Cellular metabolism of tumor-associated macrophages - functional impact and consequences

Macrophage Polarisation in the Tumour Microenvironment: Recent Research Advances and Therapeutic Potential of Different Macrophage Reprogramming

BACKGROUND

Macrophages are a critical component of the innate immune system, derived from monocytes, with significant roles in anti-inflammatory and anti-tumour activities. In the tumour microenvironment, however, macrophages are often reprogrammed into tumour-associated macrophages (TAMs), which promote tumour growth, metastasis, and therapeutic resistance.

PURPOSE

To review recent advancements in the understanding of macrophage polarisation and reprogramming, highlighting their role in tumour progression and potential as therapeutic targets.

RESEARCH DESIGN

This is a review article synthesising findings from recent studies on macrophage polarisation and reprogramming in tumour biology.

STUDY SAMPLE

Not applicable (review of existing literature).

DATA COLLECTION AND/OR ANALYSIS

Key studies were identified and summarised to explore mechanisms of macrophage polarisation and reprogramming, focusing on M1/M2 polarisation, metabolic and epigenetic changes, and pathway regulation.

RESULTS

Macrophage reprogramming in the tumour microenvironment involves complex mechanisms, including phenotypic and functional alterations. These processes are influenced by M1/M2 polarisation, metabolic and epigenetic reprogramming, and various signalling pathways. TAMs play a pivotal role in tumour progression, metastasis, and therapy resistance, making them prime targets for combination therapies.

CONCLUSIONS

Understanding the mechanisms underlying macrophage polarisation and reprogramming offers promising avenues for developing therapies to counteract tumour progression. Future research should focus on translating these insights into clinical applications for effective cancer treatment.

In Vitro and In Vivo Evaluation of Virus-Induced Innate Immunity in Mouse

The innate immune system is the first line of host defense against infection by pathogenic microorganisms, among which macrophages are important innate immune cells. Macrophages are widely distributed throughout the body and recognize and eliminate viruses through pattern recognition receptors (PRRs) to sense pathogen-associated molecular patterns (PAMPs). In the present chapter, we provide detailed protocols for vesicular stomatitis virus (VSV) amplification, VSV titer detection, isolation of mouse primary peritoneal macrophages, in vitro and in vivo VSV infection, detection of interferon-beta (IFN-β) expression, and lung injury. These protocols provide efficient and typical methods to evaluate virus-induced innate immunity in vitro and in vivo.

TDO2 inhibition counters Benzo[a]pyrene-induced immune evasion and suppresses tumorigenesis in lung adenocarcinoma

INTRODUCTION

Benzo[a]pyrene (BaP) is a toxic polycyclic aromatic hydrocarbon known as an exogenous AhR ligand. This study investigates the role of BaP in inducing immune checkpoint expression in lung adenocarcinoma (LUAD) and the underlying mechanisms involving the aryl hydrocarbon receptor (AhR) and tryptophan (Trp) metabolism.

METHODS

We assessed the expression of immune checkpoint molecules, including PD-L1 and ICOSL, in lung epithelial cell lines (BEAS-2B and H1975) exposed to BaP. The involvement of AhR in BaP-induced immune checkpoint expression was examined using AhR silencing (siAhR). Additionally, the role of Trp metabolism in BaP-mediated immune evasion was explored through culturing in Trp (-/+) condition media, treatments with the inhibitors of rate-limiting enzymes in Trp metabolism (TDO2 and IDO1) and analyses of Trp-catabolizing enzymes. The therapeutic potential of targeting Trp metabolism, specifically TDO2, was evaluated in vivo using C57BL/6 mice orthotopically inoculated with LUAD cells.

RESULTS

BaP exposure significantly upregulated the mRNA and surface expression of PD-L1 and ICOSL, with AhR playing a crucial role in this induction. Trp metabolism was found to enhance BaP-mediated immune evasion, as indicated by stronger induction of immune checkpoints in Trp (+) media and the upregulation of Trp-catabolizing enzymes. TDO2 inhibition markedly suppressed the surface expression of PD-L1 and ICOSL, demonstrating the importance of Trp metabolism in BaP-induced immune evasion. Further analysis confirmed the high TDO2 expression in lung adenocarcinoma and its association with poor patient survival. Using an orthotopic implantation mouse model, we demonstrated the inhibitory effect of two different TDO2 inhibitors on tumorigenesis, immune checkpoints, and tryptophan metabolism.

CONCLUSIONS

This study highlights the key mechanisms behind BaP-induced immune evasion in LUAD, particularly through the TDO2/AhR axis. It reveals how TDO2 inhibitors can counteract immune checkpoint activation and boost anti-tumor immunity, suggesting new paths for targeted lung cancer immunotherapy. The findings significantly improve our understanding of immune evasion in LUAD and underscore the therapeutic promise of TDO2 inhibition.

Targeting OXCT1-mediated ketone metabolism reprograms macrophages to promote antitumor immunity via CD8+ T cells in hepatocellular carcinoma

BACKGROUND & AIMS

The liver is the main organ of ketogenesis, while ketones are mainly metabolized in peripheral tissues via the critical enzyme 3-oxoacid CoA-transferase 1 (OXCT1). We previously found that ketolysis is reactivated in hepatocellular carcinoma (HCC) cells through OXCT1 expression to promote tumor progression; however, whether OXCT1 regulates antitumor immunity remains unclear.

METHODS

To investigate the expression pattern of OXCT1 in HCC in vivo, we conducted multiplex immunohistochemistry experiments on human HCC specimens. To explore the role of OXCT1 in mouse HCC tumor-associated macrophages (TAMs), we generated LysMcreOXCT1f/f (OXCT1 conditional knockout in macrophages) mice.

RESULTS

Here, we found that inhibiting OXCT1 expression in tumor-associated macrophages reduced CD8+ T-cell exhaustion through the succinate-H3K4me3-Arg1 axis. Initially, we found that OXCT1 was highly expressed in liver macrophages under steady state and that OXCT expression was further increased in TAMs. OXCT1 deficiency in macrophages suppressed tumor growth by reprogramming TAMs toward an antitumor phenotype, reducing CD8+ T-cell exhaustion and increasing CD8+ T-cell cytotoxicity. Mechanistically, high OXCT1 expression induced the accumulation of succinate, a byproduct of ketolysis, in TAMs, which promoted Arg1 transcription by increasing the H3K4me3 level in the Arg1 promoter. In addition, pimozide, an inhibitor of OXCT1, suppressed Arg1 expression as well as TAM polarization toward the protumor phenotype, leading to decreased CD8+ T-cell exhaustion and slower tumor growth. Finally, high expression of OXCT1 in macrophages was positively associated with poor survival in patients with HCC.

CONCLUSIONS

In conclusion, our results demonstrate that OXCT1 epigenetically suppresses antitumor immunity, suggesting that suppressing OXCT1 activity in TAMs could be an effective approach for treating liver cancer.

IMPACT AND IMPLICATIONS

The intricate metabolism of liver macrophages plays a critical role in shaping hepatocellular carcinoma progression and immune modulation. Targeting macrophage metabolism to counteract immune suppression presents a promising avenue for hepatocellular carcinoma treatment. Herein, we found that the ketogenesis gene OXCT1 was highly expressed in tumor-associated macrophages (TAMs) and promoted tumor growth by reprogramming TAMs toward a protumor phenotype. Pharmacological targeting or genetic downregulation of OXCT1 in TAMs enhances antitumor immunity and slows tumor growth. Our results suggest that suppressing OXCT1 activity in TAMs could be an effective approach for treating liver cancer.

Significance of Immune and Non-Immune Cell Stroma as a Microenvironment of Hepatocellular Carcinoma-From Inflammation to Hepatocellular Carcinoma Progression

Hepatocellular carcinoma (HCC) is the most common liver cancer as well as the most prevalent cause of death in the adult patient population with cirrhosis. The occurrence of HCC is primarily caused by chronic liver inflammation that might occur because of a viral infection, non-alcoholic fatty liver disease (NAFLD), or various lifestyle-associated factors. The objective of this review was to summarize the current knowledge regarding the microenvironment of HCC, indicating how immune- and non-immune-cell stroma might affect the onset and progression of HCC. Therefore, in the following narrative review, we described the role of tumor-infiltrating neutrophils, bone-marrow-derived cells, tumor-associated mast cells, cancer-associated fibroblasts, tumor-associated macrophages, liver-sinusoidal endothelial cells, lymphocytes, and certain cytokines in liver inflammation and the further progression to HCC. A better understanding of the HCC microenvironment might be crucial to introducing novel treatment strategies or combined therapies that could lead to more effective clinical outcomes.

