Tumor Cell-Intrinsic p38 MAPK Signaling Promotes IL1α-Mediated Stromal Inflammation and Therapeutic Resistance in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a KRAS-driven inflammatory program and a desmoplastic stroma, which contribute to the profoundly chemoresistant phenotype. The tumor stroma contains an abundance of cancer-associated fibroblasts (CAF), which engage in extensive paracrine cross-talk with tumor cells to perpetuate protumorigenic inflammation. IL1α, a pleiotropic, tumor cell-derived cytokine, plays a critical role in shaping the stromal landscape. To provide insights into the molecular mechanisms regulating IL1A expression in PDAC, we performed transcriptional profiling of The Cancer Genome Atlas datasets and pharmacologic screening in PDAC cells and identified p38α MAPK as a key positive regulator of IL1A expression. Both genetic and pharmacologic inhibition of p38 MAPK significantly diminished IL1α production in vitro. Chromatin- and coimmunoprecipitation analyses revealed that p38 MAPK coordinates the transcription factors Sp1 and the p65 subunit of NFκB to drive IL1A overexpression. Single-cell RNA sequencing of a highly desmoplastic murine PDAC model, Ptf1aCre/+; LSL-KrasG12D/+; Tgfbr2flox/flox (PKT), confirmed that p38 MAPK inhibition significantly decreases tumor cell-derived Il1a and attenuates the inflammatory CAF phenotype in a paracrine IL1α-dependent manner. Furthermore, p38 MAPK inhibition favorably modulated intratumoral immunosuppressive myeloid populations and augmented chemotherapeutic efficacy to substantially reduce tumor burden and improve overall survival in PKT mice. These findings illustrate a cellular mechanism of tumor cell-intrinsic p38-p65/Sp1-IL1α signaling that is responsible for sustaining stromal inflammation and CAF activation, offering an attractive therapeutic approach to enhance chemosensitivity in PDAC.

SIGNIFICANCE

Inhibition of p38 MAPK suppresses tumor cell-derived IL1α and attenuates the inflammatory stroma and immunosuppressive tumor microenvironment to overcome chemotherapeutic resistance in pancreatic cancer.

Minnelide suppresses GVHD and enhances survival while maintaining GVT responses

Allogeneic hematopoietic stem cell transplantation (aHSCT) can cure patients with otherwise fatal leukemias and lymphomas. However, the benefits of aHSCT are limited by graft-versus-host disease (GVHD). Minnelide, a water-soluble analog of triptolide, has demonstrated potent antiinflammatory and antitumor activity in several preclinical models and has proven both safe and efficacious in clinical trials for advanced gastrointestinal malignancies. Here, we tested the effectiveness of Minnelide in preventing acute GVHD as compared with posttransplant cyclophosphamide (PTCy). Strikingly, we found Minnelide improved survival, weight loss, and clinical scores in an MHC-mismatched model of aHSCT. These benefits were also apparent in minor MHC-matched aHSCT and xenogeneic HSCT models. Minnelide was comparable to PTCy in terms of survival, GVHD clinical score, and colonic length. Notably, in addition to decreased donor T cell infiltration early after aHSCT, several regulatory cell populations, including Tregs, ILC2s, and myeloid-derived stem cells in the colon were increased, which together may account for Minnelide's GVHD suppression after aHSCT. Importantly, Minnelide's GVHD prevention was accompanied by preservation of graft-versus-tumor activity. As Minnelide possesses anti-acute myeloid leukemia (anti-AML) activity and is being applied in clinical trials, together with the present findings, we conclude that this compound might provide a new approach for patients with AML undergoing aHSCT.

Remodeling of Stromal Immune Microenvironment by Urolithin A Improves Survival with Immune Checkpoint Blockade in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a significant contributor to cancer-related morbidity and mortality, and it is known for its resistance to conventional treatment regimens, including chemotherapy and immune checkpoint blockade (ICB)-based therapies. We have previously shown that Urolithin A (Uro A), a gut microbial metabolite derived from pomegranates, can target and inhibit KRAS-dependent PI3K/AKT/mTOR signaling pathways to overcome therapeutic resistance and improve survival in PDAC. However, the effect of Uro A on the tumor immune microenvironment and its ability to enhance ICB efficacy has not been explored. This study demonstrates that Uro A treatment reduces stromal fibrosis and reinvigorates the adaptive T-cell immune response to overcome resistance to PD-1 blockade in a genetically engineered mouse model (GEMM) of PDAC. Flow cytometric-based analysis of Uro A-treated mouse tumors revealed a significant attenuation of immunosuppressive tumor-associated M2-like macrophages with a concurrent increase in the infiltration of CD4⁺ and CD8⁺ T cells with memory-like phenotype along with reduced expression of the exhaustion-associated protein, PD-1. Importantly, the combination of Uro A treatment with anti-PD-1 immunotherapy promoted enhancement of the antitumor response with increased infiltration of CD4⁺ Th1 cells, ultimately resulting in a remarkable improvement in overall survival in GEMM of PDAC. Overall, our findings provide preclinical evidence for the potential of Uro A as a novel therapeutic agent to increase sensitivity to immunotherapy in PDAC and warrant further mechanistic exploration in preclinical and clinical studies.

