Multi-cancer analysis reveals universal association of oncogenic LBH expression with DNA hypomethylation and WNT-Integrin signaling pathways

Limb-Bud and Heart (LBH) is a developmental transcription co-factor deregulated in cancer, with reported oncogenic and tumor suppressive effects. However, LBH expression in most cancer types remains unknown, impeding understanding of its mechanistic function Here, we performed systematic bioinformatic and TMA analysis for LBH in >20 different cancer types. LBH was overexpressed in most cancers compared to normal tissues (>1.5-fold; p < 0.05), including colon-rectal, pancreatic, esophageal, liver, stomach, bladder, kidney, prostate, testicular, brain, head & neck cancers, and sarcoma, correlating with poor prognosis. The cancer types showing LBH downregulation were lung, melanoma, ovarian, cervical, and uterine cancer, while both LBH over- and under-expression were observed in hematopoietic malignancies. In cancers with LBH overexpression, the LBH locus was frequently hypomethylated, identifying DNA hypomethylation as a potential mechanism for LBH dysregulation. Pathway analysis identified a universal, prognostically significant correlation between LBH overexpression and the WNT-Integrin signaling pathways. Validation of the clinical association of LBH with WNT activation in gastrointestinal cancer cell lines, and in colorectal patient samples by IHC uncovered that LBH is specifically expressed in tumor cells with nuclear beta-catenin at the invasive front. Collectively, these data reveal a high degree of LBH dysregulation in cancer and establish LBH as pan-cancer biomarker for detecting WNT hyperactivation in clinical specimens.

Abstract 2879: Cell-autonomous Cxcl1 sustains tolerogenic circuitries and stromal inflammation via neutrophil-derived TNF in pancreatic cancer

Objective: We have shown that KRAS-TP53 genomic co-alteration 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 sought to define how cancer cell-autonomous transcriptional programs orchestrate tolerogenic circuitries and stromal inflammation to mediate chemoresistance.

Methods: Spatial neighborhood analysis via Imaging Mass Cytometry (IMC) was performed in human PDAC sections. Immune profiling and RNA-seq in whole tumors, bulk-RNA-seq in intratumoral 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 was examined.

Results: Interrogation of cancer cell transcriptomes and IMC architecture in human tumors reveals enrichment of Cxcl1 in KRAS-TP53 co-altered PDAC. IMC-enabled spatial neighborhood analysis in KRAS-TP53 co-altered human tumors demonstrate spatial contiguity between PanCK+CXCL1+ tumor islands and cognate CD15+CXCR2+ PMN-MDSCs, with exclusion of CD8+ T-cells from tumor cell:MDSC communities. In murine orthotopic models, silencing of cancer cell-intrinsic Cxcl1 reprograms trafficking and functional dynamics of CXCR2+ PMN-MDSCs to overcomes T-cell exclusion, and controls tumor growth in a CD8+ T-cell dependent manner. Transcriptomes from KPC-Cxcl1KO tumors reveal enrichment in pathways encoding for T-cell effector activity, and attenuation in pathways related to innate immunoregulatory function. Mechanistically, neutrophil-derived TNF emerges as a central regulator of this immunologic rewiring, with transcriptomes from intratumoral KPC-Cxcl1KO PMN-MDSCs revealing a novel MAPK-reliant Cxcr2-Ikk-Map3k8-Tnf axis. Neutrophil-derived TNF instigates feed-forward Cxcl1 overproduction from tumor cells and CAFs, T-cell dysfunction, and inflammatory CAF polarization via transmembraneTNF-TNFR2 interactions. Systemic TNFR2 inhibition via etanercept augments T-cell activation, and mitigates tumor-wide Cxcl1 production, stromal inflammation, and CAF:tumor cell IL6-STAT3 signaling to improve sensitivity to chemotherapy in vivo.

Conclusion: By decoding the link between high-risk cancer cell genotypes, cell-autonomous inflammatory programs, and myeloid-enriched and T-cell-excluded contexts, we identify a previously unrecognized role of neutrophil-derived TNF in sustaining tolerogenic circuitries and stromal inflammation in the PDAC TME. Our data suggest that targeting context-dependent TNF signaling may overcome hallmarks of therapeutic resistance in PDAC.

Citation Format: Anna Bianchi, Iago De Castro Silva, Nilesh Deshpande, Samara Singh, Siddharth Mehra, Vanessa Garrido, Ifeanyichukwu Ogobuiro, Haleh Amirian, Christine Rafie, Zhiqun Zhou, Nagaraj Nagathihalli, Alejandro Villarino, Nipun Merchant, Jashodeep Datta. Cell-autonomous Cxcl1 sustains tolerogenic circuitries and stromal inflammation via neutrophil-derived TNF in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2879.

Abstract 3627: Inhibition of tumor cell-autonomous p38 MAPK suppresses IL1α-mediated inflammatory tumor-stromal crosstalk in pancreatic adenocarcinoma

Introduction: Pancreatic ductal adenocarcinoma (PDAC) continues to face major therapeutic challenges due to its innate and acquired chemoresistance. Oncogenic, activating KRAS mutations facilitate extensive cytokine-mediated crosstalk between tumor cells and the fibrotic stroma, producing a pro-inflammatory and immunosuppressive tumor microenvironment (TME). We have identified interleukin-1α (IL1α), downstream of KRAS, as a critical mediator of the inflammatory response due to its pleiotropic effects on cancer-associated fibroblast (CAF) activation and immune evasion. However, the regulatory mechanisms of IL1α expression remain incompletely understood. We identified p38 stress-associated MAPK α (p38α) as a central, KRAS-driven regulatory pathway involved in IL1α production within PDAC tumor cells.

Methods: Differential gene expression analyses were performed on patient data from The Cancer Genome Atlas (TCGA) was queried for overactive pathways downstream KRAS in “high-IL1A” PDAC cases. Inhibition of p38α was achieved pharmacologically with pexmetinib and genetically with an shRNA lentiviral system in human and murine PDAC cell lines. ChIP-qPCR and co-immunoprecipitation were performed on a human PDAC cell line with and without p38α inhibition. Single-cell RNA sequencing (scRNA-seq) and flow cytometry were performed on tumors from a PDAC murine model, Ptf1aCre/+; LSL-KrasG12D/+; Tgfbr2flox/flox (PKT), treated with or without pexmetinib. PKT mice were treated daily with pexmetinib, gemcitabine and paclitaxel chemotherapy, or combination therapy for downstream analysis and survival studies.

Results: Both pharmacologic and genetic inhibition of p38α significantly reduced IL1A transcription and protein levels in human and murine PDAC tumor cell lines. Furthermore, p38α inhibition reduced binding of Sp1 and NF-κB to the IL1A promoter and prevented IL1α-mediated polarization of inflammatory CAFs in vitro. In PKT mice, p38α inhibition reduced tumor cell-specific Il1a and inflammatory CAF gene signatures by scRNA-seq, and favorably altered the infiltrating immune populations by flow cytometry. Lastly, pexmetinib with chemotherapy significantly reduced tumor burden and improved overall survival in a PDAC murine model.

Conclusions: These findings provide a new therapeutic opportunity to target the p38α MAPK pathway for suppression of IL1α-mediated stromal activation and combination with chemotherapy to overcome therapeutic resistance by modulating the stromal and immune microenvironment in PDAC.

Citation Format: Samara Singh, Austin R. Dosch, Siddharth Mehra, Iago de Castro Silva, Anna Bianchi, Vanessa Tonin Garrido, Zhiqun Zhou, Haleh Amirian, Edmond W. Box, Jashodeep Datta, Nagaraj Nagathihalli, Nipun B. Merchant. Inhibition of tumor cell-autonomous p38 MAPK suppresses IL1α-mediated inflammatory tumor-stromal crosstalk in pancreatic adenocarcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3627.

Abstract 653: Tumor cell-macrophage crosstalk drives immune suppression in pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) due to its unique genetic makeup and immunosuppressive tumor microenvironment (TME) produce a lack of response to current therapies. Macrophages, constitute a large innate immune subset and play a vital role in establishing an immune-suppressive microenvironment. Previously, we have identified Cyclic AMP Response Element Binding protein 1 (CREB) as a tumor cell-intrinsic oncogenic factor that promotes disease aggressiveness, poor survival, and immune suppression. Based on these, we sought to determine CREB mediated mechanisms of tumor-macrophage cross talk in driving immunosuppressive phenotype 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. CRISPR/CAS9-based genomic editing was utilized to ablate CREB (CREBKO) in KPC tumor cells. RNA-sequencing analysis was performed in KPC CREBKO tumor cells. ChIP-qPCR analysis was performed in KPC tumor cells. 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 in vivo. Additionally, these tissues were also processed for single-cell RNA (scRNA) transcriptomics analysis to evaluate the impact of CREB deletion on different cellular constituents within the TME.

Results: 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, we observed a decreased infiltration of tumor-promoting CD11b+ F4/80+ CD206+ 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. Further, CREB ablation in these tumors facilitated increased infiltration of activated effector memory CD8+ T cells and resulted in enhanced adaptive immune response. RNA transcriptomic-based analysis of CREBKO tumor cells revealed downregulation of Leukemia inhibitory factor (LIF) as of the top targets. Mechanistically, ChIP qPCR analysis after CREB1 pulldown confirmed its occupancy on LIF promoter region. Further, on exploring the role of CREB regulated LIF on immune subsets, incubation of macrophages with CREBWT conditioned media in the presence of LIF neutralizing antibody or blocking its receptor (LIFR) decreases polarization of macrophages towards M2 like phenotype.

Conclusion: These findings broaden our understanding of the tumor cell-intrinsic role of CREB in fostering immunosuppressive profile via LIF by promoting skewness of TAMs towards M2 like state in PDAC.

