A histone methylation-MAPK signaling axis drives durable epithelial-mesenchymal transition in hypoxic pancreatic cancer

The tumor microenvironment in pancreatic ductal adenocarcinoma (PDAC) plays a key role in tumor progression and response to therapy. The dense PDAC stroma causes hypovascularity, which leads to hypoxia. Here, we showed that hypoxia drives long-lasting epithelial-mesenchymal transition (EMT) in PDAC primarily through a positive-feedback histone methylation-MAPK signaling axis. Transformed cells preferentially underwent EMT in hypoxic tumor regions in multiple model systems. Hypoxia drove a cell-autonomous EMT in PDAC cells which, unlike EMT in response to growth factors, could last for weeks. Furthermore, hypoxia reduced histone demethylase KDM2A activity, suppressed PP2 family phosphatase expression, and activated MAPKs to post-translationally stabilize histone methyltransferase NSD2, leading to an H3K36me2-dependent EMT in which hypoxia-inducible factors played only a supporting role. Hypoxia-driven EMT could be antagonized in vivo by combinations of MAPK inhibitors. Collectively, these results suggest hypoxia promotes durable EMT in PDAC by inducing a histone methylation-MAPK axis that can be effectively targeted with multi-drug therapies, providing a potential strategy for overcoming chemoresistance.

Nanoparticle delivery of innate immune agonists combines with senescence-inducing agents to mediate T cell control of pancreatic cancer

Pancreatic ductal adenocarcinoma has quickly risen to become the 3rd leading cause of cancer-related death. This is in part due to its fibrotic tumor microenvironment (TME) that contributes to poor vascularization and immune infiltration and subsequent chemo- and immunotherapy failure. Here we investigated an innovative immunotherapy approach combining local delivery of STING and TLR4 innate immune agonists via lipid-based nanoparticles (NPs) co-encapsulation with senescence-inducing RAS-targeted therapies that can remodel the immune suppressive PDAC TME through the senescence-associated secretory phenotype. Treatment of transplanted and autochthonous PDAC mouse models with these regimens led to enhanced uptake of NPs by multiple cell types in the PDAC TME, induction of type I interferon and other pro-inflammatory signaling, increased antigen presentation by tumor cells and antigen presenting cells, and subsequent activation of both innate and adaptive immune responses. This two-pronged approach produced potent T cell-driven and Type I interferon-dependent tumor regressions and long-term survival in preclinical PDAC models. STING and TLR4-mediated Type I interferon signaling were also associated with enhanced NK and CD8+ T cell immunity in human PDAC. Thus, combining localized immune agonist delivery with systemic tumor-targeted therapy can synergize to orchestrate a coordinated innate and adaptive immune assault to overcome immune suppression and activate durable anti-tumor T cell responses against PDAC.

Cellular Origins and Lineage Plasticity in Cancer

All cancers arise from normal cells whose progeny acquire the cancer-initiating mutations and epigenetic modifications leading to frank tumorigenesis. The identity of those "cells-of-origin" has historically been a source of controversy across tumor types, as it has not been possible to witness the dynamic events giving rise to human tumors. Genetically engineered mouse models (GEMMs) of cancer provide an invaluable substitute, enabling researchers to interrogate the competence of various naive cellular compartments to initiate tumors in vivo. Researchers using these models have relied on lineage-specific promoters, knowledge of preneoplastic disease states in humans, and technical advances allowing more precise manipulations of the mouse germline. These approaches have given rise to the emerging view that multiple lineages within a given organ may generate tumors with similar histopathology. Here, we review some of the key studies leading to this conclusion in solid tumors and highlight the biological and clinical ramifications.

The mitochondrial Ca2+ channel MCU is critical for tumor growth by supporting cell cycle progression and proliferation

Introduction: The mitochondrial uniporter (MCU) Ca²⁺ ion channel represents the primary means for Ca²⁺ uptake by mitochondria. Mitochondrial matrix Ca²⁺ plays critical roles in mitochondrial bioenergetics by impinging upon respiration, energy production and flux of biochemical intermediates through the TCA cycle. Inhibition of MCU in oncogenic cell lines results in an energetic crisis and reduced cell proliferation unless media is supplemented with nucleosides, pyruvate or α-KG. Nevertheless, the roles of MCU-mediated Ca²⁺ influx in cancer cells remain unclear, in part because of a lack of genetic models. Methods: MCU was genetically deleted in transformed murine fibroblasts for study in vitro and in vivo. Tumor formation and growth were studied in murine xenograft models. Proliferation, cell invasion, spheroid formation and cell cycle progression were measured in vitro. The effects of MCU deletion on survival and cell-death were determined by probing for live/death markers. Mitochondrial bioenergetics were studied by measuring mitochondrial matrix Ca²⁺ concentration, membrane potential, global dehydrogenase activity, respiration, ROS production and inactivating-phosphorylation of pyruvate dehydrogenase. The effects of MCU rescue on metabolism were examined by tracing of glucose and glutamine utilization for fueling of mitochondrial respiration. Results: Transformation of primary fibroblasts in vitro was associated with increased MCU expression, enhanced MCU-mediated Ca²⁺ uptake, altered mitochondrial matrix Ca²⁺ concentration responses to agonist stimulation, suppression of inactivating-phosphorylation of pyruvate dehydrogenase and a modest increase of mitochondrial respiration. Genetic MCU deletion inhibited growth of HEK293T cells and transformed fibroblasts in mouse xenograft models, associated with reduced proliferation and delayed cell-cycle progression. MCU deletion inhibited cancer stem cell-like spheroid formation and cell invasion in vitro, both predictors of metastatic potential. Surprisingly, mitochondrial matrix [Ca²⁺], membrane potential, global dehydrogenase activity, respiration and ROS production were unaffected. In contrast, MCU deletion elevated glycolysis and glutaminolysis, strongly sensitized cell proliferation to glucose and glutamine limitation, and altered agonist-induced cytoplasmic Ca²⁺ signals. Conclusion: Our results reveal a dependence of tumorigenesis on MCU, mediated by a reliance on MCU for cell metabolism and Ca²⁺ dynamics necessary for cell-cycle progression and cell proliferation.

The mitochondrial Ca 2+ channel MCU is critical for tumor growth by supporting cell cycle progression and proliferation

The mitochondrial uniporter (MCU) Ca ²⁺ ion channel represents the primary means for Ca ²⁺ uptake into mitochondria. Here we employed in vitro and in vivo models with MCU genetically eliminated to understand how MCU contributes to tumor formation and progression. Transformation of primary fibroblasts in vitro was associated with increased MCU expression, enhanced mitochondrial Ca ²⁺ uptake, suppression of inactivating-phosphorylation of pyruvate dehydrogenase, a modest increase of basal mitochondrial respiration and a significant increase of acute Ca ²⁺ -dependent stimulation of mitochondrial respiration. Inhibition of mitochondrial Ca ²⁺ uptake by genetic deletion of MCU markedly inhibited growth of HEK293T cells and of transformed fibroblasts in mouse xenograft models. Reduced tumor growth was primarily a result of substantially reduced proliferation and fewer mitotic cells in vivo , and slower cell proliferation in vitro associated with delayed progression through S-phase of the cell cycle. MCU deletion inhibited cancer stem cell-like spheroid formation and cell invasion in vitro , both predictors of metastatic potential. Surprisingly, mitochondrial matrix Ca ²⁺ concentration, membrane potential, global dehydrogenase activity, respiration and ROS production were unchanged by genetic deletion of MCU in transformed cells. In contrast, MCU deletion elevated glycolysis and glutaminolysis, strongly sensitized cell proliferation to glucose and glutamine limitation, and altered agonist-induced cytoplasmic Ca ²⁺ signals. Our results reveal a dependence of tumorigenesis on MCU, mediated by a reliance on mitochondrial Ca ²⁺ uptake for cell metabolism and Ca ²⁺ dynamics necessary for cell-cycle progression and cell proliferation.

Tumor-Suppressive and Immune-Stimulating Roles of Cholesterol 25-hydroxylase in Pancreatic Cancer Cells

Cholesterol dependence is an essential characteristic of pancreatic ductal adenocarcinoma (PDAC). Cholesterol 25-hydroxylase (CH25H) catalyzes monooxygenation of cholesterol into 25-hydroxycholesterol, which is implicated in inhibiting cholesterol biosynthesis and in cholesterol depletion. Here, we show that, within PDAC cells, accumulation of cholesterol was facilitated by the loss of CH25H. Methylation of the CH25H gene and decreased levels of CH25H expression occurred in human pancreatic cancers and was associated with poor prognosis. Knockout of Ch25h in mice accelerated progression of Kras-driven pancreatic intraepithelial neoplasia. Conversely, restoration of CH25H expression in human and mouse PDAC cells decreased their viability under conditions of cholesterol deficit, and decelerated tumor growth in immune competent hosts. Mechanistically, the loss of CH25H promoted autophagy resulting in downregulation of MHC-I and decreased CD8+ T-cell tumor infiltration. Re-expression of CH25H in PDAC cells combined with immune checkpoint inhibitors notably inhibited tumor growth. We discuss additional benefits that PDAC cells might gain from inactivation of CH25H and the potential translational importance of these findings for therapeutic approaches to PDAC.

