Nanoparticles based transfection agents for gene delivery

Abstract

Gene therapy is an attractive approach to preventing or treating a disease by replacing defective genes, substituting missing genes or silencing unwanted gene expression. The principle of gene therapy is therefore, not only to replace a potentially deficient gene but also, and more importantly, to influence the physiology and signal transduction in the cell by overexpressing or downregulating one or several genes. Down-regulation of a gene can be achieved by the transfer of short antisense oligonucleotides (ODNs) into cells or by intracellular delivery of the more recently developed small interfering RNA (siRNA). In addition, a gene can be expressed by translocating plasmid DNA into cells containing the sequence for a gene of interest under the influence of a promotor. The vectors for delivering nucleic acids (ODNs, siRNA or plasmid DNA) to the cells are divided into two groups, viz., viral and non-viral vectors. Viral vectors have the advantage of using the machinery of host cells for the production of viral proteins. Although very efficient in vitro and in vivo, viral vectors may pose problems in terms of safety because of their immunogenicity and in some cases the potential risk of insertion of the gene into the host genome can lead to the development of cancer. Non-viral vectors comprising of cationic lipids and polymers are thought to be safer in vivo because they are immunologically inert. Also, they can accommodate a greater variety of cargo, are easier to produce and can be readily chemically modified for the purpose of improving therapeutic applications. Lipid based vectors suffer from severe limitations such as poor stability, rapid drug leakage and production difficulties. Polymeric cationic nanoparticles have been therefore, investigated extensively as an alternate to lipid based vectors. Polyethylenimine, owing to high transfection efficiency, has been extensively investigated as gene delivery vector. However, the toxicity associated with PEI, has hampered its in vivo application. The aim of this thesis has been to develop several strategies to modify PEI so as to increase its transfection efficiency and reduce toxicity. The work embodied in the thesis consists of approaches to incorporate modifications in PEI so as to reduce toxicity significantly and enhance transfection efficiency.