Citation Format: Siddharth Mehra, Vanessa Garrido, Samara Singh, Iago De Castro Silva, Zhiqun Zhou, Supriya Srinivasan, Luis Alberto Nivelo, Anna Bianchi, Andrew Adams, Haleh Amirian, Lluis Morey, Ban Yuguang, Alejandro Villarino, Jashodeep Datta, Nipun Merchant, Nagaraj Nagathihalli. Tumor cell-macrophage crosstalk drives immune suppression in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 653.

Abstract C031: Targeting granulocytic MDSC-derived inflammasome activation to overcome stromal inflammation in pancreatic cancer

Objective: The major drivers of therapeutic resistance in pancreatic ductal adenocarcinoma (PDAC) are myeloid cell-derived signaling that sustains immune tolerance/exclusion, and interleukin-1 (IL-1)-mediated inflammatory polarization of cancer-associated fibroblasts (iCAF) which promotes stromal inflammation by elaborating soluble factors (i.e., CXCL1, IL-6) that further accelerate myeloid chemotaxis. Moreover, we have recently shown that enrichment of pathways related to inflammasome activation-which involves recruitment of ASC complexes culminating in IL-1β generation—is a major contributor to chemoresistance in advanced PDAC patients. However, how these disparate pathways converge to mediate stromal inflammation in PDAC is incompletely understood. Methods: Single-cell RNA sequencing (scRNAseq) and caspase-1 luminescence assays in human and genetically engineered mouse (GEM) PDAC models were interrogated to identify cellular source of inflammasome-derived IL-1β. Gene set enrichment analysis in bulk RNA-sequencing data and signal transduction studies examined novel pathways associated with inflammasome activation in granulocytic myeloid-derived suppressor cells (gMDSC). scRNAseq and ASC-speck formation via confocal microscopy in intratumoral gMDSCs was performed in PKT mice treated with a novel anti-ASC antibody. Results: scRNAseq in human and GEM PDAC models revealed gMDSCs as the dominant source of inflammasome activation-derived IL1B expression. Functionally, caspase-1 activation and ASC-speck formation was strongest in intratumoral gMDSCs, compared with tumor-cell, CAF, macrophage, T-cell, and dendritic cell, compartments. Investigating developmental trajectories of single-cell transcriptomes in intratumoral gMDSCs from Panc02 tumors revealed an activated Cd14+ gMDSC state with strong co-expression of Cxcr2 and Il1b. As such, treatment of PKT GEM and orthotopically injected KPC tumor-bearing mice with CXCR2 inhibitor AZD5069 significantly abrogated inflammasome activation in intratumoral and splenic gMDSCs. In vitro signal transduction and RNA-seq studies revealed cooperativity between Tlr4-Myd88 and Cxcr2-Tpl2-p38 signaling in activating gMDSC-restricted inflammasome signaling. Co-culture of intratumoral gMDSCs and KPC CAFs ex vivo revealed strong induction of CAF-intrinsic Il6/Cxcl1 expression, which was dependent in part on CAF-Il1r1 expression and inflammasome activation in gMDSCs. We next used antibody to target ASC-a common downstream adaptor complex inducing inflammasomes-in vivo. Treatment of PKT mice with this anti-ASC antibody significantly attenuated ASC-speck formation in intratumoral gMDSCs as well as CAF-specific Il6/Cxcl1 expression via scRNAseq. Conclusions: These data uncover granulocytic MDSCs as the dominant source of inflammasome activation derived-IL1β in the PDAC TME, which promotes stromal inflammation via iCAF polarization. Therapeutic approaches-such as anti-ASC treatment-targeting gMDSC-intrinsic inflammasome activation may mitigate stromal inflammation and overcome therapeutic resistance in PDAC.

Citation Format: Nilesh Deshpande, Anna Bianchi, Iago De Castro Silva, Vanessa Garrido, Siddharth Mehra, Samara Singh, Ifeanyichukwu Ogobuiro, Nagaraj Nagathihalli, Nipun B. Merchant, Jashodeep Datta. Targeting granulocytic MDSC-derived inflammasome activation to overcome stromal inflammation 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 C031.

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 C059: Targeting tumor intrinsic p38 MAPK signaling to block IL-1α-mediated inflammatory tumor-stromal crosstalk in pancreatic cancer

Introduction: Pancreatic cancer (PDAC) remains a major therapeutic challenge due to its innate and acquired chemoresistance. Activating KRAS mutations, a hallmark of PDAC, mediate autocrine effects and crosstalk within the tumor microenvironment (TME), by inducing cytokines and chemokines that promote a pro-inflammatory and immunosuppressive stroma. We have identified KRAS-driven interleukin-1α (IL-1α) as a critical mediator of the inflammatory response due to its pleiotropic effects on cancer-associated fibroblast (CAF) activation and immune evasion, however the mechanisms that regulate IL-1α production remain poorly understood. In our efforts to identify targetable kinase pathways downstream of KRAS that are involved in IL-1α expression, we identified p38 stress-associated MAPK α (p38α MAPK) as a key regulatory pathway involved in IL-1α production in PDAC tumor cells. Methods: KRAS-mutant tumor cells were treated with pharmacologic inhibitors to pathways downstream KRAS and IL1A levels determined in response by qPCR. Mutant KRAS G12D plasmid was overexpressed in mouse embryonic fibroblasts, and IL-1α levels were determined in response by qPCR and ELISA with and without p38 inhibition. Inhibition of phosphorylated p38 MAPK was achieved pharmacologically with ARRY-614 and genetically with an shRNA lentiviral system in human and murine PDAC cell lines. ChIP-qPCR was performed on a human PDAC cell line with and without p38 MAPK inhibition. Tumor cells pre-treated with ARRY-614 were cocultured with human pancreatic stellate cells, and inflammatory CAF genes were measured by qPCR. Ptf1aCre/+;LSL-KrasG12D/+; Tgfbr2flox/flox (PKT) mice, a highly aggressive PDAC genetically engineered mouse model (GEMM), were treated daily with ARRY-614, chemotherapy, or combination therapy for downstream analysis. Results: Both pharmacologic and genetic inhibition of p38 MAPK significantly reduces IL1A transcription and protein levels in multiple human and murine PDAC tumor cell lines. Furthermore, p38 MAPK inhibition reduces binding of NF-kB to the IL1A promoter and prevents IL-1α-mediated activation of CAFs, characterized by a reduction in pro-inflammatory genes. Lastly, ARRY-614 in combination with chemotherapy significantly reduces overall tumor burden and favorably remodels the tumor microenvironment in a PDAC GEMM. Conclusions: These findings provide a compelling rationale to explore p38 MAPK inhibition in tumor cells as a novel treatment strategy to suppress IL-1α-mediated stromal activation and to combine p38 MAPK inhibition with chemotherapy to overcome therapeutic resistance through modulation of the stromal and immune microenvironment in PDAC.

Citation Format: Samara P. Singh, Austin R. Dosch, Siddharth Mehra, Iago de Castro Silva, Anna Bianchi, Vanessa Tonin-Garrido, Nilesh U. Deshpande, Zhiqun Zhou, Nagaraj Nagathihalli, Jashodeep Datta, Nipun B. Merchant. Targeting tumor intrinsic p38 MAPK signaling to block IL-1α-mediated inflammatory tumor-stromal crosstalk 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 C059.

Urolithin A attenuates severity of chronic pancreatitis associated with continued alcohol intake by inhibiting PI3K/AKT/mTOR signaling

Heavy alcohol consumption is the dominant risk factor for chronic pancreatitis (CP); however, treatment and prevention strategies for alcoholic chronic pancreatitis (ACP) remains limited. The present study demonstrates that ACP induction in C57BL/6 mice causes significant acinar cell injury, pancreatic stellate cell (PSC) activation, exocrine function insufficiency, and an increased fibroinflammatory response when compared with alcohol or CP alone. Although the withdrawal of alcohol during ACP recovery led to reversion of pancreatic damage, continued alcohol consumption with established ACP perpetuated pancreatic injury. In addition, phosphokinase array and Western blot analysis of ACP-induced mice pancreata revealed activation of the phosphatidylinositol 3 kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) and cyclic AMP response element binding protein (CREB) signaling pathways possibly orchestrating the fibroinflammatory program of ACP pathogenesis. Mice treated with urolithin A (Uro A, a gut-derived microbial metabolite) in the setting of ACP with continued alcohol intake (during the recovery period) showed suppression of AKT and P70S6K activation, and acinar damage was significantly reduced with a parallel reduction in pancreas-infiltrating macrophages and proinflammatory cytokine accumulation. These results collectively provide mechanistic insight into the impact of Uro A on attenuation of ACP severity through suppression of PI3K/AKT/mTOR signaling pathways and can be a useful therapeutic approach in patients with ACP with continuous alcohol intake.NEW & NOTEWORTHY Our novel findings presented here demonstrate the utility of Uro A as an effective therapeutic agent in attenuating alcoholic chronic pancreatitis (ACP) severity with alcohol continuation after established disease, through suppression of the PI3K/AKT/mTOR signaling pathway.

Emerging Role of CREB in Epithelial to Mesenchymal Plasticity of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive solid malignancy with a high rate of metastasis and therapeutic resistance as its major hallmarks. Although a defining mutational event in pancreatic cancer initiation is the presence of oncogenic KRAS, more advanced PDAC lesions accumulate additional genomic alterations, including loss of tumor suppressor gene TP53. Co-occurrence of mutant KRAS and TP53 in PDAC promotes hyperactivation of cancer cell signaling pathways driving epithelial to mesenchymal plasticity (EMP). The cellular process of EMP influences the biological behavior of cancer cells by increasing their migratory and invasive properties, thus promoting metastasis. Our previous work has demonstrated that oncogenic KRAS-mediated activation of cyclic AMP response element-binding protein 1 (CREB) is one of the critical drivers of PDAC aggressiveness. The therapeutic approach of targeting this key transcription factor attenuates tumor burden in genetically engineered mouse models (GEMMs) of this disease. Herein, we discuss the significant role of CREB in perpetuating disease aggressiveness and therapeutic resistance through the EMP process. Furthermore, this review updates the therapeutic implications of targeting CREB, highlighting the challenges and emerging approaches in PDAC.

