Development of LB244, an Irreversible STING Antagonist

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.

Discovery of indole derivatives as STING degraders

Aberrant activation of the stimulator of interferon genes (STING) pathway is associated with the development of various inflammatory and autoimmune diseases. Targeting STING for degradation represents a novel strategy for the treatment of these diseases. In this study, we designed and synthesized a series of STING-PROTACs based on a nitro-free covalent warhead and different E3 ligase binders. The representative compound 2h specifically degraded STING protein through the proteasome pathway with a DC50 value of 3.23 μM and exhibited sustained degradation activity over 72 h. Further biological studies demonstrated that compound 2h inhibited STING signaling and effectively suppressed immune-inflammatory cytokines both in vitro and in vivo. Moreover, compound 2h offered better safety compared to its warhead molecule and SP23. Collectively, compound 2h is a potent nitro-free covalent STING degrader and warrants further investigation.

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.

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.

Discovery of STING antagonists targeting cGAS-STING pathway to alleviate IMQ-induced psoriasis-like dermatitis

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway is pivotal in the immune defense against infections and cancer. However, aberrant activation of this pathway can trigger autoimmune and inflammatory diseases by inducing excessive production of type I interferon (IFN) and pro-inflammatory cytokines. Inhibition of the aberrant activation of the cGAS-STING signaling pathway by targeting STING represents a novel therapeutic strategy for these autoimmune and inflammatory disorders. In this study, we discovered three novel STING antagonists based on surface plasmon resonance (SPR), differential scanning fluorimetry (DSF), and ISRE (interferon stimulated response element)-luciferase assays. The efficacy and pharmacological mechanisms of the three STING antagonists for treating imiquimod (IMQ)-induced psoriasis-like dermatitis by western blotting (WB), flow fluorescence, and immunostaining. The three STING antagonists exhibited pan-inhibitory activities on the activation of both the human and mouse cGAS-STING signaling pathway. Intravenous and topical administration of the three antagonists alleviated the inflammation and skin lesions associated with IMQ-induced psoriasis-like dermatitis via suppression of the inflammatory cascade mediated by the IMQ-TLR-7-NF-κB/cGAS-STING-NF-κB/IL-1β-IL-1R-NF-κB/TNFα-TNF-R-NF-κB signaling axis. In conclusion, we identified three novel STING antagonists with pan-inhibitory activities against human and mouse STING, providing lead compounds for the future development of both STING antagonists and immune agents for therapeutically manipulating STING-driven diseases, such as psoriasis. Our findings offer another new therapeutic strategy for managing STING-driven autoimmune and inflammatory diseases, while also reemphasizing the critical role of the cGAS-STING signaling pathway in such conditions.

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.

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.

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.

A review on the crosstalk between non-coding RNAs and the cGAS-STING signaling pathway

In the innate immune system, the cyclic GMP-AMP synthase (cGAS)-interferon gene stimulator (STING) pathway activates the type I interferon (IFN) response and the NF-κB pathway by recognizing double-stranded DNAs, the imbalance of which plays a pivotal role in human diseases, including cancer, autoimmune and inflammatory diseases. Non-coding RNAs (ncRNAs) are a diverse group of transcripts that do not code for proteins but regulate various targets and signaling pathways in physiological and pathological processes. Recently, there has been increasing interest in investigating the interplay between the cGAS-STING pathway and ncRNAs. In this review, we provide a concise overview of the cGAS-STING pathway and ncRNAs. Then, we specifically delve into the regulation of the cGAS-STING pathway by long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), the three major classes of ncRNAs, and the influence of the cGAS-STING pathway on the expression of ncRNAs. Furthermore, we introduce the therapeutic applications targeting the cGAS-STING pathway and ncRNA therapy, and propose the utilization of drug delivery systems to deliver ncRNAs that influence the cGAS-STING pathway. Overall, this review highlights the emerging understanding of the intricate relationship between the cGAS-STING pathway and ncRNAs, shedding light on their potential as therapeutic targets in various diseases.

