Abstract C083: Deconvoluting the metastatic PDA tumor microenvironment

Pancreatic Ductal Adenocarcinoma (PDA) is the 3rd leading cause of cancer related deaths in the US with a 5-year survival of 11%. Most patients die from disseminated disease, with liver being the most frequently colonized metastatic site. In primary PDA tumors, the tumor microenvironment has been extensively linked to therapy resistance and immune suppression. However, the extent that the microenvironment in the liver metastatic niche promotes immune evasion compared to primary PDA lesions remains unclear. Importantly, strategies to effectively target metastatic disease will provide the most immediate benefit for clinical treatment of PDA. The heterogeneous tumor microenvironment has been recognized as a primary barrier to PDA treatment. Here, the immune and stromal cells are not functioning in a manner beneficial for the host. Numerous cell types have been shown to have a pro-tumor function including regulatory T cells, tumor associated macrophages (TAMs), myeloid derived suppressor cells, and cancer associated fibroblasts (CAFs). Recently, we and others have shown that there are metabolic crosstalk interactions between cancer cells, TAMs, and CAFs. These interactions function to support primary tumor growth, immune suppression, and resistance to chemotherapy. However, the degree that the cancer cell heterogeneity, immune infiltration, and stromal populations present in metastatic lesions mirror primary tumors remains unclear. To directly compare primary vs. metastatic tumors in PDA tumors, we have optimized a syngeneic experimental model to contrast primary vs. metastatic lesions. Using this system, we have identified differential programming among the different cell populations between pancreas and liver PDA lesions using single cell RNA sequencing. Further, we directly compared immune infiltration between primary and metastatic tumors using mass cytometry. Our data indicate alternative mechanisms of immune suppression in liver PDA lesions, which can be directly targeted in combination with checkpoint inhibition strategies. Overall, these data have the potential to lead to new avenues to activate or target the immune system to treat metastatic PDA, an urgent clinical need for pancreatic cancer patients.

Citation Format: Rima Singh, Christopher Halbrook, Nina Steele. Deconvoluting the metastatic PDA tumor microenvironment [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 C083.

Abstract PO-116: Deletion of Arginase 1 in myeloid cells alters the pancreatic cancer microenvironment

Pancreatic ductal adenocarcinoma (PDA) is a deadly disease with a 5-year survival of only 10%. PDA is characterized by an abundant fibroinflammatory stroma that includes abundant fibroblasts and immune cells, mainly myeloid cells. Infiltrating myeloid cells express high levels of Arginase 1 (Arg1), an enzyme that metabolizes L-arginine. Conversely, CD8+ T cells are scarce in PDA, and when present have an overwhelmingly exhausted phenotype. Whether myeloid cell Arginase is a key driver of immune suppression in pancreatic cancer is unknown. Here, we tested the hypothesis that myeloid cells in the tumor microenvironment mediate immune suppression in PDA through expression of Arg1. To test this hypothesis, we used a combination of genetically engineered pancreatic cancer mouse models and pharmacological approaches. Using a FlpO- and Cre-based dual recombinase system, we have generated a mouse model that develops pancreatic cancer spontaneously because of oncogenic Kras expression in the epithelium, while at the same time lacking Arg1 expression in the myeloid cell compartment (Ptf1a-FlpO/+;KrasFrt-STOP-Frt-G12D/+;LysMCre;Arg1f/f). To complement the genetic model and inhibit the function of Arginase systemically, we used an Arginase inhibitor (CB-1158, Incyte, Inc.) alone and in combination with an immune checkpoint blockade (anti-PD1). Using these multiple approaches, we observed decrease progression to invasive disease in the genetic model, and sensitization to immune checkpoint treatment in the transplantation model. In both settings, changes in tumor growth were accompanied by an increase in CD8+ T cell infiltration and activation. These changes support the notion that myeloid Arg1 is mediator of immune suppression in PDA, and a potential therapeutic target.

Citation Format: Rosa E. Menjivar, Zeribe Nwosu, Wenting Du, Katelyn Donahue, Carlos Espinoza, Ashley Velez-Delgado, Kristee Brown, Wei Yan, Christopher Halbrook, Yaqing Zhang, Costas Lyssiotis, Marina Pasca di Magliano. Deletion of Arginase 1 in myeloid cells alters the pancreatic cancer microenvironment [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-116.

