Ontogeny of Tumor-associated Macrophages and Its Implication in Cancer Regulation

Tumor cells induce LAMP2a expression in tumor-associated macrophage for cancer progression

BACKGROUND

Tumor cells benefit from tumor-associated macrophages (TAMs) promoting tumor growth and modulating functions of other cells in tumor microenvironment (TME). However, how tumor cells regulate the property of TAMs during tumor invasion remains to be defined.

METHODS

Mouse tumor models and cancer patients' samples were analyzed to determine LAMP2a expression in TAMs. In vitro mouse primary macrophages were used to assess LAMP2a-modulated macrophage activation, and to verify LAMP2a's target proteins. The effect of LAMP2a-knockdown on tumor progression and TME maintaining was determined by using mouse tumor models.

FINDINGS

Lysosome associated membrane protein type 2A (LAMP2a) is upregulated in TAMs by tumor cells and important for tumor progression. LAMP2a expression in TAMs, but not in tumor cells, is associated with poor prognosis in breast cancer. LAMP2a inactivation induced by either shRNA or CRISPR/Cas9 prevents TAMs activation and tumor growth. LAMP2a degrades PRDX1 (peroxiredoxin 1) and CRTC1 (CREB-regulated transcription coactivator 1) to promote macrophage pro-tumorigenic activation.

INTERPRETATION

Our study suggests that tumor cells utilize LAMP2a-PRDX1/CRTC1 axis to modulate TAMs activation and promote tumor growth, reveals the role of LAMP2a in macrophage study and TAM-targeting tumor immunotherapy. FUND: National Natural Science Foundation of China (No. 81602492); National Key Research and Development Program of China (No. 2016YFA0201402).

Tumor Microenvironment Modulates Immunological Outcomes of Myeloid Cells with mTORC1 Disruption

The role of the mTOR signaling pathway in different myeloid cell subsets is poorly understood in the context of tumor development. In this study, myeloid cell-specific Raptor knockout (KO) mice were used to determine the roles of mechanistic target of rapamycin complex 1 (mTORC1) in regulating macrophage function from Lewis lung carcinoma (LLC) s.c. tumors and lung tumor metastasis. We found no difference in tumor growth between conditional Raptor KO and control mice in the s.c. tumor models, although depletion of mTORC1 decreased the immunosuppressive function of tumor-associated macrophages (TAM). Despite the decreased immunosuppressive activity of TAM, M1-like TAM differentiation was impaired in the s.c. tumor microenvironment of mTORC1 conditional Raptor KO mice due to downregulated CD115 expression on macrophages. In addition, TNF-α production by mTORC1-deficient myeloid cells was also decreased in the s.c. LLC tumors. On the contrary, disruption of mTORC1 in myeloid cells promoted lung cancer metastasis. Accordingly, immunosuppressive interstitial macrophages/metastasis-associated macrophages (CD11b⁺F4/80^high) were accumulated in the lungs of Raptor KO mice in the LLC lung metastasis model, leading to decreased Th1 responses. Taken together, our results demonstrate that differential tumor microenvironment dictates the immunological outcomes of myeloid cells, with mTORC1 disruption leading to different tumor growth phenotypes.

Transcriptomic Profiling of the Tumor Microenvironment Reveals Distinct Subgroups of Clear Cell Renal Cell Cancer: Data from a Randomized Phase III Trial

Metastasis remains the main reason for renal cell carcinoma (RCC)-associated mortality. Tyrosine kinase inhibitors (TKI) impart clinical benefit for most patients with RCC, but the determinants of response are poorly understood. We report an integrated genomic and transcriptomic analysis of patients with metastatic clear cell RCC (ccRCC) treated with TKI therapy and identify predictors of response. Patients in the COMPARZ phase III trial received first-line sunitinib or pazopanib with comparable efficacy. RNA-based analyses revealed four distinct molecular subgroups associated with response and survival. Characterization of these subgroups identified mutation profiles, angiogenesis, and macrophage infiltration programs to be powerful predictors of outcome with TKI therapy. Notably, predictors differed by the type of TKI received. Our study emphasizes the clinical significance of angiogenesis and immune tumor microenvironment and suggests that the critical effects its various aspects have on TKI efficacy vary by agent. This has broad implications for optimizing precision treatment of RCC. SIGNIFICANCE: The determinants of response to TKI therapy in metastatic ccRCC remain unknown. Our study demonstrates that key angiogenic and immune profiles of the tumor microenvironment may affect TKI response. These findings have the potential to inform treatment personalization in patients with RCC.This article is highlighted in the In This Issue feature, p. 453.

