Development of a Potent Cyclic Peptide Inhibitor of the nNOS/PSD-95 Interaction

The complex between the N-methyl-d-aspartate
receptor (NMDAR), neuronal nitric oxide synthase (nNOS), and the postsynaptic
density protein-95 (PSD-95) is an attractive therapeutic target for
the treatment of acute ischemic stroke. The complex is formed via
the PDZ protein domains of PSD-95, and efforts to disrupt the complex
have generally been based on C-terminal peptides derived from the
NMDAR. However, nNOS binds PSD-95 through a β-hairpin motif,
providing an alternative starting point for developing PSD-95 inhibitors.
Here, we designed a cyclic nNOS β-hairpin mimetic peptide and
generated cyclic nNOS β-hairpin peptide arrays with natural
and unnatural amino acids (AAs), which provided molecular insights
into this interaction. We then optimized cyclic peptides and identified
a potent inhibitor of the nNOS/PSD-95 interaction, with the highest
affinity reported thus far for a peptide macrocycle inhibitor of PDZ
domains, which serves as a template for the development of treatment
for acute ischemic stroke.