Abstract 117: Inhibition of Hedgehog signaling alters fibroblast composition in pancreatic cancer

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease characterized by an extensive fibroinflammatory stroma, which includes abundant cancer-associated fibroblast (CAF) populations. PDAC CAFs are heterogeneous, but the nature of this heterogeneity is incompletely understood. The Hedgehog (HH) pathway functions in PDAC in a paracrine manner, with ligands secreted by cancer cells signaling to stromal cells in the microenvironment. Previous reports investigating the role of HH signaling in PDAC have been contradictory, with HH signaling alternately proposed to promote or restrict tumor growth. In light of the newly discovered CAF heterogeneity, we investigated how HH pathway inhibition reprograms the PDAC microenvironment.

Experimental Design: We used a combination of pharmacologic inhibition, gain- and loss- of-function genetic experiments, CyTOF, and single cell RNA-sequencing to study the roles of HH signaling in PDAC.

Results: We find that HH signaling is uniquely activated in fibroblasts and differentially elevated in myofibroblastic CAFs (myCAFs) compared to inflammatory CAFs (iCAFs). SHH overexpression promotes tumor growth, while HH pathway inhibition with the Smoothened antagonist LDE225 impairs tumor growth. Further, HH pathway inhibition reduces myCAF numbers and increases iCAF numbers, which correlates with a decrease in cytotoxic T cells and an expansion in Tregs, consistent with increased immune suppression.

Conclusions: HH pathway inhibition alters fibroblast composition and immune infiltration in the pancreatic cancer microenvironment.

Citation Format: Nina G. Steele, Giulia Biffi, Samantha Kemp, Yaqing Zhang, Donovan Drouillard, LiJyun Syu, Yuan Hao, Tobiloba Oni, Erin Brosnan, Ela Elyada, Abhishek Doshi, Christa Hansma, Carlos Espinoza, Ahmed Abbas, Stephanie The, Valerie Irizarry-Negron, Christopher Halbrook, Nicole Franks, Megan Hoffman, Eileen Carpenter, Zeribe Nwosu, Youngkyu Park, Howard Crawford, Costas Lyssiotis, Timothy Frankel, Arvind Rao, Filip Bednar, Andrzej Dlugosz, Jonathan Preall, David Tuveson, Benjamin Allen, Marina Pasca di Magliano. Inhibition of Hedgehog signaling alters fibroblast composition in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 117.

DDRE-24. TARGETING PURINE METABOLISM TO OVERCOME GLIOBLASTOMA THERAPY RESISTANCE

Intratumoral genomic heterogeneity in glioblastoma (GBM) is a barrier to overcoming radiation (RT) resistance. To discover genotype-independent mediators of RT resistance, we correlated RT resistance with the concentration of approximately 700 metabolites across 23 GBM cell lines. Purine metabolites, especially those containing the base guanine, were most correlated with RT resistance. Similarly, increased abundance of tumor purines was associated with decreased survival in GBM patients treated with RT. This relationship is causal. Purine supplementation protected RT-sensitive GBMs from RT and promoted the repair of RT-induced double strand DNA breaks (DSBs). In vitro and in vivo stable isotope tracing confirmed that GBM cell lines and orthotopic patient-derived xenografts primarily generated purines through the de novo synthetic pathway. RT treatment further increased de novo purine synthesis in GBM through signaling via the DNA damage response. Inhibition of de novo GTP synthesis with mycophenolic acid (MPA) sensitized multiple GBM cell lines and neurospheres to RT by slowing the repair of RT-induced DSBs. MPA-induced radiosensitization was GTP-dependent as it was rescued by nucleoside supplementation. Modulating pyrimidine metabolism affected neither RT resistance nor DSB repair, suggesting these GTP-specific effects are due to active signaling rather than its ability to act as a physical substrate for DNA repair and candidate signaling molecules have been identified. These results were recapitulated in vivo with mycophenolate mofetil (MMF), the orally bioavailable FDA-approved prodrug of MPA. MMF potentiated RT efficacy, reduced tumor guanylates and slowed the repair of RT-induced DSBs across multiple models. Because de novo purine synthesis is activated by many of the oncogenic alterations that drive GBM, its inhibition is a promising genotype-independent strategy to overcome GBM RT resistance. We have now begun a clinical trial to determine whether combining MMF and RT is safe and potentially efficacious in patients with GBM.

