Immune Cell Modulation of the Extracellular Matrix Contributes to the Pathogenesis of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy with a five-year survival rate of only 9%. PDAC is characterized by a dense, fibrotic stroma composed of extracellular matrix (ECM) proteins. This desmoplastic stroma is a hallmark of PDAC, representing a significant physical barrier that is immunosuppressive and obstructs penetration of cytotoxic chemotherapy agents into the tumor microenvironment (TME). Additionally, dense ECM promotes hypoxia, making tumor cells refractive to radiation therapy and alters their metabolism, thereby supporting proliferation and survival. In this review, we outline the significant contribution of fibrosis to the pathogenesis of pancreatic cancer, with a focus on the cross talk between immune cells and pancreatic stellate cells that contribute to ECM deposition. We emphasize the cellular mechanisms by which neutrophils and macrophages, specifically, modulate the ECM in favor of PDAC-progression. Furthermore, we investigate how activated stellate cells and ECM influence immune cells and promote immunosuppression in PDAC. Finally, we summarize therapeutic strategies that target the stroma and hinder immune cell promotion of fibrogenesis, which have unfortunately led to mixed results. An enhanced understanding of the complex interactions between the pancreatic tumor ECM and immune cells may uncover novel treatment strategies that are desperately needed for this devastating disease.

Immune-regulated IDO1-dependent tryptophan metabolism is source of one-carbon units for pancreatic cancer and stellate cells

Cancer cells adapt their metabolism to support elevated energetic and anabolic demands of proliferation. Folate-dependent one-carbon metabolism is a critical metabolic process underpinning cellular proliferation supplying carbons for the synthesis of nucleotides incorporated into DNA and RNA. Recent research has focused on the nutrients that supply one-carbons to the folate cycle, particularly serine. Tryptophan is a theoretical source of one-carbon units through metabolism by IDO1, an enzyme intensively investigated in the context of tumor immune evasion. Using in vitro and in vivo pancreatic cancer models, we show that IDO1 expression is highly context dependent, influenced by attachment-independent growth and the canonical activator IFNγ. In IDO1-expressing cancer cells, tryptophan is a bona fide one-carbon donor for purine nucleotide synthesis in vitro and in vivo. Furthermore, we show that cancer cells release tryptophan-derived formate, which can be used by pancreatic stellate cells to support purine nucleotide synthesis.

Gamma-delta T cells stimulate IL-6 production by pancreatic stellate cells in pancreatic ductal adenocarcinoma

INTRODUCTION

The immunosuppressive tumor microenvironment promotes progression of pancreatic ductal adenocarcinoma (PDAC). γδ T cells infiltrate the pancreatic tumor stroma and support tumorigenesis through αβ T cell inhibition. Pancreatic stellate cell (PSC) activation contributes to pancreatic fibrosis in PDAC, limiting the delivery and efficacy of therapeutic agents. Whether γδ T cells have direct effects on PSC activation is unknown.

METHODS

In this study, we analyzed tumor tissue from 68 patients with PDAC and determined the frequency and location of γδ T cells using immunohistochemistry and immunofluorescence. PDAC samples from the TCGA database with low and high TRGC2 expression were correlated with the expression of extracellular matrix genes. Further, PSCs were isolated from pancreatic tumor tissue and co-cultured with γδ T cells for 48 hours and cytokine production was measured using a cytometric bead array.

RESULTS

γδ T cells infiltrated the pancreatic tumor stroma and were located in proximity to PSCs. A high infiltration of γδ T cells was associated with increased expression of several extracellular matrix genes in human PDAC. In vitro, γδ T cells stimulated IL-6 production by PDAC-derived PSCs.

CONCLUSION

γδ T cells activated PSCs and modulation of this interaction may enhance the efficacy of combinational therapies in human PDAC.

Purinergic Signaling in Pancreas-From Physiology to Therapeutic Strategies in Pancreatic Cancer

The purinergic signaling has an important role in regulating pancreatic exocrine secretion. The exocrine pancreas is also a site of one of the most serious cancer forms, the pancreatic ductal adenocarcinoma (PDAC). Here, we explore how the network of purinergic and adenosine receptors, as well as ecto-nucleotidases regulate normal pancreatic cells and various cells within the pancreatic tumor microenvironment. In particular, we focus on the P2X7 receptor, P2Y2 and P2Y12 receptors, as well as A2 receptors and ecto-nucleotidases CD39 and CD73. Recent studies indicate that targeting one or more of these candidates could present new therapeutic approaches to treat pancreatic cancer. In pancreatic cancer, as much as possible of normal pancreatic function should be preserved, and therefore physiology of purinergic signaling in pancreas needs to be considered.