Abstract 1328: Deciphering the role of CREB1 in shaping the tumor immune landscape of pancreatic ductal adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) remains a major therapeutic challenge with hallmarks including oncogenic mutations, desmoplastic architecture, and an immunosuppressive tumor microenvironment (TME). Previously, we have identified Cyclic AMP Response Element Binding protein 1 (CREB) as an oncogenic transcriptional factor downstream of KRAS that promotes disease aggressiveness, poor survival, and immune exclusion. Based on these, we sought to determine the impact of tumor intrinsic CREB deletion in shaping the tumor immune microenvironment.

Methods: We have generated a novel 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 (CREBEV) vs. CREBKO tumor cells to identify CREB-mediated transcriptomic changes. Syngeneic orthotopic tumor implantation of these cells was performed into the pancreata of mice. High dimensional immunophenotyping was accomplished to assess changes in the immune subsets with CREB deletion in murine tumors. Additionally, these tissues were processed for immunohistochemical and qPCR-based analysis to assess changes in fibroinflammatory and immune mediators.

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. Additionally, CREB deletion significantly remodeled the tumor stroma, as evidenced by the reduction in the expression of fibroinflammatory and immunosuppressive markers. In assessing the immune repercussions of CREB deletion in pancreatic tumors, we observed a decreased infiltration of CD11b+ myeloid-derived suppressor cells (MDSCs) and granulocytic-PMN MDSCs (CD11b+ Ly6Ghigh Ly6Clow F4/80-), with a concomitant increase in the antigen-presenting M1-like macrophages (F4/80+ MHC-II high CD86 high). Also, CREB ablation in these tumors further facilitated increased infiltration of activated effector CD8+ T cells resulted in enhanced anti-tumor immune response within the PDAC TME. Mechanistically, RNA transcriptomic and secretome analysis in CREBKO Vs. the wild type KPC tumor cells identified several differentially expressed immunomodulatory soluble mediators responsible for shaping CREB dependent immunogenic landscape in PDAC.

Conclusion: Overall, depleting CREB reshapes the tumor immune landscape to reduce innate immunosuppressive myeloid infiltration and reinvigorate the antitumor T cell immune responses to improve overall survival in PDAC.

Citation Format: Siddharth Mehra, Vanessa Garrido, Samara Singh, Iago D Silva, Luis Alberto Nivelo, Anna Bianchi, Shrey Modi, Zhiqun Zhou, Austin Dosch, Nilesh Deshpande, Supriya Srinivasan, Christine Rafie, Ifeanyichukwu Ogobuiro, Xi Chen, Alejandro Villarino, Jashodeep Datta, Nipun Merchant, Nagaraj Nagathihalli. Deciphering the role of CREB1 in shaping the tumor immune landscape of pancreatic ductal adenocarcinoma [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 1328.

Abstract 4187: Combined MEK and STAT3 inhibition reprograms the tumor microenvironment to overcome immunotherapy resistance in pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) is characterized by immune exclusion, stromal desmoplasia, and resistance to immune checkpoint inhibition (ICI). We have previously demonstrated that reciprocally activated RAS/RAF/MEK/ERK and JAK/STAT3 pathways mediate therapeutic resistance, while combined MEK and STAT3 inhibition (MEKi+STAT3i) overcomes this resistance in preclinical PDAC models. Given the dramatic decrease in tumor burden observed following MEKi+STAT3i, we investigated its effect on the stromal and immune microenvironment.

Methods: Ptf1aCre/+KrasG12D/+Tgfbr2flox/flox (PKT) mice were treated with vehicle, trametinib (MEKi, 3.3 mg/Kg, oral gavage three times weekly), ruxolitinib (STAT3i, 20 mg/Kg, oral gavage three times weekly), αPD-1 antibody (200 µg/mouse, i.p. injection twice weekly), combined MEKi+STAT3i or MEKi+STAT3i with αPD-1 beginning at 4-4.5 weeks of age. Mice were sacrificed after four weeks of treatment and tumors were harvested for single cell RNA sequencing, and high-dimensional immune-profiling by mass cytometry and flow cytometry.

Results: Single-cell transcriptomic analysis revealed that combined MEKi+STAT3i not only altered stromal architecture but also reprogramed tumor-resident CAFs from Il6/Cxcl1-expressing inflammatory phenotype towards Ly6a/Cd34-expressing fibroblast phenotype with both mesenchymal and hematopoietic progenitor-like properties. This stromal plasticity was associated with a striking attenuation and reprogramming of F4/80+ macrophages, M2-like macrophages (F4/80+CD206+), and MDSCs (CD11b+F4/80-Ly6G+/Ly6C+), as well as enhanced trafficking of CD4+ and CD8+ T-cells which exhibited a distinct effector and anti-apoptotic transcriptional program. The addition of MEKi+STAT3i to PD-1 blockade overcomes immune checkpoint resistance by significantly augmenting anti-tumor responses and dramatically improving survival in PKT mice, compared with vehicle treatment (median 181 vs. 44 days, p&lt;0.0001) or anti-PD-1 monotherapy (median 181 vs. 57 days, p=0.0005). The addition of MEKi+STAT3i to PD-1 blockade not only augmented the recruitment of activated and memory T-cell populations, but also improved their degranulating capacity and functional cytotoxicity compared to PD-1 blockade alone. Importantly, treatment of a patient with chemotherapy-refractory metastatic PDAC with MEKi (Trametinib), STAT3i (Ruxolitinib), and PD-1 inhibitor (Nivolumab) was well-tolerated and yielded significant clinical benefit.

Conclusion: These data uncover a novel paradigm in which combined MEKi+STAT3i reprograms stromal inflammation and immune tolerance to overcome immunotherapy resistance in PDAC. The clinical efficacy of combined MEKi+STAT3i and anti-PD1 treatment provides encouraging signals for its translatability and is currently being pursued in a clinical trial.

Citation Format: Vanessa Tonin Garrido, Jashodeep Datta, Xizi Dai, Anna Bianchi, Iago De Castro Silva, Purushottam Lamichhane, Siddharth Mehra, Samara P. Singh, Austin R. Dosch, Oliver Umland, Michael n N. VanSaun, Peter J. Hosein, Nagaraj Nagathihalli, Nipun Merchant. Combined MEK and STAT3 inhibition reprograms the tumor microenvironment to overcome immunotherapy resistance 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 4187.

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&lt;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.

Abstract 1565: Targeting stromal-specific p38 MAPK signaling to stifle inflammatory reprogramming of cancer-associated fibroblasts in pancreatic cancer

Introduction: Major contributors to therapeutic resistance in pancreatic ductal adenocarcinoma (PDAC) are the desmoplastic stroma that acts as a barrier to drug delivery and effector immune cell infiltration. In our efforts to identify mediators of therapeutic resistance, we identified the pro-inflammatory cytokine interleukin-1α (IL-1) to be critical in the activation and reprogramming of neighboring cancer-associated fibroblasts (CAFs) within the stroma to a pro-inflammatory phenotype to promote myeloid cell chemotaxis. Our mechanistic studies have identified the p38 MAPK pathway as a novel mediator of IL-1-induced CAF activation from quiescent stellate cells into the inflammatory fibroblast. Our central hypothesis is that disruption of the IL-1/p38 MAPK signaling cascade in pancreatic stellate cells (PSCs) and CAFs can improve therapeutic resistance by remodeling the fibrotic stromal landscape and the overall immune microenvironment in PDAC tumors.

Methods: Inhibition of phosphorylated p38 MAPK was achieved pharmacologically with Pexmetinib and genetically with an shRNA lentiviral system in CAF and PSC cell lines. Inflammatory PSC/CAF activation was determined by qPCR, immunofluorescence, and vitamin A assay. Ptf1acre/+;LSL-KrasG12D/+; Tgfbr2flox/flox (PKT) mice were treated with the p38 inhibitor, pexmetinib (30mg/kg, daily PO), or vehicle control for 2.5 weeks prior to sacrifice. For survival studies, PKT mice were treated with vehicle, gemcitabine (20 μg/twice weekly), pexmetinib, or combination until moribund.

Results: Inhibition of p38 MAPK in PSCs prevented activation into an inflammatory fibroblast in vitro when stimulated with IL-1 or tumor cell cocultures. p38 MAPK inhibition in vivo resulted in signification reduction of PDGFR+ CAFs in a PDAC GEMM. Additionally, p38 MAPK inhibition resulted in a significant reduction of circulating myeloid cells (CD11b+) and intratumoral monocytic MDSCs (Ly6C+). p38 inhibition, in combination with chemotherapy, significantly improves overall survival in a PDAC GEMM.

Conclusions: These findings provide important mechanistic data to explore p38 MAPK inhibition to target the fibrotic stroma and reduce immunosuppressive myeloid levels in tumors and provide compelling preclinical evidence to combine pexmetinib with chemotherapy to improve overall survival in PDAC.

Citation Format: Samara Singh, Austin R. Dosch, Siddharth Mehra, Iago de Castro Silva, Anna Bianchi, Vanessa Tonin Garrido, Nilesh Deshpande, Zhiqun Zhou, Jashodeep Datta, Nagaraj Nagathihalli, Nipun Merchant. Targeting stromal-specific p38 MAPK signaling to stifle inflammatory reprogramming of cancer-associated fibroblasts 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 1565.

