SARS-CoV-2 PLpro (SARS-CoV-2 papain-like protease) is the largest of the SARS-CoV-2 non-structural proteins (212 kDa). Importantly, the amino acid sequence of SARS-CoV-2PLpro is 98 % identical to related proteases from bat coronaviruses BANAL-52 and RaTG13, and 83 % identical to the related human coronavirus SARS-CoV-1. Particularly, The active sites of SARS-CoV-1 and SARS-CoV-2 PLpro are almost identical. Moreover, SARS-CoV-2 PLpro is essential for viral replication and is considered a valid target for antiviral drug development.
SARS-CoV-2 Mpro (SARS-CoV-2 main protease) is a class of highly conserved cysteine hydrolases in coronaviruses. While SARS-CoV-2 Mpro has capable of cleaving polyproteins at multiple sites to yield multiple functional proteins. Importantly, no homolog of pro has been identified in humans, so it is feasible to develop efficacious and specific Mpro inhibitors on human proteases.
LY1 is a selective and covalent inhibitor against SARS-CoV-2 PLpro and Mpro.
LY1 binds to SARS-CoV-2 PLpro and SARS-CoV-2 Mpro with Kd values of 1.5, 2.3 µM for Mpro C145A and PLpro C111A, respectively. This inhibitor also shows significant inhibitory activity against Mpro and PLpro with IC50 values of 0.12, 0.99 µM, respectively. In SARS-CoV-2-infected Vero E6 cells, LY1 (2.5-15 μM) causes a dramatic reduction in the viral nucleoprotein (NP) levels with 5 μM. A 99.99% reduction in the viral RdRP RNA levels at 15 μM. LY1 shows no cytotoxic at 5-25 μM in SARS-CoV-2-infected Vero E6 cells. Moreover, in the 8-week toxicity study, LY1 (300 mg/kg, p.o., 4 weeks) shows no significant change in body weight and food consumption in rats.
In a word, LY1 is a potent, selective and covalent inhibitor against both SARS-CoV-2 PLpro and SARS-CoV-2 Mpro. LY1 has the potential for research on COVID-19.