Boosting antitumor responses of T lymphocytes infiltrating human prostate cancers

Eliminating a barrier: Aiming at VISTA, reversing MDSC-mediated T cell suppression in the tumor microenvironment

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment by producing remarkable clinical outcomes for patients with various cancer types. However, only a subset of patients benefits from immunotherapeutic interventions due to the primary and acquired resistance to ICIs. Myeloid-derived suppressor cells (MDSCs) play a crucial role in creating an immunosuppressive tumor microenvironment (TME) and contribute to resistance to immunotherapy. V-domain Ig suppressor of T cell activation (VISTA), a negative immune checkpoint protein highly expressed on MDSCs, presents a promising target for overcoming resistance to current ICIs. This article provides an overview of the evidence supporting VISTA's role in regulating MDSCs in shaping the TME, thus offering insights into how to overcome immunotherapy resistance.

Targeting amino acid-metabolizing enzymes for cancer immunotherapy

Despite the immune system's role in the detection and eradication of abnormal cells, cancer cells often evade elimination by exploitation of various immune escape mechanisms. Among these mechanisms is the ability of cancer cells to upregulate amino acid-metabolizing enzymes, or to induce these enzymes in tumor-infiltrating immunosuppressive cells. Amino acids are fundamental cellular nutrients required for a variety of physiological processes, and their inadequacy can severely impact immune cell function. Amino acid-derived metabolites can additionally dampen the anti-tumor immune response by means of their immunosuppressive activities, whilst some can also promote tumor growth directly. Based on their evident role in tumor immune escape, the amino acid-metabolizing enzymes glutaminase 1 (GLS1), arginase 1 (ARG1), inducible nitric oxide synthase (iNOS), indoleamine 2,3-dioxygenase 1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and interleukin 4 induced 1 (IL4I1) each serve as a promising target for immunotherapeutic intervention. This review summarizes and discusses the involvement of these enzymes in cancer, their effect on the anti-tumor immune response and the recent progress made in the preclinical and clinical evaluation of inhibitors targeting these enzymes.

Triptolide promotes differentiation of human monocytes into immunosuppressive MDSCs

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) negatively modulate immune activity. Prior investigations have shown much promise in using MDSCs-assisted immunotherapy for organ transplantation patients. Additionally, owing to its immunosuppressive activity, MDSCs can also be used to manage immune-associated disorders.

METHODS

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was employed to stimulate myeloid progenitor cell differentiation. Triptolide (PG490) was introduced toward the later phases of in vitro MDSCs induction. Lastly, real-time PCR (RT-PCR) and flow cytometry were used to assess transcript expression and cell phenotype, and a mouse skin transplantation model was established to evaluate the MDSCs-mediated immune suppression in vivo.

RESULTS

Co-stimulation with PG490 and GM-CSF potently induced myeloid-derived monocytes to form MDSCs, with remarkable immune-suppressive activity. The underlying mechanism involved downregulation of T cell proliferation, activation, enhancement of inflammatory cytokine release, as well as T cell conversion to Treg cells. PG490 strongly enhanced iNOS expression in MDSCs, and iNOS inhibition successfully reversed the immune-suppression. The PG490- and GM-CSF-induced MDSCs substantially extended survival duration of murine skin grafts, thereby validating their strong immune-suppressive activity in vivo.

CONCLUSIONS

Herein, we presented a new approach involving MDSCs-based immunosuppression in vitro. PG490 and GM-CSF co-treatment strongly induced immuno-suppressive activity in MDSCs both in vitro and in vivo. Our findings highlight the promise of applying MDSCs-based therapy in clinical organ transplantation treatment.

From the Inside Out: Exposing the Roles of Urea Cycle Enzymes in Tumors and Their Micro and Macro Environments

Catabolic pathways change in anabolic diseases such as cancer to maintain metabolic homeostasis. The liver urea cycle (UC) is the main catabolic pathway for disposing excess nitrogen. Outside the liver, the UC enzymes are differentially expressed based on each tissue's needs for UC intermediates. In tumors, there are changes in the expression of UC enzymes selected for promoting tumorigenesis by increasing the availability of essential UC substrates and products. Consequently, there are compensatory changes in the expression of UC enzymes in the cells that compose the tumor microenvironment. Moreover, extrahepatic tumors induce changes in the expression of the liver UC, which contribute to the systemic manifestations of cancer, such as weight loss. Here, we review the multilayer changes in the expression of UC enzymes throughout carcinogenesis. Understanding the changes in UC expression in the tumor and its micro and macro environment can help identify biomarkers for early cancer diagnosis and vulnerabilities that can be targeted for therapy.

Transcending frontiers in prostate cancer: the role of oncometabolites on epigenetic regulation, CSCs, and tumor microenvironment to identify new therapeutic strategies

Prostate cancer, as one of the most prevalent malignancies in males, exhibits an approximate 5-year survival rate of 95% in advanced stages. A myriad of molecular events and mutations, including the accumulation of oncometabolites, underpin the genesis and progression of this cancer type. Despite growing research demonstrating the pivotal role of oncometabolites in supporting various cancers, including prostate cancer, the root causes of their accumulation, especially in the absence of enzymatic mutations, remain elusive. Consequently, identifying a tangible therapeutic target poses a formidable challenge. In this review, we aim to delve deeper into the implications of oncometabolite accumulation in prostate cancer. We center our focus on the consequential epigenetic alterations and impacts on cancer stem cells, with the ultimate goal of outlining novel therapeutic strategies.

Anti-PD-1 immunotherapy with androgen deprivation therapy induces robust immune infiltration in metastatic castration-sensitive prostate cancer

When compared to other malignancies, the tumor microenvironment (TME) of primary and castration-resistant prostate cancer (CRPC) is relatively devoid of immune infiltrates. While androgen deprivation therapy (ADT) induces a complex immune infiltrate in localized prostate cancer, the composition of the TME in metastatic castration-sensitive prostate cancer (mCSPC), and the effects of ADT and other treatments in this context are poorly understood. Here, we perform a comprehensive single-cell RNA sequencing (scRNA-seq) profiling of metastatic sites from patients participating in a phase 2 clinical trial (NCT03951831) that evaluated standard-of-care chemo-hormonal therapy combined with anti-PD-1 immunotherapy. We perform a longitudinal, protein activity-based analysis of TME subpopulations, revealing immune subpopulations conserved across multiple metastatic sites. We also observe dynamic changes in these immune subpopulations in response to treatment and a correlation with clinical outcomes. Our study uncovers a therapy-resistant, transcriptionally distinct tumor subpopulation that expands in cell number in treatment-refractory patients.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Immunometabolism: a new dimension in immunotherapy resistance

Immune checkpoint inhibitors (ICIs) have demonstrated unparalleled clinical responses and revolutionized the paradigm of tumor treatment, while substantial patients remain unresponsive or develop resistance to ICIs as a single agent, which is traceable to cellular metabolic dysfunction. Although dysregulated metabolism has long been adjudged as a hallmark of tumor, it is now increasingly accepted that metabolic reprogramming is not exclusive to tumor cells but is also characteristic of immunocytes. Correspondingly, people used to pay more attention to the effect of tumor cell metabolism on immunocytes, but in practice immunocytes interact intimately with their own metabolic function in a way that has never been realized before during their activation and differentiation, which opens up a whole new frontier called immunometabolism. The metabolic intervention for tumor-infiltrating immunocytes could offer fresh opportunities to break the resistance and ameliorate existing ICI immunotherapy, whose crux might be to ascertain synergistic combinations of metabolic intervention with ICIs to reap synergic benefits and facilitate an adjusted anti-tumor immune response. Herein, we elaborate potential mechanisms underlying immunotherapy resistance from a novel dimension of metabolic reprogramming in diverse tumor-infiltrating immunocytes, and related metabolic intervention in the hope of offering a reference for targeting metabolic vulnerabilities to circumvent immunotherapeutic resistance.