Abstract PO-049: Single-cell transcriptomic analysis reveals interleukin-1 inhibition suppresses inflammatory cancer-associated fibroblast signaling and improves the immune response in pancreatic cancer

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is resistant to immune checkpoint blockade due to its intrinsic immunosuppressive properties. The fibroinflammatory stroma, particularly inflammatory cancer associated fibroblasts (CAFs), are a key determinant of the immune microenvironment in PDAC, however therapies aimed at broad-based targeting of PDAC stroma have been decidedly unsuccessful. Recently, interleukin-1α (IL-1) has emerged as a critical mediator of CAF activation and orchestrator of immune suppression in PDAC. We sought to explore the effects of IL-1 blockade on reprogramming the immune microenvironment and enhancing susceptibility to checkpoint inhibition through suppression of inflammatory stromal signaling in PDAC. Methods: Ptf1acre/+;LSL-KrasG12D/+; Tgfbr2flox/flox (PKT) mice were treated with the recombinant IL-1 receptor antagonist (anakinra, 50 mg/kg IP BID) or vehicle control. Single-cell cDNA library generation was performed using the 10× Chromium System. Expression matrices were processed using the R package Seurat 3.0 and clustered using AUC-based scoring algorithm. Immunophenotyping experiments were performed on single-cell suspensions using the Cytoflex platform. For survival studies, PKT mice were treated with vehicle, anti-PD1 antibody (200 μg/twice weekly), anakinra, or combination until moribund. Tissues were further processed for downstream qPCR and histologic analyses. Human pancreatic stellate cell (hPSC) and immortalized CAF cell lines procured from patient-derived xenografts were utilized for in vitro mechanistic studies. Results: Single-cell analysis revealed that anakinra treatment in PKT mice reduced levels of numerous pro-inflammatory CAF cytokines, including Cxcl1 and Il6, within CAF subclusters. Confirmatory qPCR of bulk tumor samples revealed a significant reduction in Cxcl1 and Il6 gene transcription and a global reduction in stromal fibrosis with anakinra treatment. IL-1 inhibition selectively reduced alternatively-activated macrophage (CD11b+F480+CD206+) and PMN-MDSC (CD11b+Ly6G+) populations within PDAC tumors. Combination treatment of anakinra with anti-PD1 antibody reduced tumor weight, increased intratumoral levels of effector memory (CD8+CD44+CD62L-) and activated cytotoxic (CD8+CD107+) T cells, and improved overall survival in PKT mice. In vitro studies demonstrated that conditioned media from PDAC tumor cells significantly activated Cxcl1 and Il6 gene transcription in hPSCs and CAFs in an IL-1α-dependent manner. IL-1-mediated transcription of these cytokines was abrogated by selective inhibition of both the p38 MAPK and NFκB cascades, demonstrating a coordinated effort between these signaling pathways in modulating the IL-1-induced stress response in stromal cells. Conclusions: These findings provide important mechanistic data and compelling pre-clinical evidence to explore IL-1 inhibition in combination with immune checkpoint blockade in PDAC patients.

Citation Format: Austin R. Dosch, Samara Singh, Xizi Dai, Siddharth Mehra, Anna Bianchi, Iago De Castro Silva, Supriya Srinivasan, Nagaraj Nagathihalli, Jashodeep Datta, Nipun B. Merchant. Single-cell transcriptomic analysis reveals interleukin-1 inhibition suppresses inflammatory cancer-associated fibroblast signaling and improves the immune response in pancreatic cancer [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-049.

Abstract PO-056: Targeting of cancer associated fibroblast-specific MEK1 and STAT3 to overcome immunosuppressive microenvironment in Pancreatic Ductal Adenocarcinoma (PDAC)

Background Activating KRAS mutations, stromal desmoplasia, and immune exclusion are fundamental to therapeutic resistance in PDAC. We have previously shown an inverse correlation of reciprocally-activated MEK1 and STAT3 signaling, combined inhibition of which remodels the tumor stroma resulting in enhanced effector immune cell infiltration and improved survival in an aggressive genetically engineered mouse model (GEM) of PDAC. Based on these results, we sought to determine the effects of cancer-associated fibroblasts (CAF) specific silencing of MEK1 and STAT3 on the immune microenvironment and PDAC tumor growth. Methods CRISPR/Cas9 ablation of MEK1 and STAT3 was performed in CAFs derived from LSL-KrasG12D/+; Trp53fl/+; Pdx1-Cre (KPC) GEM. RNA sequencing identified transcriptomics changes in MEK1 KO / STAT3KO CAFs vs. wildtype KPC-CAFs. The effect of CAF-specific deletion of MEK1/STAT3 in modulating the immune microenvironment was assessed using multiplex immunophenotyping in orthotopic tumor implantation models of co-cultured KPC tumor cells with MEK1KO / STAT3KO CAFs. Results CAF-specific MEK1/STAT3 ablation resulted in significant retardation of growth kinetics of 3D spheroids, as well as migration and invasion, in KPC tumor cell: CAF co-culture systems. Interestingly, the transcriptome of MEK1KO/ STAT3KO CAFs was strongly enriched for antigen-presenting machinery, IL-12, and IFN signaling pathways, while revealing downregulation of Wnt/β-catenin and collagen pathways. Multiplex cytokine arrays confirmed dramatically increased IL-12p70, IL-2, CXCL10 secretion, and decreased IL-10 secretion in MEK1KO / STAT3KO vs. wildtype. Flow cytometric analysis confirmed increased expression of class I and class II MHC, but not co stimulatory molecules, expression in these double knock out CAFs. Orthotopic implantation of MEK1KO / STAT3KO vs. wildtype CAFs with KPC tumor cells in C57BL/6 pancreata revealed significantly increased infiltration of activated effector degranulating CD8+ T-cells (CD62LlowCD44highCD107low) with reduced exhaustion phenotype (PD1highCD107low)in MEK1KO /STAT3KO vs. wild type CAF tumor-bearing mice. Conclusion CAF-specific ablation of MEK1 and STAT3 generates features suggestive of augmented antigen-presenting capacity and results in adaptive immune invigoration in the PDAC tumor microenvironment. Further mechanistic studies exploring this novel CAF-specific phenotype is warranted.

Citation Format: Siddharth Mehra, Xizi Dai, Anna Bianchi, Austin Dosch, Iago de Castro Silva, Prateek Sharma, Samara Singh, Supriya Srinivasan, Nagaraj Nagathihalli, Jashodeep Datta, Nipun Merchant. Targeting of cancer associated fibroblast-specific MEK1 and STAT3 to overcome immunosuppressive microenvironment in Pancreatic Ductal Adenocarcinoma (PDAC) [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-056.

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.

Abstract 888: Exploring the signaling and activity interactome between oncogenic RAS and the nucleotide pool-detoxifying enzyme MTH1

MutT Homolog 1 (MTH1) is a NUDIX pyrophosphorylase that hydrolyzes oxidized purine nucleoside triphosphates in the nucleotide pool, thus preventing their incorporation into DNA. Our prior work has shown that MTH1 is critical for the maintenance of multiple pro-tumorigenic phenotypes in oncogenic RAS-driven cancer cells, with its depletion leading to decreased tumor formation in vivo. Our subsequent analyses of TCGA patient datasets showed elevated MTH1 expression to be significantly associated with poorer disease-free survival in RAS-mutated cancers, such as that of the lung and pancreas. We found that MTH1 mRNA levels were positively correlated with KRAS levels even in early-stage non-small cell lung cancer patient tissues, and that the introduction of oncogenic KRAS was sufficient to upregulate MTH1 mRNA and protein levels. The aim of this study is to identify RAS-effector signaling intermediates affecting MTH1 expression and activity.

Chemical inhibitors of the MAPK/ERK, PI3K/AKT and NOX pathways, plus oncogenic RASV12-effector domain mutants (RASV12- S35/ E38/ G37/ C40), were used to identify key signaling molecular mediators of MTH1 expression in the distinct RAS isoforms (H- and K-RAS). The dependencies of the different KRASG12-mutant polymorphisms (KRASG12- C/ D/ V) on MTH1 expression and activity, as well as candidate transcription factors regulating MTH1 expression, were evaluated.

Our work shows MTH1 at the nexus of crosstalk between different effector pathways activated downstream of RAS. Dissecting these signaling intermediates are important in identifying alternate pathways of MTH1 regulation, which may manifest as resistance mechanisms to standard-of-care cancer treatments. Our work will also help understand how to best leverage MTH1 as a therapeutic target in oncogenic RAS-driven cancers driven by the different isoforms, and their respective mutant polymorphisms.

Citation Format: Govindi J. Samaranayake, Clara I. Troccoli, Christina Jayaraj, Brittany C. Durden, Nagaraj Nagathihalli, Nipun Merchant, Priyamvada Rai. Exploring the signaling and activity interactome between oncogenic RAS and the nucleotide pool-detoxifying enzyme MTH1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 888.

Abstract 5264: Metabolic reprogramming with β-alanine to overcome chemotherapy resistance in pancreatic cancer

Background: Increased aerobic glycolysis (Warburg effect) leading to acidic microenvironment confers chemoresistance to weakly basic Gemcitabine, the standard treatment in Pancreatic ductal adenocarcinoma (PDAC). Metabolomic perturbations in two PDAC cell lines having differential sensitivity to Gemcitabine was investigated by profiling over 40 metabolites using 1H-NMR spectroscopy. Notably, a significant decrease in the concentration of β-alanine (βA) was observed in Gem resistant compared to Gem sensitive cell line, suggesting βA may have a role in chemotherapy response. We aimed to evaluate the role of βA supplementation in improving Gem efficacy in Gem resistant cell lines

Methods: PDAC Panc-1 cell line extracts treated with Gem with and without βA supplementation were analysed via 1H-NMR spectroscopy. Aerobic glycolysis was quantified by measuring extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) using the Seahorse XF analyser platform. Global mRNA profiling was done by Next Generation Sequencing. Proliferation, migration and cell cycle analysis was measured by Xcelligence real time cell analysis system and flow cytometry, respectively. PANC-1 and BxPC-3 tumor xenografts treated with Gemcitabine with and without βA for 4 weeks and the tumor volumes and weights were measured.