Is Cancer Metabolism an Atavism?

The atavistic theory of cancer posits that cancer emerges and progresses through the reversion of cellular phenotypes to more ancestral types with genomic and epigenetic changes deactivating recently evolved genetic modules and activating ancient survival mechanisms. This theory aims at explaining the known cancer hallmarks and the paradox of cancer's predictable progression despite the randomness of genetic mutations. Lineweaver and colleagues recently proposed the Serial Atavism Model (SAM), an enhanced version of the atavistic theory, which suggests that cancer progression involves multiple atavistic reversions where cells regress through evolutionary stages, losing recently evolved traits first and reactivating primitive ones later. The Warburg effect, where cancer cells upregulate glycolysis and lactate production in the presence of oxygen instead of using oxidative phosphorylation, is one of the key feature of the SAM. It is associated with the metabolism of ancient cells living on Earth before the oxygenation of the atmosphere. This review addresses the question of whether cancer metabolism can be considered as an atavistic reversion. By analyzing several known characteristics of cancer metabolism, we reach the conclusion that this version of the atavistic theory does not provide an adequate conceptual frame for cancer research. Cancer metabolism spans a whole spectrum of metabolic states which cannot be fully explained by a sequential reversion to an ancient state. Moreover, we interrogate the nature of cancer metabolism and discuss its characteristics within the framework of the SAM.

Glioma hexokinase 3 positively correlates with malignancy and macrophage infiltration

BACKGROUND

Glioma is the main subtype of primary central nervous system (CNS) tumor with high malignancy and poor prognosis under current therapeutic approaches. Glycolysis and suppressive tumor microenvironment (TME) are key markers of glioma with great importance for aggressive features of glioma and inferior clinical outcomes. Hexokinase 3 (HK3) is an important rate-limiting enzyme in glycolysis, but its function in glioma remains unknown.

METHODS

This study comprehensively assessed the expression distribution and immunological effect of HK3 via pan-cancer analysis based on datasets from Genotype Tissue Expression (GTEx), Cancer Cell Line Encyclopedia (CCLE), and The Cancer Genome Atlas (TCGA). Furthermore, it explored the malignant phenotype and genomic landscape between low-HK3 and high-HK3 expression groups in gliomas from Chinese Glioma Genome Atlas (CGGA) and TCGA. Moreover, data from the TIMER website predicted the relationship between macrophage infiltration and HK3 expression. Also, single-cell sequencing data were used to validate the relationship.

RESULTS

For pan-cancer patients, HK3 was expressed in various cancers. The results showed that HK3 was highly expressed in gliomas and positively correlated with tumor-infiltrating immune cells (TIICs), immune checkpoints, immunomodulators, and chemokines. Meanwhile, HK3 expression was highest in normal immune cells and tissues. In gliomas, the expression of HK3 was found to be closely correlated with the malignant clinical characteristics and the infiltration of macrophages. Also, HK3 was proven to be positively associated with macrophage through single-cell sequencing data and immunohistochemistry techniques. Finally, it is predicted that samples with high HK3 expression are often malignant entities and also significant genomic aberrations of driver oncogenes.

CONCLUSIONS

This is the first comprehensive research to figure out the relationship between HK3 and TME characteristics in gliomas. HK3 is positively associated with macrophage infiltration and can induce the immunosuppressive TME and malignant phenotype of gliomas.

The role of AMPK in macrophage metabolism, function and polarisation

AMP-activated protein kinase (AMPK) is a ubiquitous sensor of energy and nutritional status in eukaryotic cells. It plays a key role in regulating cellular energy homeostasis and multiple aspects of cell metabolism. During macrophage polarisation, AMPK not only guides the metabolic programming of macrophages, but also counter-regulates the inflammatory function of macrophages and promotes their polarisation toward the anti-inflammatory phenotype. AMPK is located at the intersection of macrophage metabolism and inflammation. The metabolic characteristics of macrophages are closely related to immune-related diseases, infectious diseases, cancer progression and immunotherapy. This review discusses the structure of AMPK and its role in the metabolism, function and polarisation of macrophages. In addition, it summarises the important role of the AMPK pathway and AMPK activators in the development of macrophage-related diseases.

Macrophage metabolism, phenotype, function, and therapy in hepatocellular carcinoma (HCC)

The pivotal role of the tumor microenvironment (TME) in the initiation and advancement of hepatocellular carcinoma (HCC) is widely acknowledged, as it fosters the proliferation and metastasis of HCC cells. Within the intricate TME of HCC, tumor-associated macrophages (TAMs) represent a significant constituent of non-malignant cells. TAMs engage in direct communication with cancer cells in HCC, while also exerting influence on other immune cells to adopt a tumor-supportive phenotype that facilitates tumor progression. Among the multifaceted mechanisms at play, the metabolic reprogramming of both tumor cells and macrophages leads to phenotypic alterations and functional modifications in macrophages. This comprehensive review elucidates the intricate interplay between cellular metabolism and macrophage phenotype/polarization, while also providing an overview of the associated signaling molecules and potential therapeutic strategies for HCC.

Single-cell and bulk RNA-sequencing analysis to predict the role and clinical value of CD36 in lung squamous cell carcinoma

The majority of patients with lung squamous cell carcinoma are diagnosed at an advanced stage, which poses a challenge to the efficacy of chemotherapy. Therefore, the search for an early biomarker needs to be addressed. CD36 is a scavenger receptor expressed in various cell types. It has been reported that it is closely related to the occurrence and development of many kinds of tumours. However, its role in lung squamous cell carcinoma has not been reported. Our research aims to reveal the role of CD36 in lung squamous cell carcinoma by integrating single-cell RNA sequencing (scRNA-seq) and bulk RNA sequencing data. We used bioinformatics methods to explore the potential carcinogenicity of CD36 by analysing the data from the cancer genome map (TCGA), gene expression comprehensive map (GEO), human protein map (HPA) comparative toxicology genomics database (CTD) and other resources. Our study dissected the relationship between CD36 and prognosis and gene correlation, functional analysis, mutation of different tumours, infiltration of immune cells and exploring the interaction between CD36 and chemicals. The results showed that the expression of CD36 was heterogeneous. Compared with normal patients, the expression was low in lung squamous cell carcinoma. In addition, CD36 showed early diagnostic value in four kinds of tumours (LUSC, BLCA, BRCA and KIRC) and was positively or negatively correlated with the prognosis of different tumours. The relationship between CD36 and the tumour immune microenvironment was revealed by immunoinfiltration analysis, and many drugs that might target CD36 were identified by the comparative toxicological genomics database (CTD). In summary, through pancancer analysis, we found and verified for the first time that CD36 may play a role in the detection of lung squamous cell carcinoma. In addition, it has high specificity and sensitivity in detecting cancer. Therefore, CD36 can be used as an auxiliary index for early tumour diagnosis and a prognostic marker for lung squamous cell carcinoma.

Immunometabolic actions of trabectedin and lurbinectedin on human macrophages: relevance for their anti-tumor activity

In recent years, the central role of cell bioenergetics in regulating immune cell function and fate has been recognized, giving rise to the interest in immunometabolism, an area of research focused on the interaction between metabolic regulation and immune function. Thus, early metabolic changes associated with the polarization of macrophages into pro-inflammatory or pro-resolving cells under different stimuli have been characterized. Tumor-associated macrophages are among the most abundant cells in the tumor microenvironment; however, it exists an unmet need to study the effect of chemotherapeutics on macrophage immunometabolism. Here, we use a systems biology approach that integrates transcriptomics and metabolomics to unveil the immunometabolic effects of trabectedin (TRB) and lurbinectedin (LUR), two DNA-binding agents with proven antitumor activity. Our results show that TRB and LUR activate human macrophages toward a pro-inflammatory phenotype by inducing a specific metabolic rewiring program that includes ROS production, changes in the mitochondrial inner membrane potential, increased pentose phosphate pathway, lactate release, tricarboxylic acids (TCA) cycle, serine and methylglyoxal pathways in human macrophages. Glutamine, aspartate, histidine, and proline intracellular levels are also decreased, whereas oxygen consumption is reduced. The observed immunometabolic changes explain additional antitumor activities of these compounds and open new avenues to design therapeutic interventions that specifically target the immunometabolic landscape in the treatment of cancer.

