Suppression of STING signaling through epigenetic silencing and missense mutation impedes DNA damage mediated cytokine production

Signaling Through Nucleic Acid Sensors and Their Roles in Inflammatory Diseases

Recognition of pathogen-derived nucleic acids by pattern-recognition receptors (PRRs) is essential for eliciting antiviral immune responses by inducing the production of type I interferons (IFNs) and proinflammatory cytokines. Such responses are a prerequisite for mounting innate and pathogen-specific adaptive immune responses. However, host cells also use nucleic acids as carriers of genetic information, and the aberrant recognition of self-nucleic acids by PRRs is associated with the onset of autoimmune or autoinflammatory diseases. In this review, we describe the mechanisms of nucleic acid sensing by PRRs, including Toll-like receptors, RIG-I-like receptors, and DNA sensor molecules, and their signaling pathways as well as the disorders caused by uncontrolled or unnecessary activation of these PRRs.

Old Dog, New Trick: Type I IFN-Based Treatment for Acute Myeloid Leukemia

Despite strong biological rationale for the use of type-I IFNs for the treatment of acute myeloid leukemia (AML), their usage is limited to few hematologic malignancies. Here, we propose that innate immune sensing machinery, particularly the stimulator of IFN genes pathway, may be exploited to deliver antileukemic effects in AML.

Cancer cell-intrinsic STING is associated with CD8 + T-cell infiltration and might serve as a potential immunotherapeutic target in hepatocellular carcinoma

PURPOSE

The activation of stimulator of interferon genes (STING) pathway triggers the antitumor immunity by CD8 + T cells. However, the differentiated antitumor effects of STING activation in different cell types is still unclear. We aimed to investigate the expression and potential prognostic value of cancer cell-intrinsic STING in hepatocellular carcinoma (HCC), and whether STING could be a potential immunotherapeutic target of HCC was then evaluated.

METHODS

We separately assessed the expression of STING in cancer cells and infiltrating immune cells in HCC tissues. The independent clinicopathological factors associated with survival outcomes were evaluated by the multivariable analysis. The HCC orthotopic mice model were used to confirm the immunotherapeutic effects of STING agonists, and CD8 + T-cell infiltration level was analyzed through immunofluorescence and flow cytometry.

RESULTS

The expression of cancer cell-intrinsic STING was significantly reduced in HCC compared with adjacent tissues. Patients with low levels of cancer cell-intrinsic STING expression was associated with increased tumor volume (P = 0.009), higher serum AFP levels (P = 0.028), and decreased CD8 + T-cell infiltration (P = 0.002). Low levels of cancer cell-intrinsic STING expression indicated a poor overall survival (OS) and disease-free survival (DFS). Multivariate analysis demonstrated that low levels of cancer cell-intrinsic STING expression was an independent prognostic factor. Additionally, cancer cell-intrinsic STING expression was positively related with CD8 + T-cell infiltration levels in HCC patients (r = 0.308; P = 0.001). When mice with orthotopic HCC tumors treated with STING agonists, tumor growth was significantly reduced with enhanced levels of CD8 + T-cell infiltration.

CONCLUSION

Cancer cell-intrinsic STING might affect HCC tumor progression through enhancing CD8 + T-cell infiltration and can be an immunotherapeutic target for HCC.

The Evolution of STING Signaling and Its Involvement in Cancer

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway has been primarily characterized as an inflammatory mechanism in higher eukaryotes in response to cytosolic double-stranded DNA (dsDNA). Since its initial discovery, detailed mechanisms delineating the dynamic subcellular localization of its different components and downstream signaling have been uncovered, leading to attempts to harness its proinflammatory properties for therapeutic benefit in cancer. Emerging evidence, however, indicates that a crucial primordial function of STING is to promote autophagy, and that downstream interferon (IFN) signaling emerged recently in its evolutionary history. Furthermore, studies suggest that this pathway is a crucial regulator of cellular metabolism that potentially couples inflammation to nutrient availability. We focus on the evolutionarily conserved functions of STING, and we discuss how a broader understanding of this pathway can help us to better appreciate its potential role in cancer and harness it for therapeutic benefit.

Differential DNA Methylation in Prostate Tumors from Puerto Rican Men

In 2020, approximately 191,930 new prostate cancer (PCa) cases are estimated in the United States (US). Hispanic/Latinos (H/L) are the second largest racial/ethnic group in the US. This study aims to assess methylation patterns between aggressive and indolent PCa including DNA repair genes along with ancestry proportions. Prostate tumors classified as aggressive (n = 11) and indolent (n = 13) on the basis of the Gleason score were collected. Tumor and adjacent normal tissue were annotated on H&E (Haemotoxylin and Eosin) slides and extracted by macro-dissection. Methylation patterns were assessed using the Illumina 850K DNA methylation platform. Raw data were processed using the Bioconductor package. Global ancestry proportions were estimated using ADMIXTURE (k = 3). One hundred eight genes including AOX1 were differentially methylated in tumor samples. Regarding the PCa aggressiveness, six hypermethylated genes (RREB1, FAM71F2, JMJD1C, COL5A3, RAE1, and GABRQ) and 11 hypomethylated genes (COL9A2, FAM179A, SLC17A2, PDE10A, PLEKHS1, TNNI2, OR51A4, RNF169, SPNS2, ADAMTSL5, and CYP4F12) were identified. Two significant differentially methylated DNA repair genes, JMJD1C and RNF169, were found. Ancestry proportion results for African, European, and Indigenous American were 24.1%, 64.2%, and 11.7%, respectively. The identification of DNA methylation patterns related to PCa in H/L men along with specific patterns related to aggressiveness and DNA repair constitutes a pivotal effort for the understanding of PCa in this population.

Accessible Pipeline for Translational Research Using TCGA: Examples of Relating Gene Mechanism to Disease-Specific Outcomes

Bioinformatic scientists are often asked to do widespread analyses of publicly available datasets in order to identify genetic alterations in cancer for genes of interest; therefore, we sought to create a set of tools to conduct common statistical analyses of The Cancer Genome Atlas (TCGA) data. These tools have been developed in response to requests from our collaborators to ask questions, validate findings, and better understand the function of their gene of interest. We describe here what data we have used, how to obtain it, and what figures we have found useful.

SKIL facilitates tumorigenesis and immune escape of NSCLC via upregulating TAZ/autophagy axis

Immune escape is an important mechanism in tumorigenesis. The aim of this study was to investigate roles of SKIL in tumorigenesis and immune escape of non-small-cell lung cancer (NSCLC). SKIL expression levels in NSCLC cell line, clinical sample, and adjacent normal tissue were measured by quantitative PCR, western blot, or immunohistochemistry. Lentivirus was used to overexpress/silence SKIL or TAZ expression. Malignant phenotypes of NSCLC cells were evaluated by colony formation, transwell, and MTT assays, and in xenograft mice model. Syngeneic mice model and flow cytometry were used to evaluate T cell infiltration. Quantitative PCR and western blot were applied to evaluate relevant mRNA and protein levels, respectively. Co-immunoprecipitation was applied to unveil the interaction between SKIL and TAZ. SKIL expression was higher in NSCLC tissue compared to adjacent normal tissue. Silencing of SKIL inhibited malignant phenotypes of NSCLC cells and promoted T cell infiltration. SKIL-knockdown inhibited autophagy and activated the STING pathway in NSCLC cells through down-regulation of TAZ. Silencing of TAZ cancelled the effects of SKIL overexpression on malignant phenotypes and autophagy of NSCLC cells. Inhibition of autophagy reversed the effects of SKIL/TAZ overexpression on the STING pathway. In conclusion, SKIL promoted tumorigenesis and immune escape of NSCLC cells through upregulation of TAZ/autophagy axis and inhibition on downstream STING pathway.

