Discovery of an NRAS isoform and activation-state selective macrocyclic peptide

Macrocyclic peptides have gained increased attention amid claims they are a "Goldilocks" therapeutic modality that can encode the selectivity of a biologic in a footprint close to that of a small molecule. Here we attempt to find a peptide that binds selectively to NRAS, sparing HRAS and KRAS, while accessing the cytosol via passive cell permeability. To do so, we combine subtractive affinity selection with mRNA display to identify compound 1, an 11mer macrocyclic peptide which binds NRAS at a novel allosteric site between helix 3 and helix 4 of the GTPase domain. Compound 1 has total isoform selectivity and can be tuned to achieve activation-state selectivity with a single amino acid change. While it has preferential affinity for oncogenic NRAS-specific mutations, it does not inhibit NRAS function or achieve passive membrane permeability.