Cyclic AMP GMP Research Articles

The Role of the cGAS/STING Pathway in Arsenic-Induced Neurotoxicity: Insights from the Crosstalk Between Astrocytes and Neurons.

Arsenic is a detrimental environmental toxicant linked to neurological damage; however, the mechanisms involved remain incompletely understood. Chronic proinflammatory responses are thought to play a central role in arsenic-induced neurotoxicity. Astrocytes, which are the predominant glial cells in the central nervous system (CNS), release significant amounts of proinflammatory cytokines upon overactivation. However, the molecular mechanisms driving this response remain to be elucidated. This study aimed to elucidate the mechanisms underlying arsenic-induced astrocyte activation and the subsequent neuronal damage, both in vivo and in vitro. In a rat model of arsenic exposure, significant neuropathological damage was detected in the CA3 region of the hippocampus. Specifically, markers of astrocyte activation, such as glial fibrillary acidic protein (GFAP) and inducible nitric oxide synthase (iNOS), as well as the inflammatory cytokine interleukin (IL)-1β, were significantly upregulated, and apoptosis was markedly increased, indicating neurotoxic damage. Furthermore, in vitro experiments revealed that arsenic exposure induced substantial upregulation of cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), GFAP, iNOS, and IL-1β in astrocytes, accompanied by an increase in IL-1β secretion into the culture supernatant. In addition, co-culturing neurons with conditioned medium from arsenic-exposed astrocytes resulted in significant neuronal apoptosis. Importantly, the cGAS-STING pathway inhibitor H-151 effectively suppressed the arsenic-induced astrocyte activation and IL-1β secretion, while also reducing neuronal apoptosis in the conditioned medium. Collectively, these results indicate that arsenic exposure activates the cGAS-STING signaling pathway in astrocytes, enhancing proinflammatory activation and IL-1β expression, which in turn mediates neuronal apoptosis, representing a critical mechanism underlying arsenic-induced neurotoxicity.

Cordycepin ameliorates autoimmunity by promoting STING degradation via autophagy pathway.

Stimulator of interferon response cGAMP interactor 1 (STING), a central hub protein of cyclic GMP-AMP synthase (cGAS)-STING signalling pathway, has a crucial role in regulating type I interferons (IFNs) production and response. Recent studies indicate that excessive activation of STING is strongly associated with autoimmune diseases, including systemic lupus erythematosus (SLE). Searching immunomodulators that negatively regulate STING might greatly contribute to the suppression of autoimmunity. The peripheral blood mononuclear cells (PBMCs) of SLE patients, Hela cells, L929 cells and bone marrow-derived macrophages (BMDMs) from mice were used as in vitro models. While, Trex1 KO mouse autoimmune disease model was used as in vivo model. After treatment with cordycepin, a nucleoside from Cordyceps mushrooms, type I IFNs production and response were determined by western blotting, real-time polymerase chain reaction (PCR), dual-luciferase assay, enzyme-linked immunosorbent assay (ELISA), haematoxylin-eosin staining and RNA-seq. Cordycepin inhibited type I IFNs production and response in human and murine systems following cGAS-STING signalling activation. Importantly, cordycepin markedly attenuates the autoinflammatory and autoimmune responses in Trex1 KO BMDMs and Trex1 KO mice. Furthermore, cordycepin effectively suppressed the production of type I IFNs and interferon-stimulated genes (ISGs) in the PBMCs of SLE patients. Mechanistically, cordycepin promoted STING degradation via autophagy pathway upon DNA stimulation. This study shows that cordycepin promotes STING autophagic degradation to alleviate autoimmunity upon DNA stimulation. Cordycepin might be a potential therapeutic candidate for alleviating aberrant type I IFNs in autoimmune and autoinflammatory diseases.

Therapeutic targeting of cGAS-STING pathway in lung cancer.

