Metabolic vulnerability of cancer stem cells and their niche

Cancer stem cells (CSC) are the leading cause of the failure of anti-tumor treatments. These aggressive cancer cells are preserved and sustained by adjacent cells forming a specialized microenvironment, termed niche, among which tumor-associated macrophages (TAMs) are critical players. The cycle of tricarboxylic acids, fatty acid oxidation path, and electron transport chain have been proven to play central roles in the development and maintenance of CSCs and TAMs. By improving their oxidative metabolism, cancer cells are able to extract more energy from nutrients, which allows them to survive in nutritionally defective environments. Because mitochondria are crucial bioenergetic hubs and sites of these metabolic pathways, major hopes are posed for drugs targeting mitochondria. A wide range of medications targeting mitochondria, electron transport chain complexes, or oxidative enzymes are currently investigated in phase 1 and phase 2 clinical trials against hard-to-treat tumors. This review article aims to highlight recent literature on the metabolic adaptations of CSCs and their supporting macrophages. A focus is provided on the resistance and dormancy behaviors that give CSCs a selection advantage and quiescence capacity in particularly hostile microenvironments and the role of TAMs in supporting these attitudes. The article also describes medicaments that have demonstrated a robust ability to disrupt core oxidative metabolism in preclinical cancer studies and are currently being tested in clinical trials.

Spatiotemporal Controllable Sono-Nanovaccines Driven by Free-Field Based Whole-Body Ultrasound for Personalized Cancer Therapy

Therapeutic cancer vaccines fail to produce satisfactory outcomes against solid tumors since vaccine-induced anti-tumor immunity is significantly hampered by immunosuppression. Generating an in situ cancer vaccine targeting immunological cold tumor microenvironment (TME) appears attractive. Here, a type of free-field based whole-body ultrasound (US)-driven nanovaccines are constructed, named G5-CHC-R, by conjugating the sonosensitizer, Chenghai chlorin (CHC) and the immunomodulator, resiquimod (R848) on top of a super small-sized dendrimeric nanoscaffold. Once entering tumors, R848 can be cleaved from a hypoxia-sensitive linker, thus modifying the TME via converting macrophage phenotypes. The animals bearing orthotopic pancreatic cancer with intestinal metastasis and breast cancer with lung metastasis are treated with G5-CHC-R under a free-field based whole-body US system. Benefit from the deep penetration capacity and highly spatiotemporal selectiveness, G5-CHC-R triggered by US represented a superior alternative for noninvasive irradiation of deep-seated tumors and magnification of local immune responses via driving mass release of tumor antigens and "cold-warm-hot" three-state transformation of TME. In addition to irradiating primary tumors, a robust adaptive anti-tumor immunity is potentiated, leading to successful induction of systemic tumor suppression. The sono-nanovaccines with good biocompatibility posed wide applicability to a broad spectrum of tumors, revealing immeasurable potential for translational research in oncology.

A review of obstructive sleep apnea and lung cancer: epidemiology, pathogenesis, and therapeutic options

Despite undeniable advances in modern medicine, lung cancer still has high morbidity and mortality rates. Lung cancer is preventable and treatable, and it is important to identify new risk factors for lung cancer, especially those that can be treated or reversed. Obstructive sleep apnea (OSA) is a very common sleep-breathing disorder that is grossly underestimated in clinical practice. It can cause, exacerbate, and worsen adverse outcomes, including death and various diseases, but its relationship with lung cancer is unclear. A possible causal relationship between OSA and the onset and progression of lung cancer has been established biologically. The pathophysiological processes associated with OSA, such as sleep fragmentation, intermittent hypoxia, and increased sympathetic nervous excitation, may affect normal neuroendocrine regulation, impair immune function (especially innate and cellular immunity), and ultimately contribute to the occurrence of lung cancer, accelerate progression, and induce treatment resistance. OSA may be a contributor to but a preventable cause of the progression of lung cancer. However, whether this effect exists independently of other risk factors is unclear. Therefore, by reviewing the literature on the epidemiology, pathogenesis, and treatment of lung cancer and OSA, we hope to understand the relationships between the two and promote the interdisciplinary exchange of ideas between basic medicine, clinical medicine, respiratory medicine, sleep medicine, and oncology.

Tumor-specific activation of folate receptor beta enables reprogramming of immune cells in the tumor microenvironment

Folate receptors can perform folate transport, cell adhesion, and/or transcription factor functions. The beta isoform of the folate receptor (FRβ) has attracted considerable attention as a biomarker for immunosuppressive macrophages and myeloid-derived suppressor cells, however, its role in immunosuppression remains uncharacterized. We demonstrate here that FRβ cannot bind folate on healthy tissue macrophages, but does bind folate after macrophage incubation in anti-inflammatory cytokines or cancer cell-conditioned media. We further show that FRβ becomes functionally active following macrophage infiltration into solid tumors, and we exploit this tumor-induced activation to target a toll-like receptor 7 agonist specifically to immunosuppressive myeloid cells in solid tumors without altering myeloid cells in healthy tissues. We then use single-cell RNA-seq to characterize the changes in gene expression induced by the targeted repolarization of tumor-associated macrophages and finally show that their repolarization not only changes their own phenotype, but also induces a proinflammatory shift in all other immune cells of the same tumor mass, leading to potent suppression of tumor growth. Because this selective reprogramming of tumor myeloid cells is accompanied by no systemic toxicity, we propose that it should constitute a safe method to reprogram the tumor microenvironment.

Novel tumor-associated macrophage populations and subpopulations by single cell RNA sequencing

Tumor-associated macrophages (TAMs) are present in almost all solid tumor tissues. 16They play critical roles in immune regulation, tumor angiogenesis, tumor stem cell activation, tumor invasion and metastasis, and resistance to therapy. However, it is unclear how TAMs perform these functions. With the application of single-cell RNA sequencing (scRNA-seq), it has become possible to identify TAM subpopulations associated with distinct functions. In this review, we discuss four novel TAM subpopulations in distinct solid tumors based on core gene signatures by scRNA-seq, including FCN1 +, SPP1 +, C1Q + and CCL18 + TAMs. Functional enrichment and gene expression in scRNA-seq data from different solid tumor tissues found that FCN1 + TAMs may induce inflammation; SPP1 + TAMs are potentially involved in metastasis, angiogenesis, and cancer cell stem cell activation, whereas C1Q + TAMs participate in immune regulation and suppression; And CCL18 + cells are terminal immunosuppressive macrophages that not only have a stronger immunosuppressive function but also enhance tumor metastasis. SPP1 + and C1Q + TAM subpopulations can be further divided into distinct populations with different functions. Meanwhile, we will also present emerging evidence highlighting the separating macrophage subpopulations associated with distinct functions. However, there exist the potential disconnects between cell types and subpopulations identified by scRNA-seq and their actual function.

Prognostic significance of annexin A2 and tumor associated macrophages (TAMs) in metastatic renal cell carcinoma and their relation to Sunitinib resistance

Sunitinib, an antiangiogenic tyrosine kinase inhibitor, is the main treatment for metastatic renal cell carcinoma (mRCC). Development of resistance is a major obstacle against therapy success. The aim of this study was to assess annexin A2 and CD163+ tumor associated macrophages (TAMs) immunohistochemical expression in 50 mRCC cases as regard to patients' prognosis and Sunitinib response. Also, to assess the correlation between annexin A2 and TAMs expression. High annexin A2 expression and TAMs density were associated with serum calcium level (P = 0.024 and 0.037, respectively), larger tumor size (P < 0.001), high tumor grade (P = 0.014 and <0.001, respectively), and the presence of tumor necrosis (P < 0.001). High annexin A2 and TAMs expressions were related to shorter patients' overall survival (P = 0.009 and 0.001, respectively) and progression-free survival (P = 0.003 and 0.001, respectively). Annexin A2 was correlated with TAMs density (r = 0.890). Annexin A2 and TAMs are associated with poor prognostic parameters in mRCC patients, including high nuclear grade, increased tumor size, and the presence of tumor necrosis, together with shorter patients' survivals and poor response to Sunitinib. Annexin A2 expression is correlated with TAMs density suggesting immunomodulatory role of annexin A2.

FOXK1 upregulation is correlated with tumor progression and tumor associated macrophages infiltration in renal cell carcinoma

Renal cell carcinoma (RCC) is one of the most common urological cancers in adults. Forkhead box k1 (FOXK1) is a transcription factor involved in the progression of various malignant tumors. In this study, we aimed to investigate the expression and roles of FOXK1 in RCC development. Our findings revealed increased expression of FOXK1 in RCC tumor tissues and cell lines compared with normal controls. Functional assays demonstrated that knockdown of FOXK1 significantly inhibited proliferation, migration, invasion, and promoted apoptosis in RCC cells. Furthermore, FOXK1 knockdown suppressed epithelial-mesenchymal transition and Wnt signaling in RCC cells. Additionally, we observed a correlation between FOXK1 upregulation and tumor associated macrophages infiltration in RCC. These results suggest that FOXK1 acts as an oncogene in RCC and may serve as a potential therapeutic target for RCC treatment.