IMPLICATIONS

Loss of CH25H by pancreatic cancer cells may stimulate tumor progression and interfere with immunotherapies.

Phase Ib and Expansion Study of Gemcitabine, Nab-Paclitaxel, and Ficlatuzumab in Patients With Metastatic Pancreatic Cancer

BACKGROUND

In preclinical pancreatic ductal adenocarcinoma (PDAC) models, inhibition of hepatocyte growth factor (HGF) signaling using ficlatuzumab, a recombinant humanized anti-HGF antibody, and gemcitabine reduced tumor burden.

METHODS

Patients with previously untreated metastatic PDAC enrolled in a phase Ib dose escalation study with 3 + 3 design of 2 dose cohorts of ficlatuzumab 10 and 20 mg/kg administered intravenously every other week with gemcitabine 1000 mg/m2 and albumin-bound paclitaxel 125 mg/m2 given 3 weeks on and 1 week off. This was followed by an expansion phase at the maximally tolerated dose of the combination.

RESULTS

Twenty-six patients (sex, 12 male:14 female; median age, 68 years [range, 49-83 years]) were enrolled, 22 patients were evaluable. No dose-limiting toxicities were identified (N = 7 pts) and ficlatuzumab at 20 mg/kg was chosen as the maximum tolerated dose. Among the 21 patients treated at the MTD, best response by RECISTv1.1: 6 (29%) partial response, 12 (57%) stable disease, 1 (5%) progressive disease, and 2 (9%) not evaluable. Median progression-free survival and overall survival times were 11.0 months (95% CI, 7.6-11.4 months) and 16.2 months (95% CI, 9.1 months to not reached), respectively. Toxicities attributed to ficlatuzumab included hypoalbuminemia (grade 3, 16%; any grade, 52%) and edema (grade 3, 8%; any grade, 48%). Immunohistochemistry for c-Met pathway activation demonstrated higher tumor cell p-Met levels in patients who experienced response to therapy.

CONCLUSION

In this phase Ib trial, ficlatuzumab, gemcitabine, and albumin-bound paclitaxel were associated with durable treatment responses and increased rates of hypoalbuminemia and edema.

Abstract C054: Hypoxia promotes a durable epithelial-mesenchymal transition in pancreas cancer through a histone methylation-MAPK signaling axis

Pancreatic ductal adenocarcinoma (PDAC) tumors are poorly vascularized and exhibit regions of hypoxia. Here, we demonstrate that this feature of the tumor microenvironment promotes epithelial-mesenchymal transition (EMT), which occurs early in PDAC and drives chemoresistance, and we identify the underlying signaling mechanism. Analysis of publicly-available human transcriptomics and proteomics demonstrated that PDAC cells or tumors enriched in mesenchymal markers were also enriched in markers of hypoxia or HIF activity. Furthermore, in lineage-traced autochthonous, orthotopic patient-derived xenograft, and orthotopic or subcutaneous implanted cell line models of PDAC, hypoxic tumor tissue regions were enriched for neoplastic cells that had undergone EMT. In cell culture experiments, PDAC cells from human and mouse tumors exhibited an ability to undergo EMT in response to 1% O2, with loss of membranous E-cadherin, increased vimentin protein expression, and transcriptional changes indicative of both hypoxia and EMT. Moreover, EMT in response to hypoxia was substantially more persistent than that observed in response to growth factors, and a hypoxia fate mapping system revealed that once-hypoxic cells could retain mesenchymal characteristics outside hypoxic tumor regions. To understand the mechanism for EMT in response to low oxygen tension, we constructed a multivariable linear regression model of the dependence of the hypoxic gene signature on different gene sets in PDAC ductal cells, which identified MAPK signaling as the most important feature. Consistent with the model inference, in both in vitro and in vivo settings, hypoxic cells showing evidence of EMT displayed elevated MAPK signaling. We further demonstrated that MAPK activation in hypoxia was potentiated by suppressed activity of a histone demethylase and concomitant loss of protein phosphatase expression, which reinforced the mechanism by stabilizing the expression of a histone methyltransferase. Thus, this study identifies a tumor microenvironment-initiated mechanism leading to EMT and nominates several potential drug targets whose antagonism may promote PDAC chemoresponse.

Citation Format: Brooke A. Brown, Paul J. Myers, Sara J. Adair, Jason R. Pitarresi, Shiv Sah Teli, Peppi Karppinen, Ben Z. Stanger, Todd W. Bauer, Matthew J. Lazzara. Hypoxia promotes a durable epithelial-mesenchymal transition in pancreas cancer through a histone methylation-MAPK signaling axis [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 C054.

STAT3 in tumor fibroblasts promotes an immunosuppressive microenvironment in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is associated with an incredibly dense stroma, which contributes to its recalcitrance to therapy. Cancer-associated fibroblasts (CAFs) are one of the most abundant cell types within the PDAC stroma and have context-dependent regulation of tumor progression in the tumor microenvironment (TME). Therefore, understanding tumor-promoting pathways in CAFs is essential for developing better stromal targeting therapies. Here, we show that disruption of the STAT3 signaling axis via genetic ablation of Stat3 in stromal fibroblasts in a Kras G12D PDAC mouse model not only slows tumor progression and increases survival, but re-shapes the characteristic immune-suppressive TME by decreasing M2 macrophages (F480+CD206+) and increasing CD8+ T cells. Mechanistically, we show that loss of the tumor suppressor PTEN in pancreatic CAFs leads to an increase in STAT3 phosphorylation. In addition, increased STAT3 phosphorylation in pancreatic CAFs promotes secretion of CXCL1. Inhibition of CXCL1 signaling inhibits M2 polarization in vitro. The results provide a potential mechanism by which CAFs promote an immune-suppressive TME and promote tumor progression in a spontaneous model of PDAC.

Abstract 788: Prrx1 regulates acinar cell plasticity in Kras-driven pancreatic acinar-to-ductal metaplasia

Introduction: Acinar cells in the adult pancreas demonstrate cellular plasticity and undergo de-differentiation to a progenitor-like cell type with ductal characteristics after injury. This process, termed acinar-to-ductal metaplasia (ADM), is an important feature facilitating pancreas regeneration after injury. In the absence of oncogenic mutations, the ADM lesions resolve and reform the acinar compartment (adaptive ADM). However, in the presence of oncogenic Kras mutations (oncogenic ADM), acinar cells undergo neoplastic transformation after ADM and evolve to pancreatic intraepithelial neoplasia (PanIN), a well-known precursor of pancreatic ductal adenocarcinoma (PDAC). We have characterized the role of Paired-Related Homeobox1 (PRRX1) in adaptive ADM. We demonstrated through our novel conditional Prrx1 knock-out mouse model that loss of Prrx1 abrogated ADM formation. Here we explore the relationship between Prrx1 and mutant Kras on promoting ADM and a pro-ADM microenvironment.

Methods: We generated novel Pdx1-Cre;LSLKrasG12D/+;Prrx1fl/fl;Rosa26YFP/YFP (KCY Prrx1 KO) mice, in which mutant Kras is efficiently expressed and Prrx1 is deleted in a pancreas-specific manner. KCY Prrx1 WT and KO mice were sacrificed at 3 months and 5 months for histological analysis. Immunofluorescence (IF) staining for CK19, characterized for the rate of ADM formation and evaluated for F4/80 and SMA. Quantification of ADM regions, F4/80 and SMA was performed through automated cell-counting of immunofluorescence staining (IF). Dissociated acinar cell culture in collagen was utilized for the evaluation of ADM under ex vivo conditions.

Results: IF staining revealed that KCY Prrx1 KO mice had fewer ADM lesions compared to Prrx1 WT mice at 3 months. This difference became dramatically apparent at the 5 month timepoint. Additionally, lower areas of fibrosis were identified via H&E staining in KCY Prrx1 KO mice, which was accompanied with lower F4/80 and SMA positivity at both 3 months and 5 months. Ex vivo cultures also demonstrated significant reduction in ADM formation in the context of oncogenic Kras and loss of Prrx1.

Conclusions: PRRX1 can influence ADM formation in both a cell-intrinsic and cell-extrinsic manner in the presence of oncogenic KRAS. Our preliminary data suggest Prrx1 facilitates PDAC progression through PanIN formation. We will continue to investigate the mechanisms driving Prrx1-dependent ADM formation.

Citation Format: Alina L. Li, Kensuke Sugiura, Kensuke Suzuki, Jason R. Pitarresi, Anna M. Chiarella, Gizem Efe, Rohit Chandwani, Anil K. Rustgi. Prrx1 regulates acinar cell plasticity in Kras-driven pancreatic acinar-to-ductal metaplasia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 788.