Mechanisms of tumor-associated macrophages affecting the progression of hepatocellular carcinoma

Tumor-associated macrophages (TAMs) are essential components of the immune cell stroma of hepatocellular carcinoma. TAMs originate from monocytic myeloid-derived suppressor cells, peripheral blood monocytes, and kupffer cells. The recruitment of monocytes to the HCC tumor microenvironment is facilitated by various factors, leading to their differentiation into TAMs with unique phenotypes. TAMs can directly activate or inhibit the nuclear factor-κB, interleukin-6/signal transducer and signal transducer and activator of transcription 3, Wnt/β-catenin, transforming growth factor-β1/bone morphogenetic protein, and extracellular signal-regulated kinase 1/2 signaling pathways in tumor cells and interact with other immune cells via producing cytokines and extracellular vesicles, thus affecting carcinoma cell proliferation, invasive and migratory, angiogenesis, liver fibrosis progression, and other processes to participate in different stages of tumor progression. In recent years, TAMs have received much attention as a prospective treatment target for HCC. This review describes the origin and characteristics of TAMs and their mechanism of action in the occurrence and development of HCC to offer a theoretical foundation for further clinical research of TAMs.

Lipid Metabolic Regulatory Crosstalk Between Cancer Cells and Tumor-Associated Macrophages

In the tumor microenvironment, tumor-associated macrophages (TAMs) are one of the most abundant cell populations, playing key roles in tumorigenesis, chemoresistance, immune evasion, and metastasis. There is an important interaction between TAMs and cancer cells: on the one hand, tumors control the function of infiltrating macrophages, contributing to reprogramming of TAMs, and on the other hand, TAMs affect the growth of cancer cells. This review focuses on lipid metabolism changes in the complex relationship between cancer cells and TAMs. We discuss how lipid metabolism in cancer cells affects macrophage phenotypic and metabolic changes and, subsequently, how altered lipid metabolism of TAMs influences tumor progression. Identifying the metabolic changes that influence the complex interaction between tumor cells and TAMs is also an important step in exploring new therapeutic approaches that target metabolic reprogramming of immune cells to enhance their tumoricidal potential and bypass therapy resistance. Our work may provide new targets for antitumor therapies.

The biological function of tumor-derived extracellular vesicles on metabolism

Multiple studies have shown that extracellular vesicles (EVs) play a key role in the process of information transfer and material transport between cells. EVs are classified into different types according to their sizes, which includes the class of exosomes. In comparison to normal EVs, tumor-derived EVs (TDEs) have both altered components and quantities of contents. TDEs have been shown to help facilitate an environment conducive to the occurrence and development of tumor by regulation of glucose, lipids and amino acids. Furthermore, TDEs can also affect the host metabolism and immune system. EVs have been shown to have multiple clinically useful properties, including the use of TDEs as biomarkers for the early diagnosis of diseases and using the transport properties of exosomes for drug delivery. Targeting the key bioactive cargoes of exosomes could be applied to provide new strategies for the treatment of tumors. In this review, we summarize the finding of studies focused on measuring the effects of TDE on tumor-related microenvironment and systemic metabolism. Video Abstract.

Enhancing the antitumor immunosurveillance of PD-L1-targeted gene therapy for metastatic melanoma using cationized Panax Notoginseng polysaccharide

Improved curative effects with reduced toxicity has always been the ultimate goal of gene delivery vectors for tumor immunotherapy. Panax notoginseng polysaccharide (PNP), a natural plant-derived macromolecule, not only has antitumor immune activity but also has the typical structural characteristics useful for gene delivery. In this work, positively charged polyethyleneimine (PEI) was directly grafted to the backbone of PNP to induced its charge reversal and generate a functional gene vector (PNP-PEI). Moreover, a short hairpin RNA targeting the programmed death-ligand 1 (PD-L1) was loaded into PNP-PEI to generate a potentially therapeutic nanoparticle (PNP-PEI/shPD-L1). In vitro and in vivo experiments demonstrated that PNP-PEI could efficiently carry the therapeutic shPD-L1 into tumor cells and that PNP-PEI/shPD-L1 could significantly inhibit the expression of PD-L1 and growth of B16-F10 cells. Noteworthily, treatment with PNP-PEI reversed the phenotype of macrophages from M2 to M1 subtype and promoted dendritic cell maturation, which encouraged the host immunity and enhanced the therapeutic antitumor effects. In summary, this study describes a PNP-based gene delivery vector and highlights the beneficial immunopotentiating therapeutic outcomes of PNP-PEI for tumor immunotherapy.

Control of tumor-associated macrophage responses by nutrient acquisition and metabolism

Metazoan tissue specification is associated with integration of macrophage lineage cells in sub-tissular niches to promote tissue development and homeostasis. Oncogenic transformation, most prevalently of epithelial cell lineages, results in maladaptation of resident tissue macrophage differentiation pathways to generate parenchymal and interstitial tumor-associated macrophages that largely foster cancer progression. In addition to growth factors, nutrients that can be consumed, stored, recycled, or converted to signaling molecules have emerged as crucial regulators of macrophage responses in tumor. Here, we review how nutrient acquisition through plasma membrane transporters and engulfment pathways control tumor-associated macrophage differentiation and function. We also discuss how nutrient metabolism regulates tumor-associated macrophages and how these processes may be targeted for cancer therapy.

The Interface of Tumour-Associated Macrophages with Dying Cancer Cells in Immuno-Oncology

Tumour-associated macrophages (TAMs) are essential players in the tumour microenvironment (TME) and modulate various pro-tumorigenic functions such as immunosuppression, angiogenesis, cancer cell proliferation, invasion and metastasis, along with resistance to anti-cancer therapies. TAMs also mediate important anti-tumour functions and can clear dying cancer cells via efferocytosis. Thus, not surprisingly, TAMs exhibit heterogeneous activities and functional plasticity depending on the type and context of cancer cell death that they are faced with. This ultimately governs both the pro-tumorigenic and anti-tumorigenic activity of TAMs, making the interface between TAMs and dying cancer cells very important for modulating cancer growth and the efficacy of chemo-radiotherapy or immunotherapy. In this review, we discuss the interface of TAMs with cancer cell death from the perspectives of cell death pathways, TME-driven variations, TAM heterogeneity and cell-death-inducing anti-cancer therapies. We believe that a better understanding of how dying cancer cells influence TAMs can lead to improved combinatorial anti-cancer therapies, especially in combination with TAM-targeting immunotherapies.

Metabolic reprogramming in the immunosuppression of tumor-associated macrophages

ABSTRACT

Tumor-associated macrophages (TAMs) are an essential proportion of tumor-infiltrating immune cells in the tumor microenvironment (TME) and have immunosuppressive functions. The high plasticity and corresponding phenotypic transformation of TAMs facilitate oncogenesis and progression, and suppress antineoplastic responses. Due to the uncontrolled proliferation of tumor cells, metabolism homeostasis is regulated, leading to a series of alterations in the metabolite profiles in the TME, which have a commensurate influence on immune cells. Metabolic reprogramming of the TME has a profound impact on the polarization and function of TAMs, and can alter their metabolic profiles. TAMs undergo a series of metabolic reprogramming processes, involving glucose, lipid, and amino acid metabolism, and other metabolic pathways, which terminally promote the development of the immunosuppressive phenotype. TAMs express a pro-tumor phenotype by increasing glycolysis, fatty acid oxidation, cholesterol efflux, and arginine, tryptophan, glutamate, and glutamine metabolism. Previous studies on the metabolism of TAMs demonstrated that metabolic reprogramming has intimate crosstalk with anti-tumor or pro-tumor phenotypes and is crucial for the function of TAMs themselves. Targeting metabolism-related pathways is emerging as a promising therapeutic modality because of the massive metabolic remodeling that occurs in malignant cells and TAMs. Evidence reveals that the efficacy of immune checkpoint inhibitors is improved when combined with therapeutic strategies targeting metabolism-related pathways. In-depth research on metabolic reprogramming and potential therapeutic targets provides more options for anti-tumor treatment and creates new directions for the development of new immunotherapy methods. In this review, we elucidate the metabolic reprogramming of TAMs and explore how they sustain immunosuppressive phenotypes to provide a perspective for potential metabolic therapies.

