Targeting STING oligomerization with small-molecule inhibitors

Development of indole derivatives as inhibitors targeting STING-dependent inflammation

Constant activation of stimulator of interferon genes (STING), resulting from aberrant metabolism or mutations in STING1, can initiate inflammatory damage or autoimmune disease. STING antagonists have the potential to be used as therapeutics for inflammatory and autoimmune diseases. Based on the structures of the covalent STING inhibitor H151 and C178, we designed, synthesized, and evaluated a novel series of indole derivatives for STING inhibition. Several compounds exhibited efficacious STING inhibitory activity. One of these novel chemical entities, 4dc, was more potent than H151, with IC50 values of 0.14 μM in RAW-LuciaTM ISG cells and 0.39 μM in THP1-Dual™ cells. The compound effectively relieved the symptoms of renal injury in a cisplatin-induced acute kidney injury mouse model. Compound 4dc represents a new chemotype of STING inhibitor that deserves further investigation as anti-inflammatory agent.

STING inhibitors and degraders: Potential therapeutic agents in inflammatory diseases

The regulation of the STING (stimulator of interferon genes) pathway represents a promising target for a range of inflammatory diseases. This review provides an overview of the structure of STING and discusses the mechanisms by which the cyclic GMP-AMP synthase (cGAS)-STING pathway is associated with various autoinflammatory and autoimmune diseases. We explore how targeting STING inhibition or degradation can alleviate excessive inflammatory signaling and improve efficacy. Emerging strategies include inhibiting STING expression by covalently binding compounds or using ligands that target the binding pocket. In addition, selective degradation of STING via the ubiquitin-proteasome system or the lysosomal pathway shows promise. In addition, we explore the implications of modulating the cGAS-STING pathway in the context of various inflammatory diseases. Finally, we summarize the chemical properties of recently developed STING compounds and their potential clinical applications. By comprehensively reviewing the current understanding of the role of STING in inflammation and the therapeutic potential of targeting STING, we aim to identify new avenues of intervention that could improve outcomes for patients with inflammatory diseases. This review highlights the important role of STING in the regulation of inflammation and its potential as a target for innovative therapeutic strategies.

Therapeutic targeting the cGAS-STING pathway associated with protein and gene: An emerging and promising novel strategy for aging-related neurodegenerative disease

Neurodegenerative diseases (NDDs) represent a rapidly escalating global health challenge, contributing significantly to the worldwide disease burden and posing substantial threats to public health systems across nations. Among the many risk factors for neurodegeneration, aging is the major risk factor. In the context of aging, multiple factors lead to the release of endogenous DNA (especially mitochondrial DNA, mtDNA), which is an important trigger for the activation of the cGAS-STING innate immune pathway. Recent studies have identified an increasing role for activation of the cGAS-STING signaling pathway as a driver of senescence-associated secretory phenotypes (SASPs) in aging and NDDs. The cGAS-STING pathway mediates the immune sensing of DNA and is a key driver of chronic inflammation and functional decline during the aging process. Blocking cGAS-STING signaling may reduce the inflammatory response by preventing mtDNA release and enhancing mitophagy. Targeted inhibition of the cGAS-STING pathway by biological macromolecules such as natural products shows promise in therapeutic strategies for age-related NDDs. This review aims to systematically and comprehensively introduces the role of the cGAS-STING pathway in age-related NDDs in the context of aging while revealing the molecular mechanisms of the cGAS-STING pathway and its downstream signaling pathways and to develop more targeted and effective therapeutic strategies for NDDs.

Design of Potent Small-Molecule Stimulator of Interferon Gene Inhibitor and Stimulator of Interferon Gene Mutant-Specific Degrader

Stimulator of interferon genes (STING) is involved in various autoimmune diseases. However, it is challenging to develop small-molecule STING inhibitors with potent activity. Herein, we designed a small-molecule STING inhibitor and STING mutant-specific degrader by binding two coupled pockets of a STING dimer. Structure optimization selected SI-24, SI-42, and SI-43 with low nanomolar activity to inhibit 2'3'-cyclic GMP-AMP (cGAMP)-induced STING activation and release of IFN-β and CXCL-10, which were far more potent than reported STING inhibitors. Moreover, the three lead compounds suppressed cGAMP-induced oligomerization of STING and phosphorylation of interferon regulatory factor 3 (IRF3) and STING. Surprisingly, SI-43 promoted mutant-specific and proteasome-independent degradation of STINGS154 and STINGM155. Subcutaneous or oral administration of SI-24, SI-42, and SI-43 reduced serum IFN-β and CXCL-10 in the cGAMP-induced autoimmune disease mouse model. Our dual-functional compounds provide a new strategy to investigate STING function through both inhibition and mutant-specific degradation in autoimmune diseases.

cGAS-STING: mechanisms and therapeutic opportunities

The cGAS-STING pathway plays a crucial role in the innate immune system by detecting mislocalized double-stranded DNA (dsDNA) in the cytoplasm and triggering downstream signal transduction. Understanding the mechanisms by which cGAS and STING operate is vital for gaining insights into the biology of this pathway. This review provides a detailed examination of the structural features of cGAS and STING proteins, with a particular emphasis on their activation and inhibition mechanisms. We also discuss the novel discovery of STING functioning as an ion channel. Furthermore, we offer an overview of key agonists and antagonists of cGAS and STING, shedding light on their mechanisms of action. Deciphering the molecular intricacies of the cGAS-STING pathway holds significant promise for the development of targeted therapies aimed at maintaining immune homeostasis within both innate and adaptive immunity.

