Distinct populations of metastases-enabling myeloid cells expand in the liver of mice harboring invasive and preinvasive intra-abdominal tumor

Effective suppression of tumor growth and hepatic metastasis of neuroblastoma by NKT-stimulatory phenyl glycolipid

Invariant natural killer T cell (iNKT) cells produce large amounts of cytokines in response to α-Galactosylceramide (α-GalCer) stimulation. An analog containing two phenyl rings on the acyl chain, C34, was previously found to be more Th1-biased than α-GalCer and triggered greater anticancer activities against breast cancer, melanoma and lung cancer in mice. Since liver is enriched in iNKT cells, we investigated anticancer efficacy of C34 on neuroblastoma with hepatic metastasis. C34 induced Th1-biased cytokine secretions in the liver, significantly suppressed neuroblastoma growth/metastasis and prolonged mouse survival. The anti-tumor efficacy might be attributed to greater expansions of hepatic NKT, NK, CD4+ T, and CD8+ T cells as well as reduction of the number of SSCloGr1intCD11b+ subset of myeloid-derived suppressor cells (MDSCs) in the liver of tumor-bearing mice, as compared to DMSO control group. C34 also upregulated expression of CD1d and CD11c, especially in the SSCloGr1intCD11b+ subset of MDSCs, which might be killed by C34-activated NKT cells, attributing to their reduced number. In addition, C34 also induced expansion of CD4+ T, CD8+ T, and NK cells, which might eliminate neuroblastoma cells. These immune-modulating effects of C34 might act in concert in the local milieu of liver to suppress the tumor growth. Further analysis of database of neuroblastoma revealed that patients with high CD11c expression in the monocytic MDSCs in the tumor had longer survival, suggesting the potential clinical application of C34 for treatment of neuroblastoma.

Multi-parametric atlas of the pre-metastatic liver for prediction of metastatic outcome in early-stage pancreatic cancer

Metastasis occurs frequently after resection of pancreatic cancer (PaC). In this study, we hypothesized that multi-parametric analysis of pre-metastatic liver biopsies would classify patients according to their metastatic risk, timing and organ site. Liver biopsies obtained during pancreatectomy from 49 patients with localized PaC and 19 control patients with non-cancerous pancreatic lesions were analyzed, combining metabolomic, tissue and single-cell transcriptomics and multiplex imaging approaches. Patients were followed prospectively (median 3 years) and classified into four recurrence groups; early (<6 months after resection) or late (>6 months after resection) liver metastasis (LiM); extrahepatic metastasis (EHM); and disease-free survivors (no evidence of disease (NED)). Overall, PaC livers exhibited signs of augmented inflammation compared to controls. Enrichment of neutrophil extracellular traps (NETs), Ki-67 upregulation and decreased liver creatine significantly distinguished those with future metastasis from NED. Patients with future LiM were characterized by scant T cell lobular infiltration, less steatosis and higher levels of citrullinated H3 compared to patients who developed EHM, who had overexpression of interferon target genes (MX1 and NR1D1) and an increase of CD11B+ natural killer (NK) cells. Upregulation of sortilin-1 and prominent NETs, together with the lack of T cells and a reduction in CD11B+ NK cells, differentiated patients with early-onset LiM from those with late-onset LiM. Liver profiles of NED closely resembled those of controls. Using the above parameters, a machine-learning-based model was developed that successfully predicted the metastatic outcome at the time of surgery with 78% accuracy. Therefore, multi-parametric profiling of liver biopsies at the time of PaC diagnosis may determine metastatic risk and organotropism and guide clinical stratification for optimal treatment selection.

Role of T cells in liver metastasis

The liver is a major metastatic site (organ) for gastrointestinal cancers (such as colorectal, gastric, and pancreatic cancers) as well as non-gastrointestinal cancers (such as lung, breast, and melanoma cancers). Due to the innate anatomical position of the liver, the apoptosis of T cells in the liver, the unique metabolic regulation of hepatocytes and other potential mechanisms, the liver tends to form an immunosuppressive microenvironment and subsequently form a pre-metastatic niche (PMN), which can promote metastasis and colonization by various tumor cells(TCs). As a result, the critical role of immunoresponse in liver based metastasis has become increasingly appreciated. T cells, a centrally important member of adaptive immune response, play a significant role in liver based metastases and clarifying the different roles of the various T cells subsets is important to guide future clinical treatment. In this review, we first introduce the predisposing factors and related mechanisms of liver metastasis (LM) before introducing the PMN and its transition to LM. Finally, we detail the role of different subsets of T cells in LM and advances in the management of LM in order to identify potential therapeutic targets for patients with LM.

Key players of immunosuppression in epithelial malignancies: Tumor-infiltrating myeloid cells and γδ T cells

BACKGROUND

The tumor microenvironment of solid tumors governs the differentiation of otherwise non-immunosuppressive macrophages and gamma delta (γδ) T cells into strong immunosuppressors while promoting suppressive abilities of known immunosuppressors such as myeloid-derived suppressor cells (MDSCs) upon infiltration into the tumor beds.

RECENT FINDINGS

In epithelial malignancies, tumor-associated macrophages (TAMs), precursor monocytic MDSCs (M-MDSCs), and gamma delta (γδ) T cells often acquire strong immunosuppressive abilities that dampen spontaneous immune responses by tumor-infiltrating T cells and B lymphocytes against cancer. Both M-MDSCs and γδ T cells have been associated with worse prognosis for multiple epithelial cancers.

CONCLUSION

Here we discuss recent discoveries on how tumor-associated macrophages and precursor M-MDSCs as well as tumor associated-γδ T cells acquire immunosuppressive abilities in the tumor beds, promote cancer metastasis, and perspectives on how possible novel interventions could restore the effective adaptive immune responses in epithelial cancers.

Molecular mechanisms of pancreatic cancer liver metastasis: the role of PAK2

Background

Pancreatic cancer remains an extremely malignant digestive tract tumor, posing a significant global public health burden. Patients with pancreatic cancer, once metastasis occurs, lose all hope of cure, and prognosis is extremely poor. It is important to investigate liver metastasis of Pancreatic cancer in depth, not just because it is the most common form of metastasis in pancreatic cancer, but also because it is crucial for treatment planning and prognosis assessment. This study aims to delve into the mechanisms of pancreatic cancer liver metastasis, with the goal of providing crucial scientific groundwork for the development of future treatment methods and drugs.

Methods

We explored the mechanisms of pancreatic cancer liver metastasis using single-cell sequencing data (GSE155698 and GSE154778) and bulk data (GSE71729, GSE19279, TCGA-PAAD). Initially, Seurat package was employed for single-cell data processing to obtain expression matrices for primary pancreatic cancer lesions and liver metastatic lesions. Subsequently, high-dimensional weighted gene co-expression network analysis (hdWGCNA) was used to identify genes associated with liver metastasis. Machine learning algorithms and COX regression models were employed to further screen genes related to patient prognosis. Informed by both biological understanding and the outcomes of algorithms, we meticulously identified the ultimate set of liver metastasis-related gene (LRG). In the study of LRG genes, various databases were utilized to validate their association with pancreatic cancer liver metastasis. In order to analyze the effects of these agents on tumor microenvironment, we conducted an in-depth analysis, including changes in signaling pathways (GSVA), cell differentiation (pseudo-temporal analysis), cell communication networks (cell communication analysis), and downstream transcription factors (transcription factor activity prediction). Additionally, drug sensitivity analysis and metabolic analysis were performed to reveal the effects of LRG on gemcitabine resistance and metabolic pathways. Finally, functional experiments were conducted by silencing the expression of LRG in PANC-1 and Bx-PC-3 cells to validate its influence to proliferation and invasiveness on PANC-1 and Bx-PC-3 cells.