The Roles of Tumor-Associated Macrophages in Prostate Cancer

The morbidity of prostate cancer (PCa) is rising year by year, and it has become the primary cause of tumor-related mortality in males. It is widely accepted that macrophages account for 50% of the tumor mass in solid tumors and have emerged as a crucial participator in multiple stages of PCa, with the huge potential for further treatment. Oftentimes, tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) behave like M2-like phenotypes that modulate malignant hallmarks of tumor lesions, ranging from tumorigenesis to metastasis. Several clinical studies indicated that mean TAM density was higher in human PCa cores versus benign prostatic hyperplasia (BPH), and increased biopsy TAM density potentially predicts worse clinicopathological characteristics as well. Therefore, TAM represents a promising target for therapeutic intervention either alone or in combination with other strategies to halt the “vicious cycle,” thus improving oncological outcomes. Herein, we mainly focus on the fundamental aspects of TAMs in prostate adenocarcinoma, while reviewing the mechanisms responsible for macrophage recruitment and polarization, which has clinical translational implications for the exploitation of potentially effective therapies against TAMs.

Nanomedicines Targeting Metabolism in the Tumor Microenvironment

Cancer cells reprogram their metabolism to meet their growing demand for bioenergy and biosynthesis. The metabolic profile of cancer cells usually includes dysregulation of main nutritional metabolic pathways and the production of metabolites, which leads to a tumor microenvironment (TME) having the characteristics of acidity, hypoxic, and/or nutrient depletion. Therapies targeting metabolism have become an active and revolutionary research topic for anti-cancer drug development. The differential metabolic vulnerabilities between tumor cells and other cells within TME provide nanotechnology a therapeutic window of anti-cancer. In this review, we present the metabolic characteristics of intrinsic cancer cells and TME and summarize representative strategies of nanoparticles in metabolism-regulating anti-cancer therapy. Then, we put forward the challenges and opportunities of using nanoparticles in this emerging field.

The metabolic addiction of cancer stem cells

Cancer stem cells (CSC) are the minor population of cancer originating cells that have the capacity of self-renewal, differentiation, and tumorigenicity (when transplanted into an immunocompromised animal). These low-copy number cell populations are believed to be resistant to conventional chemo and radiotherapy. It was reported that metabolic adaptation of these elusive cell populations is to a large extent responsible for their survival and distant metastasis. Warburg effect is a hallmark of most cancer in which the cancer cells prefer to metabolize glucose anaerobically, even under normoxic conditions. Warburg's aerobic glycolysis produces ATP efficiently promoting cell proliferation by reprogramming metabolism to increase glucose uptake and stimulating lactate production. This metabolic adaptation also seems to contribute to chemoresistance and immune evasion, a prerequisite for cancer cell survival and proliferation. Though we know a lot about metabolic fine-tuning in cancer, what is still in shadow is the identity of upstream regulators that orchestrates this process. Epigenetic modification of key metabolic enzymes seems to play a decisive role in this. By altering the metabolic flux, cancer cells polarize the biochemical reactions to selectively generate "onco-metabolites" that provide an added advantage for cell proliferation and survival. In this review, we explored the metabolic-epigenetic circuity in relation to cancer growth and proliferation and establish the fact how cancer cells may be addicted to specific metabolic pathways to meet their needs. Interestingly, even the immune system is re-calibrated to adapt to this altered scenario. Knowing the details is crucial for selective targeting of cancer stem cells by choking the rate-limiting stems and crucial branch points, preventing the formation of onco-metabolites.

A novel strategy to fuel cancer immunotherapy: targeting glucose metabolism to remodel the tumor microenvironment

The promising results of immunotherapy in tumors have changed the current treatment modality for cancer. However, the remarkable responses are limited to a minority of patients, which is due to immune suppression in the tumor microenvironment (TME). These include the pre-exists of suppressive immune cells, physical barriers to immune infiltration, antigen and antigen presentation deficiency, and expression of inhibitory immune checkpoint molecules. Recently, increasing evidence reveal that tumor metabolism, especially abnormal glucose metabolism of tumors, plays an essential role in tumor immune escape and is a potential target to combine with immunotherapy. By glucose uptake, tumor cells alter their metabolism to facilitate unregulated cellular proliferation and survival and regulate the expression of inhibitory immune checkpoint molecules. Meanwhile, glucose metabolism also regulates the activation, differentiation, and functions of immunocytes. In addition, tumor mainly utilizes glycolysis for energy generation and cellular proliferation, which cause the TME to deplete nutrients for infiltrating immune cells such as T cells and produce immunosuppressive metabolites. Thus, therapeutics that target glucose metabolism, such as inhibiting glycolytic activity, alleviating hypoxia, and targeting lactate, have shown promise as combination therapies for different types of cancer. In this review, we summarized the functions of glucose metabolism in the tumor cells, immune cells, and tumor microenvironment, as well as strategies to target glucose metabolism in combination with immune checkpoint blockade for tumor therapy.

CD47xCD19 bispecific antibody triggers recruitment and activation of innate immune effector cells in a B-cell lymphoma xenograft model

Background

CD47/SIRPα axis is recognized as an innate immune checkpoint and emerging clinical data validate the interest of interrupting this pathway in cancer, particularly in hematological malignancies. In preclinical models, CD47/SIRPα blocking agents have been shown to mobilize phagocytic cells and trigger adaptive immune responses to eliminate tumors. Here, we describe the mechanisms afforded by a CD47xCD19 bispecific antibody (NI-1701) at controlling tumor growth in a mouse xenograft B-cell lymphoma model.

Methods

The contribution of immune effector cell subsets behind the antitumor activity of NI-1701 was investigated using flow cytometry, transcriptomic analysis, and in vivo immune-cell depletion experiments.

Results

We showed that NI-1701 treatment transformed the tumor microenvironment (TME) into a more anti-tumorigenic state with increased NK cells, monocytes, dendritic cells (DC) and MHCII^hi tumor-associated macrophages (TAMs) and decreased granulocytic myeloid-derived suppressor cells. Notably, molecular analysis of isolated tumor-infiltrating leukocytes following NI-1701 administration revealed an upregulation of genes linked to immune activation, including IFNγ and IL-12b. Moreover, TAM-mediated phagocytosis of lymphoma tumor cells was enhanced in the TME in the presence of NI-1701, highlighting the role of macrophages in tumor control. In vivo cell depletion experiments demonstrated that both macrophages and NK cells contribute to the antitumor activity. In addition, NI-1701 enhanced dendritic cell-mediated phagocytosis of tumor cells in vitro, resulting in an increased cross-priming of tumor-specific CD8 T cells.

Conclusions

The study described the mechanisms afforded by the CD47xCD19 bispecific antibody, NI-1701, at controlling tumor growth in lymphoma mouse model. NI-1701 is currently being evaluated in a Phase I clinical trial for the treatment of refractory or relapsed B-cell lymphoma (NCT04806035).

Supplementary Information

The online version contains supplementary material available at 10.1186/s40164-022-00279-w.

Lipid-Laden Macrophages and Inflammation in Atherosclerosis and Cancer: An Integrative View

Atherosclerotic arterial plaques and malignant solid tumors contain macrophages, which participate in anaerobic metabolism, acidosis, and inflammatory processes inherent in the development of either disease. The tissue-resident macrophage populations originate from precursor cells derived from the yolk sac and from circulating bone marrow-derived monocytes. In the tissues, they differentiate into varying functional phenotypes in response to local microenvironmental stimulation. Broadly categorized, the macrophages are activated to polarize into proinflammatory M1 and anti-inflammatory M2 phenotypes; yet, noticeable plasticity allows them to dynamically shift between several distinct functional subtypes. In atherosclerosis, low-density lipoprotein (LDL)-derived cholesterol accumulates within macrophages as cytoplasmic lipid droplets thereby generating macrophage foam cells, which are involved in all steps of atherosclerosis. The conversion of macrophages into foam cells may suppress the expression of given proinflammatory genes and thereby initiate their transcriptional reprogramming toward an anti-inflammatory phenotype. In this particular sense, foam cell formation can be considered anti-atherogenic. The tumor-associated macrophages (TAMs) may become polarized into anti-tumoral M1 and pro-tumoral M2 phenotypes. Mechanistically, the TAMs can regulate the survival and proliferation of the surrounding cancer cells and participate in various aspects of tumor formation, progression, and metastasis. The TAMs may accumulate lipids, but their type and their specific roles in tumorigenesis are still poorly understood. Here, we discuss how the phenotypic and functional plasticity of macrophages allows their multifunctional response to the distinct microenvironments in developing atherosclerotic lesions and in developing malignant tumors. We also discuss how the inflammatory reactions of the macrophages may influence the development of atherosclerotic plaques and malignant tumors, and highlight the potential therapeutic effects of targeting lipid-laden macrophages in either disease.

