Endosome Entrapment of CPP-ON Conjugates : Is there a Way to Overcome this Limitation ?

Abstract

Cell penetrating peptides (CPP) have been proposed as vectors for the delivery of biomolecules such as nucleic acids since poor translocation across membrane barriers is a major limitation for most of their clinical applications.Direct translocation across the plasma membrane has been proposed initially but an endocytotic mechanism of cell import is now favored at least at low CPP concentrations. Allowing escape from endocytotic compartments and avoiding degradation of the transported cargo are now considered as the major limitations, problems in common with most non-viral delivery strategies.Our group has focused on the CPP delivery of steric-block ON (using a splice redirection assay as end point) and more recently of apoptosis-regulating peptides. Although biological responses at submicromolar concentrations can be monitored, endosome escape remains limiting with arginine-rich CPPs. In keeping with these observations, cell permeabilization or endosomolytic treatments strongly lowers the active ON concentration.Assays to monitor endosomal release as well as SAR studies aiming at improving CPPs in this respect will also be described.