Lipopolysaccharide (LPS) stimulation of Pancreatic Ductal Adenocarcinoma (PDAC) and macrophages activates the NLRP3 inflammasome that influences the levels of pro-inflammatory cytokines in a co-culture model

Modified macrophages, tumor-associated macrophages (TAMs), are key contributors to the survival, growth, and metastatic behavior of pancreatic ductal adenocarcinoma (PDAC) cells. Central to the role of inflammation and TAMs lies the NLRP3 inflammasome. This study investigated the effects of LPS-stimulated inflammation on cell proliferation, levels of pro-inflammatory cytokines, and the NLRP3 inflammasome pathway in a co-culture model using PDAC cells and macrophages in the presence or absence of MCC950, a NLRP3-specific inhibitor. The effects of LPS-stimulated inflammation were tested on two PDAC cell lines (Panc 10.05 and SW 1990) co-cultured with RAW 264.7 macrophages. Cell proliferation was determined using the MTT assay. Levels of pro-inflammatory cytokines, IL-1β, and TNF-α were determined by ELISA. Western blot analyses were used to examine the expression of NLRP3 in both PDAC cells and macrophages. The co-culture and interaction between PDAC cell lines and macrophages led to pro-inflammatory microenvironment under LPS stimulation as evidenced by high levels of secreted IL-1β and TNF-α. Inhibition of the NLRP3 inflammasome by MCC950 counteracted the effects of LPS stimulation on the regulation of the NLRP3 inflammasome and pro-inflammatory cytokines in PDAC and macrophages. However, MCC950 differentially modified the viability of the metastatic vs primary PDAC cell lines. LPS stimulation increased PDAC cell viability by regulating the NLRP3 inflammasome and pro-inflammatory cytokines in the tumor microenvironment of PDAC cells/macrophages co-cultures. The specific inhibition of the NLRP inflammasome by MCC950 effectively counteracted the LPS-stimulated inflammation.

The Impact of Tumor-Associated Macrophages Found at Mammary Carcinoma Sites is Dependent Upon the Tumor Type

BACKGROUND

Previously, we reported that tumor-associated macrophages (TAM) at early sites of mammary carcinoma showed a decrease in ATP production rate and a higher dependence on oxidative phosphorylation.

METHODS

Since these changes can result from activation of AMP-activated protein kinase (AMPK) and glucose transporter 1 (Glut1) during metabolic stress, we investigated whether the TAM showed increased expression of ampk and glut1, as well as another indicator of metabolic stress, pkm2. Indeed, the TAM exhibited significant expression of pkm2, glut1, and ampk.

RESULTS

Bone marrow-derived macrophages (BMDM) co-cultured with 4T1, EMT6, and 168 in vitro similarly showed increased expression of pkm2, glut1, and ampk. Moreover, lactate, which is expressed at significant levels by all three tumors, induced expression of these same genes in BMDM suggesting that lactate may induce a metabolic stress response in these TAM. Yet, the three different mammary carcinoma models benefited from different targeting strategies. Macrophage depletion studies revealed that the TAM contributed to growth of the EMT6 tumor and metastasis of the 4T1 tumor. Targeting the stress response with the Integrated Stress Response Inhibitor (ISRIB), which targets eIF2, impacted 168 tumor progression, and ISRIB as well as FX-11, which targets lactate dehydrogenase, impacted 4T1 tumor progression and metastasis.

CONCLUSIONS

Collectively, these data demonstrate that targeting TAM or metabolism at early tumor sites can impact tumor progression. However, variability in the responses underscore the fact that the impact of macrophages differs even within three different syngeneic mammary carcinoma models.

Multifunctional Redox-Responsive Nanoplatform with Dual Activation of Macrophages and T Cells for Antitumor Immunotherapy

High expression of programmed death ligand 1 (PD-L1) and strong immune evasion ability of the tumor microenvironment (TME) are maintained through mutual regulation between different immune and stromal cells, which causes obstructions for cancer immunotherapy, especially immunosuppressive M2-like phenotype tumor-associated macrophages (TAMs). Repolarization of TAMs to the M1-like phenotype could secrete proinflammatory cytokines and reverse the immunosuppressive state of the TME. However, we found that reactive oxygen species (ROS) generated by repolarized TAMs could be a double-edged sword: ROS cause a stronger suppressive effect on CD8 T cells through an increased proportion of apoptotic regulatory T (Treg) cells. Thus, simply repolarizing TAMs while ignoring the suppressed function of T cells is insufficient for generating adequate antitumor immunity. Accordingly, we engineered multifunctional redox-responsive nanoplatform NPs (M+C+siPD-L1) with Toll-like receptor agonist (M), catalase (C), and siPD-L1 encased for coregulation of both TAMs and T cells to maximize cancer immunotherapy. Our results demonstrated that NPs (M+C+siPD-L1) showed superior biocompatibility and intratumor accumulation. For in vitro experiments, NPs (M+C+siPD-L1) simultaneously repolarized TAMs to the M1-like phenotype, hydrolyzed extra ROS, knocked down the expression of PD-L1 on tumor cells, and rescued the function of CD8 T cells suppressed by Treg cells. In both orthotopic Hepa1-6 and 4T1 tumor-bearing mouse models, NPs (M+C+siPD-L1) could effectively evoke active systemic antitumor immunity and inhibit tumor growth. The combination of repolarizing TAMs, hydrolyzing extra ROS, and knocking down the expression of PD-L1 proves to be a synergistic approach in cancer immunotherapy.

Nanoparticles Hitchhike on Monocytes for Glioblastoma Treatment after Low-Dose Radiotherapy

Glioblastomas (GBMs) are aggressive primary brain tumors with fatal outcome. Traditional chemo-radiotherapy has poor therapeutic effect and significant side effects, due to the drug and radiotherapy (RT) resistance, natural blood-brain barrier, and high-dose RT damage. Even more, tumor-associated monocytes (macrophages and microglia, TAMs) constitute up to 30%-50% of the GBM cellular content, and the tumor microenvironment (TME) in GBM is extremely immunosuppressive. Here, we synthesized nanoparticles (D@MLL) that hitchhike on circulating monocytes to target intracranial GBMs with the assistance of low-dose RT. The chemical construction of D@MLL was DOX·HCl loaded MMP-2 peptide-liposome, which could target monocytes by the surface modified lipoteichoic acid. First, low-dose RT at the tumor site increases monocyte chemotaxis and induces M1 type polarization of TAMs. Subsequently, the intravenous injected D@MLL targets circulating monocytes and hitchhikes with them to the central site of the GBM area. DOX·HCl was then released by the MMP-2 response, inducing immunogenic cell death, releasing calreticulin and high-mobility group box 1. This further contributed to TAMs M1-type polarization, dendritic cell maturation, and T cell activation. This study demonstrates the therapeutic advantages of D@MLL delivered by endogenous monocytes to GBM sites after low-dose RT, and it provides a high-precision treatment for GBMs.

Monocytes in Tumorigenesis and Tumor Immunotherapy

Monocytes are highly plastic innate immune cells that display significant heterogeneity during homeostasis, inflammation, and tumorigenesis. Tumor-induced systemic and local microenvironmental changes influence the phenotype, differentiation, and distribution of monocytes. Meanwhile, monocytes and their related cell subsets perform an important regulatory role in the development of many cancers by affecting tumor growth or metastasis. Thanks to recent advances in single-cell technologies, the nature of monocyte heterogeneity and subset-specific functions have become increasingly clear, making it possible to systematically analyze subset-specific roles of monocytes in tumorigenesis. In this review, we discuss recent discoveries related to monocytes and tumorigenesis, and new strategies for tumor biomarker identification and anti-tumor immunotherapy.

Unraveling the Immune Microenvironment in Classic Hodgkin Lymphoma: Prognostic and Therapeutic Implications

Classic Hodgkin lymphoma (cHL) is a lymphoid neoplasm composed of rare neoplastic Hodgkin and Reed-Sternberg (HRS) cells surrounded by a reactive tumor microenvironment (TME) with suppressive properties against anti-tumor immunity. TME is mainly composed of T cells (CD4 helper, CD8 cytotoxic and regulatory) and tumor-associated macrophages (TAMs), but the impact of these cells on the natural course of the disease is not absolutely understood. TME contributes to the immune evasion of neoplastic HRS cells through the production of various cytokines and/or the aberrant expression of immune checkpoint molecules in ways that have not been fully understood yet. Herein, we present a comprehensive review of findings regarding the cellular components and the molecular features of the immune TME in cHL, its correlation with treatment response and prognosis, as well as the potential targeting of the TME with novel therapies. Among all cells, macrophages appear to be a most appealing target for immunomodulatory therapies, based on their functional plasticity and antitumor potency.

Targeting immune checkpoints on tumor-associated macrophages in tumor immunotherapy

Unprecedented breakthroughs have been made in cancer immunotherapy in recent years. Particularly immune checkpoint inhibitors have fostered hope for patients with cancer. However, immunotherapy still exhibits certain limitations, such as a low response rate, limited efficacy in certain populations, and adverse events in certain tumors. Therefore, exploring strategies that can improve clinical response rates in patients is crucial. Tumor-associated macrophages (TAMs) are the predominant immune cells that infiltrate the tumor microenvironment and express a variety of immune checkpoints that impact immune functions. Mounting evidence indicates that immune checkpoints in TAMs are closely associated with the prognosis of patients with tumors receiving immunotherapy. This review centers on the regulatory mechanisms governing immune checkpoint expression in macrophages and strategies aimed at improving immune checkpoint therapies. Our review provides insights into potential therapeutic targets to improve the efficacy of immune checkpoint blockade and key clues to developing novel tumor immunotherapies.