Significance

Immunotherapeutic agents are ineffective against pancreatic cancer, mainly due to the immunosuppressive tumor microenvironment and stromal desmoplasia. Our current study demonstrates the therapeutic utility of a novel gut microbial metabolite, Uro A, to remodel the stromal-immune microenvironment and improve overall survival with anti-PD-1 therapy in pancreatic cancer.

Cell-Autonomous Cxcl1 Sustains Tolerogenic Circuitries and Stromal Inflammation via Neutrophil-Derived TNF in Pancreatic Cancer

We have shown that KRAS-TP53 genomic coalteration is associated with immune-excluded microenvironments, chemoresistance, and poor survival in pancreatic ductal adenocarcinoma (PDAC) patients. By treating KRAS-TP53 cooperativity as a model for high-risk biology, we now identify cell-autonomous Cxcl1 as a key mediator of spatial T-cell restriction via interactions with CXCR2+ neutrophilic myeloid-derived suppressor cells in human PDAC using imaging mass cytometry. Silencing of cell-intrinsic Cxcl1 in LSL-KrasG12D/+;Trp53R172H/+;Pdx-1Cre/+(KPC) cells reprograms the trafficking and functional dynamics of neutrophils to overcome T-cell exclusion and controls tumor growth in a T cell-dependent manner. Mechanistically, neutrophil-derived TNF is a central regulator of this immunologic rewiring, instigating feed-forward Cxcl1 overproduction from tumor cells and cancer-associated fibroblasts (CAF), T-cell dysfunction, and inflammatory CAF polarization via transmembrane TNF-TNFR2 interactions. TNFR2 inhibition disrupts this circuitry and improves sensitivity to chemotherapy in vivo. Our results uncover cancer cell-neutrophil cross-talk in which context-dependent TNF signaling amplifies stromal inflammation and immune tolerance to promote therapeutic resistance in PDAC.

SIGNIFICANCE

By decoding connections between high-risk tumor genotypes, cell-autonomous inflammatory programs, and myeloid-enriched/T cell-excluded contexts, we identify a novel role for neutrophil-derived TNF in sustaining immunosuppression and stromal inflammation in pancreatic tumor microenvironments. This work offers a conceptual framework by which targeting context-dependent TNF signaling may overcome hallmarks of chemoresistance in pancreatic cancer. This article is highlighted in the In This Issue feature, p. 1275.

Combined MEK and STAT3 Inhibition Uncovers Stromal Plasticity by Enriching for Cancer-Associated Fibroblasts With Mesenchymal Stem Cell-Like Features to Overcome Immunotherapy Resistance in Pancreatic Cancer

BACKGROUND & AIMS

We have shown that reciprocally activated rat sarcoma (RAS)/mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) and Janus kinase/signal transducer and activator of transcription 3 (STAT3) pathways mediate therapeutic resistance in pancreatic ductal adenocarcinoma (PDAC), while combined MEK and STAT3 inhibition (MEKi+STAT3i) overcomes such resistance and alters stromal architecture. We now determine whether MEKi+STAT3i reprograms the cancer-associated fibroblast (CAF) and immune microenvironment to overcome resistance to immune checkpoint inhibition in PDAC.

METHODS

CAF and immune cell transcriptomes in MEKi (trametinib)+STAT3i (ruxolitinib)-treated vs vehicle-treated Ptf1aCre/+;LSL-KrasG12D/+;Tgfbr2flox/flox (PKT) tumors were examined via single-cell RNA sequencing (scRNAseq). Clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeats associated protein 9 silencing of CAF-restricted Map2k1/Mek1 or Stat3, or both, enabled interrogation of CAF-dependent effects on immunologic remodeling in orthotopic models. Tumor growth, survival, and immune profiling via mass cytometry by time-of-flight were examined in PKT mice treated with vehicle, anti-programmed cell death protein 1 (PD-1) monotherapy, and MEKi+STAT3i combined with anti-PD1.

