A STING agonist preconditions against ischaemic stroke via an adaptive antiviral Type 1 interferon response

Kundu et al. report that 5,6-dimethylxanthenone-4-acetic acid (DMXAA) can activate stimulator of interferon genes (STING), triggering interferon-associated gene expression both in vitro and in vivo. They show DMXAA's STING-dependent, protective, preconditioning effects in an ischaemic stroke model, suggesting STING as a potential therapeutic target for prophylaxis against stroke. Converging lines of inquiry have highlighted the importance of the Type I antiviral response not only in defending against viruses but also in preconditioning the brain against ischaemic stroke. Despite this understanding, treatments that foster brain resilience by driving antiviral interferon responses have yet to be developed for human use. Studies from our laboratory showed that tilorone, the first human antiviral immunomodulatory agent to be developed, robustly preconditioned against stroke in mice and rats. Tilorone is a DNA intercalator; therefore, we hypothesized that it stabilizes cytosolic DNA (released from the mitochondria or the nucleus), thereby activating cyclic GMP-AMP synthase, a homeostatic DNA sensor, and its downstream pathway. This pathway involves stimulator of interferon genes (STING), tank-binding kinase 1 (TBK1), and interferon regulatory protein-3 and culminates in a protective Type I interferon response. We tested this hypothesis by examining the ability of structurally diverse small-molecule agonists of STING to protect against oxygen/glucose deprivation in vitro in mouse cortical cultures and in vivo against transient ischaemia in mice. The STING agonists significantly reduced cell death both in vitro and in vivo but failed to do so in STING knockout mice. As expected, STING agonist-induced protection was associated with the induction of interferon related genes and the effects could be abrogated in vitro by a TBK1 inhibitor. Taken together, these findings in mice identify STING as a therapeutic target for preconditioning the brain against ischaemic stroke in vitro and in vivo. Moreover, they suggest that clinically approved STING agonists such as Ganciclovir or alpha-Mangostin are candidate drugs that could be tested in humans as a prophylactic treatment to alleviate brain injury associated with ischaemic stroke.