Targeted siRNA therapy using cytoplasm-responsive nanocarriers and cell-penetrating peptides

Cell-penetrating peptides (CPPs) involved in the uptake of large molecules such as proteins, nucleotides and nanoparticles have potential as safe, non-viral carriers for gene therapy. Several kinds of cytosol-sensitive gene-polymer complexes were investigated, including disulfide crosslinked polyethylenimines, poly(amido amine)s, and polypeptides. We synthesized an artificial CPP, CH 2 R 4 H 2 C (C, cysteine [Cys]; H, histidine [His]; R, arginine [Arg]). This CPP has two Cys residues for physically trapping genes in micelles by disulfide linkage, and is conjugated either with stearic acid for enhancing transfection efficiency by local administration, or with methoxy-poly(ethylene glycol)-block-poly(ε-caprolactone) for systemic administration. Nucleotides were rigidly shielded in the nanomicelles, protected against nucleases in the blood, and spontaneously released into the reducing environment of the cytoplasm. In this review, the researches on the cytoplasm-responsive functional CPP nanocarriers for gene transfection into cells are reviewed and our trials are described in detail.