The high morbidity and mortality associated with Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) are having a major impact on public health worldwide, and this is further compounded by inadequate vaccination and the emergence of highly infectious and lethal strains of the virus, underscoring the urgent need for developing small-molecule therapeutics to combat COVID-19. The SARS-CoV-2 genome encodes two polyproteins, which are processed auto-catalytically, yielding a 3C-like protease (3CLpro), which is essential for viral replication, making it an attractive target for therapeutic intervention. We demonstrated previously in feline clinical trials that a dipeptidyl aldehyde bisulfite adduct 3CLpro inhibitor (GC376) is a highly effective antiviral compound for the treatment of feline infectious peritonitis (FIP), a fatal disease caused by FIPV, a coronavirus. This work focused on synthesizing several deuterated variants of GC376 and evaluating them in enzyme and cell-based assays, and for in vivo efficacy in a fatal mouse model of SARS-CoV-2 infection. The mechanism of action and the structural determinants associated with binding were elucidated using X-ray crystallography. Several deuterated variants showed improved efficacy compared to GC376 with EC50 values in the nanomolar range. Importantly, the inhibitors were devoid of cytotoxicity (CC50 &gt; 100 µM). The best inhibitor (EC50 of 69 nM in A549-ACE2 cells) in the series was tested in the K18-hACE2 mouse model. Infected mice (at 5 x 103 pfu) treated with the inhibitor (24hr post-infection) have demonstrated 83% survival in exp 1 and 100% survival in exp 2 at the end of the study (15 dpi), whereas 0% survival was observed in vehicle-treated mice at 2 independent experiments, resulting in significantly improved survival of inhibitor-treated mice (P = 0.011 and 0.008). Furthermore, inhibitor-treated mice showed reduced viral titers and histopathological changes in the lungs.

Post-infection treatment with a protease inhibitor increases survival of mice with a fatal SARS-CoV-2 infection

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.