Galactose-modified cationic liposomes as a liver-targeting delivery system for small interfering RNA.

We have developed a galactose-modified cationic liposome for delivery of small interfering RNA (siRNA) to the liver. The liposomes were designed to be transported into hepatocytes via the asialoglycoprotein receptor, which recognizes galactose residues. The liposomes contained a novel galactose-modified lipid, 1,2-dioleoyl-sn-glycerol-3-phosphatidyl-N-(1-deoxylactito-1-yl)ethanolamine (GDOPE). Delivery of siRNA to hepatocytes by the liposomes was evaluated by measuring the gene-silencing activity of liposome : siRNA complexes in two human hepatoma cell lines. A formulation with a cationic lipid : GDOPE ratio of 3 : 5 by weight, LIC-G5, showed the strongest activity. In mice, intravenous injection of LIC-G5 complexed with (3)H-labeled siRNA led to accumulation of radioactivity in the liver. When the hepatic cellular uptake was determined after intravenous injection into mice followed by collagenase liver perfusion, the distribution of siRNA to parenchymal cells was 1.9 times higher when LIC-G5 rather than nongalactosylated LIC was used as the carrier. The concentration of siRNA accumulated was 45 µg/ml, 30 times the concentration that produced strong gene silencing in vitro and therefore presumably sufficient for a therapeutic effect. Because increasing the cationic-lipid content of a liposome carrier generally enhances the uptake of siRNA by the liver at the expense of increased cell toxicity, we used only a moderate amount of cationic lipid in our galactose-modified carrier. LIC-G5 enhanced the uptake of siRNA by the liver without cytotoxic effects and is a promising candidate delivery system for liver-targeted siRNA therapy.

Tumor regression in mice by delivery of Bcl-2 small interfering RNA with pegylated cationic liposomes.

The pharmacokinetics and antitumor activity of pegylated small interfering RNA (siRNA)/cationic liposome complexes were studied after systemic administration to mice. We designed pegylated-lipid carriers for achieving increased plasma concentrations of RNA and hence improved accumulation of RNA in tumors by the enhanced permeability and retention effect. We compared the pharmacokinetics of siRNA complexed with liposomes incorporating pegylated lipids with longer (C-17 or C-18), shorter (C-12 to C-16), or unsaturated (C-18:1) acyl chains. When longer acyl chains were used, the plasma concentrations of siRNA obtained were dramatically higher than when shorter or unsaturated chains were used. This may be explained by the higher gel-to-liquid-crystalline phase-transition temperature (Tc) of lipids with longer acyl chains, which may form more rigid liposomes with reduced uptake by the liver. We tested a siRNA that is sequence specific for the antiapoptotic bcl-2 mRNA complexed with a pegylated liposome incorporating a C-18 lipid (PEG-LIC) by i.v. administration in a mouse model of human prostate cancer. Three-fold higher accumulation of RNA in the tumors was achieved when PEG-LIC rather than nonpegylated liposomes was used, and sequence-specific antitumor activity was observed. Our siRNA/PEG-LIC complex showed no side effects on repeated administration and the strength of its antitumor activity may be attributed to its high uptake by the tumors. Pegylation of liposomes improved the plasma retention, uptake by s.c. tumors, and antitumor activity of the encapsulated siRNA. PEG-LIC is a promising candidate for siRNA cancer therapy.