Inhibition of β-catenin/B cell lymphoma 9 protein−protein interaction using α-helix–mimicking sulfono-γ-AApeptide inhibitors

The rational design of α-helix-mimicking peptidomimetics provides a streamlined approach to discover potent inhibitors for protein-protein interactions (PPIs). However, designing cell-penetrating long peptidomimetic scaffolds equipped with various functional groups necessary for interacting with large protein-binding interfaces remains challenging. This is particularly true for targeting β-catenin/BCL9 PPIs. Here we designed a series of unprecedented helical sulfono-γ-AApeptides that mimic the binding mode of the α-helical HD2 domain of B Cell Lymphoma 9 (BCL9). Our studies show that sulfono-γ-AApeptides can structurally and functionally mimic the α-helical domain of BCL9 and selectively disrupt β-catenin/BCL9 PPIs with even higher potency. More intriguingly, these sulfono-γ-AApeptides can enter cancer cells, bind with β-catenin and disrupt β-catenin/BCL9 PPIs, and exhibit excellent cellular activity, which is much more potent than the BCL9 peptide. Furthermore, our enzymatic stability studies demonstrate the remarkable stability of the helical sulfono-γ-AApeptides, with no degradation in the presence of pronase for 24 h, augmenting their biological potential. This work represents not only an example of helical sulfono-γ-AApeptides that mimic α-helix and disrupt protein-protein interactions, but also an excellent example of potent, selective, and cell-permeable unnatural foldameric peptidomimetics that disrupt the β-catenin/BCL9 PPI. The design of helical sulfono-γ-AApeptides may lead to a new strategy to modulate a myriad of protein-protein interactions.