The presence of DNA in the cytosol triggers a protective response from the innate immune system. Cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) is an essential cytosolic DNA sensor that triggers a potent innate immune response. As a result of this signaling cascade reaction, type I interferon and other immune mediators activate an immune response. The cGAS-STING pathway has great anticancer immunity-boosting potential since it produces type I interferons. The detection of double-stranded DNA (dsDNA) in response to various stimuli initiates a protective host's cGAS-STING signals. So, it is clear that a substantial relationship is expected between cancer biotherapy and the functioning of the cGAS-STING pathway. Several STING agonists with promising outcomes have been created for preclinical cancer therapy research. Notably, immunotherapy has dramatically extended patient survival and radically altered the course of lung cancer treatment, particularly in more advanced instances. However, this method is still ineffective for a large number of lung cancer patients. cGAS-STING can overcome resistance and boost anticancer immunity by stimulating the activity of many pro-inflammatory mediators, augmenting dendritic cell cross-presentation, and initiating a tumor-specific CD8+ T cell response. This review aims to present the most recent results on the functionality of the cGAS-STING pathway in cancer progression and its potential as an immunotherapy target, with a focus on lung cancer.

An Oral Nanovaccine Secreted by Genetically Engineered and Ultrasound‐Responsive Bacteria for Colon Cancer Immunotherapy

AbstractColorectal cancers represent a major global morbidity and mortality burden, neccessitating improved treatment paradigms. In this work, an ingestible, genetically engineered Escherichia coli (E. coli) 1917 termed “E. coli (AH1‐CDA‐Co1)” is designed that upon ultrasound exposure secretes bacterial outer membrane vesicles (OMV) incorporating the AH1 tumor rejection epitope, an enzyme producing the stimulator of interferon genes (STING) agonist CDA, and the microfold cell‐targeting peptide Co1. For oral administration, a polydopamine system (iPDA) coating on bacteria is exploited to resist the acidic condition in stomach, increase the bacterial survival, and prolong the intestinal transit time. Upon harmless ultrasound exposure, sustained secretion of engineered OMV vaccines is triggered that efficiently cross the intestinal epithelium. Both cyclic GMP–AMP synthase (cGAS)‐STING and TLR4 innate immune signaling pathways are activated, triggering long‐term antigen‐specific immune responses that overcome the immunosuppressive tumor microenvironment. In subcutaneous and orthotopic murine colorectal tumor models, the E. coli (AH1‐CDA‐Co1)@iPDA system inhibits tumor growth and prolongs survival without recurrence. E. coli (AH1‐CDA‐Co1)@iPDA also inhibits tumor growth and recurrence in a postoperative orthotopic colonrectal tumor model of lymph node metastases. Taken together, E. coli (AH1‐CDA‐Co1)@iPDA demonstrates a potent oral vaccine system for improved colon cancer immunotherapy.

OMP38 of Carbapenem-Resistant Acinetobacter Baumannii-Mediated mtDNA Release Activates the cGAS-STING Signaling to Induce Inflammatory Response.

Carbapenem-resistant Acinetobacter baumannii (CRAB) has become a major threat in the treatment of bacterial infection, and immunotherapy in a non-antibiotic-dependent manner is an effective way to overcome CRAB infection. However, the role of the innate immune response in CRAB infection is poorly understood. Here, it is reported that CRAB infection induced a cytosolic DNA-sensing signaling pathway and significant IFN-β production in mice post-CRAB infection. The knockout of STING reduced bacterial burden, the production of inflammatory cytokines, and lung injury in mice post CRAB infection. The cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) and the adaptor protein stimulator of interferon genes (STING) are required for CRAB-induced IFN-β expression in macrophages. Intriguingly, CRAB utilized outer membrane vesicles (OMVs) to transport outer membrane protein 38 (OMP38) into mitochondria, triggering mitochondrial DNA (mtDNA) release into the cytosol through the mitochondrial permeability transition pore (mPTP) and activating the cGAS-STING signaling. Finally, epigallocatechin gallate (EGCG) is demonstrated to block the activation of the cGAS-STING pathway and ameliorate CRAB-induced excessive inflammatory response. These results demonstrated that the early innate immune response to CRAB infection is activated in a cGAS-STING-dependent manner, which could be a potential therapeutic target for CRAB infection.

