Neutral Liposomes and DNA Transfection

Abstract

Non viral gene transfer vectors for human gene therapy (HGT) applications represent today one of the widest fields of chemical, biological and medical research. Some authors (Kostaleros & Miller, 2005) have expressed the opinion that the future of a safe and efficient gene therapy will depend on suitable synthetic vectors of genetic material, rather than on viruses. The reason for this preference is based on the consideration that viruses, although characterized by high transfection efficiency of genetic material, may suffer from some serious disadvantages such as immune response (Marshall, 2000) and potential oncogenic activity (Hacein-Bey-Abina et al., 2003), as well as a high cost of preparation of the transferring system. On the contrary, synthetic vectors have many potential advantages, such as lack of immunogenicity and oncogenicity, no limits to the size of nucleic acids to be carried inside the cells (Harrington et al., 1997; Roush, 1997; Willard, 2000) and finally preparation procedures cheap and easy to perform. Nevertheless an awkward problem that accompanies their use is the low efficiency of the transfections in vivo. Among the synthetic vectors, the most explored by the researchers are the cationic liposomes (CLs), after Felgner and collaborators (Felgner et al., 1997) described the synthesis of the first cation lipid, N-[1(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) and demonstrated that it was able to bind DNA and transfect it both in vitro and in vivo experiments. Other cationic lipids followed and became popular, such as the commercially widely used N-[1(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulfate (DOTAP), 1,2-dioleoyl3-dimethylammonium-propane (DODAP), dimethyldioctadecylammonium bromide (DDAB) and 3β-[N-(N',N'-dimethylaminoethane)-carbamoyl]cholesterol hydrochloride (DCChol); many others were synthesized during the past years and are still being synthesized. A few years after the Felgner’s discovery scientists’ interest was focused also on cationic polymers (Wu, G.Y. & Wu; C.H., 1987), that became popular after the discovery of polyethylenimines (Boussif, 1995) and are still the object of great interest. Both classes of cationic compounds owe their interest to the formation of stable complexes with DNA, called lipoplexes and polyplexes respectively, formed through an electrostatic interaction between the cationic head of lipids and the negative phosphates of DNA. The great amount of data and experiments reported in the literature with cationic vectors and some encouraging results in in vivo transfection experiments have led to the significant milestone of 20% of the ongoing clinical trials run with synthetic vectors (Edelstein et al., 2004): however the goal of a higher efficiency is still a problem to be solved. As recently stated (Safinya et al., 2006), the long-term target of research in this area is to develop a general