Lymphocyte Changes in Severe COVID-19: Delayed Over-Activation of STING?

Upon recognition of microbial DNA or self-DNA, the cyclic-GMP-AMP synthase (cGAS) of the host catalyzes the production of the cyclic dinucleotide cGAMP. cGAMP is the main activator of STING, stimulator of interferon genes, leading to interferon synthesis through the STING-TBK1-IRF3 pathway. STING is also a hub for activation of NF-κB and autophagy. The present review details the striking similarities between T and B cell responses in severe coronavirus disease 2019 (COVID-19) and both animal or human models of STING gain of function (SAVI syndromes: STING-associated vasculopathy with onset in infancy). Those similarities may be further clues for a delayed activation of STING in severe COVID-19 patients, due to DNA damages following severe acute respiratory syndrome coronaviruses (SARS-CoV-2) infection and unusual role of STING in SARS-CoV-2 control. In early stages, Th2 differentiation are noticed in both severe COVID-19 and SAVI syndromes; then, CD4+ and CD8+ T cells functional exhaustion/senescent patterns due to TCR hyper-responsiveness are observed. T cell delayed over-responses can contribute to pneumonitis and delayed cytokine secretion with over-production of IL-6. Last, STING over-activation induces progressive CD4+ and CD8+ T lymphopenia in SAVI syndromes, which parallels what is observed in severe COVID-19. ACE2, the main receptor of SARS-CoV-2, is rarely expressed in immune cells, and it has not been yet proven that some human lymphocytes could be infected by SARS-CoV-2 through CD147 or CD26. However, STING, expressed in humans T cells, might be triggered following excessive transfer of cGAMP from infected antigen presenting cells into activated CD4+ and CD8+ T cells lymphocytes. Indeed, those lymphocytes highly express the cGAMP importer SLC19A1. Whereas STING is not expressed in human B cells, B cells counts are much less affected, either in COVID-19 or SAVI syndromes. The recognition of delayed STING over-activation in severe COVID-19 patients could prompt to target STING with specific small molecules inhibitors already designed and/or aspirin, which inhibits cGAS.

Integrity of the Antiviral STING-mediated DNA Sensing in Tumor Cells Is Required to Sustain the Immunotherapeutic Efficacy of Herpes Simplex Oncolytic Virus

Simple Summary

Oncolytic viruses are emerging immunotherapeutics in cancer treatments. The conflicting role of innate immunity in the antitumor activity of oncolytic viruses is still a matter of debate. The STING-dependent DNA sensing axis is considered detrimental for viral replication and cancer cell clearance. Accordingly, we observed that STING loss in tumor cells was associated with improved lytic potential by a herpes-based oncolytic virus. However, STING-knockout cancer cells infected with the oncolytic virus showed impaired immunogenicity, as immunogenic cell death was improperly triggered. In agreement with these observations, STING-knockout tumors raised in a murine syngeneic model were more resistant to a combined treatment of the oncolytic virus with PD-1 blockade. The present study demonstrates the antitumor benefit of antiviral immunity and sheds lights on the mechanisms of immune resistance to oncovirotherapy exerted by STING-loss in tumor cells.

Abstract

The dichotomic contribution of cancer cell lysis and tumor immunogenicity is considered essential for effective oncovirotherapy, suggesting that the innate antiviral immune response is a hurdle for efficacy of oncolytic viruses. However, emerging evidence is resizing this view. By sensing cytosolic DNA, the cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) axis can both counteract viral spread and contribute to the elicitation of adaptive immunity via type I interferon responses. In this paper, we analyzed the tumor-resident function of Sting-mediated DNA sensing in a combined approach of oncovirotherapy and PD-1 immune checkpoint blockade, in an immunocompetent murine model. While supporting increased lytic potential by oncolytic HER2-retargeted HSV-1 in vitro and in vivo, Sting-knockout tumors showed molecular signatures of an immunosuppressive tumor microenvironment. These signatures were correspondingly associated with ineffectiveness of the combination therapy in a model of established tumors. Results suggest that the impairment in antiviral response of Sting-knockout tumors, while favoring viral replication, is not able to elicit an adequate immunotherapeutic effect, due to lack of immunogenic cell death and the inability of Sting-knockout cancer cells to promote anti-tumor adaptive immune responses. Accordingly, we propose that antiviral, tumor-resident Sting provides fundamental contributions to immunotherapeutic efficacy of oncolytic viruses.

Role of cGAS-STING signaling pathway in colon cancer

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) signaling pathway is an important immune response pathway in the cytoplasm, and it is an important mechanism that regulates innate immune and adaptive immune responses. As an important mechanism that detects and responds to pathogens, the cGAS-STING signaling pathway plays a key role in mediating immunity against DNA pathogens and the body's internal immunity against tumors. Clinically, STING activators are often used for tumor treatment. Also, cGAS can act as a tumor prognostic marker. At present, related agonists of cGAS and STING have been used in clinical treatment of colon cancer, but their effects in tumors from other tissues are not clear yet. Thus, their effectiveness and safety are still needed to be further studied.

Immunomodulatory Effects of Radiotherapy

Radiation therapy (RT), an integral component of curative treatment for many malignancies, can be administered via an increasing array of techniques. In this review, we summarize the properties and application of different types of RT, specifically, conventional therapy with x-rays, stereotactic body RT, and proton and carbon particle therapies. We highlight how low-linear energy transfer (LET) radiation induces simple DNA lesions that are efficiently repaired by cells, whereas high-LET radiation causes complex DNA lesions that are difficult to repair and that ultimately enhance cancer cell killing. Additionally, we discuss the immunogenicity of radiation-induced tumor death, elucidate the molecular mechanisms by which radiation mounts innate and adaptive immune responses and explore strategies by which we can increase the efficacy of these mechanisms. Understanding the mechanisms by which RT modulates immune signaling and the key players involved in modulating the RT-mediated immune response will help to improve therapeutic efficacy and to identify novel immunomodulatory drugs that will benefit cancer patients undergoing targeted RT.

