Broad-spectrum antivirals for the emerging Middle East respiratory syndrome coronavirus

Objectives: Middle East respiratory syndrome coronavirus (MERS-CoV) has emerged to cause fatal infections in patients in the Middle East and traveler-associated secondary cases in Europe and Africa. Person-to-person transmission is evident in outbreaks involving household and hospital contacts. Effective antivirals are urgently needed. Methods: We used small compound-based forward chemical genetics to screen a chemical library of 1280 known drugs against influenza A virus in Biosafety Level-2 laboratory. We then assessed the anti-MERS-CoV activities of the identified compounds and of interferons, nelfinavir, and lopinavir because of their reported anti-coronavirus activities in terms of cytopathic effect inhibition, viral yield reduction, and plaque reduction assays in Biosafety Level-3 laboratory. Results: Ten compounds were identified as primary hits in high-throughput screening. Only mycophenolic acid exhibited low EC₅₀ and high selectivity index. Additionally, ribavirin and interferons also exhibited in-vitro anti-MERS-CoV activity. The serum concentrations achievable at therapeutic doses of mycophenolic acid and interferon-β1b were 60-300 and 3-4 times higher than the concentrations at which in-vitro anti-MERS-CoV activities were demonstrated, whereas that of ribavirin was ~2 times lower. Combination of mycophenolic acid and interferon-β1b lowered the EC₅₀ of each drug by 1-3 times. Conclusions: Interferon-β1b with mycophenolic acid should be considered in treatment trials of MERS.