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

Introduction: Chronic obstructive pulmonary disease (COPD) constitutes a worldwide health problem. There is currently an urgent and unmet need for the development of small molecule therapeutics cap...

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.

Proteases are a major enzyme group playing important roles in a wide variety of biological processes in life forms ranging from viruses to mammalians. The aberrant activity of proteases can lead to various diseases; consequently, host proteases have been the focus of intense investigation as potential therapeutic targets. A wide range of viruses encode proteases which play an essential role in viral replication and, therefore, constitute attractive targets for the development of antiviral therapeutics. There are numerous examples of successful drug development targeting cellular and viral proteases, including antivirals against human immunodeficiency virus and hepatitis C virus. Most FDA-approved antiviral agents are peptidomimetics and macrocyclic compounds that interact with the active site of a targeted protease. Norovirus proteases are cysteine proteases that contain a chymotrypsin-like fold in their 3D structures. This review focuses on our group’s efforts related to the development of norovirus protease inhibitors as potential anti-norovirus therapeutics. These protease inhibitors are rationally designed transition-state inhibitors encompassing dipeptidyl, tripeptidyl and macrocyclic compounds. Highly effective inhibitors validated in X-ray co-crystallization, enzyme and cell-based assays, as well as an animal model, were generated by launching an optimization campaign utilizing the initial hit compounds. A prodrug approach was also explored to improve the pharmacokinetics (PK) of the identified inhibitors.