Tuft cells transdifferentiate to neural-like progenitor cells in the progression of pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDA) is partly initiated through the transdifferentiation of acinar cells to metaplastic ducts that act as precursors of neoplasia and cancer. Tuft cells are solitary chemosensory cells not found in the normal pancreas but arise in metaplasia and neoplasia, diminishing as neoplastic lesions progress to carcinoma. Metaplastic tuft cells (mTCs) function to suppress tumor progression through communication with the tumor microenvironment, but their fate during progression is unknown. To determine the fate of mTCs during PDA progression, we have created a lineage tracing model that uses a tamoxifen-inducible tuft-cell specific Pou2f3CreERT/+ driver to induce transgene expression, including the lineage tracer tdTomato or the oncogene Myc. mTC lineage trace models of pancreatic neoplasia and carcinoma were used to follow mTC fate. We found that mTCs, in the carcinoma model, transdifferentiate into neural-like progenitor cells (NRPs), a cell type associated with poor survival in PDA patients. Using conditional knock-out and overexpression systems, we found that Myc activity in mTCs is necessary and sufficient to induce this Tuft-to-Neuroendocrine-Transition (TNT).

Biomarkers of pembrolizumab efficacy in advanced anal squamous cell carcinoma: analysis of a phase II clinical trial and a cohort of long-term responders.

BACKGROUND: Recent trials suggest that programmed cell death 1 (PD-1)-directed immunotherapy may be beneficial for some patients with anal squamous cell carcinoma and biomarkers predictive of response are greatly needed. METHODS: This multicenter phase II clinical trial (NCT02919969) enrolled patients with metastatic or locally advanced incurable anal squamous cell carcinoma (n=32). Patients received pembrolizumab 200 mg every 3 weeks. The primary endpoint of the trial was objective response rate (ORR). Exploratory objectives included analysis of potential predictive biomarkers including assessment of tumor-associated immune cell populations with multichannel immunofluorescence and analysis of circulating tumor tissue modified viral-human papillomavirus DNA (TTMV-HPV DNA) using serially collected blood samples. To characterize the clinical features of long-term responders, we combined data from our prospective trial with a retrospective cohort of patients with anal cancer treated with anti-PD-1 immunotherapy (n=18). RESULTS: In the phase II study, the ORR to pembrolizumab monotherapy was 9.4% and the median progression-free survival was 2.2 months. Despite the high level of HPV positivity observed with circulating TTMV-HPV DNA testing, the majority of patients had low levels of tumor-associated CD8+PD-1+ T cells on pretreatment biopsy. Patients who benefited from pembrolizumab had decreasing TTMV-HPV DNA scores and a complete responder's TTMV-HPV DNA became undetectable. Long-term pembrolizumab responses were observed in one patient from the trial (5.3 years) and three patients (2.5, 6, and 8 years) from the retrospective cohort. Long-term responders had HPV-positive tumors, lacked liver metastases, and achieved a radiological complete response. CONCLUSIONS: Pembrolizumab has durable efficacy in a rare subset of anal cancers. However, despite persistence of HPV infection, indicated by circulating HPV DNA, most advanced anal cancers have low numbers of tumor-associated CD8+PD-1+ T cells and are resistant to pembrolizumab.

DGKα/ζ inhibition lowers the TCR affinity threshold and potentiates antitumor immunity.

Diacylglycerol kinases (DGKs) attenuate diacylglycerol (DAG) signaling by converting DAG to phosphatidic acid, thereby suppressing pathways downstream of T cell receptor signaling. Using a dual DGKα/ζ inhibitor (DGKi), tumor-specific CD8 T cells with different affinities (TRP1high and TRP1low), and altered peptide ligands, we demonstrate that inhibition of DGKα/ζ can lower the signaling threshold for T cell priming. TRP1high and TRP1low CD8 T cells produced more effector cytokines in the presence of cognate antigen and DGKi. Effector TRP1high- and TRP1low-mediated cytolysis of tumor cells with low antigen load required antigen recognition, was mediated by interferon-γ, and augmented by DGKi. Adoptive T cell transfer into mice bearing pancreatic or melanoma tumors synergized with single-agent DGKi or DGKi and antiprogrammed cell death protein 1 (PD-1), with increased expansion of low-affinity T cells and increased cytokine production observed in tumors of treated mice. Collectively, our findings highlight DGKα/ζ as therapeutic targets for augmenting tumor-specific CD8 T cell function.

Transforming Growth Factor-ß Blockade in Pancreatic Cancer Enhances Sensitivity to Combination Chemotherapy.