RESULTS

MEKi+STAT3i attenuates Il6/Cxcl1-expressing proinflammatory and Lrrc15-expressing myofibroblastic CAF phenotypes while enriching for Ly6a/Cd34-expressing CAFs exhibiting mesenchymal stem cell-like features via scRNAseq in PKT mice. This CAF plasticity is associated with M2-to-M1 reprogramming of tumor-associated macrophages, and enhanced trafficking of cluster of differentiation 8+ T cells, which exhibit distinct effector transcriptional programs. These MEKi+STAT3i-induced effects appear CAF-dependent, because CAF-restricted Mek1/Stat3 silencing mitigates inflammatory-CAF polarization and myeloid infiltration in vivo. Addition of MEKi+STAT3i to PD-1 blockade not only dramatically improves antitumor responses and survival in PKT mice but also augments recruitment of activated/memory T cells while improving their degranulating and cytotoxic capacity compared with anti-PD-1 monotherapy. Importantly, treatment of a patient who has chemotherapy-refractory metastatic PDAC with MEKi (trametinib), STAT3i (ruxolitinib), and PD-1 inhibitor (nivolumab) yielded clinical benefit.

CONCLUSIONS

Combined MEKi+STAT3i mitigates stromal inflammation and enriches for CAF phenotypes with mesenchymal stem cell-like properties to overcome immunotherapy resistance in PDAC.

Abstract C040: CREB-LIF axis drives immune suppression by promoting macrophage polarization in pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) remains an aggressive malignancy, and its unique genetic makeup and immunosuppressive tumor microenvironment (TME) produce a lack of response to current therapies. Previously, we have identified Cyclic AMP Response Element Binding protein 1 (CREB) as an oncogenic transcriptional factor that promotes disease aggressiveness, poor survival, and immune suppression. Based on these, we sought to determine the role of tumor intrinsic CREB in promoting immunosuppressive TME in PDAC. Methods: We have generated a genetically engineered mouse model (GEMM) of pancreas-specific CREB deletion (CREBfl/fl) in LSL-KrasG12D/+; Trp53 R172H/+; Pdx1Cre/+ (KPC) mice that phenocopy human PDAC disease. CRISPR/CAS9-based genomic editing was utilized to ablate CREB (CREBKO) in KPC tumor cells. RNA-sequencing analysis was performed in KPC CREB wild type (CREBWT) vs. CREBKO tumor cells to identify CREB-mediated transcriptomic changes. Chromatin immunoprecipitation (ChIP-qPCR) analysis was performed in KPC tumor cells. Syngeneic orthotopic tumor implantation of these cells was performed in the pancreata of mice. Immunophenotyping was accomplished to assess changes in the immune subsets with CREB deletion invivo. Additionally, these tissues were also processed for single-cell RNA (scRNA) transcriptomics analysis to evaluate changes on different cellular constituents. Results: Pancreas-specific CREB deletion in the KPC GEMM led to a significant reduction in the primary tumor burden, liver metastases, and improved overall survival compared to wild-type KPC. In assessing the immune repercussions of CREB deletion in pancreatic tumors, we observed a decreased infiltration of tumor-promoting CD11b+ F4/80+ CD206+ [M2-like tumor-associated macrophages (TAMs)] and a concomitant increase in the antigen-presenting M1-like macrophages (F4/80+MHC-IIhighCD86high). Additionally, scRNA sequencing analysis within the macrophage compartment in CREBKO tumors revealed significant enrichment of M1 hallmark signaling pathways. Also, CREB ablation in these tumors further facilitated increased infiltration of activated effector memory CD8+ T cells and resulted in enhanced adaptive immune response within the PDAC TME. Mechanistically, RNA transcriptomic-based analysis of CREBKO tumor cells revealed, Leukemia inhibitory factor (LIF) as one of the downstream targets of CREB. ChIP qPCR analysis after CREB1 pulldown confirmed its occupancy on LIF promoter regulatory region. Incubation of macrophages with CREBWT conditioned media in the presence of LIF neutralizing antibody or blocking its receptor expression using EC359 pushed these macrophages towards an M1-like phenotype, confirming its role as a mediator of tumor cell macrophage crosstalk. Conclusion: These findings broaden our understanding of the tumor cell-intrinsic role of CREB and provide new insights into its molecular underpinnings in fostering immunosuppressive profile by promoting skewness of TAMs towards M2 phenotype in PDAC.

