Cell Penetrating Peptides
Most prospective therapeutic and diagnostic agents have very poor cell permeability and low bioavailability. Cell penetrating peptides (CPPs), also known as protein transduction domains have the ability to translocate through the cell membranes. As such, they have received formidable attention in the current advances in drug delivery as promising tools to overcome drug delivery problems. These peptides have been used to deliver drugs, imaging agents, and other therapeutic biomolecules across the cell membrane into the cytoplasm.
Although the mechanism of their intracellular translocation is not clear, the amino acid composition which gives them a net positive charge seems to play a key role in this process.1 Different studies have hypothesized that internalization occurs via endocytosis, direct transport through the cell membrane or both.
The primary structure of CPPs is generally composed of cationic residues such as arginines and lysines. Several naturally occurring and synthetic CPPs have been investigated in delivery of various cargo such as nucleic acids, proteins, quantum dots, contrast agents and small organic molecules.2 In all of these studies, CPPs exhibited minimal toxicity in biological systems, suggesting their potential as drug delivery vehicles. The table below highlights some of the most common naturally occurring and synthetic cell penetrating peptides.
In this issue, we will be discussing the various CPPs and their advances in therapeutic applications.