Discovery of orally bioavailable SARS-CoV-2 papain-like protease inhibitor as a potential treatment for COVID-19

The RNA-dependent RNA polymerase (RdRp), 3C-like protease (3CL ^pro ), and papain-like protease (PL ^pro ) are pivotal components in the viral life cycle of SARS-CoV-2, presenting as promising therapeutic targets. Currently, all FDA-approved antiviral drugs against SARS-CoV-2 are RdRp or 3CL ^pro inhibitors. However, the mutations causing drug resistance have been observed in RdRp and 3CL ^pro from SARS-CoV-2, which makes it necessary to develop antivirals with novel mechanisms. Through the application of a structure-based drug design (SBDD) approach, we discovered a series of novel potent non-covalent PL ^pro inhibitors with remarkable in vitro potency and in vivo PK properties. The co-crystal structures of PL ^pro with leads revealed that the residues D164 and Q269 around the S2 site are critical for improving the inhibitor’s potency. The lead compound GZNL-P36 not only inhibited SARS-CoV-2 and its variants at the cellular level with EC50 ranging from 58.2 nM to 306.2 nM, but also inhibited HCoV-NL63 and HCoV-229E with EC50 of 81.6 nM and 2.66 μM, respectively. Oral administration of the compound resulted in significantly improved survival and notable reductions in lung viral loads and lesions in SARS- CoV-2 infection mouse model, consistent with RNA-seq data analysis. Our results indicate that PL ^pro inhibitor is a promising SARS-CoV-2 therapy.