Determination of Polarization of Resident Macrophages and Their Effect on the Tumor Microenvironment

Interactions between tumor cells and their microenvironment have been long established as a cardinal hallmark of tumorigenesis and metastasis. To that end, tumor-associated macrophages (TAMs) have been studied extensively and were found to be typically correlated with poor prognosis in various cancers. TAMs are key elements of cancer-associated inflammation promoting cancer progression by increasing angiogenesis, inducing immunosuppression of the tumor tissue, and remodeling the extracellular matrix favoring invasion and metastasis. Since resident macrophages are characterized by substantial diversity and plasticity, understanding their polarization patterns in response to microenvironmental cues is a prime focus in the field. This chapter demonstrates an efficient manner to characterize polarization patterns of macrophages inside tumor tissues.

CD68, CD163, and matrix metalloproteinase 9 (MMP-9) co-localization in breast tumor microenvironment predicts survival differently in ER-positive and -negative cancers

Background

The role of tumor-associated macrophages (TAMs) in the cancer immune landscape and their potential as treatment targets or modulators of response to treatment are gaining increasing interest. TAMs display high molecular and functional complexity. Therefore their objective assessment as breast cancer biomarkers is critical. The aims of this study were to objectively determine the in situ expression and significance of TAM biomarkers (CD68, CD163, and MMP-9) in breast cancer and to identify subclasses of patients who could benefit from TAM-targeting therapies.

Methods

We measured CD68, CD163, and MMP-9 protein expression in formalin-fixed paraffin-embedded tissues of breast carcinomas represented in tissue microarray format using multiplexed quantitative immunofluorescence (QIF) in two independent Yale cohorts: cohort A—n = 398, estrogen receptor–positive (ER⁺) and ER⁻ cases—and the triple-negative breast cancer (TNBC)-only cohort B (n = 160). Associations between macrophage markers, ER status, and survival were assessed. Protein expression measured by QIF was compared with mRNA expression data from the METABRIC study.

Results

All three macrophage markers were co-expressed, displaying higher expression in ER⁻ cancers. High pan-macrophage marker CD68 correlated with poorer overall survival (OS) only in ER⁻ cases of cohort A (P = 0.02). High expression of CD163 protein in TAMs was associated with improved OS in ER⁻ cases (cohort A, P = 0.03 and TNBC cohort B, P = 0.04, respectively) but not in ER⁺ cancers. MMP-9 protein was not individually associated with OS. High expression of MMP-9 in the CD68⁺/CD163⁺ TAMs was associated with worse OS in ER⁺ tumors (P <0.001) but not in ER⁻ cancers. In the METABRIC dataset, mRNA levels followed the co-expression pattern observed in QIF but did not always show the same trend regarding OS.

Conclusions

Macrophage activity markers correlate with survival differently in ER⁺ and ER⁻ cancers. The association between high co-expression and co-localization of MMP-9/CD163/CD68 and poor survival in ER⁺ cancers suggests that these cancers may be candidates for macrophage-targeted therapies.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1076-x) contains supplementary material, which is available to authorized users.

Interleukin-6 induced by YAP in hepatocellular carcinoma cells recruits tumor-associated macrophages

Tumor-associated macrophages (TAMs) has been regarded as the most prominent component in tumor microenvironment. The correlation between TAM density and poor prognosis in Hepatocellular carcinoma (HCC) patients suggests a supportive role for TAMs in tumor progression. Here we employed a co-culture system to interrogate the molecular link between Yes-Associated Protein (YAP) and TAMs chemotaxis in HCC cells. We found that YAP activation was critical for the recruitment of TAMs towards HCC cells. Furthermore, cytokine array and quantitative RT-PCR analyses showed that IL-6 secreted by YAP-activated HCC cells might induce the TAMs recruitment. Interrupting YAP function by statins, the inhibitors of hydroxymethylglutaryl-CoA reductase, could robustly suppress the chemotaxis of TAMs. Together with our findings that the expression levels ofIL-6inhumanHCC tumors were highly correlated with the prognosis of HCC patients, the current study highlight the possibility of improving HCC treatment by targeting YAP-IL-6 mediated TAMs recruitment.