Abstract PO-106: The extrinsic and modulatory effects of CSF-1/CSF-1R signaling in generating an immunosuppressive pancreatic cancer tumor microenvironment and promoting metastasis

Introduction: The multistep process of the tumor cell invasion-metastasis cascade, which involves the spread of cancer cells from primary tumor sites to colonization into distant organs, is a major barrier to effective therapy. Both intrinsic factors such as genomic instability and epigenetic alterations and extrinsic factors, such as microenvironmental cues, have been implicated in contributing to the metastatic proclivity of cancer cells. The crosstalk between tumor cells and cells within the heterogenous tumor microenvironment (TME) is a critical driver of tumorigenesis. This can nurture tumor cell migration and invasion into the stroma, providing a foundation for eventual metastasis. Using our mouse models of PDAC, we have identified Colony stimulating factor 1 (Csf-1; also known as M-Csf) to be differentially and significantly upregulated. CSF-1 is secreted by tumor cells to recruit and polarize macrophages into M2-like tumor associated macrophage (TAM) phenotype through binding to its cognate tyrosine kinase receptor colony-stimulating factor 1 receptor (CSF-1R). However, the role and mechanisms of CSF-1/CSF-1R pathway in modulating other elements of the PDAC TME that contributes to invasion and metastasis has yet to be investigated. Methods: We use Pdx1-Cre; LSL-KrasG12D/+; LSL-Trp53R172H; Rosa26LSL-YFP (KPCY) mice and 2D/3D cell culture systems. We overexpressed Csf-1 and established a CRISPR system to knockout Csf-1 in our cells using ribonucleoprotein (RNP) Cas9/gRNA complex via nucleofection. These engineered cells are used to model syngeneic primary and metastatic tumor formation. We have established a novel quantitative multiplex immunofluorescence (qmIF) staining approach to characterize changes in the TME upon modulating Csf-1 expression, specifically focusing on macrophages, myeloid-derived suppressor cell (MDSC), T-cell, B-cell, fibroblast and nerve fiber markers. Results: Our data from in vivo studies suggested that Csf-1 overexpression leads to an increase in primary tumor growth and metastasis, while the depletion of Csf-1 reduces metastatic burden. The automated quantification and analysis of our unbiased IF approaches has yielded the following: CSF-1 overexpression leads to increased tumor infiltration of F4/80+CD163+CD206+ M2-polarized macrophages and decreased number of CD3+CD8+ cytotoxic T-cells, generating an immunosuppressive TME. Furthermore, our preliminary data demonstrated that Csf-1 is also upregulated in cancer associated fibroblasts (CAFs), which potentially synergizes with the epithelial compartment to attract immunosuppressive immune cells and promote immune evasion. Finally, the TCGA data reveals that metastatic PDACs have increased Csf-1 expression compared to primary tumors and overexpression of Csf-1 is associated with reduced survival. Conclusion: We have demonstrated a novel role of CSF-1 upregulation in reprogramming the TME in PDAC and fostering increased metastatic capacity. We believe this can be exploited therapeutically.

Citation Format: Gizem Efe, Kensuke Suzuki, Jason R. Pitarresi, Anna M. Chiarella, Alina L. Li, Anil K. Rustgi. The extrinsic and modulatory effects of CSF-1/CSF-1R signaling in generating an immunosuppressive pancreatic cancer tumor microenvironment and promoting metastasis [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-106.

Patient-derived organoids as a platform for modeling a patient's response to chemoradiotherapy in esophageal cancer

3D patient-derived organoids (PDOs) have been utilized to evaluate potential therapies for patients with different cancers. However, the use of PDOs created from treatment-naive patient biopsies for prediction of clinical outcomes in patients with esophageal cancer has not yet been reported. Herein we describe a pilot prospective observational study with the goal of determining whether esophageal cancer PDOs created from treatment naive patients can model or predict clinical outcomes. Endoscopic biopsies of treatment-naive patients at a single tertiary care center were used to generate esophageal cancer PDOs, which were treated with standard-of-care chemotherapy, gamma-irradiation, and newer non-standard approaches, such as proton beam therapy or two small molecule inhibitors. Clinical outcomes of patients following neoadjuvant treatment were compared to their in vitro PDO responses, demonstrating the PDO's ability to mirror clinical response, suggesting the value of PDOs in prediction of clinical response to new therapeutic approaches. Future prospective clinical trials should test the use of pre-treatment PDOs to identify specific, targeted therapies for individual patients with esophageal adenocarcinoma.

MYC levels regulate metastatic heterogeneity in pancreatic adenocarcinoma

The degree of metastatic disease varies widely amongst cancer patients and impacts clinical outcomes. However, the biological and functional differences that drive the extent of metastasis are poorly understood. We analyzed primary tumors and paired metastases using a multi-fluorescent lineage-labeled mouse model of pancreatic ductal adenocarcinoma (PDAC) - a tumor type where most patients present with metastases. Genomic and transcriptomic analysis revealed an association between metastatic burden and gene amplification or transcriptional upregulation of MYC and its downstream targets. Functional experiments showed that MYC promotes metastasis by recruiting tumor associated macrophages (TAMs), leading to greater bloodstream intravasation. Consistent with these findings, metastatic progression in human PDAC was associated with activation of MYC signaling pathways and enrichment for MYC amplifications specifically in metastatic patients. Collectively, these results implicate MYC activity as a major determinant of metastatic burden in advanced PDAC.

Calcium signaling induces a partial EMT

Epithelial plasticity, or epithelial-to-mesenchymal transition (EMT), is a well-recognized form of cellular plasticity, which endows tumor cells with invasive properties and alters their sensitivity to various agents, thus representing a major challenge to cancer therapy. It is increasingly accepted that carcinoma cells exist along a continuum of hybrid epithelial-mesenchymal (E-M) states and that cells exhibiting such partial EMT (P-EMT) states have greater metastatic competence than those characterized by either extreme (E or M). We described recently a P-EMT program operating in vivo by which carcinoma cells lose their epithelial state through post-translational programs. Here, we investigate the underlying mechanisms and report that prolonged calcium signaling induces a P-EMT characterized by the internalization of membrane-associated E-cadherin (ECAD) and other epithelial proteins as well as an increase in cellular migration and invasion. Signaling through Gαq-associated G-protein-coupled receptors (GPCRs) recapitulates these effects, which operate through the downstream activation of calmodulin-Camk2b signaling. These results implicate calcium signaling as a trigger for the acquisition of hybrid/partial epithelial-mesenchymal states in carcinoma cells.

Pancreatic plasticity: Unlocking exocrine lineage specification

In this issue of Cell Stem Cell, Huang et al. (2021) and Breunig et al. (2021) developed human stem-cell-derived organoid culture systems to recapitulate pancreatic acinar and ductal lineages. This provides opportunities to study cellular plasticity and transformation in pancreatic cancer initiation and progression.

Mutant p53 regulates Survivin to foster lung metastasis

Esophageal squamous cell carcinoma (ESCC) is one of the most lethal cancers worldwide and evolves often to lung metastasis. P53R175H (homologous to Trp53R172H in mice) is a common hot spot mutation. How metastasis is regulated by p53R175H in ESCC remains to be investigated. To investigate p53R175H-mediated molecular mechanisms, we used a carcinogen-induced approach in Trp53R172H/- mice to model ESCC. In the primary Trp53R172H/- tumor cell lines, we depleted Trp53R172H (shTrp53) and observed a marked reduction in cell invasion in vitro and lung metastasis burden in a tail-vein injection model in comparing isogenic cells (shCtrl). Furthermore, we performed bulk RNA-seq to compare gene expression profiles of metastatic and primary shCtrl and shTrp53 cells. We identified the YAP-BIRC5 axis as a potential mediator of Trp53R172H -mediated metastasis. We demonstrate that expression of Survivin, an antiapoptotic protein encoded by BIRC5, increases in the presence of Trp53R172H Furthermore, depletion of Survivin specifically decreases Trp53R172H-driven lung metastasis. Mechanistically, Trp53R172H but not wild-type Trp53, binds with YAP in ESCC cells, suggesting their cooperation to induce Survivin expression. Furthermore, Survivin high expression level is associated with increased metastasis in several GI cancers. Taken together, this study unravels new insights into how mutant p53 mediates metastasis.

PTHrP Drives Pancreatic Cancer Growth and Metastasis and Reveals a New Therapeutic Vulnerability

Pancreatic cancer metastasis is a leading cause of cancer-related deaths, yet very little is understood regarding the underlying biology. As a result, targeted therapies to inhibit metastasis are lacking. Here, we report that the parathyroid hormone-related protein (PTHrP encoded by PTHLH) is frequently amplified as part of the KRAS amplicon in patients with pancreatic cancer. PTHrP upregulation drives the growth of both primary and metastatic tumors in mice and is highly enriched in pancreatic ductal adenocarcinoma metastases. Loss of PTHrP-either genetically or pharmacologically-dramatically reduces tumor burden, eliminates metastasis, and enhances overall survival. These effects are mediated in part through a reduction in epithelial-to-mesenchymal transition, which reduces the ability of tumor cells to initiate metastatic cascade. Spp1, which encodes osteopontin, is revealed to be a downstream effector of PTHrP. Our results establish a new paradigm in pancreatic cancer whereby PTHrP is a driver of disease progression and emerges as a novel therapeutic vulnerability. SIGNIFICANCE: Pancreatic cancer often presents with metastases, yet no strategies exist to pharmacologically inhibit this process. Herein, we establish the oncogenic and prometastatic roles of PTHLH, a novel amplified gene in pancreatic ductal adenocarcinoma. We demonstrate that blocking PTHrP activity reduces primary tumor growth, prevents metastasis, and prolongs survival in mice.This article is highlighted in the In This Issue feature, p. 1601.

