Lycorine, a non-nucleoside RNA dependent RNA polymerase inhibitor, as potential treatment for emerging coronavirus infections

Background: Highly effective novel treatments need to be developed to suppress emerging coronavirus (CoV) infections such as COVID-19. The RNA dependent RNA polymerase (RdRp) among the viral proteins is known as an effective antiviral target. Lycorine is a phenanthridine Amaryllidaceae alkaloid isolated from the bulbs of Lycoris radiata (L'Her.) Herb. and has various pharmacological bioactivities including antiviral function. Purpose: We investigated the direct-inhibiting action of lycorine on CoV's RdRp, as potential treatment for emerging CoV infections. Methods: We examined the inhibitory effect of lycorine on MERS-CoV, SARS-CoV, and SARS-CoV-2 infections, and then quantitatively measured the inhibitory effect of lycorine on MERS-CoV RdRp activity using a cell-based reporter assay. Finally, we performed the docking simulation with lycorine and SARS-CoV-2 RdRp. Results: Lycorine efficiently inhibited these CoVs with IC50 values of 2.123 +/- 0.053, 1.021 +/- 0.025, and 0.878 +/- 0.022 mu M, respectively, comparable with anti-CoV effects of remdesivir. Lycorine directly inhibited MERS-CoV RdRp activity with an IC50 of 1.406 +/- 0.260 mu M, compared with remdesivir's IC50 value of 6.335 +/- 0.731 mu M. In addition, docking simulation showed that lycorine interacts with SARS-CoV-2 RdRp at the Asp623, Asn691, and Ser759 residues through hydrogen bonding, at which the binding affinities of lycorine (-6.2 kcal/mol) were higher than those of remdesivir (-4.7 kcal/mol). Conclusions: Lycorine is a potent non-nucleoside direct-acting antiviral against emerging coronavirus infections and acts by inhibiting viral RdRp activity; therefore, lycorine may be a candidate against the current COVID-19 pandemic.