Interleukin 22 Signaling Regulates Acinar Cell Plasticity to Promote Pancreatic Tumor Development in Mice

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy that invades surrounding structures and metastasizes rapidly. Although inflammation is associated with tumor formation and progression, little is known about the mechanisms of this connection. We investigate the effects of interleukin (IL) 22 in the development of pancreatic tumors in mice.

METHODS

We performed studies with Pdx1-Cre;LSL-KrasG12D;Trp53+/-;Rosa26EYFP/+ (PKCY) mice, which develop pancreatic tumors, and PKCY mice with disruption of IL22 (PKCY Il22-/-mice). Pancreata were collected at different stages of tumor development and analyzed by immunohistochemistry, immunoblotting, real-time polymerase chain reaction, and flow cytometry. Some mice were given cerulean to induce pancreatitis. Pancreatic cancer cell lines (PD2560) were orthotopically injected into C57BL/6 mice or Il22-/-mice, and tumor development was monitored. Pancreatic cells were injected into the tail veins of mice, and lung metastases were quantified. Acini were collected from C57BL/6 mice and resected human pancreata and were cultured. Cell lines and acini cultures were incubated with IL22 and pharmacologic inhibitors, and protein levels were knocked down with small hairpin RNAs. We performed immunohistochemical analyses of 26 PDACs and 5 nonneoplastic pancreas specimens.

RESULTS

We observed increased expression of IL22 and the IL22 receptor (IL22R) in the pancreas compared with other tissues in mice; IL22 increased with pancreatitis and tumorigenesis. Flow cytometry indicated that the IL22 was produced primarily by T-helper 22 cells. PKCY Il22-/-mice did not develop precancerous lesions or pancreatic tumors. The addition of IL22 to cultured acinar cells increased their expression of markers of ductal metaplasia; these effects of IL22 were prevented with inhibitors of Janus kinase signaling to signal transducer and activator of transcription (STAT) (ruxolitinib) or mitogen-activated protein kinase kinase (MEK) (trametinib) and with STAT3 knockdown. Pancreatic cells injected into Il22-/- mice formed smaller tumors than those injected into C57BL/6. Incubation of IL22R-expressing PDAC cells with IL22 promoted spheroid formation and invasive activity, resulting in increased expression of stem-associated transcription factors (GATA4, SOX2, SOX17, and NANOG), and increased markers of the epithelial-mesenchymal transition (CDH1, SNAI2, TWIST1, and beta catenin); ruxolitinib blocked these effects. Human PDAC tissues had higher levels of IL22, phosphorylated STAT3, and markers of the epithelial-mesenchymal transition than nonneoplastic tissues. An increased level of STAT3 in IL22R-positive cells was associated with shorter survival times of patients.

CONCLUSIONS

We found levels of IL22 to be increased during pancreatitis and pancreatic tumor development and to be required for tumor development and progression in mice. IL22 promotes acinar to ductal metaplasia, stem cell features, and increased expression of markers of the epithelial-mesenchymal transition; inhibitors of STAT3 block these effects. Increased expression of IL22 by PDACs is associated with reduced survival times.

Abstract A31: Investigating the effect of myeloid Arg1 deletion on tumor growth and CD8+ T-cell infiltration and activation in pancreatic cancer

PDA is characterized by an extensive fibroinflammatory stroma. This fibroinflammatory stroma is mainly composed of fibroblasts and tumor-infiltrating immune cells. The most abundant infiltrating immune cells are myeloid cells. Myeloid cells including tumor-associated macrophages (TAMs), myeloid-derived suppressor cells, and granulocytes are required for PDA tumor growth and maintenance. Myeloid cells have the ability to suppress antitumor T-cell responses in PDA, as depletion of myeloid cells restores CD8+ T-cell immunity. Our previous characterization of myeloid cells infiltrating the neoplastic pancreas has revealed that myeloid cells express high levels of Arginase 1 (Arg1), an enzyme that depletes the amino acid L-arginine from the microenvironment and a signature marker of immunosuppressive macrophages and TAMs. In turn, L-arginine is required for CD8+ T-cell activation. An increase in Arginase levels has been reported also in other cancers, including lung, gastrointestinal, and bladder cancer. Thus, Arg1 expression in myeloid cells might be a key mediator of immune suppression, although this possibility has not been investigated directly in pancreatic cancer. Based on these observations, we test the hypothesis that myeloid cell polarization in the tumor microenvironment mediates immune suppression in PDA through expression of Arginase 1. The objective of this study is to provide novel insights into the role of Arg1 in pancreatic cancer, and the overall goal is to identify new therapeutic targets for combination therapy in pancreatic cancer. We used a genetically engineered mouse model (LysM-Cre;Arg1f/f) to delete the Arg1 gene, specifically from the myeloid cell compartment (LysM+ cells), including macrophages and neutrophils. We orthotopically implanted primary mouse pancreatic cancer cell lines into C57BL/6 LysM-Cre;Arg1f/f and wild-type (WT) mice. We evaluated tumor growth and CD8+ T-cell infiltration and activation between LysM-Cre;Arg1f/f and WT control mice. We used MRI imaging to determine tumor volume, and we used immunofluorescence and mass cytometry analysis to investigate changes in immune cell infiltration. We confirmed Arg1 depletion in LysM-Cre;Arg1f/f mice by Western blotting, co-immunofluorescence, and mass cytometry. We observed a decreasing trend in tumor growth and volume in LysM-Cre;Arg1f/f mice, an increase in iNOS expression (a marker of inflammatory macrophages), and an increase in CD8+ T-cell number and activity compared to the WT. These results support the notion that Arg1 might be a moderator of immune suppression in pancreatic cancer.