Triggering receptor expressed on myeloid cells 2 (TREM2) regulates phagocytosis in glioblastoma

Glioblastomas (GBMs) are tumors of the central nervous system that remain recalcitrant to both standard of care chemo-radiation and immunotherapies. Emerging approaches to treat GBMs include depletion or re-education of innate immune cells including microglia (MG) and macrophages (MACs). Here we show myeloid cell restricted expression of triggering receptor expressed on myeloid cells 2 (TREM2) across low- and high-grade human gliomas. TREM2 expression did not correlate with immunosuppressive pathways, but rather showed strong positive association with phagocytosis markers such as lysozyme (LYZ) and CD163 in gliomas. In line with these observations in patient tumors, Trem2-/- mice did not exhibit improved survival compared to wildtype (WT) mice when implanted with mouse glioma cell lines, unlike observations previously seen in peripheral tumor models. Gene expression profiling revealed pathways related to inflammation, adaptive immunity, and autophagy that were significantly downregulated in tumors from Trem2-/- mice compared to WT tumors. Using ZsGreen-expressing CT-2A orthotopic implants, we found higher tumor antigen engulfment in Trem2+ MACs, MG, and dendritic cells. Our data uncover TREM2 as an important immunomodulator in gliomas and inducing TREM2 mediated phagocytosis can be a potential immunotherapeutic strategy for brain tumors.

Pan-cancer analysis identifies PD-L2 as a tumor promotor in the tumor microenvironment

BACKGROUND

Programmed cell death protein 1 (PD-1) receptor has two ligands,programmed death-ligand 1 (PD-L1) and PD-L2. When compared with PD-L1, PD-L2 has not received much attention, and its role remains unclear.

METHODS

The expression profiles of pdcd1lg2 (PD-L2-encoding gene) mRNA and PD-L2 protein were analyzed using TCGA, ICGC, and HPA databases. Kaplan-Meier and Cox regression analyses were used to assess the prognostic significance of PD-L2. We used GSEA, Spearman's correlation analysis and PPI network to explore the biological functions of PD-L2. PD-L2-associated immune cell infiltration was evaluated using the ESTIMATE algorithm and TIMER 2.0. The expressions of PD-L2 in tumor-associated macrophages (TAMs) in human colon cancer samples, and in mice in an immunocompetent syngeneic setting were verified using scRNA-seq datasets, multiplex immunofluorescence staining, and flow cytometry. After fluorescence-activated cell sorting, flow cytometry and qRT-PCR and transwell and colony formation assays were used to evaluate the phenotype and functions of PD-L2+TAMs. Immune checkpoint inhibitors (ICIs) therapy prediction analysis was performed using TIDE and TISMO. Last, a series of targeted small-molecule drugs with promising therapeutic effects were predicted using the GSCA platform.

RESULTS

PD-L2 was expressed in all the common human cancer types and deteriorated outcomes in multiple cancers. PPI network and Spearman's correlation analysis revealed that PD-L2 was closely associated with many immune molecules. Moreover, both GSEA results of KEGG pathways and GSEA results for Reactome analysis indicated that PD-L2 expression played an important role in cancer immune response. Further analysis showed that PD-L2 expression was strongly associated with the infiltration of immune cells in tumor tissue in almost all cancer types, among which macrophages were the most positively associated with PD-L2 in colon cancer. According to the results mentioned above, we verified the expression of PD-L2 in TAMs in colon cancer and found that PD-L2+TAMs population was not static. Additionally, PD-L2+TAMs exhibited protumor M2 phenotype and increased the migration, invasion, and proliferative capacity of colon cancer cells. Furthermore, PD-L2 had a substantial predictive value for ICIs therapy cohorts.

CONCLUSION

PD-L2 in the TME, especially expressed on TAMs, could be applied as a potential therapeutic target.

Antitumor Effect of Chalcone Derivatives against Human Prostate (LNCaP and PC-3), Cervix HPV-Positive (HeLa) and Lymphocyte (Jurkat) Cell Lines and Their Effect on Macrophage Functions

Chalcones are synthetic and naturally occurring compounds that have been widely investigated as anticancer agents. In this work, the effect of chalcones 1-18 against the metabolic viability of cervical (HeLa) and prostate (PC-3 and LNCaP) tumor cell lines was tested, to compare the activity against solid and liquid tumor cells. Their effect was also evaluated on the Jurkat cell line. Chalcone 16 showed the highest inhibitory effect on the metabolic viability of the tested tumor cells and was selected for further studies. Recent antitumor therapies include compounds with the ability to influence immune cells on the tumor microenvironment, with immunotherapy being one actual goal in cancer treatment. Therefore, the effect of chalcone 16 on the expression of mTOR, HIF-1α, IL-1β, TNF-α, IL-10, and TGF-β, after THP-1 macrophage stimulation (none, LPS or IL-4), was evaluated. Chalcone 16 significantly increased the expression of mTORC1, IL-1β, TNF-α, and IL-10 of IL-4 stimulated macrophages (that induces an M2 phenotype). HIF-1α and TGF-β were not significantly affected. Chalcone 16 also decreased nitric oxide production by the RAW 264.7 murine macrophage cell line, this effect probably being due to an inhibition of iNOS expression. These results suggest that chalcone 16 may influence macrophage polarization, inducing the pro-tumoral M2 macrophages (IL-4 stimulated) to adopt a profile closer to the antitumor M1 profile.

Disruption of CCL2 in Mesenchymal Stem Cells as an Anti-Tumor Approach against Prostate Cancer

BACKGROUND

MSCs are known to secrete abundant CCL2, which plays a crucial role in recruiting TAMs, promoting tumor progression. It is important to know whether disrupting MSC-derived CCL2 affects tumor growth.

METHODS

Murine bone marrow-derived MSCs were characterized by their surface markers and differentiation abilities. Proliferation and migration assays were performed in order to evaluate the functions of MSCs on cancer cells. CCL2 expression in MSCs was reduced by small interfering RNA (siRNA) or completely disrupted by CRISPR/Cas9 knockout (KO) approaches. An immune-competent syngeneic murine model of prostate cancer was applied in order to assess the role of tumor cell- and MSC-derived CCL2. The tumor microenvironment was analyzed to monitor the immune profile.

RESULTS

We confirmed that tumor cell-derived CCL2 was crucial for tumor growth and MSCs migration. CCL2 KO MSCs inhibited the migration of the monocyte/macrophage but not the proliferation of tumor cells in vitro. However, the mice co-injected with tumor cells and CCL2 KO MSCs exhibited anti-tumor effects when compared with those given tumor cell alone and with control MSCs, partly due to increased infiltration of CD45⁺CD11b⁺Ly6G^- mononuclear myeloid cells.

CONCLUSIONS

Disruption of MSC-derived CCL2 enhances anti-tumor functions in an immune-competent syngeneic mouse model for prostate cancer.

Melittin derived peptide-drug conjugate, M-DM1, inhibits tumor progression and induces effector cell infiltration in melanoma by targeting M2 tumor-associated macrophages

Background

Melanoma has the highest mortality rate among all the types of skin cancer. In melanoma, M2-like tumor-associated macrophages (TAMs) are associated with the invasiveness of tumor cells and a poor prognosis. Hence, the depletion or reduction of M2-TAMs is a therapeutic strategy for the inhibition of tumor progression. The aim of this study was to evaluate the therapeutic effects of M-DM1, which is a conjugation of melittin (M), as a carrier for M2-like TAMs, and mertansine (DM1), as a payload to induce apoptosis of TAMs, in a mouse model of melanoma.

Methods

Melittin and DM1 were conjugated and examined for the characterization of M-DM1 by high-performance liquid chromatography and electrospray ionization mass spectrometry. Synthesized M-DM1 were examined for in vitro cytotoxic effects. For the in vivo study, we engrafted murine B16-F10 into right flank of C57BL/6 female mice and administered an array of treatments (PBS, M, DM1, or M-DM1 (20 nmol/kg)). Subsequently, the tumor growth and survival rates were analyzed, as well as examining the phenotypes of tumor-infiltrating leukocytes and expression profiles.

Results

M-DM1 was found to specifically reduce M2-like TAMs in melanoma, which potentially leads to the suppression of tumor growth, migration, and invasion. In addition, we also found that M-DM1 improved the survival rates in a mouse model of melanoma compared to M or DM1 treatment alone. Flow cytometric analysis revealed that M-DM1 enhanced the infiltration of CD8+ cytotoxic T cells and natural killer cells (NK cells) in the tumor microenvironment.

Conclusion

Taken together, our findings highlight that M-DM1 is a prospective agent with enhanced anti-tumor effects.

