Cell Penetrating Peptides: Intracellular Pathways and Pharmaceutical Perspectives

Abstract

Cell penetrating peptides, generally categorized as amphipathic or cationic depending on their sequence, are increasingly drawing attention as a non-invasive delivery technology for macromolecules. Delivery of a diverse set of cargo in terms of size and nature ranging from small molecules to particulate cargo has been attempted using different types of cell penetrating peptides (CPPs) in vitro and in vivo. However, the internalization mechanism of CPPs is an unresolved issue to date, with dramatic changes in view regarding the involvement of endocytosis as a pathway of internalization. A key reason for the lack of consensus on the mechanism can be attributed to the methodology in deciphering the internalization mechanism. In this review, we highlight some of the methodology concerns, focus more on the internalization pathway and also provide a novel perspective about the intracellular processing of CPPs, which is a crucial aspect to consider when selecting a cell penetrating peptide as a drug delivery system. In addition, recent applications of cell penetrating peptides for the delivery of small molecules, peptides, proteins, oligonucleotides, nanoparticles and liposomes have been reviewed.

Cell-Penetrating HIV1 TAT Peptides Float on Model Lipid Bilayers

“…Previous detailed biophysical characterization of the structure and interactions of PTDs within membranes allowed important insights into the energetics of peptide translocation and the mechanisms of penetration processes (20,30,31). An especially well-studied PTD is the TAT peptide, and its cell penetrating capabilities have been characterized in detail (10 Numerous studies exist on the structures, which are adopted by PTDs in solution and in membranes, but not much is known about their mobility on or within membranes.…”

Evaluation of Cell-Penetrating Peptide/Adenovirus Particles for Transduction of CAR-Negative Cells

“…The potential of CPPs to efficiently deliver cargo is dependent on the cellular association of the CPP to the target cell and the mechanism by which the CPP/cargo is transported into the cell. The mechanism of membrane translocation of CPPs and cargo, however, has yet to be identified definitively (Zorko and Langel 2005;Patel, Zaro et al 2007) and there are conflicting studies regarding whether the CPP internalization mechanism involves energy-dependent endocytosis or a non-endocytic mechanism (Drin, Cottin et al 2003;Richard, Melikov et al 2003;Ziegler, Nervi et al 2005). Despite the fact that different CPPs internalize into cells through different mechanisms (i.e., endocytosis or energy-independent membrane perturbations), recent observations have indicated that internalization of these CPPs occurs via endocytosis when the CPPs are coupled with high molecular weight cargo (Console, Marty et al 2003;Lundberg, Wikstrom et al 2003).…”

Cell‐penetrating peptides: Nanocarrier for macromolecule delivery in living cells

“…Amphipathic CPPs have a hydrophilic face, which consists mostly of lysine residues (22). The presence of amphipathic helixes with hydrophilic and hydrophobic faces is considered as an essential structural requirement for these peptides to cross the plasma membrane at neutral pH (23).…”

“…It has also been suggested that CPP transduction occurs through a direct internalization or concurrently through nonspecific endocytosis (22) or that CPPs mainly translocate across the cell membranes in a receptor-and energy-independent manner (42). The direct transfer of CPPs may also be accomplished by changes in transmembrane potential and through the formation of inverted micelles (6,43).…”

“…The recognition processes depend on charge interaction between cationic peptide and negatively charged receptor and is modulated by pH and osmolarity (55). Once in the cytoplasm, CPPs can be rapidly degraded by cell proteases (22).…”