Citation Format: Siddharth Mehra, Vanessa T. Garrido, Samara Singh, Iago De Castro Silva, Anna Bianchi, Luis A. Nivelo, Nilesh U. Deshpande, Austin R. Dosch, Zhou Zhiqun, Supriya Srinivasan, Christine I. Rafie, Ifeanyichukwu C. Ogobuiro, Xi Chen, Alejandro Villarino, Jashodeep Datta, Nipun B. Merchant, Nagaraj Nagathihalli. CREB-LIF axis drives immune suppression by promoting macrophage polarization in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C040.

Abstract C033: KRAS-TP53 cooperativity regulates Cxcl1 to sustain tumor-permissive circuitry via granulocyte-derived CXCR2-TNF signaling in pancreatic cancer

Objective: We have recently shown that KRAS-TP53 genomic co-alteration is associated with innate immune-enriched and T-cell-excluded tumor microenvironments (TME), chemotherapy resistance, and poor survival in pancreatic ductal adenocarcinoma (PDAC) patients. We sought to define the multi-cellular crosstalk that underlies these effects by dissecting how cancer cell-autonomous transcriptional programs orchestrate tolerogenic circuitries to mediate chemoresistance in KRAS-TP53 cooperative PDAC. Methods: Spatial neighborhood analysis via Imaging Mass Cytometry (IMC) was performed in patient-derived PDAC sections. Immune profiling and bulk RNA-seq in whole tumors, as well as bulk-RNAseq in intratumoral F4/80-Ly6Ghi neutrophilic(PMN)-MDSCs in orthotopic KPC tumors with/without CRISPR/Cas9 editing of Cxcl1 was performed. Effect of TNFR2 inhibition via etanercept on ex vivo co-cultures of intratumoral PMN-MDSC with KPC tumor cells/CAFs and T-cells, as well as in orthotopic KPC models in vivo with/without gemcitabine+paclitaxel chemotherapy was performed. Results: Interrogation of cancer cell transcriptomes and IMC architecture in human tumors reveals disproportionate enrichment of Cxcl1 in KRAS-TP53 co-altered PDAC. IMC-enabled spatial neighborhood analysis in KRAS-TP53 co-altered human PDAC TMEs demonstrates strong spatial contiguity between PanCK+CXCL1+ tumor islands and cognate CD15+CXCR2+ PMN-MDSCs, with exclusion of CD8+ T-cells from tumor cell:PMN-MDSC communities. In murine orthotopic models that phenocopy T-cell excluded human PDAC, genetic silencing of tumor cell-intrinsic Cxcl1 overcomes CD8+ T-cell exclusion and controls tumor growth in a CD8+ T-cell dependent manner in vivo. Transcriptomes from KPC-Cxcl1KO tumors not only reveal enrichment in pathways encoding for T-cell effector activity but also attenuation in pathways related to innate immune function. These immune potentiating effects upon Cxcl1 silencing are driven in large part by reprogramming of trafficking dynamics and immunosuppressive potential in intratumoral CXCR2+ PMN-MDSCs. To identify neutrophil-intrinsic mechanisms that govern remodeling of the TME following Cxcl1 silencing, transcriptomes in intratumoral KPC-Cxcl1KO PMN-MDSCs reveal strong downregulation of MAPK and TNF pathways, with signaling studies implicating a novel Cxcr2-Ikk-Map3k8-Tnf axis. We uncover novel effects of neutrophil-derived TNF in promoting tumor cell-Cxcl1 production, inflammatory CAF polarization, and T-cell dysfunction in ex vivo co-cultures, predominantly via a membraneTNF-TNFR2 dependent mechanism. Systemic TNFR2 inhibition via etanercept not only augments T-cell activation, but also mitigates tumor-wide Cxcl1 production, stromal inflammation, and CAF:tumor cell IL6-STAT3 signaling to improve sensitivity to gemcitabine+paclitaxel chemotherapy in vivo. Conclusion: These data uncover novel tumor-permissive/chemoresistant circuitries in which cancer cell-intrinsic Cxcl1 sustains innate immunoregulatory and tolerogenic signaling via neutrophil-derived TNF in the PDAC TME.

Citation Format: Anna Bianchi, Iago De Castro Silva, Nilesh U. Deshpande, Siddharth Mehra, Vanessa T. Garrido, Samara Singh, Christine I. Rafie, Zhou Zhiqun, Ifeanyichukwu C. Ogobuiro, Austin R. Dosch, Nagaraj Nagathihalli, Nipun B. Merchant, Jashodeep Datta. KRAS-TP53 cooperativity regulates Cxcl1 to sustain tumor-permissive circuitry via granulocyte-derived CXCR2-TNF signaling in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C033.

