CCL2 Promotes Colorectal Carcinogenesis by Enhancing Polymorphonuclear Myeloid-Derived Suppressor Cell Population and Function. Cell Rep. 2015;12:244-257. [PMID: 26146082 PMCID: PMC4620029 DOI: 10.1016/j.celrep.2015.06.024]

CCL2/CCR2 signaling in cancer pathogenesis

Chemokines are a family of small cytokines, which guide a variety of immune/inflammatory cells to the site of tumor in tumorigenesis. A dysregulated expression of chemokines is implicated in different types of cancer including prostate cancer. The progression and metastasis of prostate cancer involve a complex network of chemokines that regulate the recruitment and trafficking of immune cells. The chemokine CCL2 and its main receptor CCR2 have been receiving particular interest on their roles in cancer pathogenesis. The up-regulation of CCL2/CCR2 and varied immune conditions in prostate cancer, are associated with cancer advancement, metastasis, and relapse. Here we reviewed recent findings, which link CCL2/CCR2 to the inflammation and cancer pathogenesis, and discussed the therapeutic potential of CCL2/CCR2 axis in cancer treatment based on results from our group and other investigators, with a major focus on prostate cancer. Video Abstract.

HOXA9 mediates and marks premalignant compartment size expansion in colonic adenomas

The transformation of normal colonic epithelium to colorectal cancer (CRC) involves a relatively ordered progression, and understanding the molecular alterations involved may aid rational design of strategies aimed at preventing or counteracting disease. Homeobox A9 (HOXA9) is an oncogene in leukemia and has been implicated in CRC pathology, although its role in disease etiology remains obscure at best. We observe that HOXA9 expression is increased in colonic adenomas compared with location-matched healthy colon epithelium. Its forced expression results in dramatic genetic and signaling changes, with increased expression of growth factors IGF1 and FLT3, super-activity of the AKT survival pathway and a concomitant increase in compartment size. Furthermore, a reduced mRNA expression of the epithelial to mesenchymal transition marker N-cadherin as well as reduced activity of the actin cytoskeletal mediator PAK was seen, which is in apparent agreement with an observed reduced migratory response in HOXA9-overexpressing cells. Thus, HOXA9 appears closely linked with adenoma growth while impairing migration and metastasis and hence is both a marker and driver of premalignant polyp growth. Colonic polyps grow but remain premalignant for up to decades. Here, we show that HOXA9 drives growth in premalignant polyps, but simultaneously prevents further transformation.

Modulation of the tumor microenvironment by natural agents: implications for cancer prevention and therapy

The development of cancer is not just the growth and proliferation of a single transformed cell, but its surrounding environment also coevolves with it. Indeed, successful cancer progression depends on the ability of the tumor cells to develop a supportive tumor microenvironment consisting of various types of stromal cells. The interactions between the tumor and stromal cells are bidirectional and mediated through a variety of growth factors, cytokines, metabolites, and other biomolecules secreted by these cells. Tumor-stromal crosstalk creates optimal conditions for the tumor growth, metastasis, evasion of immune surveillance, and therapy resistance, and its targeting is being explored for clinical management of cancer. Natural agents from plants and marine life have been at the forefront of traditional medicine. Numerous epidemiological studies have reported the health benefits imparted on the consumption of certain fruits, vegetables, and their derived products. Indeed, a significant majority of anti-cancer drugs in clinical use are either naturally occurring compounds or their derivatives. In this review, we describe fundamental cellular and non-cellular components of the tumor microenvironment and discuss the significance of natural compounds in their targeting. Existing literature provides hope that novel prevention and therapeutic approaches will emerge from ongoing scientific efforts leading to the reduced tumor burden and improve clinical outcomes in cancer patients.

TNFSF14: LIGHTing the Way for Effective Cancer Immunotherapy

Tumor necrosis factor superfamily member 14 (LIGHT) has been in pre-clinical development for over a decade and shows promise as a modality of enhancing treatment approaches in the field of cancer immunotherapy. To date, LIGHT has been used to combat cancer in multiple tumor models where it can be combined with other immunotherapy modalities to clear established solid tumors as well as treat metastatic events. When LIGHT molecules are delivered to or expressed within tumors they cause significant changes in the tumor microenvironment that are primarily driven through vascular normalization and generation of tertiary lymphoid structures. These changes can synergize with methods that induce or support anti-tumor immune responses, such as checkpoint inhibitors and/or tumor vaccines, to greatly improve immunotherapeutic strategies against cancer. While investigators have utilized multiple vectors to LIGHT-up tumor tissues, there are still improvements needed and components to be found within a human tumor microenvironment that may impede translational efforts. This review addresses the current state of this field.

Immune battle at the premalignant stage of colorectal cancer: focus on immune cell compositions, functions and cytokine products

It is now widely accepted that most human cancers, including colorectal cancers (CRCs), develop from premalignant lesions through a long-term multistep process. Host immunity is a key determinant that maintains most premalignant lesions in a stable state via immunosurveillance. However, premalignant cells use diverse strategies to escape host immunosurveillance. A switch in the immune function from immunosurveillance to immunosuppression facilitates the progression of premalignant lesions to established CRCs. This review summarizes the recent progress in understanding alterations in the immune landscape, including immune cell compositions, functions and cytokine products, in the premalignant stage of CRC and provides an updated discussion on its translational significance along the colorectal adenoma-carcinoma sequence.

Porphyromonas gingivalis Promotes Oral Squamous Cell Carcinoma Progression in an Immune Microenvironment

Increasing evidence has revealed a significant association between microorganisms and oral squamous cell carcinoma (OSCC). Porphyromonas gingivalis, the keystone pathogen in chronic periodontitis, is considered an important potential etiologic agent of OSCC, but the underlying immune mechanisms through which P. gingivalis mediates tumor progression of the oral cancer remain poorly understood. Our cohort study showed that the localization of P. gingivalis in tumor tissues was related to poor survival of patients with OSCC. Moreover, P. gingivalis infection increased oral lesion multiplicity and size and promoted tumor progression in a 4-nitroquinoline-1 oxide (4NQO)–induced carcinogenesis mouse model by invading the oral lesions. In addition, CD11b+ myeloid cells and myeloid-derived suppressor cells (MDSCs) showed increased infiltration of oral lesions. Furthermore, in vitro observations showed that MDSCs accumulated when human-derived dysplastic oral keratinocytes (DOKs) were exposed to P. gingivalis, and CXCL2, CCL2, interleukin (IL)–6, and IL-8 may be potential candidate genes that facilitate the recruitment of MDSCs. Taken together, our findings suggest that P. gingivalis promotes tumor progression by generating a cancer-promoting microenvironment, indicating a close relationship among P. gingivalis, tumor progression of the oral cancer, and immune responses.

Functional Diversity of Myeloid-Derived Suppressor Cells: The Multitasking Hydra of Cancer

Myeloid-derived suppressor cells (MDSCs) are immature suppressive cells found in tumors and immunological niches. In this article, we highlight the ability of MDSCs to promote IL-17-producing T cells (Th17) and regulatory T cells in addition to suppressing cytotoxic T cells in different tumor models. These interactions between MDSCs and T cells support tumor growth because IL-17 is tumorigenic in many cancer types and regulatory T cells suppress antitumor T cells. Besides T cells, MDSCs promote regulatory B cells and suppress overall B cell function; however, tumor-evoked regulatory B cells also regulate MDSC function, suggesting cross-regulation between MDSCs and B cells. These multiple functions shed light on how MDSCs dysregulate several arms of host immune response. Moreover, MDSCs promote tumor cell survival and angiogenesis to support tumors. Therefore, the multifunctional feature of MDSCs make them attractive immunotherapeutic targets.

