Identification of claramine and anidulafungin as entry inhibitors of Crimean–Congo hemorrhagic fever virus

Crimean–Congo hemorrhagic fever virus (CCHFV) is a tick-borne enveloped virus that causes a severe disease in humans. Despite its wide geographic distribution, no approved vaccines or therapeutics exist. In this study, we achieved high-titer production of pseudotyped virus bearing CCHFV glycoproteins with a C-terminal truncation. Screening over 3,600 small compounds using this pseudotyped virus identified claramine and anidulafungin as CCHFV entry inhibitors. These hit compounds, as well as caspofungin, which is related to anidulafungin, inhibited pseudotyped viral infection in human liver cells and vascular endothelial cells. They inhibited infection of pseudotyped virus with glycoproteins from various CCHFV strains and Hazara virus, a nairovirus closely related to CCHFV. Using a quantitative fusion assay, the identified inhibitors were shown to block membrane fusion via CCHFV glycoproteins. Moreover, they inhibited infection of replication-competent Hazara virus. Therefore, the assays developed in this study were successful in identifying CCHFV entry inhibitors that target membrane fusion.