O-GlcNAcylation regulation of cellular signaling in cancer

O-GlcNAcylation is a post-translational modification occurring on serine/threonine residues of nuclear and cytoplasmic proteins, mediated by the enzymes OGT and OGA which catalyze the addition or removal of the UDP-GlcNAc moieties, respectively. Structural changes brought by this modification lead to alternations of protein stability, protein-protein interactions, and phosphorylation. Importantly, O-GlcNAcylation is a nutrient sensor by coupling nutrient sensing with cellular signaling. Elevated levels of OGT and O-GlcNAc have been reported in a variety of cancers and has been linked to regulation of multiple cancer signaling pathways. In this review, we discuss the most recent findings on the role of O-GlcNAcylation as a metabolic sensor in signaling pathways and immune response in cancer.

Lipid-loaded tumor-associated macrophages sustain tumor growth and invasiveness in prostate cancer

Tumor-associated macrophages (TAMs) are correlated with the progression of prostatic adenocarcinoma (PCa). The mechanistic basis of this correlation and therapeutic strategies to target TAMs in PCa remain poorly defined. Here, single-cell RNA sequencing was used to profile the transcriptional landscape of TAMs in human PCa, leading to identification of a subset of macrophages characterized by dysregulation in transcriptional pathways associated with lipid metabolism. This subset of TAMs correlates positively with PCa progression and shorter disease-free survival and is characterized by an accumulation of lipids that is dependent on Marco. Mechanistically, cancer cell–derived IL-1β enhances Marco expression on macrophages, and reciprocally, cancer cell migration is promoted by CCL6 released by lipid-loaded TAMs. Moreover, administration of a high-fat diet to tumor-bearing mice raises the abundance of lipid-loaded TAMs. Finally, targeting lipid accumulation by Marco blockade hinders tumor growth and invasiveness and improves the efficacy of chemotherapy in models of PCa, pointing to combinatorial strategies that may influence patient outcomes.

Immunometabolism modulation, a new trick of edible and medicinal plants in cancer treatment

The edible and medicinal plants (EMPs) are becoming an abundant source for cancer prevention and treatment since the natural and healthy trend for modern human beings. Currently, there are more than one hundred species of EMPs widely used and listed by the national health commission of China, and most of them indicate immune or metabolic regulation potential in cancer treatment with numerous studies over the past two decades. In the present review, we focused on the metabolic influence in immunocytes and tumor microenvironment, including immune response, immunosuppressive factors and cancer cells, discussing the immunometabolic potential of EMPs in cancer treatment. There are more than five hundred references collected and analyzed through retrieving pharmacological studies deposited in PubMed by medical subject headings and the corresponding names derived from pharmacopoeia of China as a sole criterion. Finally, the immunometabolism modulation of EMPs was sketch out implying an immunometabolic control in cancer treatment.

The Metabolic Features of Tumor-Associated Macrophages: Opportunities for Immunotherapy?

Besides transformed cells, the tumors are composed of various cell types that contribute to undesirable tumor progression. Tumor-associated macrophages (TAMs) are the most abundant innate immune cells in the tumor microenvironment (TME). Within the TME, TAMs exhibit high plasticity and undergo specific functional metabolic alterations according to the availability of tumor tissue oxygen and nutrients, thus further contributing to tumorigenesis and cancer progression. Here, we review the main functional TAM metabolic patterns influenced by TME, including glycolysis, amino acid, and fatty acid metabolism. Moreover, this review discusses antitumor immunotherapies that affect TAM functionality by inducing cell repolarizing and metabolic profiles towards an antitumoral phenotype. Also, new macrophage-based cell therapeutic technologies recently developed using chimeric antigen receptor bioengineering are exposed, which may overcome all solid tumor physical barriers impeding the current adoptive cell therapies and contribute to developing novel cancer immunotherapies.

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

TIDB: a comprehensive database of trained immunity

Trained immunity is a newly emerging concept that defines the ability of the innate immune system to form immune memory and provide long-lasting protection against previously encountered antigens. Accumulating evidence reveals that trained immunity not only has broad benefits to host defense but is also harmful to the host in chronic inflammatory diseases. However, all trained immunity-related information is scattered in the literature and thus is difficult to access. Here, we describe Trained Immunity DataBase (TIDB), a comprehensive database that provides well-studied trained immunity-related genes from human, rat and mouse as well as the related literature evidence. Moreover, TIDB also provides three modules to analyze the function of the trained-immunity-related genes of interest, including Reactome pathway over-representation analysis, Gene Ontology enrichment analysis and protein–protein interaction subnetwork reconstruction. We believe TIDB will help developing valuable strategies for vaccine design and immune-mediated disease therapy.

Database URL:http://www.ieom-tm.com/tidb

Lactate dehydrogenase B regulates macrophage metabolism in the tumor microenvironment

Background: Glucose metabolism in the tumor-microenvironment is a fundamental hallmark for tumor growth and intervention therein remains an attractive option for anti-tumor therapy. Whether tumor-derived factors such as microRNAs (miRs) regulate glucose metabolism in stromal cells, especially in tumor-associated macrophages (TAMs), to hijack them for trophic support, remains elusive.

Methods: Ago-RIP-Seq identified macrophage lactate dehydrogenase B (LDHB) as a target of tumor-derived miR-375 in both 2D/3D cocultures and in murine TAMs from a xenograft mouse model. The prognostic value was analyzed by ISH and multiplex IHC of breast cancer patient tissues. Functional consequences of the miR-375-LDHB axis in TAMs were investigated upon mimic/antagomir treatment by live metabolic flux assays, GC/MS, qPCR, Western blot, lentiviral knockdown and FACS. The therapeutic potential of a combinatorial miR-375-decoy/simvastatin treatment was validated by live cell imaging.

Results: Macrophage LDHB decreased in murine and human breast carcinoma. LDHB downregulation increase aerobic glycolysis and lactagenesis in TAMs in response to tumor-derived miR-375. Lactagenesis reduced fatty acid synthesis but activated SREBP2, which enhanced cholesterol biosynthesis in macrophages. LDHB downregulation skewed TAMs to function as a lactate and sterol/oxysterol source for the proliferation of tumor cells. Restoring of LDHB expression potentiated inhibitory effects of simvastatin on tumor cell proliferation.

Conclusion: Our findings identified a crucial role of LDHB in macrophages and established tumor-derived miR-375 as a novel regulator of macrophage metabolism in breast cancer, which might pave the way for strategies of combinatorial cancer cell/stroma cell interventions.

Metabolic Codependencies in the Tumor Microenvironment

Metabolic reprogramming enables cancer cell growth, proliferation, and survival. This reprogramming is driven by the combined actions of oncogenic alterations in cancer cells and host cell factors acting on cancer cells in the tumor microenvironment. Cancer cell-intrinsic mechanisms activate signal transduction components that either directly enhance metabolic enzyme activity or upregulate transcription factors that in turn increase expression of metabolic regulators. Extrinsic signaling mechanisms involve host-derived factors that further promote and amplify metabolic reprogramming in cancer cells. This review describes intrinsic and extrinsic mechanisms driving cancer metabolism in the tumor microenvironment and how such mechanisms may be targeted therapeutically. SIGNIFICANCE: Cancer cell metabolic reprogramming is a consequence of the converging signals originating from both intrinsic and extrinsic factors. Intrinsic signaling maintains the baseline metabolic state, whereas extrinsic signals fine-tune the metabolic processes based on the availability of metabolites and the requirements of the cells. Therefore, successful targeting of metabolic pathways will require a nuanced approach based on the cancer's genotype, tumor microenvironment composition, and tissue location.