Global targetome analysis reveals critical role of miR-29a in pancreatic stellate cell mediated regulation of PDAC tumor microenvironment

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive forms of malignancies with a nearly equal incidence and mortality rates in patients. Pancreatic stellate cells (PSCs) are critical players in PDAC microenvironment to promote the aggressiveness and pathogenesis of the disease. Dysregulation of microRNAs (miRNAs) have been shown to play a significant role in progression of PDAC. Earlier, we observed a PSC-specific downregulation of miR-29a in PDAC pancreas, however, the mechanism of action of the molecule in PSCs is still to be elucidated. The current study aims to clarify the regulation of miR-29a in PSCs and identifies functionally important downstream targets that contribute to tumorigenic activities during PDAC progression.

METHODS

In this study, using RNAseq approach, we performed transcriptome analysis of paired miR-29a overexpressing and control human PSCs (hPSCs). Enrichment analysis was performed with the identified differentially expressed genes (DEGs). miR-29a targets in the dataset were identified, which were utilized to create network interactions. Western blots were performed with the top miR-29a candidate targets in hPSCs transfected with miR-29a mimic or scramble control.

RESULTS

RNAseq analysis identified 202 differentially expressed genes, which included 19 downregulated direct miR-29a targets. Translational repression of eight key pro-tumorigenic and -fibrotic targets namely IGF-1, COL5A3, CLDN1, E2F7, MYBL2, ITGA6 and ADAMTS2 by miR-29a was observed in PSCs. Using pathway analysis, we find that miR-29a modulates effectors of IGF-1-p53 signaling in PSCs that may hinder carcinogenesis. We further observe a regulatory role of the molecule in pathways associated with PDAC ECM remodeling and tumor-stromal crosstalk, such as INS/IGF-1, RAS/MAPK, laminin interactions and collagen biosynthesis.

CONCLUSIONS

Together, our study presents a comprehensive understanding of miR-29a regulation of PSCs, and identifies essential pathways associated with PSC-mediated PDAC pathogenesis. The findings suggest an anti-tumorigenic role of miR-29a in the context of PSC-cancer cell crosstalk and advocates for the potential of the molecule in PDAC targeted therapies.

Pancreatic stellate cell: Pandora's box for pancreatic disease biology

Pancreatic stellate cells (PSCs) were identified in the early 1980s, but received much attention after 1998 when the methods to isolate and culture them from murine and human sources were developed. PSCs contribute to a small proportion of all pancreatic cells under physiological condition, but are essential for maintaining the normal pancreatic architecture. Quiescent PSCs are characterized by the presence of vitamin A laden lipid droplets. Upon PSC activation, these perinuclear lipid droplets disappear from the cytosol, attain a myofibroblast like phenotype and expresses the activation marker, alpha smooth muscle actin. PSCs maintain their activated phenotype via an autocrine loop involving different cytokines and contribute to progressive fibrosis in chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC). Several pathways (e.g., JAK-STAT, Smad, Wnt signaling, Hedgehog etc.), transcription factors and miRNAs have been implicated in the inflammatory and profibrogenic function of PSCs. The role of PSCs goes much beyond fibrosis/desmoplasia in PDAC. It is now shown that PSCs are involved in significant crosstalk between the pancreatic cancer cells and the cancer stroma. These interactions result in tumour progression, metastasis, tumour hypoxia, immune evasion and drug resistance. This is the rationale for therapeutic preclinical and clinical trials that have targeted PSCs and the cancer stroma.

