERT pancreata found altered expression of immunomodulatory genes in Cxcr2 expressing myeloid-derived suppressor cells (MDSCs) and an increased number of granulocytic MDSCs, a subset of tumor promoting MDSCs. Importantly, expression levels of CXCL1 and CXCL2, known ligands for CXCR2, were also elevated in Gnat3-/-;KCERT pancreata. Consistent with the tumor-promoting role of MDSCs, aged Gnat3-/-;KC mice progressed more rapidly to metastatic carcinoma compared with KC controls. Conclusions Compromised gustatory sensing, achieved by Gnat3 ablation, enhanced the CXCL1/2–CXCR2 axis to alter the MDSC population and promoted the progression of metastatic PDA., Graphical abstract

Pancreatic ductal adenocarcinoma (PDA) is the third most common cause of cancer death in the US with a 11% 5-year survival rate. A key contributor of this dismal prognosis is early and frequent metastatic spread with limited treatment options for patients. Metastasis in PDA is facilitated by a robust fibroinflammatory response in the primary tumor site, a large portion of which is composed of infiltrating immune cells, and survival during transit to establish in the secondary site. In the primary tumor reactive stroma, we found increased eosinophils in both human and mouse PDA compared to the normal pancreas. Eosinophils are an innate immune cell best known for their ability to control parasite responses and have been implicated in either pro- or anti-cancer roles in various solid tumors. We used the ΔdblGata mice, which lack eosinophils, to study the role of eosinophils during metastatic spread using a resectable model of PDA metastasis. This model of metastasis was developed to facilitate consistent seeding of lung metastasis in approximately 50 percent of mice from a transient subcutaneous tumor which undergoes subsequent surgical removal and harvest to evaluate metastasis at 4 weeks. We found that mice lacking eosinophils have increased metastasis to the lung in our resectable model of PDA metastasis but no difference in establishment of IV injected PDA tumor cells, suggesting eosinophil control at the primary tumor site. Single cell sequencing of the subcutaneous tumors finds differences in the angiogenic subtypes, tip and stalk cells, in mice lacking eosinophils. Sequencing of eosinophil populations in humans and mice find an increase in angiogenic signaling suggesting a regulatory role in tumor cell access to the circulation. We conclude that eosinophils in PDA inhibit the metastatic process through control of angiogenic signaling. Citation Format: Megan T. Hoffman, Patrick J. Lenehan, Jennifer Wang, Lestat Ali, Li Qiang, Amiko Uchida, Sara Vayrynen, Andressa Dias Costa, Michael Dougan, Max Heckler, Jonathan Nowak, Brian W. Wolpin, Stephanie K. Dougan. Eosinophils alter metastatic spread in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B018.

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease characterized by an extensive fibroinflammatory stroma, which includes abundant cancer-associated fibroblast (CAF) populations. PDAC CAFs are heterogeneous, but the nature of this heterogeneity is incompletely understood. The Hedgehog pathway functions in PDAC in a paracrine manner, with ligands secreted by cancer cells signaling to stromal cells in the microenvironment. Previous reports investigating the role of Hedgehog signaling in PDAC have been contradictory, with Hedgehog signaling alternately proposed to promote or restrict tumor growth. In light of the newly discovered CAF heterogeneity, we investigated how Hedgehog pathway inhibition reprograms the PDAC microenvironment. Experimental Design: We used a combination of pharmacologic inhibition, gain- and loss-of-function genetic experiments, cytometry by time-of-flight, and single-cell RNA sequencing to study the roles of Hedgehog signaling in PDAC. Results: We found that Hedgehog signaling is uniquely activated in fibroblasts and differentially elevated in myofibroblastic CAFs (myCAF) compared with inflammatory CAFs (iCAF). Sonic Hedgehog overexpression promotes tumor growth, while Hedgehog pathway inhibition with the smoothened antagonist, LDE225, impairs tumor growth. Furthermore, Hedgehog pathway inhibition reduces myCAF numbers and increases iCAF numbers, which correlates with a decrease in cytotoxic T cells and an expansion in regulatory T cells, consistent with increased immunosuppression. Conclusions: Hedgehog pathway inhibition alters fibroblast composition and immune infiltration in the pancreatic cancer microenvironment.

