The objective of our research is to develop a liposomal gene delivery system that specifically targets potent therapeutic genes to breast cancers which are positive for the human epidermal growth receptor 2 (Her-2). Current liposomal gene delivery systems predominately utilize cationic lipids, which efficiently bind and deliver plasmid DNA, but also result in nonspecific gene expression in the lungs and liver tissue. We attempt to improve on specificity, by using a two-component delivery system. The first component is a cationic polyethylene glycol (PEG) grafted polylysine which carries the plasmid DNA. The polylysine/DNA particle binds nonspecifically to cells but has limited ability to bypass the endosomal membrane. The second component is an anionic Her-2 targeting liposome which is disulfide bound to the pore forming protein Listeriolysin O (LLO). These liposomes bind with high selectivity to Her-2 positive cells and once internalized into the reducing conditions of an endosome, release LLO which forms pores in the endosomal membrane. Neither component delivers DNA plasmid on its own, but if the polylysine/DNA and LLO/liposome co-localize within an endosome, the DNA is able to access the cytoplasm which leads to gene expression of the plasmid.
Using fluorescent microscopy and a cell panel, we show that labeled polylysine/DNA and LLO/liposomes have a much greater chance of co-localizing in an endosome of Her-2 positive breast cancer cells compared to Her-2 negative cells. In addition, utilizing luciferase plasmid, we demonstrate that this two-component system results in gene expression that is over 1000-fold greater in Her-2 overexpressing cells than in Her-2 negative cells. This is a vast improvement over standard cationic liposome techniques which show no specificity for Her-2 positive cells.
Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-02-02.