Results

Through a series of algorithmic filters, we identified PAK2 as a key gene promoting pancreatic cancer liver metastasis. GSVA analysis elucidated the activation of the TGF-beta signaling pathway by PAK2 to promote the occurrence of liver metastasis. Pseudo-temporal analysis revealed a significant correlation between PAK2 expression and the lower differentiation status of pancreatic cancer cells. Cell communication analysis revealed that overexpression of PAK2 promotes communication between cancer cells and the tumor microenvironment. Transcription factor activity prediction displayed the transcription factor network regulated by PAK2. Drug sensitivity analysis and metabolic analysis revealed the impact of PAK2 on gemcitabine resistance and metabolic pathways. CCK8 experiments showed that silencing PAK2 led to a decrease in the proliferative capacity of pancreatic cancer cells and scratch experiments demonstrated that low expression of PAK2 decreased invasion capability in pancreatic cancer cells. Flow cytometry reveals that PAK2 significantly inhibited apoptosis in pancreatic cancer cell lines. Molecules related to the TGF-beta pathway decreased with the inhibition of PAK2, and there were corresponding significant changes in molecules associated with EMT.

Conclusion

PAK2 facilitated the angiogenic potential of cancer cells and promotes the epithelial-mesenchymal transition process by activating the TGF-beta signaling pathway. Simultaneously, it decreased the differentiation level of cancer cells, consequently enhancing their malignancy. Additionally, PAK2 fostered communication between cancer cells and the tumor microenvironment, augments cancer cell chemoresistance, and modulates energy metabolism pathways. In summary, PAK2 emerged as a pivotal gene orchestrating pancreatic cancer liver metastasis. Intervening in the expression of PAK2 may offer a promising therapeutic strategy for preventing liver metastasis of pancreatic cancer and improving its prognosis.

The Brain Pre-Metastatic Niche: Biological and Technical Advancements

Metastasis, particularly brain metastasis, continues to puzzle researchers to this day, and exploring its molecular basis promises to break ground in developing new strategies for combatting this deadly cancer. In recent years, the research focus has shifted toward the earliest steps in the formation of metastasis. In this regard, significant progress has been achieved in understanding how the primary tumor affects distant organ sites before the arrival of tumor cells. The term pre-metastatic niche was introduced for this concept and encompasses all influences on sites of future metastases, ranging from immunological modulation and ECM remodeling to the softening of the blood-brain barrier. The mechanisms governing the spread of metastasis to the brain remain elusive. However, we begin to understand these processes by looking at the earliest steps in the formation of metastasis. This review aims to present recent findings on the brain pre-metastatic niche and to discuss existing and emerging methods to further explore the field. We begin by giving an overview of the pre-metastatic and metastatic niches in general before focusing on their manifestations in the brain. To conclude, we reflect on the methods usually employed in this field of research and discuss novel approaches in imaging and sequencing.

Guadecitabine increases response to combined anti-CTLA-4 and anti-PD-1 treatment in mouse melanoma in vivo by controlling T-cells, myeloid derived suppressor and NK cells

BACKGROUND

The combination of Programmed Cell Death 1 (PD-1) and Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4) blockade has dramatically improved the overall survival rate for malignant melanoma. Immune checkpoint blockers (ICBs) limit the tumor's immune escape yet only for approximately a third of all tumors and, in most cases, for a limited amount of time. Several approaches to overcome resistance to ICBs are being investigated among which the addition of epigenetic drugs that are expected to act on both immune and tumor cells. Guadecitabine, a dinucleotide prodrug of a decitabine linked via phosphodiester bond to a guanosine, showed promising results in the phase-1 clinical trial, NIBIT-M4 (NCT02608437).

METHODS

We used the syngeneic B16F10 murine melanoma model to study the effects of immune checkpoint blocking antibodies against CTLA-4 and PD-1 in combination, with and without the addition of Guadecitabine. We comprehensively characterized the tumor's and the host's responses under different treatments by flow cytometry, multiplex immunofluorescence and methylation analysis.

RESULTS

In combination with ICBs, Guadecitabine significantly reduced subcutaneous tumor growth as well as metastases formation compared to ICBs and Guadecitabine treatment. In particular, Guadecitabine greatly enhanced the efficacy of combined ICBs by increasing effector memory CD8+ T cells, inducing effector NK cells in the spleen and reducing tumor infiltrating regulatory T cells and myeloid derived suppressor cells (MDSC), in the tumor microenvironment (TME). Guadecitabine in association with ICBs increased serum levels of IFN-γ and IFN-γ-induced chemokines with anti-angiogenic activity. Guadecitabine led to a general DNA-demethylation, in particular of sites of intermediate methylation levels.

CONCLUSIONS

These results indicate Guadecitabine as a promising epigenetic drug to be added to ICBs therapy.

Breast cancer liver metastasis: Pathogenesis and clinical implications

Breast cancer is the most common malignant disease in female patients worldwide and can spread to almost every place in the human body, most frequently metastasizing to lymph nodes, bones, lungs, liver and brain. The liver is a common metastatic location for solid cancers as a whole, and it is also the third most common metastatic site for breast cancer. Breast cancer liver metastasis (BCLM) is a complex process. Although the hepatic microenvironment and liver sinusoidal structure are crucial factors for the initial arrest of breast cancer and progression within the liver, the biological basis of BCLM remains to be elucidated. Importantly, further understanding of the interaction between breast cancer cells and hepatic microenvironment in the liver metastasis of breast cancer will suggest ways for the development of effective therapy and prevention strategies for BCLM. In this review, we provide an overview of the recent advances in the understanding of the molecular mechanisms of the hepatic microenvironment in BCLM formation and discuss current systemic therapies for treating patients with BCLM as well as potential therapeutic development based on the liver microenvironment-associated signaling proteins governing BCLM.

Exploring the role of mast cells in the progression of liver disease

In addition to being associated with allergic diseases, parasites, bacteria, and venoms, a growing body of research indicates that mast cells and their mediators can regulate liver disease progression. When mast cells are activated, they degranulate and release many mediators, such as histamine, tryptase, chymase, transforming growth factor-β1 (TGF-β1), tumor necrosis factor–α(TNF-α), interleukins cytokines, and other substances that mediate the progression of liver disease. This article reviews the role of mast cells and their secretory mediators in developing hepatitis, cirrhosis and hepatocellular carcinoma (HCC) and their essential role in immunotherapy. Targeting MC infiltration may be a novel therapeutic option for improving liver disease progression.

Recurrence After Resection of Pancreatic Cancer: Can Radiomics Predict Patients at Greatest Risk of Liver Metastasis?

BACKGROUND

Liver metastasis (LM) after pancreatic ductal adenocarcinoma (PDAC) resection is common but difficult to predict and has grave prognosis. We combined preoperative clinicopathological variables and quantitative analysis of computed tomography (CT) imaging to predict early LM.

METHODS

We retrospectively evaluated patients with PDAC submitted to resection between 2005 and 2014 and identified clinicopathological variables associated with early LM. We performed liver radiomic analysis on preoperative contrast-enhanced CT scans and developed a logistic regression classifier to predict early LM (< 6 months).

RESULTS

In 688 resected PDAC patients, there were 516 recurrences (75%). The cumulative incidence of LM at 5 years was 41%, and patients who developed LM first (n = 194) had the lowest 1-year overall survival (OS) (34%), compared with 322 patients who developed extrahepatic recurrence first (61%). Independent predictors of time to LM included poor tumor differentiation (hazard ratio (HR) = 2.30; P < 0.001), large tumor size (HR = 1.17 per 2-cm increase; P = 0.048), lymphovascular invasion (HR = 1.50; P = 0.015), and liver Fibrosis-4 score (HR = 0.89 per 1-unit increase; P = 0.029) on multivariate analysis. A model using radiomic variables that reflect hepatic parenchymal heterogeneity identified patients at risk for early LM with an area under the receiver operating characteristic curve (AUC) of 0.71; the performance of the model was improved by incorporating preoperative clinicopathological variables (tumor size and differentiation status; AUC = 0.74, negative predictive value (NPV) = 0.86).

CONCLUSIONS

We confirm the adverse survival impact of early LM after resection of PDAC. We further show that a model using radiomic data from preoperative imaging combined with tumor-related variables has great potential for identifying patients at high risk for LM and may help guide treatment selection.