Epstein-Barr virus and immunity.

The Epstein-Barr virus has infected the vast majority of the world's population. EBV is the most common herpes virus in the human population. In childhood, viral infection is either asymptomatic or can lead to infectious mononucleosis. In a small proportion of latently infected people, especially in immunosuppressed patients, EBV causes lymphoid and epithelial malignancies and a number of autoimmune diseases, including one of the causes of the development of multiple sclerosis. Innate immunity is the first line of antiviral defense, which EBV evades using a number of strategies to achieve successful infection. EBV disrupts the innate immune signaling pathways activated by Toll-like, RIG-I-like, NOD-like and AIM2-like receptors, as well as cyclic GMP-AMP synthetase. EBV also antagonizes interferon production and signaling, including the TBK1-IRF3 and JAK-STAT pathways. Through differential modulation of proviral and antiviral mechanisms of action of caspases and other cellular life cycle regulators at different stages of infection, EBV actively interferes with apoptotic and inflammatory pathways to continue effective infection. By turning the activation of innate immunity to its advantage by triggering a pro-inflammatory reaction and proteolytic cleavage of caspases that exhibit proviral activity, the virus establishes latency or enters the lytic reactivation phase, which contributes to the development of serious life-threatening diseases, including oncogenesis. The outcome of EBV infection is regulated by a subtle interaction between innate, adaptive immunity, and viral replication. In the absence of licensed preventive vaccines, immunocorrection and antiviral therapy are the only possible ways to combat the virus and prevent diseases associated with it. Understanding the mechanisms of action of certain EBV genes involved in the life cycle at different stages of infection will help in the future to find the right approach to the development of preventive and therapeutic drugs against EBV.

HO-1 impairs the efficacy of radiotherapy by redistributing cGAS and STING in tumors.

Type I IFNs (IFN-Is) induced by radiotherapy (RT) are critical for its efficacy, while the mechanism by which tumor cells inhibit IFN-I production remains largely unsolved. By an unbiased CRISPR screen, we identified hemeoxygenase 1 (HO-1) as an RT-related regulator of IFN-I production. Mechanistically, the ER-anchored, full-length HO-1 disrupted stimulator of IFN genes (STING) polymerization and subsequent coat protein complex II-mediated (COPII-mediated) ER-Golgi transportation, leading to hampered activation of downstream signaling. This process was exacerbated by the upregulation of HO-1 expression under RT. Importantly, RT also induced HO-1 cleavage. Cleaved HO-1 underwent nuclear translocation, interacted with cyclic GMP-AMP synthase (cGAS), and inhibited its nuclear export upon irradiation, leading to suppressed 2'3'-cyclic GMP-AMP (cGAMP) production. Furthermore, we revealed that HO-1 inhibitors could enhance local and distant tumor control of RT in vivo. Clinically, higher HO-1 expression was associated with a poorer prognosis and earlier tumor relapse after RT in multiple types of patient tumors. Collectively, through comprehensive inhibition of the cGAS/STING pathway, HO-1 strongly inhibited RT-induced IFN-I production, and targeting HO-1 was shown to be a promising RT-sensitizing therapeutic strategy.

