Identification and optimization of a small molecule inhibitor of the ovarian tumor protease of the Crimean-Congo hemorrhagic fever virus

Abstract

Crimean-Congo hemorrhagic fever (CCHF) is a viral tick-borne disease with fatality rates of up to 30 %. Currently, there are no vaccines or specific antivirals available. The genome of the CCHF virus (CCHFV) encodes an ovarian tumor (OTU) protease with a deubiquitinating activity that is responsible for the evasion of the innate immune response. Therefore, the inhibition of the OTU protease could provide a strategy for the treatment of CCHFV infections. In this study, we screened for small-molecule inhibitors of CCHFV OTU using a fluorescent ubiquitin rhodamine 110 assay. We identified and validated a 2-aminothiazole hit compound (IC₅₀ = 42.3  μM) followed by structure–activity relationships (SAR) studies resulting in a new inhibitor of the CCHFV OTU protease. The most active derivative is a competitive CCHFV OTU inhibitor with an IC₅₀ value of 10.7  μM. Selectivity studies revealed that the ubiquitin-specific peptidase 7 (USP7), ubiquitin C–terminal hydrolase 5 (UCHL5), OTU deubiquitinase 1 (OTUD1), and Cezanne are also inhibited by this newly developed inhibitor indicating binding to conserved regions of the ubiquitin-binding site within the deubiquitinase superfamilies. Molecular docking into the active site of CCHFV OTU proposes starting points for further structural modifications to improve activity and selectivity. These structure–activity relationships are the first to our knowledge to be reported for the CCHFV OTU protease and will help guide further drug discovery efforts.