The Hepatic Pre-Metastatic Niche

Simple Summary

The pre-metastatic niche is a recently established concept that could lead to targeted therapies that prevent metastasis before ever occurring. Considering that 90% of cancer mortality results from metastasis, the PMN is thus a salient opportunity for intervention. The purpose of the current review is to cover what is known specifically about the hepatic pre-metastatic niche, a topic that has garnered increasing research focus within the last decade. We discuss the methods of communication between primary tumors and the liver, the involved cell populations, the key changes within liver tissue, and perspectives on the future of the field.

Abstract

Primary tumors can communicate with the liver to establish a microenvironment that favors metastatic colonization prior to dissemination, forming what is termed the “pre-metastatic niche” (PMN). Through diverse signaling mechanisms, distant malignancies can both influence hepatic cells directly as well as recruit immune cells into the PMN. The result is a set of changes within the hepatic tissue that increase susceptibility of tumor cell invasion and outgrowth upon dissemination. Thus, the PMN offers a novel step in the traditional metastatic cascade that could offer opportunities for clinical intervention. The involved signaling molecules also offer promise as biomarkers. Ultimately, while the existence of the hepatic PMN is well-established, continued research effort and use of innovative models are required to reach a functional knowledge of PMN mechanisms that can be further targeted.

Intercellular crosstalk of liver sinusoidal endothelial cells in liver fibrosis, cirrhosis and hepatocellular carcinoma

Intercellular crosstalk among various liver cells plays an important role in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Capillarization of liver sinusoidal endothelial cells (LSECs) precedes fibrosis and accumulating evidence suggests that the crosstalk between LSECs and other liver cells is critical in the development and progression of liver fibrosis. LSECs dysfunction, a key event in the progression from fibrosis to cirrhosis, and subsequently obstruction of hepatic sinuses and increased intrahepatic vascular resistance (IHVR) contribute to development of portal hypertension (PHT) and cirrhosis. More importantly, immunosuppressive tumor microenvironment (TME), which is closely related to the crosstalk between LSECs and immune liver cells like CD8+ T cells, promotes advances tumorigenesis, especially HCC. However, the connections within the crosstalk between LSECs and other liver cells during the progression from liver fibrosis to cirrhosis to HCC have yet to be discussed. In this review, we first summarize the current knowledge of how different crosstalk between LSECs and other liver cells, including hepatocytes, hepatic stellate cells (HSCs), macrophoges, immune cells in liver and extra cellular matrix (ECM) contribute to the physiological function and the progrssion from liver fibrosis to cirrhosis, or even to HCC. Then we examine current treatment strategies for LSECs crosstalk in liver fibrosis, cirrhosis and HCC.

The Role of Myeloid Cells in Hepatotoxicity Related to Cancer Immunotherapy

Drug-related hepatotoxicity is an emerging clinical challenge with the widening use of immunotherapeutic agents in the field of oncology. This is an important complication to consider as more immune oncological targets are being identified to show promising results in clinical trials. The application of these therapeutics may be complicated by the development of immune-related adverse events (irAEs), a serious limitation often requiring high-dose immunosuppression and discontinuation of cancer therapy. Hepatoxicity presents one of the most frequently encountered irAEs and a better understanding of the underlying mechanism is crucial for the development of alternative therapeutic interventions. As a novel drug side effect, the immunopathogenesis of the condition is not completely understood. In the liver, myeloid cells play a central role in the maintenance of homeostasis and promotion of inflammation. Recent research has identified myeloid cells to be associated with hepatic adverse events of various immune modulatory monoclonal antibodies. In this review article, we provide an overview of the role of myeloid cells in the immune pathogenesis during hepatoxicity related to cancer immunotherapies and highlight potential treatment options.

The dual role of neutrophils in cancer

For the past decade, the role and importance of neutrophils in cancer is being increasingly appreciated. Research has focused on the ability of cancer-related neutrophils to either support tumor growth or interfere with it, showing diverse mechanisms through which the effects of neutrophils take place. In contrast to the historic view of neutrophils as terminally differentiated cells, mounting evidence has demonstrated that neutrophils are a plastic and diverse population of cells. These dynamic and plastic abilities allow them to perform varied and sometimes opposite functions simultaneously. In this review, we summarize and detail clinical and experimental evidence for, and underlying mechanisms of, the dual impact of neutrophils' functions, both supporting and inhibiting cancer development. We first discuss the effects of various basic functions of neutrophils, namely direct cytotoxicity, secretion of reactive oxygen species (ROS), nitric oxide (NO) and proteases, NETosis, autophagy and modulation of other immune cells, on tumor growth and metastatic progression. We then describe the clinical evidence for pro- vs anti-tumor functions of neutrophils in human cancer. We believe and show that the "net" impact of neutrophils in cancer is the sum of a complex balance between contradicting effects which occur simultaneously.

MDSCs in liver cancer: A critical tumor-promoting player and a potential therapeutic target

Liver cancer is a leading cause of cancer deaths worldwide. Hepatocellular carcinoma (~75-85%) and cholangiocarcinoma (~10-15%) account for the majority of primary liver malignancies. Patients with primary liver cancer are often diagnosed with unresectable diseases and do not respond well to current therapies. The liver is also a common site of metastasis. Liver metastasis is difficult to treat, and the prognosis is poor. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with immunosuppressive activity. MDSCs are an important component of the tumor microenvironment and promote tumor progression through various mechanisms. MDSCs expand in both liver cancer patients and mouse liver cancer models. Importantly, MDSCs correlate with poor clinical outcomes for liver cancer patients. The tumor-promoting functions of MDSCs have also been shown in mouse liver cancer models. All these studies suggest that targeting MDSCs can potentially benefit liver cancer treatment. This review summarizes the current findings of MDSC regulation in liver cancer and related disease conditions.

The Role of Sinusoidal Endothelial Cells in the Axis of Inflammation and Cancer Within the Liver

Liver sinusoidal endothelial cells (LSEC) form a unique barrier between the liver sinusoids and the underlying parenchyma, and thus play a crucial role in maintaining metabolic and immune homeostasis, as well as actively contributing to disease pathophysiology. Whilst their endocytic and scavenging function is integral for nutrient exchange and clearance of waste products, their capillarisation and dysfunction precedes fibrogenesis. Furthermore, their ability to promote immune tolerance and recruit distinct immunosuppressive leukocyte subsets can allow persistence of chronic viral infections and facilitate tumour development. In this review, we present the immunological and barrier functions of LSEC, along with their role in orchestrating fibrotic processes which precede tumourigenesis. We also summarise the role of LSEC in modulating the tumour microenvironment, and promoting development of a pre-metastatic niche, which can drive formation of secondary liver tumours. Finally, we summarise closely inter-linked disease pathways which collectively perpetuate pathogenesis, highlighting LSEC as novel targets for therapeutic intervention.

Myeloid-Derived Suppressor Cells in Tumors: From Mechanisms to Antigen Specificity and Microenvironmental Regulation

Among the various immunological and non-immunological tumor-promoting activities of myeloid-derived suppressor cells (MDSCs), their immunosuppressive capacity remains a key hallmark. Effort in the past decade has provided us with a clearer view of the suppressive nature of MDSCs. More suppressive pathways have been identified, and their recognized targets have been expanded from T cells and natural killer (NK) cells to other immune cells. These novel mechanisms and targets afford MDSCs versatility in suppressing both innate and adaptive immunity. On the other hand, a better understanding of the regulation of their development and function has been unveiled. This intricate regulatory network, consisting of tumor cells, stromal cells, soluble mediators, and hostile physical conditions, reveals bi-directional crosstalk between MDSCs and the tumor microenvironment. In this article, we will review available information on how MDSCs exert their immunosuppressive function and how they are regulated in the tumor milieu. As MDSCs are a well-established obstacle to anti-tumor immunity, new insights in the potential synergistic combination of MDSC-targeted therapy and immunotherapy will be discussed.

