Schaftoside inhibits 3CL^pro and PL^pro of SARS-CoV-2 virus and regulates immune response and inflammation of host cells for the treatment of COVID-19

It is an urgent demand worldwide to control the coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The 3-chymotrypsin-like protease (3CL^pro) and papain-like protease (PL^pro) are key targets to discover SARS-CoV-2 inhibitors. After screening 12 Chinese herbal medicines and 125 compounds from licorice, we found that a popular natural product schaftoside inhibited 3CL^pro and PL^pro with IC₅₀ values of 1.73 ± 0.22 and 3.91 ± 0.19 μmol/L, respectively, and inhibited SARS-CoV-2 virus in Vero E6 cells with EC₅₀ of 11.83 ± 3.23 μmol/L. Hydrogen-deuterium exchange mass spectrometry analysis, quantum mechanics/molecular mechanics calculations, together with site-directed mutagenesis indicated the antiviral activities of schaftoside were related with non-covalent interactions with H41, G143 and R188 of 3CL^pro, and K157, E167 and A246 of PL^pro. Moreover, proteomics analysis and cytokine assay revealed that schaftoside also regulated immune response and inflammation of the host cells. The anti-inflammatory activities of schaftoside were confirmed on lipopolysaccharide-induced acute lung injury mice. Schaftoside showed good safety and pharmacokinetic property, and could be a promising drug candidate for the prevention and treatment of COVID-19.