The tumor microenvironment (TME) in pancreatic ductal adenocarcinoma (PDA) restricts vascularization and, consequently, access to blood-derived nutrients and oxygen, which impacts tumor growth. Intracellular redox imbalance is another restraint on cellular proliferation, yet it is unknown if the TME contributes to the maintenance of redox homeostasis in PDA cells. Here, we demonstrate that the loss of mitochondrial glutamate-oxaloacetate transaminase 2 (GOT2), a component in the malate-aspartate shuttle, disturbs redox homeostasis and halts proliferation of PDA cells in vitro. In contrast, GOT2 inhibition has no effect on in vivo tumor growth or tumorigenesis in an autochthonous model. We propose that this discrepancy is explained by heterocellular pyruvate exchange from the TME, including from cancer associated fibroblasts. More broadly, pyruvate similarly confers resistance to inhibitors of mitochondrial respiration. Genetic or pharmacologic inhibition of pyruvate uptake or metabolism abrogated pyruvate-mediated alleviation of reductive stress from NADH buildup. In sum, this work describes a potential resistance mechanism mediated by metabolic crosstalk within the pancreatic TME. These findings have important implications for metabolic treatment strategies since several mitochondrial inhibitors are currently in clinical trials for PDA and other cancers.

Pancreatic ductal adenocarcinoma (PDA) is unique as it is marked by a dramatic increase in the collagen deposition tumor microenvironment. This microenvironment in pancreatic tumors is composed of immune cells and reactive fibroblasts, with the tumor cells themselves comprising only a small proportion of the overall mass. Nearby normal epithelial tissue is also reactive, undergoing a transdifferentiation event known as acinar-to-ductal metaplasia (ADM), where normal acinar cells are replaced by metaplastic duct-like structures. Collectively neoplastic and metaplastic epithelium orchestrate the immune and fibrotic response, and understanding how the pancreatic epithelia communicate to the microenvironment may lead to more effective clinical treatments. Metaplastic tuft cells (MTCs) are a specialized subset of the epithelium that has the potential to drive tumor progression through communication with the microenvironment and modulate PDA progression. Also known as solitary chemosensory cells, tuft cells were first discovered in rodent luminal surfaces more than 60 years ago. They are characterized by the “tuft” of microvilli reaching into the lumen and, only recently, studies have started to determine the role of normal tuft cells in different organs. These studies determined that tuft cells have different roles depending on the organ in which they reside. Studies have shown that tuft cells are not present in a normal pancreas. MTCs are only present in the pancreas in PanINs during PDA progression in both humans and mice. Furthermore, the population of MTCs in the pancreas disappears as PDA progresses into invasive carcinoma. MTCs also express other markers outside of the taste sensing proteins, including POU2f3/SKN-1alpha, and DCLK1. We know little about the role of MTCs in the pancreas, but prior studies have suggested their role as a progenitor cell during PDA. However, these studies do not exclusively mark MTCs during their genesis in a progressive model of PDA due to a lack of mouse model as well as the complexity of culturing them ex vivo. We have generated a unique mouse model to drive lineage tracing of MTCs during PDA, and I have preliminary data to suggest that tuft cells can transdifferentiate into neuroendocrine-like cells during PDA progression. Neuroendocrine (NE) cells are found in aggressive cancers such as prostate and small cell lung cancer. They are characterized by markers such as Synaptophysin (SYP), as well as an upregulation of MYC which has been found to be more aggressive in different cancers. Rosalie Sears, at the Oregon Health and Science University, a specialist of MYC function in PDA, has shown that NE cells in the pancreas not only originate from acinar cells, where MTCs originate but whose presence is associated with poor survival and resistance to treatment in PDA. She has also shown that MYC plays a key role in the regulation of NE cells in PDA. Through my dissertation research, I will investigate tuft to NE-like transdifferentiation and its role in PDA progression. Citation Format: Daniel J. Salas-Escabillas, Megan Hoffman, Howard C. Crawford. Understanding the lineage of metaplastic tuft cells in the progression of PDA [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-059.

Pancreatic ductal adenocarcinoma (PDA) is the third most common cause of cancer death in the US with a 9% 5-year survival rate. PDA is characterized by a robust stromal reaction, a large portion of which is composed of infiltrating immune cells and supported by fibroblasts. This fibroinflammatory response promotes both the initiation and progression of PDA. Key to this progression is the crosstalk between the tumor epithelium and immune compartment. Metaplastic tuft cells (MTCs) are a subset of the neoplastic epithelium derived by the transdifferentiation of acinar cells. Tuft cells have been characterized to have a “sense-and-respond” role in luminal surfaces throughout the body, using the taste chemosensory system to promote an inflammatory response in infected and damaged tissues. Among the pancreatic epithelium, MTCs uniquely express components of the gustation sensory system including taste receptors, TRPM5 and αGustducin, as well as an array of inflammatory cytokines, suggesting they are capable of promoting an immune response to extracellular challenges. To explore this hypothesis, we ablated αGustducin, a key protein in the chemosensory cascade, in a model of pancreatitis-associated tumorigenesis. We found that neoplasia in the GNAT3-/-; KrasG12D; PTF1aCreERT mice initiates and progresses more rapidly, a difference associated with alteration in immune cell subtypes. To further quantitate changes in the immune response, we performed mass cytometry (CyTOF), as a way to explore changes in cell number and type, and single-cell sequencing, to more deeply probe the unique gene signatures of cells within the tumor stroma. These large-scale analyses suggest substantial changes in the number of T-cell and myeloid cell populations, as well as alterations of fibroblasts and myeloid cell polarity. We conclude that MTCs use chemosensory signaling to promote the formation of a tumor-suppressive microenvironment. Citation Format: Megan T. Hoffman, Stephanie The, Daniel J. Salas-Escabillas, Kathleen E. DelGiorno, Filip Bednar, Robert F. Margolskee, Arvind Rao, Howard C. Crawford. The role of metaplastic tuft cell chemosensory signaling in pancreatic cancer [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 A19.