System-Based Approaches to Delineate the Antiviral Innate Immune Landscape

Viruses pose substantial challenges for society, economy, healthcare systems, and research. Their distinctive pathologies are based on specific interactions with cellular factors. In order to develop new antiviral treatments, it is of central importance to understand how viruses interact with their host and how infected cells react to the virus on a molecular level. Invading viruses are commonly sensed by components of the innate immune system, which is composed of a highly effective yet complex network of proteins that, in most cases, mediate efficient virus inhibition. Central to this process is the activity of interferons and other cytokines that coordinate the antiviral response. So far, numerous methods have been used to identify how viruses interact with cellular processes and revealed that the innate immune response is highly complex and involves interferon-stimulated genes and their binding partners as functional factors. Novel approaches and careful experimental design, combined with large-scale, high-throughput methods and cutting-edge analysis pipelines, have to be utilized to delineate the antiviral innate immune landscape at a global level. In this review, we describe different currently used screening approaches, how they contributed to our knowledge on virus-host interactions, and essential considerations that have to be taken into account when planning such experiments.

Nuclear Membrane Rupture and Its Consequences

The nuclear envelope is often depicted as a static barrier that regulates access between the nucleus and the cytosol. However, recent research has identified many conditions in cultured cells and in vivo in which nuclear membrane ruptures cause the loss of nuclear compartmentalization. These conditions include some that are commonly associated with human disease, such as migration of cancer cells through small spaces and expression of nuclear lamin disease mutations in both cultured cells and tissues undergoing nuclear migration. Nuclear membrane ruptures are rapidly repaired in the nucleus but persist in nuclear compartments that form around missegregated chromosomes called micronuclei. This review summarizes what is known about the mechanisms of nuclear membrane rupture and repair in both the main nucleus and micronuclei, and highlights recent work connecting the loss of nuclear integrity to genome instability and innate immune signaling. These connections link nuclear membrane rupture to complex chromosome alterations, tumorigenesis, and laminopathy etiologies.

DNA Damage and Cancer Immunotherapy: A STING in the Tale

Cancer immunotherapies enhance anti-tumor immune responses using checkpoint inhibitors, such as PD-1 or PD-L1 inhibitors. Recent studies, however, have extended the scope of immunotherapeutics by unveiling DNA damage-induced innate immunity as a novel target for cancer treatment. Elucidating the interplay among the DNA damage response (DDR), cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway activation, and anti-tumoral immunity is critical for the development of effective cancer immunotherapies. Here, we discuss the current understanding of the mechanisms by which DNA damage activates immune responses that target and eradicate cancer cells. Yet, understanding how cancer cells can escape this immune surveillance and promote tumor progression represents an outstanding challenge. We highlight the most recent clinical advances, in particular how pharmacological fine-tuning of innate/adaptive immunity and its combination with DDR inhibitors, ionizing radiation (IR), and chemotherapy can be exploited to improve cancer treatment.

Influence of gene expression on survival of clear cell renal cell carcinoma

Approximately 10%‐20% of patients with clinically localized clear cell renal cell carcinoma (ccRCC) at time of surgery will subsequently experience metastatic progression. Although considerable progression was seen in the systemic treatment of metastatic ccRCC in last 20 years, once ccRCC spreads beyond the confines of the kidney, 5‐year survival is less than 10%. Therefore, significant clinical advances are urgently needed to improve overall survival and patient care to manage the growing number of patients with localized ccRCC. We comprehensively evaluated expression of 388 candidate genes related with survival of ccRCC by using TCGA RNAseq (n = 515), Total Cancer Care (TCC) expression array data (n = 298), and a well characterized Moffitt RCC cohort (n = 248). We initially evaluated all 388 genes for association with overall survival using TCGA and TCC data. Eighty‐one genes were selected for further analysis and tested on Moffitt RCC cohort using NanoString expression analysis. Expression of nine genes (AURKA, AURKB, BIRC5, CCNE1, MK167, MMP9, PLOD2, SAA1, and TOP2A) was validated as being associated with poor survival. Survival prognostic models showed that expression of the nine genes and clinical factors predicted the survival in ccRCC patients with AUC value: 0.776, 0.821 and 0.873 for TCGA, TCC and Moffitt data set, respectively. Some of these genes have not been previously implicated in ccRCC survival and thus potentially offer insight into novel therapeutic targets. Future studies are warranted to validate these identified genes, determine their biological mechanisms and evaluate their therapeutic potential in preclinical studies.

G10 is a direct activator of human STING

The cGAS/STING pathway initiates an innate immune response when DNA is detected in the cytosol. DNA bound cGAS synthesizes cyclic dinucleotides which bind and activate the adaptor STING, leading to downstream secretion of Type I interferons and other pro-inflammatory NFκB pathway cytokines. In the mouse, the STING driven innate immune response is central to immune based clearance of various tumors and this has triggered a significant effort focused on the discovery of human STING agonists for the treatment of cancer. This report uses an in vitro kinase assay to show that G10, a previously identified STING pathway activator is actually a weak but direct STING agonist and identifies other more potent leads.

Optimizing Radiation Therapy to Boost Systemic Immune Responses in Breast Cancer: A Critical Review for Breast Radiation Oncologists

Immunotherapy using immune checkpoint blockade has revolutionized the treatment of many types of cancer. Radiation therapy (RT)-particularly when delivered at high doses using newer techniques-may be capable of generating systemic antitumor effects when combined with immunotherapy in breast cancer. These systemic effects might be due to the local immune-priming effects of RT resulting in the expansion and circulation of effector immune cells to distant sites. Although this concept merits further exploration, several challenges need to be overcome. One is an understanding of how the heterogeneity of breast cancers may relate to tumor immunogenicity. Another concerns the need to develop knowledge and expertise in delivery, sequencing, and timing of RT with immunotherapy. Clinical trials addressing these issues are under way. We here review and discuss the particular opportunities and issues regarding this topic, including the design of informative clinical and translational studies.

Comprehensive elaboration of the cGAS-STING signaling axis in cancer development and immunotherapy

Cellular recognition of microbial DNA is an evolutionarily conserved mechanism by which the innate immune system detects pathogens. Cyclic GMP-AMP synthase (cGAS) and its downstream effector, stimulator of interferon genes (STING), are involved in mediating fundamental innate antimicrobial immunity by promoting the release of type I interferons (IFNs) and other inflammatory cytokines. Accumulating evidence suggests that the activation of the cGAS-STING axis is critical for antitumor immunity. The downstream cytokines regulated by cGAS-STING, especially type I IFNs, serve as bridges connecting innate immunity with adaptive immunity. Accordingly, a growing number of studies have focused on the synthesis and screening of STING pathway agonists. However, chronic STING activation may lead to a protumor phenotype in certain malignancies. Hence, the cGAS-STING signaling pathway must be orchestrated properly when STING agonists are used alone or in combination. In this review, we discuss the dichotomous roles of the cGAS-STING pathway in tumor development and the latest advances in the use of STING agonists.

