Peroxynitrite in the tumor microenvironment changes the profile of antigens allowing escape from cancer immunotherapy

The heterogeneity of neutrophils in cancer and its implication for therapeutic targeting

Neutrophils have a pivotal role in safeguarding the host against pathogens and facilitating tissue remodeling. They possess a large array of tools essential for executing these functions. Neutrophils have a critical role in cancer, where they are largely associated with negative clinical outcome and resistance to therapy. However, the specific role of neutrophils in cancer is complex and controversial, owing to their high functional diversity and acute sensitivity to the microenvironment. In this Perspective, we discuss the accumulated evidence that suggests that the functional diversity of neutrophils can be ascribed to two principal functional states, each with distinct characteristics: classically activated neutrophils and pathologically activated immunosuppressive myeloid-derived suppressor cells. We discuss how the antimicrobial factors in neutrophils can contribute to tumor progression and the fundamental mechanisms that govern the pathologically activated myeloid-derived suppressor cells. These functional states play divergent roles in cancer and thus require separate consideration in therapeutic targeting.

[Myeloid-derived suppressor cells as important factors and potential targets for breast cancer progression]

Recurrence and metastasis remain the leading cause of death in breast cancer patients due to the lack of effective treatment. A microenvironment suitable for cancer cell growth, referred to as pre-metastatic niche (PMN), is formed in distant organs before metastasis occurs. Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of immature myeloid cells with immunosuppressive effects. They can expand in large numbers in breast cancer patients and participate in the formation of PMN. MDSCs can remodel the extracellular matrix of pulmonary vascular endothelial cells and recruit cancer stem cells to promote the lung metastasis of breast cancer. Furthermore, MDSCs facilitate immune evasion of breast cancer cells to impact the efficacy of immunotherapy. It is proposed that MDSCs represent a potential therapeutic target for the inhibition of recurrence and metastasis in breast cancer. Therapeutic strategies targeting MDSCs have shown promising efficacy in preclinical studies and clinical trials. This review presents a summary of the principal factors involved in the recruitment and activation of MDSCs during the formation of PMN, and outlines MDSCs functions such as immunosuppression and the current targeted therapies against MDSCs, aiming to provide new ideas for the treatment of distant metastases in breast cancer.

Proteogenomics offers a novel avenue in neoantigen identification for cancer immunotherapy

Cancer neoantigens are tumor-specific non-synonymous mutant peptides that activate the immune system to produce an anti-tumor response. Personalized cancer vaccines based on neoantigens are currently one of the most promising therapeutic approaches for cancer treatment. By utilizing the unique mutations within each patient's tumor, these vaccines aim to elicit a strong and specific immune response against cancer cells. However, the identification of neoantigens remains challenging due to the low accuracy of current prediction tools and the high false-positive rate of candidate neoantigens. Since the concept of "proteogenomics" emerged in 2004, it has evolved rapidly with the increased sequencing depth of next-generation sequencing technologies and the maturation of mass spectrometry-based proteomics technologies to become a more comprehensive approach to neoantigen identification, allowing the discovery of high-confidence candidate neoantigens. In this review, we summarize the reason why cancer neoantigens have become attractive targets for immunotherapy, the mechanism of cancer vaccines and the advances in cancer immunotherapy. Considerations relevant to the application emerging of proteogenomics technologies for neoantigen identification and challenges in this field are described.

Boronate-Based Bioactive Compounds Activated by Peroxynitrite and Hydrogen Peroxide

Boronates react directly and stoichiometrically with peroxynitrite and hydrogen peroxide. For this reason, boronates have been widely used as peroxynitrite- and hydrogen peroxide-sensitive moieties in various donors of bioactive compounds. So far, numerous boronate-based prodrugs and theranostics have been developed, characterized, and used in biological research. Here, the kinetic aspects of their activation are discussed, and the potential benefits of modifying their original structure with a boronic or boronobenzyl moiety are described.

Small molecule probes for peroxynitrite detection

Peroxynitrite (ONOO‒/ONOOH) is a short-lived but highly reactive species that is formed in the diffusion-controlled reaction between nitric oxide and the superoxide radical anion. It can oxidize certain biomolecules and has been considered as a key cellular oxidant formed under various pathophysiological conditions. It is crucial to selectively detect and quantify ONOO- to determine its role in biological processes. In this review, we discuss various approaches used to detect ONOO‒ in cell-free and cellular systems with the major emphasis on small-molecule chemical probes. We review the chemical principles and mechanisms responsible for the formation of the detectable products, and plausible limitations of the probes. We recommend the use of boronate-based chemical probes for ONOO‒, as they react directly and rapidly with ONOO-, they produce minor but ONOO‒‒specific products, and the reaction kinetics and mechanism have been rigorously characterized. Specific experimental approaches and protocols for the detection of ONOO- in cell-free, cellular, and in vivo systems using boronate-based molecular probes are provided (as shown in Boxes 1-6).

