High-throughput split-GFP antiviral screening assay against fusogenic paramyxoviruses

The paramyxovirus family includes important pathogens such as measles and mumps viruses, as well as emerging pathogens with pandemic potential such as Nipah virus. Despite the threat to public health and the frequent identification of novel paramyxoviruses, no antiviral drugs are currently available. A hallmark of most paramyxoviruses is the induction of cell-cell fusion leading to syncytia formation. To facilitate antiviral drug discovery, we leveraged this trait and established a high-throughput split-green fluorescent protein (GFP) antiviral screening assay suitable for high-content imaging through the quantification of virus-induced GFP⁺ syncytia. The assay was validated with well-known broad-spectrum antiviral compounds against representative members of five different Paramyxovirinae genera. Using this split-GFP assay, a small-molecule repurposing library of approximately 3000 compounds was screened against recombinant Cedar virus (CedV), a nonpathogenic henipavirus. Two molecules were identified: Cathepsin Inhibitor 1 with henipavirus-specific activity and PF-543 with pan-paramyxovirus activity. Both molecules inhibit viral replication by blocking cell-cell fusion. The split-GFP assay presented here will enable the development of extensive drug discovery initiatives aimed at identifying much-needed pan-henipavirus/paramyxovirus inhibitors.