Like a Rolling Stone: Sting-Cgas Pathway and Cell-Free DNA as Biomarkers for Combinatorial Immunotherapy

Combining immune checkpoint inhibitors with other treatments likely to harness tumor immunity is a rising strategy in oncology. The exact modalities of such a combinatorial regimen are yet to be defined, and most attempts have relied so far on concomitant dosing, rather than sequential or phased administration. Because immunomodulating features are likely to be time-, dose-, and-schedule dependent, the need for biomarkers providing real-time information is critical to better define the optimal time-window to combine immune checkpoint inhibitors with other drugs. In this review, we present the various putative markers that have been investigated as predictive tools with immune checkpoint inhibitors and could be used to help further combining treatments. Whereas none of the current biomarkers, such as the PDL1 expression of a tumor mutational burden, is suitable to identify the best way to combine treatments, monitoring circulating tumor DNA is a promising strategy, in particular to check whether the STING-cGAS pathway has been activated by cytotoxics. As such, circulating tumor DNA could help defining the best time-window to administrate immune checkpoint inhibitors after that cytotoxics have been given.

Regulation of an adaptor protein STING by Hsp90β to enhance innate immune responses against microbial infections

Stimulator of interferon genes (STING) plays important roles in the DNA-mediated innate immune responses. However, the regulatory mechanism of STING in terms of stabilization is not fully understood. Here, we identified the chaperone protein Hsp90s as novel STING interacting proteins. Treatment with an Hsp90 inhibitor 17-AAG and knockdown of Hsp90β but not Hsp90α reduced STING at protein level, resulted in the suppression of IFN induction in response to stimulation with cGAMP, and infections with HSV-1 and Listeria monocytogenes. Collectively, our results suggest that the control of STING protein by Hsp90β is a critical biological process in the DNA sensing pathways.

cGAS-STING pathway in oncogenesis and cancer therapeutics

The host innate immunity offers the first line of defense against infection. However, recent evidence shows that the host innate immunity is also critical in sensing the presence of cytoplasmic DNA derived from genomic instability events, such as DNA damage and defective cell cycle progression. This is achieved through the cyclic GMP-AMP synthase (cGAS)/Stimulator of interferon (IFN) genes (STING) pathway. Here we discuss recent insights into the regulation of this pathway in cancer immunosurveillance, and the downstream signaling cascades that coordinate immune cell recruitment to the tumor microenvironment to destroy transformed cells through cellular senescence or cell death programs. Its central role in immunosurveillance positions the cGAS-STING pathway as an attractive anti-cancer immunotherapeutic drug target for chemical agonists or vaccine adjuvants and suggests a key node to be targeted in a synthetic lethal approach. We also discuss adaptive mechanisms used by cancer cells to circumvent cGAS-STING signaling and present evidence linking chronic cGAS-STING activation to inflammation-induced carcinogenesis, cautioning against the use of activating the cGAS-STING pathway as an anti-tumor immunotherapy. A deeper mechanistic understanding of the cGAS-STING pathway will aid in the identification of potentially efficacious anti-cancer therapeutic targets.

Dysregulation in nucleic acid-sensing pathway genes is associated with cancer patients' prognosis

The innate immune system, the first line of defense against pathogens, is activated by nucleic acids from microbial invaders that are recognized by nucleic acid-sensing receptors. Recent evidence affirms the ability of these receptors to respond to nucleic acids released by damaged cancer cells. The innate immune system is also involved in cancer immunosurveillance, and could be modulated for devising effective antitumor therapies by targeting nucleic acid-sensing pathways. A systematic, comprehensive analysis of dysregulation in nucleic acid-sensing pathways in cancer is required to fully understand its role. Based on multidimensional data of The Cancer Genome Atlas pan-cancer cohort, we revealed that upregulation of cytosolic DNA-sensing genes like AIM2 and CGAS was common in tumor tissues. We used 15 genes in the nucleic acid-sensing pathway to cluster all tumor patients into 2 subgroups and found that the subgroup with higher expression of nucleic acid-sensing pathway genes was associated with poorer prognosis across cancer types. However, in homologous recombination deficient patients, the nucleic acid recognition activated subgroup was associated with better prognosis, which confirms the therapeutic effect of nucleic acid recognition. This study contributes to a better understanding of the functions and mechanisms of nucleic acid recognition in cancer, lays the foundation for new therapeutic strategies, and enlarges the scope of development of new drugs.

Regulation and Consequences of cGAS Activation by Self-DNA

Cyclic GMP-AMP (cGAMP) synthase (cGAS) is a major responder to the pathogenic DNA of viruses and bacteria. Upon DNA binding, cGAS becomes enzymatically active to generate the second messenger cGAMP, leading to activation of inflammatory genes, type I interferon production, autophagy, and cell death. Following genotoxic stress, cGAS can also respond to endogenous DNA, deriving from mitochondria, endogenous retroelements, and chromosomes to affect cellular signaling, secretion, and cell fate decisions. However, under unperturbed conditions, signaling from self-DNA is largely, but not completely, inhibited. Here we review how endogenous DNA is exposed to cGAS, how signaling is attenuated but activated under pathological conditions, and how low-level signaling under unperturbed conditions might prime antipathogenic responses.

Radiotherapy Cooperates with IL15 to Induce Antitumor Immune Responses

Focal radiotherapy can promote cross-presentation of tumor antigens to T cells, but by itself, it is insufficient to induce therapeutically effective T-cell responses. The common gamma-chain cytokine IL15 promotes and sustains the proliferation and effector function of CD8⁺ T cells but has limited activity against poorly immunogenic tumors that do not elicit significant spontaneous T-cell responses. Here, we show that radiotherapy and subcutaneous IL15 had complementary effects and induced CD8⁺ T-cell-mediated tumor regression and long-term protective memory responses in two mouse carcinoma models unresponsive to IL15 alone. Mechanistically, radiotherapy-induced IFN type I production and Batf3-dependent conventional dendritic cells type 1 (cDC1) were required for priming of tumor-specific CD8⁺ T cells and for the therapeutic effect of the combination. IL15 cooperated with radiotherapy to activate and recruit cDC1s to the tumor. IL15 alone and in complex with a hybrid molecule containing the IL15α receptor have been tested in early-phase clinical trials in patients with cancer and demonstrated good tolerability, especially when given subcutaneously. Expansion of natural killer (NK) cells and CD8⁺ T cells was noted, without clear clinical activity, suggesting further testing of IL15 as a component of a combinatorial treatment with other agents. Our results provide the rationale for testing combinations of IL15 with radiotherapy in the clinic.

Balancing STING in antimicrobial defense and autoinflammation

Rapid detection of microbes is crucial for eliciting an effective immune response. Innate immune receptors survey the intracellular and extracellular environment for signs of a microbial infection. When they detect a pathogen-associated molecular pattern (PAMP), such as viral DNA, they alarm the cell about the ongoing infection. The central signaling hub in sensing of viral DNA is the stimulator of interferon genes (STING). Upon activation, STING induces downstream signaling events that ultimately result in the production of type I interferons (IFN I), important cytokines in antimicrobial defense, in particular towards viruses. In this review, we describe the molecular features of STING, including its upstream sensors and ligands, its sequence and structural conservation, common polymorphisms, and its localization. We further highlight how STING activation requires a careful balance: its activity is essential for antiviral defense, but unwanted activation through mutations or accidental recognition of self-derived DNA causes autoinflammatory diseases. Several mechanisms, such as post-translational modifications, ensure this balance by fine-tuning STING activation. Finally, we discuss how viruses evade detection of their genomes by either exploiting cells that lack a functional DNA sensing pathway as a niche or by interfering with STING activation through viral evasion molecules. Insight into STING's exact mechanisms in health and disease will guide the development of novel clinical interventions for microbial infections, autoinflammatory diseases, and beyond.

