Single Mutations Reshape the Structural Correlation Network of the DMXAA-Human STING Complex

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.

Loops Mediate Agonist-Induced Activation of the Stimulator of Interferon Genes Protein

The stimulator of interferon genes (STING) is an important therapeutic target for cancer diseases. The activated STING recruits downstream tank-binding kinase 1 (TBK1) to trigger several important immune responses. However, the molecular mechanism of how agonist molecules mediate the STING-TBK1 interactions remains elusive. Here, we performed molecular dynamics simulations to capture the conformational changes of STING and TBK1 upon agonist binding. Our simulations revealed that multiple helices (α5-α7) and especially three loops (loop 6, loop 8, and C-terminal tail) of STING participated in the allosteric mediation of the STING-TBK1 interactions. Consistent results were also observed in the simulations of the constitutive activating mutant of STING (R284S). We further identified α5 as a key region in this agonist-induced activation mechanism of STING. Free-energy perturbation calculations of multiple STING agonists demonstrated that an alkynyl group targeting α5 is a determinant for agonist activities. These results not only offer deeper insights into the agonist-induced allosteric mediation of STING-TKB1 interactions but also provide a guidance for future drug development of this important therapeutic target.

Discovery of Novel STING Inhibitors Based on the Structure of the Mouse STING Agonist DMXAA

The stimulator-of-interferon-gene (STING) protein is involved in innate immunity. The drug DMXAA (5,6-dimethylxanthenone-4-acetic acid) proved to be a potent murine-STING (mSTING) agonist but had little effect on human-STING (hSTING). In this paper, we draw upon the comparison of different crystal structures and protein-ligand interaction relationships analysis to venture the hypothesis that the drug design of DMXAA variants has the potential to convert STING agonists to inhibitors. Based on our previous discovery of two DMXAA analogs, 3 and 4 (both could bind to STING), we structurally optimized them and synthesized new derivatives, respectively. In binding assays, we found compounds 11 and 27 to represent STING binders that were superior to the original structures and discussed the structure-activity relationships. All target compounds were inactive in cellular assays for the screening of STING agonistic activity. Gratifyingly, we identified 11 and 27 as STING inhibitors with micromolar activity in both hSTING and mSTING pathways. In addition, 11 and 27 inhibited the induction of interferon and inflammatory cytokines activated by 2'3'-cGAMP without apparent cytotoxicity. These findings break the rigid thinking that DMXAA provides the structural basis specifically for STING agonists and open up more possibilities for developing novel STING agonists or inhibitors.

The stimulator of interferon genes (STING) agonists for treating acute myeloid leukemia (AML): current knowledge and future outlook

Acute myeloid leukemia (AML) is an aggressive hematologic cancer in adults. Some patients exhibit restricted T cell infiltration and do not respond to routine treatments. This may be prevented by enhancing adaptive immunity by stimulating innate immune cells inside the tumor microenvironment (TME). To activate the adaptive immunological reaction against tumors, type I interferons (IFNs) can promote the presentation of tumor-specific cytotoxic T lymphocyte (CTL) cell recruitment. During the activation of innate immunity, cyclic di-nucleotides (CDNs) bind to and stimulate the stimulator of interferon genes (STING), a protein localized inside the endoplasmic reticulum (ER) membrane, resulting in the expression of type I IFNs. The efficacy of STING agonists as effective stimulators of the anti-tumor response in AML is being investigated in numerous clinical studies. Therefore, the purpose of this investigation was to thoroughly review existing knowledge in this field and provide perspective into the clinical potential of STING agonists in AML.

How Fragile We Are: Influence of Stimulator of Interferon Genes (STING) Variants on Pathogen Recognition and Immune Response Efficiency

The stimulator of interferon genes (STING) protein is a cornerstone of the human immune response. Its activation by cGAMP in the presence of cytosolic DNA stimulates the production of type I interferons and inflammatory cytokines. In the human population, several STING variants exist and exhibit dramatic differences in their activity, impacting the efficiency of the host defense against infections. Understanding the molecular mechanisms of these variants opens perspectives for personalized medicine treatments against diseases such as viral infections, cancers, or autoinflammatory diseases. Through microsecond-scale molecular modeling simulations, contact analyses, and machine learning techniques, we reveal the dynamic behavior of four STING variants (wild type, G230A, R293Q, and G230A/R293Q) and rationalize the variability of efficiency observed experimentally. Our results show that the decrease in STING activity is linked to a stiffening of key structural elements of the binding cavity together with changes in the interaction patterns within the protein.