Discovery of Potent STING Inhibitors Bearing a Difluorobenzodioxol Structural Motif as Potent Anti-Inflammatory Agents

Given the critical role of STING in autoimmune and inflammatory disorders, the development of targeted small-molecule inhibitors has been a promising strategy for the treatment of these diseases. Nevertheless, the currently reported STING inhibitors suffer from limited structural diversity, species sensitivity, and poor activity; therefore, none are suitable for clinical investigation. Herein, we performed a structural modification campaign on the tool compound 6 (H-151) based on its potential metabolic hotspots. Compound 66, bearing a difluorobenzodioxol moiety, was identified as one of the most potent STING inhibitors with IC50 values of 116 and 96.3 nM for h- and m-STING, respectively. This compound exhibited a notable enhancement in metabolic properties, especially in terms of metabolic stability. A mechanism study verified that 66 engaged with STING in a covalent manner akin to that of 6. In both the cisplatin-induced acute kidney injury and TREX1 D18N mouse models, 66 significantly alleviated tissue injury and inflammation.

Oligomerization of STING and Chemical Regulatory Strategies

Stimulator of interferon genes (STING) plays a crucial role in innate immunity. Upon the recognition of cytosolic dsDNA, STING undergoes several structural changes, with oligomerization playing a key role in initiating a cascade of immune responses. Therefore, controlling the STING pathway by manipulating STING oligomerization is a practical strategy. This review focuses on the detailed mechanism of STING oligomerization, highlighting its decisive role. It also describes oligomerization-based strategies to regulate STING protein, such as the use of small-molecule agonists and biomacromolecules, highlighting their interaction modes and potential therapeutic applications. This knowledge may lead to the development of innovative approaches for treating cancer and immune disorders.

Carnosic Acid Directly Targets STING C-Terminal Tail to Improve STING-Mediated Inflammatory Diseases

cGAS (cyclic GMP-AMP synthase)-STING (stimulator of interferon genes) signaling plays a vital role in innate immunity, while its deregulation may lead to a wide variety of autoinflammatory and autoimmune diseases. It is essential to identify specifically effective lead compounds to inhibit the signaling. Herein, it is shown that carnosic acid (CA), an active ingredient of medicinal plant Rosmarinus officinalis L., specifically suppressed cGAS-STING pathway activation and the subsequent inflammatory responses. Mechanistically, CA directly bound to STING C-terminal tail (CTT), impeded the recruitment of TANK-binding kinase 1 (TBK1) onto STING signalosome, thereby blocking the phosphorylation of STING and interferon regulatory factor 3 (IRF3) nuclear translocation. Importantly, CA dramatically attenuated STING-mediated inflammatory responses in vivo. Consistently, CA has a salient ameliorative effect on autoinflammatory disease model mediated by Trex1 deficiency, via inhibition of the cGAS-STING signaling. Notably, the study further indicates that phenolic hydroxyl groups are essential for CA-mediated STING inhibitory activity. Collectively, the results thus identify STING as one of the crucial targets of CA for mediating CA's anti-inflammatory activity, and further reveal that STING CTT may be a novel promising target for drug development.

ADSL-generated fumarate binds and inhibits STING to promote tumour immune evasion

Highly aggressive tumours have evolved to restrain the cGAS-STING pathway for immune evasion, and the mechanisms underlying this hijacking remain unknown. Here we demonstrate that hypoxia induces robust STING activation in normal mammary epithelial cells but not in breast cancer cells. Mechanistically, adenylosuccinate lyase (ADSL), a key metabolic enzyme in de novo purine synthesis, is highly expressed in breast cancer tissues and is phosphorylated at T350 by hypoxia-activated IKKβ. Phosphorylated ADSL interacts with STING at the endoplasmic reticulum, where ADSL-produced fumarate binds to STING, leading to the inhibition of cGAMP binding to STING, STING activation and subsequent IRF3-dependent cytokine gene expression. Disrupting the ADSL-STING association promotes STING activation and blunts tumour growth. Notably, a combination treatment with ADSL endoplasmic reticulum translocation-blocking peptide and anti-PD-1 antibody induces an additive inhibitory effect on tumour growth accompanying a substantially increased immune response. Notably, ADSL T350 phosphorylation levels are inversely correlated with levels of STING activation and predicate poor prognosis in patients with breast cancer. These findings highlight a pivotal role of the metabolite fumarate in inhibiting STING activation and uncover new strategies to improve immune-checkpoint therapy by targeting ADSL-moonlighting function-mediated STING inhibition.