Nrf2 activation drive macrophages polarization and cancer cell epithelial-mesenchymal transition during interaction

Background

The M2 phenotype of tumor-associated macrophages (TAM) inhibits the anti-tumor inflammation, increases angiogenesis and promotes tumor progression. The transcription factor Nuclear Factor (erythroid-derived 2)-Like 2 (Nrf2) not only modulates the angiogenesis but also plays the anti-inflammatory role through inhibiting pro-inflammatory cytokines expression; however, the role of Nrf2 in the cancer cell and macrophages interaction is not clear.

Methods

Hepatocellular carcinoma cells (Hep G2 and Huh 7) and pancreatic cancer cells (SUIT2 and Panc-1) were co-cultured with monocytes cells (THP-1) or peripheral blood monocytes derived macrophages, then the phenotype changes of macrophages and epithelial-mesenchymal transition of cancer cells were detected. Also, the role of Nrf2 in cancer cells and macrophages interaction were investigated.

Results

In this study, we found that cancer cells could induce an M2-like macrophage characterized by up-regulation of CD163 and Arg1, and down-regulation of IL-1b and IL-6 through Nrf2 activation. Also, Nrf2 activation of macrophages promoted VEGF expression. The Nrf2 activation of macrophages correlated with the reactive oxygen species induced by cancer cells derived lactate. Cancer cells educated macrophages could activate Nrf2 of the cancer cells, in turn, to increase cancer cells epithelial-mesenchymal transition (EMT) through paracrine VEGF. These findings suggested that Nrf2 played the important role in the cancer cells and macrophages interaction.

Conclusions

Macrophage Nrf2 activation by cancer cell-derived lactate skews macrophages polarization towards an M2-like phenotype and educated macrophages activate Nrf2 of the cancer cells to promote EMT of cancer cells. This study provides a new understanding of the role of Nrf2 in the cancer cell and TAM interaction and suggests a potential therapeutic target.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0262-x) contains supplementary material, which is available to authorized users.

Crosstalk between hepatic tumor cells and macrophages via Wnt/β-catenin signaling promotes M2-like macrophage polarization and reinforces tumor malignant behaviors

Tumor-associated macrophages (TAMs) are a major component of tumor microenvironment (TME) and play pivotal roles in the progression of hepatocellular carcinoma (HCC). Wnt signaling is evolutionarily conserved and participates in liver tumorigenesis. Several studies have shown that macrophage-derived Wnt ligands can activate Wnt signaling in tumor cells. However, whether Wnt ligands secreted by tumor cells can trigger Wnt signaling in macrophages is still elusive. In this study, we first verified that canonical Wnt/β-catenin signaling was activated during monocyte-to-macrophage differentiation and in M2-polarized macrophages. Knockdown of β-catenin in M2 macrophages exhibited stronger antitumor characteristics when cocultured with Hepa1-6 HCC cells in a series of experiments. Activation of Wnt signaling promoted M2 macrophage polarization through c-Myc. Moreover, co-culturing naïve macrophages with Hepa1-6 HCC cells in which Wnt ligands secretion was blocked by knockdown of Wntless inhibited M2 polarization in vitro. Consistently, the growth of HCC tumor orthotopically inoculated with Wntless-silenced Hepa1-6 cells was impeded, and the phenotype of M2-like TAMs was abrogated due to attenuated Wnt/β-catenin signaling in TAMs, leading to subverted immunosuppressive TME. Finally, we confirmed the correlation between M2 macrophage polarization and nuclear β-catenin accumulation in CD68⁺ macrophages in human HCC biopsies. Taken together, our study indicates that tumor cells-derived Wnt ligands stimulate M2-like polarization of TAMs via canonical Wnt/β-catenin signaling, which results in tumor growth, migration, metastasis, and immunosuppression in HCC. To block Wnts secretion from tumor cells and/or Wnt/β-catenin signal activation in TAMs may be potential strategy for HCC therapy in future.

