Abstract
The development of cationic liposomes for gene delivery has been ongoing for almost 20 years; however, despite extensive efforts to develop a successful therapeutic agent, there has been limited progress towards generating an effective pharmaceutical product. Since the introduction of N-(1-[2,3-dioleyloxy]propyl)-N,N,N-trimethylammonium chloride, an immense number of different cationic lipids have been synthesised and used to formulate cationic liposome–DNA complexes. Structural modification of the cationic lipids and the addition of components within the delivery system that can facilitate the fusion, cellular uptake and targeting of liposome–DNA complexes have all been used in a bid to enhance their transfection efficiency. Unfortunately, the overall impact of these improvements is still nominal, with the vast majority of clinical trials (∼ 85%) continuing to rely on more potent viral delivery of DNA despite their associated toxicity issues. Key characteristics of the most effective cationic liposomes for the delivery of plasmid DNA (from a consensus of the literature) is identified here and the problems of converting these attributes into an effective pharmaceutical product are outlined.