Schematic representation of peptide-mediated siRNA delivery strategies into cells. (A) Cell-penetrating peptides (CPPs), including cationic, amphipathic, and targeting/homing peptides. (B) Endosome-disrupting peptides, including fusogenic, pH-sensitive amphipathic, and proton buffering peptides. (C) Multifunctional peptide complexes. (D) Alternative peptide/protein strategies, including targeting/homing peptide-siRNA bioconjugates and recombinant RNA binding fusion proteins. dsRBD, double-stranded RNA binding domain; RISC, RNA-induced silencing complex.