Interference with immune evasion of SARS-CoV-2 and their prospective variants by using protease inhibitors

Faculty-development competitive research grants program for 2023-2025

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the global outbreak of the COVID-19 pandemic. Severe and critical complications of COVID-19 results from a dysregulation of the immune- and coagulation systems, contributing to the formation of systemic inflammation and thrombosis. The attachment of the SARS-CoV-2 spike (S) protein to the angiotensin-converting enzyme 2 (ACE2) is a prerequisite for infection of the host cell. The SARS-CoV-2 S protein harbors two subunits, the S1 and S2, whereby the interface of S1 and S2 (S1/S2), particularly the polybasic sequence, an amino acid motif which is proteolytically digested by the serine protease furin, is essential for priming of the S protein. In contrast to the S2’ fusion peptide being generated mainly by the transmembrane protease serine subtype 2 (TMPRSS2). The fusion peptide is crucial for merging the virus with the host cell membrane and the entrance into the cell followed by a productive infection, which is due to viral replication in the cytosol and cell-to-cell transmission.
At the site of infection, immune cells, such as neutrophils, infiltrate and become activated, releasing neutrophil serine proteases (NSPs), including neutrophil elastase (NE), proteinase 3 (PR3), cathepsin G (CatG), and neutrophil serine protease 4 (NSP4), which support an immune response. On the downside, NSPs might support the entrance of SARS-CoV-2 to the host cell since mutations on the S protein could enhance its priming by NSPs followed by increasing the infection. This scenario represents an immune evasion strategy by the virus to take advantage of host proteases. Particularly the appearance of additional SARS-CoV-2 variants harboring amino acid substitutions in the polybasic sequence of the S1/S2 interface and possibly at the S2’ subunit might increase the proteolytic hydrolysis at these positions by NSPs. Indeed, such mutations generate novel proteolytic cleavage sites, as we have recently published, indicating the need to investigate the proteolytic inhibition of NSPs, furin, and TMPRSS2 by new protease inhibitors to interfere with viral infection.