Double-Stapled Peptide Scan Yields Potent Fusion Inhibitors of Respiratory Syncytial Virus

Respiratory syncytial virus infection (RSV) is a major global health concern, particularly in infants and elderly populations. In this work, we have screened and identified 3 double-stapled peptides derived from a minimal domain of the RSV F heptad repeat, namely 3/4i, 3/4m, and 4/4g, which are potent inhibitors of RSV fusion and remain active against viral escape mutants resistant to small-molecule fusion inhibitors. Our structural activity relationship (SAR) analysis demonstrates that combining a limited set of staples is sufficient to achieve high antiviral potency. X-ray crystallography revealed that the enhanced potency of 3/4i and 3/4m primarily arises from strong hydrophobic interactions between the N-terminal staple and the trimeric HR1 coiled coil of RSV F. In vivo pharmacokinetic, imaging, and feasibility studies in RSV-infected Balb/c mice further support intranasal administration as a promising route for delivering these stapled peptides to the lung, highlighting their potential as therapeutics against RSV.