Results: βA supplementation in Gem resistant cells results in: (1) decreased basal glycolytic rate, proton leak and ATP production; (2) increased pyruvate, decreased lactic acid and NAD+ concentrations with decreased LDH-A transcription; also increased carnosine levels with a more basic pH in the conditioned media; (3) enhanced sensitivity to Gem treatment, with a significant reduction in proliferation, cell migration, and increased apoptosis and relative hENt-1 mRNA levels and (5) xenograft tumor volumes and weights were significantly reduced upon βA supplementation.

Conclusion: βA supplementation reprograms cell metabolism by normalizing energy production and reducing microenvironment acidification, thus enhancing chemo-sensitivity in Gem resistant PDAC cells and xenografts. βA can be potentially used as a co-therapeutic in PDAC.

Note: This abstract was not presented at the meeting.

Citation Format: Danny Yakoub, Smitha T. Totiger, Alexandra Moran, Sujit Suwal, Julio Pimentel, Lauren O'Donell, Jamie Walls, Nagaraj Nagathihalli, Nipun Merchant. Metabolic reprogramming with β-alanine to overcome chemotherapy resistance in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5264.

Abstract 5042: CREB transgenic mice to study alcohol-associated pancreatic carcinogenesis

Background: Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related deaths in the United States. Chronic alcohol (&gt;60 grams/day) consumption is strongly associated with the risk of PDAC development. The metabolites generated from alcohol have been shown to cause significant pancreatic injury. Although the association of alcohol with PDAC progression has been established, the details of the underlying molecular and cellular mechanisms governing this process are unknown. Our study revealed that alcohol-associated pancreatic carcinogenesis correlates with CXCL12-induced activation of cyclic AMP response element binding protein (CREB). In this study, we examined newly developed CREB knockout (CREBfl/fl) mouse in pancreas.

Methods: Human pancreatic epithelial lines (HPNE), HPNE cells with KRAS (HPNE-KRAS), pancreatic stellate cells (PSCs), pancreatic intraepithelial neoplasia (PanIN) mouse cell lines (LSL-KrasG12D/+; Pdx1Cre/+) and cancer-associated fibroblasts (CAFs) cells were exposed to chronic alcohol (50 mM) and analyzed for phospho-kinases in cell lysates and cytokines in conditioned media. Inducible Ptf1aCreERTM;KRASG12D/+ (iPK) mice and CREB knockout (CREBfl/fl) with KRAS activation [Ptf1aCreERTM;KRASG12D/+;CREBfl/fl (iPKCREBKO)] mice were used to investigate the effect of alcohol on CREB activation and the role of CREB in alcohol-associated PDAC pathogenesis. iPK and iPKCREBKO mice were exposed to Lieber-DeCarli alcohol diet for up to 14 weeks with or without caerulein injections. The number of acinar cells (amylase), ducts (cytokeratin 19), PanIN lesions (alcian blue positive), fibrosis (sirius red) and activation of CREB were measured by immunohistochemistry at 6 and 14 weeks of alcohol exposure in vivo. Serum obtained from alcohol-fed iPK and iPKCREBKO mice were analyzed for significant cytokine release upon alcohol exposure in vivo. We then determined the biologic effects of pharmacologic CREB inhibition in iPK mice exposed to alcohol diet.

Results: We found increased pCREB levels in HPNE and HPNE-KRAS cells upon treatment with alcohol, which was further associated with the up-regulation of the CXCL12 protein in the conditioned media. Serum CXCL12 and tissue pCREB levels were high in alcohol fed iPK mice when compared to their corresponding control diet-fed mice. Blocking CXCL12 with Plerixafor, a CXCL12-CXCR4 axis inhibitor, decreased alcohol-induced pCREB levels. Finally, exposure of iPK mice to an alcohol diet coupled with cerulein administration significantly increased the number of PanIN lesions (alcian blue+ cells), and decreased acinar cells when compared to alcohol-fed iPKCREBKO mice.

Conclusion: These findings implicate CREB as a critical oncogenic driver in alcohol addiction-induced pancreatic carcinogenesis. Additionally, CXCL12 represents an important mediator of CREB activation, which can be pharmacologically targeted.

Citation Format: Tulasigeri Totiger, Supriya Srinivasan, Michael VanSaun, Chandrashekhar Joshi, Chanjuan Shi, Xizi Dai, Rajinder Dawra, Alexander Gaidarski, Eric Nestler, Nipun Merchant, Nagaraj Nagathihalli. CREB transgenic mice to study alcohol-associated pancreatic carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5042.

Abstract 1249: Animal model in the prevention of alcoholic pancreatitis

Background: Alcohol abuse is a major risk factor for pancreatitis. Alcohol addiction-induced molecular pathogenesis of pancreatitis remains obscure, and no current effective treatment exists. Therefore, approaches to investigate pathogenesis, prevention and cellular mechanisms by which alcohol causes pancreatitis are necessary for establishing therapeutics. Our efforts demonstrate that alcohol induces activation of a major intracellular transcriptional factor, cyclic AMP response element-binding protein (CREB). We further investigated the functional role of CREB in alcohol-induced pathogenesis of pancreatitis using cellular and genetic mouse models of pancreas.

Materials and Methods: Human tissue microarrays were immunostained to determine the significance of pCREB expression among pancreatic tissues obtained from normal and chronic pancreatitis. Rat acinar cell line AR42J and mouse PSCs (mPSCs) were exposed to alcohol (50 mMol/L). Inducible Ptf1aCreERTM knockin mice and Ptf1aCreERTM;CREBfl/fl (iPC) mice were fed with Lieber Decarli diet alcohol or regular diet for 14 weeks with or without caerulein (50 µg/kg). Mice were then euthanized 24 hours after the last caerulein injection, and pancreas tissues were processed for morphometric analysis (necrosis, vacuolization, hemorrhage, edema and inflammation) and immunohistochemical analysis of amylase, trichrome blue, SMA, collagen 1, fibronectin and pCREB expression. To determine whether alcohol accelerated morbidity in mice, we evaluated pathogenesis of chronic pancreatitis by analyzing acinar atrophy and pancreatic fibrosis.

Results: Expression of pCREB was significantly higher (p &lt;0.001) in chronic pancreatitis vs. normal patient tissues, confirming the role of activated CREB in pancreatitis. Activated CREB levels were very high in alcohol-fed Ptf1aCreERTM mice when compared with control diet-fed mice. Pancreatic sections from alcohol-fed mice challenged with caerulein revealed significantly higher score of acinar cell vacuolization and necrosis, inflammatory infiltrate and hemorrhage compared with minimal lesions in control diet-fed animals receiving caerulein. Pancreatic sections from alcohol-fed Ptf1aCreERTM animals showed higher score of histologic injury, extracellular matrix deposition, collagen deposition and increased pancreatic fibrosis when compared with control-fed mice. iPC mice showed decrease in the pathogenesis of chronic pancreatitis when compared to Ptf1aCreERTM mice with alcohol.

Conclusion: CREB is overexpressed in pancreatitis and alcohol activates CREB, which then drives pathogenesis of pancreatitis. Severity of pancreatitis in response to alcohol is diminished in the absence of CREB. Therefore, we conclude that targeting CREB represents a promising treatment for alcohol-induced pancreatitis.

Citation Format: Supriya Srinivasan, Tulasigeri Totiger, Michael VanSaun, Fanuel Messaggio, Chanjuan Shi, Austin Dosch, Eric Nestler, Nipun Merchant, Nagaraj Nagathihalli. Animal model in the prevention of alcoholic pancreatitis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1249.

Abstract 2802: High fat diet increases development of hepatocellular carcinoma in glycine N-methyltransferase deficient mice

Introduction: Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide. HCC typically arises in patients with chronic liver disease or cirrhosis, yet it is increasingly associated with non-alcoholic fatty liver disease (NAFLD), specifically nonalcoholic steatohepatitis (NASH) in the absence of cirrhosis. NAFLD is associated with obesity, metabolic syndrome, and/or patients with type II diabetes. Our previous studies have shown that high fat diet induced hepatic steatosis increases proliferation of hepatocytes and the growth of malignant tumors in a murine model. Glycine N-MethylTransferase (GNMT) expression is lost in over 95% of HCC, and mice deficient in GNMT develop spontaneous HCC by 6 months of age. We hypothesized that GNMT deficient mice would have an increased susceptibility for the development and growth of HCC when a fed high fat diet.

Methods: Wildtype and GNMT deficient mice were placed on lean diet (LD, 13% calories from fat) or high fat diet (HFD, 42% calories from fat) at eight weeks of age. An initial cohort of mice were sacrificed after 3 months on diet (6 months of age) to assess for early tumor burden. A second cohort of mice was analyzed by magnetic resonance imaging (MRI) after 6 months on diet (9 months of age) and then sacrificed to assess for late stage disease. All mice were assessed for body weight, liver weight, pancreatic weight, and proliferative index (Ki67).