Leveraging the ROS-TME Axis for Cancer Treatment

The discovery of reactive oxygen species (ROS) dates back to the early 20th century [...].

Targeting catalase in cancer

Healthy cells have developed a sophisticated network of antioxidant molecules to prevent the toxic accumulation of reactive oxygen species (ROS) generated by diverse environmental stresses. On the opposite, cancer cells often exhibit high levels of ROS and an altered levels of antioxidant molecules compared to normal cells. Among them, the antioxidant enzyme catalase plays an essential role in cell defense against oxidative stress through the dismutation of hydrogen peroxide into water and molecular oxygen, and its expression is often decreased in cancer cells. The elevation of ROS in cancer cells provides them proliferative advantages, and leads to metabolic reprogramming, immune escape and metastasis. In this context, catalase is of critical importance to control these cellular processes in cancer through various mechanisms. In this review, we will discuss the major progresses and challenges in understanding the role of catalase in cancer for this last decade. This review also aims to provide important updates regarding the regulation of catalase expression, subcellular localization and discuss about the potential role of microbial catalases in tumor environment. Finally, we will describe the different catalase-based therapies and address the advantages, disadvantages, and limitations associated with modulating catalase therapeutically in cancer treatment.

Multifunctional Sensors for Successive Detection of Endogenous ONOO- and Mitochondrial Viscosity: Discriminating Normal to Cancer Models

Diagnosing cancer in its early stages can play an important role in prolonging the lifespan of patients, which demands the use of powerful tools to detect biomarkers accurately. However, since most fluorescent probes described for cancer diagnosis are limited to recognizing a single molecule, achieving the high accuracy criteria remains difficult. Here, sensor 1 is constructed for the sequential detection of D, ONOO-, and viscosity. Initially, sensor 1 detected D and underwent an intramolecular charge transfer mechanism, resulting in the formation of 2 and fluorescence quenching at 587 nm. Subsequently, the intermediate (2) monitored ONOO- and reproduced sensor 1 reversibly with fluorescence enhancement at 496 nm, showing concentration-related quantitative analysis. Similar sensing processes were observed in monitoring ONOO- and viscosity by synthetically developed sensor 2. The proposed mechanisms of sensors 1 and 2 are verified through various characterizations (1H NMR, HR-MS, and HPLC) and DFT calculations. Investigations on endogenous ONOO- and mitochondrial viscosity in cancer (HeLa) and normal (NCM460) cells were conducted to distinguish cancerous cells from normal cells. We anticipated that sensor 2 could effectively serve as a reliable bioanalytical reagent for cancer diagnosis at an earlier stage through sequential detection of two cancer markers, ONOO- and mitochondrial viscosity, in living cells. Importantly, sensor 2 has been employed for imaging ONOO- in normal and liver injury mouse models and tissues, achieving outstanding results.

Hydrogen peroxide responsive theranostics for cancer-selective activation of DNA alkylators and real-time fluorescence monitoring in living cells

Triple negative breast cancer (TNBC) is a notoriously difficult disease to treat, and many of the existing TNBC chemotherapeutics lack tumor selectivity and the capability for simultaneously visualizing and monitoring their own activity in the biological context. However, TNBC cells have been known to generate high levels of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2). To this end, three novel small molecule theranostics 1a, 1c, and 2 consisting of both H2O2-responsive nitrogen mustard prodrug and profluorophore character have been designed, synthesized, and evaluated as targeted cancer therapeutics and bioimaging agents. The three theranostics comprise of boronate esters that deactivate nitrogen mustard functional groups and fluorophores but allow their selective activation through H2O2-specific oxidative deboronation for the release of the active drug and fluorophore. The three theranostics demonstrated H2O2-inducible DNA-alkylating capability and fluorescence turn-on properties in addition to selective anticancer activity. They are particularly effective in killing TNBC MDA-MB-468 cells with high H2O2 level while safe to normal epithelial MCF-10A cell. The conjugated boron-masked fluorophores in 1c and 2 are highly responsive towards H2O2, which enabled tracking of the theranostics in living cellular mitochondria and nucleus organelles. The three theranostics 1a, 1c, and 2 are capable of both selective release of the active drug to take effect in H2O2-rich cancer sites and simultaneously monitoring its activity. This single molecule system is of utmost importance to understand the function, efficacy, and mechanism of the H2O2-activated prodrugs and theranostics within the living recipient.