The Emerging Role of Myeloid-Derived Suppressor Cells in the Glioma Immune Suppressive Microenvironment

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of myeloid progenitor and precursor cells at different stages of differentiation, which play an important role in tumor immunosuppression. Glioma is the most common and deadliest primary malignant tumor of the brain, and ample evidence supports key contributions of MDSCs to the immunosuppressive tumor microenvironment, which is a key factor stimulating glioma progression. In this review, we summarize the source and characterization of MDSCs, discuss their immunosuppressive functions, and current approaches that target MDSCs for tumor control. Overall, the review provides insights into the roles of MDSC immunosuppression in the glioma microenvironment and suggests that MDSC control is a powerful cellular therapeutic target for currently incurable glioma tumors.

Liver Tumor Microenvironment

The tumor microenvironment (TME) has recently been recognized as an important part of tumor development and growth. TME is a dynamic system orchestrated by immune, cancer and inflammatory cells, as well as the stromal tissue and surrounding extracellular matrix. While TME of primary hepatic tumors is usually characterized by a strong inflammatory background, the TME of liver metastases typically consists of otherwise healthy liver tissue. Chronic inflammation and hypoxia are key to the development and progression of primary liver cancer. The injury caused by chronic inflammation creates a condition of immune evasion that initiates a cascade of events that eventually leads to liver carcinogenesis.With liver metastases, primary tumors "prime" the target organs via secreting factors that induce expansion of myeloid cell populations and create a solid ground for successful cancer settlement. Once in the liver, metastatic cells begin a neovascularization process that is driven mainly by VEGF and FGF. Due to high mortality rates associated with liver cancer, as well as the limited effective treatment options for advanced disease, new therapies are urgently needed. Targeting a single molecule in a number of interactions between the tumor and the TME is highly unlikely to reduce tumor growth. Future trials should focus on combination therapies (i.e. targeted therapies combined with immunotherapy) to treat liver malignancies efficiently.

RIP3 promotes colitis-associated colorectal cancer by controlling tumor cell proliferation and CXCL1-induced immune suppression

Rationale: Necroptosis is a programmed form of non-apoptotic cell death that requires receptor-interacting protein 3 (RIP3). RIP3 has been shown to be relevant in multiple tumor types and has differential impact on tumor progression. We investigated whether RIP3 is involved in the progression of colitis-associated cancer (CAC) in mice.

Methods: Tissues from colorectal cancer patients were examined for RIP3 expression. CAC was induced using azoxymethane (AOM) injection followed by dextran sodium sulfate (DSS) treatment in RIP3-deficient or wild-type mice. Colon tissues were collected and analyzed by Western blotting and gene expression profile analyses. Immune cell infiltration and CXCL1 expression were examined by flow cytometry and Real-time PCR, respectively.

Results: RIP3 expression was upregulated in mouse CAC and human colon cancer. RIP3-deficient mice showed significantly attenuated colitis-associated tumorigenesis. Bone marrow transplantation experiments suggested that RIP3's function in hematopoietic cells primarily contributes to the phenotype. RIP3 supported epithelial proliferation and tumor growth via JNK signaling but had no effect on apoptosis. RIP3 deletion increased T cell accumulation and reduced infiltration by immunosuppressive subsets of myeloid cells during acute colitis and CAC. The immune-suppressive tumor microenvironment was dependent on RIP3-induced expression of the chemokine attractant CXCL1, and administration of recombinant CXCL1 during CAC restored tumorigenesis in Rip3^-/- mice.

Conclusion: Our results reveal an unexpected function of RIP3 in enhancing the proliferation of premalignant intestinal epithelial cells (IECs) and promoting myeloid cell-induced adaptive immune suppression. These two distinct mechanisms of RIP3-induced JNK and CXCL1 signalling contribute to CAC progression.

Metabolic and functional reprogramming of myeloid-derived suppressor cells and their therapeutic control in glioblastoma

Glioblastoma, also known as glioblastoma multi-forme, is the most common and deadliest form of high-grade malignant brain tumors with limited available treatments. Within the glioblastoma tumor microenvironment (TME), tumor cells, stromal cells, and infiltrating immune cells continuously interact and exchange signals through various secreted factors including cytokines, chemokines, growth factors, and metabolites. Simultaneously, they dynamically reprogram their metabolism according to environmental energy demands such as hypoxia and neo-vascularization. Such metabolic re-programming can determine fates and functions of tumor cells as well as immune cells. Ultimately, glioma cells in the TME transform immune cells to suppress anti-tumor immune cells such as T, natural killer (NK) cells, and dendritic cells (DC), and evade immune surveillance, and even to promote angiogenesis and tumor metastasis. Glioma-associated microglia/macrophages (GAMM) and myeloid-derived suppressor cells (MDSC) are most abundantly recruited and expanded myeloid lineage cells in glioblastoma TME and mainly lead to immunosuppression. In this review, of myeloid cells we will focus on MDSC as an important driver to induce immunosuppression in glioblastoma. Here, we review current literature on immunosuppressive functions and metabolic reprogramming of MDSCs in glioblastoma and discuss their metabolic pathways as potential therapeutic targets to improve current incurable glioblastoma treatment.

Roles of Myeloid-Derived Suppressor Cells in Cancer Metastasis: Immunosuppression and Beyond

Metastasis is the direst face of cancer, and it is not a feature solely dependent on cancer cells; however, a complex interaction between cancer cells and host causes this process. Investigating the mechanisms of metastasis can lead to its control. Myeloid-derived suppressor cells (MDSCs) are key components of tumor microenvironment that favor cancer progression. These cells result from altered myelopoiesis in response to the presence of tumor. The most recognized function of MDSCs is suppressing anti-tumor immune responses. Strikingly, these cells are among important players in cancer dissemination and metastasis. They can exert their effect on metastatic process by affecting anti-cancer immunity, epithelial-mesenchymal transition, cancer stem cell formation, angiogenesis, establishing premetastatic niche, and supporting cancer cell survival and growth in metastatic sites. In this article, we review and discuss the mechanisms by which MDSCs contribute to cancer metastasis.

STAT3 inhibition induces Bax-dependent apoptosis in liver tumor myeloid-derived suppressor cells

Immunosuppressive myeloid-derived suppressor cells (MDSC) subvert antitumor immunity and limit the efficacy of chimeric antigen receptor T cells (CAR-T). Previously, we reported that the GM-CSF/JAK2/STAT3 axis drives liver-associated MDSC (L-MDSC) proliferation and blockade of this axis rescued antitumor immunity. We extended these findings in our murine liver metastasis (LM) model, by treating tumor-bearing mice with STAT3 inhibitors (STATTIC or BBI608) to further our understanding of how STAT3 drives L-MDSC suppressive function. STAT3 inhibition caused significant reduction of tumor burden as well as L-MDSC frequencies due to decrease in pSTAT3 levels. L-MDSC isolated from STATTIC or BBI608-treated mice had significantly reduced suppressive function. STAT3 inhibition of L-MDSC was associated with enhanced antitumor activity of CAR-T. Further investigation demonstrated activation of apoptotic signaling pathways in L-MDSC following STAT3 inhibition as evidenced by an upregulation of the pro-apoptotic proteins Bax, cleaved caspase-3, and downregulation of the anti-apoptotic protein Bcl-2. Accordingly, there was also a decrease of pro-survival markers, pErk and pAkt, and an increase in pro-death marker, Fas, with activation of downstream JNK and p38 MAPK. These findings represent a previously unrecognized link between STAT3 inhibition and Fas-induced apoptosis of MDSCs. Our findings suggest that inhibiting STAT3 has potential clinical application for enhancing the efficacy of CAR-T cells in LM through modulation of L-MDSC.