The role of the cGAS-STING pathway in chronic pulmonary inflammatory diseases

The innate immune system plays a vital role in the inflammatory process, serving as a crucial mechanism for the body to respond to infection, cellular stress, and tissue damage. The cGAS-STING signaling pathway is pivotal in the onset and progression of various autoimmune diseases and chronic inflammation. By recognizing cytoplasmic DNA, this pathway initiates and regulates inflammation and antiviral responses within the innate immune system. Consequently, the regulation of the cGAS-STING pathway has become a prominent area of interest in the treatment of many diseases. Chronic inflammatory lung diseases, such as chronic obstructive pulmonary disease (COPD), asthma, and pulmonary fibrosis, are characterized by persistent or recurrent lung inflammation and tissue damage, leading to diminished respiratory function. This paper explores the mechanism of action of the cGAS-STING signaling pathway in these diseases, examines the development of STING inhibitors and nanomaterial applications, and discusses the potential clinical application prospects of targeting the cGAS-STING pathway in chronic inflammatory lung diseases.

Orally bioavailable STING antagonist synthesized via multi-component Povarov-Doebner type reaction

Aberrant activation of the cGAS-STING signaling results in innate immune response induction. Herein, we report HSKB142, an orally bioavailable compound containing the 3H-pyrazolo [4,3-f]quinoline synthesized via a Povarov-Doebner MCR. HSKB142 is non-cytotoxic towards immune cells and suppresses type-1 interferon expression in human THP-1 monocytes upon treatment with 2'3'-cGAMP.

Cyclopeptide Inhibitors Target the N-Terminal Tail of STING and Alleviate Autoinflammation

Cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway is a crucial component of innate immunity that plays a vital role in protecting against pathogen infections and cellular stress. However, aberrant activation of cGAS-STING pathway is related to inflammatory and autoimmune diseases. Here, we developed cyclopeptide STING inhibitors by cyclizing the N-terminal tail (NTT) of STING. These cyclopeptides selectively inhibited the activation of STING pathway in human or murine cell lines. Mechanistically, the inhibitors directly bound to STING, and subsequently blocked the aggregation and activation of STING. In addition, the optimal inhibitor STi-2 significantly suppressed proinflammatory cytokine production and systemic inflammation in Trex1-/- mice. Overall, our work facilitates the development of specific inhibitors of STING as potential therapies for cGAS-STING associated autoinflammatory diseases.

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.

How to treat monogenic SLE?

Systemic lupus erythematosus is a rare and life-threatening autoimmune disease characterized by autoantibodies against double-stranded DNA, with an immunopathology that remains partially unclear. New insights into the disease have been provided by the discovery of key mutations leading to the development of monogenic SLE, occurring in the context of early-onset disease, syndromic lupus, or familial clustering. The increased frequency of discovering these mutations in recent years, thanks to the advent of genetic screening, has greatly enhanced our understanding of the immunopathogenesis of SLE. These monogenic defects include defective clearance of apoptotic bodies, abnormalities in nucleic acid sensing, activation of the type-I interferon pathway, and the breakdown of tolerance through B or T cell activation or lymphocyte proliferation due to anomalies in TLR signalling and/or NFκB pathway overactivation. The translation of genetic discoveries into therapeutic strategies is presented here, within the framework of personalized therapy.

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.

