The efficiency with which polycationic peptides penetrate the cytosol depends on the number and overall patterning of arginine residues. While general trends and unusually penetrant patterns of arginine residues have been discovered, prior work has not effectively leveraged high-throughput screens to measure cytosolic penetration rather than total cell uptake. In this work, we adapted the chloroalkane penetration assay, which exclusively measures cytosolic penetration, to screen peptide libraries in a high-throughput, quantitative, and automation-ready manner. We demonstrate the usefulness of the screening platform by efficiently exploring how the number, patterning, and stereochemistry of arginine residues affect the cytosolic penetration of a model 10-residue peptide.

Recycling of receptors from the endosomal recycling compartment to the plasma membrane is a critical cellular process, and recycling is particularly important for maintaining invasiveness in solid tumors. In this work, we continue our efforts to inhibit EHD1, a critical adaptor protein involved in receptor recycling. We applied a diversity-oriented macrocyclization approach to produce cyclic peptides with varied conformations, but that each contain a motif that binds to the EH domain of EHD1. Screening these uncovered several new inhibitors for EHD1's EH domain, the most potent of which bound with a K of 3.1μM. Several of the most potent inhibitors were tested in a cellular assay that measures extent of vesicle recycling. Inhibiting EHD1 could potentially slow cancer invasiveness and metastasis, and these cyclic peptides represent the most potent inhibitors of EHD1 to date.