Citation Format: Rosa E. Menjivar, Christopher Halbrook, Ashley Velez, Fatima Lima, Carlos Espinoza, Stefanie Galban, Yaqing Zhang, Costas Lyssiotis, Marina Pasca di Magliano. Investigating the effect of myeloid Arg1 deletion on tumor growth and CD8+ T-cell infiltration and activation in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A31.

Abstract A52: Modulation of Hedgehog signaling alters immune infiltration in pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDA) has a dismal 5-year survival rate of 9%, making this disease one of the deadliest human malignancies. Primary barriers to the treatment of pancreatic cancer include extensive stromal interactions and sustained immune suppression. Aberrant Hedgehog (HH) pathway activity is a hallmark of pancreatic tumorigenesis. Tumor-derived HH ligands signal in a paracrine fashion to the surrounding stroma to influence tumor growth. Expression of HH ligands increases during PDA progression, and previous work has shown that genetic deletion of Sonic HH from the epithelium of mice with pancreatic tumors results in increased Indian HH (Ihh) expression.

Methods: Ihh was deleted in tumor cells lines (IhhKO) derived from a genetically engineered mouse model of pancreatic cancer (KrasG12D;Trp;P48-Cre), using CRISPR/Cas-9 gene editing to assess the role of Ihh in the tumor microenvironment. The level of HH signaling was determined using tumor cell co-cultures with Gli1lacZ fibroblasts (derived from mice with a lacZ reporter allele knocked into the Gli1 locus), in which beta galactosidase activity serves as a readout for HH signaling. WT and IhhKO tumor cells were orthotopically transplanted into the pancreas of syngeneic C57BL/6 mice. Human pancreas samples were obtained from surgical resection of pancreatic adenocarcinoma or fine-needle biopsy procedure (FNB). Immune profiling of mouse and human pancreatic tumors was performed using Cytometry Time-of-Flight analysis, and tumor composition was analyzed by single-cell RNA sequencing. In vitro cultures with pancreatic fibroblasts treated with either WT or IhhKO tumor cell conditioned media (CM) were cultured to assess tumor crosstalk.

Results: Tumor cells lacking Ihh were generated through CRISPR/Cas-9 deletion, and this was confirmed by qRT-PCR. Co-culture of IhhKO tumor cells with Gli1lacZ fibroblasts results in decreased Gli1 expression both in vitro and in vivo. Immune profiling revealed that tumors lacking Ihh have significantly fewer macrophages (CD11b+/F4/80+), resulting in decreased presence of immunosuppressive factors such as arginase 1 and PDL1. Immune profiling of human PDA revealed similar populations of immunosuppressive myeloid cells present in tumors. In vitro co-cultures demonstrated CCL2 expression was reduced in pancreatic fibroblasts cultured with IhhKO-CM, providing mechanistic insight into the in vivo phenotype observed. Further, scRNA seq analysis suggests that modulation of HH signaling in the tumor microenvironment alters chemokine and immunomodulatory signaling pathways driven by fibroblasts in the pancreatic tumor microenvironment.

Significance of Impact: HH signaling in pancreatic fibroblasts contributes to the establishment of an immune-suppressive environment in pancreatic cancer. Combining methods to target HH signaling and immune checkpoint therapy has translational potential in treating pancreatic cancer patients.