Abstract 2513: MDSC-derived TNF is a novel regulator of T-cell dysfunction in pancreatic cancer

Introduction: Abundance of myeloid-derived suppressor cells (MDSC) and a dysfunctional T-cell compartment are defining hallmarks of therapeutic resistance in pancreatic ductal adenocarcinoma (PDAC). Using congenic in vivo murine models to phenocopy extremes of T-cell enrichment or exclusion, we sought to interrogate central MDSC-mediated mechanisms that govern immune tolerance in PDAC.

Methods: Orthotopically implanted T-cell-excluded (Tcelllo) vs T-cell-enriched (T-cellhi) congenic KPC tumors, and intratumoral Ly6G+F4/80- MDSCs from both clones, were subjected to RNA sequencing. Ex vivo co-cultures evaluated the effects of intratumoral MDSC on splenic T-cells. Orthotopically injected KPC-T-celllo mice were treated with etanercept vs. vehicle, and immunophenotyping via flow cytometry was performed.

Results: RNA-seq of KPC T-celllo vs. T-cellhi tumors revealed enrichment of myeloid immunoregulatory pathways, and downregulation of leukocyte activation/cytotoxicity pathways. Flow cytometry revealed a dramatic increase in MDSCs infiltrating KPC-Tcelllo tumors (P<0.001). To decipher MDSC-intrinsic mechanisms associated with T-cell exclusion, RNA-seq of MDSCs infiltrating T-cellhi clones revealed relative downregulation of MAPK signaling, and cytokine profiling of MDSCs conditioned with MAPK inhibitor trametinib revealed marked reduction in TNF secretion. Confocal microscopy confirmed striking decrease in TNF in MDSCs isolated from KPC- T-cellhi vs. Tcelllo tumors. Ex vivo MDSC-T-cell co-cultures significantly attenuated T-cell proliferation and activation (via IFN-γ release) while favoring T-cell apoptosis, which could be rescued by pre-conditioning MDSCs with either etanercept (TNFR2 decoy receptor) or MAPK pathway inhibitors. Orthotopically injected KPC-T-celllo tumor-bearing mice treated with etanercept demonstrated a remodeled TME vs. vehicle-treated mice, with attenuation in MDSC trafficking, enrichment in CD4+/CD8+ T-cell infiltration, and reduction in T-cell exhaustion.

Conclusion: MDSC-derived TNF regulates T-cell dysfunction in PDAC via a MAPK-dependent mechanism. Compartment-specific inhibition of TNF may be a provocative strategy to overcome immune tolerance in PDAC.

Citation Format: Anna Bianchi, Iago De Castro Silva, Nilesh U. Deshpande, Siddharth Mehra, Samara Singh, Austin R. Dosch, Vanessa T. Garrido, Christine I. Rafie, Nagaraj Nagathihalli, Nipun Merchant, Jashodeep Datta. MDSC-derived TNF is a novel regulator of T-cell dysfunction in pancreatic cancer [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 2513.

Obesity enriches for tumor protective microbial metabolites and treatment refractory cells to confer therapy resistance in PDAC

Obesity causes chronic inflammation and changes in gut microbiome. However, how this contributes to poor survival and therapy resistance in patients with pancreatic cancer remain undetermined. Our current study shows that high fat diet-fed obese pancreatic tumor bearing mice do not respond to standard of care therapy with gemcitabine and paclitaxel when compared to corresponding control diet-fed mice. C57BL6 mice were put on control and high fat diet for 1 month following with pancreatic tumors were implanted in both groups. Microbiome of lean (control) and obese (high fat diet fed) mice was analyzed. Fecal matter transplant from control mice to obese mice sensitized tumors to chemotherapy and demonstrated extensive cell death. Analysis of gut microbiome showed an enrichment of queuosine (Q) producing bacteria in obese mice and an enrichment of S-adenosyl methionine (SAM) producing bacteria in control diet-fed mice. Further, supplementation of obese animals with SAM sensitized pancreatic tumors to chemotherapy. Treatment of pancreatic cancer cells with Q increased PRDX1 involved in oxidative stress protection. In parallel, tumors in obese mice showed increase in CD133+ treatment refractory tumor populations compared to control animals. These observations indicated that microbial metabolite Q accumulation in high fat diet-fed mice protected tumors from chemotherapy induced oxidative stress by upregulating PRDX1. This protection could be reversed by treatment with SAM. We conclude that relative concentration of SAM and queuosine in fecal samples of pancreatic cancer patients can be developed as a potential biomarker and therapeutic target in chemotherapy refractory pancreatic cancer.