Research Advances in How the cGAS-STING Pathway Controls the Cellular Inflammatory Response

Double-stranded DNA (dsDNA) sensor cyclic-GMP-AMP synthase (cGAS) along with the downstream stimulator of interferon genes (STING) acting as essential immune-surveillance mediators have become hot topics of research. The intrinsic function of the cGAS-STING pathway facilitates type-I interferon (IFN) inflammatory signaling responses and other cellular processes such as autophagy, cell survival, senescence. cGAS-STING pathway interplays with other innate immune pathways, by which it participates in regulating infection, inflammatory disease, and cancer. The therapeutic approaches targeting this pathway show promise for future translation into clinical applications. Here, we present a review of the important previous works and recent advances regarding the cGAS-STING pathway, and provide a comprehensive understanding of the modulatory pattern of the cGAS-STING pathway under multifarious pathologic states.

Inflammatory microenvironment remodelling by tumour cells after radiotherapy

The development of immune checkpoint inhibitors (ICIs) is revolutionizing the way we think about cancer treatment. Even so, for most types of cancer, only a minority of patients currently benefit from ICI therapies. Intrinsic and acquired resistance to ICIs has focused research towards new combination therapy approaches that seek to increase response rates, the depth of remission and the durability of benefit. In this Review, we describe how radiotherapy, through its immunomodulating effects, represents a promising combination partner with ICIs. We describe how recent research on DNA damage response (DDR) inhibitors in combination with radiotherapy may be used to augment this approach. Radiotherapy can kill cancer cells while simultaneously triggering the release of pro-inflammatory mediators and increasing tumour-infiltrating immune cells - phenomena often described colloquially as turning immunologically 'cold' tumours 'hot'. Here, we focus on new developments illustrating the key role of tumour cell-autonomous signalling after radiotherapy. Radiotherapy-induced tumour cell micronuclei activate cytosolic nucleic acid sensor pathways, such as cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING), and propagation of the resulting inflammatory signals remodels the immune contexture of the tumour microenvironment. In parallel, radiation can impact immunosurveillance by modulating neoantigen expression. Finally, we highlight how tumour cell-autonomous mechanisms might be exploited by combining DDR inhibitors, ICIs and radiotherapy.

LncRNA NEAT1 Interacted With DNMT1 to Regulate Malignant Phenotype of Cancer Cell and Cytotoxic T Cell Infiltration via Epigenetic Inhibition of p53, cGAS, and STING in Lung Cancer

Purpose

Lung cancer is the main cause of cancer-related mortality worldwide. We report here the biological role of nuclear paraspeckle assembly transcript 1 (NEAT1) in the pathogenesis of lung cancer and the underlying mechanisms.

Methods

Reverse transcription–quantitative polymerase chain reaction (RT-qPCR) and Western blotting analysis were used to evaluate expression of mRNA and protein. RNA immunoprecipitation (RIP) assay, chromatin immunoprecipitation followed by qPCR analysis, and reporter assay were used to detect DNA/RNA and protein binding. Tumor-infiltrating lymphocytes were assessed with hematoxylin-eosin staining. Cytotoxic T cell infiltration was evaluated with flow cytometric analysis and immunohistochemistry (IHC) staining. The changes of cell viability and cell invasive and migratory ability were analyzed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), colony formation, and Transwell assays, respectively. Syngeneic tumor model was set up to evaluate antitumor effect.

Results

The results showed that NEAT1 was overexpressed in lung cancer tissues and cancer cell lines. This aberrant expression was closely related with tumor stage and lymph node metastasis. Tumor sample with high CD8⁺ showed lower NEAT1 expression. In vitro studies displayed that inhibition of NEAT1 with shRNA resulted in suppression of survival and migration/invasion of lung cancer cells. On the other side, NEAT1 was found to promote tumor growth via inhibiting cytotoxic T cell immunity in syngeneic models. Finally, NEAT1 was found to interact with DNMT1, which in turn inhibited P53 and cyclic GMP-AMP synthase stimulator of interferon genes (cGAS/STING) expression.

Conclusion

Our findings demonstrated that NEAT1 interacted with DNMT1 to regulate cytotoxic T cell infiltration in lung cancer via inhibition of cGAS/STING pathway. The results provided the novel mechanistic insight into the pathogenesis of lung cancer.

Immunogenic cell death in colon cancer prevention and therapy

Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide. The colonic mucosa constitutes a critical barrier and a major site of immune regulation. The immune system plays important roles in cancer development and treatment, and immune activation caused by chronic infection or inflammation is well-known to increase cancer risk. During tumor development, neoplastic cells continuously interact with and shape the tumor microenvironment (TME), which becomes progressively immunosuppressive. The clinical success of immune checkpoint blockade therapies is limited to a small set of CRCs with high tumor mutational load and tumor-infiltrating T cells. Induction of immunogenic cell death (ICD), a type of cell death eliciting an immune response, can therefore help break the immunosuppressive TME, engage the innate components, and prime T cell-mediated adaptive immunity for long-term tumor control. In this review, we discuss the current understanding of ICD induced by antineoplastic agents, the influence of driver mutations, and recent developments to harness ICD in colon cancer. Mechanism-guided combinations of ICD-inducing agents with immunotherapy and actionable biomarkers will likely offer more tailored and durable benefits to patients with colon cancer.

The abscopal effect 67 years later: from a side story to center stage

For over a century, ionising radiation has been used to treat cancer based on its cytotoxic effects on tumour cells. Technical progress has enabled more precise targeting of the tumour to reduce normal tissue toxicity while delivering higher radiation doses per fraction of treatment.In 1953, unexpected regression in lesions outside of the irradiated field were noted by an observant physician, RH Mole, who named such phenomenon "abscopal effect" from the Latin ab (position away from) and scopus (mark or target), in an article published in this journal. Clinical abscopal responses have been reported over the years but because of their very rare occurrence they could not be methodically studied, remaining akin to a curiosity. Nevertheless, their occurrence has ignited interest in studying the systemic effects of radiotherapy. Progress in dissecting the mechanisms that govern the function of the immune system in cancer has enabled to study the implication of immunity in the abscopal effect of radiation. It has become clear that ionising radiation activates canonical pathways of response to viral infections, and can stimulate antitumour immunity. These immune stimulatory effects of radiation have become clinically relevant in the current era of cancer immunotherapy, rendering abscopal responses in patients an attainable aim. Here, we will briefly review the parallel evolutions of two separate fields of medicine, radiation therapy and cancer immunology, and discuss their therapeutic partnership.