BACKGROUND & AIMS: Transforming growth factor-b (TGFb) plays pleiotropic roles in pancreatic cancer, including promoting metastasis, attenuating CD8 T-cell activation, and enhancing myofibroblast differentiation and deposition of extracellular matrix. However, single-agent TGFb inhibition has shown limited efficacy against pancreatic cancer in mice or humans. METHODS: We evaluated the TGFß-blocking antibody NIS793 in combination with gemcitabine/nanoparticle (albumin-bound)-paclitaxel or FOLFIRINOX (folinic acid [FOL], 5-fluorouracil [F], irinotecan [IRI] and oxaliplatin [OX]) in orthotopic pancreatic cancer models. Single-cell RNA sequencing and immunofluorescence were used to evaluate changes in tumor cell state and the tumor microenvironment. RESULTS: Blockade of TGFß with chemotherapy reduced tumor burden in poorly immunogenic pancreatic cancer, without affecting the metastatic rate of cancer cells. Efficacy of combination therapy was not dependent on CD8 T cells, because response to TGFß blockade was preserved in CD8-depleted or recombination activating gene 2 (RAG2-/-) mice. TGFß blockade decreased total α-smooth muscle actin-positive fibroblasts but had minimal effect on fibroblast heterogeneity. Bulk RNA sequencing on tumor cells sorted ex vivo revealed that tumor cells treated with TGFß blockade adopted a classical lineage consistent with enhanced chemosensitivity, and immunofluorescence for cleaved caspase 3 confirmed that TGFß blockade increased chemotherapy-induced cell death in vivo. CONCLUSIONS: TGFß regulates pancreatic cancer cell plasticity between classical and basal cell states. TGFß blockade in orthotropic models of pancreatic cancer enhances sensitivity to chemotherapy by promoting a classical malignant cell state. This study provides scientific rationale for evaluation of NIS793 with FOLFIRINOX or gemcitabine/nanoparticle (albumin-bound) paclitaxel chemotherapy backbone in the clinical setting and supports the concept of manipulating cancer cell plasticity to increase the efficacy of combination therapy regimens.

Pancreatic Neoplasms Are Frighteningly Common: A Role for Immune Surveillance?

SUMMARY: Carpenter and colleagues analyze organ donors to find that pancreatic intraepithelial neoplasia (PanIN), the precursor lesions of pancreatic ductal adenocarcinoma, are highly prevalent in the average healthy adult starting from a young age. Why these precursor lesions do not progress to cancer in most people is a mystery. See related article by Carpenter et al., p. 1324 (1).

cIAP1/2 Antagonism Induces Antigen-Specific T Cell-Dependent Immunity.

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.

Ornithine aminotransferase supports polyamine synthesis in pancreatic cancer.

There is a need to develop effective therapies for pancreatic ductal adenocarcinoma (PDA), a highly lethal malignancy with increasing incidence1 and poor prognosis2. Although targeting tumour metabolism has been the focus of intense investigation for more than a decade, tumour metabolic plasticity and high risk of toxicity have limited this anticancer strategy3,4. Here we use genetic and pharmacological approaches in human and mouse in vitro and in vivo models to show that PDA has a distinct dependence on de novo ornithine synthesis from glutamine. We find that this process, which is mediated through ornithine aminotransferase (OAT), supports polyamine synthesis and is required for tumour growth. This directional OAT activity is usually largely restricted to infancy and contrasts with the reliance of most adult normal tissues and other cancer types on arginine-derived ornithine for polyamine synthesis5,6. This dependency associates with arginine depletion in the PDA tumour microenvironment and is driven by mutant KRAS. Activated KRAS induces the expression of OAT and polyamine synthesis enzymes, leading to alterations in the transcriptome and open chromatin landscape in PDA tumour cells. The distinct dependence of PDA, but not normal tissue, on OAT-mediated de novo ornithine synthesis provides an attractive therapeutic window for treating patients with pancreatic cancer with minimal toxicity.

Metabolic requirement for GOT2 in pancreatic cancer depends on environmental context.

Mitochondrial glutamate-oxaloacetate transaminase 2 (GOT2) is part of the malate-aspartate shuttle, a mechanism by which cells transfer reducing equivalents from the cytosol to the mitochondria. GOT2 is a key component of mutant KRAS (KRAS*)-mediated rewiring of glutamine metabolism in pancreatic ductal adenocarcinoma (PDA). Here, we demonstrate that the loss of GOT2 disturbs redox homeostasis and halts proliferation of PDA cells in vitro. GOT2 knockdown (KD) in PDA cell lines in vitro induced NADH accumulation, decreased Asp and α-ketoglutarate (αKG) production, stalled glycolysis, disrupted the TCA cycle, and impaired proliferation. Oxidizing NADH through chemical or genetic means resolved the redox imbalance induced by GOT2 KD, permitting sustained proliferation. Despite a strong in vitro inhibitory phenotype, loss of GOT2 had no effect on tumor growth in xenograft PDA or autochthonous mouse models. We show that cancer-associated fibroblasts (CAFs), a major component of the pancreatic tumor microenvironment (TME), release the redox active metabolite pyruvate, and culturing GOT2 KD cells in CAF conditioned media (CM) rescued proliferation in vitro. Furthermore, blocking pyruvate import or pyruvate-to-lactate reduction prevented rescue of GOT2 KD in vitro by exogenous pyruvate or CAF CM. However, these interventions failed to sensitize xenografts to GOT2 KD in vivo, demonstrating the remarkable plasticity and differential metabolism deployed by PDA cells in vitro and in vivo. This emphasizes how the environmental context of distinct pre-clinical models impacts both cell-intrinsic metabolic rewiring and metabolic crosstalk with the TME.

Inhibition of Hedgehog Signaling Alters Fibroblast Composition in Pancreatic Cancer.

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 Gustatory Sensory G-Protein GNAT3 Suppresses Pancreatic Cancer Progression in Mice.

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.

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.

PDX1 dynamically regulates pancreatic ductal adenocarcinoma initiation and maintenance.

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.