siRNA delivery to lung-metastasized tumor by systemic injection with cationic liposomes

Context: Cationic liposomes can efficiently deliver siRNA to the lung by intravenous injection of cationic liposome/siRNA complexes (lipoplexes). Objective: The aim of this study was to examine a formulation of cationic liposomes for siRNA delivery to lung metastasis of breast tumor. Materials and methods: For the preparation of cationic liposomes, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or dimethyldioctadecylammonium bromide (DDAB) as a cationic lipid and cholesterol (Chol) or 1,2-dioleoyl-L-alpha-glycero-3-phosphatidylethanolamine (DOPE) as a neutral lipid were used. In vitro and in vivo gene silencing effects by cationic lipoplexes were evaluated after transfection into stably luciferase-expressing human breast tumor MCF-7-Luc cells and after intravenous injection into mice with lung MCF-7-Luc metastasis, respectively. Intracellular localization of siRNA after transfection into MCF-7 cells by cationic lipoplexes and biodistribution of siRNA after intravenous injection of cationic lipoplexes into the mice with lung metastasis were examined by confocal and fluorescent microscopy analyses, respectively. Results: In in vitro transfection, DOTAP/DOPE and DDAB/DOPE lipoplexes of luciferase siRNA strongly suppressed luciferase activity in MCF-7-Luc cells, but DOTAP/Chol and DDAB/Chol lipoplexes did not, although DOTAP/Chol and DDAB/Chol lipoplexes exhibited higher cellular uptake than DOTAP/DOPE and DDAB/DOPE lipoplexes. When their cationic lipoplexes were intravenously injected into mice with lung MCF-7-Luc metastasis, siRNAs were mainly accumulated in the lungs; however, the reduced luciferase activities in the lung-metastasized tumors were observed only by injections of DOTAP/Chol and DOTAP/DOPE lipoplexes, but not by DDAB/Chol and DDAB/DOPE lipoplexes. Conclusions: DOTAP-based liposomes might be useful as an in vivo siRNA delivery carrier that can induce gene silencing in lung-metastasized tumors.