PYHIN1 regulates pro-inflammatory cytokine induction rather than innate immune DNA sensing in airway epithelial cells

Animal cells use pattern-recognition receptors (PRRs) to detect specific pathogens. Pathogen detection mounts an appropriate immune response, including interferon and cytokine induction. The intracellular PRR-signaling pathways that detect DNA viruses have been characterized, particularly in myeloid cells. In these pathways, cGMP-AMP synthase (cGAS) and the pyrin and HIN domain family member (PYHIN) protein interferon-γ–inducible protein 16 (IFI16) detect DNA and signal via stimulator of interferon genes protein (STING). However, although airway epithelial cells are frontline sentinels in detecting pathogens, information on how they respond to DNA viruses is limited, and the roles of PYHIN proteins in these cells are unknown. Here, we examined expression and activities of cGAS, STING, and PYHINs in human lung epithelial cells. A549 epithelial cells, commonly used for RNA-sensing studies, failed to respond to DNA because they lacked STING expression, and ectopic STING expression restored a cGAS-dependent DNA response in these cells. In contrast, NuLi-1 immortalized human bronchial epithelial cells did express STING, which was activated after DNA stimulation and mediated DNA-dependent gene induction. PYHIN1, which like IFI16 has been proposed to be a viral DNA sensor, was the only PYHIN protein expressed in both airway epithelial cell types. However, rather than having a role in DNA sensing, PYHIN1 induced proinflammatory cytokines in response to interleukin-1 (IL-1) or tumor necrosis factor α (TNFα) stimulation. Of note, PYHIN1, via its HIN domain, directly induced IL-6 and TNFα transcription, revealing that PYHIN proteins play a role in proinflammatory gene induction in airway epithelial cells.

Selective Loss of Responsiveness to Exogenous but Not Endogenous Cyclic-Dinucleotides in Mice Expressing STING-R231H

Stimulator of interferon genes (STING) plays a central role in innate immune responses to viral and intracellular bacterial infections, and cellular damage. STING is a cytosolic sensor of cyclic dinucleotides (CDNs) including those produced by pathogenic bacteria and those arising endogenously as products of the DNA sensor cGAS (e.g., 2′3′ cGAMP). The two most common alternative allelic variants of STING in humans are STING-R71H-G230A-R293Q (STING-HAQ) and STING-R232H that are found in 20.4% and 13.7–17.6% of the population, respectively. To determine the biologic consequences of these genotypic variations, we generated knock-in mice containing the murine equivalents of each variant and studied their responsiveness to CDNs. Homozygous STING-HAQ (R71H-I229A-R292Q) and STING-R231H mice were found to be unresponsive to all exogenous CDNs tested (ci-di-GMP, ci-di-AMP, 3′3′ cGAMP and Rp,Rp-CDA). Responses of homozygous STING-HAQ mice to endogenous 2′3′ cGAMP was also greatly impaired. However, homozygous STING-R231H mice are fully responsive to 2′3′ cGAMP. Analysis of heterozygous mice revealed reduced responsiveness to exogenous and endogenous CDNs in mice carrying a single copy of STING-HAQ, while STING-R231H heterozygous mice exhibit reduced responsiveness to exogenous but not endogenous CDNs. These findings confirm and extend previous reports by demonstrating differing impact of allelic variation of STING on the ability to sense and respond to exogenous vs. endogenous CDNs. Finally, the STING-R231H variant mouse represents a useful tool with which to examine the relative contributions of STING sensing of exogenous and endogenous CDNs in the context of bacterial infections and CDN-based cancer immunotherapeutics.

CD73 Blockade Promotes Dendritic Cell Infiltration of Irradiated Tumors and Tumor Rejection

The ability of focal radiotherapy to promote priming of tumor-specific CD8⁺ T cells and increase responses to immunotherapy is dependent on infiltration of the tumor by Batf3-dependent conventional dendritic cell type 1 (cDC1) cells. Such infiltration is driven by radiotherapy-induced IFN type I (IFN-I). Other signals may also modulate cDC1 infiltration of irradiated tumors. Here we found increased expression of adenosine-generating enzymes CD38 and CD73 in irradiated mouse and human breast cancer cells and increased adenosine in mouse tumors following radiotherapy. CD73 blockade alone had no effect. CD73 blockade with radiotherapy restored radiotherapy-induced cDC1 infiltration of tumors in settings where radiotherapy induction of IFN-I was suboptimal. In the absence of radiotherapy-induced IFN-I, blockade of CD73 was required for rejection of the irradiated tumor and for systemic tumor control (abscopal effect) in the context of cytotoxic T-lymphocyte-associated protein 4 blockade. These results suggest that CD73 may be a radiation-induced checkpoint, and that CD73 blockade in combination with radiotherapy and immune checkpoint blockade might improve patient response to therapy.

STING pathway agonism as a cancer therapeutic

The fact that a subset of human cancers showed evidence for a spontaneous adaptive immune response as reflected by the T cell-inflamed tumor microenvironment phenotype led to the search for candidate innate immune pathways that might be driving such endogenous responses. Preclinical studies indicated a major role for the host STING pathway, a cytosolic DNA sensing pathway, as a proximal event required for optimal type I interferon production, dendritic cell activation, and priming of CD8⁺ T cells against tumor-associated antigens. STING agonists are therefore being developed as a novel cancer therapeutic, and a greater understanding of STING pathway regulation is leading to a broadened list of candidate immune regulatory targets. Early phase clinical trials of intratumoral STING agonists are already showing promise, alone and in combination with checkpoint blockade. Further advancement will derive from a deeper understanding of STING pathway biology as well as mechanisms of response vs resistance in individual cancer patients.

SV40 Large T Antigen Is Not Responsible for the Loss of STING in 293T Cells but Can Inhibit cGAS-STING Interferon Induction

Several DNA viruses have evolved antagonists to inhibit the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) DNA-sensing immune pathway. This includes DNA viral oncogenes that antagonize the cGAS-STING pathway by binding STING through the LxCxE motif. The 293T human cells are widely used in biology studies as they are highly transfectable. While parental 293 cells express high levels of STING, 293T cells lack STING and are unable to induce interferon antiviral responses to cytosolic DNA. Additionally, 293T cells express the SV40 polyomavirus large T antigen (LT) which enhances the replication of transfected DNA plasmids carrying the SV40 origin of replication. Since SV40 LT also encodes the LxCxE motif, the lack of STING expression in 293T cells is commonly assumed to be due to SV40 large T antigen. We find that SV40 LT does not alter exogenously expressed and endogenous levels of STING protein. We show that STING transcription is suppressed in 293T cells but is not driven by SV40. This study also revealed that SV40 LT does indeed inhibit cGAS-STING interferon induction, but through a mechanism distinct from other DNA virus oncogenes. Collectively, these results indicate that while SV40 LT can inhibit cGAS-STING interferon induction, it does so in an unanticipated manner.