Notch Signaling in Myeloid Cells as a Regulator of Tumor Immune Responses

Cancer immunotherapy, which stimulates or augments host immune responses to treat malignancies, is the latest development in the rapidly advancing field of cancer immunology. The basic principles of immunotherapies are either to enhance the functions of specific components of the immune system or to neutralize immune-suppressive signals produced by cancer cells or tumor microenvironment cells. When successful, these approaches translate into long-term survival for patients. However, durable responses are only seen in a subset of patients and so far, only in some cancer types. As for other cancer treatments, resistance to immunotherapy can also develop. Numerous research groups are trying to understand why immunotherapy is effective in some patients but not others and to develop strategies to enhance the effectiveness of immunotherapy. The Notch signaling pathway is involved in many aspects of tumor biology, from angiogenesis to cancer stem cell maintenance to tumor immunity. The role of Notch in the development and modulation of the immune response is complex, involving an intricate crosstalk between antigen-presenting cells, T-cell subpopulations, cancer cells, and other components of the tumor microenvironment. Elegant studies have shown that Notch is a central mediator of tumor-induced T-cell anergy and that activation of Notch1 in CD8 T-cells enhances cancer immunotherapy. Tumor-infiltrating myeloid cells, including myeloid-derived suppressor cells, altered dendritic cells, and tumor-associated macrophages along with regulatory T cells, are major obstacles to the development of successful cancer immunotherapies. In this article, we focus on the roles of Notch signaling in modulating tumor-infiltrating myeloid cells and discuss implications for therapeutic strategies that modulate Notch signaling to enhance cancer immunotherapy.

Notch Signaling in Macrophages in the Context of Cancer Immunity

Macrophages play both tumor-suppressing and tumor-promoting roles depending on the microenvironment. Tumor-associated macrophages (TAMs) are often associated with poor prognosis in most, but not all cancer. Understanding how macrophages become TAMs and how TAMs interact with tumor cells and shape the outcome of cancer is one of the key areas of interest in cancer therapy research. Notch signaling is involved in macrophage activation and its effector functions. Notch signaling has been indicated to play roles in the regulation of macrophage activation in pro-inflammatory and wound-healing processes. Recent evidence points to the involvement of canonical Notch signaling in the differentiation of TAMs in a breast cancer model. On the other hand, hyperactivation of Notch signaling specifically in macrophages in tumors mass has been shown to suppress tumor growth in an animal model of cancer. Investigations into how Notch signaling is regulated in TAMs and translates into pro- or anti-tumor functions are still largely in their infancy. Therefore, in this review, we summarize the current understanding of the conflicting roles of Notch signaling in regulating the effector function of macrophages and the involvement of Notch signaling in TAM differentiation and function. Furthermore, how Notch signaling in TAMs affects the tumor microenvironment is reviewed. Finally, the direct or indirect cross-talk among TAMs, tumor cells and other cells in the tumor microenvironment via Notch signaling is discussed along with the possibility of its clinical application. Investigations into Notch signaling in macrophages may lead to a more effective way for immune intervention in the treatment of cancer in the future.

Tumor-derived extracellular vesicles activate primary monocytes

Tumor cells educate immune effector cells in their vicinity by releasing factors that manipulate their phenotype and function. In fact, the thus generated immunosuppressive tumor microenvironment constitutes an integral part and a hallmark of solid tumors and contributes significantly to tumor development and immune escape. It has long been thought that soluble factors like prostaglandin E2 and TGF-β are the main mediators of these effects. But tumor cells also constantly release large number of extracellular vesicles (EVs), which are important conveyors of immune responses. We show here that tumor-derived EVs interact with primary monocytes and induce an activated phenotype, which is also observed in tumor-associated macrophages. Thus, both tumor-derived EVs and soluble factors together collaborate to form the immunosuppressive milieu of the tumor environment.

The tumour microenvironment creates a niche for the self-renewal of tumour-promoting macrophages in colon adenoma

Circulating CCR2⁺ monocytes are crucial for maintaining the adult tissue-resident F4/80^hiMHCII^hi macrophage pool in the intestinal lamina propria. Here we show that a subpopulation of CCR2-independent F4/80^hiMHCII^low macrophages, which are the most abundant F4/80^hi cells in neonates, gradually decline in number in adulthood; these macrophages likely represent the fetal contribution to F4/80^hi cells. In colon adenomas of Apc^Min/+ mice, F4/80^hiMHCII^low macrophages are not only preserved, but become the dominant subpopulation among tumour-resident macrophages during tumour progression. Furthermore, these pro-tumoural F4/80^hiMHCII^low and F4/80^hiMHCII^hi macrophages can self-renew in the tumour and maintain their numbers mostly independent from bone marrow contribution. Analyses of colon adenomas indicate that CSF1 may be a key facilitator of macrophage self-renewal. In summary, the tumour microenvironment creates an isolated niche for tissue-resident macrophages that favours macrophage survival and self-renewal.