The role of tumor metabolism in modulating T-Cell activity and in optimizing immunotherapy

Immunotherapy has revolutionized cancer treatment and revitalized efforts to harness the power of the immune system to combat a variety of cancer types more effectively. However, low clinical response rates and differences in outcomes due to variations in the immune landscape among patients with cancer continue to be major limitations to immunotherapy. Recent efforts to improve responses to immunotherapy have focused on targeting cellular metabolism, as the metabolic characteristics of cancer cells can directly influence the activity and metabolism of immune cells, particularly T cells. Although the metabolic pathways of various cancer cells and T cells have been extensively reviewed, the intersections among these pathways, and their potential use as targets for improving responses to immune-checkpoint blockade therapies, are not completely understood. This review focuses on the interplay between tumor metabolites and T-cell dysfunction as well as the relationship between several T-cell metabolic patterns and T-cell activity/function in tumor immunology. Understanding these relationships could offer new avenues for improving responses to immunotherapy on a metabolic basis.

Autoimmunity and Carcinogenesis: Their Relationship under the Umbrella of Autophagy

The immune system and autophagy share a functional relationship. Both innate and adaptive immune responses involve autophagy and, depending on the disease’s origin and pathophysiology, it may have a detrimental or positive role on autoimmune disorders. As a “double-edged sword” in tumors, autophagy can either facilitate or impede tumor growth. The autophagy regulatory network that influences tumor progression and treatment resistance is dependent on cell and tissue types and tumor stages. The connection between autoimmunity and carcinogenesis has not been sufficiently explored in past studies. As a crucial mechanism between the two phenomena, autophagy may play a substantial role, though the specifics remain unclear. Several autophagy modifiers have demonstrated beneficial effects in models of autoimmune disease, emphasizing their therapeutic potential as treatments for autoimmune disorders. The function of autophagy in the tumor microenvironment and immune cells is the subject of intensive study. The objective of this review is to investigate the role of autophagy in the simultaneous genesis of autoimmunity and malignancy, shedding light on both sides of the issue. We believe our work will assist in the organization of current understanding in the field and promote additional research on this urgent and crucial topic.

MDSCs in sepsis-induced immunosuppression and its potential therapeutic targets

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. In sepsis, a complicated immune response is initiated, which varies over time with sustained excessive inflammation and immunosuppression. Identifying a promising way to orchestrate sepsis-induced immunosuppression is a challenge. Myeloid-derived suppressor cells (MDSCs) comprise pathologically activated neutrophils and monocytes with potent immunosuppressive activity. They play an important part in inhibiting innate and adaptive immune responses, and have emerged as part of the immune response in sepsis. MDSCs numbers are persistently high in sepsis patients, and associated with nosocomial infections and other adverse clinical outcomes. However, their characteristics and functional mechanisms during sepsis have not been addressed fully. Our review sheds light on the features and suppressive mechanism of MDSCs. We also review the potential applications of MDSCs as biomarkers and targets for clinical treatment of sepsis.

Relationship between 4-Hydroxynonenal (4-HNE) as Systemic Biomarker of Lipid Peroxidation and Metabolomic Profiling of Patients with Prostate Cancer

An oxidative degradation product of the polyunsaturated fatty acids, 4-hydroxynonenal (4-HNE), is of particular interest in cancer research due to its concentration-dependent pleiotropic activities affecting cellular antioxidants, metabolism, and growth control. Although an increase in oxidative stress and lipid peroxidation was already associated with prostate cancer progression a few decades ago, the knowledge of the involvement of 4-HNE in prostate cancer tumorigenesis is limited. This study investigated the appearance of 4-HNE-protein adducts in prostate cancer tissue by immunohistochemistry using a genuine 4-HNE monoclonal antibody. Plasma samples of the same patients and samples of the healthy controls were also analyzed for the presence of 4-HNE-protein adducts, followed by metabolic profiling using LC-ESI-QTOF-MS and GC-EI-Q-MS. Finally, the analysis of the metabolic pathways affected by 4-HNE was performed. The obtained results revealed the absence of 4-HNE-protein adducts in prostate carcinoma tissue but increased 4-HNE-protein levels in the plasma of these patients. Metabolomics revealed a positive association of different long-chain and medium-chain fatty acids with the presence of prostate cancer. Furthermore, while linoleic acid positively correlated with the levels of 4-HNE-protein adducts in the blood of healthy men, no correlation was obtained for cancer patients indicating altered lipid metabolism in this case. The metabolic pathway of unsaturated fatty acids biosynthesis emerged as significantly affected by 4-HNE. Overall, this is the first study linking 4-HNE adduction to plasma proteins with specific alterations in the plasma metabolome of prostate cancer patients. This study revealed that increased 4-HNE plasma protein adducts could modulate the unsaturated fatty acids biosynthesis pathway. It is yet to be determined if this is a direct result of 4-HNE or whether they are produced by the same underlying mechanisms. Further mechanistic studies are needed to grasp the biological significance of the observed changes in prostate cancer tumorigenesis.

Sema4D silencing increases the sensitivity of nivolumab to B16-F10 resistant melanoma via inhibiting the PI3K/AKT signaling pathway

Melanoma is a common skin tumor that causes a high rate of mortality, especially in Europe, North America and Oceania. Immunosuppressants such as anti-PD-1 have been used in the treatment of malignant melanoma, however, nearly 60% of patients do not respond to these treatments. Sema4D, also called CD100, is expressed in T cells and tumor tissues. Sema4D and its receptor, Plexin-B1, play crucial roles in the process of immune regulation, angiogenesis, and tumor progression. The role of Sema4D in melanoma with anti-PD-1 resistance is poorly understood. Through a combination of molecular biology techniques and in silico analysis, the role of Sema4D in improving anti-PD-L1 sensitivity in melanoma was explored. The results showed that the expression of Sema4D, Plexin-B1 and PD-L1 was significantly increased in B16-F10R cells. Sema4D knockdown synergizes with anti-PD-1 treatment, cell viability, cell invasion and migration were significantly decreased, while the apoptosis was increased, the growth of tumors on the mice was also inhibited. Mechanistically, bioinformatics analysis revealed that Sema4D is involved in the PI3K/AKT signaling pathway; the downregulation of p-PI3K/PI3K and p-AKT/AKT expression were observed in Sema4D knockdown, therefore, nivolumab resistance is related to Sema4D and Sema4D silencing can improve sensitivity to nivolumab via inhibition of the PI3K/AKT signaling pathway.

The immunosuppression pathway of tumor-associated macrophages is controlled by heme oxygenase-1 in glioblastoma patients

The immunosuppressive tumor microenvironment (TME) in glioblastoma (GBM) is mainly driven by tumor-associated macrophages (TAMs). We explored whether their sustained iron metabolism and immunosuppressive activity were correlated, and whether blocking the central enzyme of the heme catabolism pathway, heme oxygenase-1 (HO-1), could reverse their tolerogenic activity. To this end, we investigated iron metabolism in bone marrow-derived macrophages (BMDMs) isolated from GBM specimens and in in vitro-derived macrophages (Mφ) from healthy donor (HD) blood monocytes. We found that HO-1 inhibition abrogated the immunosuppressive activity of both BMDMs and Mφ, and that immunosuppression requires both cell-to-cell contact and soluble factors, as HO-1 inhibition abolished IL-10 release, and significantly reduced STAT3 activation as well as PD-L1 expression. Interestingly, not only did HO-1 inhibition downregulate IDO1 and ARG-2 gene expression, but also reduced IDO1 enzymatic activity. Moreover, T cell activation status affected PD-L1 expression and IDO1 activity, which were upregulated in the presence of activated, but not resting, T cells. Our results highlight the crucial role of HO-1 in the immunosuppressive activity of macrophages in the GBM TME and demonstrate the feasibility of reprogramming them as an alternative therapeutic strategy for restoring immune surveillance.