Orally Bioavailable and Site-Selective Covalent STING Inhibitor Derived from a Macrocyclic Marine Diterpenoid

Pharmacological inhibition of the cGAS-STING-controlled innate immune pathway is an emerging therapeutic strategy for a myriad of inflammatory diseases. Here, we report GHN105 as an orally bioavailable covalent STING inhibitor. Late-stage diversification of the briarane-type diterpenoid excavatolide B allowed the installation of solubility-enhancing functional groups while enhancing its activity as a covalent STING inhibitor against multiple human STING variants, including the S154 variant responsible for a genetic autoimmune disease. Selectively engaging the membrane-proximal Cys91 residue of STING, GHN105 dose-dependently inhibited cGAS-STING signaling and type I interferon responses in cells and in vivo. Moreover, orally administered GHN105 exhibited on-target engagement in vivo and markedly reversed key pathological features in a delayed treatment of the acute colitis mouse model. Our study provided proof of concept that the synthetic briarane analog GHN105 serves as a safe, site-selective, and orally active covalent STING inhibitor and devises a regimen that allows long-term systemic administration.

The cGAS-STING pathway in cancer immunity: dual roles, therapeutic strategies, and clinical challenges

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is a crucial component of the host's innate immunity and plays a central role in detecting cytosolic double-stranded DNA from endogenous and exogenous sources. Upon activation, cGAS synthesizes cGAMP, which binds to STING, triggering a cascade of immune responses, including the production of type I interferons and pro-inflammatory cytokines. In the context of cancers, the cGAS-STING pathway can exert dual roles: on the one hand, it promotes anti-tumor immunity by enhancing antigen presentation, stimulating T-cell responses, and inducing direct tumor cell apoptosis. On the other hand, chronic activation, particularly in tumors with chromosomal instability, can lead to immune suppression and tumor progression. Persistent cGAS-STING signaling results in the up-regulation of immune checkpoint molecules such as PD-L1, contributing to immune evasion and metastasis. Consequently, anti-tumor strategies targeting the cGAS-STING pathway have to consider the balance of immune activation and the immune tolerance caused by chronic activation. This review explores the mechanisms underlying both the anti-tumor and protumor roles of the cGAS-STING pathway, with a focus on potential therapeutic approaches, and the challenges faced in their clinical application, along with corresponding solutions.

Implications of tissue specific STING protein flux and abundance on inflammation and the development of targeted therapeutics

Drugs targeting the ER-resident innate immune receptor Stimulator of Interferon Genes (STING) are in development for treatments of cancer and inflammatory diseases. Accurate determination of STING receptor levels in normal and disease tissue is an essential component of modeling pharmacology and drug-target disposition. Using metabolic labeling with deuterium oxide paired with high resolution mass spectrometry, we report the protein fractional synthesis rates and turnover of STING in wild-type (C57BL/6) and inflamed mice carrying the Trex1 D18N mutation (Trex1D18N) as a STING-dependent model of human Acardi-Goutiéres syndrome. Remarkably, STING protein half-life is tissue specific with the shortest half-life of 4 days in colon and lymph node and longest half-life of 24 days in skeletal muscle. Despite the relative increase in STING protein abundance in the inflamed Trex1D18N mouse, the overall kinetics of protein degradation and resynthesis was similar between Trex1D18N and WT mice. The extent of tissue specific interferon stimulated gene transcription, a hallmark of SLE linked pathophysiology, correlates with the extend of increased STING levels in Trex1D18N tissues and appears inversely proportional to the turnover rate of STING. Understanding STING's fractional protein synthesis rate and half-life provides a valuable component of quantitative modeling of drug pharmacology, dose frequency and targeting tissues of STING directed therapies.

Discovery of an Orally Bioavailable STING Inhibitor with In Vivo Anti-Inflammatory Activity in Mice with STING-Mediated Inflammation

The cyclic GMP-AMP synthase (cGAS)-stimulator of the interferon genes (STING) pathway plays a key role in triggering interferon and inflammatory responses against microbial invasion or tumor. However, aberrant activation of the cGAS-STING pathway is associated with a variety of inflammatory and autoimmune diseases, and thus inhibition of STING is regarded as a potential new approach to treating these diseases. Herein, we report a series of novel indolyl-urea derivatives as STING inhibitors. The representative compound 42 exhibited potent STING inhibitory activity, acceptable pharmacokinetic properties, and good in vivo safety profiles. Mechanistically, 42 could block the palmitoylation of the STING protein and STING downstream signaling. Importantly, oral administration of 42 could effectively suppress STING-mediated inflammation in 10-carboxymethyl-9-acridanone (CMA)-treated mouse and Trex1-/- mouse. Together, compound 42 represents a promising STING inhibitor for treating STING-associated inflammatory and autoimmune diseases.

Targeting common disease pathomechanisms to treat amyotrophic lateral sclerosis

The motor neuron disease amyotrophic lateral sclerosis (ALS) is a devastating condition with limited treatment options. The past few years have witnessed a ramping up of translational ALS research, offering the prospect of disease-modifying therapies. Although breakthroughs using gene-targeted approaches have shown potential to treat patients with specific disease-causing mutations, the applicability of such therapies remains restricted to a minority of individuals. Therapies targeting more general mechanisms that underlie motor neuron pathology in ALS are therefore of considerable interest. ALS pathology is associated with disruption to a complex array of key cellular pathways, including RNA processing, proteostasis, metabolism and inflammation. This Review details attempts to restore cellular homeostasis by targeting these pathways in order to develop effective, broadly-applicable ALS therapeutics.