LncRNA AK036396 Inhibits Maturation and Accelerates Immunosuppression of Polymorphonuclear Myeloid-Derived Suppressor Cells by Enhancing the Stability of Ficolin B

Long noncoding RNAs (lncRNA) are emerging as crucial regulators of cell biology. However, the role of lncRNAs in the development and function of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) remains unclear. Here, we identified that the lncRNA F730016J06Rik (AK036396) was highly expressed in PMN-MDSCs and that lncRNA AK036396 knockdown promoted the maturation and decreased the suppressive function of PMN-MDSCs. Ficolin B (Fcnb), the expression of which could be assessed as a surrogate for PMN-MDSC development, was the predicted target gene of lncRNA AK036396 based on microarray results. LncRNA AK036396 knockdown attenuated Fcnb protein stability in a manner dependent on the ubiquitin-proteasome system. Moreover, Fcnb inhibition downregulated the suppressive function of PMN-MDSCs. In addition, the expression of human M-ficolin, which is an ortholog of mouse Fcnb, was increased and positively correlated with arginase1 (ARG1) expression. This suppressive molecule is released by MDSCs, and its production is commonly used to represent the suppressive activity of MDSCs in patients with lung cancer, suggesting clinical relevance for these findings. These results indicate that lncRNA AK036396 can inhibit maturation and accelerate immunosuppression of PMN-MDSCs by enhancing Fcnb protein stability.

The role of tumor-associated macrophages in gastric cancer development and their potential as a therapeutic target

Gastric cancer (GC) represents the fifth cause of cancer-related death worldwide. Molecular biology has become a central area of research in GC and there are currently at least three major classifications available to elucidate the mechanisms that drive GC oncogenesis. Further, tumor microenvironment seems to play a crucial role, and tumor-associated macrophages (TAMs) are emerging as key players in GC development. TAMs are cells derived from circulating chemokine- receptor-type 2 (CCR2) inflammatory monocytes in blood and can be divided into two main types, M1 and M2 TAMs. M2 TAMs play an important role in tumor progression, promoting a pro-angiogenic and immunosuppressive signal in the tumor. The diffuse GC subtype, in particular, seems to be strongly characterized by an immuno-suppressive and pro-angiogenic phenotype. No molecular targets in this subgroup have yet been identified. There is an urgent need to understand the molecular pathways and tumor microenvironment features in the GC molecular subtypes. The role of anti-angiogenics and checkpoint inhibitors has recently been clinically validated in GC. Both ramucirumab, a fully humanized IgG1 monoclonal anti-vascular endothelial growth factor receptor 2 (VEGFR2) antibody, and checkpoint inhibitors in Epstein Bar Virus (EBV) and Microsatellite Instable (MSI) subtypes, have proved beneficial in advanced GC. Nevertheless, there is a need to identify predictive markers of response to anti-angiogenics and immunotherapy in clinical practice for a personalized treatment approach. The importance of M2 TAMs in development of solid tumors is currently gaining increasing interest. In this literature review we analyze immune microenvironment composition and signaling related to M1 and M2 TAMs in GC as well as its potential role as a therapeutic target.

A Novel Lactic Acid Bacteria Mixture: Macrophage-Targeted Prophylactic Intervention in Colorectal Cancer Management

Colorectal cancer (CRC) is one of the most common forms of cancer. Its onset from chronic inflammation is widely accepted. Moreover, dysbiosis plays an undeniable role, thus the use of probiotics in CRC has been suggested. They exhibit both anti- and pro-inflammatory properties and restore balance in the microbiota. The aim of this study was to investigate the immunomodulatory properties of six lactobacilli with probiotic features in an in vitro model of macrophage-like cells and to test these pooled probiotics for their anti-tumour properties in a chemically induced CRC model using Wistar male rats. Upon co-culture of M1- and M2-like macrophages with lactobacilli, cytokine release (TNF-α, IL-1β, IL-18, IL-23) and phagocytic activity using fluorescent-labelled bacteria were tested. The effects of orally administered probiotics on basic cancer and immune parameters and cytokine concentration (TNF-α, IL-1β, IL-18) in colon tumours were studied. Tested lactobacilli exhibited both pro- and anti-inflammatory properties in in vitro conditions. In vivo study showed that the administration of probiotics was able to decrease multiplicity, volume and total tumour numbers, restore colon length (p < 0.05) and increase IL-18 production (p < 0.05) in tumour tissue. These data indicate both an immunomodulatory effect of probiotics on distinct macrophage subsets and a protective effect against chemically-induced CRC.

Myeloid-Derived Suppressor Cells as a Therapeutic Target for Cancer

The emergence of immunotherapy has been an astounding breakthrough in cancer treatments. In particular, immune checkpoint inhibitors, targeting PD-1 and CTLA-4, have shown remarkable therapeutic outcomes. However, response rates from immunotherapy have been reported to be varied, with some having pronounced success and others with minimal to no clinical benefit. An important aspect associated with this discrepancy in patient response is the immune-suppressive effects elicited by the tumour microenvironment (TME). Immune suppression plays a pivotal role in regulating cancer progression, metastasis, and reducing immunotherapy success. Most notably, myeloid-derived suppressor cells (MDSC), a heterogeneous population of immature myeloid cells, have potent mechanisms to inhibit T-cell and NK-cell activity to promote tumour growth, development of the pre-metastatic niche, and contribute to resistance to immunotherapy. Accumulating research indicates that MDSC can be a therapeutic target to alleviate their pro-tumourigenic functions and immunosuppressive activities to bolster the efficacy of checkpoint inhibitors. In this review, we provide an overview of the general immunotherapeutic approaches and discuss the characterisation, expansion, and activities of MDSCs with the current treatments used to target them either as a single therapeutic target or synergistically in combination with immunotherapy.

Models for Monocytic Cells in the Tumor Microenvironment

Monocytes (Mos) are immune cells that critically regulate cancer, enabling tumor growth and modulating metastasis. Mos can give rise to tumor-associated macrophages (TAMs) and Mo-derived dendritic cells (moDCs), all of which shape the tumor microenvironment (TME). Thus, understanding their roles in the TME is key for improved immunotherapy. Concurrently, various biological and mechanical factors including changes in local cytokines, extracellular matrix production, and metabolic changes in the TME affect the roles of monocytic cells. As such, relevant TME models are critical to achieve meaningful insight on the precise functions, mechanisms, and effects of monocytic cells. Notably, murine models have yielded significant insight into human Mo biology. However, many of these results have yet to be confirmed in humans, reinforcing the need for improved in vitro human TME models for the development of cancer interventions. Thus, this chapter (1) summarizes current insight on the tumor biology of Mos, TAMs, and moDCs, (2) highlights key therapeutic applications relevant to these cells, and (3) discusses various TME models to study their TME-related activity. We conclude with a perspective on the future research trajectory of this topic.