Hypoxia-Driven Oncometabolite L-2HG Maintains Stemness-Differentiation Balance and Facilitates Immune Evasion in Pancreatic Cancer

In pancreatic cancer, the robust fibroinflammatory stroma contributes to immune suppression and renders tumors hypoxic, altering intratumoral metabolic pathways and leading to poor survival. One metabolic enzyme activated during hypoxia is lactate dehydrogenase A (LDHA). As a result of its promiscuous activity under hypoxia, LDHA produces L-2 hydroxyglutarate (L-2HG), an epigenetic modifier, that regulates the tumor transcriptome. However, the role of L-2HG in remodeling the pancreatic tumor microenvironment is not known. Here we used mass spectrometry to detect L-2HG in serum samples from patients with pancreatic cancer, comprising tumor cells as well as stromal cells. Both hypoxic pancreatic tumors as well as serum from patients with pancreatic cancer accumulated L-2HG as a result of promiscuous activity of LDHA. This abnormally accumulated L-2HG led to H3 hypermethylation and altered gene expression, which regulated a critical balance between stemness and differentiation in pancreatic tumors. Secreted L-2HG inhibited T-cell proliferation and migration, suppressing antitumor immunity. In a syngeneic orthotopic model of pancreatic cancer, inhibition of LDH with GSK2837808A decreased L-2HG, induced tumor regression, and sensitized tumors to anti-PD1 therapy. In conclusion, hypoxia-mediated promiscuous activity of LDH produces L-2HG in pancreatic tumor cells, regulating the stemness-differentiation balance and contributing to immune evasion. Targeting LDH can be developed as a potential therapy to sensitize pancreatic tumors to checkpoint inhibitor therapy. SIGNIFICANCE: This study shows that promiscuous LDH activity produces L-2HG in pancreatic tumor and stromal cells, modulating tumor stemness and immune cell function and infiltration in the tumor microenvironment.

Stroma secreted IL6 selects for "stem-like" population and alters pancreatic tumor microenvironment by reprogramming metabolic pathways

Pancreatic adenocarcinoma is a devastating disease with an abysmal survival rate of 9%. A robust fibro-inflammatory and desmoplastic stroma, characteristic of pancreatic cancer, contribute to the challenges in developing viable therapeutic strategies in this disease. Apart from constricting blood vessels and preventing efficient drug delivery to the tumor, the stroma also contributes to the aggressive biology of cancer along with its immune-evasive microenvironment. In this study, we show that in pancreatic tumors, the developing stroma increases tumor initiation frequency in pancreatic cancer cells in vivo by enriching for CD133 + aggressive "stem-like" cells. Additionally, the stromal fibroblasts secrete IL6 as the major cytokine, increases glycolytic flux in the pancreatic tumor cells, and increases lactate efflux in the microenvironment via activation of the STAT signaling pathway. We also show that the secreted lactate favors activation of M2 macrophages in the tumor microenvironment, which excludes CD8 + T cells in the tumor. Our data additionally confirms that the treatment of pancreatic tumors with anti-IL6 antibody results in tumor regression as well as decreased CD133 + population within the tumor. Furthermore, inhibiting the lactate efflux in the microenvironment reduces M2 macrophages, and makes pancreatic tumors more responsive to anti-PD1 therapy. This suggests that stromal IL6 driven metabolic reprogramming plays a significant role in the development of an immune-evasive microenvironment. In conclusion, our study shows that targeting the metabolic pathways affected by stromal IL6 can make pancreatic tumors amenable to checkpoint inhibitor therapy.

Targeting tumor-intrinsic hexosamine biosynthesis sensitizes pancreatic cancer to anti-PD1 therapy

