Interferon-β and mycophenolic acid are potent inhibitors of middle east respiratory syndrome coronavirus in cell-based assays

The Middle East respiratory syndrome coronavirus (MERS-CoV) presents a novel emerging threat to public health worldwide. Several treatments for infected individuals have been suggested including IFN, ribavirin and passive immunotherapy with convalescent plasma. Administration of IFN-α2b and ribavirin has improved outcomes of MERS-CoV infection in rhesus macaques when administered within 8 h post-challenge. However, detailed and systematic evidence on the activity of other clinically available drugs is limited. Here we compared the susceptibility of MERS-CoV with different IFN products (IFN-α2b, IFN-γ, IFN-universal, IFN-α2a and IFN-β), as well as with two antivirals, ribavirin and mycophenolic acid (MPA), against MERS-CoV (Hu/Jordan-N3/2012) in vitro. Of all the IFNs tested, IFN-β showed the strongst inhibition of MERS-CoV in vitro, with an IC₅₀ of 1.37 U ml^-1, 41 times lower than the previously reported IC₅₀ (56.08 U ml^-1) of IFN-α2b. IFN-β inhibition was confirmed in the virus yield reduction assay, with an IC₉₀ of 38.8 U ml^-1. Ribavirin did not inhibit viral replication in vitro at a dose that would be applicable to current treatment protocols in humans. In contrast, MPA showed strong inhibition, with an IC₅₀ of 2.87 mM. This drug has not been previously tested against MERS-CoV and may provide an alternative to ribavirin for treatment of MERS-CoV. In conclusion, IFN-β, MPA or a combination of the two may be beneficial in the treatment of MERS-CoV or as a post-exposure intervention in high-risk patients with known exposures to MERS-CoV.