Synthetic macrocyclic peptides are an emerging molecular class for both targeting intracellular protein-protein interactions (PPIs) and providing an oral modality for drug targets typically addressed by biologics. Display technologies, such as mRNA and phage display, often yield peptides that are too large and too polar to achieve passive permeability or oral bioavailability without substantial off-platform medicinal chemistry. Herein, we use DNA-encoded cyclic peptide libraries to discover a neutral nonapeptide, UNP-6457, that inhibits MDM2-p53 interaction with an IC50 of 8.9 nM. X-ray structural analysis of the MDM2-UNP-6457 complex revealed mutual binding interactions and identified key ligand modification points which may be tuned to enhance its pharmacokinetic profile. These studies showcase how tailored DEL libraries can directly yield macrocyclic peptides benefiting from low MW, TPSA, and HBD/HBA counts that are capable of potently inhibiting therapeutically relevant protein-protein interactions.
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