ABSTRACT
The coronavirus disease 2019 (COVID-19) pandemic has caused more than six million deaths worldwide since 2019. Although vaccines are available, novel variants of coronavirus are expected to appear continuously, and there is a need for a more effective remedy for coronavirus disease. In this report, we isolated eupatin from Inula japonica flowers and showed that it inhibits the coronavirus 3 chymotrypsin-like (3CL) protease as well as viral replication. We showed that eupatin treatment inhibits SARS-CoV-2 3CL-protease, and computational modeling demonstrated that it interacts with key residues of 3CL-protease. Further, the treatment decreased the number of plaques formed by human coronavirus OC43 (HCoV-OC43) infection and decreased viral protein and RNA levels in the media. These results indicate that eupatin inhibits coronavirus replication.
Subject(s)
COVID-19 , Humans , SARS-CoV-2 , Peptide Hydrolases , Protease Inhibitors/pharmacology , Protease Inhibitors/chemistry , Flavonoids/pharmacology , Endopeptidases , Antiviral Agents/pharmacologyABSTRACT
In our ongoing efforts to identify effective natural antiviral agents, four methoxy flavonoids (1-4) were isolated from the Inula britannica flower extract. Their structures were elucidated using nuclear magnetic resonance. Flavonoids 1-4 exhibited inhibitory activity against SARS- CoV-2 3CLpro with IC50 values of 41.6 ± 2.5, 35.9 ± 0.9, 32.8 ± 1.2, and 96.6 ± 3.4 µM, respectively. Flavonoids 1-3 inhibited 3CLpro in a competitive manner. Based on molecular simulations, key amino acids that form hydrogen bond with inhibitor 3 were identified. Finally, we found that inhibitors (1-3) suppressed HCoV-OC43 coronavirus proliferation at micromole concentrations.