Hematologic dysfunction in cancer: Mechanisms, effects on antitumor immunity, and roles in disease progression

With the major advances in cancer immunology and immunotherapy, it is critical to consider that most immune cells are short-lived and need to be continuously replenished from hematopoietic stem and progenitor cells. Hematologic abnormalities are prevalent in cancer patients, and many ground-breaking studies over the past decade provide insights into their underlying cellular and molecular mechanisms. Such studies demonstrate that the dysfunction of hematopoiesis is more than a side-effect of cancer pathology, but an important systemic feature of cancer disease. Here we review these many advances, covering the cancer-associated phenotypes of hematopoietic stem and progenitor cells, the dysfunction of myelopoiesis and erythropoiesis, the importance of extramedullary hematopoiesis in cancer disease, and the developmental origins of tumor associated macrophages. We address the roles of many secreted mediators, signaling pathways, and transcriptional and epigenetic mechanisms that mediate such hematopoietic dysfunction. Furthermore, we discuss the important contribution of the hematopoietic dysfunction to cancer immunosuppression, the possible avenues for therapeutic intervention, and highlight the unanswered questions and directions for future work. Overall, hematopoietic dysfunction is established as an active component of the cancer disease mechanisms and an important target for therapeutic intervention.

Development of functional nanomedicines for tumor associated macrophages-focused cancer immunotherapy

Clinical cancer immunotherapies are usually impeded by tumor immunosuppression driven by tumor associated macrophages (TAMs). Thus, TAMs can be considered as a promising therapeutic target for improved immunotherapy, and TAMs-focused molecular targeting agents have made ideal progress in clinical practice. Even so, most TAMs-targeting agents still cannot cover up their own shortcomings as free drugs. The emergence of multifunctional nanomaterials can expectedly endow these therapeutic cargoes with high solubility, favorable pharmacokinetic distribution, cell-specific delivery, and controlled release. Here, the underlying mechanisms of tumor immunosuppression caused by TAMs are first emphatically elucidated, and then the basic design of TAMs-focused immune-nanomedicines are discussed, mainly including diverse categories of nanomaterials, targeted and stimulus-responsive modifications, and TAM imaging in nanomedicines. A summary of current TAMs-targeting immunotherapeutic mechanisms based on functional nanomedicines for TAMs elimination and/or repolarization is further presented. Lastly, some severe challenges related to functional nanomedicines for TAMs-focused cancer immunotherapy are proposed, and some feasible perspectives on clinical translation of TAMs-associated anticancer immunonanomedicines are provided. It is hoped that, with rapid development of nanomedicine in cancer immunotherapy, TAMs-focused therapeutic strategies may be anticipated to become an emerging immunotherapeutic modality for future clinical cancer treatment.

The Effect of Arginase on Canine T-Lymphocyte Functions and its Modulation by All-Trans Retinoid Acid (ATRA) in Canine Monocyte-Derived Macrophages

Immunosuppressive myeloid cells in the tumor microenvironment play a major role in suppressing tumor immunity via the production of arginase, IL-10, and others. The objectives of this study were to determine the ability of all-trans retinoic acid (ATRA) to decrease the expression of arginase and other soluble mediators by canine monocyte-derived macrophages (MDMs) and to determine the inhibitory activity of arginase on canine T-lymphocytes. The immunomodulatory ability of ATRA (2 µM) on canine MDMs was evaluated via reverse transcription quantitative PCR (RT-qPCR), flow cytometry, arginase activity assay, and enzyme-linked immunoassay (ELISA). Arginase effects on T-lymphocyte phenotype and proliferation were then evaluated by flow cytometry. ATRA consistently decreased MDM expression of IL6, TGFB1, NOS2, ARG1, and CIITA transcripts, by approximately 2-4-fold, although this did not reach statistical significance for ARG1 or CIITA. Furthermore, arginase activity was decreased in ATRA-treated MDMs while the MDM phenotype remained unchanged. Arginase decreased the expression of granzyme B on CD8+ T-lymphocytes and inhibited CD4+ and CD8+ T-lymphocyte proliferation. These findings suggested that ATRA could inhibit canine MDM production of soluble inflammatory/immunosuppressive mediators. These data also revealed that arginase decreased canine T-lymphocyte proliferation and granzyme B expression. Further studies are needed to determine whether ATRA could reverse the immunosuppressive effects of myeloid cells on canine T-lymphocytes in vivo.

Polymersomes-mediated Delivery of CSF1R Inhibitor to Tumor Associated Macrophages Promotes M2 to M1-like Macrophage Repolarization

The crosstalk between cancer cells and tumor associated macrophages (TAMs) within the tumor environment modulates tumor progression at all stages of cancer disease. TAMs are predominantly M2-like polarized macrophages with tumor-promoting activities. Nonetheless, they can be repolarized to tumoricidal M1-like macrophages through macrophage colony stimulating factor 1 receptor inhibition (CSF1Ri). CSF1Ri is being explored as multifaced therapeutic approach to suppress TAMs tumor-promoting functions and reduce cancer cell aggressiveness and viability. However, treatment with CSF1Ri results in significant TAMs death, thereby extinguishing the possibility of generating tumoricidal M1-like macrophages. Immunotherapy has improved overall patient's survival in some cancer types, but also caused frequent off-target toxicity. Approaches to balance efficacy versus toxicity are needed. Herein, a CSF1Ri loaded polymersomes (PM) based delivery platform is developed to promote M2-like macrophage repolarization. When testing in vitro on primary human monocyte-derived macrophages (MDMs), CSF1Ri loaded PM are preferentially taken up by M2-like macrophages and enhance M2 to M1-like macrophage repolarization while minimizing cytotoxicity in comparison to the free drug. When testing in a MDMs-MDA-MB-231 breast cancer cell co-culture model, CSF1Ri loaded PM further retain their M2 to M1-like macrophages polarization capacity. This CSF1Ri loaded PM-based platform system represents a promising tool for macrophage-based immunotherapy approaches. This article is protected by copyright. All rights reserved.

[Interference of P2X4 receptor expression in tumor-associated macrophages suppresses migration and invasion of glioma cells]

OBJECTIVE

To investigate the effect of interference of P2X4 receptor expression in tumor-associated macrophages (TAMs) on invasion and migration of glioma cells.

METHODS

C57BL/6 mouse models bearing gliomas in the caudate nucleus were examined for glioma pathology with HE staining and expressions of Iba-1 and P2X4 receptor with immunofluorescence assay. RAW264.7 cells were induced into TAMs using conditioned medium from GL261 cells, and the changes in mRNA expressions of macrophage polarization-related markers and the mRNA and protein expressions of P2X4 receptor were detected with RT-qPCR and Western blotting. The effect of siRNA-mediated P2X4 interference on IL-1β and IL-18 mRNA and protein expressions in the TAMs was detected with RT-qPCR and Western blotting. GL261 cells were cultured in the conditioned medium from the transfected TAMs, and the invasion and migration abilities of the cells were assessed with Transwell invasion and migration experiment.

RESULTS

The glioma tissues from the tumor-bearing mice showed a significantly greater number of Iba-1-positive cells, where an obviously increased P2X4 receptor expression was detected (P=0.001), than the brain tissues of the control mice (P < 0.001). The M2 macrophage markers (Arg-1 and IL-10) and M1 macrophage markers (iNOS and TNF-α) were both significantly up-regulated in the TAMs derived from RAW264.7 cells (all P < 0.01), but the up-regulation of the M2 macrophage markers was more prominent; the expression levels of P2X4 receptor protein and mRNA were both increased in the TAMs (P < 0.05). Interference of P2X4 receptor expression significantly lowered the mRNA(P < 0.01)and protein (P < 0.01, P < 0.05)expression levels of IL-1β and IL-18 in the TAMs and obviously inhibited the ability of the TAMs to promote invasion and migration of the glioma cells (P < 0.05).

CONCLUSION

Interference of P2X4 receptor in the TAMs suppresses the migration and invasion of glioma cells possibly by lowering the expressions of IL-1β and IL-18.

CSF-1R inhibitor, pexidartinib, sensitizes esophageal adenocarcinoma to PD-1 immune checkpoint blockade in a rat model

Esophageal adenocarcinoma (EAC) is a leading cause of cancer deaths. Pexidartinib, a multi-gene tyrosine kinase inhibitor, through targeting CSF-1R, down modulates macrophage mediated pro-survival tumor signaling. Previously, CSF-1R inhibitors have successfully shown to enhance antitumor activity of PD-1/PD-L1 inhibitors by suppressing tumor immune evasion, in solid tumors. In this study, we investigated the antitumor activity of pexidartinib alone or in combination with blockade of PD-1 in a de novo EAC rat model. Here, we showed limited toxicity with significant tumor shrinkage in pexidartinib treated animals compared to controls, single agent and in combination with a PD-1 inhibitor, AUNP-12. Suppression of CSF-1/CSF-1R axis resulted in enhanced infiltration of CD3+CD8+ T cells with reduced M2 macrophage polarization, in the tumor microenvironment (TME). Endpoint tissue gene expression in pexidartinib treated animals demonstrated upregulation of BAX, Cas3, TNFα, IFNγ and IL6 and downregulation of Ki67, IL13, IL10, TGFβ and Arg1 (p<0.05). Additionally, among the pexidartinib treated animals responders compared to non-responders demonstrated a significant upregulation of pre-treatment CSF-1 gene, confirming that tumor associated macrophage suppression directly translates to clinical benefit. Moreover, a post-treatment serum cytokine assay exhibited similar systemic trends as the gene expression in the TME, depicting increases in pro-inflammatory cytokines and decreases in anti-inflammatory cytokines. In conclusion, our study established a promising combinatorial strategy using a CSF-1R inhibitor to overcome resistance to PD-1/PD-L1 axis blockade in an EAC model, providing the rationale for future clinical strategies.