Pharmacological potential of cyclic nucleotide signaling in immunity

Cyclic nucleotides are important signaling molecules that play many critical physiological roles including controlling cell fate and development, regulation of metabolic processes, and responding to changes in the environment. Cyclic nucleotides are also pivotal regulators in immune signaling, orchestrating intricate processes that maintain homeostasis and defend against pathogenic threats. This review provides a comprehensive examination of the pharmacological potential of cyclic nucleotide signaling pathways within the realm of immunity. Beginning with an overview of the fundamental roles of cAMP and cGMP as ubiquitous second messengers, this review delves into the complexities of their involvement in immune responses. Special attention is given to the challenges associated with modulating these signaling pathways for therapeutic purposes, emphasizing the necessity for achieving cell-type specificity to avert unintended consequences. A major focus of the review is on the recent paradigm-shifting discoveries regarding specialized cyclic nucleotide signals in the innate immune system, notably the cGAS-STING pathway. The significance of cyclic dinucleotides, exemplified by 2'3'-cGAMP, in controlling immune responses against pathogens and cancer, is explored. The evolutionarily conserved nature of cyclic dinucleotides as antiviral agents, spanning across diverse organisms, underscores their potential as targets for innovative immunotherapies. Findings from the last several years have revealed a striking diversity of novel bacterial cyclic nucleotide second messengers which are involved in antiviral responses. Knowledge of the existence and precise identity of these molecules coupled with accurate descriptions of their associated immune defense pathways will be essential to the future development of novel antibacterial therapeutic strategies. The insights presented herein may help researchers navigate the evolving landscape of immunopharmacology as it pertains to cyclic nucleotides and point toward new avenues or lines of thinking about development of therapeutics against the pathways they regulate.

Emerging and Re-emerging Warheads for Targeted Covalent Inhibitors: An Update

Covalent inhibitors and other types of covalent modalities have seen a revival in the past two decades, with a variety of new targeted covalent drugs having been approved in recent years. A key feature of such molecules is an intrinsically reactive group, typically a weak electrophile, which enables the irreversible or reversible formation of a covalent bond with a specific amino acid of the target protein. This reactive group, often called the "warhead", is a critical determinant of the ligand's activity, selectivity, and general biological properties. In 2019, we summarized emerging and re-emerging warhead chemistries to target cysteine and other amino acids (Gehringer, M.; Laufer, S. A. J. Med. Chem. 2019, 62, 5673-5724; DOI: 10.1021/acs.jmedchem.8b01153). Since then, the field has rapidly evolved. Here we discuss the progress on covalent warheads made since our last Perspective and their application in medicinal chemistry and chemical biology.

Development of STING degrader with double covalent ligands

Stimulator of interferon genes (STING), a homodimeric membrane receptor localized in the endoplasmic reticulum, plays a pivotal role in signaling innate immune responses. Inhibitors and proteolysis-targeting chimeras (PROTACs) targeting STING are promising compounds for addressing autoinflammatory and autoimmune disorders. In this study, we used a minimal covalent handle recently developed as the ligand portion of an E3 ligase. The engineered STING degrader with a low molecular weight compound covalently binds to STING and E3 ligase. Degrader 2 showed sustained STING degradation activity at lower concentrations (3 µM, 48 h, about 75 % degradation) compared to a reported STING PROTAC, SP23. This discovery holds significance for its potential in treating autoinflammatory and autoimmune diseases, offering promising avenues for developing more efficacious STING-targeted therapies.

Analysis of structure-activity relationship of indol-3-yl-N-phenylcarbamic amides as potent STING inhibitors

A structure-activity relationship (SAR) study of stimulator of interferon gene (STING) inhibition was performed using a series of indol-3-yl-N-phenylcarbamic amides and indol-2-yl-N-phenylcarbamic amides. Among these analogs, compounds 10, 13, 15, 19, and 21 inhibited the phosphorylation of STING and interferon regulatory factor 3 (IRF3) to a greater extent than the reference compound, H-151. All five analogs showed stronger STING inhibition than H-151 on the 2',3'-cyclic GMP-AMP-induced expression of interferon regulatory factors (IRFs) in a STINGR232 knock-in THP-1 reporter cell line. The half-maximal inhibitory concentration of the most potent compound, 21, was 11.5 nM. The molecular docking analysis of compound 21 and STING combined with the SAR study suggested that the meta- and para-positions of the benzene ring of the phenylcarbamic amide moiety could be structurally modified by introducing halides or alkyl substituents.