Growth of pancreatic cancers with hemizygous chromosomal 17p loss of MYBBP1A can be preferentially targeted by PARP inhibitors

Here, we selectively target pancreatic ductal adenocarcinoma (PDAC) cells harboring a hemizygous gene essential for cell growth. MYB binding protein 1A (MYBBP1A), encoding a chromatin-bound protein, is hemizygous in most of the PDAC due to a chromosome 17p deletion that also spans TP53 We find that hemizygous MYBBP1A loss in isogenic PDAC cells promotes tumorigenesis but, paradoxically, homozygous MYBBP1A loss is associated with impaired cell growth and decreased tumorigenesis. Poly-adenosine 5'-diphosphate-ribose polymerase 1 (PARP1) interacts with MYBBP1A and displaces it from chromatin. Small molecules, such as olaparib, that trap PARP1 to chromatin are able to evict the minimal pool of chromatin-bound MYBBP1A protein in MYBBP1A hemizygous cells and impair cell growth, greater than its impact on wild-type cells. Our findings reveal how a cell essential gene with one allele lost in cancer cells can be preferentially susceptible to a specific molecular therapy, when compared to wild-type cells.

Abstract PO-057: Collateral amplification of the PTHrP gene drives pancreatic cancer growth and metastasis and reveals a new therapeutic vulnerability

Purpose: Metastasis is the leading cause of cancer-related death in PDAC, yet very little is understood regarding the underlying biology. As a result, targeted therapies to inhibit metastasis are lacking. Whole-genome sequencing has established that the squamous/quasi-mesenchymal/basal-like PDAC subtype, which is characterized by its high metastatic proclivity, is annotated by KRAS gene amplification. Here, we report that the squamous lineage gene parathyroid hormone-related protein (PTHrP encoded by PTHLH) is located directly adjacent to KRAS and is co-amplified in metastatic PDAC patients. We hypothesize that this collateral amplification of PTHrP may exert its own oncogenic and pro-metastatic phenotype beyond KRAS and set out to determine if this will confer a novel therapeutic vulnerability.

Methods: We generated a novel genetically engineered mouse model whereby we deleted the cytokine Pthlh in the autochthonous KPCY model. To functionally demonstrate the oncogenic and pro-metastatic roles of PTHrP, we further employed genetic deletion and pharmacological inhibition in orthotopic injection, tail vein metastasis assays, mouse hospital pre-clinical trials, and patient-derived 3D organoid models.

Results: In silico analysis established that PTHLH is co-amplified along with KRAS in TCGA, is specifically enriched in metastatic patients from the COMPASS trial and correlates with significantly decreased overall survival in both cohorts. Further examination revealed that PTHLH is a squamous/quasi-mesenchymal/basal-like lineage marker. We generated KPCY-PthlhCKO mice and showed that they have significantly reduced primary and metastatic tumor burden and dramatically increased overall survival relative to KPCY controls. In parallel experiments, we treated mice with an anti-PTHrP neutralizing monoclonal antibody, which similarly reduced primary and metastatic tumor growth. Finally, RNA-seq revealed a downstream mechanism whereby PTHrP is important for metastatic competency through induction of EMT, thus facilitating entry into the metastatic cascade. Loss of PTHrP reduced the ability of tumor cells to undergo EMT, resulting in a nearly complete elimination of disseminating cells in KPCY-PthlhCKO mice. Thus, KPCY-PthlhCKO tumors are locked in a well-differentiated epithelial state and are unable to initiate the metastatic process.

Conclusions: This work has demonstrated the importance of the previously unappreciated role for PTHrP signaling in pancreatic cancer cell plasticity and metastasis, and future studies will look to translate anti-PTHrP therapy into clinical trials. In a broader sense, we establish a new paradigm of collateral amplification, where an assumed passenger gene (PTHLH) is co-amplified along with a known oncogene (KRAS) and endows the evolving tumor with its own oncogenic and pro-metastatic phenotype.

Citation Format: Jason R. Pitarresi, Robert J. Norgard, Anna M. Chiarella, Richard Kremer, Ben Z. Stanger, Anil K. Rustgi. Collateral amplification of the PTHrP gene drives pancreatic cancer growth and metastasis and reveals a new therapeutic vulnerability [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-057.

Abstract PO-026: The mitochondrial calcium uniporter contributes to PDAC development and invasion

Pancreatic ductal adenocarcinoma (PDAC) has an exceptionally poor prognosis, with about 50,000 new cases and 45,000 deaths each year. While novel chemotherapeutics targeted to driver pathways and immune responses have increased the overall survival rate of cancer patients in general, these improvements are rarely seen in PDAC. PDAC often metastasizes early, and metastases ultimately lead to death in many PDAC patients. A stronger understanding of disease mechanisms and new therapeutic modalities are desperately needed to improve outcomes for many patients. Previously, we showed that cancer cell lines of multiple types are “addicted” to constitutive Ca++ flow into mitochondria through the mitochondrial calcium uniporter (MCU) at endoplasmic reticulum-mitochondria contact sites. We hypothesized that mitochondrial Ca++ influx through MCU contributes to cancer cell development, proliferation, and metastasis in PDAC by promoting metabolic activity within mitochondria. We now show that mRNA expression of MCU is elevated in a subset of pancreatic cancer patients, and high MCU protein expression correlates with poor survival outcomes. In addition, MCU gene expression is associated with the expression of a number of genes which associate with metastasis and/or poor survival outcomes, including ADAM proteins, KRAS, and RAC1. To further examine the role of MCU in PDAC, we used the Pdx1cre; KrasLSL-G12D/+; p53fl/+, Rosa26LSL-YFP/LSL-YFP; Mcufl/fl (KPCY) murine model of PDAC. We generated KPCY-McuKO (knockout) animals and cell lines from their YFP-positive tissues for further analysis. Cell lines developed from KPCY-McuKO pancreatic tissues fail to take up Ca++ into mitochondria in a manner that is rescued by stable re-expression of MCU. This Ca++ uptake is associated with an increase in pyruvate dehydrogenase activation. In these cells, MCU expression is also associated with an increase in cell motility, self-renewal capacity, and cell proliferation. Re-expression of MCU in these cells is associated with a morphological change to a more fibroblastic morphology indicative of epithelial to mesenchymal transition (EMT), including decreased surface expression of e-cadherin. These findings suggest that MCU may contribute to growth and metastasis. Indeed, in an immunocompetent, syngeneic orthotopic model of murine PDAC using one of these cell lines, tumor growth and metastasis were greatly ablated. Such results suggest that MCU-mediated influx of mitochondrial Ca++ contributes to PDAC development and metastasis and may present a therapeutic target for cancer treatment.

Citation Format: Jillian S. Weissenrieder, Jason R. Pitarresi, Emily Fernandez-Garcia, Ben Z. Stanger, Anil K. Rustgi, J. Kevin Foskett. The mitochondrial calcium uniporter contributes to PDAC development and invasion [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-026.

EMT, MET, Plasticity, and Tumor Metastasis

Cancer cell identity and plasticity are required in transition states, such as epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET), in primary tumor initiation, progression, and metastasis. The functional roles of EMT, MET, and the partial state (referred to as pEMT) may vary based on the type of tumor, the state of dissemination, and the degree of metastatic colonization. Herein, we review EMT, MET, pEMT, and plasticity in the context of tumor metastasis.

Pharmacologic Activation of the G Protein-Coupled Estrogen Receptor Inhibits Pancreatic Ductal Adenocarcinoma

BACKGROUND & AIMS

Female sex is associated with lower incidence and improved clinical outcomes for most cancer types including pancreatic ductal adenocarcinoma (PDAC). The mechanistic basis for this sex difference is unknown. We hypothesized that estrogen signaling may be responsible, despite the fact that PDAC lacks classic nuclear estrogen receptors.

METHODS

Here we used murine syngeneic tumor models and human xenografts to determine that signaling through the nonclassic estrogen receptor G protein-coupled estrogen receptor (GPER) on tumor cells inhibits PDAC.

RESULTS

Activation of GPER with the specific, small molecule, synthetic agonist G-1 inhibited PDAC proliferation, depleted c-Myc and programmed death ligand 1 (PD-L1), and increased tumor cell immunogenicity. Systemically administered G-1 was well-tolerated in PDAC bearing mice, induced tumor regression, significantly prolonged survival, and markedly increased the efficacy of PD-1 targeted immune therapy. We detected GPER protein in a majority of spontaneous human PDAC tumors, independent of tumor stage.

CONCLUSIONS

These data, coupled with the wide tissue distribution of GPER and our previous work showing that G-1 inhibits melanoma, suggest that GPER agonists may be useful against a range of cancers that are not classically considered sex hormone responsive and that arise in tissues outside of the reproductive system.