Results: GNMT deficient mice failed to gain weight when placed on HFD, which remained at levels equivalent to wildtype LD mice. At three months of age, wildtype mice on HFD had significantly enlarged livers due to hepatic steatosis. HFD fed GNMT deficient mouse livers were nearly 50% the size of wildtype livers and contained only minimal fatty deposits. Further, livers from HFD and LD fed GNMT mice were equivalent after 3 months, yet they were larger than wildtype mice fed LD. After six months on diet, MRI analysis showed significantly larger livers in HFD fed GNMT mice compared to LD fed GNMT mice due to extensive tumor burden. All wildtype mice lacked any tumors after six months regardless of diet. Histological analysis revealed a heightened cellular proliferation via Ki67 staining in GNMT deficient livers compared to wildtype livers. In comparison, GNMT silencing also occurs in pancreatic cancer, yet none of the GNMT deficient mice developed pancreatic tumors. However, small focal areas of pancreatitis were detected regardless of diet. Additionally, pancreatic weight was significantly decreased in HFD fed GNMT deficient mice compared the LD GNMT deficient mice.

Conclusions: While high fat diet did not induce obesity in GNMT deficient mice, it significantly increased cellular proliferation and primary tumor growth in the liver. Understanding dietary factors that impact the microenvironment of the liver and contribute to HCC development and progression is vital to finding new therapeutics for this malignancy.

Citation Format: Michael N. VanSaun, Alisha Mendonsa, Fanuel Messaggio, Nagaraj Nagathihalli, Lee Gorden. High fat diet increases development of hepatocellular carcinoma in glycine N-methyltransferase deficient mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2802. doi:10.1158/1538-7445.AM2017-2802

Abstract 5259: Urolithin A prevents pancreatic tumor growth and increases survival by inhibiting PI3K/PDK1 and STAT3 signaling

Pancreatic ductal adenocarcinoma (PDAC) is the 3rd leading cause of cancer-related mortality in the United States. Most patients present with an advanced disease and the majority die within five years, many surviving less than six months. Cytotoxic chemotherapy including Gemcitabine (Gem), FOLFIRINOX, nab-paclitaxel offer modest improvement in survival, albeit at the cost of increased side effects and unwanted toxicities. Therefore, developing novel chemotherapeutic agents for PDAC treatment is critical to improve survival. Ellagic acid/ellatitannins are abundantly present in the pomegranate and berries, are actively metabolized by the intestinal microflora to Urolithin A (UA). Oral administration of UA has shown to be highly bioavailable and non-toxic. UA inhibits multiple kinases that are known to be involved in PDAC progression and metastasis. Therefore, we hypothesized that UA would elicit potent anti-cancer therapeutic potential in PDAC. The effect of UA on kinase activity was assessed . Inhibition of AKT (downstream of PI3K/PDK1), p70 S6 Kinase (PS6K) and STAT3 activation was quantified in PDAC cells treated with UA in dose-dependent manner. The mechanism of action was validated for UA’s activity on PI3K/PDK1, PS6K and STAT3 activation using immunoblot analysis. MiaPaCa2 cells were treated with specific inhibitors for either AKT (MK2206) or STAT3 (AZD1480) and analyzed for tumorigenicity. UA treated PDAC cells were analyzed for cell proliferation, cell invasion and colony formation. Cell cycle analysis and cell apoptosis were measured by flow cytometry. To test the efficacy of UA in vivo, cells were implanted subcutaneously in athymic nude mice. The animals received UA daily and tumor volume was measured for 5 weeks. Next, we assessed tumor growth and overall survival (OS) in PKT (Ptf1acre/+;LSL-KrasG12D;Tgfbr2fl/fl) mice, an aggressive genetically engineered PDAC mouse model, in response to UA and/or Gem treatment. Tissues from the xenografts and PKT mice treated with vehicle or UA were analyzed for cell proliferation (Ki67) and apoptosis (cleaved Caspase 3) by immunohistochemistry. High expression levels of activated STAT3 or AKT correlate with decreased survival in PDAC. UA treated MiaPaCa2 cells showed significant dose-dependent increase in apoptosis and decrease in anchorage-independent growth. UA inhibited AKT, PS6K and STAT3 signaling. As a single agent, UA effectively reduced in vivo PDAC tumor growth. Immunohistochemistry of UA treated tissues from tumor xenografts and PKT mice showed inhibition of Ki67 positive tumor cells and increased cleaved caspase 3 staining. PKT mice treated with UA showed a decrease in tumor size and an increased OS when compared to vehicle or Gem treated mice alone. These findings show that UA is a novel inhibitor/modulator/regulator for multiple signaling pathways in PDAC. These results suggest UA has potential for pre-clinical development in pancreatic cancer.

Citation Format: Supriya Srinivasan, Venkatakrishna Jala, Kumar Honnenahally, Jason Castellanos, Praveen Kumar Vermula, Michael VanSaun, Nipun Merchant, Nagaraj Nagathihalli. Urolithin A prevents pancreatic tumor growth and increases survival by inhibiting PI3K/PDK1 and STAT3 signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5259. doi:10.1158/1538-7445.AM2017-5259

Abstract B75: Targeting the immune-microenvironment with combined inhibition of MEK and STAT3 in a mouse model of pancreatic cancer

Introduction: Activating KRAS mutations are commonly found in PDAC and lead to constitutive downstream activation of MEK, which results in uncontrolled proliferation. We have previously shown that MEK inhibition results in activation of STAT3 signaling which confers drug resistance and continued cancer cell growth while combined STAT3 and MEK inhibition overcomes this resistance. Since STAT3 is a critical mediator of cytokine signaling and MEK is a mediator of cytokine production, we sought to determine the effects of MEK and STAT3 inhibition on the immune tumor microenvironment (TME). Tumor infiltrating immune/inflammatory cells, such as regulatory T cells (Tregs), myeloid –derived suppressor cells (MDSCs) and macrophages support tumor growth and contribute to therapeutic resistance. We hypothesized that combined MEK and STAT3 inhibition down regulates the suppressive immune infiltrates and promotes an anti-tumor microenvironment.

Experimental procedure: To understand the effect of MEK and/or STAT3 inhibition of PDAC cells, three dimensional spheroid cultures of PDAC cells (MiaPaCa-2, Panc-1, BxPC3) were prepared. Spheroid cultures were treated with inhibitors to MEK (AZD6244) and/or STAT3 (AZD1480) for 10 days. At the end of treatment, spheroids were quantified for size and metabolic activity. To determine in vivo effects, Ptf1a Cre/+ ; LSL-KrasG12D; Tgfbr2fl/fl (PKT) mice were treated with either vehicle, MEK inhibition, STAT3 inhibition, or the combination for 2 weeks. Post-treated pancreatic tissue was extracted, weighed, and examined for pancreatic integrity using immuno-histological and enzymatic analyses. Alternately, the pancreas and spleen were extracted from the mice, cells were isolated from the tissue, and subsequently labeled with antigens for macrophages (CD45, F4/80, CD86, CD80, CD206, CD204), myeloid cells (CD45, CD11b, Ly6g, Ly6c), and T cells (CD45, CD3e, CD4, CD8, CD25, FoxP3) before assessing population percentages by flow cytometric analysis.

Results: Treatment with MEK inhibition resulted in slightly reduced spheroid size and metabolic activity; however, combined MEK/STAT3 treatment led to a significant decrease in spheroid size as well as metabolic activity. In PKT mice, treatment with combined inhibitors for MEK and STAT3 resulted in the enhanced suppression of tumor formation compared to either agent alone. Histological analysis of combined MEK/STAT3 significantly inhibited tumor size, maintained a higher percentage of pancreatic integrity, displaying increased percentage of normal acini, reduced CK-19 staining, reduced collagen deposition and minimal alcian blue stain. Analysis of the tumor immune infiltrates revealed a significant reduction in the immunosuppressive/tumor promoting myeloid derived suppressor cell (MDSC) population (CD45+CD11b+Ly6g+Ly6c+) and regulatory T cell population (CD45+CD3e+CD4+CD25+FoxP3+) in the pancreas of mice treated with combined MEK/STAT3 inhibition compared to control mice or mice treated with single agents. Alternately, combined MEK/STAT3 inhibition promoted an increased neutrophil population (7AAD-CD11b+Ly6c+Ly6g-), but a decreased inflammatory M1 macrophage population (CD45+F4/80+CD80+CD86+).

Conclusions: Combined MEK/STAT3 inhibition downregulates the tumor promoting immune infiltrates resulting in dramatically reduced tumor burden and enhanced normal pancreatic tissue in a highly aggressive mouse model of pancreatic cancer.

Citation Format: Casey Roberts, Michael N. VanSaun, Purushottam Lamichhane, Fanuel Messaggio, Krisztina Kovacs, Supriya Srinivasan, Xizi Dai, Jennifer Barretta, Nagaraj Nagathihalli, Nipun B. Merchant.{Authors}. Targeting the immune-microenvironment with combined inhibition of MEK and STAT3 in a mouse model of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B75.

Abstract B71: Resistance to MEK inhibition in pancreatic cancer is associated with amphiregulin mediated EGFR-STAT3 activation

Introduction: Mutations in the KRAS oncogene occur in the majority of pancreatic ductal adenocarcinomas (PDAC), resulting in aberrant activation of the MAPK (RAS-RAF-MEK-ERK) pathway, driving malignant progression. Targeting KRAS has remained an elusive goal. Therefore, efforts have focused on targeting downstream effectors of RAS. The clinical efficacy of MEK inhibitors in other malignancies confirms that targeting the MAPK pathway has therapeutic potential. Unfortunately, clinical trials of MAPK-directed therapies have been unsuccessful in PDAC. Here, we report a novel mechanism of resistance to MAPK-directed therapies, which is associated with amphiregulin (AREG)-mediated activation of EGFR-STAT3 signaling.