Targeting CD89 on tumor-associated macrophages overcomes resistance to immune checkpoint blockade

BACKGROUND

Despite the survival benefits observed with immune checkpoint blockade (ICB) treatment-programmed cell death-1/programmed cell death ligand-1 (PD-1/PD-L1), many patients with cancer have not benefited from these agents because of impaired antigen presentation and other resistance mechanisms. To overcome resistance to checkpoint therapy, we designed bispecific antibodies (BsAbs) targeting CD89 and tumor antigens. We demonstrated their immunomodulatory efficacy as a separate treatment strategy or combined with immune checkpoint inhibitors.

METHODS

We have previously generated a heterodimeric one-arm IgG1 Fc-based bispecific antibody. For animal efficacy studies, murine tumors in a humanized transgenic mice model were used to determine the effects of CD89-bispecific antibodies on antigen presentation and immune cell recruitment. The efficacy of the CD89 bispecific antibody against tumors resistant to pembrolizumab was evaluated in double-transgenic mice.

RESULTS

BsAbs targeting CD89 on tumor-associated macrophages (TAMs) increased the ratio of M1:M2 and activated the antigen presentation, leading to increased cytotoxic T cell-mediated tumor regression. CD89-BsAbs also potentiated a combinational antitumor effect with PD-1/PD-L1 inhibitors and overcame the ICB resistance by augmenting cytotoxic T-cell infiltration and reshaping tumor immune microenvironment. In an hCD89/hPD-1 double transgenic mouse model engrafted with pembrolizumab-resistant B16-HER2 tumor cells, the HER2-CD89 bispecific antibody potently inhibited tumor growth.

CONCLUSIONS

CD89 BsAbs targeting tumor antigens and TAMs controlled tumor growth in animal models by improving antigen presentation and T-cell infiltration. Our results suggest a general strategy for overcoming resistance to ICB.

Mechanisms of Resistance and Strategies to Combat Resistance in PD-(L)1 Blockade

Prolonged survival and durable responses in several late-stage cancers such as melanoma and lung cancer have been made possible with the use of immune checkpoint inhibitors targeting the programmed cell-death protein 1 (PD-1) or its ligand PD-L1. While it is prudent to focus on the unprecedented and durable clinical responses, there are subsets of cancer patients that do not respond to immunotherapies or respond early and then relapse later. Many pathways of resistance have been characterized, and more continue to be uncovered. To overcome the development of resistance, an in-depth investigation is necessary to identify alternative immune receptors and signals with the overarching goal of expanding treatment options for those with demonstrated resistance to PD1 checkpoint immunotherapy. In this mini-review, we will discuss the mechanisms by which tumors exhibit resistance to anti-PD-1/PD-L1 immunotherapy and explore strategies to overcome such resistances.

Targeting arginase-1 exerts antitumor effects in multiple myeloma and mitigates bortezomib-induced cardiotoxicity

Multiple myeloma (MM) remains an incurable malignancy of plasma cells despite constantly evolving therapeutic approaches including various types of immunotherapy. Increased arginase activity has been associated with potent suppression of T-cell immune responses in different types of cancer. Here, we investigated the role of arginase 1 (ARG1) in Vκ*MYC model of MM in mice. ARG1 expression in myeloid cells correlated with tumor progression and was accompanied by a systemic drop in ʟ-arginine levels. In MM-bearing mice antigen-induced proliferation of adoptively transferred T-cells was strongly suppressed and T-cell proliferation was restored by pharmacological arginase inhibition. Progression of Vκ*MYC tumors was significantly delayed in mice with myeloid-specific ARG1 deletion. Arginase inhibition effectively inhibited tumor progression although it failed to augment anti-myeloma effects of bortezomib. However, arginase inhibitor completely prevented development of bortezomib-induced cardiotoxicity in mice. Altogether, these findings indicate that arginase inhibitors could be further tested as a complementary strategy in multiple myeloma to mitigate adverse cardiac events without compromising antitumor efficacy of proteasome inhibitors.

Arginase-2-specific cytotoxic T cells specifically recognize functional regulatory T cells

Background

High expression of the metabolic enzyme arginase-2 (ARG2) by cancer cells, regulatory immune cells, or cells of the tumor stroma can reduce the availability of arginine (L-Arg) in the tumor microenvironment (TME). Depletion of L-Arg has detrimental consequences for T cells and leads to T-cell dysfunction and suppression of anticancer immune responses. Previous work from our group has demonstrated the presence of proinflammatory ARG2-specific CD4 T cells that inhibited tumor growth in murine models on activation with ARG2-derived peptides. In this study, we investigated the natural occurrence of ARG2-specific CD8 T cells in both healthy donors (HDs) and patients with cancer, along with their immunomodulatory capabilities in the context of the TME.

Materials and methods

A library of 15 major histocompatibility complex (MHC) class I-restricted ARG2-derived peptides were screened in HD peripheral blood mononuclear cells using interferon gamma (IFN-γ) ELISPOT. ARG2-specific CD8 T-cell responses were identified using intracellular cytokine staining and ARG2-specific CD8 T-cell cultures were established by enrichment and rapid expansion following in vitro peptide stimulation. The reactivity of the cultures toward ARG2-expressing cells, including cancer cell lines and activated regulatory T cells (Tregs), was assessed using IFN-γ ELISPOT and a chromium release assay. The Treg signature was validated based on proliferation suppression assays, flow cytometry and quantitative reverse transcription PCR (RT-qPCR). In addition, vaccinations with ARG2-derived epitopes were performed in the murine Pan02 tumor model, and induction of ARG2-specific T-cell responses was evaluated with IFN-γ ELISPOT. RNAseq and subsequent GO-term and ImmuCC analysis was performed on the tumor tissue.

Results

We describe the existence of ARG2-specific CD8⁺ T cells and demonstrate these CD8⁺ T-cell responses in both HDs and patients with cancer. ARG2-specific T cells recognize and react to an ARG2-derived peptide presented in the context of HLA-B8 and exert their cytotoxic function against cancer cells with endogenous ARG2 expression. We demonstrate that ARG2-specific T cells can specifically recognize and react to activated Tregs with high ARG2 expression. Finally, we observe tumor growth suppression and antitumorigenic immunomodulation following ARG2 vaccination in an in vivo setting.

Conclusion

These findings highlight the ability of ARG2-specific T cells to modulate the immunosuppressive TME and suggest that ARG2-based immunomodulatory vaccines may be an interesting option for cancer immunotherapy.

Drug repurposing in cancer neuroscience: From the viewpoint of the autophagy-mediated innervated niche

Based on the bidirectional interactions between neurology and cancer science, the burgeoning field “cancer neuroscience” has been proposed. An important node in the communications between nerves and cancer is the innervated niche, which has physical contact with the cancer parenchyma or nerve located in the proximity of the tumor. In the innervated niche, autophagy has recently been reported to be a double-edged sword that plays a significant role in maintaining homeostasis. Therefore, regulating the innervated niche by targeting the autophagy pathway may represent a novel therapeutic strategy for cancer treatment. Drug repurposing has received considerable attention for its advantages in cost-effectiveness and safety. The utilization of existing drugs that potentially regulate the innervated niche via the autophagy pathway is therefore a promising pharmacological approach for clinical practice and treatment selection in cancer neuroscience. Herein, we present the cancer neuroscience landscape with an emphasis on the crosstalk between the innervated niche and autophagy, while also summarizing the underlying mechanisms of candidate drugs in modulating the autophagy pathway. This review provides a strong rationale for drug repurposing in cancer treatment from the viewpoint of the autophagy-mediated innervated niche.