Murine models for familial pancreatic cancer: Histopathology, latency and drug sensitivity among cancers of Palb2, Brca1 and Brca2 mutant mouse strains

Alterations of the PALB2 tumor suppressor gene have been identified in familial breast, ovarian and pancreatic cancer cases. PALB2 cooperates with BRCA1/2 proteins through physical interaction in initiation of homologous recombination, in maintenance of genome integrity following DNA double-strand breaks. To determine if the role of PALB2 as a linker between BRCA1 and BRCA2 is critical for BRCA1/2-mediated tumor suppression, we generated Palb2 mouse pancreatic cancer models and compared tumor latencies, phenotypes and drug responses with previously generated Brca1/2 pancreatic cancer models. For development of Palb2 pancreatic cancer, we crossed conditional Palb2 null mouse with mice carrying the Kras^G12D; p53^R270H; Pdx1-Cre (KPC) constructs, and these animals were observed for pancreatic tumor development. Individual deletion of Palb2, Brca1 or Brca2 genes in pancreas per se using Pdx1-Cre was insufficient to cause tumors, but it reduced pancreata size. Concurrent expression of mutant Kras^G12D and p53^R270H, with tumor suppressor inactivated strains in Palb2-KPC, Brca1-KPC or Brca2-KPC, accelerated pancreatic ductal adenocarcinoma (PDAC) development. Moreover, most Brca1-KPC and some Palb2-KPC animals developed mucinous cystic neoplasms with PDAC, while Brca2-KPC and KPC animals did not. 26% of Palb2-KPC mice developed MCNs in pancreata, which resemble closely the Brca1 deficient tumors. However, the remaining 74% of Palb2-KPC animals developed PDACs without any cysts like Brca2 deficient tumors. In addition, the number of ADM lesions and immune cells infiltrations (CD3⁺ and F/480⁺) were significantly increased in Brca1-KPC tumors, but not in Brca2-KPC tumors. Interestingly, the level of ADM lesions and infiltration of CD3⁺ or F/480⁺ cells in Palb2-KPC tumors were intermediate between Brca1-KPC and Brca2-KPC tumors. As expected, disruption of Palb2 and Brca1/2 sensitized tumor cells to DNA damaging agents in vitro and in vivo. Altogether, Palb2-KPC PDAC exhibited features observed in both Brca1-KPC and Brca2-KPC tumors, which could be due to its role, as a linker between Brca1 and Brca2.

Abstract B43: p120 catenin loss drives pancreatic cancer EMT and metastasis through activation of PTHrP-mediated calcium signaling

Purpose: An unbiased approach to discover candidate cancer genes in pancreatic ductal adenocarcinoma (PDAC) identified the p120 catenin gene (Ctnnd1) as one of the top 20 driver genes, and further analysis revealed that P120CTN loss correlated with reduced survival. Results presented herein used genetically engineered mouse models (GEMMs) to show that P120CTN is a potent metastasis suppressor in PDAC.

Methods: We employed orthotopic injection, tail vein metastasis assays, and mouse hospital preclinical trials to show that deletion or pharmacologic inhibition of Parathyroid Hormone Related Protein (PTHrP/PTHLH), a signaling element downstream of P120CTN, delayed tumor development and metastatic outgrowth. Finally, we generated a novel GEMM of Pthlh deletion to demonstrate in the autochthonous KPC model that loss of PTHrP phenocopies anti-PTHrP therapy by blocking both primary and metastatic tumor growth.

Results: We have generated a mouse model to delete the gene Ctnnd1, whose gene product p120 catenin (P120CTN) is necessary for E-cadherin stability, resulting in enhanced epithelial-to-mesenchymal transition (EMT) and metastasis in KPC animals. Specifically, we show that KPC-p120ctncKO mice have a dramatically enhanced metastatic phenotype relative to KPC controls, suggesting that P120CTN is a critical factor in metastatic cell dissemination. An unbiased screen of tumor cells isolated from these mice identified misregulated calcium signaling through the Parathyroid Hormone Related Protein (PTHrP) as a previously unappreciated contributor to EMT and metastasis. Genetic deletion of the gene that codes for PTHrP in orthotopic transplantation experiments showed significantly reduced tumor growth and metastasis, establishing PTHrP as an oncogenic and prometastatic secreted peptide. Furthermore, treatment with anti-PTHrP monoclonal antibodies reduced tumor cell proliferation and migration in vitro, demonstrating that anti-PTHrP therapies may be of clinical benefit. Importantly, we generated KPC-PthlhcKO mice and showed that they have significantly reduced primary and metastatic tumor burden and increased survival relative to KPC controls. In parallel experiments, we treated KPC mice in a preclinical trial with anti-PTHrP neutralizing antibodies, which delayed both primary and metastatic tumor growth. Finally, analysis of human samples demonstrated that increased PTHLH expression is associated with significantly decreased survival, and that a subset of patients have PTHLH genomic amplifications.

Conclusions: This novel work has demonstrated the importance of the previously unappreciated role that PTHrP-mediated calcium signaling plays in pancreatic cancer cellular plasticity and metastasis, and future studies will look to determine the efficacy of anti-PTHrP monoclonal antibodies with a view towards translation in human clinical trials.

Citation Format: Jason R. Pitarresi, Robert J. Norgard, Ben Z. Stanger, Anil K. Rustgi. p120 catenin loss drives pancreatic cancer EMT and metastasis through activation of PTHrP-mediated calcium signaling [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 B43.

Abstract B38: Calcium signaling induces a partial EMT in pancreatic ductal adenocarcinoma

Metastasis and chemoresistance—the two main reasons for the high mortality of cancer—are associated with a form of cellular plasticity known as epithelial-to-mesenchymal transition (EMT). Cancer cells undergoing EMT become invasive, facilitating metastasis, and undergo a shift in their vulnerability to antineoplastic drugs. In recent work, it has been shown that EMT does not involve a single mechanism but rather a diversity of programs, yielding a continuum of cell phenotypes along the epithelial-mesenchymal spectrum. We previously developed a lineage-traced model of pancreatic ductal adenocarcinoma (PDA) to study EMT in the context of stochastically-arising tumors. As expected, epithelial-mesenchymal plasticity in some tumors involves transcriptional repression of the epithelial state, resulting in a “classical EMT” (C-EMT) phenotype. Surprisingly, however, epithelial-mesenchymal plasticity in the majority of tumors involves post-transcriptional repression of the epithelial state, resulting in a “partial EMT” (P-EMT) phenotype. These two plasticity programs are associated with other aspects of tumor biology as well, including distinct modes of cellular invasion. Here, we identify calcium signaling in pancreatic cancer cells as a regulator of the P-EMT phenotype. Prolonged calcium flux induces PDA cells to remove E-cadherin (ECAD) and other epithelial proteins from the surface and relocalize it intracellularly. This loss of the epithelial phenotype occurs without changes in the abundance of mRNAs for these proteins, reminiscent of the P-EMT phenotype observed in tumors in vivo. In addition, inhibition of the calcium-signaling protein calmodulin blunts this EMT-inducing effect. These results implicate calcium signaling as a mediator of partial EMT phenotypes.

Citation Format: Robert J. Norgard, Ravikanth Maddipati, Nicole M. Aiello, David Balli, Jason R. Pitarresi, Derick N. Rosario-Berrios, Jinyang Li, Salina Yuan, Taiji Yamazoe, Yogev Sela, Allyson J. Merrell, Maximilian D. Wengyn, Kathryn Sun, Anil K. Rustgi, Ben Z. Stanger. Calcium signaling induces a partial EMT in pancreatic ductal adenocarcinoma [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 B38.

PRRX1 isoforms cooperate with FOXM1 to regulate the DNA damage response in pancreatic cancer cells

PRRX1 is a homeodomain transcriptional factor, which has two isoforms, PRXX1A and PRRX1B. The PRRX1 isoforms have been demonstrated to be important in pancreatic cancer, especially in the regulation of epithelial-to-mesenchymal transition (EMT) in Pancreatic Ductal Adenocarcinoma (PDAC) and of mesenchymal-to-epithelial transition (MET) in liver metastasis. In order to determine the functional underpinnings of PRRX1 and its isoforms, we have unraveled a new interplay between PRRX1 and the FOXM1 transcriptional factors. Our detailed biochemical analysis reveals the direct physical interaction between PRRX1 and FOXM1 proteins that requires the PRRX1A/B 200-222/217 amino acid (aa) region and the FOXM1 Forkhead domain. Additionally, we demonstrate the cooperation between PRRX1 and FOXM1 in the regulation of FOXM1-dependent transcriptional activity. Moreover, we establish FOXM1 as a critical downstream target of PRRX1 in pancreatic cancer cells. We demonstrate a novel role for PRRX1 in the regulation of genes involved in DNA repair pathways. Indeed, we show that expression of PRRX1 isoforms may limit the induction of DNA damage in pancreatic cancer cells. Finally, we demonstrate that targeting FOXM1 with the small molecule inhibitor FDI6 suppress pancreatic cancer cell proliferation and induces their apoptotic cell death. FDI6 sensitizes pancreatic cancer cells to Etoposide and Gemcitabine induced apoptosis. Our data provide new insights into PRRX1's involvement in regulating DNA damage and provide evidence of a possible PRRX1-FOXM1 axis that is critical for PDAC cells.