The cross-talk between the cGAS-STING signaling pathway and chronic inflammation in the development of musculoskeletal disorders

Musculoskeletal disorders (MSDs) comprise diverse conditions affecting bones, joints, and muscles, leading to pain and loss of function, and are one of the most prevalent and major global health concerns. One of the hallmarks of MSDs is DNA damage. Once accumulated in the cytoplasm, the damaged DNA is sensed by the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway, which triggers the induction of type I interferons and inflammatory cytokines. Thus, this pathway connects the musculoskeletal and immune systems. Inhibitors of cGAS or STING have shown promising therapeutic effects in the pre-clinical models of several MSDs. Systemic, chronic, low-grade inflammation (SCLGI) underlies the development and maintenance of many MSDs. Failure to resolve SCLGI has been hypothesized to play a critical role in the development of chronic diseases, suggesting that the successful resolution of SCLGI will result in the alleviation of their related symptomatology. The process of inflammation resolution is feasible by specialized pro-resolving mediators (SPMs), which are enzymatically generated from dietary essential polyunsaturated fatty acids (PUFAs). The supplementation of SPMs or their stable, small-molecule mimetics and receptor agonists has revealed beneficial effects in inflammation-related animal models, including arthropathies, osteoporosis, and muscle dystrophy, suggesting a translational potential in MSDs. In this review, we substantiate the hypothesis that the use of cGAS-STING signaling pathway inhibitors together with SCLG-resolving compounds may serve as a promising new therapeutic approach for MSDs.

The STING signaling pathways and bacterial infection

As antibiotic-resistant bacteria continue to emerge frequently, bacterial infections have become a significant and pressing challenge to global public health. Innate immunity triggers the activation of host responses by sensing "non-self" components through various pattern recognition receptors (PRRs), serving as the first line of antibacterial defense. Stimulator of interferon genes (STING) is a PRR that binds with cyclic dinucleotides (CDN) to exert effects against bacteria, viruses, and cancer by inducing the production of type I interferon and inflammatory cytokines, and facilitating regulated cell death. Currently, drugs targeting the STING signaling pathway are predominantly applied in the fields of modulating host immune defense against cancer and viral infections, with relatively limited application in treating bacterial infections. Given the significant immunomodulatory functions of STING in the interaction between bacteria and hosts, this review summarizes the research progress on STING signaling pathways and their roles in bacterial infection, as well as the novel functions of STING modulators, aiming to offer insights for the development of antibacterial drugs.

Design, synthesis, and evaluation of thiazolecarboxamide derivatives as stimulator of interferon gene inhibitors

Stimulator of interferon gene (STING) plays critical roles in the cytoplasmic DNA-sensing pathway and in the induction of inflammatory response. Aberrant cytoplasmic DNA accumulation and STING activation are implicated in numerous inflammatory and autoimmune diseases. Here, we reported the discovery of a series of thiazolecarboxamide-based STING inhibitors through a molecular planarity/symmetry disruption strategy. The privileged compound 15b significantly inhibited STING signaling and suppressed immune-inflammatory cytokine levels in both human and murine cells. In vivo experiments demonstrated 15b effectively ameliorated immune-inflammatory cytokines upregulation in MSA-2-stimulated and Trex1-D18N mice. Furthermore, compound 15b exhibited enhanced efficacy in suppressing interferon-stimulated gene 15 (ISG15), a critical positive feedback regulator of STING. Overall, compound 15b deserves further development for the treatment of STING-associated inflammatory and autoimmune diseases.

Discovering covalent cyclic peptide inhibitors of peptidyl arginine deiminase 4 (PADI4) using mRNA-display with a genetically encoded electrophilic warhead

Covalent drugs can achieve high potency with long dosing intervals. However, concerns remain about side-effects associated with off-target reactivity. Combining macrocyclic peptides with covalent warheads provides a solution to minimise off-target reactivity: the peptide enables highly specific target binding, positioning a weakly reactive warhead proximal to a suitable residue in the target. Here we demonstrate the direct discovery of covalent cyclic peptides using encoded libraries containing a weakly electrophilic cysteine-reactive fluoroamidine warhead. We combine direct incorporation of the warhead into peptide libraries using the flexible in vitro translation system with a peptide selection approach that identifies only covalent target binders. Using this approach, we identify potent and selective covalent inhibitors of the peptidyl arginine deiminase, PADI4 or PAD4, that react exclusively at the active site cysteine. We envisage this approach will enable covalent peptide inhibitor discovery for a range of related enzymes and expansion to alternative warheads in the future.

D-aring to explore: New approaches to gasdermin D targeting

Novel inhibitors of pyroptosis promise breakthroughs in treating inflammatory diseases and malignant tumors. In this issue of Cell Chemical Biology, Hu et al.1 identify two repurposed drugs that selectively target gasdermin D (GSDMD) oligomers, effectively suppressing pyroptosis while reducing off-target effects typical of cysteine-based inhibitors.

