Non-Viral Vehicles: Principles, Applications, and Challenges in Gene Delivery

Gene therapy is often referred to as transfer of transgenes into the somatic cells of a patient to obtain a therapeutic effect .One of the goals for all such therapies is efficient and safe delivery of the desired extrinsic genes into target cells, thereby increasing the therapeutic efficiency (Robson & Hirst, 2003). This has been a major obstacle in gene therapy experiments (Sarbolouki et al., 2000; Sadeghizadeh et al., 2008). To address this problem, there has been an increasing number of reports in the development of efficient gene delivery vehicles in recent years (Sadeghizadeh et al., 2008). Clinical trials have also focused on the delivery of genes directly to the target area e.g. tumor sites by intratumoral administration of both viral and non-viral delivery agents. But the problem remains to be overcome yet, as majority of tumors are not accessible for direct injection. A number of strategies are now being developed to target viral and non-viral delivery agents to tumor sites. These include genetically modifying viral carriers and incorporating a novel tumor-specific ligand into the viral coat proteins to direct the viral system to a tissue receptor and also incorporation of tissue specific ligands and monoclonal antibodies onto the surface of non-viral carriers (Robson & Hirst, 2003). The delivery of the carrier system to the target site is however not the end of the goal. Efficient entrance of the gene or drug into the cells and expression of therapeutic gene are also the next hurdles to be overcome. There are several techniques for delivery of genes as well as drugs into eukaryotic cells using similar carriers practiced in-vitro and in-vivo. The in-vivo efficacy of a gene or drug delivery system depends on its capability to pass the main extracellular and intracellular barriers encountered from the site of administration to entry into the nucleus of desired cells (Sarbolouki et al., 2000; Sadeghizadeh et al., 2008). The therapeutic effect of a gene therapy experiment would be expected once the introduced transgene in target cells is considered as part of the genetic component of host cell and leads to the production of a new functional protein. To date, this type of gene transfer known as transfection (Lewin, 2007; Singleton & Sainsbury, 1995) has been studied widely and various techniques have been developed for it, each possessing its own advantages and shortcomings. Generally speaking, gene delivery techniques are classified into viral and