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., Neuroendocrine differentiation of epithelial tumor cells can contribute to cancer cell resistance and survival. Here, the authors show that dysregulated c-Myc promotes neuroendocrine differentiation in pancreatic ductal adenocarcinoma, leading to poor survival and chemoresistance.

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

Pancreatic ductal adenocarcinoma (PDA) is the second most common cause of cancer death in the US with a 10% 5-year survival rate and, as such, is one of the most common deadly cancers. PDA is characterized by a robust stromal reaction, a large portion of which is composed of infiltrating immune cells. This inflammatory response has been previously shown to promote both the initiation and progression of PDA. Current research has been to understand the interaction between tumor cells and infiltrating immune cells and the contribution to cancer progression. In this work we focus on a specific cell population present in the epithelium during pancreatic tumorigenesis called a tuft cell. Tuft cells have been found in luminal surfaces throughout the body, most notably characterized in the intestine where these cells have been shown to directly regulate the immune response to parasitic infection, but have also been found in the nasal, respiratory and bladder epithelium. These solitary chemosensory cells, as they are also known, use a common chemosensory pathway, previously characterized in type-II taste cells, in order to interact with the luminal environment. Interestingly, tuft cells in the metaplastic pancreas uniquely express TRPM5 and alpha-gustducin, both components of the chemosensory cascade, suggesting these cells have the potential to mediate a response to extracellular signals. Pancreatic tuft cells also make an array of cytokines and immunomodulatory factors that can directly alter the immune response in the tumor microenvironment. These data leads us to hypothesize that tuft cells utilize the chemosensory response pathway to remodel the tumor microenvironment in PDA. In order to answer this question, we ablated a key protein in the chemosensory cascade, alpha-gustducin, and found that this loss increases aggressiveness in a model of pancreatitis-associated tumorigenesis. We are currently exploring differences in the tumor microenvironment that may explain these results. Citation Format: Megan T. Hoffman, Howard Crawford. Tuft cell chemosensory signaling during pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1004.

The tuft cell is a chemosensory cell type that can interpret signals from luminal surfaces throughout the body in order to activate downstream effectors. One clear effector pathway of the tuft cell promotes a type-two immune response in the intestine after parasitic infection, suggesting that this cell population has the ability to communicate with the immune system. Furthermore, tuft cells have also been shown to activate sensory nerve fibers to lead to the production of a neuroinflammatory signal in the nasal epithelium. Therefore, tuft cells can promote effector inflammatory responses through direct immune cell signaling and through sensory nerve fibers. Pancreatic ductal adenocarcinoma (PDA) is characterized by a robust stromal reaction, a large component of which is composed of an immune response. It has been previously studied that this inflammatory response can function to promote both the initiation and progression of PDA. One mechanism by which inflammatory cells can be recruited to the pancreas is through neuroinflammatory pathways. Work with collaborators has shown that pancreatic sensory neurons are required for the progression of PDA, as ablation of this cell type significantly prolongs survival. Interestingly, tuft cells in the metaplastic pancreas have been shown to appear during transdifferentiation and progression to PDA. These tuft cells also possess key signaling elements that have the potential to mediate the response to extracellular signals, such as α-gustducin and TRPM5. Metaplastic tuft cells also produce the proteins necessary to make or release prostaglandins, acetylcholine and ATP, all of which can stimulate either a direct immunomodulatory signal or activate sensory nerve fibers. This leads us to hypothesize that tuft cells are a key mediator of signals to the stromal immune compartment and to sensory neurons in order to promote a robust immune response. In order to answer this question we are using chemosensory knockout animals to ablate critical signaling components of the chemosensory cascade to study the progression of PDA. Citation Format: Megan T. Hoffman, Shan Gao, Howard Crawford.{Authors}. Tuft cell signaling can induce pancreatic inflammation and promote pancreatic ductal adenocarcinoma. [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 B69.