Progress of cGAS-STING signaling pathway-based modulation of immune response by traditional Chinese medicine in clinical diseases

The cGAS-STING signaling pathway is a critical component of the innate immune response, playing a significant role in various diseases. As a central element of this pathway, STING responds to both endogenous and exogenous DNA stimuli, triggering the production of interferons and pro-inflammatory cytokines to enhance immune defenses against tumors and pathogens. However, dysregulated activation of the STING pathway is implicated in the pathogenesis of multiple diseases, including autoinflammation, viral infections, and cancer. Traditional Chinese Medicines (TCMs), which have a long history of use, have been associated with positive effects in disease prevention and treatment. TCM formulations (e.g., Lingguizhugan Decoction, Yi-Shen-Xie-Zhuo formula) and active compounds (e.g., Glabridin, Ginsenoside Rd) can modulate the cGAS-STING signaling pathway, thereby influencing the progression of inflammatory, infectious, or oncological diseases. This review explores the mechanisms by which TCMs interact with the cGAS-STING pathway to regulate immunity, focusing on their roles in infectious diseases, malignancies, and autoimmune disorders.

Targeting STING oligomerization with licochalcone D ameliorates STING-driven inflammatory diseases

The development of STING inhibitors for the treatment of STING-related inflammatory diseases continues to encounter significant challenges. The activation of STING is a multi-step process that includes binding with cGAMP, self-oligomerization, and translocation from the endoplasmic reticulum to the Golgi apparatus, ultimately inducing the expression of IRF3 and NF-κB-mediated interferons and inflammatory cytokines. It has been demonstrated that disruption of any of these steps can effectively inhibit STING activation. Traditional structure-based drug screening methodologies generally focus on specific binding sites. In this study, a TransformerCPI model based on protein primary sequences and independent of binding sites is employed to identify compounds capable of binding to the STING protein. The natural product Licochalcone D (LicoD) is identified as a potent and selective STING inhibitor. LicoD does not bind to the classical ligand-binding pocket; instead, it covalently modifies the Cys148 residue of STING. This modification inhibits STING oligomerization, consequently suppressing the recruitment of TBK1 and the nuclear translocation of IRF3 and NF-κB. LicoD treatment ameliorates the inflammatory phenotype in Trex1-1- mice and inhibits the progression of DSS-induced colitis and AOM/DSS-induced colitis-associated colon cancer (CAC). In summary, this study reveals the potential of LicoD in treating STING-driven inflammatory diseases. It also demonstrates the utility of the TransformerCPI model in discovering allosteric compounds beyond the conventional binding pockets.

ROS responsive nanozyme loaded with STING silencing for the treatment of sepsis-induced acute lung injury

Acute lung injury (ALI) is a common complication of sepsis and a leading cause of mortality in septic patients. Studies indicate that STING may play a crucial role in the pathogenesis of sepsis-induced ALI by interacting with the PARP-1/NLRP3 pathway. Therefore, targeting STING inhibition has potential as a novel therapeutic strategy for ALI. However, effective inhibition remains challenging due to the widespread expression of STING across various tissues. In this study, we developed a nanozyme-based drug delivery system, DSPE-TK-mPEG-MnO2@siSTING (abbreviated as DTmM@siSTING), using DSPE-TK-mPEG-MnO2 as the carrier, and characterized it via scanning electron microscopy, dynamic light scattering, nanoparticle size analysis, and gel electrophoresis. To evaluate the therapeutic effects of DTmM@siSTING, an in vitro ALI cell model and an in vivo ALI mouse model were established, assessing the nanozyme's impact on ROS levels, inflammatory responses, and the PARP-1/NLRP3 pathway in sepsis-induced ALI. Results demonstrated that DTmM@siSTING exhibited good physiological stability. In vitro, DTmM@siSTING significantly reduced ROS levels, myeloperoxidase activity, and expression of inflammatory cytokines, while also inhibiting PARP-1/NLRP3 pathway activation. In vivo experiments further revealed that DTmM@siSTING effectively delivered siSTING to the lungs, mitigating sepsis-induced ALI and associated inflammatory responses. Additionally, DTmM@siSTING displayed excellent biocompatibility. In summary, our findings suggest that DTmM@siSTING significantly enhances the therapeutic efficacy of siSTING, alleviating ALI by inhibiting ROS production, inflammatory responses, and activation of the PARP-1/NLRP3 pathway. This novel approach presents a promising therapeutic avenue for sepsis-induced ALI.

