In vitro activity: C-176 is a highly potent, covalent and selective small-molecule antagonist/inhibitor of the stimulator of interferon genes (STING) protein, which is a central signalling component of the intracellular DNA sensing pathway. Mechanistically, C-176 covalently targets the predicted transmembrane cysteine residue 91 and thereby block the activation-induced palmitoylation of STING. The palmitoylation of STING is essential for its assembly into multimeric complexes at the Golgi apparatus and, in turn, for the recruitment of downstream signalling factors. C-176 and its derivatives reduce STING-mediated inflammatory cytokine production in both human and mouse cells. Furthermore, C-176 attenuates pathological features of autoinflammatory disease in mice. In summary, this work uncovers a mechanism by which STING can be inhibited pharmacologically and demonstrates the potential of therapies that target STING for the treatment of autoinflammatory disease.

Kinase Assay: C-176 strongly reduces STING-mediated, but not RIG-I- or TBK1-mediated, IFNβ reporter activity. Pretreatment with C-176 markedly reduce the CMA-mediated induction of serum levels of type I IFNs and IL-6.

Cell Assay: C-176 and its derivatives reduce STING-mediated inflammatory cytokine production in both human and mouse cells.