The hepatic pre-metastatic niche in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most aggressive malignancies to date, largely because it is associated with high metastatic risk. Pancreatic tumors have a characteristic tendency to metastasize preferentially to the liver. Over the past two decades, it has become evident that the otherwise hostile milieu of the liver is selectively preconditioned at an early stage to render it more conducive to the engraftment and growth of disseminated cancer cells, a concept defined as pre-metastatic niche (PMN) formation. Pancreatic cancer cells exploit components of the tumor microenvironment to facilitate their migration out of the primary tumor, which often involves conversion of pancreatic cancer cells from an epithelial to a mesenchymal phenotype via the epithelial-to-mesenchymal transition. Pancreatic stellate cells and matrix stiffness have been put forward as major drivers of invasiveness in PDAC. Even before the onset of pancreatic cancer cell dissemination, soluble factors and extracellular vesicles secreted by the primary tumor, and possibly even premalignant lesions, help shape a supportive niche in the liver by providing vascular docking sites for circulating tumor cells, enhancing vascular permeability, remodeling the extracellular matrix and recruiting immunosuppressive inflammatory cells. Emerging evidence suggests that some of these tumor-derived factors may represent powerful diagnostic or prognostic biomarkers. Though our understanding of the mechanisms driving PMN formation in PDAC has expanded considerably, many outstanding questions and challenges remain. Further studies dissecting the molecular and cellular events involved in hepatic PMN formation in PDAC will likely improve diagnosis and open new avenues from a therapeutic standpoint.

CCR5 in recruitment and activation of myeloid-derived suppressor cells in melanoma

Malignant melanoma is characterized by the development of chronic inflammation in the tumor microenvironment, leading to the accumulation of myeloid-derived suppressor cells (MDSCs). Using ret transgenic mouse melanoma model, we found a significant migration of MDSCs expressing C-C chemokine receptor (CCR)5 into primary tumors and metastatic lymph nodes, which was correlated with tumor progression. An increased CCR5 expression on MDSCs was associated with elevated concentrations of CCR5 ligands in melanoma microenvironment. In vitro experiments showed that the upregulation of CCR5 expression on CD11b+Gr1+ immature myeloid cells was induced by CCR5 ligands, IL-6, GM-CSF, and other inflammatory factors. Furthermore, CCR5+ MDSCs infiltrating melanoma lesions displayed a stronger immunosuppressive pattern than their CCR5- counterparts. Targeting CCR5/CCR5 ligand signaling via a fusion protein mCCR5-Ig, which selectively binds and neutralizes all three CCR5 ligands, increased the survival of tumor-bearing mice. This was associated with a reduced migration and immunosuppressive potential of tumor MDSCs. In melanoma patients, circulating CCR5+ MDSCs were increased as compared to healthy donors. Like in melanoma-bearing mice, we observed an enrichment of these cells and CCR5 ligands in tumors as compared to the peripheral blood. Our findings define a critical role for CCR5 not only in the recruitment but also in the activation of MDSCs in tumor lesions, suggesting that novel strategies of melanoma treatment could be based on blocking CCR5/CCR5 ligand interactions.

An Immunosuppressive Dendritic Cell Subset Accumulates at Secondary Sites and Promotes Metastasis in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) after complete surgical resection is often followed by distant metastatic relapse for reasons that remain unclear. In this study, we investigated how the immune response at secondary sites affects tumor spread in murine models of metastatic PDAC. Early metastases were associated with dense networks of CD11b⁺CD11c⁺MHC-II⁺CD24⁺CD64^lowF4/80^low dendritic cells (DC), which developed from monocytes in response to tumor-released GM-CSF. These cells uniquely expressed MGL2 and PD-L2 in the metastatic microenvironment and preferentially induced the expansion of T regulatory cells (Treg) in vitro and in vivo Targeted depletion of this DC population in Mgl2^DTR hosts activated cytotoxic lymphocytes, reduced Tregs, and inhibited metastasis development. Moreover, blocking PD-L2 selectively activated CD8 T cells at secondary sites and suppressed metastasis, suggesting that the DCs use this particular pathway to inhibit CD8 T-cell-mediated tumor immunity. Phenotypically similar DCs accumulated at primary and secondary sites in other models and in human PDAC. These studies suggest that a discrete DC subset both expands Tregs and suppresses CD8 T cells to establish an immunosuppressive microenvironment conducive to metastasis formation. Therapeutic strategies to block the accumulation and immunosuppressive activity of such cells may help prevent PDAC progression and metastatic relapse after surgical resection. Cancer Res; 77(15); 4158-70. ©2017 AACR.

Neutrophils promote hepatic metastasis growth through fibroblast growth factor 2-dependent angiogenesis in mice

Hepatic metastases are amenable to ablation; however, many patients are not suitable candidates for such therapy and recurrence is common. The tumor microenvironment is known to be essential for metastatic growth, yet identification of plausible targets for cancer therapy in the microenvironment has proven elusive. We found that human colorectal cancer liver metastases and murine gastrointestinal experimental liver metastases are infiltrated by neutrophils. Plasticity in neutrophils has recently been shown to lead to both protumor and antitumor effects. Here, neutrophils promoted the growth of hepatic metastases, given that depletion of neutrophils in already established, experimental, murine liver metastases led to diminished metastatic growth. Decreased growth was associated with reductions in vascular density and branching suggestive of vessel normalization. Metastasis-associated neutrophils expressed substantially more fibroblast growth factor 2 (FGF2) than naïve neutrophils, indicating neutrophil polarization by the tumor microenvironment. Administration of FGF2 neutralizing antibody to mice bearing experimental liver metastases phenocopied neutrophil depletion by reducing liver metastatic colony growth, vascular density, and branching.

CONCLUSION

Here, we show, using FGF2 as an example, that identification of factors responsible for the protumoral effects of infiltrating myeloid cells can be used to target established liver metastases. Such therapies could be utilized to limit disease progression and potentiate the effects of standard ablative therapies. (Hepatology 2017;65:1920-1935).

Dectin 1 activation on macrophages by galectin 9 promotes pancreatic carcinoma and peritumoral immune tolerance

The progression of pancreatic oncogenesis requires immune-suppressive inflammation in cooperation with oncogenic mutations. However, the drivers of intratumoral immune tolerance are uncertain. Dectin 1 is an innate immune receptor crucial for anti-fungal immunity, but its role in sterile inflammation and oncogenesis has not been well defined. Furthermore, non-pathogen-derived ligands for dectin 1 have not been characterized. We found that dectin 1 is highly expressed on macrophages in pancreatic ductal adenocarcinoma (PDA). Dectin 1 ligation accelerated the progression of PDA in mice, whereas deletion of Clec7a-the gene encoding dectin 1-or blockade of dectin 1 downstream signaling was protective. We found that dectin 1 can ligate the lectin galectin 9 in mouse and human PDA, which results in tolerogenic macrophage programming and adaptive immune suppression. Upon disruption of the dectin 1-galectin 9 axis, CD4+ and CD8+ T cells, which are dispensable for PDA progression in hosts with an intact signaling axis, become reprogrammed into indispensable mediators of anti-tumor immunity. These data suggest that targeting dectin 1 signaling is an attractive strategy for developing an immunotherapy for PDA.

Cancer Manipulation of Host Physiology: Lessons from Pancreatic Cancer

Homeostasis is a fundamental property of living organisms enabling the human body to withstand internal and external insults. In several chronic diseases, and especially in cancer, many homeostatic mechanisms are deranged. Pancreatic cancer in particular is notorious for its ability to invoke an intense fibroinflammatory stromal reaction facilitating its progression and resistance to treatment. In the past decade, several seminal discoveries have elucidated previously unrecognized modes of commandeering the host's defense systems. Here we review novel discoveries in pancreatic cancer immunobiology and attempt to integrate the notion of deranged homeostasis in the pathogenesis of this disease. We also highlight areas of controversy and obstacles that need to be overcome, hoping to further our mechanistic insight into this malignancy.

Tumor regulation of the tissue environment in the liver

The tumor microenvironment (TME) in the liver plays an important role in primary and metastatic liver tumor formation and tumor growth promotion. Cellular and non-cellular components of the TME significantly influence tumor development, growth, metastatic spread, anti-tumor immunity and response to tumor therapy. The cellular components of the TME in the liver not only consist of infiltrating immune cells, but also of liver-resident cells such as liver sinusoidal endothelial cells (LSEC) and hepatic stellate cells (HSC), which promote tumor growth by negatively regulating tumor-associated immune responses. In this review, we characterize cells of the TME with pro- and anti-tumor function in primary and metastatic liver tumors. Furthermore, we summarize mechanisms that permit growth of hepatic tumors despite the occurrence of spontaneous anti-tumor immune responses and how novel therapeutic approaches targeting the TME could unleash tumor-specific immune responses to improve survival of liver cancer patients.

