Twenty years of cell-penetrating peptides: from molecular mechanisms to therapeutics

Abstract

The recent discovery of new potent therapeutic molecules that do not reach the clinic due to poor delivery and low bioavailability have made of delivery a key stone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including cell-penetrating peptides (CPPs). CPPs were first discovered based on the potency of several proteins to enter cells. Numerous CPPs have been described so far, which can be grouped into two major classes, the first requiring chemical linkage with the drug for cellular internalization and the second involving formation of stable, non-covalent complexes with drugs. Nowadays, CPPs constitute very promising tools for non-invasive cellular import of cargo and have been successfully applied for in vitro and in vivo delivery of therapeutic molecules varying from small chemical molecule, nucleic acids, proteins, peptides, liposomes and particles. This review will focus on the structure/function and cellular uptake mechanism of CPPs in the general context of drug delivery. We will also highlight the application of peptide carriers for the delivery of therapeutic molecules and provide an update of their clinical evaluation.

Figure 1

Model of cellular uptake and intracellular trafficking of cell-penetrating peptides (CPPs). Cellular uptake of CPP by the covalent (CPP-CS) and non-covalent (CPP-NCS) strategies. (1) Binding of CPPs or CPP/cargo complexes to extracellular matrix via the cell surface proteoglycan platform, (2) clustering of GlucosAminoGlycan platform triggers selective activation of small GTPase and remodelling of the actin network, (3) increase of membrane fluidity or microdomain dynamic promotes the cell entry and release in the cytosol of CPP-NCS and of CPP-CS (at high concentrations) via membrane fusion or cellular uptake of CPP-CS/CPP-NCS via (4) endocytosis pathway (a: caveolin-dependent, b: clathrin-dependent, c: clathrin-and caveolin-independent) or (5) macropinocytosis. After endocytic capture, CPP-CS can escape from lysosomal degradation and enter the cytosol and the nucleus (6), remain in the early or late endosomes (7), or be delivered in the Golgi apparatus and the endoplasmic reticulum (8).