Experimental procedure: The effects of MEK inhibition on the phosphorylation of multiple signaling proteins and EGF family ligands was assessed. Activation of MAPK and STAT3 was quantified in human pancreatic tissues, and then correlated with overall survival (OS). Cell lysates from mouse PanIN lines derived from the LSL-KrasG12D/+;Pdx1Cre/+ and PDA line from LSL-KrasG12D/+; Trp53R172H/+;Pdx1Cre/+ mouse models of PDAC were immunoblotted for activated MAPK and STAT3 expression. AREG release was measured in the conditioned media of PDAC cells treated with MEK, EGFR, STAT3, and/or TACE inhibitors and TACE siRNA knock down cells treated with MEK, EGFR, or STAT3 inhibitors. Cell invasion, colony formation, spheroid formation, metabolic activity, cell cycle analysis, and apoptosis assays were performed with human PDAC cells treated with inhibitors for TACE, MEK, EGFR and STAT3 in combinations. PDAC xenografts and patient derived xenografts (PDXs) were treated either with vehicle, the MEK inhibitor AZD6244, the STAT3 inhibitor AZD1480 or both drugs and analyzed for spheroid growth. PKT mice (Ptf1acre/+;LSL-KrasG12D;Tgfbr2fl/fl) were treated with AZD6244 and AZD1480 and assessed for OS. Tissues from the xenografts and PKT mice were analyzed for cell proliferation and apoptosis markers. Plasma from the PKT mice treated with the drugs and their combinations was analyzed released AREG by ELISA.

Results: Targeting the MAPK pathway is a novel approach to inhibit KRAS mutant tumor progression and improve therapeutic response in PDAC. However, our results show that MAPK inhibition leads to activation of TACE and EGFR and subsequent activation of STAT3 signaling. Combined inhibition of MEK/STAT3 or MEK/EGFR resulted in sustained blockade of MEK, EGFR and STAT3 signaling, decreased cell invasion, colony formation, reduced spheroid size, and metabolic activity in vitro. Growth of flank PDAC xenografts and human PDX tumors in vivo were significantly decreased with combined MEK and STAT3 inhibition when compared to vehicle or monotherapy treatment. OS in PKT mice was extended to a median of 85 days with combined MEK and STAT3 inhibition vs. 52 days for vehicle treated mice (p &lt; 0.001). AREG release was significantly reduced with combined MEK/STAT3 inhibition. TACE siRNA in PDAC cells confirms the role of AREG release in mediating EGFR signaling and overcoming MEK inhibitor resistance. Evaluation of TACE activation and AREG shedding/release in response to MEK inhibition demonstrated that resistance to MEK inhibition in PDAC is mediated by reactivation of the STAT3 pathway, which is strongly influenced by increased AREG production.

Conclusions: Our study provides insights into the molecular mechanisms that help explain the heterogeneous response and therapeutic resistance of PDAC to MAPK pathway inhibition and provide a strong rationale that AREG mediated EGFR-STAT3 pathway activation is a major resistance mechanism that impairs the efficacy of MEK inhibitors.

Citation Format: Nagaraj Nagathihalli, Jason Castellanos, Chanjuan Shi, Casey Roberts, Michael VanSaun, Nipun Merchant.{Authors}. Resistance to MEK inhibition in pancreatic cancer is associated with amphiregulin mediated EGFR-STAT3 activation. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B71.

Abstract B78: RAD51 sensitizes pancreatic cancer cells to AKT inhibition

Introduction: Cell survival after DNA damage relies on DNA repair processes to protect the integrity of the genome. The repair process involves DNA homologous recombination system that requires numerous factors including the recombinase RAD51 and BRCA2, which co-localize to replication centers within the damaged cell nucleus. The defective DNA repair mechanisms in cancer cells can be exploited for therapy, when abrogated DNA double-strand breaks (DSB) repair causes genomic instability and increase in cancer cell sensitivity to consequential cellular apoptosis. Targeted therapies are challenged by emergence of tumor cell resistance associated with downstream components of KRAS signaling pathways in pancreatic ductal adenocarcinoma (PDAC). It is, therefore, essential to develop novel therapeutic strategies to overcome chemoresistance. The PI3K/AKT pathway is activated in human PDAC and mouse models of KRAS-driven PDAC. We sought to determine the effects of RAD51 on therapeutic sensitivity and resistance to AKT inhibition.

Experimental procedure: RAD51 expression was determined in human pancreatic tissues from a tissue microarray (TMA) and analyzed for overall survival (OS). Cell lysates from mouse cell lines derived from the LSL-KrasG12D/+;Pdx1Cre/+ (PanIN) and LSL-KrasG12D/+; Trp53R172H/+;Pdx1Cre/+ (PDA and LMP) genetic mouse models of PDAC were immunoblotted for RAD51 expression. IC50 values of B02 (a RAD51 inhibitor) treatment in human PDAC cell lines were determined. Orthotopic tumors were generated with direct injections of luciferase-tagged PANC1 cells and were treated with B02. Bioluminescence imaging (BLI) was utilized to monitor orthotopic tumor growth and treatment response. Colony formation, spheroid generation size and metabolic activity, cell cycle analysis and apoptosis assays were performed in human PDAC cells treated with inhibitors for RAD51 (B02) and/or AKT (MK2206). PDA (express low RAD51) and LMP (express high RAD51) cell lines from mice were treated with B02 and/or MK2206 and analyzed for their colony forming ability. The in vitro sensitivities of BRCA2 deficient Capan1 and BRCA2 proficient MiaPaCa2 cell lines to MK2206 were compared by analyzing cell proliferation and colony formation. RAD51 knockdown cells were treated with MK2206 and analyzed for cell proliferation and apoptosis using flow cytometry.

Results: RAD51 expression confirmed a stepwise increase from normal pancreas to chronic pancreatitis through advancing grade and stage of PDAC. Patients with PDAC tumors expressing high levels of RAD51 had significantly higher tumor grade, stage, and lower OS when compared with patients with tumors that had low RAD51 expression (median survival of 15 months vs 37 months, respectively; P=0.025). BRCA2 deficient Capan1 PDAC cells were sensitive to MK2206 when compared to BRCA2 proficient MiaPaCa2 cells. Bioluminescent imaging (BLI) guided tumor growth analysis confirmed that RAD51 inhibition with B02 treatment decreased tumor growth in PDAC cells. B02 and MK2206 treated PDA and LMP cells showed synergistic downregulation of colony formation in comparison to either B02 or MK2206 drugs treated cells. RAD51 knockdown cells treated with MK2206 showed enhanced cell apoptosis and attenuated cell proliferation.

Conclusions: Our findings indicate that RAD51 inhibition increases sensitivity to AKT inhibition. RAD51 expression levels in PDAC tumors may be useful in identification of PDAC patients who will benefit from this therapy.

Citation Format: Surpiya Srinivasan, Chanjuan Shi, Casey Roberts, Xizi Dai, Fanuel Messaggio, Krisztina Kovacs, Michael VanSaun, Nipun Merchant, Nagaraj Nagathihalli.{Authors}. RAD51 sensitizes pancreatic cancer cells to AKT inhibition. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B78.

Abstract 2618: Oncogenic mutant KRAS modulates CREB activation through MEK-ERK and AKT signaling in pancreatic cancer

Introduction: Cyclic AMP (cAMP) response element binding (CREB) overexpression in pancreatic ductal adenocarcinoma (PDAC) is associated with poor outcome, however, the mechanism(s) driving CREB overexpression in PDAC are not fully understood. We investigated the association of CREB activation with oncogenic KRAS, MEK-ERK and AKT signaling pathways.

Experimental procedure: Mouse lines derived from the Ptf1aCre/+; LSL-KrasG12D/+ (K518), Ptf1acre/+;LSL-KrasG12D/+;Tgfbr2flox/flox (PKT), LSL-KrasG12D/+;Pdx1Cre/+ (PanIN) and LSL-KrasG12D/+; Trp53R172H/+;Pdx1Cre/+ (PDA) mouse models of PDAC, human immortalized pancreatic ductal epithelial lines (HPDE6-E6E7 or H6c7, HPNE E6/E7 and HPNE E6/E7/KRAS) were immunoblotted for phospho-CREB (pCREB) and total CREB expression. KRAS mutant PDAC cell lines and CREB shRNA flank xenografts (PKT GEMM and nude mice) were treated with CREB (ICG-001), MEK (AZD6244) and AKT (MK-2206) inhibitors. The effects on downstream signaling targets were interrogated with cell cycle, apoptosis, survival and anchorage-independent growth analysis. Human CREB shRNA cells were treated with AZD6244 and MK-2206 to confirm the molecular mechanism of the CREB inhibition together with MEK and AKT.

Results: The expression of pCREB was higher in cells with KRAS mutation. MEK inhibition resulted in activation of AKT, while combined inhibition of CREB and MEK prevented AKT reactivation. Treatment with the combination of MEK and CREB inhibitors significantly decreased tumorigenic potential and increased cell apoptosis. Combined MEK, AKT and CREB inhibition synergistically enhanced these effects further, more so in KRAS mutant cell lines. To explore the relationship of CREB, MEK and AKT signaling in vivo, PKT mice were treated with their respective inhibitors individually and in combination. Either CREB/MEK or CREB/AKT two drug combinations significantly extended the median survival compared with individual agents. Lysates from MEK and AKT inhibited tumors showed decreased phosphorylation of CREB, confirming that CREB is activated through both, MEK and AKT signaling in vivo.

Conclusions: Our study demonstrates that oncogenic KRAS activation enhances the expression of CREB through MEK and AKT signaling. CREB inhibition results in increased sensitivity to MEK and AKT targeted therapy in KRAS mutant PDACs.

Citation Format: Jason Castellanos, Supriya Srinivasan, Kumar Honnenahally, Chanjuan Shi, Michael VanSaun, David Robbins, Nipun Merchant, Nagaraj Nagathihalli. Oncogenic mutant KRAS modulates CREB activation through MEK-ERK and AKT signaling in pancreatic cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2618.