Molecular Pathways: The Necrosome-A Target for Cancer Therapy

Necroptosis is a caspase-8-independent cell death that requires coactivation of receptor-interacting protein 1 (RIP1) and receptor-interacting protein 3 (RIP3) kinases. The necrosome is a complex consisting of RIP1, RIP3, and Fas-associated protein with death domain leading to activation of the pseudokinase mixed lineage kinase like followed by a rapid plasma membrane rupture and inflammatory response through the release of damage-associated molecular patterns and cytokines. The necrosome has been shown to be relevant in multiple tumor types, including pancreatic adenocarcinoma, melanoma, and several hematologic malignancies. Preclinical data suggest that targeting this complex can have differential impact on tumor progression and that the effect of necroptosis on oncogenesis is cell-type and context dependent. The emerging data suggest that targeting the necrosome may lead to immunogenic reprogramming in the tumor microenvironment in multiple tumors and that combining therapies targeting the necrosome with either conventional chemotherapy or immunotherapy may have beneficial effects. Thus, understanding the interplay of necroptotic cell death, transformed cells, and the immune system may enable the development of novel therapeutic approaches. Clin Cancer Res; 23(5); 1132-6. ©2016 AACR.

The Role of Myeloid-Derived Suppressor Cells (MDSC) in Cancer Progression

The immunosuppressive tumor microenvironment represents not only one of the key factors stimulating tumor progression but also a strong obstacle for efficient tumor immunotherapy. Immunosuppression was found to be associated with chronic inflammatory mediators including cytokines, chemokines and growth factors produced by cancer and stroma cells. Long-term intensive production of these factors induces the formation of myeloid-derived suppressor cells (MDSCs) representing one of the most important players mediating immunosuppression. Moreover, MDSCs could not only inhibit anti-tumor immune reactions but also directly stimulate tumor growth and metastasis. Therefore, understanding the mechanisms of their generation, expansion, recruitment and activation is required for the development of novel strategies for tumor immunotherapy.

Role of the Microenvironment in Liver Metastasis: From Pre- to Prometastatic Niches

Liver metastases remain a major barrier to successful management of malignant disease, particularly for cancers of the gastrointestinal tract but also for other malignancies, such as breast carcinoma and melanoma. The ability of metastatic cells to survive and proliferate in the liver is determined by the outcome of complex, reciprocal interactions between tumor cells and different local resident subpopulations, including the sinusoidal endothelium, stellate, Kupffer, and inflammatory cells that are mediated through cell-cell and cell-extracellular matrix adhesion and the release of soluble factors. Cross-communication between different hepatic resident cells in response to local tissue damage and inflammation and the recruitment of bone marrow cells further enhance this intercellular communication network. Both resident and recruited cells can play opposing roles in the progression of metastasis, and the balance of these divergent effects determines whether the tumor cells will die, proliferate, and colonize the new site or enter a state of dormancy. Moreover, this delicate balance can be tilted in favor of metastasis, if factors produced by the primary tumor precondition the microenvironment to form niches of activated resident cells that promote tumor expansion. This review aims to summarize current knowledge on these diverse interactions and the impact they can have on the clinical management of hepatic metastases. Clin Cancer Res; 22(24); 5971-82. ©2016 AACR.

Neutrophils and Granulocytic MDSC: The Janus God of Cancer Immunotherapy

Neutrophils are the most abundant circulating blood cell type in humans, and are the first white blood cells recruited at the inflammation site where they orchestrate the initial immune response. Although their presence at the tumor site was recognized in the 1970s, until recently these cells have been neglected and considered to play just a neutral role in tumor progression. Indeed, in recent years neutrophils have been recognized to play a dual role in tumor development by either assisting the growth, angiogenesis, invasion, and metastasis or by exerting tumoricidal action directly via the secretion of antitumoral compounds, or indirectly via the orchestration of antitumor immunity. Understanding the biology of these cells and influencing their polarization in the tumor micro- and macro-environment may be the key for the development of new therapeutic strategies, which may finally hold the promise of an effective immunotherapy for cancer.

γδ T Cells Support Pancreatic Oncogenesis by Restraining αβ T Cell Activation

Inflammation is paramount in pancreatic oncogenesis. We identified a uniquely activated γδT cell population, which constituted ∼40% of tumor-infiltrating T cells in human pancreatic ductal adenocarcinoma (PDA). Recruitment and activation of γδT cells was contingent on diverse chemokine signals. Deletion, depletion, or blockade of γδT cell recruitment was protective against PDA and resulted in increased infiltration, activation, and Th1 polarization of αβT cells. Although αβT cells were dispensable to outcome in PDA, they became indispensable mediators of tumor protection upon γδT cell ablation. PDA-infiltrating γδT cells expressed high levels of exhaustion ligands and thereby negated adaptive anti-tumor immunity. Blockade of PD-L1 in γδT cells enhanced CD4(+) and CD8(+) T cell infiltration and immunogenicity and induced tumor protection suggesting that γδT cells are critical sources of immune-suppressive checkpoint ligands in PDA. We describe γδT cells as central regulators of effector T cell activation in cancer via novel cross-talk.

Chemokines accentuating protumoral activities in oral cancer microenvironment possess an imperious stratagem for therapeutic resolutions

Chemokines, the chemotactic cytokines have established their role in tumorigenesis and tumor progression. Studies, which explored their role in oral cancer for protumoral activity, point towards targeting chemokines for oral squamous cell carcinoma therapy. The need of the hour is to emphasize/divulge in the activities of chemokine ligands and their receptors in the tumor microenvironment for augmentation of such stratagems. This progressing sentience of chemokines and their receptors has inspired this review which is an endeavour to comprehend their role as an aid in accentuating hallmarks of cancer and targeted therapy.

Radiation Therapy Induces Macrophages to Suppress T-Cell Responses Against Pancreatic Tumors in Mice

BACKGROUND & AIMS

The role of radiation therapy in the treatment of patients with pancreatic ductal adenocarcinoma (PDA) is controversial. Randomized controlled trials investigating the efficacy of radiation therapy in patients with locally advanced unresectable PDA have reported mixed results, with effects ranging from modest benefit to worse outcomes compared with control therapies. We investigated whether radiation causes inflammatory cells to acquire an immune-suppressive phenotype that limits the therapeutic effects of radiation on invasive PDAs and accelerates progression of preinvasive foci.

METHODS

We investigated the effects of radiation therapy in p48(Cre);LSL-Kras(G12D) (KC) and p48(Cre);LSLKras(G12D);LSL-Trp53(R172H) (KPC) mice, as well as in C57BL/6 mice with orthotopic tumors grown from FC1242 cells derived from KPC mice. Some mice were given neutralizing antibodies against macrophage colony-stimulating factor 1 (CSF1 or MCSF) or F4/80. Pancreata were exposed to doses of radiation ranging from 2 to 12 Gy and analyzed by flow cytometry.

RESULTS

Pancreata of KC mice exposed to radiation had a higher frequency of advanced pancreatic intraepithelial lesions and more foci of invasive cancer than pancreata of unexposed mice (controls); radiation reduced survival time by more than 6 months. A greater proportion of macrophages from radiation treated invasive and preinvasive pancreatic tumors had an immune-suppressive, M2-like phenotype compared with control mice. Pancreata from mice exposed to radiation had fewer CD8(+) T cells than controls, and greater numbers of CD4(+) T cells of T-helper 2 and T-regulatory cell phenotypes. Adoptive transfer of T cells from irradiated PDA to tumors of control mice accelerated tumor growth. Radiation induced production of MCSF by PDA cells. A neutralizing antibody against MCSF prevented radiation from altering the phenotype of macrophages in tumors, increasing the anti-tumor T-cell response and slowing tumor growth.

CONCLUSIONS

Radiation treatment causes macrophages murine PDA to acquire an immune-suppressive phenotype and disabled T-cell-mediated anti-tumor responses. MCSF blockade negates this effect, allowing radiation to have increased efficacy in slowing tumor growth.