The Cytosolic DNA-Sensing cGAS-STING Pathway in Cancer

The recognition of DNA as an immune-stimulatory molecule is an evolutionarily conserved mechanism to initiate rapid innate immune responses against microbial pathogens. The cGAS-STING pathway was discovered as an important DNA-sensing machinery in innate immunity and viral defense. Recent advances have now expanded the roles of cGAS-STING to cancer. Highly aggressive, unstable tumors have evolved to co-opt this program to drive tumorigenic behaviors. In this review, we discuss the link between the cGAS-STING DNA-sensing pathway and antitumor immunity as well as cancer progression, genomic instability, the tumor microenvironment, and pharmacologic strategies for cancer therapy. SIGNIFICANCE: The cGAS-STING pathway is an evolutionarily conserved defense mechanism against viral infections. Given its role in activating immune surveillance, it has been assumed that this pathway primarily functions as a tumor suppressor. Yet, mounting evidence now suggests that depending on the context, cGAS-STING signaling can also have tumor and metastasis-promoting functions, and its chronic activation can paradoxically induce an immune-suppressive tumor microenvironment.

Immune induction strategies to enhance responses to PD-1 blockade: lessons from the TONIC trial

Programmed cell death protein 1 (PD-1) blockade is only effective in a minority of patients, prompting the search for combinatorial therapies that increase responses. Identifying effective combinations requires lengthy testing and so far has shown few successes. To accelerate progress Voorwerk and colleagues (Nat Med. 25(6):920-8, 2019) used an adaptive trial design to compare 4 short-course therapies (radiotherapy, cyclophosphamide, cisplatin and doxorubicin) for their ability to improve the tumor immune microenvironment and enhance responses to subsequent PD-1 blockade in women with metastatic triple negative breast cancer, a disease with low response rate to PD-1 blockade. They reported the first phase of the trial that enrolled 12 to 17 patients per arm to "pick the winner" induction treatment. Higher objective response rates (ORR) compared to no induction were observed only in the arm containing doxorubicin, which proceeded to phase II. These results raise a number of questions about testing local versus systemic induction treatments and whether sequencing with PD-1 blockade is appropriate in light of evidence supporting concomitant treatment, at least for radiotherapy. Small imbalances in baseline characteristics can also influence results obtained with limited numbers of patients per arm. We hope that these considerations will help future adaptive, signal-finding combination immunotherapy studies.

The cGAS Paradox: Contrasting Roles for cGAS-STING Pathway in Chromosomal Instability

Chromosomal instability (CIN) is an intricate phenomenon that is often found in human cancer, characterized by persisting errors in chromosome segregation. This ongoing chromosome mis-segregation results in structural and numerical chromosomal abnormalities that have been widely described to promote tumor evolution. In addition to being a driver of tumor evolution, recent evidence demonstrates CIN to be the central node of the crosstalk between a tumor and its surrounding microenvironment, as mediated by the cGAS-STING pathway. The role that cGAS-STING signaling exerts on CIN tumors is both complex and paradoxical. On one hand, the cGAS-STING axis promotes the clearance of CIN tumors through recruitment of immune cells, thus suppressing tumor progression. On the other hand, the cGAS-STING pathway has been described to be the major regulator in the promotion of metastasis of CIN tumors. Here, we review this dual role of the cGAS-STING pathway in the context of chromosomal instability and discuss the potential therapeutic implications of cGAS-STING signaling for targeting CIN tumors.

STING (or SRC) Like an ICB: Priming the Immune Response in Pancreatic Cancer

Pancreatic adenocarcinoma is associated with a poor prognosis and resistance to immune checkpoint blockade. Zhang and colleagues demonstrate that inhibiting DNA repair by pharmacologic blockade or siRNA silencing of ataxia telangiectasia mutated (ATM) increases type I IFN release via a cGAS/STING-independent, SRC-dependent mechanism in models of pancreatic cancer. Furthermore, combining ATM inhibition and radiotherapy amplifies type I IFN signaling, increases programmed death ligand 1 (PD-L1) expression, tumor CD8⁺ T cells, and proinflammatory tumor macrophages. Finally, the combination of ATM silencing, radiotherapy, and PD-L1 blockade markedly improves in vivo murine tumor responses, supporting further investigation of this promising approach in pancreatic adenocarcinoma.See related article by Zhang et al., p. 3940.

Inflammatory signaling in genomically instable cancers

Recent studies have shown that genomic instability in tumor cells leads to activation of inflammatory signaling through the cGAS/STING pathway. In this review, we describe multiple ways by which genomic instability leads to cGAS/STING-mediated inflammatory signaling, as well as the consequences for tumor development and the tumor microenvironment. Also, we elaborate on how tumor cells have apparently evolved to escape the immune surveillance mechanisms that are triggered by cGAS/STING signaling. Finally, we describe how cGAS/STING-mediated inflammatory signaling can be therapeutically targeted to improve therapy responses.

Type I interferon signaling, regulation and gene stimulation in chronic virus infection

Type I Interferons (IFN-I) mediate numerous immune interactions during viral infections, from the establishment of an antiviral state to invoking and regulating innate and adaptive immune cells that eliminate infection. While continuous IFN-I signaling plays critical roles in limiting virus replication during both acute and chronic infections, sustained IFN-I signaling also leads to chronic immune activation, inflammation and, consequently, immune exhaustion and dysfunction. Thus, an understanding of the balance between the desirable and deleterious effects of chronic IFN-I signaling will inform our quest for IFN-based therapies for chronic viral infections as well as other chronic diseases, including cancer. As such the factors involved in induction, propagation and regulation of IFN-I signaling, from the initial sensing of viral nucleotides within the cell to regulatory downstream signaling factors and resulting IFN-stimulated genes (ISGs) have received significant research attention. This review summarizes recent work on IFN-I signaling in chronic infections, and provides an update on therapeutic approaches being considered to counter such infections.

Radiotherapy induces responses of lung cancer to CTLA-4 blockade

Focal radiation therapy enhances systemic responses to anti-CTLA-4 antibodies in preclinical studies and in some patients with melanoma1-3, but its efficacy in inducing systemic responses (abscopal responses) against tumors unresponsive to CTLA-4 blockade remained uncertain. Radiation therapy promotes the activation of anti-tumor T cells, an effect dependent on type I interferon induction in the irradiated tumor4-6. The latter is essential for achieving abscopal responses in murine cancers6. The mechanisms underlying abscopal responses in patients treated with radiation therapy and CTLA-4 blockade remain unclear. Here we report that radiation therapy and CTLA-4 blockade induced systemic anti-tumor T cells in chemo-refractory metastatic non-small-cell lung cancer (NSCLC), where anti-CTLA-4 antibodies had failed to demonstrate significant efficacy alone or in combination with chemotherapy7,8. Objective responses were observed in 18% of enrolled patients, and 31% had disease control. Increased serum interferon-β after radiation and early dynamic changes of blood T cell clones were the strongest response predictors, confirming preclinical mechanistic data. Functional analysis in one responding patient showed the rapid in vivo expansion of CD8 T cells recognizing a neoantigen encoded in a gene upregulated by radiation, supporting the hypothesis that one explanation for the abscopal response is radiation-induced exposure of immunogenic mutations to the immune system.

