Cytoplasm-Responsive Delivery Systems for siRNA Using Cell-Penetrating Peptide Nanomicelles

Arginine-rich cell-penetrating peptides (CPPs) involved in the uptake of large molecules such as proteins, nucleotides and even nanoparticles are non-viral carriers for nucleotides. The core-shell-type polyion complexes with a disulfide cross-linked siRNA to poly(L-lysine) or poly(aspartic acid) respond to a reducing environment and achieve higher siRNA transfection efficiency. We synthesized a stable analog of transactivator of transcription (Tat) and a cytoplasm-responsive CPP, CH2R4H2C (C, cysteine [Cys]; H, histamine [His]; R, arginine [Arg]), having 2 Cys residues (for physically trapping in micelles by disulfide linkage); we conjugated the CPP with stearic acid for topical administration or with methoxy-poly(ethylene glycol)-block-poly(ε-caprolactone) for sustained systemic circulation.Nucleotides were rigidly shielded in the surface of nanomicelles, protected against nucleases in the blood, and persistently released into the reductive environment of the cytoplasm (glutathione, 0.5-10 mM). In this review, we describe DNA vaccination and delivery of siRNA into the cytoplasm using these functional CPP-conjugated nanomicelles.