A novel small molecule Enpp1 inhibitor improves tumor control following radiation therapy by targeting stromal Enpp1 expression

The uniqueness in each person’s cancer cells and variation in immune infiltrates means that each tumor represents a unique problem, but therapeutic targets can be found among their shared features. Radiation therapy alters the interaction between the cancer cells and the stroma through release of innate adjuvants. The extranuclear DNA that can result from radiation damage of cells can result in production of the second messenger cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) by cyclic GMP-AMP synthase (cGAS). In turn, cGAMP can activate the innate sensor stimulator of interferon genes (STING), resulting in innate immune activation. Ectonucleotide pyrophosphatase/phosphodiesterase 1 (Enpp1) is a phosphodiesterase that can be expressed by cancer cells that can degrade cGAMP, thus can decrease or block STING activation following radiation therapy, impairing the innate immunity that is critical to support adaptive immune control of tumors. We observed that many human and murine cancer cells lack Enpp1 expression, but that Enpp1 is expressed in cells of the tumor stroma where it limits tumor control by radiation therapy. We demonstrate in preclinical models the efficacy of a novel Enpp1 inhibitor and show that this inhibitor improves tumor control by radiation even where the cancer cells lack Enpp1. This mechanism requires STING and type I interferon (IFN) receptor expression by non-cancer cells and is dependent on CD8 T cells as a final effector mechanism of tumor control. This suggests that Enpp1 inhibition may be an effective partner for radiation therapy regardless of whether cancer cells express Enpp1. This broadens the potential patient base for whom Enpp1 inhibitors can be applied to improve innate immune responses following radiation therapy.

An immunostimulatory liponanogel reveals immune activation-enhanced drug delivery and therapeutic efficacy in cancer

The clinical use of immunostimulatory polyinosinic:polycytidylic acid (pIC) for cancer therapy has been notably limited by its low tumor accumulation and poor cytosolic delivery to activate innate immune sensors. Here, we report a liponanogel (LNG)-based platform to address these challenges. The immunostimulatory LNG consists of an ionizable lipid shell coating a nanogel made of hyaluronic acid (HA), Mn2+ and pIC, which is denoted as LNG-Mn-pIC (LMP). The protonation of internal HA within acidic endosomes increases the endosomal membrane permeability and facilitates the cytosolic delivery of pIC. Moreover, Mn2+, previously reported to activate the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, synergizes with pIC to activate innate immune cells. Remarkably, intravenously injected LMP significantly induces tumor vasculature disruption and tumor cell apoptosis in an innate immune activation-dependent manner, facilitating the LMP delivery into tumors and leading to enhanced antitumor immunity that potently inhibits or even completely regresses the established tumors. In summary, this immunostimulatory LNG platform not only serves as a useful tool to uncover the immune activation-enhanced drug delivery profile but also represents a broadly applicable platform for effective cancer immunotherapy.

The cGAS-STING pathway activates transcription factor TFEB to stimulate lysosome biogenesis and pathogen clearance.

Induction of autophagy is an ancient function of the cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway through which autophagic cargoes are delivered to lysosomes for degradation. However, whether lysosome function is also modulated by the cGAS-STING pathway remains unknown. Here, we discovered that the cGAS-STING pathway upregulated lysosomal activity by stimulating lysosome biogenesis independently of the downstream protein kinase TANK-binding kinase 1 (TBK1). STING activation enhanced lysosome biogenesis through inducing the nuclear translocation of transcription factor EB (TFEB) as well as its paralogs transcription factor E3 (TFE3) and microphthalmia-associated transcription factor (MITF). STING-induced lipidation of GABA type A receptor-associated protein (GABARAP), an autophagy-related protein, on STING vesicles was responsible for TFEB activation. Membrane-bound GABARAP sequestered the GTPase-activating protein folliculin (FLCN) and FLCN-interacting protein (FNIP) complex to block its function toward the Rag GTPases Ras-related GTP-binding C and D (RagC and RagD), abolishing mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent phosphorylation and inactivation of TFEB. Functionally, STING-induced lysosome biogenesis within cells facilitated the clearance of cytoplasmic DNA and invading pathogens. Thus, our findings reveal that induction of lysosome biogenesis is another important function of the cGAS-STING pathway.

6-shogaol attenuates cisplatin induced emesis by inhibiting the mtDNA-cGAS-STING signaling pathway in a rat pica model.

