Cationic and amphipathic cell-penetrating peptides (CPPs): Their structures and in vivo studies in drug delivery

Over the past few decades, cell penetrating peptides (CPPs) have become an important class of drug carriers for small molecules, proteins, genes and nanoparticle systems. CPPs represent a very diverse set of short peptide sequences (10-30 amino acids), generally classified as cationic or amphipathic, with various mechanisms in cellular internalization. In this review, a more comprehensive assessment of the chemical structural characteristics, including net cationic charge, hydrophobicity and helicity was assembled for a large set of commonly used CPPs, and compared to results from numerous in vivo drug delivery studies. This detailed information can aid in the design and selection of effective CPPs for use as transport carriers in the delivery of different types of drug for therapeutic applications.