Mechanisms Underlying Metastatic Pancreatic Cancer

Pancreatic ductal adenocarcinoma is an overwhelming fatal disease that often presents with overt metastases and ultimately causes the majority of cancer-associated deaths. The mechanisms underlying the metastatic cascade are complex, and research in recent years has begun to provide insights into the underlying drivers of this phenomenon. It has become clear that cancer cells, in particular pancreatic cancer cells, possess properties of plasticity involving bidirectional transition between epithelial and mesenchymal identities. Furthermore, recent work has begun to establish that there are distinct hybrid states between purely epithelial and purely mesenchymal states that cancer cells may reside, in order to thrive at different stages of carcinogenesis. We discuss how this plasticity is important for different phases of the metastatic cascade, from delamination to colonization, and how different epithelial-mesenchymal states may affect metastatic organotropism. In this review, we summarize the current understanding of pancreatic cancer cell plasticity and metastasis, and highlight current model systems that can be used to study these phenomena.

Disruption of stromal hedgehog signaling initiates RNF5-mediated proteasomal degradation of PTEN and accelerates pancreatic tumor growth

Disrupting paracrine Hedgehog signaling in pancreatic cancer stroma through genetic deletion of fibroblast Smoothened leads to proteasomal degradation of fibroblast PTEN and accelerates tumor growth.

The contribution of the tumor microenvironment to pancreatic ductal adenocarcinoma (PDAC) development is currently unclear. We therefore examined the consequences of disrupting paracrine Hedgehog (HH) signaling in PDAC stroma. Herein, we show that ablation of the key HH signaling gene Smoothened (Smo) in stromal fibroblasts led to increased proliferation of pancreatic tumor cells. Furthermore, Smo deletion resulted in proteasomal degradation of the tumor suppressor PTEN and activation of oncogenic protein kinase B (AKT) in fibroblasts. An unbiased proteomic screen identified RNF5 as a novel E3 ubiquitin ligase responsible for degradation of phosphatase and tensin homolog (PTEN) in Smo-null fibroblasts. Ring Finger Protein 5 (Rnf5) knockdown or pharmacological inhibition of glycogen synthase kinase 3β (GSKβ), the kinase that marks PTEN for ubiquitination, rescued PTEN levels and reversed the oncogenic phenotype, identifying a new node of PTEN regulation. In PDAC patients, low stromal PTEN correlated with reduced overall survival. Mechanistically, PTEN loss decreased hydraulic permeability of the extracellular matrix, which was reversed by hyaluronidase treatment. These results define non-cell autonomous tumor-promoting mechanisms activated by disruption of the HH/PTEN axis and identifies new targets for restoring stromal tumor-suppressive functions.

Regulation of Epithelial Plasticity Determines Metastatic Organotropism in Pancreatic Cancer

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

The LIN28B-IMP1 post-transcriptional regulon has opposing effects on oncogenic signaling in the intestine

RNA-binding proteins (RBPs) are expressed broadly during both development and malignant transformation, yet their mechanistic roles in epithelial homeostasis or as drivers of tumor initiation and progression are incompletely understood. Here we describe a novel interplay between RBPs LIN28B and IMP1 in intestinal epithelial cells. Ribosome profiling and RNA sequencing identified IMP1 as a principle node for gene expression regulation downstream from LIN28B In vitro and in vivo data demonstrate that epithelial IMP1 loss increases expression of WNT target genes and enhances LIN28B-mediated intestinal tumorigenesis, which was reversed when we overexpressed IMP1 independently in vivo. Furthermore, IMP1 loss in wild-type or LIN28B-overexpressing mice enhances the regenerative response to irradiation. Together, our data provide new evidence for the opposing effects of the LIN28B-IMP1 axis on post-transcriptional regulation of canonical WNT signaling, with implications in intestinal homeostasis, regeneration and tumorigenesis.

Abstract PR04: p120 catenin loss drives pancreatic cancer EMT and metastasis through activation of calcium signaling

Purpose: We have generated a mouse model to delete the gene Ctnnd1, whose gene product p120 catenin (p120ctn) is necessary for E-CADHERIN stability, resulting in enhanced metastasis in the conventional KPC pancreatic tumor mouse model. An unbiased screen of tumor cells isolated from these mice identified misregulated calcium signaling as a previously unappreciated contributor to epithelial-to-mesenchymal transition (EMT) and metastasis. Thus, our overarching hypothesis is that p120ctn loss in pancreatic cancer drives EMT and metastasis through functional upregulation of the calcium signaling component PTHLH.

Background: Pancreatic ductal adenocarcinoma (PDAC) is a major health issue, with only 7% of patients surviving beyond 5 years, and increases in PDAC-associated deaths project this disease to be the second leading cause of cancer deaths by 2020. An unbiased approach to discover candidate cancer genes in PDAC identified the p120 catenin gene as one of the top 20 PDAC cancer genes, and further analysis revealed that p120ctn loss was associated with reduced PDAC patient survival. Recent work from our lab further demonstrated that conditional p120ctn/Ctnnd1 deletion in the esophagus was sufficient to drive invasive squamous cell carcinoma, establishing p120ctn/Ctnnd1 as a bona fide tumor-suppressor gene. Results presented herein determined the in vivo role of p120ctn loss in PDAC tumorigenesis and metastasis through genetic mouse models and unbiased RNA-seq analysis.

Methods: A PDAC mouse model was established to study the role of p120ctn in pancreatic carcinogenesis and metastasis. Specifically, LSL-KrasG12D/+; p53fl/+; Pdx1cre; Rosa26LSL-YFP; Ctnnd1fl/wt mice (herein KPCY-p120CKO) were generated to determine the effect of conditional p120ctn loss on pancreatic cancer. Furthermore, RNA-seq was performed on p120-intact or p120-null pancreatic tumor cells isolated from these mice to identify novel mechanisms of pancreatic tumorigenesis and metastasis.

Results: We demonstrate p120ctn loss as a catastrophic event for tumor epithelial cell identity in vivo, leading to enhanced EMT and metastasis. Specifically, we show that KPCY-p120CKO mice have an enhanced metastatic phenotype relative to KPCY controls. Our data therefore suggest that p120ctn is a critical factor in metastatic cell dissemination, and that p120ctn loss results in tumor cells being “locked” in a mesenchymal phenotype by failing to stabilize E-cadherin at the metastatic site. To determine the mechanism of enhanced EMT and metastasis, RNA-seq analysis of p120ctn-null tumor cells was performed, which surprisingly revealed aberrant activation of calcium signaling. Unexpectedly, two of the top five most upregulated genes in p120ctn-null cells were the secreted factor Pthlh and the kinase Camk2b, both of which are key signaling molecules involved in calcium signaling. We demonstrate that PTHLH binding to its cognate receptor leads to cytosolic calcium ion (Ca2+) release, resulting in phosphorylation and activation of CaMKII. We further establish that genetic deletion or pharmacologic inhibition of Pthlh results in proliferation and migration defects. Moreover, orthotopic implantation of KPC-PthlhNULL tumor cell lines reduced tumor growth and metastasis in vivo. Finally, we show that PDAC patients with high expression of Pthlh have significantly decreased survival, suggesting that calcium signaling may be a potent oncogenic pathway in pancreatic cancer and that blocking this pathway may be of therapeutic benefit.

Conclusions: This work has demonstrated the importance of the previously unappreciated role of calcium signaling in pancreatic cancer progression and metastasis, and future studies will look to determine the efficacy of calcium-modulating therapeutics in preclinical models of pancreatic cancer.

This abstract is also being presented as Poster A42.

Citation Format: Jason R. Pitarresi, Maximilian Reichert, Basil Bakir, Leticia Moreira, Lauren Simon, Anil K. Rustgi. p120 catenin loss drives pancreatic cancer EMT and metastasis through activation of calcium signaling [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr PR04.

ETV5 regulates ductal morphogenesis with Sox9 and is critical for regeneration from pancreatitis

BACKGROUND

The plasticity of pancreatic acinar cells to undergo acinar to ductal metaplasia (ADM) has been demonstrated to contribute to the regeneration of the pancreas in response to injury. Sox9 is critical for ductal cell fate and important in the formation of ADM, most likely in concert with a complex hierarchy of, as yet, not fully elucidated transcription factors.

RESULTS

By using a mouse model of acute pancreatitis and three dimensional organoid culture of primary pancreatic ductal cells, we herein characterize the Ets-transcription factor Etv5 as a pivotal regulator of ductal cell identity and ADM that acts upstream of Sox9 and is essential for Sox9 expression in ADM. Loss of Etv5 is associated with increased severity of acute pancreatitis and impaired ADM formation leading to delayed tissue regeneration and recovery in response to injury.

CONCLUSIONS

Our data provide new insights in the regulation of ADM with implications in our understanding of pancreatic homeostasis, pancreatitis and epithelial plasticity. Developmental Dynamics 247:854-866, 2018. © 2018 Wiley Periodicals, Inc.