Ginger (Zingiber officinale Rosc.) is a traditional anti-emetic herb. 6-shogaol, the main active compound of ginger, is reported to possess a variety of bioactivities. This study aimed to investigate the anti-emetic effect of 6-shogaol in a cisplatin-induced pica rat model and explore its underlying mechanism. sThe rat pica model was established by intraperitoneal injection of cisplatin. The pathological damage of gastric antrum and ileum were observed by hematoxylin-eosin staining. The levels of serum 8-Hydroxy-desoxyguanosine (8-OHdG) were detected by ELISA. The expression of ZO1 tight junction protein (TJP-1) and occludin in ileum were determined by IHC. The levels of 8-oxo G DNA glycosylase 1 (OGG1), flap endonuclease 1 (FEN1), cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), phospho-STING (p-STING), TANK binding kinase 1 (TBK1), phospho-TBK1 (pTBK1), nuclear factor kappa-B (NF-κB) and phospho-NF-κB (p-NF-κB) in gastric antrum and ileum were assayed by western blotting. We found that 6-shogaol significantly improved pica behavior in rats by downregulating NF-κB and IL-1β level, and ameliorating inflammatory damage in gastric antrum and ileum. Mechanistically, cGAS-STING axis activated by mtDNA is responsible for the cisplatin-induced gastrointestinal inflammatory responses. 6-Shogaol inhibited the mtDNA-cGAS-STING signaling pathway by increasing the level of base-excision repair enzyme OGG1 and decreasing the level of endonuclease FEN1. This study indicates that 6-shogaol has a therapeutic effect against chemotherapy-induced nausea and vomiting (CINV), potentially attributable to the suppression of the mtDNA-cGAS-STING signaling pathway.

CGAS/STING pathway modulation in polyhexamethyleneguanidine phosphate-induced immune dysregulation and pulmonary fibrosis using human monocytic cells (THP-1) and male C57BL/6 mice

ABSTRACT Polyhexamethyleneguanidine phosphate (PHMG), a widely used antimicrobial agent, has been implicated in humidifier disinfectant-associated lung injuries (HDLI). PHMG exposure suppressed interferon regulatory factor 3 (IRF3) activation and interferon-β (IFN-β) expression induced by a cGAS agonist or a STING agonist in human monocytic cells (THP-1), which are known to transition to alveolar macrophages during pulmonary fibrosis development. However, the mechanisms underlying PHMG-induced pulmonary toxicity in lung remain unclear. Thus, it was of interest to investigate the effects of PHMG on the innate immune system in male C57BL/6 mouse, focusing on the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway and potential role in pulmonary fibrosis. Intratracheal administration of PHMG (1 or 2 mg/kg) in mice resulted in lung fibrosis, as evidenced by H&E staining with Szapiel scoring, Masson’s trichrome staining with Ashcroft scoring, and increased mRNA levels of TGF-β and collagen type I. Interestingly, lower dose of PHMG enhanced IFN-β production in the lungs, whereas higher dose decreased IFN-β levels, indicating a biphasic effect that initially promotes inflammation but ultimately impairs host defense mechanisms, leading to pulmonary fibrosis. Our findings demonstrate the critical role of the cGAS/STING pathway in PHMG-induced mouse lung injury and suggest that targeting this pathway might serve as a potential therapeutic strategy for treating pulmonary fibrosis.

Macrophage biomimetic intelligent hollow MnO2 nanoparticle for synergistic sonodynamic-immunotherapy of glioblastoma by crossing blood brain barrier

