Although anti-angiogenic
therapy is predicted to be an effective
therapy for treating
cancer, selectively targeting
tumor endothelial cells (TECs), and not normal endothelial cells, remains a major obstacle. Modifying a
drug carrier with a targeting
ligand is a popular strategy for developing an active-targeting type drug delivery system (DDS). We previously reported that a
cyclo(Arg-Gly-Asp-D-Phe-Lys) (cRGD)-equipped
liposome that contains encapsulated
siRNA (RGD-MEND) achieved an efficient therapeutic outcome in a murine
cancer model. To develop a more efficient TEC-targeting DDS, we examined the effect of the length of the
polyethylene glycol (PEG) that is used as a
peptide-linker on the
cholesterol-scaffold, and liposomal composition on the efficiency of delivery of
siRNA to cRGD receptor αVβ3
integrin positive cells. An RGD-MEND modified with shorter linker/no-linker, PEG350 or no-PEG, showed a higher cellular uptake in vitro. However, a shorter or no-linker RGD-
cholesterol-modified MEND showed no silencing effect despite its high, in vitro silencing efficiency. To examine the possibility that the
cholesterol-scaffold
ligand was removed from the surface of the RGD-MEND by interactions with
serum proteins, the RGD-MEND was incubated in the presence of a 50% serum
solution. The cellular uptake of the
cholesterol-scaffold
ligand was drastically reduced by the incubation in serum. Increasing the
cholesterol ratio in the
lipid envelope and adding a helper
lipid improved the in vivo knockdown efficiency, probably due to an enhanced
ligand retention, even in in vivo conditions. The findings reported herein suggest that the
lipid composition and the
ligand scaffold of the MEND are major factors in successfully developing an efficient active-targeting DDS.