Emerging strategies in targeting tumor-resident myeloid cells for cancer immunotherapy

Immune checkpoint inhibitors targeting programmed cell death protein 1, programmed death-ligand 1, and cytotoxic T-lymphocyte-associated protein 4 provide deep and durable treatment responses which have revolutionized oncology. However, despite over 40% of cancer patients being eligible to receive immunotherapy, only 12% of patients gain benefit. A key to understanding what differentiates treatment response from non-response is better defining the role of the innate immune system in anti-tumor immunity and immune tolerance. Teleologically, myeloid cells, including macrophages, dendritic cells, monocytes, and neutrophils, initiate a response to invading pathogens and tissue repair after pathogen clearance is successfully accomplished. However, in the tumor microenvironment (TME), these innate cells are hijacked by the tumor cells and are imprinted to furthering tumor propagation and dissemination. Major advancements have been made in the field, especially related to the heterogeneity of myeloid cells and their function in the TME at the single cell level, a topic that has been highlighted by several recent international meetings including the 2021 China Cancer Immunotherapy workshop in Beijing. Here, we provide an up-to-date summary of the mechanisms by which major myeloid cells in the TME facilitate immunosuppression, enable tumor growth, foster tumor plasticity, and confer therapeutic resistance. We discuss ongoing strategies targeting the myeloid compartment in the preclinical and clinical settings which include: (1) altering myeloid cell composition within the TME; (2) functional blockade of immune-suppressive myeloid cells; (3) reprogramming myeloid cells to acquire pro-inflammatory properties; (4) modulating myeloid cells via cytokines; (5) myeloid cell therapies; and (6) emerging targets such as Siglec-15, TREM2, MARCO, LILRB2, and CLEVER-1. There is a significant promise that myeloid cell-based immunotherapy will help advance immuno-oncology in years to come.

Targeting the antigen processing and presentation pathway to overcome resistance to immune checkpoint therapy

Despite the significant clinical advances with the use of immune checkpoint inhibitors (ICIs) in a wide range of cancer patients, response rates to the therapy are variable and do not always result in long-term tumor regression. The development of ICI-resistant disease is one of the pressing issue in clinical oncology, and the identification of new targets and combination therapies is a crucial point to improve response rates and duration. Antigen processing and presentation (APP) pathway is a key element for an efficient response to ICI therapy. Indeed, malignancies that do not express tumor antigens are typically poor infiltrated by T cells and unresponsive to ICIs. Therefore, improving tumor immunogenicity potentially increases the success rate of ICI therapy. In this review, we provide an overview of the key elements of the APP machinery that can be exploited to enhance tumor immunogenicity and increase the efficacy of ICI-based immunotherapy.

Targeted Arginine Metabolism Therapy: A Dilemma in Glioma Treatment

Efforts in the treatment of glioma which is the most common primary malignant tumor of the central nervous system, have not shown satisfactory results despite a comprehensive treatment model that combines various treatment methods, including immunotherapy. Cellular metabolism is a determinant of the viability and function of cancer cells as well as immune cells, and the interplay of immune regulation and metabolic reprogramming in tumors has become an active area of research in recent years. From the perspective of metabolism and immunity in the glioma microenvironment, we elaborated on arginine metabolic reprogramming in glioma cells, which leads to a decrease in arginine levels in the tumor microenvironment. Reduced arginine availability significantly inhibits the proliferation, activation, and function of T cells, thereby promoting the establishment of an immunosuppressive microenvironment. Therefore, replenishment of arginine levels to enhance the anti-tumor activity of T cells is a promising strategy for the treatment of glioma. However, due to the lack of expression of argininosuccinate synthase, gliomas are unable to synthesize arginine; thus, they are highly dependent on the availability of arginine in the extracellular environment. This metabolic weakness of glioma has been utilized by researchers to develop arginine deprivation therapy, which ‘starves’ tumor cells by consuming large amounts of arginine in circulation. Although it has shown good results, this treatment modality that targets arginine metabolism in glioma is controversial. Exploiting a suitable strategy that can not only enhance the antitumor immune response, but also “starve” tumor cells by regulating arginine metabolism to cure glioma will be promising.

Diurnal Expression of PD-1 on Tumor-Associated Macrophages Underlies the Dosing Time-Dependent Antitumor Effects of the PD-1/PD-L1 Inhibitor BMS-1 in B16/BL6 Melanoma-Bearing Mice

Cancer cells have acquired several pathways to escape from host immunity in the tumor microenvironment. Programmed death 1 (PD-1) receptor and its ligand PD-L1 are involved in the key pathway of tumor immune escape, and immune checkpoint therapy targeting PD-1 and PD-L1 has been approved for the treatment of patients with certain types of malignancies. Although PD-1 is a well-characterized receptor on T cells, the immune checkpoint receptor is also expressed on tumor-associated macrophages (TAM), a major immune component of the tumor microenvironment. In this study, we found significant diurnal oscillation in the number of PD-1-expressing TAMs collected from B16/BL6 melanoma-bearing mice. The levels of Pdcd1 mRNA, encoding PD-1, in TAMs also fluctuated in a diurnal manner. Luciferase reporter and bioluminescence imaging analyses revealed that a NF-κB response element in the upstream region of the Pdcd1 gene is responsible for its diurnal expression. A circadian regulatory component, DEC2, whose expression in TAMs exhibited diurnal oscillation, periodically suppressed NF-κB-induced transactivation of the Pdcd1 gene, resulting in diurnal expression of PD-1 in TAMs. Furthermore, the antitumor efficacy of BMS-1, a small molecule inhibitor of PD-1/PD-L1, was enhanced by administering it at the time of day when PD-1 expression increased on TAMs. These findings suggest that identification of the diurnal expression of PD-1 on TAMs is useful for selecting the most appropriate time of day to administer PD-1/PD-L1 inhibitors.

IMPLICATIONS

Selecting the most appropriate dosing time of PD-1/PD-L1 inhibitors may aid in developing cancer immunotherapy with higher efficacy.

Overcoming Immune Resistance With Radiation Therapy in Prostate Cancer

Prostate cancer is the second most common cancer in men and represents a significant healthcare burden worldwide. Therapeutic options in the metastatic castration-resistant setting remain limited, despite advances in androgen deprivation therapy, precision medicine and targeted therapies. In this review, we summarize the role of immunotherapy in prostate cancer and offer perspectives on opportunities for future development, based on current knowledge of the immunosuppressive tumor microenvironment. Furthermore, we discuss the potential for synergistic therapeutic strategies with modern radiotherapy, through modulation of the tumor microenvironment. Emerging clinical and pre-clinical data suggest that radiation can convert immune desert tumors into an inflamed immunological hub, potentially sensitive to immunotherapy.

Autoimmunity and Cancer-Two Sides of the Same Coin

Autoimmune disease results from the immune response against self-antigens, while cancer develops when the immune system does not respond to malignant cells. Thus, for years, autoimmunity and cancer have been considered as two separate fields of research that do not have a lot in common. However, the discovery of immune checkpoints and the development of anti-cancer drugs targeting PD-1 (programmed cell death receptor 1) and CTLA-4 (cytotoxic T lymphocyte antigen 4) pathways proved that studying autoimmune diseases can be extremely helpful in the development of novel anti-cancer drugs. Therefore, autoimmunity and cancer seem to be just two sides of the same coin. In the current review, we broadly discuss how various regulatory cell populations, effector molecules, genetic predisposition, and environmental factors contribute to the loss of self-tolerance in autoimmunity or tolerance induction to cancer. With the current paper, we also aim to convince the readers that the pathways involved in cancer and autoimmune disease development consist of similar molecular players working in opposite directions. Therefore, a deep understanding of the two sides of immune tolerance is crucial for the proper designing of novel and selective immunotherapies.

