Marine diterpenoid targets STING palmitoylation in mammalian cells

Marine-derived STING inhibitors, excavatolide B promote wound repair in full-thickness-incision rats

The process of wound healing encompasses both inflammatory and proliferative stages. Excessive inflammation is known to impede the healing of chronic wounds. Activation of the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway causes inflammation during cellular stress and tissue damage. Herein, we examined the anti-inflammatory effects of the marine-derived STING antagonist excavatolide B (EXCB) and its derivatives, EXCB-61 and EXCB-79, in full-thickness-incision rats. Wound area measurements, histopathological observations, and immunohistochemical analyses were performed to evaluate the roles of these compounds in wound healing. These three compounds were found to have low toxicity, with EXCB promoting Hs68 human dermal fibroblast migration and proliferation. EXCB and EXCB61 treatments, but not EXCB79, reduced the wound area. The histopathological results showed a significant decrease in immune cell infiltration and mast cell accumulation in all compound-treated groups. Immunohistochemical analysis revealed that EXCB and its derivatives reduced cGAS-STING pathway factors such as STING, phosphorylated TANK-binding kinase 1, nuclear factor kappa-light-chain-enhancer of activated B cells, and M1 macrophages while increasing the expression of angiogenic factors vascular endothelial growth factor and CD31, as well as M2 macrophages and collagen I/III deposition. We conclude that marine-derived STING antagonists can attenuate inflammatory responses by inhibiting the cGAS-STING pathway and promoting angiogenesis, thereby aiding wound healing.

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.

Regulation of pattern recognition receptor signaling by palmitoylation

Pattern recognition receptors (PRRs), consisting of Toll-like receptors, RIG-I-like receptors, cytosolic DNA sensors, and NOD-like receptors, sense exogenous pathogenic molecules and endogenous damage signals to maintain physiological homeostasis. Upon activation, PRRs stimulate the sensitization of nuclear factor κB, mitogen-activated protein kinase, TANK-binding kinase 1-interferon (IFN) regulatory factor, and inflammasome signaling pathways to produce inflammatory factors and IFNs to activate Janus kinase/signal transducer and activator of transcription signaling pathways, resulting in anti-infection, antitumor, and other specific immune responses. Palmitoylation is a crucial type of post-translational modification that reversibly alters the localization, stability, and biological activity of target molecules. Here, we discuss the available knowledge on the biological roles and underlying mechanisms linked to protein palmitoylation in modulating PRRs and their downstream signaling pathways under physiological and pathological conditions. Moreover, recent advances in the use of palmitoylation as an attractive therapeutic target for disorders caused by the dysregulation of PRRs were summarized.

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.

Toward the Briarane Core via 1,3-Dipolar Cycloaddition

The complete C20 framework of brianthein W was established, featuring hydroboration/allylation, to provide the C1-C2 quaternary/tertiary stereoarray with excellent stereocontrol. Intramolecular nitrile oxide cycloaddition (INOC) was adopted as the key transformation to establish the trans-fused 6/10-bicyclic ring system. Evolution of the second INOC event revealed the intricacies governing regioselectivity, which ultimately led to construction of the highly strained 10-membered carbocycle.

Immunomodulatory and anti-angiogenesis effects of excavatolide B and its derivatives in alleviating atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin condition primarily driven by T helper 2 (Th2) cytokines, resulting in skin barrier defects, angiogenesis, and inflammatory responses. The marine natural product excavatolide B (EXCB), isolated from the Formosan Gorgonian coral Briareum stechei, exhibits anti-inflammatory and analgesic properties. To enhance solubility, EXCB is chemically modified into the derivatives EXCB-61 salt and EXCB-79. The study aims to investigate the therapeutic effects of these compounds on dinitrochlorbenzene (DNCB)-induced skin damage and to elucidate the underlying anti-inflammatory and anti-angiogenesis mechanism. In vitro, using lipopolysaccharide (LPS)-induced RAW 264.7 cells, all compounds at 10 μM significantly inhibited expression of inflammatory proteins (inducible nitric oxide synthase and cyclooxygenase-2), vascular endothelial growth factor (VEGF), and cytokines (interleukin (IL)-1β, IL-6, and IL-17A). In vivo, topical application of these compounds on DNCB-induced AD mice alleviated skin symptoms, reduced serum levels of IgE, IL-4, IL-13, IL-17, and interferon-γ, and moderated histological phenomena such as hyperplasia, inflammatory cell infiltration, and angiogenesis. The three compounds restored the expression of skin barrier-related proteins (loricrin, filaggrin, and claudin-1) and reduced the expression of angiogenesis-related proteins (VEGF and platelet endothelial cell adhesion molecule-CD31) in the tissues. This is the first study to indicate that EXCB, EXCB-61 salt, and EXCB-79 can treat AD disease by reducing inflammation and angiogenesis. Hence, they may be considered potential candidates for the development of new drugs for AD.