Blocking NHE1 stimulates glioma tumor immunity by restoring OXPHOS function of myeloid cells

Background: Immunosuppressive tumor microenvironment (TME) in glioblastoma (GBM) is one of the contributing factors for failed immunotherapies. Therefore, there is an urgent need to better understand TME and to identify novel modulators of TME for more effective GBM therapies. We hypothesized that H⁺ extrusion protein Na/H exchanger 1 (NHE1) plays a role in dysregulation of glucose metabolism and immunosuppression of GBM. We investigated the efficacy of blockade of NHE1 activity in combination with temozolomide (TMZ) therapy in increasing anti-tumor immunity. Methods: Mouse syngeneic intracranial glioma model was used to test four treatment regimens: DMSO (Vehicle-control), TMZ, NHE1 specific inhibitor HOE642, or TMZ+HOE642 (T+H) combination. Ex vivo ¹H/¹⁹Fluorine magnetic resonance imaging (MRI) with cell tracking agent Vsense was performed to monitor the infiltration of glioma-associated microglia/myeloid cells (GAMs). Glucose metabolism and transcriptome profiles were analyzed by Seahorse analyzer and bulk RNA-sequencing. The impact of selective Nhe1 deletion in GAMs on sensitivity to anti-PD-1 therapy was evaluated in transgenic NHE1 knockout (KO) mice. Results: Among the tested treatment regimens, the T+H combination therapy significantly stimulated the infiltration of GAMs and T-cells; up-regulated Th1 activation, and mitochondrial oxidative phosphorylation (OXPHOS) pathway genes, increased glucose uptake and mitochondrial mass, and decreased aerobic glycolysis in GAMs. Selective deletion of Nhe1 in Cx3cr1⁺ Nhe1 KO mice increased anti-tumor immunity and sensitivity to TMZ plus anti-PD-1 combinatorial therapy. Conclusions: NHE1 plays a role in developing glioma immunosuppressive TME in part by dysregulating glucose metabolism of GAMs and emerges as a therapeutic target for improving glioma immunity.

Exosome-mediated metabolic reprogramming: the emerging role in tumor microenvironment remodeling and its influence on cancer progression

Metabolic reprogramming is reported to be one of the hallmarks of cancer, which is an adaptive mechanism by which fast-growing cancer cells adapt to their increasing energy demands. Recently, extracellular vesicles (EVs) known as exosomes have been recognized as crucial signaling mediators in regulating the tumor microenvironment (TME). Meanwhile, the TME is a highly heterogeneous ecosystem incorporating cancer cells, fibroblasts, adipocytes, endothelial cells, mesenchymal stem cells, and extracellular matrix. Accumulated evidence indicates that exosomes may transfer biologically functional molecules to the recipient cells, which facilitate cancer progression, angiogenesis, metastasis, drug resistance, and immunosuppression by reprogramming the metabolism of cancer cells and their surrounding stromal cells. In this review, we present the role of exosomes in the TME and the underlying mechanism of how exosomes exacerbate tumor development through metabolic reprogramming. In addition, we will also discuss the potential role of exosomes targeting metabolic process as biomarkers for tumor diagnosis and prognosis, and exosomes-mediated metabolic reprogramming as potential targets for cancer therapy. Furthermore, a better understanding of the link between exosomes and metabolic reprogramming, and their impact on cancer progression, would provide novel insights for cancer prevention and treatment in the future.

Enhanced lipid biosynthesis in human tumor-induced macrophages contributes to their protumoral characteristics

Background

Tumor-associated macrophages (TAMs) are key components of the tumor microenvironment (TME) in non-medullary thyroid carcinoma (TC) and neuroblastoma (NB), being associated with a poor prognosis for patients. However, little is known about how tumors steer the specific metabolic phenotype and function of TAMs.

Methods

In a human coculture model, transcriptome, metabolome and lipidome analysis were performed on TC-induced and NB-induced macrophages. The metabolic shift was correlated to functional readouts, such as cytokine production and reactive oxygen species (ROS) production, including pharmacological inhibition of metabolic pathways.

Results

Based on transcriptome and metabolome analysis, we observed a strong upregulation of lipid biosynthesis pathways in TAMs. Subsequently, lipidome analysis revealed that tumor-induced macrophages have an increased total lipid content and enriched levels of intracellular lipids, especially phosphoglycerides and sphingomyelins. Strikingly, this metabolic shift in lipid synthesis contributes to their protumoral functional characteristics: blocking key enzymes of lipid biosynthesis in the tumor-induced macrophages reversed the increased inflammatory cytokines and the capacity to produce ROS, two well-known protumoral factors in the TME.

Conclusions

Taken together, our data show that tumor cells can stimulate lipid biosynthesis in macrophages to induce protumoral cytokine and ROS responses and advocate lipid biosynthesis as a potential therapeutic target to reprogram the TME.

Cathepsin Inhibition Modulates Metabolism and Polarization of Tumor-Associated Macrophages

Simple Summary

Stroma-infiltrating tumor-associated macrophages (TAM) play an important role in regulating tumor progression and chemoresistance. Many tumor-infiltrating macrophage populations can be identified by preferential expression of distinct marker genes associated with an M2 phenotype and may execute tumor-promoting functions by enhancing tissue remodeling, facilitating angiogenesis, and suppressing immune responses. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype. For this purpose, we investigated the molecular effects of cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH₂, led to a polarization shift from M2- to M1 macrophages, associated with distinct alterations in lysosomal signaling and lipid metabolism. This could be therapeutically exploited in tumors with strong infiltration of M2-macrophages, thereby possibly reverting M2 polarization, overcoming drug resistance, and improving the prognosis of our patients.

Abstract

Stroma-infiltrating immune cells, such as tumor-associated macrophages (TAM), play an important role in regulating tumor progression and chemoresistance. These effects are mostly conveyed by secreted mediators, among them several cathepsin proteases. In addition, increasing evidence suggests that stroma-infiltrating immune cells are able to induce profound metabolic changes within the tumor microenvironment. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype in more detail. For this purpose, we investigated the molecular effects of pharmacological cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH₂, led to changes in cellular recycling processes characterized by an increased expression of autophagy- and lysosome-associated marker genes and reduced adenosine triphosphate (ATP) content. Decreased cathepsin activity in primary macrophages further led to distinct changes in fatty acid metabolites associated with increased expression of key modulators of fatty acid metabolism, such as fatty acid synthase (FASN) and acid ceramidase (ASAH1). The altered fatty acid profile was associated with an increased synthesis of the pro-inflammatory prostaglandin PGE₂, which correlated with the upregulation of numerous NF_kB-dependent pro-inflammatory mediators, including interleukin-1 (IL-1), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-alpha (TNFα). Our data indicate a novel link between cathepsin activity and metabolic reprogramming in macrophages, demonstrated by a profound impact on autophagy and fatty acid metabolism, which facilitates a pro-inflammatory micromilieu generally associated with enhanced tumor elimination. These results provide a strong rationale for therapeutic cathepsin inhibition to overcome the tumor-promoting effects of the immune-evasive tumor micromilieu.

Metabolic reprograming of tumor-associated macrophages

A large body of scientific evidence corroborated by clinical and animal model experiments indicates that tumor-associated macrophages (TAMs) play a crucial role in tumor development and progression. TAMs are a key immune cell type present in tumor microenvironment (TME) and associated with poor prognosis, drug resistance, enhanced angiogenesis and metastasis in cancer. TAMs are a phenotypically diverse population of myeloid cells which display tremendous plasticity and dynamic metabolic nature. A complete interpretation of pro-tumoral and anti-tumoral metabolic switch in TAMs is essential to understand immune evasion mechanisms in cancer. Recent studies have also implicated epigenetic mechanisms as significantly regulators of TAM functions. In this review we provide an overview of metabolic circuitry in TAMs, its impact on immune effector cells and interventions aimed at rewiring the metabolic circuits in TAMs. Mechanisms responsible for TAM polarization in cancer are also discussed.

