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Antitumor activity of a systemic STING-activating non-nucleotide cGAMP mimetic

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Science  21 Aug 2020:
Vol. 369, Issue 6506, pp. 993-999
DOI: 10.1126/science.abb4255

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Targeting STING for cancer therapy

Activation of the STING (stimulator of interferon genes) protein by cyclic dinucleotide metabolites plays a critical role in antitumor immunity. The development of synthetic STING agonists is therefore being pursued as a strategy for cancer therapy, but the inherent instability of dinucleotides has limited current efforts. Pan et al. and Chin et al. identified stable STING agonists that act in a “closed” conformation similar to the natural STING ligand, cyclic guanosine monophosphate–adenosine monophosphate (see the Perspective by Gajewski and Higgs). The small molecules can be given orally—an advantage over previously developed STING agonists, which required intratumoral administration. After oral or systemic administration in mice, the agonists activated STING and diverse immune cell types to promote antitumor immunity. These studies represent progress toward clinically viable STING agonists for cancer immunotherapy.

Science, this issue p. eaba6098, p. 993; see also p. 921

Abstract

Stimulator of interferon genes (STING) links innate immunity to biological processes ranging from antitumor immunity to microbiome homeostasis. Mechanistic understanding of the anticancer potential for STING receptor activation is currently limited by metabolic instability of the natural cyclic dinucleotide (CDN) ligands. From a pathway-targeted cell-based screen, we identified a non-nucleotide, small-molecule STING agonist, termed SR-717, that demonstrates broad interspecies and interallelic specificity. A 1.8-angstrom cocrystal structure revealed that SR-717 functions as a direct cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) mimetic that induces the same “closed” conformation of STING. SR-717 displayed antitumor activity; promoted the activation of CD8+ T, natural killer, and dendritic cells in relevant tissues; and facilitated antigen cross-priming. SR-717 also induced the expression of clinically relevant targets, including programmed cell death 1 ligand 1 (PD-L1), in a STING-dependent manner.

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