Therapeutically Active RIG-I Agonist Induces Immunogenic Tumor Cell Killing in Breast Cancers

Cancer immunotherapies that remove checkpoint restraints on adaptive immunity are gaining clinical momentum but have not achieved widespread success in breast cancers, a tumor type considered poorly immunogenic and which harbors a decreased presence of tumor-infiltrating lymphocytes. Approaches that activate innate immunity in breast cancer cells and the tumor microenvironment are of increasing interest, based on their ability to induce immunogenic tumor cell death, type I IFNs, and lymphocyte-recruiting chemokines. In agreement with reports in other cancers, we observe loss, downregulation, or mutation of the innate viral nucleotide sensor retinoic acid-inducible gene I (RIG-I/DDX58) in only 1% of clinical breast cancers, suggesting potentially widespread applicability for therapeutic RIG-I agonists that activate innate immunity. This was tested using an engineered RIG-I agonist in a breast cancer cell panel representing each of three major clinical breast cancer subtypes. Treatment with RIG-I agonist resulted in upregulation and mitochondrial localization of RIG-I and activation of proinflammatory transcription factors STAT1 and NF-κB. RIG-I agonist triggered the extrinsic apoptosis pathway and pyroptosis, a highly immunogenic form of cell death in breast cancer cells. RIG-I agonist also induced expression of lymphocyte-recruiting chemokines and type I IFN, confirming that cell death and cytokine modulation occur in a tumor cell-intrinsic manner. Importantly, RIG-I activation in breast tumors increased tumor lymphocytes and decreased tumor growth and metastasis. Overall, these findings demonstrate successful therapeutic delivery of a synthetic RIG-I agonist to induce tumor cell killing and to modulate the tumor microenvironment in vivo Significance: These findings describe the first in vivo delivery of RIG-I mimetics to tumors, demonstrating a potent immunogenic and therapeutic effect in the context of otherwise poorly immunogenic breast cancers. Cancer Res; 78(21); 6183-95. ©2018 AACR.

The Multifaceted Role of Chromosomal Instability in Cancer and Its Microenvironment

Chromosomal instability (CIN) is a hallmark of human cancer, and it is associated with poor prognosis, metastasis, and therapeutic resistance. CIN results from errors in chromosome segregation during mitosis, leading to structural and numerical chromosomal abnormalities. In addition to generating genomic heterogeneity that acts as a substrate for natural selection, CIN promotes inflammatory signaling by introducing double-stranded DNA into the cytosol, engaging the cGAS-STING anti-viral pathway. These multipronged effects distinguish CIN as a central driver of tumor evolution and as a genomic source for the crosstalk between the tumor and its microenvironment, in the course of immune editing and evasion.

KDM5 histone demethylases repress immune response via suppression of STING

Cyclic GMP-AMP (cGAMP) synthase (cGAS) stimulator of interferon genes (STING) senses pathogen-derived or abnormal self-DNA in the cytosol and triggers an innate immune defense against microbial infection and cancer. STING agonists induce both innate and adaptive immune responses and are a new class of cancer immunotherapy agents tested in multiple clinical trials. However, STING is commonly silenced in cancer cells via unclear mechanisms, limiting the application of these agonists. Here, we report that the expression of STING is epigenetically suppressed by the histone H3K4 lysine demethylases KDM5B and KDM5C and is activated by the opposing H3K4 methyltransferases. The induction of STING expression by KDM5 blockade triggered a robust interferon response in a cytosolic DNA-dependent manner in breast cancer cells. This response resulted in resistance to infection by DNA and RNA viruses. In human tumors, KDM5B expression is inversely associated with STING expression in multiple cancer types, with the level of intratumoral CD8⁺ T cells, and with patient survival in cancers with a high level of cytosolic DNA, such as human papilloma virus (HPV)-positive head and neck cancer. These results demonstrate a novel epigenetic regulatory pathway of immune response and suggest that KDM5 demethylases are potential targets for antipathogen treatment and anticancer immunotherapy.

Pathogens often find ways to turn down cell-intrinsic antipathogen immune responses by the host. Similarly, cancer cells use various mechanisms to evade attack by immune cells. One of the common mechanisms is suppression of the stimulator of interferon genes (STING)-dependent innate immune response. Using potent and specific small-molecule inhibitors and genetic-depletion approaches, we found that the silenced STING pathway can be reactivated in breast cancer cells by suppressing KDM5 demethylases. Activation of the STING pathway led to a robust interferon response, which blocked viral infection, and was associated with increased tumor-infiltrated lymphocytes and better patient survival in multiple cancer types. This discovery has major clinical implications for treating both pathogen infection and cancer because KDM5 inhibition provides a fast, robust, and reversible control of innate immune response. Since the discovery of histone demethylase activity of KDM5 proteins a decade ago, significant efforts have been dedicated to developing KDM5 inhibitors for clinical applications. In fact, a KDM5 inhibitor recently entered phase I clinical trial for treatment of hepatitis B infection. Here, we provide mechanistic insights on how KDM5 inhibitors block viral infection. Moreover, our results suggest that KDM5 inhibitors can also be combined with other cancer immunotherapies.

Structure of the Human cGAS-DNA Complex Reveals Enhanced Control of Immune Surveillance

Cyclic GMP-AMP synthase (cGAS) recognition of cytosolic DNA is critical for immune responses to pathogen replication, cellular stress, and cancer. Existing structures of the mouse cGAS-DNA complex provide a model for enzyme activation but do not explain why human cGAS exhibits severely reduced levels of cyclic GMP-AMP (cGAMP) synthesis compared to other mammals. Here, we discover that enhanced DNA-length specificity restrains human cGAS activation. Using reconstitution of cGAMP signaling in bacteria, we mapped the determinant of human cGAS regulation to two amino acid substitutions in the DNA-binding surface. Human-specific substitutions are necessary and sufficient to direct preferential detection of long DNA. Crystal structures reveal why removal of human substitutions relaxes DNA-length specificity and explain how human-specific DNA interactions favor cGAS oligomerization. These results define how DNA-sensing in humans adapted for enhanced specificity and provide a model of the active human cGAS-DNA complex to enable structure-guided design of cGAS therapeutics.

Harnessing RIG-I and intrinsic immunity in the tumor microenvironment for therapeutic cancer treatment

Cancer immunotherapies that remove checkpoint restraints on adaptive immunity are gaining clinical momentum. Approaches aimed at intrinsic cellular immunity in the tumor microenvironment are less understood, but are of intense interest, based on their ability to induce tumor cell apoptosis while orchestrating innate and adaptive immune responses against tumor antigens. The intrinsic immune response is initiated by ancient, highly conserved intracellular proteins that detect viral infection. For example, the RIG-I-like receptors (RLRs), a family of related RNA helicases, detect viral oligonucleotide patterns of certain RNA viruses. RLR activation induces immunogenic cell death of virally infected cells, accompanied by increased inflammatory cytokine production, antigen presentation, and antigen-directed immunity against virus antigens. Approaches aimed at non-infectious RIG-I activation in cancers are being tested as a treatment option, with the goal of inducing immunogenic tumor cell death, stimulating production of pro-inflammatory cytokines, enhancing tumor neoantigen presentation, and potently increasing cytotoxic activity of tumor infiltrating lymphocytes. These studies are finding success in several pre-clinical models, and are entering early phases of clinical trial. Here, we review pre-clinical studies of RLR agonists, including the successes and challenges currently faced RLR agonists on the path to clinical translation.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.