Metabolism in tumor microenvironment: Implications for cancer immunotherapy

Tumor microenvironment is a special environment for tumor survival, which is characterized by hypoxia, acidity, nutrient deficiency, and immunosuppression. The environment consists of the vasculature, immune cells, extracellular matrix, and proteins or metabolic molecules. A large number of recent studies have shown that not only tumor cells but also the immune cells in the tumor microenvironment have undergone metabolic reprogramming, which is closely related to tumor drug resistance and malignant progression. Tumor immunotherapy based on T cells gives patients new hope, but faces the dilemma of low response rate. New strategies sensitizing cancer immunotherapy are urgently needed. Metabolic reprogramming can directly affect the biological activity of tumor cells and also regulate the differentiation and activation of immune cells. The authors aim to review the characteristics of tumor microenvironment, the metabolic changes of tumor‐associated immune cells, and the regulatory role of metabolic reprogramming in cancer immunotherapy.

Obesity induces limited changes to systemic and local immune profiles in treatment-naive human clear cell renal cell carcinoma

Understanding the effects of obesity on the immune profile of renal cell carcinoma (RCC) patients is critical, given the rising use of immunotherapies to treat advanced disease and recent reports of differential cancer immunotherapy outcomes with obesity. Here, we evaluated multiple immune parameters at the genetic, soluble protein, and cellular levels in peripheral blood and renal tumors from treatment-naive clear cell RCC (ccRCC) subjects (n = 69), to better understand the effects of host obesity (Body Mass Index "BMI" ≥ 30 kg/m2) in the absence of immunotherapy. Tumor-free donors (n = 38) with or without obesity were used as controls. In our ccRCC cohort, increasing BMI was associated with decreased percentages of circulating activated PD-1+CD8+ T cells, CD14+CD16neg classical monocytes, and Foxp3+ regulatory T cells (Tregs). Only CD14+CD16neg classical monocytes and Tregs were reduced when obesity was examined as a categorical variable. Obesity did not alter the percentages of circulating IFNγ+ CD8 T cells or IFNγ+, IL-4+, or IL-17A+ CD4 T cells in ccRCC subjects. Of 38 plasma proteins analyzed, six (CCL3, IL-1β, IL-1RA, IL-10, IL-17, and TNFα) were upregulated specifically in ccRCC subjects with obesity versus tumor-free controls with obesity. IGFBP-1 was uniquely decreased in ccRCC subjects with obesity versus non-obese ccRCC subjects. Immunogenetic profiling of ccRCC tumors revealed that 93% of examined genes were equivalently expressed and no changes in cell type scores were found in stage-matched tumors from obesity category II/III versus normal weight (BMI ≥ 35 kg/m2 versus 18.5-24.9 kg/m2, respectively) subjects. Intratumoral PLGF and VEGF-A proteins were elevated in ccRCC subjects with obesity. Thus, in ccRCC patients with localized disease, obesity is not associated with widespread detrimental alterations in systemic or intratumoral immune profiles. The effects of combined obesity and immunotherapy administration on immune parameters remains to be determined.

Defining trained immunity and its role in health and disease

Immune memory is a defining feature of the acquired immune system, but activation of the innate immune system can also result in enhanced responsiveness to subsequent triggers. This process has been termed ‘trained immunity’, a de facto innate immune memory. Research in the past decade has pointed to the broad benefits of trained immunity for host defence but has also suggested potentially detrimental outcomes in immune-mediated and chronic inflammatory diseases. Here we define ‘trained immunity’ as a biological process and discuss the innate stimuli and the epigenetic and metabolic reprogramming events that shape the induction of trained immunity.

Here a group of leaders in the field define our current understanding of ‘trained immunity’, which refers to the memory-type responses that occur in the innate immune system. The authors discuss our current understanding of the key epigenetic and metabolic processes involved in trained immunity and consider its relevance in immune-mediated diseases and cancer.

Up-regulation of indoleamine 2,3-dioxygenase 1 (IDO1) expression and catalytic activity is associated with immunosuppression and poor prognosis in penile squamous cell carcinoma patients

Background

Indoleamine 2,3‐dioxygenase 1 (IDO1) and tryptophan (Trp) catabolism have been demonstrated to play an important role in tumor immunosuppression. This study examined the expression and catalytic activity of IDO1 in penile squamous cell carcinoma (PSCC) and explored their clinical significance.

Methods

IDO1 expression level, serum concentrations of Trp and kynurenine (Kyn) were examined in 114 PSCC patients by immunohistonchemistry and solid‐phase extraction‐liquid chromatography‐tandem mass spectrometry. The survival was analyzed using Kaplan‐Meier method and the log‐rank test. Hazard ratio of death was analyzed via univariate and multivariate Cox regression. Immune cell types were defined by principal component analysis. The correlativity was assessed by Pearson's correlation analysis.

Results

The expression level of IDO1 in PSCC cells was positively correlated with serum Kyn concentration and Kyn/Trp radio (KTR; both P < 0.001) but negatively correlated with serum Trp concentration (P = 0.001). Additionally, IDO1 up‐regulation in cancer cells and the increase of serum KTR were significantly associated with advanced N stage (both P < 0.001) and high pathologic grade (P = 0.008 and 0.032, respectively). High expression level of IDO1 in cancer cells and serum KTR were associated with short disease‐specific survival (both P < 0.001). However, besides N stage (hazard radio [HR], 6.926; 95% confidence interval [CI], 2.458‐19.068; P < 0.001) and pathologic grade (HR, 2.194; 95% CI, 1.021‐4.529; P = 0.038), only serum KTR (HR, 2.780; 95% CI, 1.066‐7.215; P = 0.036) was an independent predictor for PSCC prognosis. IDO1 expression was positively correlated with the expression of interferon‐γ (IFNγ, P < 0.001) and immunosuppressive markers (programmed cell death protein 1, cytotoxic T‐lymphocyte‐associated protein 4 and programmed death‐ligand 1 and 2; all P < 0.05), and the infiltration of immune cells (including cytotoxic T lymphocytes, regulatory T lymphocytes, tumor‐associated macrophages, and myeloid‐derived suppressor cells; all P < 0.001) in PSCC tissues. Furthermore, the expression of IDO1 was induced by IFNγ in a dose‐dependent manner in PSCC cells.

Conclusions

IFNγ‐induced IDO1 plays a crucial role in immunoediting and immunosuppression in PSCC. Additionally, serum KTR, an indicator of IDO1 catabolic activity, can be utilized as an independent prognostic factor for PSCC.

The Metabolic Remodelling in Lung Cancer and Its Putative Consequence in Therapy Response

Lung cancer is the leading cause of cancer-related deaths worldwide in both men and women. Conventional chemotherapy has failed to provide long-term benefits for many patients and in the past decade, important advances were made to understand the underlying molecular/genetic mechanisms of lung cancer, allowing the unfolding of several other pathological entities. Considering these molecular subtypes, and the appearance of promising targeted therapies, an effective personalized control of the disease has emerged, nonetheless benefiting a small proportion of patients. Although immunotherapy has also appeared as a new hope, it is still not accessible to the majority of patients with lung cancer.The metabolism of energy and biomass is the basis of cellular survival. This is true for normal cells under physiological conditions and it is also true for pathophysiologically altered cells, such as cancer cells. Thus, knowledge of the metabolic remodelling that occurs in cancer cells in the sense of, on one hand, surviving in the microenvironment of the organ in which the tumour develops and, on the other hand, escaping from drugs conditioned microenvironment, is essential to understand the disease and to develop new therapeutic approaches.

Metabolic crosstalk in the breast cancer microenvironment

During tumorigenesis, breast tumour cells undergo metabolic reprogramming, which generally includes enhanced glycolysis, tricarboxylic acid cycle activity, glutaminolysis and fatty acid biosynthesis. However, the extension and functional importance of these metabolic alterations may diverge not only according to breast cancer subtypes, but also depending on the interaction of cancer cells with the complex surrounding microenvironment. This microenvironment comprises a variety of non-cancerous cells, such as immune cells (e.g. macrophages, lymphocytes, natural killer cells), fibroblasts, adipocytes and endothelial cells, together with extracellular matrix components and soluble factors, which influence cancer progression and are predictive of clinical outcome. The continuous interaction between cancer and stromal cells results in metabolic competition and symbiosis, with oncogenic-driven metabolic reprogramming of cancer cells shaping the metabolism of neighbouring cells and vice versa. This review addresses current knowledge on this metabolic crosstalk within the breast tumour microenvironment (TME). Improved understanding of how metabolism in the TME modulates cancer development and evasion of tumour-suppressive mechanisms may provide clues for novel anticancer therapeutics directed to metabolic targets.