Though emerging novel theranostics based intelligent nanomaterials for cancers are promising ways to solve the disadvantages of traditional therapeutic methods, poor targeting of these nanomaterials and the presence of blood–brain barrier (BBB) in glioblastoma (GBM) seriously reduces the efficacy of GBM treatment. Herein, an intelligent nanoparticle consisting of macrophage membrane coated hollow manganese dioxide loading ce6 (MM-HMnO2@Ce6) was prepared, which could be used for magnetic resonance imaging (MRI) guided sonodynamic therapy (SDT)-immunotherapy of in situ GBM. Comparing to early reports, MM-HMnO2@Ce6 could target intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) receptors on endothelial cells of GBM, and cross BBB, which enhanced the efficiency of GBM treatment. What’s more, the as-prepared nanoparticle also monitored the process of targeting and crossing BBB by MRI due to its tumour microenvironment (TME) responsive feature. What’s more, the detailed therapeutic mechanisms were also determined to be by generating reactive oxygen species (ROS), activating immature DCs and activating the cGAS (cyclic GMP-AMP synthase)-STING (stimulator of interferon genes) pathway. Overall, this work showcases a remarkable synergistic anticancer effect of SDT-immunotherapy, and also proposes new avenues for research in utilizing MnO2 nanomaterials for GBM treatment.

Engineering Autologous Cell-Derived Exosomes to Boost Melanoma-Targeted Radio-Immunotherapy by Cascade cGAS-STING Pathway Activation.

Radio-immunotherapy has offered emerging opportunities to treat invasive melanoma due to its immunostimulatory performances to activate antitumor immune responses. However, the immunosuppressive microenvironment and insufficient response rate significantly limit the practical efficacy. This study presents an autologous cell-derived exosomes (Exo)-engineered nanoagonist (MnExo@cGAMP) containing with metalloimmunotherapeutic agent (Mn2+ ions) and nucleotidyltransferase (2',3'-cGAMP, a STING agonist) for boosting melanoma-targeted radio-immunotherapy by cascade cGAS-STING pathway activation. The MnExo@cGAMP can efficiently accumulate in tumor cells due to the autologous targeting performance. Once internalized by tumor cells, the released Mn2+ ions will enhance stimulator of interferon gene (STING) binding and sensitize cyclic GMP-AMP (cGAS) to radiotherapy-induced double-straned DNA (dsNDA), resulting in amplification of cGAS-STING pathway activation together with X-ray irradiation. Meanwhile, loaded 2',3'-cGAMP can directly augment pathway activity acting as a secondary messenger. These cascade activations of cGAS-STING pathway trigger the overexpression of type I interferon, promote dendritic cells (DCs) maturation, antigen presentation, and increase CD8+ T cell activation, resulting effective radio-immunotherapeutic outcome by overcoming immune-suppression in melanoma. This study demonstrates a targeted therapeutic modality involving metalloimmunotherapy and agonist for efficient melanoma radio-immunotherapy by cascade cGAS-STING pathway activation.

Cadmium exposure triggers alveolar epithelial cell pyroptosis by inducing mitochondrial oxidative stress and activating the cGAS-STING pathway

BackgroundCadmium is a ubiquitous toxic metal and environmental pollutant. More and more studies have shown that cadmium exposure can damage lung function. Alveolar epithelial cells (AECs) are structural cells that maintain the stability of lung function. The injury of AECs is an essential determinant of many lung diseases. In the lung, cadmium accumulation can cause damage to AECs. However, the specific mechanism is still unclear. This study aimed to explore the key mechanism underlying the injury of AECs caused by cadmium exposure.MethodsThe main modes of death of AECs induced by cadmium exposure were evaluated in vivo and in vitro. Transcriptomic changes of AECs induced by cadmium exposure were analyzed using RNA-sequence. Mitochondrial ROS scavengers (mitoQ), voltage-dependent anion channel 1 (VDAC1) oligomer inhibitor (VBIT4), and cyclic GMP-AMP synthase (cGAS) inhibitor (RU.521) were used to assess whether cadmium exposure triggered pyroptosis of AECs by inducing mitochondrial stress to activate the cGAS-STING-NLRP3 axis.ResultsIn this study, the expression of pyroptosis-related proteins was significantly up-regulated in the cadmium-exposed AECs, while the expression of apoptosis, necroptosis, and ferroptosis-related proteins had no significant up-regulated. The pan-caspase inhibitor ZVAD-FMK significantly reduced cell death. Thus, our research indicates that pyroptosis is the primary type of AEC death exported to cadmium. Mechanistically, RNA-seq and Western Blot results showed that cadmium exposure activated the cGAS-STING pathway in AECs and promoted pyroptosis by activating the NLRP3 inflammasome. Further investigation of the mechanism found that cadmium exposure caused mitochondrial oxidative stress, which led to mtDNA leakage into the cytoplasm and activated the cGAS-STING pathway. In addition, inhibition of the cGAS-STING pathway significantly alleviated lung injury induced by cadmium exposure in mice.ConclusionOur study confirmed that pyroptosis of AECs was a vital mechanism of lung injury after cadmium exposure in a cGAS-STING-dependent manner, which may provide a new target for the treatment of lung diseases induced by cadmium exposure.