Redundant role of PAD2 and PAD4 in the development of cardiovascular lesions in a mouse model of Kawasaki disease vasculitis

Kawasaki disease (KD) is the leading cause of acquired heart disease in children. While circulating neutrophils are increased and activated during acute KD, it is unclear whether neutrophils and neutrophil extracellular traps (NETs) contribute to the pathogenesis of KD. Peptidylarginine deiminase 4 (PAD4), an enzyme involved in protein citrullination and essential for NETs formation, is implicated in the pathogenesis of various diseases. Here, we used the Lactobacillus casei cell wall extract (LCWE)-induced mouse model of KD vasculitis to determine the contribution of PAD4 in KD vasculitis. We found that the pan-PADs inhibitor, Cl-amidine, significantly reduced LCWE-induced cardiovascular lesions, but neutrophil-specific Padi4 KO mice did not impact the development of KD vasculitis. While in vitro treatment of macrophages, which highly express Padi4, with Cl-amidine inhibited IL-1β secretion, macrophage-specific Padi4 KO mice did not reduce the lesions. Padi4-/- mice also developed KD vasculitis, AFM30a, a PAD2 inhibitor, significantly reduced KD vasculitis in Padi4-/- mice, indicating a compensatory role of PAD2 in PAD4 deficiency. We also identified several citrullinated proteins in macrophages with constitutively active NLRP3 inflammasome that were inhibited by Cl-amidine treatment, suggesting that protein citrullination participates in NLRP3 inflammasome activation. These data indicate a dispensable role for PAD4-dependent NETs formation, and a redundant role of PAD2 and PAD4 in this murine KD vasculitis. The cardioprotective effects of Cl-amidine to reduce the severity of murine KD vasculitis are not limited to PAD4 inhibition and may include decreased citrullination in the inflammasome pathway.

cGAS/STING signalling pathway in senescence and oncogenesis

The cGAS/STING signaling pathway is a crucial component of the innate immune system, playing significant roles in sensing cytosolic DNA, regulating cellular senescence, and contributing to oncogenesis. Recent advances have shed new lights into the molecular mechanisms governing pathway activation in multiple pathophysiological settings, the indispensable roles of cGAS/STING signaling in cellular senescence, and its context-dependent roles in cancer development and suppression. This review summarizes current knowledge related to the biology of cGAS/STING signaling pathway and its participations into senescence and oncogenesis. We further explore the clinical implications and therapeutic potential for cGAS/STING targeted therapies, and faced challenges in the field. With a focus on molecular mechanisms and emerging pharmacological targets, this review underscores the importance of future studies to harness the therapeutic potential of the cGAS/STING pathway in treating senescence-related disorders and cancer. Advanced understanding of the regulatory mechanisms of cGAS/STING signaling, along with the associated deregulations in diseases, combined with the development of new classes of cGAS/STING modulators, hold great promises for creating novel and effective therapeutic strategies. These advancements could address current treatment challenges and unlock the full potential of cGAS/STING in treating senescence-related disorders and oncogenesis.

DNA-sensing pathways in health, autoinflammatory and autoimmune diseases

Detection of microbial DNA is a primary means of host defense. In mammalian cells, DNA-sensing pathways induce robust anti-microbial responses and initiation of adaptive immunity, leading to the eventual clearance of the infectious agent. However, while conferring the advantage of broad detection capability, the sequence-independent recognition mechanisms of most DNA sensors pose a significant challenge for mammalian cells to maintain ignorance to self-DNA under homeostatic conditions. In this Review, we summarize the fundamentals of DNA-sensing pathways and the intricate regulatory networks that keep these pathways in check. In addition, we describe how regulatory restraints can be defective and underlie human autoinflammatory and autoimmune diseases. Further, we discuss therapies in development that limit inflammation fueled by self-DNA or inappropriate activation of DNA-sensing pathways.

Endoplasmic reticulum stress, autophagy, neuroinflammation, and sigma 1 receptors as contributors to depression and its treatment

The etiological factors contributing to depression and other neuropsychiatric disorders are largely undefined. Endoplasmic reticulum stress pathways and autophagy are well-defined mechanisms that play critical functions in recognizing and resolving cellular stress and are possible targets for the pathophysiology and treatment of psychiatric and neurologic illnesses. An increasing number of studies indicate the involvement of endoplasmic reticulum stress and autophagy in the control of neuroinflammation, a contributing factor to multiple neuropsychiatric illnesses. Initial inflammatory triggers induce endoplasmic reticulum stress, leading to neuroinflammatory responses. Subsequently, induction of autophagy by neurosteroids and other signaling pathways that converge on autophagy induction are thought to participate in resolving neuroinflammation. The aim of this review is to summarize our current understanding of the molecular mechanisms governing the induction of endoplasmic reticulum stress, autophagy, and neuroinflammation in the central nervous system. Studies focused on innate immune factors, including neurosteroids with anti-inflammatory roles will be reviewed. In the context of depression, animal models that led to our current understanding of molecular mechanisms underlying depression will be highlighted, including the roles of sigma 1 receptors and pharmacological agents that dampen endoplasmic reticulum stress and associated neuroinflammation.

Protein-protein interactions in cGAS-STING pathway: a medicinal chemistry perspective

Protein-protein interactions (PPIs) play pivotal roles in biological processes and are closely linked with human diseases. Research on small molecule inhibitors targeting PPIs provides valuable insights and guidance for novel drug development. The cGAS-STING pathway plays a crucial role in regulating human innate immunity and is implicated in various pathological conditions. Therefore, modulators of the cGAS-STING pathway have garnered extensive attention. Given that this pathway involves multiple PPIs, modulating PPIs associated with the cGAS-STING pathway has emerged as a promising strategy for modulating this pathway. In this review, we summarize an overview of recent advancements in medicinal chemistry insights into cGAS-STING PPI-based modulators and propose alternative strategies for further drug discovery based on the cGAS-STING pathway.