Arginase: An emerging and promising therapeutic target for cancer treatment

Arginase is a key hydrolase in the urea cycle that hydrolyses L-arginine to urea and L-ornithine. Increasing number of studies in recent years demonstrate that two mammalian arginase isoforms, arginase 1 (ARG1) and arginase 2 (ARG2), were aberrantly upregulated in various types of cancers, and played crucial roles in the regulation of tumor growth and metastasis through various mechanisms such as regulating L-arginine metabolism, influencing tumor immune microenvironment, etc. Thus, arginase receives increasing focus as an attractive target for cancer therapy. In this review, we provide a comprehensive overview of the physiological and biological roles of arginase in a variety of cancers, and shed light on the underlying mechanisms of arginase mediating cancer cells growth and development, as well as summarize the recent clinical research advances of targeting arginase for cancer therapy.

Nitric oxide favours tumour-promoting inflammation through mitochondria-dependent and -independent actions on macrophages

Production of nitric oxide (NO) has been demonstrated in several malignancies, however its role remains not fully understood, specifically in relation to the metabolic and functional implications that it may have on immune cells participating in tumorigenesis. Here, we show that inducible NO synthase (iNOS) is expressed in cancers of the colon and the prostate, mainly by tumour cells, and NO generation is evidenced by widespread nitrotyrosine (NT) staining in tumour tissue. Furthermore, presence of NT is observed in the majority of tumour-associated macrophages (TAMs), despite low iNOS expression by these cells, suggesting that NO from the tumour microenvironment affects TAMs. Indeed, using a co-culture model, we demonstrate that NO produced by colon and prostate cancer cells is sufficient to induce NT formation in neighbouring macrophages. Moreover, exposure to exogenous NO promotes mitochondria-dependent and -independent changes in macrophages, which orientate their polarity towards an enhanced pro-inflammatory phenotype, whilst decreasing antigen-presenting function and wound healing capacity. Abrogating endogenous NO generation in murine macrophages, on the other hand, decreases their pro-inflammatory phenotype. These results suggest that the presence of NO in cancer may regulate TAM metabolism and function, favouring the persistence of inflammation, impairing healing and subverting adaptive immunity responses.

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Nitric oxide (NO) from the cancer microenvironment acts on tumour-associated macrophages (TAMs).

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NO induces a phenotypic shift in macrophages through mitochondria-dependent and -independent pathways.

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NO favours pro-inflammatory cytokine production whilst decreasing macrophage function as antigen presenting cell.

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NO impairs repair function of macrophages.

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Presence of NO in cancer may regulate TAM metabolism and function, favouring tumour-promoting inflammation.

Personalizing First-Line Management of Metastatic Renal Cell Carcinoma: Leveraging Current and Novel Therapeutic Options

The treatment of metastatic renal cell carcinoma (RCC) has been revolutionized by advances in immunotherapeutic and targeted agents. Therapeutic approaches to RCC in these categories have recently evolved to include immune checkpoint inhibitors, novel vascular endothelial growth factor receptor-targeting tyrosine kinase inhibitors, and combinations of those agents. Multiple regimens within each category have been approved for use in the first-line treatment of clear cell and non-clear cell RCC. However, few of these regimens have been directly compared, leading to a new clinical challenge for physicians: how to select a first-line treatment regimen for an individual patient from among multiple approved options. In the modern era of RCC management, the initial treatment selection therefore becomes highly personalized and depends on numerous patient-specific factors, including histopathologic and clinical features of the disease, comorbid conditions, and psychosocial and economic factors. This review details current first-line treatment options for the management of metastatic RCC and proposes a framework whereby treatment selection can be optimized for individual patients.

Targeting tumor innervation: premises, promises, and challenges

A high intratumoral nerve density is correlated with poor survival, high metastasis, and high recurrence across multiple solid tumor types. Recent research has revealed that cancer cells release diverse neurotrophic factors and exosomes to promote tumor innervation, in addition, infiltrating nerves can also mediate multiple tumor biological processes via exosomes and neurotransmitters. In this review, through seminal studies establishing tumor innervation, we discuss the communication between peripheral nerves and tumor cells in the tumor microenvironment (TME), and revealed the nerve-tumor regulation mechanisms on oncogenic process, angiogenesis, lymphangiogenesis, and immunity. Finally, we discussed the promising directions of ‘old drugs newly used’ to target TME communication and clarified a new line to prevent tumor malignant capacity.

The evolving role of immune cells in prostate cancer

Prostate cancer is the most commonly diagnosed cancer and the second leading cause of cancer-related death among men in western countries. Androgen deprivation therapy (ADT) is considered the standard therapy for recurrent prostate cancer; however, this therapy may lead to ADT resistance and tumor progression, which seems to be regulated by epithelial-mesenchymal transition (EMT) and/or neuroendocrine differentiation (NED). In addition, recent data suggested the involvement of either adaptive or innate infiltrated immune cells in the initiation, progression, metastasis, and treatment of prostate cancer. In this review, we outlined the characteristics and roles of these immune cells in the initiation, progression, metastasis, and treatments of prostate cancer. We also summarized the current therapeutic strategies in targeting immune cells of the prostate tumor microenvironment.

Arginine and Arginases Modulate Metabolism, Tumor Microenvironment and Prostate Cancer Progression

Arginine availability and activation of arginine-related pathways at cancer sites have profound effects on the tumor microenvironment, far beyond their well-known role in the hepatic urea cycle. Arginine metabolism impacts not only malignant cells but also the surrounding immune cells behavior, modulating growth, survival, and immunosurveillance mechanisms, either through an arginase-mediated effect on polyamines and proline synthesis, or by the arginine/nitric oxide pathway in tumor cells, antitumor T-cells, myeloid-derived suppressor cells, and macrophages. This review presents evidence concerning the impact of arginine metabolism and arginase activity in the prostate cancer microenvironment, highlighting the recent advances in immunotherapy, which might be relevant for prostate cancer. Even though further research is required, arginine deprivation may represent a novel antimetabolite strategy for the treatment of arginine-dependent prostate cancer.

The Role of Non-essential Amino Acids in T Cell Function and Anti-tumour Immunity

T cell activation, differentiation and proliferation is dependent upon and intrinsically linked to a capacity to modulate and adapt cellular metabolism. Antigen-induced activation stimulates a transcriptional programme that results in metabolic reprogramming, enabling T cells to fuel anabolic metabolic pathways and provide the nutrients to sustain proliferation and effector responses. Amino acids are key nutrients for T cells and have essential roles as building blocks for protein synthesis as well as in numerous metabolic pathways. In this review, we discuss the roles for uptake and biosynthesis of non-essential amino acids in T cell metabolism, activation and effector function. Furthermore, we highlight the effects of amino acid metabolism and depletion by cancer cells on T cell anti-tumour function and discuss approaches to modulate and improve T cell metabolism for improved anti-tumour function in these nutrient-depleted microenvironments.

Combining inhibition of galectin-3 with and before a therapeutic vaccination is critical for the prostate-tumor-free outcome

BACKGROUND

Prostate cancer (PCa) is a major health problem worldwide. Taxol derivatives-based chemotherapies or immunotherapies are usually proposed depending on the symptomatic status of the patient. In the case of immunotherapy, tumors develop robust immune escape mechanisms that abolish any protective response, and to date why prostate cancer is one of the most resistant diseases remains unresolved.

