Rapid discovery of pseudorabies virus inhibitors repurposed from the antimicrobial agent ciprofloxacin

Pseudorabies virus (PRV) is a significant pathogen impacting swine health and poses high zoonotic risks to humans. Effective antiviral treatments for PRV remain limited, underscoring the need for novel therapeutic strategies. In this study, ciprofloxacin was identified as a repurposed promising candidate with significant in vitro inhibition of PRV replication based on our inference from PNU-183792, an HSV-1 DNA polymerase inhibitor, that quinolones have the potential to act as anti-PRV drugs. Compound A1 was firstly hopping from ciprofloxacin and PNU-183792, showing more than 500-fold higher anti-PRV activity than ciprofloxacin with an EC₅₀ of 2.21 nM. Then, C2 was obtained from rapid optimization of replacing the benzyl and cyclopropyl groups of A1, which showed excellent inhibition of PRV replication with an EC₅₀ of 0.29 nM and MIC₈₀ in range of 1.6-8 nM. Pharmacokinetic studies demonstrated favorable properties for C2, with good plasma exposure following intraperitoneal administration. In vivo studies in Kunming mice showed that C2 inhibited PRV replication by up to 99 %. These results suggest that quinolone-based inhibitors, particularly C2, represent a viable therapeutic approach for the treatment of PRV infections and warrant further preclinical development.