High-fat diet-induced dysbiosis mediates MCP-1/CCR2 axis-dependent M2 macrophage polarization and promotes intestinal adenoma-adenocarcinoma sequence

High‐fat diet (HFD) is a well‐known risk factor for gut microbiota dysbiosis and colorectal cancer (CRC). However, evidence relating HFD, gut microbiota and carcinogenesis is limited. Our study aimed to demonstrate that HFD‐induced gut dysbiosis promoted intestinal adenoma‐adenocarcinoma sequence. In clinical study, we found that HFD increased the incidence of advanced colorectal neoplasia (AN). The expression of monocyte chemoattractant protein 1 (MCP‐1), CC chemokine receptor 2 (CCR2) and CD163 in CRC patients with HFD was significantly higher than that in CRC patients with normal diet. When it comes to the Apc^min/+ mice, HFD consumption could induce gut dysbiosis and promote intestinal carcinogenesis, accompanying with activation of MCP‐1/CCR2 axis that recruited and polarized M2 tumour‐associated macrophages. Interestingly, transfer of faecal microbiota from HFD‐fed mice to another batch of Apc^min/+ mice in the absence of HFD could also enhance carcinogenesis without significant body weight gain and induced MCP‐1/CCR2 axis activation. HFD‐induced dysbiosis could also be transmitted. Meanwhile, antibiotics cocktail treatment was sufficient to inhibit HFD‐induced carcinogenesis, indicating the vital role of dysbiosis in cancer development. Conclusively, these data indicated that HFD‐induced dysbiosis accelerated intestinal adenoma‐adenocarcinoma sequence through activation of MCP‐1/CCR2 axis, which would provide new insight into better understanding of the mechanisms and prevention for HFD‐related CRC.

The Role of the Immune Infiltrate in Distinct Cancer Types and Its Clinical Implications : Lymphocytic Infiltration in Colorectal Cancer

Colorectal cancer (CRC) represents a major public health challenges, with one of the highest incidences worldwide. The two affected anatomical sites in CRC, i.e. the colon and the rectum, share important underlying features, but often differ in terms of therapeutic management. Current guidelines for CRC define its clinical stratification according to classical, tumor cell-based and pathological parameters. Novel ground-breaking findings in the recent years revealed the prominent role of the immune system in shaping CRC development. This chapter provides a detailed overview of the main genomic and immune features driving (or hampering) CRC progression, with a focus on the main immune cells and factors shaping its evolution. Furthermore, we discuss how tumor-infiltrating immunity could be leveraged both for therapeutic and stratification purposes.

More Than Just Attractive: How CCL2 Influences Myeloid Cell Behavior Beyond Chemotaxis

Monocyte chemoattractant protein-1 (MCP-1/CCL2) is renowned for its ability to drive the chemotaxis of myeloid and lymphoid cells. It orchestrates the migration of these cell types both during physiological immune defense and in pathological circumstances, such as autoimmune diseases including rheumatoid arthritis and multiple sclerosis, inflammatory diseases including atherosclerosis, as well as infectious diseases, obesity, diabetes, and various types of cancer. However, new data suggest that the scope of CCL2's functions may extend beyond its original characterization as a chemoattractant. Emerging evidence shows that it can impact leukocyte behavior, influencing adhesion, polarization, effector molecule secretion, autophagy, killing, and survival. The direction of these CCL2-induced responses is context dependent and, in some cases, synergistic with other inflammatory stimuli. The involvement of CCL2 signaling in multiple diseases renders it an interesting therapeutic target, although current targeting strategies have not met early expectations in the clinic. A better understanding of how CCL2 affects immune cells will be pivotal to the improvement of existing therapeutic approaches and the development of new drugs. Here, we provide an overview of the pleiotropic effects of CCL2 signaling on cells of the myeloid lineage, beyond chemotaxis, and highlight how these actions might help to shape immune cell behavior and tumor immunity.

Serum levels of the chemokine CCL2 are elevated in malignant pleural mesothelioma patients

BACKGROUND

Malignant pleural mesothelioma (MPM) is a debilitating disease of the pleural cavity. It is primarily associated with previous inhalation of asbestos fibers. These fibers initiate an oxidant coupled inflammatory response. Repeated exposure to asbestos fibers results in a prolonged inflammatory response and cycles of tissue damage and repair. The inflammation-associated cycles of tissue damage and repair are intimately involved in the development of asbestos-associated cancers. Macrophages are a key component of asbestos-associated inflammation and play essential roles in the etiology of a variety of cancers. Macrophages are also a source of C-C motif chemokine ligand 2 (CCL2), and a variety of tumor-types express CCL2. High levels of CCL2 are present in the pleural effusions of mesothelioma patients, however, CCL2 has not been examined in the serum of mesothelioma patients.

METHODS

The present study was carried out with 50 MPM patients and 356 subjects who were possibly exposed to asbestos but did not have disease symptoms and 41 healthy volunteers without a history of exposure to asbestos. The levels of CCL2 in the serum of the study participants was determined using ELISA.

RESULTS

Levels of CCL2 were significantly elevated in the serum of patients with advanced MPM.

CONCLUSIONS

Our findings are consistent with the premise that the CCL2/CCR2 axis and myeloid-derived cells play an important role in MPM and disease progression. Therapies are being developed that target CCL2/CCR2 and tumor resident myeloid cells, and clinical trials are being pursued that use these therapies as part of the treatment regimen. The results of trials with patients with a similar serum CCL2 pattern as MPM patients will have important implications for the treatment of MPM.

Chemokines and their receptors promoting the recruitment of myeloid-derived suppressor cells into the tumor

Myeloid-derived suppressor cells (MDSCs) expand in tumor-bearing host. They suppress anti-tumor immune response and promote tumor growth. Chemokines play a vital role in recruiting MDSCs into tumor tissue. They can also induce the generation of MDSCs in the bone marrow, maintain their suppressive activity, and promote their proliferation and differentiation. Here, we review CCL2/CCL12-CCR2, CCL3/4/5-CCR5, CCL15-CCR1, CX3CL1/CCL26-CX3CR1, CXCL5/2/1-CXCR2, CXCL8-CXCR1/2, CCL21-CCR7, CXCL13-CXCR5 signaling pathways, their role in MDSCs recruitment to tumor tissue, and their correlation with tumor development, metastasis and prognosis. Targeting chemokines and their receptors may serve as a promising strategy in immunotherapy, especially combined with other strategies such as chemotherapy, cyclin-dependent kinase or immune checkpoints inhibitors.

MET inhibitors in cancer: pitfalls and challenges

Introduction: The HGF/MET axis is a key therapeutic pathway in cancer; it is aberrantly activated because of mutations, fusions, amplification or aberrant ligand production. Extensive efforts have been made to discover predictive factors of anti-MET therapeutic efficacy, but they have mostly unsuccessful. An understanding of the intrinsic and acquired mechanism of MET resistance will be fundamental for the development of new therapeutic interventions.Areas covered: This article provides a systematic review of phase II randomized and phase III clinical trials investigating the use of MET inhibitors in the treatment of cancer. We discuss preliminary findings on efficacy and methodologic design flaws in these trials.Expert opinion: MET inhibitors showed poor activity in unselected patients or patients selected by MET expression, p-MET or high HGF basal levels. The efficacy in advanced solid tumors is very modest and in phase III clinical trials, survival differences did not fulfill the stringent requirements of ESMO-Magnitude Clinical Benefit Score (MCBS). Prospective novel liquid biomarker-driven studies and novel trial designs such as Umbrella and Basket trials are necessary to progress MET inhibitor development.

Inflammation induced by incomplete radiofrequency ablation accelerates tumor progression and hinders PD-1 immunotherapy

Radiofrequency ablation (RFA) promotes tumor antigen-specific T cell responses and enhances the effect of immunotherapy in preclinical settings. Here we report that the existence of remnant tumor masses due to incomplete RFA (iRFA) is associated with earlier new metastases and poor survival in patients with colorectal cancer liver metastases (CRCLM). Using mouse models, we demonstrate that iRFA promotes tumor progression and hinders the efficacy of anti-PD-1 therapy. Immune analysis reveals that iRFA induces sustained local inflammation with predominant myeloid suppressor cells, which inhibit T cell function in tumors. Mechanistically, tumor cell-derived CCL2 is critical for the accumulation of monocytes and tumor-associated macrophages (TAMs). The crosstalk between TAMs and tumor cells enhances the CCL2 production by tumor cells. Furthermore, we find that administration of a CCR2 antagonist or the loss of CCL2 expression in tumor cells enhances the antitumor activity of PD-1 blockade, providing a salvage alternative for residual tumors after iRFA.

