Non-Viral Gene Delivery Systems Based on Cholesterol Cationic Lipids: Structure-Activity Relationships

Abstract

Gene therapy as an alternative to conventional medicine implies the elimination of the cause of a disease via the introduction of therapeutic nucleic acids (antisense oligonucleotide, or siRNA, or transgene expressing plasmid DNA, or aptamers, etc) into the cells of the organism (Blau & Springer, 1995; Lv et al., 2006; Karmali & Chaudhuri, 2007; Rayburn & Zhang R., 2008; and references in it). However, efficient delivery of genes at the physiological level into cells of living organism (‘‘transfection’’) is always more simple in theory than in practice. Both the therapeutic nucleic acids and cell membrane are negatively charged and therefore the spontaneous entry of naked nucleic acid inside cells is unlikely to be an efficient process. In other words, the development of clinically viable gene-targeted therapeutics and the design of safe and efficient gene delivery reagents (‘‘transfection vectors’’) are inseparable problems. (Templeton, Ed. 2010). Prior to reaching the nucleus, the therapeutic nucleic acids must overcome a number of biological barriers, in particular, the cellular, endosomal, and nuclear membranes. This process is achieved by the utilization of appropriate delivery systems, that protect the genetic material from the destructive action of enzymes and encourage their penetration into the intracellular space, transfer through the nuclear membrane, and further expression in the nucleus (Eliyahu et al., 2005). In addition, these delivery systems should be nontoxic, non-immunogenic and biocompatible. The administration of genes for therapeutic purposes can be achieved using one of three different approaches. The first approach consists of a direct injection of naked nonprotected DNA into the cell resulting in a high level of transgene expression. The simplicity of this approach ensures it can be reasonably applied in a number of experimental protocols (Huang et al., Eds.; 2005). However, therapeutic application of unprotected naked nucleic acids is limited by the easily accessible organs (skin or muscles) for direct injection and is not applicable for systemic delivery due to a number of factors, the most important of which being extracellular nucleases. Gene-modified viruses and virus like particles represent the second approach for the cellular delivery of therapeutic nucleic acids. Viruses are efficient in transducing cells. However, the safety concerns regarding the use of viruses in humans make non-viral delivery systems an attractive alternative.