METHODS

By using a combination of clinical data to study the transcriptome of metastasis samples from patients with castration-refractory prostate cancer, and state of the art cellular and molecular biology assays in samples from tumor-bearing mice that have been submitted to surgical resection of the tumor before receiving a vaccination, we answered several essential questions in the field of immunotherapy for prostate cancer. We also used two different methods to inhibit the expression of galectin-3 (Gal-3) in tumor cells: a stable RNA interference method to control the expression of this galectin efficiently only in tumor cells, and low and non-cytotoxic doses of docetaxel to easily transfer our findings to clinical settings.

RESULTS

Herein, we show for the first time that Gal-3 expressed by prostate tumor cells is the main immune checkpoint responsible for the failure of vaccine-based immunotherapy. Our results show that low and non-cytotoxic doses of docetaxel lead to the inhibition of Gal-3 expression in PCa cells as well as in clinical samples of patients with metastatic and castration-resistant PCa promoting a Th1 response. We thus optimized a prostate cancer animal model that undergoes surgical resection of the tumor to mimic prostatectomy usually performed in patients. Importantly, using Gal-3-knocked down-PCa cells or low and non-cytotoxic doses of taxane before vaccination, we were able to highly control tumor recurrence through a direct impact on the proliferation and infiltration of CD8+ cytotoxic T.

CONCLUSIONS

Thus, Gal-3 expression by PCa cells is a crucial inhibitor for the success of immunotherapy, and low doses of docetaxel with non-cytotoxic effect on leukocyte survival could be used before immunotherapy for all patients with PCa to reduce the expression of this critical negative immune checkpoint, pre-conditioning the tumor-microenvironment to activate an antitumor immune response and promote tumor-free outcome.

The Role of Somatic Mutations on the Immune Response of the Tumor Microenvironment in Prostate Cancer

Immunotherapy has improved patient survival in many types of cancer, but for prostate cancer, initial results with immunotherapy have been disappointing. Prostate cancer is considered an immunologically excluded or cold tumor, unable to generate an effective T-cell response against cancer cells. However, a small but significant percentage of patients do respond to immunotherapy, suggesting that some specific molecular subtypes of this tumor may have a better response to checkpoint inhibitors. Recent findings suggest that, in addition to their function as cancer genes, somatic mutations of PTEN, TP53, RB1, CDK12, and DNA repair, or specific activation of regulatory pathways, such as ETS or MYC, may also facilitate immune evasion of the host response against cancer. This review presents an update of recent discoveries about the role that the common somatic mutations can play in changing the tumor microenvironment and immune response against prostate cancer. We describe how detailed molecular genetic analyses of the tumor microenvironment of prostate cancer using mouse models and human tumors are providing new insights into the cell types and pathways mediating immune responses. These analyses are helping researchers to design drug combinations that are more likely to target the molecular and immunological pathways that underlie treatment failure.

How to turn up the heat on the cold immune microenvironment of metastatic prostate cancer

BACKGROUND

Advanced prostate cancer remains one of the most common and deadly cancers, despite advances in treatment options. Immunotherapy has provided little benefit to a majority of patients, largely due to the immunosuppressive tumor microenvironment that gives rise to inherently "cold tumors". In this review, we discuss the immunopathology of the prostate tumor microenvironment, strategies for treating prostate cancer with immunotherapies, and a perspective on potential approaches to enhancing the efficacy of immunotherapies.

METHODS

Databases, including PubMed, Google Scholar, and Cochrane, were searched for articles relevant to the immunology of prostate cancer. We discuss the impact of different types of treatments on the immune system, and potential mechanisms through which prostate cancer evades the immune system.

RESULTS

The tumor microenvironment associated with prostate cancer is highly immunosuppressive due to (1) the function of regulatory T cells, tumor-associated macrophages, and myeloid-derived suppressor cells (MDSCs), (2) the cytokine milieu secreted by tumor stromal cells and fibroblasts, and (3) the production of adenosine via prostatic acid phosphatase. Both adenosine and tumor growth factor beta (TGF-beta) serve as potent immunosuppressive molecules that could also represent potential therapeutic targets. While there have been many immunotherapy trials in prostate cancer, the majority of these trials have targeted a single immunosuppressive mechanism resulting in limited clinical efficacy. Future approaches will require the integration of improved patient selection as well as use of combination therapies to address multiple mechanisms of resistance.

CONCLUSION

Prostate cancer inherently gives rise to multiple immunosuppressive mechanisms that have been difficult to overcome with any one immunotherapeutic approach. Enhancing the clinical activity of immunotherapies will require strategic combinations of multiple therapies to address the emerging mechanisms of tumor immune resistance.

Annexin A1 as a Regulator of Immune Response in Cancer

Annexin A1 is a 37 kDa phospholipid-binding protein that is expressed in many tissues and cell types, including leukocytes, lymphocytes and epithelial cells. Although Annexin A1 has been extensively studied for its anti-inflammatory activity, it has been shown that, in the cancer context, its activity switches from anti-inflammatory to pro-inflammatory. Remarkably, Annexin A1 shows pro-invasive and pro-tumoral properties in several cancers either by eliciting autocrine signaling in cancer cells or by inducing a favorable tumor microenvironment. Indeed, the signaling of the N-terminal peptide of AnxA1 has been described to promote the switching of macrophages to the pro-tumoral M2 phenotype. Moreover, AnxA1 has been described to prevent the induction of antigen-specific cytotoxic T cell response and to play an essential role in the induction of regulatory T lymphocytes. In this way, Annexin A1 inhibits the anti-tumor immunity and supports the formation of an immunosuppressed tumor microenvironment that promotes tumor growth and metastasis. For these reasons, in this review we aim to describe the role of Annexin A1 in the establishment of the tumor microenvironment, focusing on the immunosuppressive and immunomodulatory activities of Annexin A1 and on its interaction with the epidermal growth factor receptor.

PMA induces the differentiation of monocytes into immunosuppressive MDSCs

The induction of immune tolerance without the use of immunosuppressive drugs is a crucial problem in organ transplantation. The use of myeloid-derived suppressor cells (MDSCs) as a cell-based adjuvant immunosuppressive therapy is a bright clinical prospect in organ transplantation. MDSCs with stable immunosuppressive activities can be used to treat immune-related diseases. In this study, macrophage colony-stimulating factor (M-CSF) was used to promote myeloid progenitor cell differentiation, and phorbol 12-myristate 13-acetate (PMA) was added to induce MDSCs at the later stage of induction in vitro. Cell phenotypes were detected by flow cytometry and mRNA was detected by real-time-polymerase chain reaction (RT-PCR). A mouse skin transplantation model was used to investigate the cell inhibitory function. The combination of PMA and M-CSF induced the differentiation of myeloid-derived monocytes into MDSCs. MDSCs were found to induce immune tolerance by inhibiting the proliferation and activation of T cells, promoting cytokine secretion and inducing T cell transformation to regulatory T cells (T_reg ). PMA significantly up-regulated the expression of Arg-1 and the Arg-1 protein expression in MDSCs and arginase 1 (Arg-1) inhibitor nor-NOHA reversed the MDSC immunosuppressive activity, indicating the involvement of the Arg-1 pathway in MDSC-mediated immunosuppression. M-CSF + PMA-induced MDSCs also significantly prolonged the survival time of skin grafts in mice, showing that MDSCs exert immunosuppressive effects in vivo. We describe a novel scheme to induce immunosuppressive MDSCs in vitro. MDSCs induced by M-CSF with PMA showed stable immunosuppression. MDSCs induced by this protocol may benefit patients with organ transplantation through immune regulation.

