Optimized small-molecule 3C-like protease inhibitors show potency against human coronaviruses in both cell culture and a mouse model.

Significance: Protease inhibitors targeting viral 3C-like protease are attractive therapeutic options for COVID-19. Here, we synthesized deuterated variants of a coronavirus protease inhibitor, GC376, and determined the therapeutic efficacy in a lethal mouse model. The transgenic mice infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a causative agent of COVID-19, develop lung pathology resembling that of severe COVID-19 patients and were used for antiviral drug testing. The deuterated variants of GC376 have improved potency against SARS-CoV-2 in in vitro assays. Furthermore, treatment with a deuterated variant starting at 24 h postinfection resulted in significantly increased survival of mice compared to vehicle-treated mice. The results suggest that deuterated variants have excellent potential as antiviral agents against SARS-CoV-2.