Radiofrequency ablation is used to treat metastatic colorectal cancer. In this study, the authors show that incomplete ablation of tumours results in metastases and show in mouse models that the chemokine CCL2 recruits myeloid cells to the partially ablated tumours, which can block T cell function.

Tumor angiogenesis: causes, consequences, challenges and opportunities

Tumor vascularization occurs through several distinct biological processes, which not only vary between tumor type and anatomic location, but also occur simultaneously within the same cancer tissue. These processes are orchestrated by a range of secreted factors and signaling pathways and can involve participation of non-endothelial cells, such as progenitors or cancer stem cells. Anti-angiogenic therapies using either antibodies or tyrosine kinase inhibitors have been approved to treat several types of cancer. However, the benefit of treatment has so far been modest, some patients not responding at all and others acquiring resistance. It is becoming increasingly clear that blocking tumors from accessing the circulation is not an easy task to accomplish. Tumor vessel functionality and gene expression often differ vastly when comparing different cancer subtypes, and vessel phenotype can be markedly heterogeneous within a single tumor. Here, we summarize the current understanding of cellular and molecular mechanisms involved in tumor angiogenesis and discuss challenges and opportunities associated with vascular targeting.

PIPKIγ Regulates CCL2 Expression in Colorectal Cancer by Activating AKT-STAT3 Signaling

Colorectal cancer (CRC) remains the third most commonly diagnosed cancer, ranking second among the most common causes of cancer-related mortality. Immune checkpoint therapy has recently been shown to have great potential. However, only some patients respond to immune checkpoint blockade, indicating the unmet need for determining the underlying mechanism of colorectal cancer immunosuppression. In this study, we analyzed The Cancer Genome Atlas (TCGA) datasets and found that high expression of PIPKIγ positively correlated with tumor-associated macrophage infiltration. Further loss-of-function studies revealed that silencing PIPKIγ greatly reduced CCL2 expression at both the mRNA and protein levels, leading to weak chemotaxis of cancer cells to macrophages. Mechanistically, PIPKIγ facilitated PI3K-Akt-mTOR signaling pathway activation to increase STAT3 phosphorylation levels, thus triggering CCL2 transcription to enhance tumor-associated macrophage recruitment. These findings identify the PIPKIγ signaling pathway as a new actor in colorectal cancer immunosuppression and a potential therapeutic target for this common cancer.

Granulocytic myeloid-derived suppressor cells correlate with outcomes undergoing neoadjuvant chemotherapy for bladder cancer

OBJECTIVES

It remains unclear whether the immunologic status of cells in peripheral blood can be used as a prognostic indicator of response to treatment for patients with neoadjuvant chemotherapy (NAC). This study sought to evaluate whether the proportion of granulocytic myeloid-derived suppressor cells (G-MDSCs) and monocytic myeloid-derived suppressor cells could correlate with pathologic response in bladder cancer patients receiving NAC.

PATIENTS AND METHODS

Pretreatment peripheral blood levels of G-MDSCs and monocytic myeloid-derived suppressor cells were measured by flow cytometry. We divided patients into high and low (above and below the median, respectively) groups based on the median value for each immune cell subset and compared outcomes of the two groups.

RESULTS

A significant pathological response (pT0-1) was attained in 13% (6 of 45) of patients with high G-MDSCs compared with 58% (26 of 45) of patients with low G-MDSCs (P < 0.001). Patients with high G-MDSCs had significantly shorter disease specific survival and progression-free survival (both P < 0.001). In the multivariate analysis for survival, high G-MDSCs and pathological response emerged as independent prognostic factor for progression-free survival (P < 0.001 and P = 0.017) and disease-specific survival (P < 0.001 and P = 0.014).

CONCLUSIONS

Pretreatment peripheral G-MDSCs may represent a potential marker for the outcome of patients treated with cisplatin-based NAC.

The inhibitory effects of butein on cell proliferation and TNF-α-induced CCL2 release in racially different triple negative breast cancer cells

Drug resistance is the leading cause of breast cancer-related mortality in women, and triple negative breast cancer (TNBC) is the most aggressive subtype, affecting African American women more aggressively compared to Caucasians women. Of all cancer-related deaths, 15 to 20% are associated with inflammation, where proinflammatory cytokines have been implicated in the tumorigenesis process. The current study investigated the effects of the polyphenolic compound butein (2',3,4,4'-tetrahydroxychalcone) on cell proliferation and survival, as well as its modulatory effect on the release of proinflammatory cytokines in MDA-MB-231 (Caucasian) and MDA-MB-468 (African American) TNBC cell. The results obtained showed that butein decreased cell viability in a time and dose-dependent manner, and after 72-h of treatment, the cell proliferation rate was reduced in both cell lines. In addition, butein was found to have higher potency in MDA-MB-468, exhibiting anti-proliferative effects in lower concentrations. Apoptosis assays demonstrated that butein (50 μM) increased apoptotic cells in MDA MB-468, showing 60% of the analyzed cells in the apoptotic phase, compared to 20% in MDA-MB-231 cells. Additionally, butein downregulated both protein and mRNA expression of the proinflammatory cytokine, CCL2, and IKBKE in TNFα-activated Caucasian cells, but not in African Americans. This study demonstrates butein potential in cancer cell suppression showing a higher cytotoxic, anti-proliferative, and apoptotic effects in African Americans, compared to Caucasians TNBC cells. It also reveals the butein inhibitory effect on CCL2 expression with a possible association with IKBKE downregulation in MDA-MB-231 cells only, indicating that Caucasians and African Americans TNBC cells respond differently to butein treatment. The obtained findings may provide an explanation regarding the poor therapeutic response in African American patients with advanced TNBC.

Efficacy and clinical monitoring strategies for immune checkpoint inhibitors and targeted cytokine immunotherapy for locally advanced and metastatic colorectal cancer

Colorectal cancer (CRC) is the fourth most common cancer type and is the second leading cause of cancer deaths annually in the United States. Conventional treatment options include postoperative (adjuvant) and preoperative (neoadjuvant) chemotherapy and radiotherapy. Although these treatment modalities have shown to decrease tumor burden, a major limitation to chemothearpy/radiotherapy is the high recurrence rate in patients. Immune-modulation strategies have emerged as a promising new therapeutic avenue to reduce this recurrence rate while minimizing undesirable systemic side effects. This review will focus specifically on the mechanisms of monoclonal antibodies: immune checkpoint inhibitors and cytokines, as well as current drugs approved by the Food and Drug Administration (FDA) and new clinical/pre-clinical trials. Finally, this review will investigate emerging methods used to monitor tumor response post-treatment.

Klotho-mediated targeting of CCL2 suppresses the induction of colorectal cancer progression by stromal cell senescent microenvironments

Senescent microenvironments play an important role in tumor progression. Here, we report that doxorubicin (DOX)‐pretreated or replicative senescent stromal cells (WI‐38 and HUVEC) promote colorectal cancer (CRC) cell growth and invasion in vitro and in vivo. These pro‐tumorigenic effects were attenuated by exogenous administration of Klotho, an anti‐aging factor. We subsequently identified several senescence‐associated secretory phenotype (SASP)‐associated genes, including CCL2, which were significantly upregulated in both types of senescent stromal cells during replication and DNA damage‐induced senescence. Importantly, we found that the secretion of CCL2 by senescent stromal cells was significantly higher than that seen in nonsenescent cells or in senescent cells pretreated with Klotho. Notably, CCL2 was found to accelerate CRC cell proliferation and invasion, while this effect could be blocked by administration of a specific CCR2 antagonist. We further show that Klotho can suppress NF‐κB activation during DOX‐induced senescence and thus block CCL2 transcription. Low expression of Klotho, or high expression of CCL2 in patient tumor tissues, correlated with poor overall survival of CRC patients. Collectively, our findings suggest that senescent stromal cells are linked to progression of CRC. Klotho can suppress the senescent stromal cell‐associated triggering of CRC progression by inhibiting the expression of SASP factors including CCL2. The identification of key SASP factors such as CCL2 may provide potential therapeutic targets for improving CRC therapy.

