Orally efficacious lead of the AVG inhibitor series targeting a dynamic interface in the respiratory syncytial virus polymerase

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory infections in infants and the immuno-compromised, yet no efficient therapeutic exists. We have identified the AVG class of allosteric inhibitors of RSV RNA synthesis. Here, we demonstrate through biolayer interferometry and in vitro RNA-dependent RNA polymerase (RdRP) assays that AVG compounds bind to the viral polymerase, stalling the polymerase in initiation conformation. Resistance profiling revealed a unique escape pattern, suggesting a discrete docking pose. Affinity mapping using photoreactive AVG analogs identified the interface of polymerase core, capping, and connector domains as a molecular target site. A first-generation lead showed nanomolar potency against RSV in human airway epithelium organoids but lacked in vivo efficacy. Docking pose-informed synthetic optimization generated orally efficacious AVG-388, which showed potent efficacy in the RSV mouse model when administered therapeutically. This study maps a druggable target in the RSV RdRP and establishes clinical potential of the AVG chemotype against RSV disease.