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.

Targeting ROS in cancer: rationale and strategies

Reactive oxygen species (ROS) in biological systems are transient but essential molecules that are generated and eliminated by a complex set of delicately balanced molecular machineries. Disruption of redox homeostasis has been associated with various human diseases, especially cancer, in which increased ROS levels are thought to have a major role in tumour development and progression. As such, modulation of cellular redox status by targeting ROS and their regulatory machineries is considered a promising therapeutic strategy for cancer treatment. Recently, there has been major progress in this field, including the discovery of novel redox signalling pathways that affect the metabolism of tumour cells as well as immune cells in the tumour microenvironment, and the intriguing ROS regulation of biomolecular phase separation. Progress has also been made in exploring redox regulation in cancer stem cells, the role of ROS in determining cell fate and new anticancer agents that target ROS. This Review discusses these research developments and their implications for cancer therapy and drug discovery, as well as emerging concepts, paradoxes and future perspectives.

Macrophages, IL-10, and nitric oxide increase, induced by hyperglycemic conditions, impact the development of murine melanoma B16F10-Nex2

Epidemiological studies show a strong correlation between diabetes and the increased risk of developing different cancers, including melanoma. In the present study, we investigated the impact of a streptozotocin (STZ)-induced hyperglycemic environment on B16F10-Nex2 murine melanoma development. Hyperglycemic male C57Bl/6 mice showed increased subcutaneous tumor development, partially inhibited by metformin. Tumors showed increased infiltrating macrophages, and augmented IL-10 and nitric oxide (NO) concentrations. In vivo neutralization of IL-10, NO synthase inhibition, and depletion of macrophages reduced tumor development. STZ-treated TLR4 KO animals showed delayed tumor development; the transfer of hyperglycemic C57Bl/6 macrophages to TLR4 KO reversed this effect. Increased concentrations of IL-10 present in tumor homogenates of hyperglycemic mice induced a higher number of pre-angiogenic structures in vitro, and B16F10-Nex2 cells incubated with different glucose concentrations in vitro produced increased levels of IL-10. In summary, our findings show that a hyperglycemic environment stimulates murine melanoma B16F10-Nex2 primary tumor growth, and this effect is dependent on tumor cell stimulation, increased numbers of macrophages, and augmented IL-10 and NO concentrations. These findings show the involvement of tumor cells and other components of the tumor microenvironment in the development of subcutaneous melanoma under hyperglycemic conditions, defining novel targets for melanoma control in diabetic patients.

GPCR-Gα13 Involvement in Mitochondrial Function, Oxidative Stress, and Prostate Cancer

Gα13 and Gα12, encoded by the GNA13 and GNA12 genes, respectively, are members of the G12 family of Gα proteins that, along with their associated Gβγ subunits, mediate signaling from specific G protein-coupled receptors (GPCRs). Advanced prostate cancers have increased expression of GPCRs such as CXC Motif Chemokine Receptor 4 (CXCR4), lysophosphatidic acid receptor (LPAR), and protease activated receptor 1 (PAR-1). These GPCRs signal through either the G12 family, or through Gα13 exclusively, often in addition to other G proteins. The effect of Gα13 can be distinct from that of Gα12, and the role of Gα13 in prostate cancer initiation and progression is largely unexplored. The oncogenic effect of Gα13 on cell migration and invasion in prostate cancer has been characterized, but little is known about other biological processes such as mitochondrial function and oxidative stress. Current knowledge on the link between Gα13 and oxidative stress is based on animal studies in which GPCR-Gα13 signaling decreased superoxide levels, and the overexpression of constitutively active Gα13 promoted antioxidant gene activation. In human samples, mitochondrial superoxide dismutase 2 (SOD2) correlates with prostate cancer risk and prognostic Gleason grade. However, overexpression of SOD2 in prostate cancer cells yielded conflicting results on cell growth and survival under basal versus oxidative stress conditions. Hence, it is necessary to explore the effect of Gα13 on prostate cancer tumorigenesis, as well as the effect of Gα13 on SOD2 in prostate cancer cell growth under oxidative stress conditions.