Increased Incidence of Colon Tumors in AOM-Treated Apc 1638N/+ Mice Reveals Higher Frequency of Tumor Associated Neutrophils in Colon Than Small Intestine

Colorectal cancer (CRC) is one of the most common cancers and a major cause of mortality. Mice with truncating Apc germline mutations have been used as a standard model of CRC, but most of the Apc-mutated lines develop multiple tumors in the proximal small intestine and rarely in the colon precluding detailed analysis of colon tumor microenvironment. Our aim was to develop a model with higher resemblance to human CRC and to characterize tumor infiltrating immune cells in spontaneously developing colon tumors compared to small intestinal tumors. Therefore, the Apc^1638N/+ line was treated repeatedly with azoxymethane (AOM) and 90% colon tumor incidence and 4 to 5 colon tumors per mouse were achieved. Of note, AOM treatment specifically increased the tumor burden in the colon, but not in the small intestine. Histological grading and WNT-signaling activity did not differ significantly between small intestinal and colon tumors with some lesions progressing to invasive adenocarcinoma in both locations. However, characterization of the intratumoral myeloid cell compartment revealed a massive infiltration of colon tumors with neutrophils − 6-fold higher than in small intestinal tumors. Moreover, CCL17-expressing macrophages and dendritic cells accumulated in the tumors indicating the establishment of a tumor-promoting immunosuppressive environment. Thus, Apc^1638N/+ mice treated with AOM are a suitable and straightforward model to study the influence of immune cells and chemokines on colon carcinogenesis.

Immune Effects of M51R Vesicular Stomatitis Virus Treatment of Carcinomatosis From Colon Cancer

BACKGROUND

The purpose of this study was to analyze the oncolytic and immunomodulatory functions of an M protein mutant of vesicular stomatitis virus (M51R VSV) in a murine model of peritoneal surface dissemination from colon cancer (PSD from CRC).

METHODS

Luciferase-expressing CT26 peritoneal tumors were established in Balb/c mice to evaluate the impact of M51R VSV treatment on intraperitoneal tumor growth and overall survival. The mice were treated with either intraperitoneal phosphate buffered saline (n = 10) or 5 × 10⁶ PFU M51R VSV (n = 10) at 5 d after tumor implantation. Tumor bioluminescence was measured every 3 d during the 60-day study period. The immunomodulatory effect of M51R VSV treatment was evaluated in mice treated with either intraperitoneal phosphate buffered saline (n = 21) or M51R VSV (n = 21). Peritoneal lavages were collected at days 1, 3, and 7 after M51R VSV treatment for flow cytometry and multiplex cytokine bead analysis.

RESULTS

A single, intraperitoneal treatment with M51R VSV inhibited the growth of PSD from CRC as evidenced by decreased bioluminescence and improved survival. This treatment approach also resulted in significantly higher frequencies of peritoneal CD4+ T (10.95 ± 1.17 versus 6.19 ± 0.44, P = 0.004) and B1b cells (5.01 ± 0.97 versus 2.20 ± 0.2, P = 0.024). On the other hand, treatment with M51R VSV resulted in fewer myeloid-derived suppressor cells relative to controls (10.66 ± 1.48 versus 14.47 ± 1.06, P = 0.035). M51R-treated peritoneal cavities also contained lower concentrations of immunosuppressive monocyte chemoattractant protein-1 and interleukin 6 cytokines relative to controls.

CONCLUSIONS

Our findings suggest that M51R VSV alters the innate and adaptive immune responses in PSD from CRC. Future studies will delineate specific components of antitumor immunity that result in its therapeutic effect.

The Tumor Microenvironment in Colorectal Cancer Therapy

The current standard-of-care for metastatic colorectal cancer (mCRC) includes chemotherapy and anti-angiogenic or anti-epidermal growth factor receptor (EGFR) monoclonal antibodies, even though the addition of anti-angiogenic agents to backbone chemotherapy provides little benefit for overall survival. Since the approval of anti-angiogenic monoclonal antibodies bevacizumab and aflibercept, for the management of mCRC over a decade ago, extensive efforts have been devoted to discovering predictive factors of the anti-angiogenic response, unsuccessfully. Recent evidence has suggested a potential correlation between angiogenesis and immune phenotypes associated with colorectal cancer. Here, we review evidence of interactions between tumor angiogenesis, the immune microenvironment, and metabolic reprogramming. More specifically, we will highlight such interactions as inferred from our novel immune-metabolic (IM) signature, which groups mCRC into three distinct clusters, namely inflamed-stromal-dependent (IM Cluster 1), inflamed-non stromal-dependent (IM Cluster 2), and non-inflamed or cold (IM Cluster 3), and discuss the merits of the IM classification as a guide to new immune-metabolic combinatorial therapeutic strategies in mCRC.

Peri-operative monocyte count is a marker of poor prognosis in gastric cancer: increased monocytes are a characteristic of myeloid-derived suppressor cells

Gastric cancer (GC) is the most common malignant tumor in digestive organs, and the prognosis of GC patients who have undergone surgery remains poor because of frequent recurrence. Therefore, the identification of new markers to predict the outcome of these patients is needed. Monocyte count is a negative prognostic factor associated with inflammation. We investigated the relationship between peripheral monocytes in the peri-operative period and prognosis in GC patients. A high pre-operative monocyte count was identified as a prognostic factor in a retrospective analysis of 278 stage II and III GC patients who underwent curative gastrectomy. In contrast, an increased post-operative monocyte count compared to the pre-operative monocyte count was a marker of poor prognosis, particularly for early relapse. In a prospective analysis of 75 GC patients, a subset of the increased post-operative monocytes was similar to CD14+ HLA-DR- CD11b+ CD33+ cells by flow cytometry, and these monocytes produced IDO and arginase and suppressed T cell functions; therefore, we classified these cells as monocytic myeloid-derived suppressive cells (M-MDSCs). Peri-operative neutrophils and C-reactive protein (CRP), which are also related to inflammation, did not affect the prognosis of GC patients, and a neutrophil immunosuppressive function was not observed. These results suggest that peripheral monocytes in the peri-operative period in GC patients are a useful marker for the prognosis of GC patients, and a subset of increased post-operative monocytes may be characterized as M-MDSCs.

Monocyte heterogeneity and functions in cancer

Monocytes are innate immune cells of the mononuclear phagocyte system that have emerged as important regulators of cancer development and progression. Our understanding of monocytes has advanced from viewing these cells as a homogenous population to a heterogeneous system of cells that display diverse responses to different stimuli. During cancer, different monocyte subsets perform functions that contribute to both pro- and antitumoral immunity, including phagocytosis, secretion of tumoricidal mediators, promotion of angiogenesis, remodeling of the extracellular matrix, recruitment of lymphocytes, and differentiation into tumor-associated macrophages and dendritic cells. The ability of cancer to evade immune recognition and clearance requires protumoral signals to outweigh ongoing attempts by the host immune system to prevent tumor growth. This review discusses current understanding of monocyte heterogeneity during homeostasis, highlights monocyte functions in cancer progression, and describes monocyte-targeted therapeutic strategies for cancer treatment.