Tumor-associated GM-CSF overexpression induces immunoinhibitory molecules via STAT3 in myeloid-suppressor cells infiltrating liver metastases

Assumptions that liver immune cells and immunosuppressive pathways are similar to their counterparts in other spaces have led to gaps in our understanding of intrahepatic neoplasm aggressiveness. Myeloid-derived suppressor cells (MDSCs) are potent inhibitors of antitumor immunity and pose a major obstacle to solid tumor treatment. Liver MDSCs (L-MDSCs) associated with liver metastases (LM) are particularly problematic by contributing to intrahepatic immunosuppression that promotes tumor progression. L-MDSCs have been reported to expand in response to granulocyte-macrophages colony-stimulating factor (GM-CSF) and suppress antitumor immunity in LM. To extend these findings, we examined mechanisms of intrahepatic immunosuppression exploited by L-MDSCs. We found that the majority of L-MDSCs co-expressed GM-CSF receptor (GM-CSF-R), indoleamine 2,3-dioxygenase (IDO) and programmed death ligand 1 (PD-L1), while demonstrating high levels of signal transducer and activator of transcription factor 3 (STAT3) activation. GM-CSF-secreting tumor cells induced STAT3 phosphorylation in L-MDSCs in addition to expression of IDO and PD-L1. GM-CSF or GM-CSF-R blockade markedly reduced L-MDSC IDO and PD-L1 expression, implicating tumor-derived GM-CSF in supporting L-MDSC-immunoinhibitory molecule expression. Small-molecule inhibitors of Janus-activated kinase 2 (JAK2) and STAT3 also dramatically diminished IDO and PD-L1 expression in L-MDSCs. We determined that STAT3 exerts transcriptional control over L-MDSC IDO and PD-L1 expression by binding to the IDO1 and PD-L1 promoters. Our data suggest that the GM-CSF/JAK2/STAT3 axis in L-MDSCs drives immunosuppression in a model of LM and blockade of this pathway may enable rescue of intrahepatic antitumor immunity.

The necrosome promotes pancreatic oncogenesis via CXCL1 and Mincle-induced immune suppression

Neoplastic pancreatic epithelial cells are believed to die through caspase 8-dependent apoptotic cell death, and chemotherapy is thought to promote tumour apoptosis. Conversely, cancer cells often disrupt apoptosis to survive. Another type of programmed cell death is necroptosis (programmed necrosis), but its role in pancreatic ductal adenocarcinoma (PDA) is unclear. There are many potential inducers of necroptosis in PDA, including ligation of tumour necrosis factor receptor 1 (TNFR1), CD95, TNF-related apoptosis-inducing ligand (TRAIL) receptors, Toll-like receptors, reactive oxygen species, and chemotherapeutic drugs. Here we report that the principal components of the necrosome, receptor-interacting protein (RIP)1 and RIP3, are highly expressed in PDA and are further upregulated by the chemotherapy drug gemcitabine. Blockade of the necrosome in vitro promoted cancer cell proliferation and induced an aggressive oncogenic phenotype. By contrast, in vivo deletion of RIP3 or inhibition of RIP1 protected against oncogenic progression in mice and was associated with the development of a highly immunogenic myeloid and T cell infiltrate. The immune-suppressive tumour microenvironment associated with intact RIP1/RIP3 signalling depended in part on necroptosis-induced expression of the chemokine attractant CXCL1, and CXCL1 blockade protected against PDA. Moreover, cytoplasmic SAP130 (a subunit of the histone deacetylase complex) was expressed in PDA in a RIP1/RIP3-dependent manner, and Mincle--its cognate receptor--was upregulated in tumour-infiltrating myeloid cells. Ligation of Mincle by SAP130 promoted oncogenesis, whereas deletion of Mincle protected against oncogenesis and phenocopied the immunogenic reprogramming of the tumour microenvironment that was induced by RIP3 deletion. Cellular depletion suggested that whereas inhibitory macrophages promote tumorigenesis in PDA, they lose their immune-suppressive effects when RIP3 or Mincle is deleted. Accordingly, T cells, which are not protective against PDA progression in mice with intact RIP3 or Mincle signalling, are reprogrammed into indispensable mediators of anti-tumour immunity in the absence of RIP3 or Mincle. Our work describes parallel networks of necroptosis-induced CXCL1 and Mincle signalling that promote macrophage-induced adaptive immune suppression and thereby enable PDA progression.

Down-regulation of S100A9 inhibits osteosarcoma cell growth through inactivating MAPK and NF-κB signaling pathways

Background

Osteosarcoma (OS) is well-known for poor prognosis due to its high incidence of proliferation and metastasis. Researches have provided valuable insights into the tumorigenesis of S100A9 in some cancers. We aimed to understand the expression level, functions and mechanisms of S100A9 in human osteosarcoma for the first time.

Methods

The expression of S100A9 protein was detected in 120 human osteosarcoma tissues and 40 normal human bone tissues using tissue microarrays analysis. The knockdown of S100A9 induced by RNA interference (RNAi) method in three osteosarcoma cell lines (U2OS, 143B, MG63) was applied to analyze the effects of S100A9 on cell proliferation, cell cycle distribution, migration, invasion and xenotransplanted tumors. Moreover, MAPK-ERK1/2, MAPK-p38, NF-κB-p65, NF-κB-p50, p21, p27, CDK2 and CDK4 were tested.

Results

The expression of S100A9 was increased in human osteosarcoma issues and was positively correlated with clinical classification and survival rate. Down-regulation of S100A9 inhibited OS cellular proliferation, migration, invasion and cell cycle S phase in vitro and suppressed tumor formation in vivo with the reduction on PCNA and Ki67 proliferation index. Our data also demonstrated that knockdown of S100A9 repressed the protein levels of phospho-ERK1/2, phospho-p50, phospho-p65 except phospho-p38, and prompted up-regulation of p21 and p27 leading to inactivation of cyclin dependent kinase 2(CDK2) and cyclin dependent kinase 4(CDK4).

Conclusions

S100A9 might be a significant role for predicting osteosarcoma prognosis and down-regulation of S100A9 could be used as a potential target for gene therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2294-1) contains supplementary material, which is available to authorized users.

The diverse roles of the TNF axis in cancer progression and metastasis

Metastasis is a multi-step process that ultimately depends on the ability of disseminating cancer cells to establish favorable communications with their microenvironment. The tumor microenvironment consists of multiple and continuously changing cellular and molecular components. One of the factors regulating the tumor microenvironment is TNF-α, a pleiotropic cytokine that plays key roles in apoptosis, angiogenesis, inflammation and immunity. TNF-α can have both pro- and anti-tumoral effects and these are transmitted via two major receptors, the 55 kDa TNFR1 and the 75 kDa TNFR2 that have distinct, as well as overlapping functions. TNFR1 is ubiquitously expressed while the expression of TNFR2 is more restricted, mainly to immune cells. While TNFR1 can transmit pro-apoptotic or pro-survival signals through a complex network of downstream mediators, the role of TNFR2 is less well understood. One of its main functions is to act as a survival factor and moderate the pro-apoptotic effects of TNFR1, particularly in immune cells. In this review, we summarize the evidence for the involvement of the TNF system in the progression of the metastatic process from its contribution to the early steps of tumor cell invasion to its role in the colonization of distant sites, particularly the liver. We show how the TNF receptors each contribute to these processes by regulating and shaping the tumor microenvironment. Current evidence and concepts on the potential use of TNF targeting agents for cancer prevention and therapy are discussed.

TLR9 ligation in pancreatic stellate cells promotes tumorigenesis

Zambirinis et al. show that TLR9 stimulation has a protumorigenic effect in pancreatic carcinoma by inducing pancreatic stellate cells to become fibrogenic and produce chemokines that stimulate epithelial cell proliferation. Activation of TLR9 results also in an immune suppressive tumor microenvironment via recruitment of regulatory T cells and induction of myeloid-derived suppressor cell proliferation.