γδ T Cell-mediated Tumor Immunity is Tightly Regulated by STING and TGF-β Signaling Pathways.

The STING pathway plays a critical role in tumor immunosurveillance. However, the precise mechanisms by which STING regulates gammadelta(γδ) T cell function during tumor progression remain unclear. Herein, we find that tumor-derived cyclic GMP-AMP (cGAMP) activates a distinct STING pathway by inducing TBK1-mediated phosphorylation of Eomes in γδ T cells during the early stage of tumor development is demonstrated. This activation leads to interferon-gamma (IFN-γ) production and consequent tumor surveillance. However, at advanced stages of tumor progression, the accumulation of immune-suppressive cytokine transforming growth factor-beta (TGF-β) downregulates STING levels, compromising the function of γδ T cells. Notably, the synergism between TGF-β inhibition and STING agonists effectively counteracts the immunosuppressive tumor microenvironment, thereby augmenting the antitumoral effects of γδ T cells. These findings present a novel mechanism involving STING-mediated IFN-γ production in γδ T cells and hold significant implications for the development of potent immunotherapeutic approaches against cancer.

The 4EHP-mediated translational repression of cGAS impedes the host immune response against DNA viruses

A critical host response against viral infections entails the activation of innate immune signaling that culminates in the production of antiviral proteins. DNA viruses are sensed by the cytosolic pattern recognition receptor cyclic GMP-AMP synthase (cGAS), which initiates a signaling pathway that results in production of proinflammatory cytokines such as Interferon-β (IFN-β) and activation of the antiviral response. Precise regulation of the antiviral innate immune response is required to avoid deleterious effects of its overactivation. We previously reported that the 4EHP/GIGYF2 translational repressor complex reduces the translation of Ifnb1 mRNA, which encodes IFN-β, upon RNA viral infections. Here, we report a distinct regulatory mechanism by which 4EHP controls replication of DNA viruses by translational repression of the Cgas mRNA, which encodes the DNA viral sensor cGAS. We show that 4EHP is required for effective translational repression of Cgas mRNA triggered by miR-23a. Upon infection, 4EHP deficiency bolsters the elicited innate immune response against the diverse DNA viruses Herpes simplex virus 1 (HSV-1) and Vaccinia Virus (VacV) and concomitantly reduces their rate of replication in vitro and in vivo. This study elucidates an intrinsic regulatory mechanism of the host response to DNA viruses which may provide unique opportunities for countering viral infections.

PH and Redox Dual-Responsive Nanoparticle with Enhanced Dendritic Cell Maturation for Cancer Therapy.