Characterization of myeloid-derived suppressor cells and cytokines GM-CSF, IL-10 and MCP-1 in dogs with malignant melanoma receiving a GD3-based immunotherapy

Melanoma in humans and canines is an aggressive and highly metastatic cancer. The mucosal forms in both species share genetic and histopathologic features, making dogs a valuable spontaneous disease animal model. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells of myeloid origin with immunosuppressive capabilities, which are increased in many human cancers and contribute to tumor immune evasion. They are a possible target to improve immunotherapy outcomes. Current information regarding MDSCs in canines is minimal, limiting their use as translational model for the study of MDSCs. The objective of this study was to characterize major MDSCs subsets (monocytic and polymorphonuclear) and the cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 10 (IL-10) and monocyte chemoattractant protein-1 (MCP-1) in canines with malignant melanoma and to evaluate changes in MDSCs and the cytokines over time in response to a GD3-based active immunotherapy. Whole blood and serum collected from 30 healthy controls and 33 patients enrolled in the University of Florida melanoma vaccine trial were analyzed by flow cytometry with canine specific CD11b, MHCII and anti-human CD14 antibodies to assess ostensibly polymorphonuclear-MDSC (CD11b⁺ MHCII^- CD14^-) and monocytic-MDSC (CD11b⁺ MHCII^- CD14⁺) subsets. IL-10, MCP-1 and both MDSCs subsets were significantly elevated in melanoma dogs versus controls. Both MDSCs subsets decreased significantly following GD3-based immunotherapy administration but no significant changes in cytokines were seen over time. To our knowledge, this is the first report documenting increased monocytic-MDSCs in canine melanoma. This is consistent with human malignant melanoma data, supporting dogs as a valuable model for therapeutic intervention studies.

Tuning the Tumor Myeloid Microenvironment to Fight Cancer

The tumor microenvironment (TME) of diverse cancer types is often characterized by high levels of infiltrating myeloid cells including monocytes, macrophages, dendritic cells, and granulocytes. These cells perform a variety of functions in the TME, varying from immune suppressive to immune stimulatory roles. In this review, we summarize the different myeloid cell populations in the TME and the intratumoral myeloid targeting approaches that are being clinically investigated, and discuss strategies that identify new myeloid subpopulations within the TME. The TME therapies include agents that modulate the functional activities of myeloid populations, that impact recruitment and survival of myeloid subpopulations, and that functionally reprogram or activate myeloid populations. We discuss the benefits, limitations and potential side effects of these therapeutic approaches.

The Emerging Role of YAP/TAZ in Tumor Immunity

Yes-associated protein (YAP)/WW domain-containing transcription regulator 1 (TAZ) is an important transcriptional regulator and effector of the Hippo signaling pathway that has emerged as a critical determinant of malignancy in many human tumors. YAP/TAZ expression regulates the cross-talk between immune cells and tumor cells in the tumor microenvironment through its influence on T cells, myeloid-derived suppressor cells, and macrophages. However, the mechanisms underlying these effects are poorly understood. An improved understanding of the role of YAP/TAZ in tumor immunity is essential for exploring innovative tumor treatments and making further breakthroughs in antitumor immunotherapy. This review primarily focuses on the role of YAP/TAZ in immune cells, their interactions with tumor cells, and how this impacts on tumorigenesis, progression, and therapy resistance.

Potentials of C-C motif chemokine 2-C-C chemokine receptor type 2 blockers including propagermanium as anticancer agents

Inflammation plays an essential role in the development and progression of most cancers. Chemokine C‐C motif chemokine 2 (CCL2) and its receptor C‐C chemokine receptor type 2 (CCR2) constitute a key signaling axis in inflammation that has recently attracted much interest on the basis of evidence showing its association with cancer progression. Propagermanium (3‐oxygermylpropionic acid polymer) is an organogermanium compound that is given for the treatment of hepatitis B in Japan and which inhibits the CCL2‐CCR2 signaling pathway. Herein, we review the importance of the CCL2‐CCR2 axis as a target in cancer treatment as shown by studies in mice and humans with pharmacological agents including propagermanium.

Temporal and spatial profile of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in ischemic stroke in mice

Although T cells play important roles in the pathophysiology of ischemic stroke, the dynamics of T cells remains unclear. In cancer, polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) contribute to the maintenance of the tumor microenvironment by suppressing T cells. However, the presence of these cells has never been examined in ischemic brain. Therefore, we examined the temporal and spatial profiles of PMN-MDSCs, which are defined as the CD11b⁺Ly6C^lowLy6G⁺ cells with higher expression levels of Nox2 and C/EBP Homologous Protein (CHOP) mRNA than normal neutrophil. Fluorescence-activated cell sorter (FACS) analysis showed that the count of CD11b⁺Ly6C^lowLy6G⁺ cells was increased in the ischemic hemisphere and bone marrow at 72 hours, as well as in the spleen 24 hours after transient middle cerebral artery occlusion in mice. In contrast, the contralateral hemisphere, normal bone marrow, and normal spleen contained few CD11b⁺Ly6C^lowLy6G⁺ cells. Real-time reverse transcription polymerase chain reaction revealed that CD11b⁺Ly6C^lowLy6G⁺ cells sorted from brain and spleen 72 hours after ischemia had greater expression of Nox2 and CHOP mRNA than neutrophils in bone marrow, suggesting that these cells constitute PMN-MDSCs. Immunohistochemistry showed that CD11b⁺Ly6G⁺ cells were located in the ischemic core and border zone, indicating that PMN-MDSCs might be endemic to these regions. Although neutrophils are believed to invade infarct regions 48–72 hours after ischemia, the present study suggested that some of these cells are in fact PMN-MDSCs. Further studies on the function of PMN-MDSCs might unveil the unknown mechanisms of T cell activation and recruitment in ischemic stroke.

Myeloid Derived Suppressor Cells Interactions With Natural Killer Cells and Pro-angiogenic Activities: Roles in Tumor Progression

Myeloid-derived suppressor cells (MDSCs) contribute to the induction of an immune suppressive/anergic, tumor permissive environment. MDSCs act as immunosuppression orchestrators also by interacting with several components of both innate and adaptive immunity. Natural killer (NK) cells are innate lymphoid cells functioning as primary effector of immunity, against tumors and virus-infected cells. Apart from the previously described anergy and hypo-functionality of NK cells in different tumors, NK cells in cancer patients show pro-angiogenic phenotype and functions, similar to decidual NK cells. We termed the pro-angiogenic NK cells in the tumor microenvironment "tumor infiltrating NK" (TINKs), and peripheral blood NK cells in cancer patients "tumor associated NK" (TANKs). The contribution of MDSCs in regulating NK cell functions in tumor-bearing host, still represent a poorly explored topic, and even less is known on NK cell regulation of MDSCs. Here, we review whether the crosstalk between MDSCs and NK cells can impact on tumor onset, angiogenesis and progression, focusing on key cellular and molecular interactions. We also propose that the similarity of the properties of tumor associated/tumor infiltrating NK and MDSC with those of decidual NK and decidual MDSCs during pregnancy could hint to a possible onco-fetal origin of these pro-angiogenic leukocytes.