Modulation of Toll-like receptor (TLR) signaling can have protective or protumorigenic effects on oncogenesis depending on the cancer subtype and on specific inflammatory elements within the tumor milieu. We found that TLR9 is widely expressed early during the course of pancreatic transformation and that TLR9 ligands are ubiquitous within the tumor microenvironment. TLR9 ligation markedly accelerates oncogenesis, whereas TLR9 deletion is protective. We show that TLR9 activation has distinct effects on the epithelial, inflammatory, and fibrogenic cellular subsets in pancreatic carcinoma and plays a central role in cross talk between these compartments. Specifically, TLR9 activation can induce proinflammatory signaling in transformed epithelial cells, but does not elicit oncogene expression or cancer cell proliferation. Conversely, TLR9 ligation induces pancreatic stellate cells (PSCs) to become fibrogenic and secrete chemokines that promote epithelial cell proliferation. TLR9-activated PSCs mediate their protumorigenic effects on the epithelial compartment via CCL11. Additionally, TLR9 has immune-suppressive effects in the tumor microenvironment (TME) via induction of regulatory T cell recruitment and myeloid-derived suppressor cell proliferation. Collectively, our work shows that TLR9 has protumorigenic effects in pancreatic carcinoma which are distinct from its influence in extrapancreatic malignancies and from the mechanistic effects of other TLRs on pancreatic oncogenesis.

Emerging roles of myeloid derived suppressor cells in hepatic inflammation and fibrosis

Myeloid derived suppressor cells (MDSC) are a heterogeneous population of immune cells that are potent suppressors of immune responses. MDSC emerge in various compartments in the body, such as blood, bone marrow or spleen, especially in conditions of cancer, infections or inflammation. MDSC usually express CD11b, CD33, and low levels of human leukocyte antigen-DR in humans or CD11b and Gr1 (Ly6C/G) in mice, and they can be further divided into granulocytic or monocytic MDSC. The liver is an important organ for MDSC induction and accumulation in hepatic as well as extrahepatic diseases. Different hepatic cells, especially hepatic stellate cells, as well as liver-derived soluble factors, including hepatocyte growth factor and acute phase proteins (SAA, KC), can promote the differentiation of MDSC from myeloid cells. Importantly, hepatic myeloid cells like neutrophils, monocytes and macrophages fulfill essential roles in acute and chronic liver diseases. Recent data from patients with liver diseases and animal models linked MDSC to the pathogenesis of hepatic inflammation, fibrosis and hepatocellular carcinoma (HCC). In settings of acute hepatitis, MDSC can limit immunogenic T cell responses and subsequent tissue injury. In patients with chronic hepatitis C, MDSC increase and may favor viral persistence. Animal models of chronic liver injury, however, have not yet conclusively clarified the involvement of MDSC for hepatic fibrosis. In human HCC and mouse models of liver cancer, MDSC are induced in the tumor environment and suppress anti-tumoral immune responses. Thus, the liver is a primary site of MDSC in vivo, and modulating MDSC functionality might represent a promising novel therapeutic target for liver diseases.

Process of hepatic metastasis from pancreatic cancer: biology with clinical significance

PURPOSE

Pancreatic cancer shows a remarkable preference for the liver to establish secondary tumors. Selective metastasis to the liver is attributed to the development of potential microenvironment for the survival of pancreatic cancer cells. This review aims to provide a full understanding of the hepatic metastatic process from circulating pancreatic cancer cells to their settlement in the liver, serving as a basic theory for efficient prediction and treatment of metastatic diseases.

METHODS

A systematic search of relevant original articles and reviews was performed on PubMed, EMBASE and Cochrane Library for the purpose of this review.

RESULTS

Three interrelated phases are delineated as the contributions of the interaction between pancreatic cancer cells and the liver to hepatic metastasis process. Chemotaxis of disseminated pancreatic cancer cells and simultaneous defensive formation of platelets or neutrophils facilitate specific metastasis toward the liver. Remodeling of extracellular matrix and stromal cells in hepatic lobules and angiogenesis induced by proangiogenic factors support the survival and growth of clinical micrometastasis colonizing the liver. The bimodal role of the immune system or prevalence of cancer cells over the immune system makes metastatic progression successfully proceed from micrometastasis to macrometastasis.

CONCLUSIONS

Pancreatic cancer is an appropriate research object of cancer metastasis representing more than a straight cascade. If any of the successive or simultaneous phases, especially tumor-induced immunosuppression, is totally disrupted, hepatic metastasis will be temporarily under control or even cancelled forever. To shrink cancers on multiple fronts and prolong survival for patients, novel oral or intravenous anti-cancer agents covering one or different phases of metastatic pancreatic cancer are expected to be integrated into innovative strategies on the premise of safety and efficacious biostability.

Hepatic myeloid-derived suppressor cells in cancer

Myeloid-derived suppressor cells are key components of tumor-induced immune suppression. They are composed of a heterogeneous population of immature myeloid cells that abrogates innate and adaptive immune responses. Myeloid-derived suppressor cells accumulate not only in peripheral blood, secondary lymphoid organs and tumors, but also in the liver in preclinical tumor models and in hepatocellular carcinoma patients. The liver, continuously exposed to food and microbial antigens from the intestine, avoids autoimmune damage through the use of specialized mechanisms of immune tolerance. In the context of cancer, myeloid-derived suppressor cells profit the intrinsic tolerogenic properties of the liver to accumulate and exert various immune-suppressive and tumor-promoting mechanisms which go from inducing immune cell dysfunction to supporting the generation of liver metastases. In this review, we seek to describe the phenotype, function, accumulation and therapeutic targeting of hepatic myeloid-derived suppressor cells both in preclinical settings and in the context of human hepatocellular carcinoma.

Myeloid-Derived Suppressor Cells and Therapeutic Strategies in Cancer

Development of solid cancer depends on escape from host immunosurveillance. Various types of immune cells contribute to tumor-induced immune suppression, including tumor associated macrophages, regulatory T cells, type 2 NKT cells, and myeloid-derived suppressor cells (MDSCs). Growing body of evidences shows that MDSCs play pivotal roles among these immunosuppressive cells in multiple steps of cancer progression. MDSCs are immature myeloid cells that arise from myeloid progenitor cells and comprise a heterogeneous immune cell population. MDSCs are characterized by the ability to suppress both adaptive and innate immunities mainly through direct inhibition of the cytotoxic functions of T cells and NK cells. In clinical settings, the number of circulating MDSCs is associated with clinical stages and response to treatment in several cancers. Moreover, MDSCs are reported to contribute to chemoresistant phenotype. Collectively, targeting MDSCs could potentially provide a rationale for novel treatment strategies in cancer. This review summarizes recent understandings of MDSCs in cancer and discusses promissing clinical approaches in cancer patients.

Tumor-induced CD11b(+) Gr-1(+) myeloid-derived suppressor cells exacerbate immune-mediated hepatitis in mice in a CD40-dependent manner

Immunosuppressive CD11b(+) Gr-1(+) myeloid-derived suppressor cells (MDSCs) accumulate in the livers of tumor-bearing (TB) mice. We studied hepatic MDSCs in two murine models of immune-mediated hepatitis. Unexpectedly, treatment of TB mice with Concanavalin A (Con A) or α-galactosylceramide resulted in increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) serum levels in comparison to tumor-free mice. Adoptive transfer of hepatic MDSCs into naïve mice exacerbated Con A induced liver damage. Hepatic CD11b(+) Gr-1(+) cells revealed a polarized proinflammatory gene signature after Con A treatment. An IFN-γ-dependent upregulation of CD40 on hepatic CD11b(+) Gr-1(+) cells along with an upregulation of CD80, CD86, and CD1d after Con A treatment was observed. Con A treatment resulted in a loss of suppressor function by tumor-induced CD11b(+) Gr-1(+) MDSCs as well as enhanced reactive oxygen species (ROS)-mediated hepatotoxicity. CD40 knockdown in hepatic MDSCs led to increased arginase activity upon Con A treatment and lower ALT/AST serum levels. Finally, blockade of arginase activity in Cd40(-/-) tumor-induced myeloid cells resulted in exacerbation of hepatitis and increased ROS production in vivo. Our findings indicate that in a setting of acute hepatitis, tumor-induced hepatic MDSCs act as proinflammatory immune effector cells capable of killing hepatocytes in a CD40-dependent manner.