Identification of compounds targeting porcine reproductive and respiratory syndrome virus nsp3 and evaluation of their antiviral efficacy.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major threat to global pig farming. Vaccines face challenges like viral recombination and low immunogenicity, highlighting the need for new antivirals. Using molecular docking technology, we screened 200 small molecules interacting with viral nonstructural protein 3 (nsp3) from a bioactive compound library. Based on the strength of these interactions and their antiviral efficacy, six compounds - Caffeic acid phenethyl ester (CAPE), BSB, KT203, N-Caffeoyl O-methyltyramine (NCOM), C646, and KS370G - were selected, each showing more than 50% inhibition of infection at a concentration of 20 µM. Notably, BSB demonstrated inhibitory effects only at 20 µM, whereas others exhibited effects at 5 µM, with a dose-dependent enhancement of their efficacy as concentrations increased. Pre-, co-, and post-treatment experiments revealed that C646 consistently inhibited viral replication, while KS370G was most effective as a pre-treatment. This suggests that early intervention is most effective in reducing viral replication. Both C646 and KS370G began to exert sustained inhibition of PRRSV after 12 h post-infection, with effects observed against multiple PRRSV strains. In conclusion, we identified six compounds as potential candidates for combating PRRSV infection, highlighting the significance of targeting PRRSV virulence proteins in discovering antivirals.