Development of nitroalkene-based inhibitors to target STING-dependent inflammation

Stimulator of Interferon Genes (STING) is essential for the inflammatory response to cytosolic DNA. Despite that aberrant activation of STING is linked to an increasing number of inflammatory diseases, the development of inhibitors has been challenging, with no compounds in the pipeline beyond the preclinical stage. We previously identified endogenous nitrated fatty acids as novel reversible STING inhibitors. With the aim of improving the specificity and efficacy of these compounds, we developed and tested a library of nitroalkene-based compounds for in vitro and in vivo STING inhibition. The structure-activity relationship study revealed a robustly improved electrophilicity and reduced degrees of freedom of nitroalkenes by conjugation with an aromatic moiety. The lead compounds CP-36 and CP-45, featuring a β-nitrostyrene moiety, potently inhibited STING activity in vitro and relieved STING-dependent inflammation in vivo. This validates the potential for nitroalkene compounds as drug candidates for STING modulation to treat STING-driven inflammatory diseases, providing new robust leads for preclinical development.

The balance of STING signaling orchestrates immunity in cancer

Over the past decade, it has become clear that the stimulator of interferon genes (STING) pathway is critical for a variety of immune responses. This endoplasmic reticulum-anchored adaptor protein has regulatory functions in host immunity across a spectrum of conditions, including infectious diseases, autoimmunity, neurobiology and cancer. In this Review, we outline the central importance of STING in immunological processes driven by expression of type I and III interferons, as well as inflammatory cytokines, and we look at therapeutic options for targeting STING. We also examine evidence that challenges the prevailing notion that STING activation is predominantly beneficial in combating cancer. Further exploration is imperative to discern whether STING activation in the tumor microenvironment confers true benefits or has detrimental effects. Research in this field is at a crossroads, as a clearer understanding of the nuanced functions of STING activation in cancer is required for the development of next-generation therapies.

Agonists and Inhibitors of the cGAS-STING Pathway

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is pivotal in immunotherapy. Several agonists and inhibitors of the cGAS-STING pathway have been developed and evaluated for the treatment of various diseases. The agonists aim to activate STING, with cyclic dinucleotides (CDNs) being the most common, while the inhibitors aim to block the enzymatic activity or DNA binding ability of cGAS. Meanwhile, non-CDN compounds and cGAS agonists are also gaining attention. The omnipresence of the cGAS-STING pathway in vivo indicates that its overactivation could lead to undesired inflammatory responses and autoimmune diseases, which underscores the necessity of developing both agonists and inhibitors of the cGAS-STING pathway. This review describes the molecular traits and roles of the cGAS-STING pathway and summarizes the development of cGAS-STING agonists and inhibitors. The information is supposed to be conducive to the design of novel drugs for targeting the cGAS-STING pathway.

Compound Danshen Dripping Pill effectively alleviates cGAS-STING-triggered diseases by disrupting STING-TBK1 interaction

BACKGROUND

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon (IFN) genes (STING) pathway is critical in the innate immune system and can be mobilized by cytosolic DNA. The various inflammatory and autoimmune diseases progression is highly correlated with aberrant cGAS-STING pathway activation. While some cGAS-STING pathway inhibitor were identified, there are no drugs that can be applied to the clinic. Compound Danshen Dripping Pill (CDDP) has been successfully used in clinic around the world, but the most common application is limited to cardiovascular disease. Therefore, the purpose of the present investigation was to examine whether CDDP inhibits the cGAS-STING pathway and could be used as a therapeutic agent for multiple cGAS-STING-triggered diseases.

METHODS

BMDMs, THP1 cells or Trex1-/- BMDMs were stimulated with various cGAS-STING-agonists after pretreatment with CDDP to detect the function of CDDP on IFN-β and ISGs productionn. Next, we detect the influence on IRF3 and P65 nuclear translocation, STING oligomerization and STING-TBK1-IRF3 complex formation of CDDP. Additionally, the DMXAA-mediated activation mice model of cGAS-STING pathway was used to study the effects of CDDP. Trex1-/- mice model and HFD-mediated obesity model were established to clarify the efficacy of CDDP on inflammatory and autoimmune diseases.

RESULTS

CDDP efficacy suppressed the IRF3 phosphorylation or the generation of IFN-β, ISGs, IL-6 and TNF-α. Mechanistically, CDDP did not influence the STING oligomerization and IRF3-TBK1 and STING-IRF3 interaction, but remarkably eliminated the STING-TBK1 interaction, ultimately blocking the downstream responses. In addition, we also clarified that CDDP could suppress cGAS-STING pathway activation triggered by DMXAA, in vivo. Consistently, CDDP could alleviate multi-organ inflammatory responses in Trex1-/- mice model and attenuate the inflammatory disorders, incleding obesity-induced insulin resistance.