Tissue-resident F4/80^hi macrophages can be found both in normal gut as well as in intestinal tumours. Here the authors show that in the colon these macrophages are CCR2-dependent, while in tumours they gain the ability to self-renew, relying on CSF1 and promoting cancer progression.

Tumor-associated macrophages (TAMs) depend on ZEB1 for their cancer-promoting roles

Accumulation of tumor-associated macrophages (TAMs) associates with malignant progression in cancer. However, the mechanisms that drive the pro-tumor functions of TAMs are not fully understood. ZEB1 is best known for driving an epithelial-to-mesenchymal transition (EMT) in cancer cells to promote tumor progression. However, a role for ZEB1 in macrophages and TAMs has not been studied. Here we describe that TAMs require ZEB1 for their tumor-promoting and chemotherapy resistance functions in a mouse model of ovarian cancer. Only TAMs that expressed full levels of Zeb1 accelerated tumor growth. Mechanistically, ZEB1 expression in TAMs induced their polarization toward an F4/80low pro-tumor phenotype, including direct activation of Ccr2 In turn, expression of ZEB1 by TAMs induced Ccl2, Cd74, and a mesenchymal/stem-like phenotype in cancer cells. In human ovarian carcinomas, TAM infiltration and CCR2 expression correlated with ZEB1 in tumor cells, where along with CCL2 and CD74 determined poorer prognosis. Importantly, ZEB1 in TAMs was a factor of poorer survival in human ovarian carcinomas. These data establish ZEB1 as a key factor in the tumor microenvironment and for maintaining TAMs' tumor-promoting functions.

Distribution pattern of tumor associated macrophages predicts the prognosis of gastric cancer

Purpose

As mayor biomarkers in tumor microenvironment (TME), tumor associated macrophages (TAMs) of gastric cancer (GC) still needs further studies in terms of the number and distribution pattern.

Methods

Herein, tissue microarrays (TMA) incorporating 494 GC surgical samples in duplicate were stained for TAMs infiltration analysis. TAMs number was counted according to the locations, including infiltrating macrophages in cancer nest (MC), in invasive front (MF) and in stroma (MS). Correlations between TAMs number, distribution pattern and clinic-pathological features and survival analyses were performed.

Results

Infiltrating macrophages number in GC tissues was much higher than that in peritumoral tissues. TAMs number was not significantly correlated with the overall survival (OS). TAMs distribution pattern could be categorized into MC or MF/MS dominant pattern, and correlated with histological grade (P =0.001). The median OS of MF/MS dominant pattern (22.1, 95%CI: 23.5-28.9) was significantly shorter than that of MC dominant pattern (25.6, 95%CI: 28.5-35.6) (P =0.002). By receiver operating characteristic curve (ROC) analysis, the predictive value of TAMs distribution pattern was superior to histological grade and pM stage, but inferior to pN and TNM stage.

Conclusions

TAMs distribution pattern could be an independent prognostic factor for the OS of GC patients, and patients with MF/MS dominant pattern had worse outcomes.

Applying nanomedicine in maladaptive inflammation and angiogenesis

Inflammation and angiogenesis drive the development and progression of multiple devastating diseases such as atherosclerosis, cancer, rheumatoid arthritis, and inflammatory bowel disease. Though these diseases have very different phenotypic consequences, they possess several common pathophysiological features in which monocyte recruitment, macrophage polarization, and enhanced vascular permeability play critical roles. Thus, developing rational targeting strategies tailored to the different stages of the journey of monocytes, from bone marrow to local lesions, and their extravasation from the vasculature in diseased tissues will advance nanomedicine. The integration of in vivo imaging uniquely allows studying nanoparticle kinetics, accumulation, clearance, and biological activity, at levels ranging from subcellular to an entire organism, and will shed light on the fate of intravenously administered nanomedicines. We anticipate that convergence of nanomedicines, biomedical engineering, and life sciences will help to advance clinically relevant therapeutics and diagnostic agents for patients with chronic inflammatory diseases.

