Peptide-based inhibitors of protein–protein interactions

Protein-protein interactions (PPIs) are key elements of several important biological processes and have emerged as valuable targets in medicinal chemistry. Importantly, numerous specific protein-protein interactions (e.g., p53-HDM2 and Bcl-2-BH3 domains) were found to be involved in the development of several diseases, including various types of cancer. In general, the discovery of new synthetic PPI inhibitors is a challenging task because protein surfaces have not evolved in a manner that allows for specific binding of low molecular weight compounds. Here, we review the discovery strategies for peptide-based PPI inhibitors. Although peptide-based drug candidates exhibit significant drawbacks (in particular, low proteolytic stability), modifications of either the side chains or backbone could provide molecules of interest. Moreover, due to the large molecular size of peptide-based compounds, the discovery of molecules that specifically interact with extended protein surfaces is possible. Two major strategies for constructing peptide-based PPI inhibitors are as follows: (a) cyclization (e.g., stapled peptides) and (b) modification of the backbone structure (e.g., β-peptides and peptoids). These approaches for constructing PPI inhibitors enhance both the inhibitory activity and pharmacokinetic properties compared with non-modified α-peptides.