Peroxynitrite: a multifaceted oxidizing and nitrating metabolite

Peroxynitrite, a short-lived and reactive oxidant, emerges from the diffusion-controlled reaction between the superoxide radical and nitric oxide. Evidence shows that peroxynitrite is a critical mediator in physiological and pathological processes such as the immune response, inflammation, cancer, neurodegeneration, vascular dysfunction, and aging. The biochemistry of peroxynitrite is multifaceted, involving one- or two-electron oxidations and nitration reactions. This minireview highlights recent findings of peroxynitrite acting as a metabolic mediator in processes ranging from oxidative killing to redox signaling. Selected examples of nitrated proteins (i.e., 3-nitrotyrosine) are surveyed to underscore the role of this post-translational modification on cell homeostasis. While accumulated evidence shows that large amounts of peroxynitrite participates of broad oxidation and nitration events in invading pathogens and host tissues, a closer look supports that low to moderate levels selectively trigger signal transduction cascades. Peroxynitrite probes and redox-based pharmacology are instrumental to further understand the biological actions of this reactive metabolite.

HMGB1 Expression Levels Correlate with Response to Immunotherapy in Non-Small Cell Lung Cancer

Purpose

High-mobility group box 1 protein (HMGB1) is subject to exportin 1 (XPO1)-dependent nuclear export, and it is involved in functions implicated in resistance to immunotherapy. We investigated whether HMGB1 mRNA expression was associated with response to immune checkpoint inhibitors (ICI) in non-small cell lung cancer (NSCLC).

Patients and Methods

RNA was isolated from pretreatment biopsies of patients with advanced NSCLC treated with ICI. Gene expression analysis of several genes, including HMGB1, was conducted using the NanoString Counter analysis system (PanCancer Immune Profiling Panel). Western blotting analysis and cell viability assays in EGFR and KRAS mutant cell lines were carried out. Evaluation of the antitumoral effect of ICI in combination with XPO1 blocker (selinexor) and trametinib was determined in a murine Lewis lung carcinoma model.

Results

HMGB1 mRNA levels in NSCLC patients treated with ICI correlated with progression-free survival (PFS) (median PFS 9.0 versus 18.0 months, P=0.008, hazard ratio=0.30 in high versus low HMGB1). After TNF-α stimulation, HMGB1 accumulates in the cytoplasm of PC9 cells, but this accumulation can be prevented by using selinexor or antiretroviral drugs. Erlotinib or osimertinib with selinexor in EGFR-mutant cells and trametinib plus selinexor in KRAS mutant abolish tumor cell proliferation. Selinexor with a PD-1 inhibitor with or without trametinib abrogates the tumor growth in the murine Lewis lung cancer model.

Conclusion

An in-depth exploration of the functions of HMGB1 mRNA and protein is expected to uncover new potential targets and provide a basis for treating metastatic NSCLC in combination with ICI.

Simultaneous Visualization and Depletion of Peroxynitrite by a Simple Aggregation-Induced Emission Nanoprobe for Preventing Breast Cancer Metastasis after Surgery

Inflammation has been confirmed to be closely related to the development of tumors, while peroxynitrite (ONOO-) is one of the most powerful oxidative pro-inflammatory factors. Although ONOO- can kill bacteria through oxidation, it will activate matrix metalloproteinases (MMPs), accelerate the degradation of the extracellular matrix (ECM), and subsequently lead to the activation and release of other tumor promotion factors existing in the ECM, promoting tumor metastasis and invasion. Herein, we report a simple aggregation-induced emission (AIE) nanoprobe (NP), TPE-4NMB, that can simultaneously visualize and deplete ONOO-. The probe can light up the endogenous and exogenous ONOO- in cells and selectively inhibit the proliferation and migration of 4T1 cells by inducing an intracellular redox homeostasis imbalance through ONOO- depletion. After being modified with DSPE-PEG2000, the TPE-4NMB NPs can be used to image ONOO- induced by various models in vivo; especially, it can monitor the dynamic changes of ONOO- level in the residual tumor after surgery, which can provide evidence for clarifying the association between surgery, ONOO-, and cancer metastasis. Excitingly, inhibited tumor volume growth and decreased counts of lung metastases were observed in the TPE-4NMB NPs group, which can be attributed to the downregulated expression of MMP-9 and transforming growth factor-β (TGF-β), increased cell apoptosis, and inhibited epithelial-mesenchymal transition (EMT) mediated by ONOO-. The results will provide new evidence for clarifying the relationship between surgery, ONOO-, and tumor metastasis and serve as a new intervention strategy for preventing tumor metastasis after tumor resection.