Pan-cancer analysis reveals NUP37 as a prognostic biomarker correlated with the immunosuppressive microenvironment in glioma

Nucleoporin 37 kDa (NUP37), a member of the nucleoporin family, has been reported to regulate the proliferation and apoptosis of several tumor types. However, its role in the tumor immune microenvironment is unclear. Here, we evaluated the expression, methylation, copy number alteration, and prognostic significance of NUP37 using RNA-seq and clinical data from The Cancer Genome Atlas. We observed higher expression of NUP37 in 28 of 29 tumor types, and high NUP37 expression predicted worse survival status of patients in 15 tumors. Using data from the cBioportal database, we described the gene variation of NUP37 in glioma and pan-cancer. We further assessed the role of NUP37 in the tumor immune microenvironment using immune infiltration data. NUP37 expression was positively associated with the infiltration levels of immunosuppressive cells, such as nTregs, iTregs, and tumor-associated macrophages, and negatively correlated with immune killer cells, such as CD8+ T and NK cells across cancers. Furthermore, NUP37 expression was associated with immune checkpoints and immune regulation-related genes. The half-maximal inhibitory concentrations of anti-cancer drugs were obtained from the Genomics of Drug Sensitivity in the Cancer database. The correlation between half-maximal inhibitory concentration and NUP37 expression was evaluated. The patients with the evaluated expression of NUP37 were resistant to several anti-cancer drugs. These results suggest that NUP37 is a potential oncogene and prognostic biomarker in glioma and pan-cancer. Tumor tissues with high NUP37 expression exist in a relatively immunosuppressive microenvironment and are resistant to several anti-cancer drugs.

TRIB1 regulates tumor growth via controlling tumor-associated macrophage phenotypes and is associated with breast cancer survival and treatment response

Molecular mechanisms that regulate tumor-associated macrophage (TAM) phenotype and function are incompletely understood. The pseudokinase TRIB1 has been reported as a regulator of macrophage phenotypes, both in mouse and human systems.

Methods: Bioinformatic analysis was used to investigate the link between TRIB1 expression in breast cancer and therapeutic response to chemotherapy. In vivo models of breast cancer included immune-competent mice to characterize the consequences of altered (reduced or elevated) myeloid Trib1 expression on tumor growth and composition of stromal immune cell populations.

Results: TRIB1 was highly expressed by TAMs in breast cancer and high TRIB1 expression correlated with response to chemotherapy and patient survival. Both overexpression and knockout of myeloid Trib1 promote mouse breast tumor growth, albeit through different molecular mechanisms. Myeloid Trib1 deficiency led to an early acceleration of tumor growth, paired with a selective reduction in perivascular macrophage numbers in vivo and enhanced oncogenic cytokine expression in vitro. In contrast, elevated levels of Trib1 in myeloid cells led to an increased late-stage mammary tumor volume, coupled with a reduction of NOS2 expressing macrophages and an overall reduction of macrophages in hypoxic tumor regions. In addition, we show that myeloid Trib1 is a previously unknown, negative regulator of the anti-tumor cytokine IL-15, and that increased myeloid Trib1 expression leads to reduced IL-15 levels in mammary tumors, with a consequent reduction in the number of T-cells that are key to anti-tumor immune responses.

Conclusions: Together, these results define a key role for TRIB1 in chemotherapy responses for human breast cancer and provide a mechanistic understanding for the importance of the control of myeloid TRIB1 expression in the development of this disease.

FUCA2 Is a Prognostic Biomarker and Correlated With an Immunosuppressive Microenvironment in Pan-Cancer

Background

The expression of Fucosidase, alpha-L-2 (FUCA2) varies across tumors. However, its role in various tumor types and relationship with the tumor immune microenvironment (TIME) is poorly defined.

Methods

We analyzed profiles of FUCA2 expression using datasets from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases. Next, gene alteration, clinical characteristics and prognostic values of FUCA2 were elucidated based on TCGA pan-cancer data. This was followed by gene set enrichment analysis by R software. Relationships between FUCA2 expression and immune infiltration and immune-related genes were also evaluated. Moreover, the association of immune cell infiltration with FUCA2 expression was evaluated across three different sources of immune cell infiltration data, namely the TIMER online, ImmuCellAI databases, as well as a published study. In addition, MTT assays was also conducted to validate the oncogene role of FUCA2 in lung cancer cells.

Results

FUCA2 was upregulated in most tumors, and this was significantly associated with poor survival rates. Gene set enrichment analysis uncovered that FUCA2 correlated with immune pathways in different tumor types. FUCA2 expression was positively related to tumor associated macrophages (TAMs), especially M2-like TAMs. Moreover, FUCA2 level showed a positive relationship with most immunosuppression genes, including programmed death-ligand 1 (PD-L1), transforming growth factor beta 1 (TGFB1), and interleukin-10 (IL10) in most cancer types. FUCA2 knockdown inhibited the cell viability in lung cancer cells.

Conclusions

Our study reveals that FUCA2 is a potential oncogene and is indicative biomarker of a worse prognosis in pan-cancer. High FUCA2 expression may contribute to increased infiltration of TAMs and associates with an immunosuppressive microenvironment, providing a potential target for tumor therapy.

Exosome-Mediated Crosstalk Between Tumor and Tumor-Associated Macrophages

Exosomes are nanosized vesicles, derived from the endolysosomal compartment of cells and can shuttle diverse biomolecules such as nucleic acids, proteins, lipids, amino acids, and metabolites, which can reflect their origin cells. Delivery of these cargoes to recipient cells enables exosomes to influence diverse cellular functions. As one of the most abundant immune cells in the tumor microenvironment, tumor-associated macrophages (TAMs) are educated by the tumor milieu, which is rich in cancer cells and stroma components, to exert functions such as the promotion of tumor growth, immunosuppression, angiogenesis, and cancer cell dissemination. Herein, we focus on exosomes-mediated intercellular communication between tumor cells and TAM in the tumor microenvironment, which may provide new targets for anti-tumor treatment. In this review, we highlight the most recent studies on the effect of tumor/macrophage-derived exosomes on macrophage/tumor function in different cancer types.

LncRNA-SNHG1 promotes macrophage M2-like polarization and contributes to breast cancer growth and metastasis

Breast cancer is one of the most common malignant cancers among women. Cancer cells and adjacent cells determine the development of the disease. Tumor associated macrophages (TAMs) are involved in the regulation of different stages of cancer progression. LncRNAs play an important role in tumor growth and metastasis. However, the function of lncRNA in macrophage and tumor cell interaction is poorly described. Here we reported that lncRNA SNHG1 functioned as a modulator of M2 macrophage polarization and regulated tumor growth and angiogenesis. We indicated that knockdown of SNHG1 inhibited M2 macrophage polarization by suppression of STAT6 phosphorylation. SNHG1 silencing significantly alleviated migration of MCF-7 cells and tube formation of Human Umbilical Vein Endothelial Cells (HUVEC). Furthermore, we found that implantation of cell mixture of MCF-7 cells and macrophages promoted tumor growth and angiogenesis. However, knockdown of SNHG1 in macrophages reversed that effect. Collectively, we demonstrated the important role of lncRNA SNHG1 in macrophages and breast cancer cells interaction. We highlight the essential effect of lncRNA in tumor progression and provide a new method for the prevention and treatment of breast tumor metastasis.

Tumor Associated Macrophages and TAMs-Based Anti-Tumor Nanomedicines

As an important part of tumor microenvironment, tumor associated macrophages (TAMs) play a vital role in the occurrence, development, invasion, and metastasis of many malignant tumors and can significantly promote the formation of tumor blood vessels and lymphatic vessels, hence TAMs are greatly associated with poor prognosis. The research on nanomedicine has achieved huge progress, and nano-drugs have been widely utilized to treat various diseases through different mechanisms. Therefore, developing nano-drugs that are based on TAMs-associated anti-tumor mechanisms to effectively suppress tumor growth is expected to be a promising research filed. This paper introduces relevant information about TAMs in terms of their origin, and their roles in tumor genesis, development and metastasis. Furthermore, TAMs-related anti-tumor nano-drugs are summarized. Specifically, a wide range of nano-drugs targeting at TAMs are introduced, and categorized according to their therapeutic mechanisms toward tumors. Additionally, various nano delivery platforms using TAMs as cell carriers which aim at inhibiting tumor growth are reviewed. These two parts elucidate that the exploration of nanomedicine is essential to the study on TAMs-related anti-tumor strategies. This review is also intended to provide novel ideas for in-depth investigation on anti-tumor molecular mechanisms and nano-drug delivery systems based on TAMs.