Discovery of Non-Nucleotide Small-Molecule STING Agonists via Chemotype Hybridization

The identification of agonists of the stimulator of interferon genes (STING) pathway has been an area of intense research due to their potential to enhance innate immune response and tumor immunogenicity in the context of immuno-oncology therapy. Initial efforts to identify STING agonists focused on the modification of 2',3'-cGAMP (1) (an endogenous STING activator ligand) and other closely related cyclic dinucleotides (CDNs). While these efforts have successfully identified novel CDNs that have progressed into the clinic, their utility is currently limited to patients with solid tumors that STING agonists can be delivered to intratumorally. Herein, we report the discovery of a unique class of non-nucleotide small-molecule STING agonists that demonstrate antitumor activity when dosed intratumorally in a syngeneic mouse model.

Development of small molecule inhibitors/agonists targeting STING for disease

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) -stimulator of interferon genes (STING) signaling pathway is the primary immune response pathway in the cytoplasm. Pharmacological regulation of the STING pathway has good characteristics in both structure and function, which plays a significant role in the immunotherapy of autoimmune diseases, autoinflammatory diseases, and cancer. In this review, we summarized the activation of STING signaling pathway, the STING-related diseases, the development principle and the latest progress of inhibitors and agonists targeting STING. Our review demonstrates that STING signal pathway is a promising drug target, providing effective clues and correct guidance for the discovery of novel small molecule inhibitors/agonists that targeted STING for cancer, autoimmune, and inflammatory diseases.

Co-Administration of Vadimezan and Recombinant Coagulase-NGR Inhibits Growth of Melanoma Tumor in Mice

Purpose: Tumor vascular targeting appeared as an appealing approach to fight cancer, though, the results from the clinical trials and drugs in the market were proved otherwise. The promise of anti-angiogenic therapy as the leading tumor vascular targeting strategy was negatively affected with the discovery that tumor vascularization can occur non-angiogenic mechanisms such as co-option. An additional strategy is induction of tumor vascular infarction and ischemia. Methods: Such that we used truncated coagulase (tCoa) coupled to tumor endothelial targeting moieties to produce tCoa-NGR fusion proteins. We showed that tCoa-NGR can bypass coagulation cascade to induce selective vascular thrombosis and infarction of mild and highly proliferative solid tumors in mice. Moreover, combination therapy can be used to improve the potential of cancer vascular targeting modalities. Herein, we report combination of tCoa-NGR with vascular disrupting agent (VDA), vadimezan. Results: Our results show that synergistic work of these two agents can significantly suppress growth of B16-F10 melanoma tumors in C57/BL6 mice. Conclusion: For the first time, we used the simultaneous benefits of two strategies for inducing thrombosis and destruction of tumor vasculature as spatial co-operation. The tCoa-NGR induce thrombosis which reduces blood flow in the peripheral tumor region. And combined with the action of DMXAA, which target inner tumor mass, growth and proliferation of melanoma tumors can be significantly suppressed.

Evolution of diffusion and structure of six n-alkanes in carbon dioxide at infinite dilution over wide temperature and pressure ranges: a molecular dynamics study

Over wide temperature and pressure ranges, the molecular dynamics simulation is performed to study the mass transfer of six n-alkanes from n-C₅H₁₂ to n-C₁₀H₂₂ in CO₂ at infinite dilution by calculating the diffusion coefficients, which have not yet been measured by experiment. Meanwhile, the structural properties of these systems are explored. It is found that under different temperature and pressure conditions, the variation trends of the radial distribution functions of n-alkanes are quite different, while the variation trends of the average coordination number of n-alkanes can be divided into three types. The radius of gyration and the solvent accessible surface area are both affected by temperature and carbon chain length, but their variation trends are different, and it could explain the abnormal variation trends of the radial distribution functions and the average coordination number. Graphical abstract Over wide temperature and pressure ranges, the variation trends of the average coordination number of n-alkanes can be divided into three types.

STING modulators: Predictive significance in drug discovery

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) - stimulator of interferon genes (STING) signaling pathway plays the critical role in the immune response to DNA. Pharmacological modulation of the STING pathway has been well characterized both from structural and functional perspectives, which paves the way for the drug design of small modulators by medicinal chemists. Here, we outline recent progress in studies on the STING pathway, the structure and biological function of STING, the STING related disease, as well as the rationale and progress in the development of STING modulators. Our review demonstrates that STING is a promising drug target, and providing clues for the discovery of novel STING agonists and antagonists for the potential treatment of various disease including microbial infectious diseases, cancer, and autoimmune disease.