Redox Biomarkers and Matrix Remodeling Molecules in Ovarian Cancer

Ovarian cancer (OC) has emerged as the leading cause of death due to gynecological malignancies among women. Oxidative stress and metalloproteinases (MMPs) have been shown to influence signaling pathways and afflict the progression of carcinogenesis. Therefore, the assessment of matrix-remodeling and oxidative stress intensity can determine the degree of cellular injury and often the severity of redox-mediated chemoresistance. The study group comprised 27 patients with serous OC of which 18% were classified as Federation of Gynecology and Obstetrics (FIGO) stages I/II, while the rest were diagnosed grades III/IV. The control group comprised of 15 ovarian tissue samples. The results were compared with genetic data from The Cancer Genome Atlas. Nitro-oxidative stress, inflammation and apoptosis biomarkers were measured colorimetrically/fluorometrically or via real-time PCR in the primary ovarian tumor and healthy tissue. Stratification of patients according to FIGO stages revealed that high-grade carcinoma exhibited substantial alterations in redox balance, including the accumulation of protein glycoxidation and lipid peroxidation products. TCGA data demonstrated only limited prognostic usefulness of the studied genes. In conclusion, high-grade serous OC is associated with enhanced tissue oxidative/nitrosative stress and macromolecule damage that could not be overridden by the simultaneously augmented measures of antioxidant defense. Therefore, it can be assumed that tumor cells acquire adaptive mechanisms that enable them to withstand the potential toxic effects of elevated reactive oxygen species.

Myeloid-derived suppressor cells in cancer and cancer therapy

Anticancer agents continue to dominate the list of newly approved drugs, approximately half of which are immunotherapies. This trend illustrates the considerable promise of cancer treatments that modulate the immune system. However, the immune system is complex and dynamic, and can have both tumour-suppressive and tumour-promoting effects. Understanding the full range of immune modulation in cancer is crucial to identifying more effective treatment strategies. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that develop in association with chronic inflammation, which is a hallmark of cancer. Indeed, MDSCs accumulate in the tumour microenvironment, where they strongly inhibit anticancer functions of T cells and natural killer cells and exert a variety of other tumour-promoting effects. Emerging evidence indicates that MDSCs also contribute to resistance to cancer treatments, particularly immunotherapies. Conversely, treatment approaches designed to eliminate cancer cells can have important additional effects on MDSC function, which can be either positive or negative. In this Review, we discuss the interplay between MDSCs and various other cell types found in tumours as well as the mechanisms by which MDSCs promote tumour progression. We also discuss the relevance and implications of MDSCs for cancer therapy.

A metabolic perspective on nitric oxide function in melanoma

Nitric oxide (NO) generated from nitric oxide synthase (NOS) exerts a dichotomous effect in melanoma, suppressing or promoting tumor progression. This dichotomy is thought to depend on the intracellular NO concentration and the cell type in which it is generated. Due to its central role in the metabolism of multiple critical constituents involved in signaling and stress, it is crucial to explore NO's contribution to the metabolic dysfunction of melanoma. This review will discuss many known metabolites linked to NO production in melanoma. We discuss the synthesis of these metabolites, their role in biochemical pathways, and how they alter the biological processes observed in the melanoma tumor microenvironment. The metabolic pathways altered by NO and the corresponding metabolites reinforce its dual role in melanoma and support investigating this effect for potential avenues of therapeutic intervention.

Breaking the mold: Overcoming resistance to immune checkpoint inhibitors

Immune checkpoint blockade-based therapies are effective against a sorts of cancers. However, drug resistance is a problem that cannot be ignored. This review intends to elucidate the mechanisms underlying drug tolerance induced by PD-1/PD-L1 inhibitors, as well as to outline proposed mechanism-based combination therapies and small molecule drugs that target intrinsic immunity and immune checkpoints. According to the differences of patients and types of cancer, the optimization of individualized combination therapy will help to enhance PD-1/PD-L1-mediated immunoregulation, reduce chemotherapy resistance, and provide new ideas for chemotherapy-resistant cancer.