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

Advancing to the era of cancer immunotherapy

Cancer greatly affects the quality of life of humans worldwide and the number of patients suffering from it is continuously increasing. Over the last century, numerous treatments have been developed to improve the survival of cancer patients but substantial progress still needs to be made before cancer can be truly cured. In recent years, antitumor immunity has become the most debated topic in cancer research and the booming development of immunotherapy has led to a new epoch in cancer therapy. In this review, we describe the relationships between tumors and the immune system, and the rise of immunotherapy. Then, we summarize the characteristics of tumor‐associated immunity and immunotherapeutic strategies with various molecular mechanisms by showing the typical immune molecules whose antibodies are broadly used in the clinic and those that are still under investigation. We also discuss important elements from individual cells to the whole human body, including cellular mutations and modulation, metabolic reprogramming, the microbiome, and the immune contexture. In addition, we also present new observations and technical advancements of both diagnostic and therapeutic methods aimed at cancer immunotherapy. Lastly, we discuss the controversies and challenges that negatively impact patient outcomes.

Increased Arginase1 expression in tumor microenvironment promotes mammary carcinogenesis via multiple mechanisms

Arginine metabolism plays a significant role in regulating cell function, affecting tumor growth and metastatization. To study the effect of the arginine-catabolizing enzyme Arginase1 (ARG1) on tumor microenvironment, we generated a mouse model of mammary carcinogenesis by crossbreeding a transgenic mouse line overexpressing ARG1 in macrophages (FVBArg+/+) with the MMTV-Neu mouse line (FVBNeu+/+). This double transgenic line (FVBArg+/-;Neu+/+) showed a significant shortening in mammary tumor latency, and an increase in the number of mammary nodules. Transfer of tumor cells from FVBNeu+/+ into either FVB wild type or FVBArg+/+ mice resulted in increase regulatory T cells in the tumor infiltrate, suggestive of an impaired antitumor immune response. However, we also found increased frequency of tumor stem cells in tumors from FVBArg+/-;Neu+/+ transgenic compared with FVBNeu+/+ mice, suggesting that increased arginine metabolism in mammary tumor microenvironment may supports the cancer stem cells niche. We provide in vivo evidence of a novel, yet unexploited, mechanism through which ARG1 may contribute to tumor development.

Immunometabolism in the Tumor Microenvironment

Advances in immunotherapy have underscored the importance of antitumor immune responses in controlling cancer. However, the tumor microenvironment (TME) imposes several obstacles to the proper function of immune cells, including a metabolically challenging and immunosuppressive microenvironment. The increased metabolic activity of tumor cells can lead to the depletion of key nutrients required by immune cells and the accumulation of byproducts that hamper antitumor immunity. Furthermore, the presence of suppressive immune cells, such as regulatory T cells and myeloid-derived suppressor cells, and the expression of immune inhibitory receptors can negatively impact immune cell metabolism and function. This review summarizes the metabolic reprogramming that is characteristic of various immune cell subsets, discusses how the metabolism and function of immune cells are shaped by the TME, and highlights how therapeutic interventions aimed at improving the metabolic fitness of immune cells and alleviating the metabolic constraints in the TME can boost antitumor immunity.

Immune and metabolic checkpoints blockade: Dual wielding against tumors

Recent advances in cancer immunotherapy have raised hopes for treating cancers that are resistant to conventional therapies. Among the various immunotherapy methods, the immune checkpoint (IC) blockers were more promising and have paved their way to the clinic. Tumor cells induce the expression of ICs on the immune cells and derive them to a hyporesponsive exhausted phenotype. IC blockers could hinder immune exhaustion in the tumor microenvironment and reinvigorate immune cells for an efficient antitumor response. Despite the primary success of IC blockers in the clinic, the growing numbers of refractory cases require an in-depth study of the cellular and molecular mechanisms underlying IC expression and function. Immunometabolism is recently found to be a key factor in the regulation of immune responses. Activated or exhausted immune cells exploit different metabolic pathways. Tumor cells can suppress antitumor responses via immunometabolism alteration. Therefore, it is expected that concurrent targeting of ICs and immunometabolism pathways can cause immune cells to restore their antitumor activity. In this review, we dissected the reciprocal interactions of immune cell metabolism with expression and signaling of ICs in the tumor microenvironment. Recent findings on dual targeting of ICs and metabolic checkpoints have also been discussed.

Smoothing T cell roads to the tumor: Chemokine post-translational regulation

We described a novel tumor-associated immunosuppressive mechanism based on post-translational modifications of chemokines by reactive nitrogen species (RNS). To overcome tumor immunosuppressive hindrances, we designed and developed a new drug, AT38, that inhibits RNS generation at the tumor site. Combinatorial approaches with AT38 boost the effectiveness of cancer immunotherapy protocols.

Metabolism of Amino Acids in Cancer

Metabolic reprogramming has been widely recognized as a hallmark of malignancy. The uptake and metabolism of amino acids are aberrantly upregulated in many cancers that display addiction to particular amino acids. Amino acids facilitate the survival and proliferation of cancer cells under genotoxic, oxidative, and nutritional stress. Thus, targeting amino acid metabolism is becoming a potential therapeutic strategy for cancer patients. In this review, we will systematically summarize the recent progress of amino acid metabolism in malignancy and discuss their interconnection with mammalian target of rapamycin complex 1 (mTORC1) signaling, epigenetic modification, tumor growth and immunity, and ferroptosis. Finally, we will highlight the potential therapeutic applications.

Elevated gaseous luminal nitric oxide and circulating IL-8 as features of Helicobacter pylori-induced gastric inflammation

BACKGROUND

Gastric nitric oxide (NO) production in response to Helicobacter pylori via inducible nitric oxide synthase (iNOS) is suggested as a biomarker of inflammation and cytotoxicity. The aim of this study was to investigate relationships between gastric [NO], immunological biomarkers and histopathology.

MATERIALS AND METHODS

Esophagogastroduodenoscopy was done in 96 dyspepsia patients. Luminal [NO] was measured by chemiluminescence. Biopsies were taken from gastric antrum and corpus for culture and histopathology. H. pylori IgG was detected by immunoblot assay. Biobanked plasma from 76 dyspepsia patients (11 H. pylori positives) was analyzed for 39 cytokines by multiplexed ELISA.

RESULTS

H. pylori-positive patients had higher [NO] (336 ± 26 ppb, mean ± 95% CI, n = 77) than H. pylori-negative patients (128 ± 47 ppb, n = 19) (P < 0.0001). Histopathological changes were found in 99% of H. pylori-positive and 37% of H. pylori-negative patients. Histopathological concordance was 78-100% between corpus and antrum. Correlations were found between gastric [NO] and severity of acute, but not chronic, inflammation. Plasma IL-8 (increased in H. pylori positives) had greatest difference between positive and negative groups, with eotaxin, MIP-1β, MCP-4, VEGF-A, and VEGF-C also higher (P < 0.004 to P < 0.032). Diagnostic odds ratios using 75% cut-off concentration were 7.53 for IL-8, 1.15 for CRP, and 2.88 for gastric NO.

CONCLUSIONS

Of the parameters tested, increased gastric [NO] and circulating IL-8 align most consistently and selectively in H. pylori-infected patients. Severity of mucosal inflammatory changes is proportional to luminal [NO], which might be tied to IL-8 production. It is proposed that IL-8 be further investigated as a blood biomarker of treatment outcomes.

The Expression of CD74-Regulated Inflammatory Markers in Stage IV Melanoma: Risk of CNS Metastasis and Patient Survival

Simple Summary

Although many immunotherapies produce positive initial clinical responses, most advanced cancer patients recur so that there is an urgent need to identify and counteract both the intrinsic resistance as well as acquired mechanisms. During our studies on the mechanisms of resistance, we have identified a set of related protein markers, which we now employ to generate a useful signature of, associated with microenvironmental oxidative stress. Our study examines inflammatory marker expression in stage IV melanoma that are associated with survival outcome and risk of developing central nervous system (CNS) metastasis. Our data here presents CD74 as a prognostic tumor marker associated with good survival in stage IV melanoma. Additionally, the tumor cell nitrotyrosine (NT) expression predicts a greater risk of developing CNS metastasis in those patients. Our understanding of complex cancer cell and their response in the chronic inflammation environment would help us develop better treatments for melanoma.

