Summary Coronaviruses express a nucleocapsid protein (N) that is essential for viral replication, transcription, and virion assembly. Phosphorylation of N from SARS-CoV (responsible for SARS) by glycogen synthase kinase 3 (GSK- 3) is required for its function. GSK-3 inhibition attenuates infectivity of SARS-CoV and other coronaviruses and is therefore an intriguing therapeutic strategy for coronavirus infections. Lithium, a widely used medication, directly inhibits GSK-3 and impairs N phosphorylation, viral transcription, replication, and infectivity of diverse coronaviruses. However, GSK-3 phosphorylation of N protein from SARS-CoV-2 (the cause of COVID19) has not been reported. This proposal leverages our long-standing expertise with GSK-3 to block N function and SARS-CoV-2 replication. In a preliminary review of 70,000 subjects undergoing PCR testing for SARS- CoV-2, we found that patients on lithium had reduced risk of COVID19 (odds ration = 0.5 [0.36 - 0.80], p = 0.0002). We show that phosphorylation of N from SARS-CoV-2 is inhibited by lithium and that other GSK-3 inhibitors block N phosphorylation with IC50s in the low micromolar range. GSK3 loss of function supports that GSK-3 is required for SARS-CoV-2 N protein phosphorlyation. We identified clinically-tolerated drugs that unexpectedly inhibit GSK-3 and impair N phosphorylation at clinically-tolerated levels. Aim 1 of this proposal describes approaches to enhance inhibition of N phosphorylation by lithium and by selective GSK-3 inhibitors, with a focus on those shown to be safe in humans through clinical trials for other diseases. As GSK-3 phosphorylation of N protein requires pre-phosphorylation at a distinct site by another, unkown protein kinase, Aim 2 will identify and target the priming kinase as an alternative strategy to block SARS-CoV-2 transcription and replication. This aim will also test whether inhibitors of either GSK-3 or the priming kinase interfere with replication of other pathogenic coronaviruses. If successful, the project will identify clinically safe medications that can be repurposed to treat COVID19 as well as future coronavirus outbreaks.