KCS

RNA interference (RNAi) is a natural response of eukaryotic cells to double-stranded RNA (dsRNA) leading to silencing of homologous gene transcripts by ~21 nucleotide (nt) dsRNAs, termed short interfering RNAs (siRNAs). While siRNAs have been rapidly appreciated to silence genes, efficient and non-toxic vectors for primary cells and for systemic in vivo delivery remain lacking. Several siRNA-delivery vehicles, including cell-penetrating peptides (CPPs), have been developed but their utility is often restricted by entrapment following endocytosis. Hence, developing CPPs that promote endosomal escape is a prerequisite for successful siRNA implementation. We here present buforin IIb, a synthetic analog of buforin II that contains a proline hinge between the two α-helices and a model α-helical sequence at the C-terminus (3× RLLR), in order to facilitate endosomal release of siRNAs. Stable buforin IIb-conjugated siRNAs enter entire cell populations and rapidly promote endosomal escape, resulting in robust RNAi responses in MCF-7 cells, with buforin IIb-mediated delivery being independent of cell confluence. These results imply that the peptide, in addition to having utility for RNAi screens in vitro, displays great therapeutic potential.