Emerging role of glycosylation in the polarization of tumor-associated macrophages

Tumors are formed by several cell types interacting in a complex environment of soluble and matrix molecules. The crosstalk between the cells and extracellular components control tumor fate. Macrophages are highly plastic and diverse immune cells that are known to be key regulators of this complex network, which is mostly because they can adjust their metabolism and reprogram their phenotype and effector function. Here, we review the studies that disclose the central role of metabolism and tumor microenvironment in shaping the phenotype and function of macrophages, highlighting the importance of the hexosamine biosynthetic pathway. We further discuss growing evidence of nutrient-sensitive protein modifications such as O-GlcNAcylation and extracellular glycosylation in the function and polarization of tumor-associated macrophages.

UPLC-MS-based metabolomics reveals metabolic dysregulation in ALDH1A1-overexpressed lung adenocarcinoma cells

INTRODUCTION

Specific oncogenotypes can produce distinct metabolic changes in cancer. Recently it is considered that metabolic reprograming contributes heavily to drug resistance. Aldehyde dehydrogenase 1A1 (ALDH1A1), is overexpressed in drug resistant lung adenocarcinomas and may be the cause of acquired drug resistance. However, how ALDH1A1 affects metabolic profiling in lung adenocarcinoma cells remains elusive.

OBJECTIVE

We sought to investigate metabolic alterations induced by ALDH1A1 in lung adenocarcinoma in order to better understand the reprogramming and metabolic mechanism of resistance induced by ALDH1A1.

METHODS

Metabolic alterations in lung adenocarcinoma HCC827-ALDH1A1 cells were analyzed by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). HCC827-ALDH1A1 metabolic signatures were extracted by univariate and multivariate statistical analysis. Furthermore, metabolite enrichment analysis and pathway analysis were performed using MetaboAnalyst 4.0 software.

RESULTS

Twenty-two metabolites were positively identified using authentic standards, including uridine monophosphate (UMP), uridine diphosphate (UDP), adenosine diphosphate (ADP), malic acid, malonyl-coenzyme A, nicotinamide adenine dinucleotide (NAD), coenzyme A and so on. Furthermore, metabolic pathway analysis revealed several dysregulated pathways in HCC827-ALDH1A1 cells, including nucleotide metabolism, urea cycle, tricarboxylic acid (TCA) cycle, and glycerol phospholipid metabolism etc. CONCLUSION: Lung cancer is the most frequent cause of cancer-related deaths worldwide. Nearly all patients eventually undergo disease progression due to acquired resistance. Mechanisms of biological acquired resistance need to be identified. Our study identified altered metabolites in HCC827-ALDH1A1 cells, enhancing our knowledge of lung adenocarcinoma metabolic alterations induced by ALDH1A1, creating a novel therapeutic pathway. These metabolic signatures of ALDH1A1 overexpression may shed light on molecular mechanisms in drug-resistant tumors, and on candidate drug targets. Furthermore, new molecular targets may provide the foundation for potential anticancer strategies for lung cancer therapy.

Metabolism within the tumor microenvironment and its implication on cancer progression: An ongoing therapeutic target

Since reprogramming energy metabolism is considered a new hallmark of cancer, tumor metabolism is again in the spotlight of cancer research. Many studies have been carried out and many possible therapies have been developed in the last years. However, tumor cells are not alone. A series of extracellular components and stromal cells, such as endothelial cells, cancer-associated fibroblasts, tumor-associated macrophages, and tumor-infiltrating T cells, surround tumor cells in the so-called tumor microenvironment (TME). Metabolic features of these cells are being studied in deep in order to find relationships between metabolism within the TME and tumor progression. Moreover, it cannot be forgotten that tumor growth is able to modulate host metabolism and homeostasis, so that TME is not the whole story. Importantly, the metabolic switch in cancer is just a consequence of the flexibility and adaptability of metabolism and should not be surprising. Treatments of cancer patients with combined therapies including antitumor agents with those targeting stromal cell metabolism, antiangiogenic drugs, and/or immunotherapy are being developed as promising therapeutics.

PTEN Hamartoma Tumor Syndrome and Immune Dysregulation

Carriers of a pathogenic germline mutations in the PTEN gene, a well-known tumor suppressor gene, are at increased risk of multiple benign and malignant tumors, e.g. breast, thyroid, endometrial and colon cancer. This is called PTEN Hamartomous Tumor Syndrome (PHTS). PHTS patients may also have an increased risk of immunological dysregulation, such as autoimmunity and immune deficiencies. The effects of PTEN on the immune system have been studied in murine knockout models demonstrating that loss of PTEN function leads to dysregulation of the immune response. This results in susceptibility to autoimmunity, impaired B cell class switching with subsequent hypogammaglobulinemia. Additionally, a decreased ability of dendritic cells to prime CD8⁺ T cells was observed, leading to impaired tumor eradication. Immune dysfunction in PHTS patients has not yet been extensively studied but might be a manageable contributing factor to the increased cancer risk in PHTS.

Effect of Stromal Cells in Tumor Microenvironment on Metastasis Initiation

The cellular environment where tumor cells reside is called the tumor microenvironment (TME), which consists of borders, blood vessels, lymph vessels, extracellular matrix (ECM), stromal cells, immune/inflammatory cells, secreted proteins, RNAs and small organelles. By dynamically interacting with tumor cells, stromal cells participate in all stages of tumor initiation, progression, metastasis, recurrence and drug response, and consequently, affect the fate of patients. During the processes of tumor evolution and metastasis initiation, stromal cells in TME also experience some changes and play roles in both the suppression and promotion of metastasis, while the overall function of stromal cells is beneficial for cancer cell survival and movement. In this review, we examine the effects of stromal cells in TME on metastasis initiation, including angiogenesis, epithelial-mesenchymal transition (EMT) and invasion. We also highlight functions of proteins, RNAs and small organelles secreted by stromal cells in their influences on multiple stages of tumor metastasis.

Metabolic Modulation in Macrophage Effector Function

Traditionally cellular respiration or metabolism has been viewed as catabolic and anabolic pathways generating energy and biosynthetic precursors required for growth and general cellular maintenance. However, growing literature provides evidence of a much broader role for metabolic reactions and processes in controlling immunological effector functions. Much of this research into immunometabolism has focused on macrophages, cells that are central in pro- as well as anti-inflammatory responses—responses that in turn are a direct result of metabolic reprogramming. As we learn more about the precise role of metabolic pathways and pathway intermediates in immune function, a novel opportunity to target immunometabolism therapeutically has emerged. Here, we review the current understanding of the regulation of macrophage function through metabolic remodeling.

The potential role of leptin in tumor invasion and metastasis

The adipocyte-released hormone-like cytokine/adipokine leptin behaves differently in obesity compared to its functions in the normal healthy state. In obese individuals, elevated leptin levels act as a pro-inflammatory adipokine and are associated with certain types of cancers. Further, a growing body of evidence suggests that higher circulating leptin concentrations and/or elevated expression of leptin receptors (Ob-R) in tumors may be poor prognostic factors. Although the underlying pathological mechanisms of leptin's association with poor prognosis are not clear, leptin can impact the tumor microenvironment in several ways. For example, leptin is associated with a number of biological components that could lead to tumor cell invasion and distant metastasis. This includes interactions with carcinoma-associated fibroblasts, tumor promoting effects of infiltrating macrophages, activation of matrix metalloproteinases, transforming growth factor-β signaling, etc. Recent studies also have shown that leptin plays a role in the epithelial-mesenchymal transition, an important phenomenon for cancer cell migration and/or metastasis. Furthermore, leptin's potentiating effects on insulin-like growth factor-I, epidermal growth factor receptor and HER2/neu have been reported. Regarding unfavorable prognosis, leptin has been shown to influence both adenocarcinomas and squamous cell carcinomas. Features of poor prognosis such as tumor invasion, lymph node involvement and distant metastasis have been recorded in several cancer types with higher levels of leptin and/or Ob-R. This review will describe the current scenario in a precise manner. In general, obesity indicates poor prognosis in cancer patients.