CONCLUSION

CDDP is a specifically cGAS-STING pathway inhibitor. Furthermore, we provide novel mechanism for CDDP and discovered a clinical agent for the therapy of cGAS-STING-triggered inflammatory and autoimmune diseases.

Black carp ATG16L1 negatively regulates STING-mediated antiviral innate immune response

The precise control of interferon (IFN) production is indispensable for the host to eliminate invading viruses and maintain a homeostatic state. In mammals, stimulator of interferon genes (STING) is a prominent adaptor involved in antiviral immune signaling pathways. However, the regulatory mechanism of piscine STING has not been thoroughly investigated. Here, we report that autophagy related 16 like 1 (bcATG16L1) of black carp (Mylopharyngodon piceus) is a negative regulator in black carp STING (bcSTING)-mediated signaling pathway. Initially, we substantiated that knockdown of bcATG16L1 increased the transcription of IFN and ISGs and enhanced the antiviral activity of the host cells. Subsequently, we identified that bcATG16L1 inhibited the bcSTING-mediated IFN promoter activation and proved that bcATG16L1 suppressed bcSTING-mediated antiviral ability. Furthermore, we revealed that bcATG16L1 interacted with bcSTING and the two proteins shared a similar subcellular distribution. Mechanically, we found that bcATG16L1 attenuated the oligomerization of bcSTING, which was a key step for bcSTING activation. Taken together, our results indicate that bcATG16L1 interacts with bcSTING, dampens the oligomerization of bcSTING, and negatively regulates bcSTING-mediated antiviral activity.

Applications of cryo-EM in drug development for STING

STING is a critical adaptor protein in the cGAS-mediated DNA-sensing innate immune pathway. Binding of the second messenger cGAMP generated by cGAS to STING induces the high-order oligomerization and activation of the STING dimer. STING is a promising target for diseases associated with the cGAS/STING pathway such as cancer and autoimmune diseases. Recent applications of cryo-EM to STING have led to exciting progress in the understanding of its regulatory mechanism. Cryo-EM structures of STING bound to either cGAMP mimetics or novel small molecule ligands not only revealed the action mechanisms of these ligands but also suggested new ways to modulate the activity of STING for therapeutic purposes. Some of these recent studies are highlighted here.

Mechanism and therapeutic potential of targeting cGAS-STING signaling in neurological disorders

DNA sensing is a pivotal component of the innate immune system that is responsible for detecting mislocalized DNA and triggering downstream inflammatory pathways. Among the DNA sensors, cyclic GMP-AMP synthase (cGAS) is a primary player in detecting cytosolic DNA, including foreign DNA from pathogens and self-DNA released during cellular damage, culminating in a type I interferon (IFN-I) response through stimulator of interferon genes (STING) activation. IFN-I cytokines are essential in mediating neuroinflammation, which is widely observed in CNS injury, neurodegeneration, and aging, suggesting an upstream role for the cGAS DNA sensing pathway. In this review, we summarize the latest developments on the cGAS-STING DNA-driven immune response in various neurological diseases and conditions. Our review covers the current understanding of the molecular mechanisms of cGAS activation and highlights cGAS-STING signaling in various cell types of central and peripheral nervous systems, such as resident brain immune cells, neurons, and glial cells. We then discuss the role of cGAS-STING signaling in different neurodegenerative conditions, including tauopathies, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as aging and senescence. Finally, we lay out the current advancements in research and development of cGAS inhibitors and assess the prospects of targeting cGAS and STING as therapeutic strategies for a wide spectrum of neurological diseases.

STING channels its proton power

Induction of type I interferon by the STING pathway is a cornerstone of innate immunity. STING also turns on non-canonical autophagy and inflammasome activation although the underlying mechanisms remain ill defined. Liu et al.1 discovered that STING forms a channel that directs proton efflux from the Golgi to drive these responses.

Development of LB244, an Irreversible STING Antagonist

The cGMP-AMP Synthase (cGAS)-Stimulator of Interferon Genes (STING) pathway plays a critical role in sensing dsDNA localized to the cytosol, resulting in the activation of a robust inflammatory response. While cGAS-STING signaling is essential for antiviral immunity, aberrant STING activation is observed in amyotrophic lateral sclerosis (ALS), lupus, and autoinflammatory diseases such as Aicardi-Goutières syndrome (AGS) and STING associated vasculopathy with onset in infancy (SAVI). Significant efforts have therefore focused on the development of STING inhibitors. In a concurrent submission, we reported that BB-Cl-amidine inhibits STING-dependent signaling in the nanomolar range, both in vitro and in vivo. Considering this discovery, we sought to generate analogs with higher potency and proteome-wide selectivity. Herein, we report the development of LB244, which displays nanomolar potency and inhibits STING signaling with markedly enhanced proteome-wide selectivity. Moreover, LB244 mirrored the efficacy of BB-Cl-amidine in vivo. In summary, our data identify novel chemical entities that inhibit STING signaling and provide a scaffold for the development of therapeutics for treating STING-dependent inflammatory diseases.