Novel cell penetrating peptides with multiple motifs composed of RGD and its analogs

► Peptides with multiple motifs composed of RGD and its analogs induce liposome uptake into most cells. ► The peptides shows no cytotoxicity at 100μM. ► The internalized liposome encapsulating siRNA induce the siRNA-mediated gene silencing. ► The peptide with the motifs are considered as a new type of cell penetrating peptide. Cell penetrating peptides (CPPs) have been used to transport macromolecules into cells. Most CPPs have properties such as a strong polycationic charge, amphipathic basic, and hydrophobicity. In this study, we designed the peptides with multiple motifs composed of RGD and its analogs to induce integrin-mediated endocytosis as well as endosomal escape by forming an amphipathic helix in acidic endosomes. These peptides were proved less toxic to animal cells than those without acidic residues. Unexpectedly, peptide conjugated liposomes could penetrate into cells regardless of integrins. The replacement of all aspartic acids by glutamic acids did not prevent the peptide-mediated liposome uptake, and the higher basic and leucine contents enhanced the gene silencing activity of siRNA encapsulated in the liposomes. The peptide is considered to be a new type of CPP which can be used for drug delivery.