Citation Format: Nina Steele, Samantha Kemp, Valerie Irizarry-Negron, Veerin Sirihorachai, Ahmed Abbas, Eileen Carpenter, Christopher Halbrook, Carlos Espinoza, Costas Lyssiotis, Howard Crawford, Timothy Frankel, Filip Bednar, Ben Allen, Marina Pasca di Magliano. Modulation of Hedgehog signaling alters immune infiltration in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A52.

Metabolism and epigenetics of pancreatic cancer stem cells

Pancreatic Cancer (PDA) is an aggressive malignancy characterized by early spread and a high mortality. Current studies suggest that a subpopulation of cells exist within tumors, cancer stem cell (CSC), which are capable of self-renewal and give rise to unique progeny which form the major neoplastic cellular component of tumors. While CSCs constitute a small cellular subpopulation within the tumor, their resistance to chemotherapy and radiation make them an important therapeutic target for eradication. Along with distinctive phenotypic properties, CSCs possess a unique metabolic plasticity allowing them to rapidly respond and adapt to environmental changes. These cells and their progeny also display a significantly altered epigenetic state with distinctive patterns of DNA methylation. Several mechanisms of cross-talk between epigenetic and metabolic pathways in PDA exist which ultimately contribute to the observed cellular plasticity and enhanced tumorigenesis. In this review we discuss various examples of this metabolic-epigenetic interplay and how it may constitute a new avenue for therapy specifically targeting CSCs in PDA.

Abstract 4499: Determining the role of discoidin domain receptors 1 and 2 in the pathogenesis of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is an aggressive and devastating cancer often characterized by an intense collagen-rich, fibrotic response. In the presence of an oncogenic Kras mutation, the pancreas undergoes an initial morphological event in which normal acinar cells transdifferentiate into a ductal-like phenotype in a process called acinar-ductal metaplasia (ADM). ADM advances into pre-cancerous lesions, followed by a subsequent replacement of epithelium with a collagen-dense stromal reaction as PDA progresses. Discoidin domain receptors, DDR1 and DDR2, are a unique family of tyrosine receptor kinases that bind to collagen and activate downstream cellular responses that affect cell proliferation, migration, and adhesion. Our preliminary data shows that during Kras-induced ADM in vitro DDR1 is downregulated and is accompanied by an upregulation of DDR2 expression. Immunohistochemistry on human tissue microarrays reveals DDR1 is expressed in normal epithelia and pre-neoplastic lesions, but downregulated during advanced PDA. Conversely, DDR2 is upregulated in metaplastic lesions and advanced carcinoma as well as in the stroma at all stages of progression, suggesting DDRs may play a differential role throughout the PDA.

DDR1 is expressed in epithelial cells and associated with disease states such as fibrosis and various cancers, including PDA. To study the role of DDR1 in pancreatitis, a known risk factor of PDA, we used DDR1-null mice (DDR1-/-) with our cerulein-induced pancreatitis protocol. DDR1 ablation induces tissue damage and impairs recovery from extended cerulein treatment. To understand the role of DDR1 in tumorigenesis, we mated DDR1-/- mice in the KrasG12D/+; Ptf1aCre/+ (KC model) of pancreatic neoplasia. The absence of DDR1 in the KC model does not inhibit nor delay tumorigenesis, however, pancreata are smaller with less differentiated morphology than wild-type KC animals. In contrast, DDR2 is expressed in mesenchymal cells and has been implicated in EMT, cell proliferation, tumor invasion, and required for metastasis in breast cancer, however, its significance in PDA remains unknown. Our preliminary data shows DDR2 co-stains with neuroendocrine positive cells within neoplastic lesions that are associated with poor patient survival. To further investigate the role of DDR2 in tumor progression we have successfully mated a conditional, global DDR2 knockout mouse (DDR2fl/fl; β-actinCreERT2) with our novel KrasFSF-G12D/+;p53FRT/+ ;Ptf1a-FlpO/+ (KPF) aggressive PDA mouse model. Collectively, the results from these studies will help determine the role of DDRs throughout the initiation and progression of PDA and help define a potential point of regulation at the interface between the epithelial-stromal interactions.

Citation Format: Jeanine Ruggeri, Christopher Halbrook, Anjum Sohail, Rafael Fridman, Howard Crawford. Determining the role of discoidin domain receptors 1 and 2 in the pathogenesis of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4499.