Failure of active targeting by a cholesterol-anchored ligand and improvement by altering the lipid composition to prevent ligand desorption.

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 αVß3 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.

Efficient siRNA Delivery by Lipid Nanoparticles Modified with a Nonstandard Macrocyclic Peptide for EpCAM-Targeting.

The development of a specific, effective method for the delivery of therapeutics including small molecules and nucleic acids to tumor tissue remains to be solved. Numerous types of lipid nanoparticles (LNPs) have been developed in attempts to achieve this goal. However, LNPs are probably not taken up by target cells because cancer-targeting LNPs are typically modified with poly(ethylene glycol) (PEG), which inhibits the cellular uptake of LNPs, to passively accumulate in tumor tissue via the enhanced permeability and retention (EPR) effect. It would clearly be important to develop a LNP with both a prolonged circulation and cancer-specific efficient uptake for use in an innovative nanodrug delivery system. Herein, we assessed the effect of nonstandard macrocyclic peptides against the epithelial cell adhesion molecule (EpCAM) Epi-1, which was discovered by a random nonstandard peptides integrated discovery (RaPID) system, on the cellular uptake and therapeutics delivery of LNPs. A liposomal siRNA delivery system (MEND) was modified with an Epi-1 lipid-derivative (EpCAM-targeting MEND; ET-MEND). The resulting ET-MEND showed a more than 27-fold increase in cellular uptake in EpCAM-positive cell lines. In the case of negative cells, cellular uptake and the efficiency of the ET-MEND for delivering therapeutics were comparable with those of nonmodified MEND. In addition, when systemically injected, the ET-MEND successfully inhibited gene expression in the tumor tissue at a dose of 0.5 mg siRNA/kg without any obvious toxicity. These results suggest that a combination of a specific peptide ligand can be used to identify a RaPID system and that the use of such a MEND for liposomal drug delivery has the potential for use in developing a system for the efficacious delivery of pharmaceuticals to various cancer cells.

The Delivery of Small Interfering RNA to Hepatic Stellate Cells Using a Lipid Nanoparticle Composed of a Vitamin A-Scaffold Lipid-Like Material.

Hepatic stellate cells (HSCs) are responsible for hepatic fibrosis and liver cirrhosis via their ability to produce extracellular matrices such as collagens and elastin. However, a strategy for delivering cargoes to HSCs has not been established yet. We herein report on attempts to deliver small interfering RNA (siRNA) to HSCs using several types of SS-cleavable proton-activated lipid-like materials (ssPalms) that contained myristic acid (ssPalmM) or hydrophobic vitamin A (ssPalmA) and E (ssPalmE) as hydrophobic scaffolds. We initially verified that hepatic fibrosis could induce the treatment with tetrachloromethane in terms of collagen fibrils and the expression of marker genes, type I collagen α-1, transforming growth factor ß, heat shock protein 47, and α-smooth muscle actin. The siRNA silencing efficiency of the 3 LNPs was then compared using fibrosis-induced mice. Of the materials tested, LNPssPalmA showed the highest efficiency, with an effective (ED)50 of approximately 0.25 mg siRNA/kg. The LNPssPalmA showed a significant inhibitory effect on collagen production at a dose of 3.0 mg siRNA/kg with no evidence of any severe adverse effects. In conclusion, LNPssPalmA holds considerable potential for use in the treatment of HSCs-mediated diseases.

Modality of tumor endothelial VEGFR2 silencing-mediated improvement in intratumoral distribution of lipid nanoparticles.

The vascular endothelial growth factor (VEGF)-mediated enhancement in vascular permeability is considered to be a major factor in tumor-targeting delivery via the enhanced permeability and retention (EPR) effect. We previously reported that the silencing of the endothelial VEGF receptor (VEGFR2) by a liposomal siRNA system (RGD-MEND) resulted in an enhanced intratumoral distribution of polyethylene glycol (PEG)-modified liposomes (LPs) in a renal cell carcinoma, a type of hypervascularized cancer, although the inhibition of VEGF signaling would be expected to decrease the permeability of the tumor vasculature. We herein report that the enhancement in the intratumoral distribution of LPs by VEGFR2 inhibition was dependent on the vascular type of the tumor (stroma vessel type; SV and tumor vessel type; TV). In the case of TV-type tumors (renal cell carcinoma and hepatocellular carcinoma), inhibiting VEGFR2 improved intratumoral distribution, while no effect was found in the case of SV-type tumors (colorectal cancer). Moreover, through a comparison of the intratumoral distribution of LPs with a variety of physical properties (100nm vs 400nm, neutral vs negative vs positive), VEGFR2 inhibition was found to alter the tumor microenvironment, including heparan sulfate proteoglycans (HSPGs). In addition, the results regarding the effect of the size of nanoparticles indicated that VEGFR2 inhibition improved the penetration of nanoparticles through the vessel wall, but not via permeability, suggesting the involvement of an unknown mechanism. Our findings suggest that a combination of anti-angiogenic therapy and delivery via the EPR effect would be useful in certain cases, and that altering the tumor microenvironment by VEGFR2 blockade has a drastic effect on the intratumoral distribution of nanoparticles.

Remodeling of the Extracellular Matrix by Endothelial Cell-Targeting siRNA Improves the EPR-Based Delivery of 100 nm Particles.

A number of nano drug delivery systems have recently been developed for cancer treatment, most of which are based on the enhanced permeability and retention effect. The advantages of the enhanced permeability and retention effect can be attributed to immature vasculature. Herein we evaluated the intratumoral distribution of lipid nanoparticles when the VEGF receptor 2 on tumor endothelial cells was inhibited by liposomal siRNA. VEGF receptor 2 inhibition resulted in an increase in intratumoral distribution and therapeutic efficacy despite the maturation of the tumor vasculature. A small molecule inhibitor against matrix metalloproteinase and macrophage depletion cancelled the improvement in the distribution of the lipid nanoparticles, suggesting that remodeling of tumor microenvironment played a role in the facilitated intratumoral distribution via the down-regulation of VEGF receptor 2. Accordingly, our results suggest that the enhanced permeability and retention effect is dependent, not only on the structure of the tumor vasculature, but also on the dynamics of the tumor microenvironment including extracellular matrix remodeling. Regulating the tumor microenvironment and the extracellular matrix by delivering tumor endothelial cell-targeting siRNA could potentiate the enhanced permeability and retention effect-based strategy.