IL-6 and PD-L1 antibody blockade combination therapy reduces tumour progression in murine models of pancreatic cancer

OBJECTIVE

Limited efficacy of immune checkpoint inhibitors in pancreatic ductal adenocarcinoma (PDAC) has prompted investigation into combination therapy. We hypothesised that interleukin 6 (IL-6) blockade would modulate immunological features of PDAC and enhance the efficacy of anti-programmed death-1-ligand 1 (PD-L1) checkpoint inhibitor therapy.

DESIGN

Transcription profiles and IL-6 secretion from primary patient-derived pancreatic stellate cells (PSCs) were analyzed via Nanostring and immunohistochemistry, respectively. In vivo efficacy and mechanistic studies were conducted with antibodies (Abs) targeting IL-6, PD-L1, CD4 or CD8 in subcutaneous or orthotopic models using Panc02, MT5 or KPC-luc cell lines; and the aggressive, genetically engineered PDAC model (Kras^LSL-G12D, Trp53^LSL-R270H, Pdx1-cre, Brca2^F/F (KPC-Brca2 mice)). Systemic and local changes in immunophenotype were measured by flow cytometry or immunohistochemical analysis.

RESULTS

PSCs (n=12) demonstrated prominent IL-6 expression, which was localised to stroma of tumours. Combined IL-6 and PD-L1 blockade elicited efficacy in mice bearing subcutaneous MT5 (p<0.02) and Panc02 tumours (p=0.046), which was accompanied by increased intratumoural effector T lymphocytes (CD62L^-CD44^-). CD8-depleting but not CD4-depleting Abs abrogated the efficacy of combined IL-6 and PD-L1 blockade in mice bearing Panc02 tumours (p=0.0016). This treatment combination also elicited significant antitumour activity in mice bearing orthotopic KPC-luc tumours and limited tumour progression in KPC-Brca2 mice (p<0.001). Histological analysis revealed increased T-cell infiltration and reduced α-smooth muscle actin cells in tumours from multiple models. Finally, IL-6 and PD-L1 blockade increased overall survival in KPC-Brca2 mice compared with isotype controls (p=0.0012).

CONCLUSIONS

These preclinical results indicate that targeted inhibition of IL-6 may enhance the efficacy of anti-PD-L1 in PDAC.

IL-18 Drives ILC3 Proliferation and Promotes IL-22 Production via NF-κB

Group 3 innate lymphoid cells (ILC3s) are important regulators of the immune system, maintaining homeostasis in the presence of commensal bacteria, but activating immune defenses in response to microbial pathogens. ILC3s are a robust source of IL-22, a cytokine critical for stimulating the antimicrobial response. We sought to identify cytokines that can promote proliferation and induce or maintain IL-22 production by ILC3s and determine a molecular mechanism for this process. We identified IL-18 as a cytokine that cooperates with an ILC3 survival factor, IL-15, to induce proliferation of human ILC3s, as well as induce and maintain IL-22 production. To determine a mechanism of action, we examined the NF-κB pathway, which is activated by IL-18 signaling. We found that the NF-κB complex signaling component, p65, binds to the proximal region of the IL22 promoter and promotes transcriptional activity. Finally, we observed that CD11c+ dendritic cells expressing IL-18 are found in close proximity to ILC3s in human tonsils in situ. Therefore, we identify a new mechanism by which human ILC3s proliferate and produce IL-22, and identify NF-κB as a potential therapeutic target to be considered in pathologic states characterized by overproduction of IL-18 and/or IL-22.

Stromal ETS2 Regulates Chemokine Production and Immune Cell Recruitment during Acinar-to-Ductal Metaplasia

Preclinical studies have suggested that the pancreatic tumor microenvironment both inhibits and promotes tumor development and growth. Here we establish the role of stromal fibroblasts during acinar-to-ductal metaplasia (ADM), an initiating event in pancreatic cancer formation. The transcription factor V-Ets avian erythroblastosis virus E26 oncogene homolog 2 (ETS2) was elevated in smooth muscle actin–positive fibroblasts in the stroma of pancreatic ductal adenocarcinoma (PDAC) patient tissue samples relative to normal pancreatic controls. LSL-Kras^G12D/+; LSL-Trp53^R172H/+; Pdx-1-Cre (KPC) mice showed that ETS2 expression initially increased in fibroblasts during ADM and remained elevated through progression to PDAC. Conditional ablation of Ets-2 in pancreatic fibroblasts in a Kras^G12D-driven mouse ADM model decreased the amount of ADM events. ADMs from fibroblast Ets-2–deleted animals had reduced epithelial cell proliferation and increased apoptosis. Surprisingly, fibroblast Ets-2 deletion significantly altered immune cell infiltration into the stroma, with an increased CD8+ T-cell population, and decreased presence of regulatory T cells (Tregs), myeloid-derived suppressor cells, and mature macrophages. The mechanism involved ETS2-dependent chemokine ligand production in fibroblasts. ETS2 directly bound to regulatory sequences for Ccl3, Ccl4, Cxcl4, Cxcl5, and Cxcl10, a group of chemokines that act as potent mediators of immune cell recruitment. These results suggest an unappreciated role for ETS2 in fibroblasts in establishing an immune-suppressive microenvironment in response to oncogenic Kras^G12D signaling during the initial stages of tumor development.

The ETS family of oncogenic transcription factors in solid tumours

Findings over the past decade have identified aberrant activation of the ETS transcription factor family throughout all stages of tumorigenesis. Specifically in solid tumours, gene rearrangement and amplification, feed-forward growth factor signalling loops, formation of gain-of-function co-regulatory complexes and novel cis-acting mutations in ETS target gene promoters can result in increased ETS activity. In turn, pro-oncogenic ETS signalling enhances tumorigenesis through a broad mechanistic toolbox that includes lineage specification and self-renewal, DNA damage and genome instability, epigenetics and metabolism. This Review discusses these different mechanisms of ETS activation and subsequent oncogenic implications, as well as the clinical utility of ETS factors.

Long-lived keratin 15+ esophageal progenitor cells contribute to homeostasis and regeneration

The esophageal lumen is lined by a stratified squamous epithelium comprised of proliferative basal cells that differentiate while migrating toward the luminal surface and eventually desquamate. Rapid epithelial renewal occurs, but the specific cell of origin that supports this high proliferative demand remains unknown. Herein, we have described a long-lived progenitor cell population in the mouse esophageal epithelium that is characterized by expression of keratin 15 (Krt15). Genetic in vivo lineage tracing revealed that the Krt15 promoter marks a long-lived basal cell population able to self-renew, proliferate, and generate differentiated cells, consistent with a progenitor/stem cell population. Transcriptional profiling demonstrated that Krt15+ basal cells are molecularly distinct from Krt15- basal cells. Depletion of Krt15-derived cells resulted in decreased proliferation, thereby leading to atrophy of the esophageal epithelium. Further, Krt15+ cells were radioresistant and contributed to esophageal epithelial regeneration following radiation-induced injury. These results establish the presence of a long-lived and indispensable Krt15+ progenitor cell population that provides additional perspective on esophageal epithelial biology and the widely prevalent diseases that afflict this epithelium.

Genetic ablation of Smoothened in pancreatic fibroblasts increases acinar-ductal metaplasia

Liu et al. show that disruption of paracrine Hedgehog signaling via genetic ablation of Smoothened (Smo) in stromal fibroblasts in a Kras^G12D mouse model increased acinar-to-ductal metaplasia (ADM). Smo-deleted fibroblasts had higher expression of transforming growth factor-α (Tgfα) mRNA and secreted higher levels of TGFα, leading to activation of EGFR signaling in acinar cells and increased ADM.

The contribution of the microenvironment to pancreatic acinar-to-ductal metaplasia (ADM), a preneoplastic transition in oncogenic Kras-driven pancreatic cancer progression, is currently unclear. Here we show that disruption of paracrine Hedgehog signaling via genetic ablation of Smoothened (Smo) in stromal fibroblasts in a Kras^G12D mouse model increased ADM. Smo-deleted fibroblasts had higher expression of transforming growth factor-α (Tgfa) mRNA and secreted higher levels of TGFα, leading to activation of EGFR signaling in acinar cells and increased ADM. The mechanism involved activation of AKT and noncanonical activation of the GLI family transcription factor GLI2. GLI2 was phosphorylated at Ser230 in an AKT-dependent fashion and directly regulated Tgfa expression in fibroblasts lacking Smo. Additionally, Smo-deleted fibroblasts stimulated the growth of Kras^G12D/Tp53^R172H pancreatic tumor cells in vivo and in vitro. These results define a non-cell-autonomous mechanism modulating Kras^G12D-driven ADM that is balanced by cross-talk between Hedgehog/SMO and AKT/GLI2 pathways in stromal fibroblasts.

Abstract A40: Genetic ablation of Smoothened in tumor-associated fibroblasts promotes pancreatic tumorigenesis

Purpose of Study: Pancreatic cancer is an overwhelming fatal disease with less than 5% of patients surviving beyond 5 years. The most prominent histopathological hallmark of pancreatic cancer is its uniquely dense stromal reaction as evidenced by recent reports that highlight the significant role of stromal fibroblasts on pancreatic tumor cell biology. We used novel mouse models to show that genetic inactivation of Smoothened (Smo) in stromal fibroblasts accelerated Kras-initiated tumorigenesis.

