Broad-spectrum antiviral GS-5734 to treat MERS-CoV and related emerging CoV

Zoonotic viruses, like filoviruses and coronaviruses (CoV), represent a continuous and growing threat to globalpublic health because they unpredictably emerge causing devastating outbreaks of pandemic disease. In the21st century, severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratorysyndrome coronavirus (MERS-CoV) emerged from zoonotic pools of viruses, causing severe disease inhumans. MERS-CoV is endemic in camels in the Middle East with continuous new infections in humans.Although SARS-CoV is not currently a threat, several "prepandemic" SARS-like CoVs have been isolated frombats that replicate efficiently in human cells and are resistant to existing therapies. With the unpredictableoverlap of human and wild animal ecologies, the potential for novel CoV emergence into humans is highlyprobable. Currently, there are no approved antiviral therapies for any human CoV infection. Broad-spectrumCoV therapies that control known human and zoonotic CoV infections would address an immediate unmetmedical need and could counter future pandemic episodes. In partnership with Gilead Sciences, we havedemonstrated that the nucleoside prodrug, GS-5734, is highly efficacious in inhibiting multiple human andzoonotic CoV in vitro and SARS-CoV in vivo. The primary goal of our program is to accelerate the preclinicaldevelopment of GS-5734 and promote IND licensure for the MERS-CoV indication. To thoroughly evaluate thebreadth of antiviral activity and predict efficacy against future emerging CoV, we will also assess efficacyagainst a panel of CoV representative of family-wide genetic diversity, including prepandemic zoonotic strainspoised for emergence. Focusing on the highly pathogenic MERS-CoV, our unique partnership integrates: i)metagenomics and recombinant virus synthetic genome recovery, ii) primary human lung cell models, iii)cutting edge virology and biochemistry, iv) robust murine and primate models of human disease and v) state ofthe art metabolic and pharmacokinetic analysis. In Aim 1, we refine the pharmacokinetics, pharmacodynamicsand breadth of GS-5734 through efficacy and metabolism studies in various primary human cells with a diversearray of human and zoonotic CoV and through the evaluation of in vivo efficacy in murine and non-humanprimate models of MERS- and SARS-CoV. In Aim 2, we select for resistance against SARS-CoV and MERS-CoV, and determine the effect of resistance on virus replication, fitness and susceptibility to treatment. In Aim3, we determine if the mechanism of action of GS-5734 is a result of direct effects on viral RNA replicationand/or alteration of antiviral immunity via deep sequencing and single molecule RNA fluorescence in situhybridization of vehicle or drug treated infected cells and mice. We articulate a development strategy for broad-spectrum therapeutics that could be extended to a multitude of emerging viral pathogens threatening globalpublic health.