A Prognostic Role for Circulating microRNAs Involved in Macrophage Polarization in Advanced Non-Small Cell Lung Cancer

Circulating microRNAs (miRNAs) are key regulators of the crosstalk between tumor cells and immune response. In the present study, miRNAs (let-7c, miR-26a, miR-30d, miR-98, miR-195, miR-202) reported to be involved in the polarization of macrophages were examined for associations with the outcomes of non-small cell lung cancer (NSCLC) patients (N = 125) treated with first-line platinum-based chemotherapy. RT-qPCR was used to analyze miRNA expression levels in the plasma of patients prior to treatment. In our results, disease progression was correlated with high miR-202 expression (HR: 2.335; p = 0.040). Additionally, high miR-202 expression was characterized as an independent prognostic factor for shorter progression-free survival (PFS, HR: 1.564; p = 0.021) and overall survival (OS, HR: 1.558; p = 0.024). Moreover, high miR-202 independently predicted shorter OS (HR: 1.989; p = 0.008) in the non-squamous (non-SqCC) subgroup, and high miR-26a was correlated with shorter OS in the squamous (SqCC) subgroup (10.07 vs. 13.53 months, p = 0.033). The results of the present study propose that the expression levels of circulating miRNAs involved in macrophage polarization are correlated with survival measures in NSCLC patients, and their role as potential biomarkers merits further investigation.

Tumor Associated Macrophages, as the Dominant Immune Cells, Are an Indispensable Target for Immunologically Cold Tumor-Glioma Therapy?

Tumor microenvironment (TME) is the cornerstone of the occurrence, development, invasion and diffusion of the malignant central nerve system (CNS) tumor, glioma. As the largest number of inflammatory cells in glioma TME, tumor associated macrophages (TAMs) and their secreted factors are indispensable to the progression of glioma, which is a well-known immunologically “cold” tumor, including the growth of tumor cells, invasion, migration, angiogenesis, cancer immunosuppression and metabolism. TAMs intimately interface with the treatment failure and poor prognosis of glioma patients, and their density increases with increasing glioma grade. Recently, great progress has been made in TAM-targeting for anti-tumor therapy. According to TAMs’ function in tumorigenesis and progression, the major anti-tumor treatment strategies targeting TAMs are to hinder macrophage recruitment in TME, reduce TAMs viability or remodel TAMs phenotype from M2 to M1. Different approaches offer unique and effective anti-tumor effect by regulating the phagocytosis, polarization and pro-tumor behaviors of macrophages in the therapy of glioma. The present review summarizes the significant characteristics and related mechanisms of TAMs and addresses the related research progress on targeting TAMs in glioma.

CAFs Interacting With TAMs in Tumor Microenvironment to Enhance Tumorigenesis and Immune Evasion

Cancer associated fibroblasts (CAFs) and tumor associated macrophages (TAMs) are among the most important and abundant players of the tumor microenvironment. CAFs as well as TAMs are known to play pivotal supportive roles in tumor growth and progression. The number of CAF or TAM cells is mostly correlated with poor prognosis. Both CAFs and TAMs are in a reciprocal communication with the tumor cells in the tumor milieu. In addition to such interactions, CAFs and TAMs are also involved in a dynamic and reciprocal interrelationship with each other. Both CAFs and TAMs are capable of altering each other's functions. Here, the current understanding of the distinct mechanisms about the complex interplay between CAFs and TAMs are summarized. In addition, the consequences of such a mutual relationship especially for tumor progression and tumor immune evasion are highlighted, focusing on the synergistic pleiotropic effects. CAFs and TAMs are crucial components of the tumor microenvironment; thus, they may prove to be potential therapeutic targets. A better understanding of the tri-directional interactions of CAFs, TAMs and cancer cells in terms of tumor progression will pave the way for the identification of novel theranostic cues in order to better target the crucial mechanisms of carcinogenesis.

The Prognostic Value of CD206 in Solid Malignancies: A Systematic Review and Meta-Analysis

Simple Summary

The role of innate immune cells in the tumor microenvironment (TME), more specifically the presence of the tumor associated macrophages (TAMs), is becoming more important in the prognosis and treatment of patients diagnosed with malignancies. The aim of this systematic review and meta-analysis was to assess the potential prognostic value of CD206-expressing TAMs, a subclass of macrophages, which were previously proposed to negatively impact the patient’s prognosis. We identified 27 manuscripts describing the role of CD206 in patient prognosis for 14 different tumor types. Despite a large heterogeneity in the results, we identified a significantly worse overall and disease-free survival for patients with increased CD206-expressing TAMs in the TME. The use of CD206-expressing TAMs could therefore be used as a prognostic marker in patients diagnosed with solid malignancies.

Abstract

An increased presence of CD206-expressing tumor associated macrophages in solid cancers was proposed to be associated with worse outcomes in multiple types of malignancies, but contradictory results are published. We performed a reproducible systematic review and meta-analysis to provide increased evidence to confirm or reject this hypothesis following the Preferred Reporting Items for Systematic Reviews and Meta-analyses statement. The Embase, Web of Science, and MEDLINE-databases were systematically searched for eligible manuscripts. A total of 27 papers studying the prognostic impact of CD206 in 14 different tumor types were identified. Meta-analyses showed a significant impact on the overall survival (OS) and disease-free survival (DFS). While no significant differences were revealed in progression-free survival (PFS) and disease-specific survival (DSS), a shift towards negative survival was correlated with increased CD206-expresion. As a result of the different tumor types, large heterogeneity was present between the different tumor types. Subgroup analysis of hepatocellular carcinoma and gastric cancers revealed no heterogeneity, associated with a significant negative impact on OS in both groups. The current systematic review displays the increased presence CD206-expressing macrophages as a significant negative prognostic biomarker for both OS and DFS in patients diagnosed with solid cancers. Because a heterogenous group of tumor types was included in the meta-analysis, the results cannot be generalized. These results can, however, be used to further lead follow-up research to validate the specific prognostic value of CD206 in individual tumor types and therapeutic approaches.

Crosstalk between Macrophages and Myxoid Liposarcoma Cells Increases Spreading and Invasiveness of Tumor Cells

Myxoid liposarcoma (MLPS) is the second most common subtype of liposarcoma and has tendency to metastasize to soft tissues. To date, the mechanisms of invasion and metastasis of MLPS remain unclear, and new therapeutic strategies that improve patients' outcomes are expected. In this study, we analyzed by immunohistochemistry the immune cellular components and microvessel density in tumor tissues from patients affected by MLPS. In order to evaluate the effects of primary human MLPS cells on macrophage polarization and, in turn, the ability of macrophages to influence invasiveness of MLPS cells, non-contact and 3D organotypic co-cultures were set up. High grade MLPS tissues were found heavily vascularized, exhibited a CD3, CD4, and CD8 positive T lymphocyte-poor phenotype and were massively infiltrated by CD163 positive M2-like macrophages. Conversely, low grade MLPS tissues were infiltrated by a discrete amount of CD3, CD4, and CD8 positive T lymphocytes and a scarce amount of CD163 positive macrophages. Kaplan-Meier analysis revealed a shorter Progression Free Survival in MLPS patients whose tumor tissues were highly vascularized and heavily infiltrated by CD163 positive macrophages, indicating a clear-cut link between M2-like macrophage abundance and poor prognosis in patients. Moreover, we documented that, in co-culture, soluble factors produced by primary human MLPS cells induce macrophage polarization toward an M2-like phenotype which, in turn, increases MLPS cell capability to spread into extracellular matrix and to cross endothelial monolayers. The identification of M2-like polarization factors secreted by MLPS cells may allow to develop novel targeted therapies counteracting MLPS progression.

The Use of Iron Oxide Nanoparticles to Reprogram Macrophage Responses and the Immunological Tumor Microenvironment

The synthesis and functionalization of iron oxide nanoparticles (IONPs) is versatile, which has enhanced the interest in studying them as theranostic agents over recent years. As IONPs begin to be used for different biomedical applications, it is important to know how they affect the immune system and its different cell types, especially their interaction with the macrophages that are involved in their clearance. How immune cells respond to therapeutic interventions can condition the systemic and local tissue response, and hence, the final therapeutic outcome. Thus, it is fundamental to understand the effects that IONPs have on the immune response, especially in cancer immunotherapy. The biological effects of IONPs may be the result of intrinsic features of their iron oxide core, inducing reactive oxygen species (ROS) and modulating intracellular redox and iron metabolism. Alternatively, their effects are driven by the nanoparticle coating, for example, through cell membrane receptor engagement. Indeed, exploiting these properties of IONPs could lead to the development of innovative therapies. In this review, after a presentation of the elements that make up the tumor immunological microenvironment, we will review and discuss what is currently known about the immunomodulatory mechanisms triggered by IONPs, mainly focusing on macrophage polarization and reprogramming. Consequently, we will discuss the implications of these findings in the context of plausible therapeutic scenarios for cancer immunotherapy.

CCDC137 Is a Prognostic Biomarker and Correlates With Immunosuppressive Tumor Microenvironment Based on Pan-Cancer Analysis

Background

The coiled-coil domain containing (CCDC) family proteins have important biological functions in various diseases. However, the coiled-coil domain containing 137 (CCDC137) was rarely studied. We aim to investigate the role of CCDC137 in pan-cancer.

