The process of introducing drugs into cells has always proved a major challenge for scientists. However, cell-permeable peptides (CPPs) have the ability to enter the plasma membrane of a cell independent of a membrane receptor. They are usually small peptides 10–30 residues in length with positively charged amino acid sequences.
CPPs are capable of delivering biologically active cargo to the cell interior. The desired therapeutic cargo could be attached to a CPP and then delivered to an intracellular target, thereby overcoming the entry restrictions set by the plasma membrane.
CPPs have gained widespread popularity as very promising non-viral transmembrane delivery vectors. Although they have been used successfully for carrying different cargoes of varying sizes and nature (plasmid DNA, peptides, proteins, nanoparticles, quantum dots, etc.), the most rapid progress has been made with the delivery of oligonucleotides (ONs).