Pancreatic ductal adenocarcinoma (PDAC) is considered to be a highly immunosuppressive and heterogenous neoplasm. Despite improved knowledge regarding the genetic background of the tumor and better understanding of the tumor microenvironment, immune checkpoint inhibitor therapy (targeting CTLA4, PD1, PDL1) has not been very successful against PDAC. The robust desmoplastic stroma, along with an extensive extracellular matrix (ECM) that is rich in hyaluronan, plays an integral role in this immune evasion. Hexosamine biosynthesis pathway (HBP), a shunt pathway of glycolysis, is a metabolic node in cancer cells that can promote survival pathways on the one hand and influence the hyaluronan synthesis in the ECM on the other. The rate-limiting enzyme of the pathway, glutamine-fructose amidotransferase 1 (GFAT1), uses glutamine and fructose 6-phosphate to eventually synthesize uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). In the current manuscript, we targeted this glutamine-utilizing enzyme by a small molecule glutamine analog (6-diazo-5-oxo-l-norleucine [DON]). Our results showed that DON decreased the self-renewal potential and metastatic ability of tumor cells. Further, treatment with DON decreased hyaluronan and collagen in the tumor microenvironment, leading to an extensive remodeling of the ECM and an increased infiltration of CD8+ T cells. Additionally, treatment with DON sensitized pancreatic tumors to anti-PD1 therapy, resulting in tumor regression and prolonged survival.

Abstract B17: Long noncoding RNA growth arrest specific 5 (GAS5) as a proliferation «brake» in aggressive population of CD133+ cells responsible for recurrence in PDAC

The presence of quiescent, therapy-resistant population of tumor cells is often attributed to extreme metastasis and tumor recurrence. This population, often described as cancer stem cells (CSCs), or tumor-initiating cells (TICs), is enriched in a tumor as a result of microenvironmental (hypoxia) or chemotherapeutic stress. In pancreatic cancer, CD133+ cells have been described as a representation of this aggressive TIC population and are most responsible for tumor relapse in patients. This population adapts to stress by turning on mechanisms to halt cell cycle progression. Upon removal of the stress, these cells restart their cell cycle and regain their proliferative nature. Growth Arrest Specific 5 (GAS5) is a long noncoding RNA critical for this process and is overexpressed in PDAC. 13C-Glucose labeling was used for glucose flux assay to track the use of glucose and other metabolites in CD133+ and CD133- populations of pancreatic cancer cells. CD133+/- cell populations were sorted with magnetic sorting or flow cytometry sorting techniques. Lentiviral stable transfection of human CD133 cDNA in MIA PaCa-2 cell line was used to obtain a CD133 overexpressing cell line. siGAS5 and siSOX2 were used to knock down genes in CD133Hi cell lines. Glucocorticoid receptor (GR) activity was assessed using GRE dual luciferase assay system (Qiagen). MTT-based assay was used for proliferation and BrDU incorporation assay was used for measure of nucleic acid synthesis. Fluorescent in situ hybridization using human GAS5 RNA probe (Stellaris) was used to visualize GAS5 localization in human PDAC vs. normal adjacent FFPE samples as well as xenograft FFPE samples. Our results show for the first time that the emergence of CD133+ population coincides with upregulation of GAS5, which reprograms cell cycle to slow proliferation by inhibiting GR-mediated cell cycle control. The CD133+ population further routed glucose through the pentose phosphate pathway, a predominantly biosynthetic pathway, in spite of being quiescent in nature. However, this did not result in immediate nucleic acid synthesis. Upon inhibiting GAS5, these cells were released from growth arrest and restarted nucleic acid synthesis and proliferation. Additionally, this study shows that GAS5 regulates cell cycle through GR, which it is known to bind and inhibit. CD133Hi cells with high GAS5 expression had low GR activity, and stimulation of these cells with dexamethasone was able to increase cell proliferation. Our study thus shows that GAS5 acts as a molecular switch for regulating quiescence and growth arrest in CD133+ population, allowing these cells to overcome chemical and environmental stressors and leading to the aggressive nature of pancreatic tumors.

Citation Format: Nikita S. Sharma, Brittany C. Durden, Prisca Gnamlin, Vineet K. Gupta, Kousik Kesh, Vanessa T. Garrido, Ashok Saluja, Sulagna Banerjee. Long noncoding RNA growth arrest specific 5 (GAS5) as a proliferation «brake» in aggressive population of CD133+ cells responsible for recurrence in PDAC [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 B17.