Myeloid-derived cells in prostate cancer progression: phenotype and prospective therapies

Prostate cancer is the second most common cause of cancer mortality in men in the United States. As is the case for other tumor types, accumulating evidence suggests an important role for myeloid-derived cells in the promotion and progression of prostate cancer. Here, we briefly describe myeloid-derived cells that interact with tumor cells and what is known about their immune suppressive function. We next discuss new evidence for tumor cell-mediated myeloid infiltration via the PI3K/PTEN/AKT signaling pathway and an alternative mechanism for immune evasion that may be regulated by an endoplasmic reticulum stress response. Finally, we discuss several interventions that target myeloid-derived cells to treat prostate cancer.

Tumor-associated macrophages: implications in cancer immunotherapy

Tumor-associated macrophages (TAMs), representing most of the leukocyte population in solid tumors, demonstrate great phenotypic heterogeneity and diverse functional capabilities under the influence of the local tumor microenvironment. These anti-inflammatory and protumorigenic macrophages modulate the local microenvironment to facilitate tumor growth and metastasis. In this review, we examine the origin of TAMs and the complex regulatory networks within the tumor microenvironment that facilitate the polarization of TAMs toward a protumoral phenotype. More extensively, we evaluate the mechanisms by which TAMs mediate angiogenesis, metastasis, chemotherapeutic resistance and immune evasion. Lastly, we will highlight novel interventional strategies targeting TAMs in preclinical studies and in early clinical trials that have significant potential in improving efficacy of current chemotherapeutic and/or immunotherapeutic approaches.

Promotion of Tumor Invasion by Tumor-Associated Macrophages: The Role of CSF-1-Activated Phosphatidylinositol 3 Kinase and Src Family Kinase Motility Signaling

Macrophages interact with cells in every organ to facilitate tissue development, function and repair. However, the close interaction between macrophages and parenchymal cells can be subverted in disease, particularly cancer. Motility is an essential capacity for macrophages to be able to carry out their various roles. In cancers, the macrophage's interstitial migratory ability is frequently co-opted by tumor cells to enable escape from the primary tumor and metastatic spread. Macrophage accumulation within and movement through a tumor is often stimulated by tumor cell production of the mononuclear phagocytic growth factor, colony-stimulating factor-1 (CSF-1). CSF-1 also regulates macrophage survival, proliferation and differentiation, and its many effects are transduced by its receptor, the CSF-1R, via phosphotyrosine motif-activated signals. Mutational analysis of CSF-1R signaling indicates that the major mediators of CSF-1-induced motility are phosphatidyl-inositol-3 kinase (PI3K) and one or more Src family kinase (SFK), which activate signals to adhesion, actin polymerization, polarization and, ultimately, migration and invasion in macrophages. The macrophage transcriptome, including that of the motility machinery, is very complex and highly responsive to the environment, with selective expression of proteins and splice variants rarely found in other cell types. Thus, their unique motility machinery can be specifically targeted to block macrophage migration, and thereby, inhibit tumor invasion and metastasis.

Inflammation and Cancer: Extra- and Intracellular Determinants of Tumor-Associated Macrophages as Tumor Promoters

One of the hallmarks of cancer-related inflammation is the recruitment of monocyte-macrophage lineage cells to the tumor microenvironment. These tumor infiltrating myeloid cells are educated by the tumor milieu, rich in cancer cells and stroma components, to exert functions such as promotion of tumor growth, immunosuppression, angiogenesis, and cancer cell dissemination. Our review highlights the ontogenetic diversity of tumor-associated macrophages (TAMs) and describes their main phenotypic markers. We cover fundamental molecular players in the tumor microenvironment including extra- (CCL2, CSF-1, CXCL12, IL-4, IL-13, semaphorins, WNT5A, and WNT7B) and intracellular signals. We discuss how these factors converge on intracellular determinants (STAT3, STAT6, STAT1, NF-κB, RORC1, and HIF-1α) of cell functions and drive the recruitment and polarization of TAMs. Since microRNAs (miRNAs) modulate macrophage polarization key miRNAs (miR-146a, miR-155, miR-125a, miR-511, and miR-223) are also discussed in the context of the inflammatory myeloid tumor compartment. Accumulating evidence suggests that high TAM infiltration correlates with disease progression and overall poor survival of cancer patients. Identification of molecular targets to develop new therapeutic interventions targeting these harmful tumor infiltrating myeloid cells is emerging nowadays.

