Theaflavin 3-gallate inhibits the main protease (M(pro)) of SARS-CoV-2 and reduces its count in vitro

The main protease (M(pro)) of SARS-CoV-2 has been recognized as an attractive drug target because of its central role in viral replication. Our previous preliminary molecular docking studies showed that theaflavin 3-gallate (a natural bioactive molecule derived from theaflavin and found in high abundance in black tea) exhibited better docking scores than repurposed drugs (Atazanavir, Darunavir, Lopinavir). In this study, conventional and steered MD-simulations analyses revealed stronger interactions of theaflavin 3-gallate with the active site residues of M(pro) than theaflavin and a standard molecule GC373 (a known inhibitor of M(pro) and novel broad-spectrum anti-viral agent). Theaflavin 3-gallate inhibited M(pro) protein of SARS-CoV-2 with an IC(50) value of 18.48 ± 1.29 μM. Treatment of SARS-CoV-2 (Indian/a3i clade/2020 isolate) with 200 μM of theaflavin 3-gallate in vitro using Vero cells and quantifying viral transcripts demonstrated reduction of viral count by 75% (viral particles reduced from Log10(6.7) to Log10(6.1)). Overall, our findings suggest that theaflavin 3-gallate effectively targets the M(pro) thus limiting the replication of the SARS-CoV-2 virus in vitro.