Synthesis and Pharmacological Evaluation of Tetrahydro-γ-carboline Derivatives as Potent Anti-inflammatory Agents Targeting Cyclic GMP–AMP Synthase

Abstract

The activation of cyclic GMP–AMP synthase (cGAS) by double-stranded DNA is implicated in the pathogenesis of many hyperinflammatory and autoimmune diseases, and the cGAS-targeting small molecule has emerged as a novel therapeutic strategy for treating these diseases. However, the currently reported cGAS inhibitors are far beyond maturity, barely demonstrating in vivo efficacy. Inspired by the structural novelty of compound 5 (G140), we conducted a structural optimization on both its side chain and the central tricyclic core, leading to several subseries of compounds, including those unexpectedly cyclized complex ones. Compound 25 bearing an N-glycylglycinoyl side chain was identified as the most potent one with cellular IC50 values of 1.38 and 11.4 μM for h- and m-cGAS, respectively. Mechanistic studies confirmed its direct targeting of cGAS. Further, compound 25 showed superior in vivo anti-inflammatory effects in the lipopolysaccharide-induced mouse model. The encouraging result of compound 25 provides solid evidence for further pursuit of cGAS-targeting inhibitors as a new anti-inflammatory treatment.

Current understanding of the cGAS-STING signaling pathway: Structure, regulatory mechanisms, and related diseases

“…Several drugs have been shown to modulate cGAS-STING and their well-defined regulatory mechanisms fall into several broad categories, including cGAS inhibitors and STING inhibitors. Inhibitors of cGAS ( An et al., 2015 , 2017 , 2018 ; Chu et al., 2021 ; Lu et al., 2022 ; Steinhagen et al., 2018 ; Wang et al., 2018a ) act primarily through three mechanisms, i.e., blocking cGAS-DNA binding, inhibiting cGAS catalytic sites ( Hall et al., 2017 ; Lama et al., 2019 ; Tan et al., 2021 ; Vincent et al., 2017 ; Xu et al., 2020b ), and affecting post-translational modifications of cGAS ( Dai et al., 2019 ). Inhibitors of STING act by inhibiting STING-cGAMP binding ( Hong et al., 2021 ; Li et al., 2018b ; Siu et al., 2019 ) and affecting STING palmitoylation ( Haag et al., 2018 ; Hansen et al., 2018a ; Vinogradova et al., 2020 ), dimerization, or transportation ( Gao et al., 2022 ).…”

The Crucial Roles and Research Advances of cGAS-STING Pathway in Cutaneous Disorders

“…Coincidentally, Tan et al . also identified a tetrahydro-γ-carboline derivative called Compound 25, potently inhibiting both human and mouse cGAS [ 76 ]. More importantly, Compound 25 demonstrated superior in vivo anti-inflammatory effects in the lipopolysaccharide-induced mouse model [ 76 ], providing evidence for its future use as an anti-inflammatory treatment.…”

Investigating the Activation Mechanism Differences between Human and Mouse cGAS by Molecular Dynamics Simulations

“…Many efforts have been devoted to developing small molecule drugs through in vitro and in silico experiments. ,− Some inhibitors designed for mouse cGAS (mcGAS) or human cGAS (hcGAS) have been found to have low affinity in the other species. ,,,, One possible reason behind this phenomenon is that although cGAS is a highly conserved protein, 40% of sequences between cGAS of these two species are different (Figure A), and their structures also differ (Figure B,C). Structural differences exist not only in many loop regions between hcGAS and mcGAS of both apo- and DNA-bound states, but also in the activation loop and β-sheet between these two species’ cGAS of the apo-state especially.…”