Hypoxia Inducible Factor 1 (HIF-1) Recruits Macrophage to Activate Pancreatic Stellate Cells in Pancreatic Ductal Adenocarcinoma

Hypoxia inducible factor 1 (HIF-1) is a transcription factor composed of two subunits, namely, HIF-1α and HIF-1β, in which HIF-1β is constitutively expressed. HIF-1 upregulates several hypoxia-responsive proteins, including angiogenesis factors, glycolysis solution enzymes, and cell survival proteins. HIF-1 is also associated with the degree of inflammation in the tumor region, but the exact mechanism remains unclear. This study aims to identify the molecular mechanism of recruiting monocytes/macrophages by HIF-1α in pancreatic ductal adenocarcinoma (PDAC) and the effects of macrophages on pancreatic stellate cells (PSCs). Immunohistochemistry (IHC) was performed for cluster of differentiation 68 (CD68), HIF-1α, and chemical chemokines 2 (CCL2). Western blot, real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), chromatin immunoprecipitation assay, and The Cancer Genome Atlas (TCGA) were used to verify the correlation between HIF-1α and CCL2 at protein and nucleic acid levels. Monocytes/macrophages were co-cultured with PSCs to observe their interaction. Samples showed significant correlation between CD68 and HIF-1α (t-test, p < 0.05). HIF-1α recruited monocytes/macrophages by promoting CCL2 secretion. Moreover, macrophages could accelerate the activation of PSCs. HIF-1α might promote inflammation and fibrosis of PDAC through CCL2 secretion, which may provide a novel target to treat PDAC patients.

Pancreatic cancer and its stroma: A conspiracy theory

Pancreatic cancer is characterised by a prominent desmoplastic/stromal reaction that has received little attention until recent times. Given that treatments focusing on pancreatic cancer cells alone have failed to significantly improve patient outcome over many decades, research efforts have now moved to understanding the pathophysiology of the stromal reaction and its role in cancer progression. In this regard, our Group was the first to identify the cells (pancreatic stellate cells, PSCs) that produced the collagenous stroma of pancreatic cancer and to demonstrate that these cells interacted closely with cancer cells to facilitate local tumour growth and distant metastasis. Evidence is accumulating to indicate that stromal PSCs may also mediate angiogenesis, immune evasion and the well known resistance of pancreatic cancer to chemotherapy and radiotherapy. This review will summarise current knowledge regarding the critical role of pancreatic stellate cells and the stroma in pancreatic cancer biology and the therapeutic approaches being developed to target the stroma in a bid to improve the outcome of this devastating disease.

High expression of Galectin-1 in pancreatic stellate cells plays a role in the development and maintenance of an immunosuppressive microenvironment in pancreatic cancer

Galectin-1 is implicated in making tumor cells immune privileged, in part by regulating the survival of infiltrating T cells. Galectin-1 is strongly expressed in activated pancreatic stellate cells (PSCs); however, whether this is linked to tumor cell immune escape in pancreatic cancer is unknown. Galectin-1 was knocked down in PSCs isolated from pancreatic tissues using small interfering RNA (siRNA), or overexpressed using recombinant lentiviruses, and the PSCs were cocultured with T cells. CD3(+) , CD4(+) and CD8(+) T cell apoptosis was detected by flow cytometry; T cell IL-2, IL-4, IL-5 and INF-γ production levels were quantified using ELISA. Immunohistochemical analysis showed increased numbers of PSCs expressed Galectin-1 (p < 0.01) and pancreatic cancers had increased CD3(+) T cell densities (p < 0.01) compared to normal pancreas or chronic pancreatitis samples. In coculture experiments, PSCs that overexpressed Galectin-1 induced apoptosis of CD4(+) T cells (p < 0.01) and CD8(+) T cells (p < 0.05) significantly, compared to normal PSCs. Knockdown of Galectin-1 in PSCs increased CD4(+) T cell (p < 0.01) and CD8(+) T cell viability (p < 0.05). Supernatants from T cells cocultured with PSCs that overexpressed Galectin-1 contained significantly increased levels of Th2 cytokines (IL-4 and IL-5, p < 0.01) and decreased Th1 cytokines (IL-2 and INF-γ, p < 0.01). However, the knockdown of PSC Galectin-1 had the opposite effect on Th1 and Th2 cytokine secretion. Our study suggests that the overexpression of Galectin-1 in PSCs induced T cell apoptosis and Th2 cytokine secretion, which may regulate PSC-dependent immunoprivilege in the pancreatic cancer microenvironment. Galectin-1 may provide a novel candidate target for pancreatic cancer immunotherapy.