Abstract 2537: CDK4/6 inhibition synergizes with KRAS-MAPK pathway targeting in pancreatic cancer

Introduction:

Pancreatic ductal adenocarcinoma (PDAC) is one of the most difficult human malignancies to treat due to its innate and acquired therapeutic resistance. Our hypothesis is that cyclin-dependent kinase 4 (CDK4) mediates therapeutic resistance to targeting of the KRAS-MAPK pathway in PDAC.

Experimental Procedure:

We characterized the expression of total and phosphorylated Retinoblastoma (Rb) and MEK protein levels in KRAS wild-type (BxPC3) and KRAS mutant (PANC1, MiaPaca2) human PDAC cell lines at baseline and with MEK and CDK4 inhibition alone or in combination. We then assessed the effects of combined therapy on cell-cycle progression and tumorigenicity (in vitro and in vivo). Finally, using the Ptf1a cre/+;LSL-Kras G12D/+;Tgfbr2 flox/flox (PKT) mouse model of PDAC, we assessed the in vivo overall tumor growth and survival after combined treatment with CDK4/6 and MEK inhibitors.

Results:

Rb functions as a tumor suppressor, and it is inactivated when phosphorylated by CDK4-Cyclin-D1. The CDK4/6 inhibitor (LEE011) effectively inhibits phosphorylation of Rb in cell lines regardless of KRAS mutational status. Combined inhibition of CDK4/6 and MEK (MEK162) decreased phosphorylation of RB and MAPK expression synergistically in the KRAS mutant cell lines, but not the KRAS wild-type BxPC3 cell line. Cell cycle progression was delayed effectively with MEK inhibition alone in the KRAS wild-type cell line, yet only combined CDK4/6 and MEK inhibition effectively delayed cell cycle progression in the KRAS mutant cell lines. Colony formation and invasion were also significantly decreased when Kras mutant cells were treated with combined CDK4/6 and MEK inhibition compared to all monotherapy and control groups. Finally, treatment of PKT mice resulted in a modest increase in OS with MEK inhibition alone, but mice receiving combined CDK4/6 and MEK inhibition exhibited a four-fold increase in OS.

Conclusions:

Combined inhibition of CDK4/6 and MEK results in significantly enhanced therapeutic efficacy and prolonged survival in the aggressive PKT mouse model of PDAC. This study suggests that concurrent inhibition of CDK4/6 and MEK may be an effective treatment for PDAC.

Citation Format: Jason A. Castellanos, Nagaraj Nagathihalli, Michael N. Van Saun, Cameron Kasmai, Yanhua Xiong, Nipun Merchant. CDK4/6 inhibition synergizes with KRAS-MAPK pathway targeting in pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2537. doi:10.1158/1538-7445.AM2015-2537

Abstract 924: GM-CSF induces CREB signaling pathways and modulates tobacco carcinogen-induced pancreatic tumorigenesis

Introduction: Nicotine and nitrosamine exposure from smoking causes pancreatic cell injury and contributes to a cascade of oncogenic events that may be contributing to the rising rate of pancreatic cancer (PDAC). Cytokines activate kinases and transcription factors including cyclic AMP response element binding (CREB) protein. CREB activation through phosphorylation regulates diverse cellular responses. We studied whether granulocyte-macrophage colony stimulating factor (GM-CSF)-dependent phosphorylated CREB plays a role in smoking-induced pathogenesis of PDAC.

Experimental procedure: Human tissue microarray analysis was performed to determine the significance of pCREB expression amongst smokers and non-smokers. Total RNA extracted from immortalized human pancreatic ductal cell (H6c7) and pancreatic intraepithelial neoplasia (PanIN) mouse cell lines (LSL-KrasG12D/+; Pdx1Cre/+) were treated with tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and RNA sequencing (RNA-seq) was performed. Network, pathway and functional analyses of the transcriptome were conducted. To analyze the signaling pathway involved in NNK-induced tumorigenicity, we performed a phospho-kinase antibody array and cytokine antibody array on NNK treated H6c7 and PanIN cells or conditioned media (CM) protein. Western blot and ELISA were used to validate the array data findings. NNK-induced activation of GM-CSF, G-CSF and IL-6 were blocked using monoclonal antibodies. PKT (Ptf1acre/+;LSL-KrasG12D/+;Tgfbr2flox/flox) mice and nude mice with MiaPaCa2 flank xenografts were treated with MEK inhibition (AZD6244) with or without NNK/in vivo smoking. Tumors from these mice were immunoblotted for phosphorylation of MEK1/2, MSK1/2, RSK and CREB. PDAC cells with CREB siRNA or human rGM-CSF were treated with NNK and analyzed for in vitro functional assays and EMT characteristics.

Results: Expression of pCREB was significantly higher (p&lt;0.001) in smokers when compared to non-smokers. Overall survival of smokers with high pCREB expression in their primary tumor was associated with significantly decreased median survival when compared to non-smokers with low pCREB expression. Exposure of cells to NNK resulted in phosphorylation of CREB, c-Jun and β-catenin, and release of GM-CSF, G-CSF and IL-6. RNA-seq analysis confirmed activation of MEK/ERK signaling. Studies were performed to elucidate the possible regulatory mechanism behind NNK mediated induction of GM-CSF and its downstream signaling. Importantly, blocking GM-CSF inhibited NNK-induced phosphorylation of CREB and it was mediated through MEK signaling. The in vivo and in vitro tumorigenicity assays showed an increase in the tumorigenic potential and EMT of NNK treated PDAC cells.

Conclusions: Our study demonstrates that NNK induces pancreatic tumorigenesis through GM-CSF mediated activation of CREB.

Citation Format: Jason Castellanos, Kumaraswamy Honnenahally, Chanjuan Shi, Nipun Merchant, Nagaraj Nagathihalli. GM-CSF induces CREB signaling pathways and modulates tobacco carcinogen-induced pancreatic tumorigenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 924. doi:10.1158/1538-7445.AM2015-924

Abstract 299: Modulation of the leptin receptor in pancreatic cancer cells mediates tumor growth

Background: Pancreatic cancer is the fourth leading cause of cancer death with a five year survival rate around 5%, which has not changed in 30 years. Obesity and increased abdominal adipose tissue independently correlate with an increased relative risk for the development of pancreatic cancer. These conditions have been associated with altered levels of adipokines, or adipose secreted cytokines. Circulating serum levels of the adipokine leptin are increasesddramatically in obese patients as well as in high fat diet induced obese mice. Leptin has been shown to induce oncogenic signaling in breast and prostate cancer. We have previously shown an increase in orthotopic pancreatic tumor size in high fat diet induced obese mice compared with regular diet control mice. We hypothesize that leptin signaling mediates pancreatic tumorigenesis. Methods: Leptin receptor status was determined in human as well as murine pancreatic cell lines. Leptin stimulated cell proliferation was determined using a modified BrdU assay. Leptin receptor levels were knocked down in human and murine pancreatic tumor cells using a shRNAmir approach. Leptin receptor shRNA Panc02 knockdown cells were injected orthotopically into the pancreas of C57/Bl6J mice on regular or high fat diet to determine the contribution of leptin to pancreatic tumor growth. Results: We have detected the long form of the leptin receptor in five human and four murine pancreatic cancer cell lines. In vitro administration of leptin stimulated proliferation of Panc1 and CFPAC1 cell lines, which was abrogated with co-incubation of a leptin antagonist. To better understand the mechanism of leptin-mediated signaling, we studied downstream targets and identified a significant increase in phosphorylation of STAT3 in Panc1, BXPC3 and CFPAC1 cell lines after leptin treatment. Orhtotopic injection of leptin receptor shRNA Panc02 cells into normal and obese mice showed a markedly diminished tumor growth in obese mice when compared to the nonsilencing control Panc02 cell growth in obese mice. Conclusion: These results implicate leptin as a mediator of pancreatic tumorigenesis and suggest that leptin activation is mediated in part through STAT3 signaling. Knockdown of the leptin receptor results in inhibition of high fat diet associated tumor growth in vivo.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 299. doi:1538-7445.AM2012-299

Smoking attenuates transforming growth factor-β-mediated tumor suppression function through downregulation of Smad3 in lung cancer

Epidemiologic studies have shown that most cases of lung cancers (85%-90%) are directly attributable to cigarette smoking. Although much information has been gained about the effects of cigarette smoking on various signaling pathways causing lung cancer, nothing is known about the effect of cigarette smoking on the TGF-β-induced tumor suppressor function in lung cancer. To address this issue, lung adenocarcinoma A549 and immortalized bronchial epithelial HPL1A cells were chronically treated with cigarette smoke condensate (CSC) and dimethyl sulfoxide (as a control) to mimic the conditions of long-term cigarette smoking. Prolonged exposure of these cells to CSC resulted in a decrease in Smad3 and Smad4 complex formation and TGF-β-mediated transcription due to reduced expression of Smad3. Long-term CSC treatment reduced apoptosis, increased cell viability, decreased TGF-β-mediated growth inhibition, and enhanced tumorigenicity. The decrease in apoptosis is due to the upregulation of Bcl-2, which is a downstream target of Smad3. Re-expression of Smad3 in the CSC-treated cells restored TGF-β signaling, increased apoptosis, and decreased cell viability and tumorigenicity. Withdrawal of CSC treatment resulted in the restoration of Smad3 expression, reduction in cell viability, and increased TGF-β-mediated growth inhibition. Expression of Smad3 is lower in lung tumors of current smokers than that observed in never-smokers. Collectively, these data provide evidence that cigarette smoking promotes tumorigenicity partly by abrogating TGF-β-mediated growth inhibition and apoptosis by reducing expression of Smad3.