Tumor Associated Macrophages as Therapeutic Targets for Breast Cancer

Tumor-associated macrophages (TAMs) are the most abundant inflammatory infiltrates in the tumor stroma. TAMs promote tumor growth by suppressing immunocompetent cells, including neovascularization and supporting cancer stem cells. In the chapter, we discuss recent efforts in reprogramming or inhibiting tumor-protecting properties of TAMs, and developing potential strategies to increase the efficacy of breast cancer treatment.

Assessment of the Number and Phenotype of Macrophages in the Human BMB Samples of CML

Macrophages have emerged as a key player in tumor biology. However, their number and phenotype in human bone marrow of biopsy (BMB) samples of chronic myeloid leukemia (CML) and their association with disease progression from an initial chronic phase (CP) to accelerated phase (AP) to advanced blast phase (BP) are still unclear. BMB samples from 127 CML patients and 30 patients with iron-deficiency anemia (IDA) as control group were analyzed by immunohistochemistry. The expression levels of CD68, CD163, and CD206 in BMB samples of CML patients were significantly higher than those in the patients of control group (P < 0.01), and we observed that their positive expression was gradually elevated during the transformation of CML-CP to AP to BP (P < 0.01). However, the expressions of CD68, CD163, and CD206 in released group were downregulated and contrasted to these in control group; there exists statistical significance (P < 0.01). The percentage ratio of CD163 and CD206 to CD68 was pronounced to be increasing from CML-CP to AP to BP (P < 0.01). Hence, the higher proportion of CD68⁺, CD163⁺ and CD206⁺ macrophages in BMB samples can be considered a key factor for disease progression of CML patients. Targeting macrophages, especially the M2 phenotype may help in designing therapeutic strategies for CML.

Pro-Tumoral Inflammatory Myeloid Cells as Emerging Therapeutic Targets

Since the observation of Virchow, it has long been known that the tumor microenvironment constitutes the soil for the infiltration of inflammatory cells and for the release of inflammatory mediators. Under certain circumstances, inflammation remains unresolved and promotes cancer development. Here, we review some of these indisputable experimental and clinical evidences of cancer related smouldering inflammation. The most common myeloid infiltrate in solid tumors is composed of myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). These cells promote tumor growth by several mechanisms, including their inherent immunosuppressive activity, promotion of neoangiogenesis, mediation of epithelial-mesenchymal transition and alteration of cellular metabolism. The pro-tumoral functions of TAMs and MDSCs are further enhanced by their cross-talk offering a myriad of potential anti-cancer therapeutic targets. We highlight these main pro-tumoral mechanisms of myeloid cells and give a general overview of their phenotypical and functional diversity, offering examples of possible therapeutic targets. Pharmacological targeting of inflammatory cells and molecular mediators may result in therapies improving patient condition and prognosis. Here, we review experimental and clinical findings on cancer-related inflammation with a major focus on creating an inventory of current small molecule-based therapeutic interventions targeting cancer-related inflammatory cells: TAMs and MDSCs.

New Mechanisms of Tumor-Associated Macrophages on Promoting Tumor Progression: Recent Research Advances and Potential Targets for Tumor Immunotherapy

The majority of basic and clinical studies have shown a protumor function of tumor-associated macrophages (TAMs), which represent a large proportion of matrix cells. TAMs promote tumorigenesis, and their number is related to the malignancy degree and poor prognosis of many kinds of tumors. Macrophage plasticity makes it possible to change the tumor microenvironment and remodel antitumor immunity during cancer immunotherapy. Increasing numbers of studies have revealed the effects of TAMs on the tumor microenvironment, for example, via promotion of tumor growth and tumorigenesis and through an increase in the number of cancer stem cells or via facilitation of angiogenesis, lymphangiogenesis, and metastasis. Investigators also proposed tumor-immunological treatments targeting TAMs by inhibiting TAM recruitment and differentiation, by regulating TAM polarization, and by blocking factors and pathways associated with the protumor function of TAMs. This comprehensive review presents recent research on TAMs in relation to prediction of poor outcomes, remodeling of the tumor immune microenvironment, and immunological targeted therapies.