The six amino acid antimicrobial peptide bLFcin6 penetrates cells and delivers siRNA.

Cell-penetrating peptides (CPPs) are a new class of vectors with high pharmaceutical potential to deliver bioactive cargos into cells. Here, we characterized bLFcin(6) , a six amino acid peptide derived from bovine lactoferricin, as a CPP. Uptake of bLFcin(6) was measured by flow cytometry. The ability to delivery siRNA was analyzed in HeLa cells. bLFcin(6) exhibited concentration-dependent uptake and intracellular distribution. Below 7.5 μm, uptake of bLFcin(6) was significantly lower than uptake of TAT (P < 0.05) because bLFcin(6) has fewer cationic amino acids. Compared to CPP(5) (RLRWR) and CPP(6) (PFVYLI), bLFcin(6) had a significantly higher internalization ratio above 2.5 μm because it has two tryptophan residues. Uptake of bLFcin(6) starts with an ionic cell-surface interaction. It is then rapidly internalized by lipid raft-dependent macropinocytosis, followed by release from macropinosomes into the cytosol and nucleus. Moreover, bLFcin(6) formed stable electrostatic complexes with siRNA and delivered siRNA into cells, resulting in significant knockout activity at both the mRNA and protein levels. The knockout activity of siRNA delivered by bLFcin(6) was similar to that mediated by TAT, although knockout by bLFcin(6) required a higher molar ratio. In this study, bLFcin(6) was tested for its ability to act as an siRNA-delivering CPP.