Research Method: We used a genetically engineered mouse model of pancreatic cancer that relies on constitutive activation of the Kras oncogene in the epithelium. We simultaneously employed cre-loxP technology to conditionally delete Smo exclusively in the fibroblast compartment of the pancreas, thus disrupting the crucial hedgehog paracrine signaling loop between pancreatic tumor cells and fibroblasts.

Novel Findings: We showed that deletion of Smo in stromal fibroblasts accelerated pancreatic tumorigenesis through a mechanism involving destabilization of fibroblast PTEN protein. Down-regulation of PTEN enhanced TGF-α production in stromal fibroblasts, and increased epithelial cell transformation and proliferation through epithelial growth factor receptor (EGFR). A selective SMO inhibitor also decreased PTEN in a Kras mouse model as well as in human primary pancreatic cancer associated fibroblasts. Importantly, in pancreatic ductal adenocarcinoma (PDAC) patient samples, low PTEN expression correlated with low SMO expression and with reduced overall survival. These results define a pathway that reprograms stromal fibroblasts from a tumor suppressive phenotype to a tumor promoting phenotype, thus highlighting the dual functions of stromal fibroblasts in pancreatic cancer and the molecular consequences of loss of the hedgehog pathway. Thus, a more comprehensive understanding of tumor-stroma interactions is required to assure effective implementation of targeted therapies.

Conclusions and Implications: Recent pre-clinical reports suggest the pancreatic tumor microenvironment functions predominantly to inhibit tumor growth, challenging the concept of tumor stroma as a therapeutic target. Our results provide molecular insight into how the balance between the opposing activities of tumor stromal fibroblasts is maintained, and potentially identifies targets for restoring stromal tumor suppressive functions. In summary, we demonstrate that ablation of paracrine hedgehog signaling in SMA-positive fibroblasts leads to proteasome-mediated degradation of the PTEN tumor suppressor protein and subsequent activation of oncogenic pathways.

Citation Format: Jason R. Pitarresi, Michael C. Ostrowski. Genetic ablation of Smoothened in tumor-associated fibroblasts promotes pancreatic tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A40.

Single agent BMS-911543 Jak2 inhibitor has distinct inhibitory effects on STAT5 signaling in genetically engineered mice with pancreatic cancer

The Jak/STAT pathway is activated in human pancreatic ductal adenocarcinoma (PDAC) and cooperates with mutant Kras to drive initiation and progression of PDAC in murine models. We hypothesized that the small-molecule Jak2 inhibitor (BMS-911543) would elicit anti-tumor activity against PDAC and decrease immune suppressive features of the disease. We used an aggressive genetically engineered PDAC model with mutant KrasG12D, tp53R270H, and Brca1 alleles (KPC-Brca1 mice). Mice with confirmed tumor burden were treated orally with vehicle or 30 mg/kg BMS-911543 daily for 14 days. Histologic analysis of pancreata from treated mice revealed fewer foci of adenocarcinoma and significantly decreased Ki67+ cells versus controls. In vivo administration of BMS-911543 significantly reduced pSTAT5 and FoxP3 positive cells within the pancreas, but did not alter STAT3 phosphorylation. Continuous dosing of KPC-Brca1 mice with BMS-911543 resulted in a median survival of 108 days, as compared to a median survival of 87 days in vehicle treated animals, a 23% increase (p = 0.055). In vitro experiments demonstrated that PDAC cell lines were poorly sensitive to BMS-911543, requiring high micromolar concentrations to achieve targeted inhibition of Jak/STAT signaling. Similarly, BMS-911543 had little in vitro effect on the viability of both murine and human PDAC-derived stellate cell lines. However, BMS-911543 potently inhibited phosphorylation of pSTAT3 and pSTAT5 at low micromolar doses in human PBMC and reduced in vitro differentiation of Foxp3+ T regulatory cells. These results indicate that single agent Jak2i deserves further study in preclinical models of PDAC and has distinct inhibitory effects on STAT5 mediated signaling.

Abstract B01: Ets-2 acts as a novel oncogene in cancer associated fibroblasts and promotes pancreatic tumor initiation and development

Purpose of Study:Pancreatic cancer remains an overwhelmingly fatal disease with approximately 95% of patients dying within 5 years of diagnosis. Many recent reports have highlighted the emerging role that stromal cells’fibroblasts in particular’have on pancreatic tumor cell biology. It has become apparent that new models of pancreatic cancer that accurately portray the tumor microenvironment (TME) are necessary to move the field forward. Advances in genetic tools to modulate the TME developed in our lab have allowed us the unique opportunity to manipulate specific stromal cell compartments. Our overarching hypothesis is: Ets-2 in the pancreatic tumor-associated stroma promotes tumor initiation and development by regulating essential signaling pathways in fibroblasts and is critical for tumor-stroma co-evolution.

Research Method: In this study we use a previously validated and well-studied genetically engineered mouse model of pancreatic cancer that relies on constitutive activation of the Kras oncogene tumor cell lineage. We simultaneously employ lox-cre technology to conditionally delete our gene of interest exclusively in the fibroblast compartment of the pancreas. For this study we delete the transcription factor Ets-2, which has previously been shown to effect tumor initiation and growth in mammary stroma.

Novel Findings: Here we show that Ets-2 in pancreatic tumor-associated stroma promotes tumor formation by regulating essential signaling pathways in stromal fibroblasts and is critical for tumor-stroma co-evolution. We conditionally deleted Ets-2 in cancer associated fibroblasts (CAFs), thus altering stroma-tumor crosstalk and resulting in delayed tumor initiation. Specifically, we saw a decrease in pre-cancerous acinar-to-ductal metaplasic (ADM) and pancreatic intraepithelial neoplastic (PanIN) lesions in mice null for Ets-2 in the fibroblast compartment. In order to investigate the mechanism by which Ets-2 is able to effect progression of tumors from the fibroblast compartment, we developed a method for harvesting and purifying primary pancreatic CAFs. We performed microarray and gene expression analysis on Ets-2 deleted CAFs and saw significantly decreased expression of secreted factors. The altered secretome upon Ets-2 deletion in fibroblasts was crucially lacking tumor necrosis factor alpha (TNFα), a known pro-tumor ligand in pancreatic carcinogenesis. Furthermore, we found evolutionarily conserved Ets-2 transcription factor binding sites in the proximal promoter of TNFα, suggesting that Ets-2 directly regulates TNFα transcription. Thus we have shown that Ets-2 ablation in pancreatic fibroblasts delays pancreatic tumor initiation through the pro-tumor ligand TNFα.

Conclusions and Implications:This report shows that deleting a gene in pancreatic fibroblasts causes a change in tumor-stroma co-evolution and that Ets-2 is able to act as a novel oncogene in cancer associated fibroblasts to promote pancreatic carcinogenesis. We have shown that Ets-2 deletion significantly changed the biological role of the CAFs and negatively effects tumor growth. This finding is relevant to the field of pancreatic cancer because it shows that the pancreatic TME can play a driver role in overall tumor initiation and development. These collective findings contribute to our lab’s overall hypothesis that the tumor microenvironment is not a mere bystander or byproduct of tumor development, but rather that it can drive tumor evolution amongst a variety of cancers.

Citation Format: Jason R. Pitarresi, Jinghai Wu, Sarah Woelke, Raleigh Kladney, Maria Cuitino, Lianbo Yu, Ostrowski C. Michael. Ets-2 acts as a novel oncogene in cancer associated fibroblasts and promotes pancreatic tumor initiation and development. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B01.

Protein kinase C Beta in the tumor microenvironment promotes mammary tumorigenesis

Protein kinase C beta (PKCβ) expression in breast cancer is associated with a more aggressive tumor phenotype, yet the mechanism for how PKCβ is pro-tumorigenic in this disease is still unclear. Interestingly, while it is known that PKCβ mediates angiogenesis, immunity, fibroblast function and adipogenesis, all components of the mammary tumor microenvironment (TME), no study to date has investigated whether stromal PKCβ is functionally relevant in breast cancer. Herein, we evaluate mouse mammary tumor virus–polyoma middle T-antigen (MMTV–PyMT) induced mammary tumorigenesis in the presence and absence of PKCβ. We utilize two model systems: one where PKCβ is deleted in both the epithelial and stromal compartments to test the global requirement for PKCβ on tumor formation, and second, where PKCβ is deleted only in the stromal compartment to test its role in the TME. MMTV–PyMT mice globally lacking PKCβ live longer and develop smaller tumors with decreased proliferation and decreased macrophage infiltration. Similarly, when PKCβ is null exclusively in the stroma, PyMT-driven B6 cells form smaller tumors with diminished collagen deposition. These experiments reveal for the first time a tumor promoting role for stromal PKCβ in MMTV–PyMT tumorigenesis. In corroboration with these results, PKCβ mRNA (Prkcb) is increased in fibroblasts isolated from MMTV–PyMT tumors. These data were confirmed in a breast cancer patient cohort. Combined these data suggest the continued investigation of PKCβ in the mammary TME is necessary to elucidate how to effectively target this signaling pathway in breast cancer.