Screening of FDA-approved drugs using a MERS-CoV clinical isolate from South Korea identifies potential therapeutic options for COVID-19

Therapeutic options for coronavirus remain limited. To address this unmet medical need, we screened 5,406 compounds, including United States Food and Drug Administration (FDA)- approved drugs and bioactives, for activity against a South Korean Middle East respiratory syndrome coronavirus (MERS-CoV) clinical isolate. Among 221 identified hits, 54 had therapeutic indexes (TI) greater than 6. Time-of-addition studies with selected drugs demonstrated eight and four FDA-approved drugs acted on the early and late stages of the viral life cycle, respectively. Confirmed hits included several cardiotonic agents (TI>100), atovaquone, an anti-malarial (TI>34), and ciclosonide, an inhalable corticosteroid (TI>6). Furthermore, utilizing the severe acute respiratory syndrome CoV-2 (SARS-CoV-2), combinations of remedesivir with selected dugs were evaluated, which identified ciclosonide and nelfinavir to be additive and synergistic drugsin vitro, respectively. Together, we screened FDA-approved drugs using patient-derived MERS-CoV, triaged hits to discriminate between early and late viral life cycle inhibitors, confirmed selected drugs using SARS-CoV-2, and demonstrated the added value of selected medications in combination with remedesivir. Our results identify potential therapeutic options for MERS-CoV infections, and provide a basis to treat coronavirus disease 2019 (COVID-19) and other coronavirus-related illnesses.