Discovery of novel natural flavonoids as potent antiviral candidates against hepatitis C virus NS5B polymerase

The non-structural 5B (NS5B) polymerase of hepatitis C virus (HCV) is an attractive target for antiviral intervention. Quercetagetin (Que) is a natural flavonoid, which has been exhibited to have anti-HCV property through inhibition of RNA binding to NS5B. The last few decades have witnessed a growing interest in the extraction of natural flavonoids with a plethora of different biological activities. Considering the high therapeutic potential of Que, the aim of this study is to explore wide structure entities with potent activity using Que as a prototype. A virtual screen protocol involving docking and molecular dynamics has been performed to examine the potency of forty-three natural flavonoids which recently extracted from plants for inhibition of NS5B. During two screening stages, two compounds 24 and 41 were identified to have more favorable binding affinity to NS5B as compared to Que. The comparative analysis showed that there is a significant difference in the binding free energy of Que and 41 (ΔΔG_bind = -11.17 kcal/mol). It was revealed that van der Waals (vdW) interaction drives the binding process of both 24 and 41 and plays an important role in increasing their activities relative to Que. PHE162 serves as a crucial residue in both the NS5B-24 and NS5B-41 systems, contributing the most vdW energy by π-π interaction, suggesting that aromatic interactions are critical for the binding of 24 and 41 to NS5B. Moreover, hydrogen bond analysis indicates that the hydrogen bonds formed by LYS98, THR137, ASP164 and ARG168, can play important roles in the increased binding affinity of 41 to NS5B relative to Que. The findings of this study will provide useful structure-activity relationship (SAR) guidelines for the design of novel inhibitors with improved/enhanced therapeutic activities in the treatment of hepatitis C.

Dynamic Structural Differences between Human and Mouse STING Lead to Differing Sensitivity to DMXAA

The stimulator-of-interferon-genes (STING) protein is involved in innate immunity. It has recently been shown that modulation of STING can lead to an aggressive antitumor response. DMXAA is an antitumor agent that had shown great promise in murine models but failed in human clinical trials. The molecular target of DMXAA was subsequently shown to be murine STING (mSTING); however, human STING (hSTING) is insensitive to DMXAA. Molecular dynamics simulations were employed to investigate the differences between hSTING and mSTING that could influence DMXAA binding. An initial set of simulations was performed to investigate a single lid region mutation G230I in hSTING (corresponding residue in mSTING is an Ile), which rendered the protein sensitive to DMXAA. The simulations found that an Ile side chain was enough to form a steric barrier that prevents exit of DMXAA, whereas in WT hSTING, the Gly residue that lacks a side chain formed a porous lid region that allowed DMXAA to exit. A second set of molecular dynamics simulations compared the tendency of STING to be in an open-inactive conformation or a closed-active conformation. The results show that hSTING prefers to be in an open-inactive conformation even with cGAMP, the native ligand, bound. On the other hand, mSTING prefers a closed-active conformation even without a ligand bound. These results highlight the challenges in translating a mouse active STING compound into a human active compound, while also providing avenues to pursue for designing a small-molecule drug targeting human STING.

Covalent vs. Non-Covalent Inhibition: Tackling Drug Resistance in EGFR - A Thorough Dynamic Perspective

A persistent challenge in the treatment of non-small cell lung cancer (NSCLC) with EGFR is the emergence of drug-resistant caused by somatic mutations. The EGFR L858R/T790 M double mutant (EGFR^DM ) was found to be the most alarming variant. Despite the development of a wide range of inhibitors, none of them could inhibit EGFR^DM effectively. Recently, 11h and 45a, have been found to be potent inhibitors against EGFR^DM through two distinctive mechanisms, non-covalent and covalent binding, respectively. However, the structural and dynamic implications of the two modes of inhibitions remain unexplored. Herein, two molecular dynamics simulation protocols, coupled with free-energy calculations, were applied to gain insight into the atomistic nature of each binding mode. The comparative analysis confirmed that there is a significant difference in the binding free energy between 11h and 45a (ΔΔG_bind =-21.17 kcal/mol). The main binding force that governs the binding of both inhibitors is vdW, with a higher contribution for 45a. Two residues ARG841 and THR854 were found to have curtailed role in the binding of 45a to EGFR^DM by stabilizing its flexible alcohol chain. The 45a binding to EGFR^DM induces structural rearrangement in the active site to allow easier accessibility of 45a to target residue CYS797. The findings of this work can substantially shed light on new strategies for developing novel classes of covalent and non-covalent inhibitors with increased specificity and potency.