Comparative RNA sequencing reveals that HPV16 E6 abrogates the effect of E6*I on ROS metabolism

High-risk Human Papillomavirus infections are responsible for anogenital and oropharyngeal cancers. Alternative splicing is an important mechanism controlling HPV16 gene expression. Modulation in the splice pattern leads to polycistronic HPV16 early transcripts encoding a full length E6 oncoprotein or truncated E6 proteins, commonly named E6*. Spliced E6*I transcripts are the most abundant RNAs produced in HPV-related cancers. To date, the biological function of the E6*I isoform remains controversial. In this study, we identified, by RNA sequencing, cellular targets deregulated by E6*I, among which genes related to ROS metabolism. Concomitantly, E6*I-overexpressing cells display high levels of ROS. However, co-overexpression of both E6 and E6*I has no effect on ROS production. In HPV16-infected cells expressing different E6/E6*I levels, we show that the newly identified targets CCL2 and RAC2 are increased by E6*I but decreased by E6 expression, suggesting that E6 abrogates the effect of E6*I. Taken together, these data support the idea that E6*I acts independently of E6 to increase ROS production and that E6 has the ability to counteract the effects of E6*I. This asks the question of how E6*I can be considered separately of E6 in the natural history of HPV16 infection.

Phenotypic and transcriptomic characterization of canine myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are key players in immune evasion, tumor progression and metastasis. MDSCs accumulate under various pathological states and fall into two functionally and phenotypically distinct subsets that have been identified in humans and mice: polymorphonuclear (PMN)-MDSCs and monocytic (M)-MDSCs. As dogs are an excellent model for human tumor development and progression, we set out to identify PMN-MDSCs and M-MDSCs in clinical canine oncology patients. Canine hypodense MHC class II-CD5-CD21-CD11b+ cells can be subdivided into polymorphonuclear (CADO48A+CD14-) and monocytic (CADO48A-CD14+) MDSC subsets. The transcriptomic signatures of PMN-MDSCs and M-MDSCs are distinct, and moreover reveal a statistically significant similarity between canine and previously published human PMN-MDSC gene expression patterns. As in humans, peripheral blood frequencies of canine PMN-MDSCs and M-MDSCs are significantly higher in dogs with cancer compared to healthy control dogs (PMN-MDSCs: p < 0.001; M-MDSCs: p < 0.01). By leveraging the power of evolution, we also identified additional conserved genes in PMN-MDSCs of multiple species that may play a role in MDSC function. Our findings therefore validate the dog as a model for studying MDSCs in the context of cancer.

Human telomerase reverse transcriptase recruits the β-catenin/TCF-4 complex to transactivate chemokine (C-C motif) ligand 2 expression in colorectal cancer

BACKGROUND AND AIM

Various molecular mechanisms are involved in the pathogenesis of colorectal cancer (CRC), one of the leading fatal diseases. Although human telomerase reverse transcriptase (hTERT) is critical in promoting CRC development, its regulatory mechanism is still elusive. Chemokine (C-C motif) ligand 2 (CCL2) is important to CRC pathogenesis, but the upstream regulation of CCL2 requires further investigation. Therefore, we aim to investigate the crosstalk mechanism between hTERT and CCL2 and its involvement in the pathogenesis of CRC.

METHODS

The expression relationship between hTERT and CCL2 was verified in CRC and adjacent tissues by immunohistochemistry. Lentiviruses or plasmids were used to regulate hTERT and CCL2 expression. The roles of hTERT and CCL2 in cell growth and migration were studied using CCK8 and transwell assays. The interaction between hTERT and CCL2 was detected by a luciferase reporter assay, immunofluorescence and ChIP assays. The β-catenin/TCF-4 complex was confirmed by COIP.

RESULTS

Both hTERT and CCL2 expression levels were markedly increased in CRC tissues compared to the adjacent stroma. Moreover, myeloid-derived suppressor cells (MDSCs) were found in tumor areas with higher expression levels of hTERT and CCL2. hTERT promoted HCT116 cell migration and invasion by increasing CCL2 expression. Mechanistically, ectopic hTERT facilitated the nuclear translocation of canonical β-catenin and the formation of a complex with downstream effector TCF-4, which eventually activated the CCL2 promoter.

CONCLUSIONS

hTERT may promote CRC by recruiting β-catenin/TCF-4 complex to transactivate CCL2 expression, which is a novel crosstalk mechanism likely involved in the pathogenesis of CRC.

RIPK3-Induced Inflammation by I-MDSCs Promotes Intestinal Tumors

Myeloid-derived suppressor cells (MDSC) promote colorectal cancer by several mechanisms, including suppression of antitumor T cells and production of tumorigenic factors. We previously showed that an intermediate MDSC subset (I-MDSC) is expanded in an intestinal tumor model (Apc^Min/+ mice), but the importance of this subset in promoting tumors is unclear. Here, we show that I-MDSCs are a distinct heterogeneous subset due to differential and reduced expression of the monocytic marker, Ly6C, and granulocytic marker, Ly6G. Besides causing necroptotic cell death, receptor-interacting protein kinase 3 (RIPK3) has an alternate function as a signaling component inducing cytokine synthesis. We evaluated whether RIPK3 regulates inflammatory cytokines in I-MDSCs to assess the nonimmunosuppressive function of I-MDSCs in promoting tumors. Inhibition of RIPK3 with the commercially available small-molecule inhibitor GSK 872 showed that RIPK3-mediated inflammation promoted intestinal tumors in two intestinal tumor models, Apc^Min/+ mice and an MC38 transplantable tumor model. Mechanistically, RIPK3 signaling in I-MDSC increased tumor size by expanding IL17-producing T cells in MC38 tumors. Collectively, these data suggest RIPK3 signaling as a potential therapeutic target in colorectal cancer. SIGNIFICANCE: The specific role of RIPK3 in intestinal tumors and MDSC function sheds light on a key inflammatory mechanism driving tumorigenesis and allows for possible therapeutic intervention.

Co-delivery of RNAi and chemokine by polyarginine nanocapsules enables the modulation of myeloid-derived suppressor cells

Myeloid-Derived Suppressor Cells (MDSCs), immunosuppressive cells that promote tumor growth, represent an attractive target in cancer immunotherapy. However, the clinical success of this strategy is limited by the lack of efficient drug delivery vehicles targeting this cell compartment. The objective of this work was to develop a delivery carrier, multilayer polymer nanocapsules, with the capacity to co-encapsulate two types of immunomodulatory drugs, a chemokine and an RNAi sequence, aimed at reverting MDSC-mediated immunosuppression. The chemokine CCL2, intended to attract monocyte-macrophage MDSCs, was encapsulated within the L2 inverse micellar aqueous domains of the lipid core of these nanocapsules. On the other hand, two different RNAi sequences that modulate the CCAAT/enhancer-binding protein beta (C/EBPβ) pathway, shC/EBPβ and miR 142-3p, were successfully associated to their polymer shell. These RNAi sequences were covered by subsequent layers of polyarginine and hyaluronic acid, thereby creating multi-layered assemblies that protected them and facilitated their targeted delivery. The in vitro studies performed in primary MDSCs cultures showed the capacity of miR 142-3p-loaded nanocapsules to reduce the highly immunosuppressive monocyte-macrophage subset. Additionally, the encapsulation of CCL2 within the nanocapsules induced a potent monocyte-macrophage chemoattraction that could be used to direct the therapy to these cell subsets. Finally, in vitro and in vivo studies showed the capacity of shC/EBPβ-loaded nanocapsules to downregulate C/EBPβ levels in MDSCs and to reduce monocyte differentiation into tumor-associated macrophages in an MCA-203 fibrosarcoma mice model. In conclusion, the multilayer polymer nanocapsules described here are efficient vehicles for the co-delivery of proteins and RNA, and are potential candidates as nanomedicines for the modulation of MDSCs.

