Effective small interfering RNA delivery in vitro via a new stearylated cationic peptide

A crucial bottleneck in RNA interference-based gene therapy is the lack of safe and efficient delivery systems. Here, a novel small interfering RNA (siRNA) delivery peptide, STR-HK, was constructed by conjugating a stearyl end to the N-terminus of the peptide sequence HHHPKPKRKV, where PKPKRKV is an altered sequence of the nucleus localization signal (PKKKRKV) and contributes to the cytosol localization of STR-HK–siRNA complexes. Histidine is a linker and plays an important role in disrupting the endosomal membrane via the proton sponge effect. As expected, STR-HK formed complexes with siRNA with a particle size of 80–160 nm in diameter and efficiently delivered Cy3-labeled glyceraldehyde 3-phosphate dehydrogenase siRNA into PC-3 human prostate cancer cells. The transfection efficiency of STR-HK at molar ratio of 60/1 was comparable to that of Lipofectamine 2000, one of the most efficient commercially available transfection reagents. Furthermore, the STR-HK–siRNA complexes exhibited minimal cytotoxicity, which was significantly lower than that of Lipofectamine. Taken together, the strategy of conjugating the stearyl moiety with HHHPKPKRKV as a non-viral siRNA delivery system is advantageous.