Methods

CCDC137 expression was evaluated in RNA sequence expression profilers of pan-cancer and normal tissues from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) database. The influence of CCDC137 on the prognosis of tumor patients was analyzed using clinical survival data from TCGA. Function and pathway enrichment analysis was performed to explore the role of CCDC137 using the R package “clusterProfiler.” We further analyzed the correlation of immune cell infiltration score of TCGA samples and CCDC137 expression using TIMER2 online database.

Results

CCDC137 was over-expressed and associated with worse survival status in various tumor types. CCDC137 expression was positively correlated with tumor associated macrophages (TAMs) and cancer associated fibroblasts (CAFs) in Lower Grade Glioma (LGG) and Uveal Melanoma (UVM). In addition, high CCDC137 expression was positively correlated with most immunosuppressive genes, including TGFB1, PD-L1, and IL10RB in LGG and UVM.

Conclusions

Our study identified CCDC137 as an oncogene and predictor of worse survival in most tumor types. High CCDC137 may contribute to elevated infiltration of TAMs and CAFs and be associated with tumor immunosuppressive status.

Targeted Repolarization of Tumor-Associated Macrophages via Imidazoquinoline-Linked Nanobodies

Tumor-associated macrophages (TAMs) promote the immune suppressive microenvironment inside tumors and are, therefore, considered as a promising target for the next generation of cancer immunotherapies. To repolarize their phenotype into a tumoricidal state, the Toll-like receptor 7/8 agonist imidazoquinoline IMDQ is site-specifically and quantitatively coupled to single chain antibody fragments, so-called nanobodies, targeting the macrophage mannose receptor (MMR) on TAMs. Intravenous injection of these conjugates result in a tumor- and cell-specific delivery of IMDQ into MMRhigh TAMs, causing a significant decline in tumor growth. This is accompanied by a repolarization of TAMs towards a pro-inflammatory phenotype and an increase in anti-tumor T cell responses. Therefore, the therapeutic benefit of such nanobody-drug conjugates may pave the road towards effective macrophage re-educating cancer immunotherapies.

Prospective Analyses of Lifestyle Factors Related to Energy Balance and Ovarian Cancer Risk by Infiltration of Tumor-Associated Macrophages

BACKGROUND

Lifestyle factors related to energy balance have been associated with ovarian cancer risk and influence the tumor immune microenvironment, including tumor-associated macrophages (TAM). However, no studies have assessed whether these factors differentially impact ovarian cancer risk by TAM densities.

METHODS

We conducted a prospective analysis in the Nurses' Health Studies to examine the associations of physical activity, sitting time, and a food-based empirical dietary inflammatory pattern (EDIP) score with invasive epithelial ovarian cancer risk by TAM density assessed by immunohistochemistry. We considered density of CD68 (marker of total TAMs) and CD163 (marker of pro-carcinogenic M2-type TAMs), and their ratios. We used multivariable Cox proportional hazards regression to calculate hazard ratios (HR) and 95% confidence intervals (CI) of exposures with risk of ovarian tumors with high versus low TAMs, including analyses stratified by body mass index.

RESULTS

Analyses included 312 incident ovarian cancer cases with TAM measurements. Physical activity, sitting time, and EDIP score were not differentially associated with ovarian cancer risk by TAM densities (P heterogeneity > 0.05). Among overweight and obese women, higher EDIP score was associated with increased risk of CD163 low-density tumors (HR comparing extreme tertiles, 1.57; 95% CI, 0.88-2.80; P trend = 0.01), but not CD163 high-density tumors (comparable HR, 1.16; 95% CI, 0.73-1.86; P trend = 0.24), though this difference was not statistically significant (P heterogeneity = 0.22).

CONCLUSIONS

We did not observe differential associations between lifestyle factors and ovarian cancer risk by TAM densities.

IMPACT

Future investigations examining the interplay between other ovarian cancer risk factors and the tumor immune microenvironment may help provide insight into ovarian cancer etiology.

Macrophage Biology and Mechanisms of Immune Suppression in Breast Cancer

Macrophages are crucial innate immune cells that maintain tissue homeostasis and defend against pathogens; however, their infiltration into tumors has been associated with adverse outcomes. Tumor-associated macrophages (TAMs) represent a significant component of the inflammatory infiltrate in breast tumors, and extensive infiltration of TAMs has been linked to poor prognosis in breast cancer. Here, we detail how TAMs impede a productive tumor immunity cycle by limiting antigen presentation and reducing activation of cytotoxic T lymphocytes (CTLs) while simultaneously supporting tumor cell survival, angiogenesis, and metastasis. There is an urgent need to overcome TAM-mediated immune suppression for durable anti-tumor immunity in breast cancer. To date, failure to fully characterize TAM biology and classify multiple subsets has hindered advancement in therapeutic targeting. In this regard, the complexity of TAMs has recently taken center stage owing to their subset diversity and tightly regulated molecular and metabolic phenotypes. In this review, we reveal major gaps in our knowledge of the functional and phenotypic characterization of TAM subsets associated with breast cancer, before and after treatment. Future work to characterize TAM subsets, location, and crosstalk with neighboring cells will be critical to counteract TAM pro-tumor functions and to identify novel TAM-modulating strategies and combinations that are likely to enhance current therapies and overcome chemo- and immuno-therapy resistance.

CCRL2 promotes antitumor T-cell immunity via amplifying TLR4-mediated immunostimulatory macrophage activation

Macrophages are the key regulator of T-cell responses depending on their activation state. C-C motif chemokine receptor-like 2 (CCRL2), a nonsignaling atypical receptor originally cloned from LPS-activated macrophages, has recently been shown to regulate immune responses under several inflammatory conditions. However, whether CCRL2 influences macrophage function and regulates tumor immunity remains unknown. Here, we found that tumoral CCRL2 expression is a predictive indicator of robust antitumor T-cell responses in human cancers. CCRL2 is selectively expressed in tumor-associated macrophages (TAM) with immunostimulatory phenotype in humans and mice. Conditioned media from tumor cells could induce CCRL2 expression in macrophages primarily via TLR4, which is negated by immunosuppressive factors. Ccrl2 ^-/- mice exhibit accelerated melanoma growth and impaired antitumor immunity characterized by significant reductions in immunostimulatory macrophages and T-cell responses in tumor. Depletion of CD8⁺ T cells or macrophages eliminates the difference in tumor growth between WT and Ccrl2 ^-/- mice. Moreover, CCRL2 deficiency impairs immunogenic activation of macrophages, resulting in attenuated antitumor T-cell responses and aggravated tumor growth in a coinjection tumor model. Mechanically, CCRL2 interacts with TLR4 on the cell surface to retain membrane TLR4 expression and further enhance its downstream Myd88-NF-κB inflammatory signaling in macrophages. Similarly, Tlr4 ^-/- mice exhibit reduced CCRL2 expression in TAM and accelerated melanoma growth. Collectively, our study reveals a functional role of CCRL2 in activating immunostimulatory macrophages, thereby potentiating antitumor T-cell response and tumor rejection, and suggests CCLR2 as a potential biomarker candidate and therapeutic target for cancer immunotherapy.

Combined Effects of Myeloid Cells in the Neuroblastoma Tumor Microenvironment

Despite multimodal treatment, survival chances for high-risk neuroblastoma patients remain poor. Immunotherapeutic approaches focusing on the activation and/or modification of host immunity for eliminating tumor cells, such as chimeric antigen receptor (CAR) T cells, are currently in development, however clinical trials have failed to reproduce the preclinical results. The tumor microenvironment is emerging as a major contributor to immune suppression and tumor evasion in solid cancers and thus has to be overcome for therapies relying on a functional immune response. Among the cellular components of the neuroblastoma tumor microenvironment, suppressive myeloid cells have been described as key players in inhibition of antitumor immune responses and have been shown to positively correlate with more aggressive disease, resistance to treatments, and overall poor prognosis. This review article summarizes how neuroblastoma-driven inflammation induces suppressive myeloid cells in the tumor microenvironment and how they in turn sustain the tumor niche through suppressor functions, such as nutrient depletion and generation of oxidative stress. Numerous preclinical studies have suggested a range of drug and cellular therapy approaches to overcome myeloid-derived suppression in neuroblastoma that warrant evaluation in future clinical studies.

Artificial Tumor Microenvironments in Neuroblastoma

Simple Summary

Children with high-risk neuroblastoma have limited therapeutic options poor survival rates. The neuroblastoma tumor microenvironment contributes the lack of response to many interventions so innovative methods are needed to study the effects of the tumor microenvironment on new therapies. In this manuscript, we review the current literature related to the components of the tumor microenvironment and to the use of three-dimensional printing as modality to study cancer. This review highlights the potential for using three-dimensional printing to create an artificial tumor microenvironment in the presence of neuroblastoma to provide improved preclinical testing of novel therapies.

