Evaluation of the cell permeability of bicyclic peptoids and bicyclic peptide-peptoid hybrids.

Bicyclization has proven to be an effective strategy for significantly restricting conformational flexibility in peptides and peptidomimetics such as peptoids. Such constrained bicyclic peptoids would have far higher conformational rigidity than monocyclic and linear ones, allowing them to have enhanced binding affinity and selectivity for their biological targets. Herein, we show that bicyclic peptoids have superior cellular uptake efficiency than their linear counterparts regardless of their side chains and ring sizes. As a representative example, an 8-mer bicyclic peptoid achieves a CP50 value of 1.2 µM, which is > 5-times superior to the corresponding linear peptoid. Additionally, we also demonstrate that bicyclic peptide-peptoid hybrids are much more cell-permeable than native peptides. Due to their favorable properties including improved cellular uptake, resistance to proteolytic degradation, relatively large sizes, and enormous structural diversity, constrained bicyclic peptoids and peptide-peptoid hybrids will play an important role as potential drug leads, especially in targeting intracellular protein-protein interactions, which are traditionally considered undruggable.

Hydrophobic Tagging-Mediated Degradation of Transcription Coactivator SRC-1.

Steroid receptor coactivator-1 (SRC-1) is a transcription coactivator playing a pivotal role in mediating a wide range of signaling pathways by interacting with related transcription factors and nuclear receptors. Aberrantly elevated SRC-1 activity is associated with cancer metastasis and progression, and therefore, suppression of SRC-1 is emerging as a promising therapeutic strategy. In this study, we developed a novel SRC-1 degrader for targeted degradation of cellular SRC-1. This molecule consists of a selective ligand for SRC-1 and a bulky hydrophobic group. Since the hydrophobic moiety on the protein surface could mimic a partially denatured hydrophobic region of a protein, SRC-1 could be recognized as an unfolded protein and experience the chaperone-mediated degradation in the cells through the ubiquitin-proteasome system (UPS). Our results demonstrate that a hydrophobic-tagged chimeric molecule is shown to significantly reduce cellular levels of SRC-1 and suppress cancer cell migration and invasion. Together, these results highlight that our SRC-1 degrader represents a novel class of therapeutic candidates for targeting cancer metastasis. Moreover, we believe that the hydrophobic tagging strategy would be widely applicable to develop peptide-based protein degraders with enhanced cellular activity.