Optimization of siRNA Delivery Method into the Liver by Sequential Injection of Polyglutamic Acid and

Previously, we developed a novel siRNA transfer method to the liver by sequential intravenous in-jection of poly-L-glutamic acid (PGA) and cationic liposome/siRNA complex (cationic lipoplex). In this study, we examined the effects of the charge ratio (+/−) of cationic liposome/siRNA, molecular weight of PGA and cationic lipid of cationic liposome on the biodistribution of siRNA after sequen-tial injection of PGA plus cationic lipoplex. When 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/cholesterol (Chol) lipoplex was intravenously injected into mice, the accumulation of siRNA was mainly observed in the lungs. In contrast, when DOTAP/Chol lipoplex was intrave-nously injected at 1 min after intravenous injection of PGA, siRNA was largely accumulated in the liver. The charge ratio (+/−) of DOTAP/Chol liposome/siRNA did not affect the biodistribution of siRNA after sequential injection. As regards the molecular weight of PGA, the accumulation of siRNA was observed mainly in the liver after the sequential injection of PGA of 20.5, 38, 64 or 200 kDa plus DOTAP/Chol lipoplex. Furthermore, to examine the effect of cationic lipid of cationic li-posome on the biodistribution of siRNA, we prepared other cationic liposomes composed of 1,2-di-O-octadecenyl-3-trimethylammonium propane chloride (DOTMA)/Chol, dimethyldioctadecylam