Repurposing in COVID-19: Can we identify new antivirals

There are an urgent need for antivirals to treat the newly emerged SARS-CoV-2. We set out to develop cell-based screens to repurpose existing drugs for use against SARS-CoV-2. Our goal was to identify both direct-acting and host-targeted antivirals. We have screened an in-house repurposing library of ~3,000 drugs in three distinct cell types permissive to SARS-CoV-2 infection: monkey kidney cells (Vero), human hepatocytes (Huh7.5) and human lung epithelial cells (Calu-3). There were 6 actives in Vero, 33 in Huh7.5 and 88 in Calu-3, with little overlap. While direct-acting antivirals such as remdesivir are active in all three cell types, we found few antivirals that were broadly active suggesting that the host dependencies are distinct in different cell types. Indeed, exploring entry pathways  revealed that in in lung epithelial Calu-3 cells entry is pH-independent and cathepsin-independent but requires TMPRSS2,. In contrast entry in Vero and Huh7.5 cells requires low pH and triggering by acid-dependent cathepsin proteases and is independent of TMPRSS2. Moreover, we found 9 drugs are antiviral in both hepatocytes and lung cells, 7 of which have been tested in humans, and 3 are FDA approved including Cyclosporine which we found is targeting Cyclophilin rather than Calcineurin for its antiviral activity revealing essential host targets that have the potential for rapid clinical implementation Specifically, I will discuss antiviral screening strategies and validation paradigms and discuss the implications of the cell type specificity. In addition, I will discuss some of our antivirals and mechanisms by which they function to block SARS-CoV-2 infection.

Learning Objectives:

1. Strategies for antiviral screening

2. Importance of cell types in antiviral discovery

3. Cellular dependencies of SARS-CoV-2 in the lung epithelium