Multiscale imaging of peroxynitrite in gliomas with a blood-brain barrier permeable probe reveals its potential as a biomarker and target for glioma treatment

Cancer development is driven by diverse processes, and metabolic alterations are among the primary characteristics. Multiscale imaging of aberrant metabolites in cancer is critical to understand the pathology and identify new targets for treatment. While peroxynitrite (ONOO^-) is reported being enriched in some tumors and plays important tumorigenic roles, whether it is upregulated in gliomas remains unexplored. To determine the levels and roles of ONOO^- in gliomas, efficient tools especially those with desirable blood-brain barrier (BBB) permeability and can realize the in situ imaging of ONOO^- in multiscale glioma-related samples are indispensable. Herein, we proposed a strategy of physicochemical property-guided probe design, which resulted in the development of a fluorogenic probe NOSTracker for smartly tracking ONOO^-. The probe showed sufficient BBB permeability. ONOO^- triggered oxidation of its arylboronate group was automatically followed by a self-immolative cleavage of a fluorescence-masking group, liberating its fluorescence signal. The probe was not only highly sensitive and selective towards ONOO^-, but its fluorescence favored desirable stability in various complex biological milieus. Guaranteed by these properties, multiscale imaging of ONOO^- was realized in vitro in patient-derived primary glioma cells, ex vivo in clinical glioma slices, and in vivo in the glioma of live mice. The results showed the upregulation of ONOO^- in gliomas. Furthermore, a specific ONOO^- scavenger uric acid (UA) was pharmaceutically used to downregulate ONOO^- in glioma cell lines, and an anti-proliferative effect was observed. These results taken together imply the potential of ONOO^- as a biomarker and target for glioma treatment, and propose NOSTracker as a reliable tool to further explore the role of ONOO^- in glioma development.

Fluorescent Detection of Peroxynitrite Produced by Myeloid-Derived Suppressor Cells in Cancer and Inhibition by Dasatinib

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that expand dramatically in many cancer patients. This expansion contributes to immunosuppression in cancer and reduces the efficacy of immune-based cancer therapies. One mechanism of immunosuppression mediated by MDSCs involves production of the reactive nitrogen species peroxynitrite (PNT), where this strong oxidant inactivates immune effector cells through destructive nitration of tyrosine residues in immune signal transduction pathways. As an alternative to analysis of nitrotyrosines indirectly generated by PNT, we used an endoplasmic reticulum (ER)-targeted fluorescent sensor termed PS3 that allows direct detection of PNT produced by MDSCs. When the MDSC-like cell line MSC2 and primary MDSCs from mice and humans were treated with PS3 and antibody-opsonized TentaGel microspheres, phagocytosis of these beads led to production of PNT and generation of a highly fluorescent product. Using this method, we show that splenocytes from a EMT6 mouse model of cancer, but not normal control mice, produce high levels of PNT due to elevated numbers of granulocytic (PMN) MDSCs. Similarly, peripheral blood mononuclear cells (PBMCs) isolated from blood of human melanoma patients produced substantially higher levels of PNT than healthy human volunteers, coincident with higher peripheral MDSC levels. The kinase inhibitor dasatinib was found to potently block the production of PNT both by inhibiting phagocytosis in vitro and by reducing the number of granulocytic MDSCs in mice in vivo, providing a chemical tool to modulate the production of this reactive nitrogen species (RNS) in the tumor microenvironment.

Neoantigens: promising targets for cancer therapy

Recent advances in neoantigen research have accelerated the development and regulatory approval of tumor immunotherapies, including cancer vaccines, adoptive cell therapy and antibody-based therapies, especially for solid tumors. Neoantigens are newly formed antigens generated by tumor cells as a result of various tumor-specific alterations, such as genomic mutation, dysregulated RNA splicing, disordered post-translational modification, and integrated viral open reading frames. Neoantigens are recognized as non-self and trigger an immune response that is not subject to central and peripheral tolerance. The quick identification and prediction of tumor-specific neoantigens have been made possible by the advanced development of next-generation sequencing and bioinformatic technologies. Compared to tumor-associated antigens, the highly immunogenic and tumor-specific neoantigens provide emerging targets for personalized cancer immunotherapies, and serve as prospective predictors for tumor survival prognosis and immune checkpoint blockade responses. The development of cancer therapies will be aided by understanding the mechanism underlying neoantigen-induced anti-tumor immune response and by streamlining the process of neoantigen-based immunotherapies. This review provides an overview on the identification and characterization of neoantigens and outlines the clinical applications of prospective immunotherapeutic strategies based on neoantigens. We also explore their current status, inherent challenges, and clinical translation potential.

Peroxynitrite promotes immune evasion by reducing tumor antigenicity

A study by Tcyganov et al.¹ demonstrates that peroxynitrite, an oxidant abundant in the tumor microenvironment, changes the repertoire of MHC class I peptides presented by tumors and limits immune recognition. Peroxynitrite inhibition in combination with immune checkpoint blockade enhances efficacy preclinically.