The role of CCR5 in directing the mobilization and biological function of CD11b+Gr1+Ly6Clow polymorphonuclear myeloid cells in cancer

Bone marrow (BM) cells of the hematopoietic system, also known as BM-derived leukocytes (BMD), are mobilized from the BM to the blood and then colonize tumor sites. These cells then become key players in either promoting or regulating the development and progression of tumors. Among the cells that suppress anti-tumor immunity are regulatory T cells (Tregs), tumor-associated macrophages (TAMS) and myeloid-derived suppressor cells (MDSC). MDSC comprise CD11b+Gr1+Ly6Clow polymorphonuclear myeloid cells (PMN-MDSC), and CD11b+Gr1+Ly6Chigh monocytic myeloid cells (Mo-MDSC). Several studies including ours have identified the CCR2-CCL2 axis as the key driver of the mobilization of monocytic cells from the BM to the blood and later their colonization at the tumor site. The current review focuses on the mechanisms by which PMN-MDSC are mobilized from the BM to the blood and later to the tumor site, and their clinical implications.

KIAA1549-BRAF Expression Establishes a Permissive Tumor Microenvironment Through NFκB-Mediated CCL2 Production

KIAA1549-BRAF is the most frequently identified genetic mutation in sporadic pilocytic astrocytoma (PA), creating a fusion BRAF (f-BRAF) protein with increased BRAF activity. Fusion-BRAF-expressing neural stem cells (NSCs) exhibit increased cell growth and can generate glioma-like lesions following injection into the cerebella of naïve mice. Increased Iba1⁺ monocyte (microglia) infiltration is associated with murine f-BRAF-expressing NSC-induced glioma-like lesion formation, suggesting that f-BRAF-expressing NSCs attract microglia to establish a microenvironment supportive of tumorigenesis. Herein, we identify Ccl2 as the chemokine produced by f-BRAF-expressing NSCs, which is critical for creating a permissive stroma for gliomagenesis. In addition, f-BRAF regulation of Ccl2 production operates in an ERK- and NFκB-dependent manner in cerebellar NSCs. Finally, Ccr2-mediated microglia recruitment is required for glioma-like lesion formation in vivo, as tumor do not form in Ccr2-deficient mice following f-BRAF-expressing NSC injection. Collectively, these results demonstrate that f-BRAF expression creates a supportive tumor microenvironment through NFκB-mediated Ccl2 production and microglia recruitment.

Immunosuppression mediated by myeloid-derived suppressor cells (MDSCs) during tumour progression

Under steady-state conditions, bone marrow-derived immature myeloid cells (IMC) differentiate into granulocytes, macrophages and dendritic cells (DCs). This differentiation is impaired under chronic inflammatory conditions, which are typical for tumour progression, leading to the accumulation of IMCs. These cells are capable of inducing strong immunosuppressive effects through the expression of various cytokines and immune regulatory molecules, inhibition of lymphocyte homing, stimulation of other immunosuppressive cells, depletion of metabolites critical for T cell functions, expression of ectoenzymes regulating adenosine metabolism, and the production of reactive species. IMCs are therefore designated as myeloid-derived suppressor cells (MDSCs), and have been shown to accumulate in tumour-bearing mice and cancer patients. MDSCs are considered to be a strong contributor to the immunosuppressive tumour microenvironment and thus an obstacle for many cancer immunotherapies. Consequently, numerous studies are focused on the characterisation of MDSC origin and their relationship to other myeloid cell populations, their immunosuppressive capacity, and possible ways to inhibit MDSC function with different approaches being evaluated in clinical trials. This review analyses the current state of knowledge on the origin and function of MDSCs in cancer, with a special emphasis on the immunosuppressive pathways pursued by MDSCs to inhibit T cell functions, resulting in tumour progression. In addition, we describe therapeutic strategies and clinical benefits of MDSC targeting in cancer.

Targeting macrophages: therapeutic approaches in cancer

Infiltration of macrophages in solid tumours is associated with poor prognosis and correlates with chemotherapy resistance in most cancers. In mouse models of cancer, macrophages promote cancer initiation and malignant progression by stimulating angiogenesis, increasing tumour cell migration, invasion and intravasation and suppressing antitumour immunity. At metastatic sites, macrophages promote tumour cell extravasation, survival and subsequent growth. Each of these pro-tumoural activities is promoted by a subpopulation of macrophages that express canonical markers but have unique transcriptional profiles, which makes tumour-associated macrophages (TAMs) good targets for anticancer therapy in humans through either their ablation or their re-differentiation away from pro-tumoural towards antitumoural states. In this Review, we evaluate the state of the art of TAM-targeting strategies, focusing on the limitations and potential side effects of the different therapies such as toxicity, rebound effects and compensatory mechanisms. We provide an extensive overview of the different types of therapy used in the clinic and their limitations in light of known macrophage biology and propose new strategies for targeting TAMs.

Toll like receptor 7 expressed by malignant cells promotes tumor progression and metastasis through the recruitment of myeloid derived suppressor cells

In non-small cell lung carcinoma (NSCLC), stimulation of toll-like receptor 7 (TLR7), a receptor for single stranded RNA, is linked to tumor progression and resistance to anticancer chemotherapy. However, the mechanism of this effect has been elusive. Here, using a murine model of lung adenocarcinoma, we demonstrate a key role for TLR7 expressed by malignant (rather than by stromal and immune) cells, in the recruitment of myeloid derived suppressor cells (MDSCs), induced after TLR7 stimulation, resulting in accelerated tumor growth and metastasis. In adenocarcinoma patients, high TLR7 expression on malignant cells was associated with poor clinical outcome, as well as with a gene expression signature linked to aggressiveness and metastastic dissemination with high abundance of mRNA encoding intercellular adhesion molecule 1 (ICAM-1), cytokeratins 7 and 19 (KRT-7 and 19), syndecan 4 (SDC4), and p53. In addition, lung tumors expressing high levels of TLR7 have a phenotype of epithelial mesenchymal transition with high expression of vimentin and low abundance of E-cadherin. These data reveal a crucial role for cancer cell-intrinsic TLR7 expression in lung adenocarcinoma progression.

Circulating inflammatory markers and colorectal cancer risk: A prospective case-cohort study in Japan

Blood levels of inflammation-related markers may reveal molecular pathways contributing to carcinogenesis. To date, prospective associations with colorectal cancer (CRC) risk have been based on few studies with limited sets of analytes. We conducted a case-cohort study within the Japan Public Health Center-based Prospective Study Cohort II, comparing 457 incident CRC cases during median 18 years follow-up with a random subcohort of 774 individuals. Baseline plasma levels of 62 cytokines, soluble receptors, acute-phase proteins, and growth factor markers were measured using Luminex bead-based assays. We estimated hazard ratios (HRs) associating each marker with CRC risk by Cox proportional hazards models adjusted for potential confounders. Subanalyses compared cases by years after blood draw (<5 vs. ≥5) and anatomical subsite (colon vs. rectum). Linear trends in quantiles of four C-C motif ligand (CCL) chemokines, one C-X-C motif ligand (CXCL) chemokine, and a soluble receptor were nominally associated with CRC risk based on p_trend < 0.05, but none met false discovery rate corrected statistical significance. HRs for the 4th vs. 1st quartile were: 1.69 for CCL2/MCP1, 1.61 for soluble tumor necrosis factor receptor 2, 1.39 for CCL15/MIP1D, 1.35 for CCL27/CTACK, 0.70 for CXCL6/GCP2 and 0.61 for CCL3/MIP1A. Among cases diagnosed 5+ years after enrollment, CCL2/MCP1, CCL3/MIP1A and CXCL6/GCP2 retained nominal statistical significance. There were no significant differences in associations between colon and rectum. Our findings implicate chemokine alterations in colorectal carcinogenesis, but require replication for confirmation. Noninvasive chemokine assays may have potential application in colorectal cancer screening and etiologic research.