Discovering Serum Stable Protein–Protein Interaction Inhibitors with N-Terminus-Capped Bicyclic Phage Libraries

High Resolution Image Download MS PowerPoint Slide Protein–protein interactions (PPIs) play many important roles in physiology and disease, yet are often difficult to inhibit by synthetic molecules. Peptides are well-suited for targeting the typically large PPI interfaces because their intermediate size allows them to bind to broad protein surfaces with high specificity. Multicyclic peptide-based inhibitors are particularly appealing for their greater structural rigidity and increased resistance to proteolytic degradation. In this study, we utilized our recently described cysteine-directed proximity-driven bicyclization cross-linker, bischlorooxime N -hydroxysuccinimide (BC-OSu), to construct N-terminus-capped bicyclic phage libraries. These bicyclic phage libraries were screened against two protein targets, Keap1 and the SARS-CoV-2 Spike protein. For both protein targets, multiple bicyclic ligands were readily identified with superior potency over those of their disulfide precursors. Importantly, these N-terminus-capped peptide bicycles exhibited remarkable stability in human serum, while their disulfide precursors degraded rapidly and primarily through N-terminal truncation. These results collectively showcase the potential and stability advantages of the N-terminus-capped bicyclic phage libraries.