Cell-penetrating peptides as versatile vehicles for oligonucleotide delivery

Abstract

Short regulatory oligonucleotides (ONs) have a great therapeutic potential for the modulation of gene expression due to their high specificity and low toxicity. The major obstacles for in vivo clinical applications of ONs are the poor permeability of plasma membrane to nucleic acids and the sensitivity of ONs to enzymatic degradation. Hence, various delivery vehicles have been developed to ensure the transduction of ONs into cells. Among these, the cell-penetrating peptides (CPPs) have gained quickly broadening popularity as promising nonviral transmembrane delivery vectors. For coupling of nucleic acids to CPPs, two distinct strategies may be applied-covalent and noncovalent. The majority of earlier studies have used covalent coupling of CPPs to ONs. However, the number of studies demonstrating very high therapeutic potential of noncovalent complexes of ONs with novel CPP-based delivery vehicles is explosively increasing. In this review, the recent developments in the application of CPP-mediated oligonucleotide delivery by noncovalent strategy will be discussed.

Figure 1

The formation, cellular uptake, and intracellular trafficking of noncovalent CPP–ON complexes. (a) Formation of CPP–ON nanocomplexes through electrostatic and hydrophobic interactions (blue, ON; red, CPP). (b) Internalization mechanisms of CPP–ON nanocomplexes (Cav, caveolin-mediated endocytosis; CCV, clathrin-mediated endocytosis; MP, macropinocytosis; Pen, penetration). (c) Intracellular trafficking of CPP–ON complexes. Complexes that internalize into cells via endocytic pathways are being entrapped inside vesicular structures. For biological functioning, the endosomal escape followed by complex dissociation should occur. The final intracellular localization (nucleus or cytoplasm) of complexes is determined by the applied oligonucleotide. CPP, cell-penetrating peptide; ON, oligonucleotide.