Identification of New Compounds against PRRSV Infection by Directly Targeting CD163

The porcine reproductive and respiratory syndrome viruses (PRRSV) led to a global panzootic and huge economical losses to the pork industry. PRRSV targets the scavenger receptor CD163 for productive infection. However, currently no effective treatment is available to control the spread of this disease. Using bimolecular fluorescence complementation (BiFC) assays, we screened a set of small molecules potentially targeting the scavenger receptor cysteine-rich domain 5 (SRCR5) of CD163. We found that the assay examining protein-protein interactions (PPI) between PRRSV glycoprotein 4 (GP4) and the CD163-SRCR5 domain mainly identifies compounds that potently inhibit PRRSV infection, while examining the PPI between PRRSV-GP2a and the SRCR5 domain maximized the identification of positive compounds, including additional ones with various antiviral capabilities. These positive compounds significantly inhibited both types 1 and 2 PRRSV infection of porcine alveolar macrophages. We confirmed that the highly active compounds physically bind to the CD163-SRCR5 protein, with dissociation constant (K) values ranging from 28 to 39 μM. Structure-activity-relationship (SAR) analysis revealed that although both the 3-(morpholinosulfonyl)anilino and benzenesulfonamide moieties in these compounds are critical for the potency to inhibit PRRSV infection, the morpholinosulfonyl group can be replaced by chlorine substituents without significant loss of antiviral potency. Our study established a system for throughput screening of natural or synthetic compounds highly effective on blocking of PRRSV infection and shed light on further SAR modification of these compounds. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses to the swine industry worldwide. Current vaccines cannot provide cross protection against different strains, and there are no effective treatments available to hamper the spread of this disease. In this study, we identified a group of new small molecules that can inhibit the PRRSV interaction with its specific receptor CD163 and dramatically block the infection of both types 1 and type 2 PRRSVs to host cells. We also demonstrated the physical association of these compounds with the SRCR5 domain of CD163. In addition, molecular docking and structure-activity relationship analyses provided new insights for the CD163/PRRSV glycoprotein interaction and further improvement of these compounds against PRRSV infection.