A Bioluminescent 3CL(Pro) Activity Assay to Monitor SARS-CoV-2 Replication and Identify Inhibitors

Mathieu, Cyrille; Touret, Franck; Jacquemin, Clémence; Janin, Yves L.; Nougairède, Antoine; Brailly, Manon; Mazelier, Magalie; Décimo, Didier; Vasseur, Virginie; Hans, Aymeric; Valle-Casuso, José-Carlos; de Lamballerie, Xavier; Horvat, Branka; André, Patrice; Si-Tahar, Mustapha; Lotteau, Vincent; Vidalain, Pierre-Olivier

Our therapeutic arsenal against viruses is very limited and the current pandemic of SARS-CoV-2 highlights the critical need for effective antivirals against emerging coronaviruses. Cellular assays allowing a precise quantification of viral replication in high-throughput experimental settings are essential to the screening of chemical libraries and the selection of best antiviral chemical structures. To develop a reporting system for SARS-CoV-2 infection, we generated cell lines expressing a firefly luciferase maintained in an inactive form by a consensus cleavage site for the viral protease 3CL(Pro) of coronaviruses, so that the luminescent biosensor is turned on upon 3CL(Pro) expression or SARS-CoV-2 infection. This cellular assay was used to screen a metabolism-oriented library of 492 compounds to identify metabolic vulnerabilities of coronaviruses for developing innovative therapeutic strategies. In agreement with recent reports, inhibitors of pyrimidine biosynthesis were found to prevent SARS-CoV-2 replication. Among the top hits, we also identified the NADPH oxidase (NOX) inhibitor Setanaxib. The anti-SARS-CoV-2 activity of Setanaxib was further confirmed using ACE2-expressing human pulmonary cells Beas2B as well as human primary nasal epithelial cells. Altogether, these results validate our cell-based functional assay and the interest of screening libraries of different origins to identify inhibitors of SARS-CoV-2 for drug repurposing or development.