A Mouse Model for Betacoronavirus Subgroup 2c Using a Bat Coronavirus Strain HKU5 Variant

Agnihothram, Sudhakar; Yount, Boyd L.; Donaldson, Eric F.; Huynh, Jeremy; Menachery, Vineet D.; Gralinski, Lisa E.; Graham, Rachel L.; Becker, Michelle M.; Tomar, Sakshi; Scobey, Trevor D.; Osswald, Heather L.; Whitmore, Alan; Gopal, Robin; Ghosh, Arun K.; Mesecar, Andrew; Zambon, Maria; Heise, Mark; Denison, Mark R.; Baric, Ralph S.

The BtCoV HKU5-SE virus contains an authentic set of subgroup 2c replicase, accessory, and other structural proteins, providing a robust platform for evaluating the breadth of activity of antiviral drugs against the group 2c CoVs. Among the Coronaviridae, nsp5 (3CLpro) inhibitors have been shown to be successful in inhibiting SARS-CoV replication in vitro (22, 23) . Using biochemical assays, the candidate drug GRL-001 inhibits MERS-CoV and BtCoV HKU5-SE nsp5 protease activity (24) and reduces MERS-CoV and BtCoV HKU5-SE replication by over 100-fold in vitro. Although an intact monolayer was observed in drug-treated cells at 36 h p.i., the virus titers were reduced only 10-fold. Similar differences have been reported for coronavirus papainlike protease (PLP) inhibitors (43) . The drug might be slowing down the virus growth cycle and retarding the development of cytopathic effect (CPE). In addition to blocking the effects of 3CLpro, GRL-001 might interact with other host proteins activated during virus infection and prevent cell death. Nevertheless, its broad therapeutic action against distant group 2c CoVs supports the hypothesis that GRL-001 is an effective inhibitor of 3CLpro activities in multiple subgroup 2c CoVs, providing a potential candidate drug for future outbreaks. It is likely that GRL-001 will require modifications to improve its durability, biodistribution, and potency in vivo.