Abstract

Innate inflammatory features have been found in melanoma tumors from patients at all stages, and molecular analysis has identified definitive inflammatory proteins expressed by tumors cells in patients who presents the worst prognosis. We have previously observed weakened outcomes in patients with constitutive expression of inducible nitric oxide synthase (iNOS), macrophage migration inhibitory factor (MIF) and improved outcomes with CD74 expression in stage III melanoma. In our current study, we tested our hypothesis on CD74-regulated inflammatory markers’ expression in stage IV melanoma tumors whether the signature is associated with survival outcome and/or risk of developing CNS metastasis. We retrospectively identified 315 patients with stage IV melanoma. In a tissue microarray (TMA), we examined the expression of cells with CD74, its receptor MIF, and downstream inflammatory markers iNOS, nitrotyrosine (NT), cyclooxygenase (COX)-2 and microsomal prostaglandin E synthase-1 (mPGES1). We analyzed the association of those inflammatory markers with overall survival time (OS) and time to CNS metastasis using Kaplan–Meier survival analyses. Our data validates CD74 as a useful prognostic tumor cell protein marker associated with favorable OS as in stage III melanomas, while the tumor NT expression strongly predicts an increased risk of developing CNS metastasis (p = 0.0008) in those patients.

The Role of Nitric Oxide in Cancer: Master Regulator or NOt?

Nitric oxide (NO) is a key player in both the development and suppression of tumourigenesis depending on the source and concentration of NO. In this review, we discuss the mechanisms by which NO induces DNA damage, influences the DNA damage repair response, and subsequently modulates cell cycle arrest. In some circumstances, NO induces cell cycle arrest and apoptosis protecting against tumourigenesis. NO in other scenarios can cause a delay in cell cycle progression, allowing for aberrant DNA repair that promotes the accumulation of mutations and tumour heterogeneity. Within the tumour microenvironment, low to moderate levels of NO derived from tumour and endothelial cells can activate angiogenesis and epithelial-to-mesenchymal transition, promoting an aggressive phenotype. In contrast, high levels of NO derived from inducible nitric oxide synthase (iNOS) expressing M1 and Th1 polarised macrophages and lymphocytes may exert an anti-tumour effect protecting against cancer. It is important to note that the existing evidence on immunomodulation is mainly based on murine iNOS studies which produce higher fluxes of NO than human iNOS. Finally, we discuss different strategies to target NO related pathways therapeutically. Collectively, we present a picture of NO as a master regulator of cancer development and progression.

A review of fasting effects on the response of cancer to chemotherapy

BACKGROUND & AIMS

Studies suggest that fasting before or during chemotherapy may induce differential stress resistance, reducing the adverse effects of chemotherapy and enhancing the efficacy of drugs. In this article, we review the effects of fasting, including intermittent, periodic, water-only short-term fasting, and caloric restriction on the responsiveness of tumor cells to cytotoxic drugs, their protective effect on normal cells, and possible mechanisms of action.

METHODS

We could not perform a systematic review due to the wide variation in the study population, design, dependent measures, and outcomes (eg, type of cancer, treatment variation, experimental setting, etc.). However, a systematic approach to search and review literature was used. The electronic databases PubMed (MEDLINE), Scopus, and Embase were searched up to July 2020.

RESULTS

Fasting potentially improves the response of tumor cells to chemotherapy by (1) repairing DNA damage in normal tissues (but not tumor cells); (2) upregulating autophagy flux as a protection against damage to organelles and some cancer cells; (3) altering apoptosis and increasing tumor cells' sensitivity to the apoptotic stimuli, and preventing apoptosis-mediated damage to normal cells; (4) depleting regulatory T cells and improving the stimulation of CD8 cells; and (5) accumulating unfolded proteins and protecting cancer cells from immune surveillance. We also discuss how 'fasting-mimicking diet' as a modified form of fasting enables patients to eat a low calorie, low protein, and low sugar diet while achieving similar metabolic outcomes of fasting.

CONCLUSION

This review suggests the potential benefits of fasting in combination with chemotherapy to reduce tumor progression and increase the effectiveness of chemotherapy. However, with limited human trials, it is not possible to generalize the findings from animal and in vitro studies. More human studies with adequate sample size and follow-ups are required to confirm these findings.

Galectin-3 in Prostate Cancer Stem-Like Cells Is Immunosuppressive and Drives Early Metastasis

Galectin-3 (Gal-3) is an extracellular matrix glycan-binding protein with several immunosuppressive and pro-tumor functions. The role of Galectin-3 in cancer stem-like cells (CSCs) is poorly investigated. Here, we show that prostate CSCs also colonizing prostate-draining lymph nodes of transgenic adenocarcinoma of the mouse prostate (TRAMP) mice overexpress Gal-3. Gal-3 contributes to prostate CSC-mediated immune suppression because either Gal-3 silencing in CSCs, or co-culture of CSCs and T cells in the presence of the Gal-3 inhibitor N-Acetyl-D-lactosamine rescued T cell proliferation. N-Acetyl-D-lactosamine also rescued the proliferation of T cells in prostate-draining lymph nodes of TRAMP mice affected by prostate intraepithelial neoplasia. Additionally, Gal-3 impacted prostate CSC tumorigenic and metastatic potential in vivo, as Gal-3 silencing in prostate CSCs reduced both primary tumor growth and secondary invasion. Gal-3 was also found expressed in more differentiated prostate cancer cells, but with different intracellular distribution as compared to CSCs, which suggests different functions of Gal-3 in the two cell populations. In fact, the prevalent nuclear and cytoplasmic distribution of Gal-3 in prostate CSCs made them less susceptible to apoptosis, when compared to more differentiated prostate cancer cells, in which Gal-3 was predominantly intra-cytoplasmic. Finally, we found Gal-3 expressed in human and mouse prostate intraepithelial neoplasia lesions and in metastatic lymph nodes. All together, these findings identify Gal-3 as a key molecule and a potential therapeutic target already in the early phases of prostate cancer progression and metastasis.

The Prognostic Value of Indoleamine-2,3-Dioxygenase Gene Expression in Urine of Prostate Cancer Patients Undergoing Radical Prostatectomy as First Treatment of Choice

Prostate cancer (PCa) is a slow-growing tumor representing one of the major causes of all new cancer cases and cancer mortality in men worldwide. Although screening methods for PCa have substantially improved, the outcome for patients with advanced PCa remains poor. The elucidation of the molecular mechanism that drives the progression from a slow-growing, organ-confined tumor to a highly invasive and castration-resistant PCa (CRPC) is therefore important. We have already proved the diagnostic potential of indoleamine-2,3-dioxygenase (IDO) when detected in urine of individuals at risk of developing PCa. The aim of this study was to implement IDO as a prognostic marker for PCa patients undergoing surgical treatment. We have thus conducted an observational study by collecting 100 urine samples from patients undergoing radical prostatectomy as first treatment of choice. To test the integrity of our investigation, scale dilution cells of an established PC3 cell line were added to urine of healthy donors and used for gene expression analysis by a TaqMan assay on the catalytic part of IDO mRNA. Our data show that the quantification of IDO mRNA in urine of patients has a very promising ability to identify patients at high risk of cancer advancement, as defined by Gleason score. Our goal is to lay the groundwork to develop a superior test for PCa. The data generated are thus necessary (i) to strengthen the IDO-based diagnostic/prognostic test and (ii) to provide patients and clinicians with an affordable and easy screening test.