Abstract

In the quest to advance neuroblastoma therapeutics, there is a need to have a deeper understanding of the tumor microenvironment (TME). From extracellular matrix proteins to tumor associated macrophages, the TME is a robust and diverse network functioning in symbiosis with the solid tumor. Herein, we review the major components of the TME including the extracellular matrix, cytokines, immune cells, and vasculature that support a more aggressive neuroblastoma phenotype and encumber current therapeutic interventions. Contemporary treatments for neuroblastoma are the result of traditional two-dimensional culture studies and in vivo models that have been translated to clinical trials. These pre-clinical studies are costly, time consuming, and neglect the study of cofounding factors such as the contributions of the TME. Three-dimensional (3D) bioprinting has become a novel approach to studying adult cancers and is just now incorporating portions of the TME and advancing to study pediatric solid. We review the methods of 3D bioprinting, how researchers have included TME pieces into the prints, and highlight present studies using neuroblastoma. Ultimately, incorporating the elements of the TME that affect neuroblastoma responses to therapy will improve the development of innovative and novel treatments. The use of 3D bioprinting to achieve this aim will prove useful in developing optimal therapies for children with neuroblastoma.

HILPDA Is a Prognostic Biomarker and Correlates With Macrophage Infiltration in Pan-Cancer

Background: The protein hypoxia-inducible lipid droplet-associated (HILPDA) is differentially expressed in various tumors. However, its role and correlation with immune cell infiltration in most tumors remain unclear. Methods: HILPDA expression was analyzed in pan-cancer data from The Cancer Genome Atlas (TCGA) database. The influence of HILPDA in clinical prognosis was evaluated using clinical survival data from TCGA. Enrichment analysis of HILPDA was conducted using the R package "clusterProfiler." We downloaded the immune cell infiltration score of TCGA samples from published articles and analyzed the correlation between the magnitude of immune cell infiltration and HILPDA expression. Results: HILPDA was highly expressed and associated with worse overall survival, disease-specific survival, and progression-free interval in most tumor types. In addition, HILPDA expression was significantly associated with the glycolysis pathway and infiltration of immune cells. Tumor-associated macrophage (TAM) infiltration increased in tissues with high HILPDA expression in most tumor types. Immunosuppressive genes, such as PD-L1, PD-1, TGFB1, and TGFBR1 were positively correlated with HILPDA. Conclusions: Our study suggests that HILPDA is a marker of poor prognosis. High HILPDA may contribute to TAM infiltration and be associated with tumor immunosuppression status.

Characterization of the inflammatory microenvironment and hepatic macrophage subsets in experimental hepatocellular carcinoma models

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide. HCC typically develops on a background of chronic inflammation and fibrosis with tumor associated macrophages (TAMs) playing an important role in chronic inflammation-induced HCC and progression. However, the liver harbors unique macrophages, resident liver Kupffer cells (KCs) and monocyte-derived macrophages (Mo-Mφ), and their contribution to HCC and to the population of TAMs is incompletely known. Here, we characterized the tumor microenvironment and the proportion and transcriptional profile of hepatic macrophages (Mφ) in two commonly used HCC mouse models. A gradually increased expression of inflammatory, immune regulatory, fibrotic and cell proliferation pathways and markers was observed during diethylnitrosamine (DEN)- and non-alcoholic steatohepatitis (NASH)-induced HCC development. The transcriptional phenotypes of isolated hepatic Mφ subsets were clearly distinct and shifted during HCC development, with mixed pro-inflammatory and tumor-promoting expression profiles. There were marked differences between the models as well, with Mφ in NASH-HCC exhibiting a more immunomodulatory phenotype, in conjunction with an upregulation of lipid metabolism genes. Our data show that at least some infiltrated macrophages display expression of pro-tumoral markers, and that Kupffer cells are part of the population of TAMs and enhance tumor progression. These insights are useful to further unravel sequential pathogenic events during hepatocarcinogenesis and direct future development of new treatment strategies for HCC.

Distinct Populations of Immune-Suppressive Macrophages Differentiate from Monocytic Myeloid-Derived Suppressor Cells in Cancer

Here, we report that functional heterogeneity of macrophages in cancer could be determined by the nature of their precursors: monocytes (Mons) and monocytic myeloid-derived suppressor cells (M-MDSCs). Macrophages that are differentiated from M-MDSCs, but not from Mons, are immune suppressive, with a genomic profile matching that of M-MDSCs. Immune-suppressive activity of M-MDSC-derived macrophages is dependent on the persistent expression of S100A9 protein in these cells. S100A9 also promotes M2 polarization of macrophages. Tissue-resident- and Mon-derived macrophages lack expression of this protein. S100A9-dependent immune-suppressive activity of macrophages involves transcription factor C/EBPβ. The presence of S100A9-positive macrophages in tumor tissues is associated with shorter survival in patients with head and neck cancer and poor response to PD-1 antibody treatment in patients with metastatic melanoma. Thus, this study reveals the pathway of the development of immune-suppressive macrophages and suggests an approach to their selective targeting.

Is sCD163 a Clinical Significant Prognostic Value in Cancers? A Systematic Review and Meta-Analysis

Background

Tumor associated macrophages (TAMs), a kind of inflammatory cells in the tumor microenvironment, are crucial for the occurrence and development of various tumors which increased the expression of CD163. Nevertheless, not much has been established regarding soluble CD163 and its connection to tumor diagnosis. In this case, a meta-analysis was conducted to determine the tumor diagnostic importance of serum sCD163.

Methods

In order to assess the correlation between sCD163 and the overall survival (OS) or progression-free survival (PFS) among tumor patients, a systematic perusal of literature published until June 2020 was conducted. Relevant data were primarily obtained from papers that have the following qualifications: 1) a confidence interval (CI) of 95%; 2) a report of the hazard ratios; and, 3) pooled by means of the Mantel-Haenszel random-effect representation.

Results

For the final meta-analysis, eight papers comprised of 1,236 cases were involved. Through pooled investigation, it was determined that a correlation exists between elevated serum sCD163 and worse OS (HR = 2.24, 95% CI: 1.50-3.35, P < 0.001) and PFS (HR = 3.90, 95% CI: 2.33-6.52, P < 0.001) among tumor cases. Subgroup analysis stratified by medium age at diagnosis demonstrated that patients over 60 years old with high sCD163 had worse OS (HR 2.28, 95% CI: 1.58-3.29, P < 0.001) than under 60 (HR 1.43, 95% CI: 1.15-1.77, P = 0.001). Subgroup analysis revealed that analysis method and medium age at diagnosis were the potential source of heterogeneity.

Conclusions

Overall, diagnosis of tumor cases can be adversely determined through substantial sCD163 levels. Consequently, it is encouraged that extensive researches regarding the rates of cancer survival be accomplished.

Regulation of PD-L1 Expression by NF-κB in Cancer

Immune checkpoints are inhibitory receptor/ligand pairs regulating immunity that are exploited as key targets of anti-cancer therapy. Although the PD-1/PD-L1 pair is one of the most studied immune checkpoints, several aspects of its biology remain to be clarified. It has been established that PD-1 is an inhibitory receptor up-regulated by activated T, B, and NK lymphocytes and that its ligand PD-L1 mediates a negative feedback of lymphocyte activation, contributing to the restoration of the steady state condition after acute immune responses. This loop might become detrimental in the presence of either a chronic infection or a growing tumor. PD-L1 expression in tumors is currently used as a biomarker to orient therapeutic decisions; nevertheless, our knowledge about the regulation of PD-L1 expression is limited. The present review discusses how NF-κB, a master transcription factor of inflammation and immunity, is emerging as a key positive regulator of PD-L1 expression in cancer. NF-κB directly induces PD-L1 gene transcription by binding to its promoter, and it can also regulate PD-L1 post-transcriptionally through indirect pathways. These processes, which under conditions of cellular stress and acute inflammation drive tissue homeostasis and promote tissue healing, are largely dysregulated in tumors. Up-regulation of PD-L1 in cancer cells is controlled via NF-κB downstream of several signals, including oncogene- and stress-induced pathways, inflammatory cytokines, and chemotherapeutic drugs. Notably, a shared signaling pathway in epithelial cancers induces both PD-L1 expression and epithelial–mesenchymal transition, suggesting that PD-L1 is part of the tissue remodeling program. Furthermore, PD-L1 expression by tumor infiltrating myeloid cells can contribute to the immune suppressive features of the tumor environment. A better understanding of the interplay between NF-κB signaling and PD-L1 expression is highly relevant to cancer biology and therapy.

Targeting a scavenger receptor on tumor-associated macrophages activates tumor cell killing by natural killer cells

Tumor-associated macrophages (TAMs) can have protumor properties, including suppressing immune responses, promoting vascularization and, consequently, augmenting tumor progression. To stop TAM-mediated immunosuppression, we use a novel treatment by injecting antibodies specific for scavenger receptor MARCO, which is expressed on a specific subpopulation of TAMs in the tumor. We now report the location of this TAM as well as the pleiotropic mechanism of action of anti-MARCO antibody treatment on tumor progression and further show that this is potentially relevant to humans. Using specific targeting, we observed decreased tumor vascularization, a switch in the metabolic program of MARCO-expressing macrophages, and activation of natural killer (NK) cell killing through TNF-related apoptosis-inducing ligand (TRAIL). This latter activity reverses the effect of melanoma cell-conditioned macrophages in blocking NK activation and synergizes with T cell-directed immunotherapy, such as antibodies to PD-1 or PD-L1, to enhance tumor killing. Our study thus reveals an approach to targeting the immunosuppressive tumor microenvironment with monoclonal antibodies to enhance NK cell activation and NK cell-mediated killing. This can complement existing T cell-directed immunotherapy, providing a promising approach to combinatorial immunotherapy for cancer.