Covalent Peptide Evolution: Redefining Protein–Protein Interaction Inhibition Through Phage Display

Covalent cyclic peptides represent a transformative approach for targeting challenging protein-protein interactions (PPIs) characterized by flat, extensive binding surfaces. Recent advances in electrophilic phage display now enable the evolution of these peptides through integrating sulfur(VI) fluoride exchange (SuFEx) chemistry with functional selection strategies. This innovative platform combines genetic encoding with site-specific cyclization and warhead incorporation to generate high-affinity, irreversible binders. When targeting the SARS-CoV-2 Spike-ACE2 interface, the approach produced sub-100 nM inhibitors with >10-fold improved potency over non-covalent analogues. The methodology's success against this clinically relevant target underscores its potential to address longstanding challenges in PPI modulation, particularly for high-value targets in oncology and neurodegeneration. By combining covalent engagement with phage display's evolutionary power, this technology establishes a new paradigm for developing mechanistically validated peptide therapeutics against previously intractable interactions.