FURIN and COVID-19: Results from previous studies suggest three possibilities to inhibit coronavirus disease 2019 (COVID-19) (Table 1): (i) the inhibition of S-protein binding to ACE2 (either via the catalytic site or another domain of ACE2) [21]; (ii) the inhibition of viral entry (i.e., furin and transmembrane protease serine 2 (TMPRSS2)) [22]; and (iii) the inhibition of enzymes involved in viral replication or immune escape (i.e., 3CLpro and NSP3) [23].