Long non-coding RNA GAS5 acts as proliferation "brakes" in CD133+ cells responsible for tumor recurrence

Presence of quiescent, therapy evasive population often described as cancer stem cells (CSC) or tumor initiating cells (TIC) is often attributed to extreme metastasis and tumor recurrence. This population is typically enriched in a tumor as a result of microenvironment or chemotherapy induced stress. The TIC population adapts to this stress by turning on cell cycle arrest programs that is a “fail-safe” mechanism to prevent expansion of malignant cells to prevent further injury. Upon removal of the “stress” conditions, these cells restart their cell cycle and regain their proliferative nature thereby resulting in tumor relapse. Growth Arrest Specific 5 (GAS5) is a long-non-coding RNA that plays a vital role in this process. In pancreatic cancer, CD133+ population is a typical representation of the TIC population that is responsible for tumor relapse. In this study, we show for the first time that emergence of CD133+ population coincides with upregulation of GAS5, that reprograms the cell cycle to slow proliferation by inhibiting GR mediated cell cycle control. The CD133+ population further routed metabolites like glucose to shunt pathways like pentose phosphate pathway, that were predominantly biosynthetic in spite of being quiescent in nature but did not use it immediately for nucleic acid synthesis. Upon inhibiting GAS5, these cells were released from their growth arrest and restarted the nucleic acid synthesis and proliferation. Our study thus showed that GAS5 acts as a molecular switch for regulating quiescence and growth arrest in CD133+ population, that is responsible for aggressive biology of pancreatic tumors.

Key endothelial cell angiogenic mechanisms are stimulated by the circulating milieu in sickle cell disease and attenuated by hydroxyurea

As hypoxia-induced inflammatory angiogenesis may contribute to the manifestations of sickle cell disease, we compared the angiogenic molecular profiles of plasma from sickle cell disease individuals and correlated these with in vitro endothelial cell-mediated angiogenesis-stimulating activity and in vivo neovascularization. Bioplex demonstrated that plasma from patients with steady-state sickle cell anemia contained elevated concentrations of pro-angiogenic factors (angiopoietin-1, basic fibroblast growth factor, vascular endothelial growth factor, vascular endothelial growth factor-D and placental growth factor) and displayed potent pro-angiogenic activity, significantly increasing endothelial cell proliferation, migration and capillary-like structure formation. In vivo neovascularization of Matrigel plugs was significantly greater in sickle cell disease mice than in non-sickle cell disease mice, consistent with an up-regulation of angiogenesis in the disease. In plasma from patients with hemoglobin SC disease without proliferative retinopathy, anti-angiogenic endostatin and thrombospondin-2 were significantly elevated. In contrast, plasma from hemoglobin SC individuals with proliferative retinopathy had a pro-angiogenic profile and more significant effects on endothelial cell proliferation and capillary formation than plasma from patients without retinopathy. Hydroxyurea therapy was associated with significant reductions in plasma angiogenic factors and inhibition of endothelial cell-mediated angiogenic mechanisms and neovascularization. Thus, individuals with sickle cell anemia or hemoglobin SC disease with retinopathy present a highly angiogenic circulating milieu, capable of stimulating key endothelial cell-mediated angiogenic mechanisms. Combination anti-angiogenic therapy to prevent the progression of unregulated neovascularization and associated manifestations in sickle cell disease, such as pulmonary hypertension, may be indicated; furthermore, the benefits and drawbacks of the potent anti-angiogenic effects of hydroxyurea should be clarified.

Neutrophils of rheumatoid arthritis patients on anti-TNF-α therapy and in disease remission present reduced adhesive functions in association with decreased circulating neutrophil-attractant chemokine levels

Neutrophils participate in the initiation and progression of rheumatoid arthritis (RA) although the exact mechanisms responsible for neutrophil accumulation in rheumatoid joints are not understood. This study compared the adhesive and chemotactic functions of neutrophils from RA patients in activity (DAS28 > 3.2) and not in activity (DAS28 < 2.6) and observed the effects of different treatment approaches on these functions. Neutrophils were isolated from healthy controls (CON), and patients with active or inactive RA in use of therapy not specific for RA (NSAIDs), in use of DMARDs and in use of anti-TNF-α therapy. Adhesive and chemotactic properties were evaluated using in vitro assays; adhesion molecule expression was assessed by flow cytometry and real-time PCR and circulating chemokines were determined by ELISA. No significant alterations in the adhesive and chemotactic properties of neutrophils from active RA were observed when compared to CON neutrophils, independently of treatment regimen. In contrast, neutrophils from RA patients in disease remission presented reduced adhesive properties and a lower spontaneous chemotactic capacity, in association with decreased adhesion molecule expression, although profiles of alterations differed for those patients on DMARDs and those on anti-TNF-α therapy. Circulating levels of the major neutrophilic chemokines, IL-8 and epithelial neutrophil activating peptide-78, were also significantly decreased in those patients demonstrating a clinical response. Remission of RA appears to be associated with ameliorations in aspects important for neutrophil adhesion and chemotaxis; whether these alterations contribute to decrease neutrophil migration to the synovial fluid, with consequent improvements in the clinical manifestations of RA, remains to be determined.