Type I interferons (IFNs) are essential for activating dendritic cells (DCs) and presenting tumor-associated antigens to T cells. IFNs are primarily produced from DCs among immune cells. A combination of chemotherapy and metalloimmunotherapy induces IFN production by activating the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. However, chemotherapeutic agents deplete DC populations, suppressing immunostimulatory activities, despite their potent anticancer activities. Furthermore, an optimal ratio between chemotherapeutic agents and metal for activating DCs at the highest level has not been reported, and evidence for ensuring DC survival is lacking. In this study, we hypothesized that there is an optimal ratio to yield the highest DC maturation and anticancer activity with minimal DC depletion. To demonstrate it, we have designed a pH and redox dual-responsive nanoparticle, MnO2@BSA@DOX (MD), to prevent DCs from depleting and activate the cGAS-STING pathway both in cancer cells and DCs, inducing considerable levels of IFNs and maturation. MD consists of a core-layer structure, a manganese dioxide (MnO2) core, and a cross-linked layer with bovine serum albumin (BSA) and doxorubicin (DOX), with a specific ratio of DOX to manganese. MD exhibits structure-based selectivity between cancer cells and DCs by targeting the extracellular pH of the tumor microenvironment and intracellular redox reactions in cancer cells. Among various formulations, the 1:1 ratio shows the highest maturation with no significant depletion. Moreover, it induces distinct cytotoxicity in cancer cells through apoptosis and cGAS-STING activation, leading to increased calreticulin expression and enhanced DC phagocytosis. Consequently, it results in superior tumor suppression and prolonged survival with the high accumulation of MD in the tumor and no observed systemic toxicities, highlighting its potential as a therapeutic agent in cancer treatments.

A Phosphotriester-Masked Dideoxy-cGAMP Derivative as a Cell-Permeable STING Agonist.

2'3'-cyclic GMP-AMP (cGAMP) is a cyclic dinucleotide second messenger in which guanosine and adenosine are connected by one 3'-5' and one 2'-5' phosphodiester linkage. It is formed in the cytosol upon detection of pathogenic DNA by the enzyme guanosine-monophosphate-adenosine monophosphate synthase (cGAS). cGAMP subsequently binds to the adaptor protein stimulator of interferon genes (STING) to elicit an innate immune response leading to the production of type I interferons and cytokines. STING agonists are a highly promising avenue for an immuno-oncological anticancer therapy. A particular challenge with cyclic dinucleotide STING agonists are the two negative charges of the phosphodiester linkages, which strongly reduce the ability of such compounds to penetrate cell membranes. The development of cell-permeable STING agonists that can stimulate the immune system, enhancing their anticancer potency is currently of utmost importance in the field. Here, we report the development of a dideoxy derivative of cGAMP as a phosphotriester prodrug, where the negative charge of the phosphate backbone has been masked with a thioester. We found that this thioester-protected compound features a dramatic increase in its cellular potency that rises from EC50 = 5 mM to 25 nM. The new compound is envisioned to enable an efficient STING-agonist-based anticancer therapy.

Tandem-Controlled Dynamic DNA Assembly Enables Temporally-Selective Orthogonal Regulation of cGAS-STING Stimulation.

Despite advances in the controlled reconfiguration of DNA structures for biological applications, the dearth of strategies that allow for orthogonal regulation of immune pathways remains a challenge. Here, we report for the first time an endogenous and exogenous tandem-regulated DNA assembly strategy that enables orthogonally controlled stimulation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. A DNA motif containing two palindromic sequences is engineered with an abasic site (AP)-connected blocking sequence to inhibit its self-assembly function, while apurinic/apyrimidinic endonuclease 1 (APE1)-triggered enzymatic cleavage of the AP site enables the reconfiguration and self-assembly of DNA motif into long double-stranded structures, thus realizing allosteric activation of the catalytic activity of cGAS to produce 2'3'-cyclic-GMP-AMP for STING stimulation. Importantly, we demonstrate that APE1-regulated DNA assembly allows for cell-selective activation of cGAS-STING signaling. Furthermore, by re-engineering the DNA motif with a photocleavable group, enzyme-triggered DNA assembly allows the cGAS-STING stimulation to operate (switched "ON''), whereas light-mediated fragmentation of the double-stranded DNA enables termination of such stimulation (switched "OFF"), thereby achieving orthogonal control over immune regulation. This work highlights an endogenous and exogenous tandem regulated strategy to modulate the cGAS-STING pathway in an orthogonally controlled manner.