ABSTRACT
Gene therapy represents a new paradigm of therapy for diseases, where the disease is treated at the molecular level by restoring defective biological functions or reconstituting homeostatic mechanisms within cells. The ability to engineer the in vivo production of therapeutic genebased products compartmentally within the cells would help in combating the unmet medical needs for certain genetic and end-stage diseases such as cancer and acquired immunodeciency syndrome (AIDS) (Liu et al. 2006). The clinical trials of gene therapy were initiated nearly two decades ago, and underwent several cycles of ups and downs (Plautz et al. 1993, Blaese et al. 1995, MacGregor et al. 1998, Hacein-Bey-Abina et al. 2003, Raper et al. 2003, Edelstein et al. 2004). However, signicant hurdles continue to remain, and emphasis is now on improving the safety of viral vectors and the efciency of nonviral systems (Rolland 2005). The limitations of viral vectors, especially those pertaining to its safety concerns have prompted the development
8.1 Gene Therapy with DNA: The Next Generation of Blockbuster Therapeutics .................... 177 8.2 Colloidal Delivery Systems for DNA ................................................................................... 179
8.2.1Polymeric Nanocarriers ............................................................................................ 179 8.2.2Liposomes ................................................................................................................. 181 8.2.3Hydrogels .................................................................................................................. 183 8.2.4 Polymeric Micelles ................................................................................................... 183 8.2.5 Inorganic Nanoparticles ............................................................................................ 184
8.3Routes of Administration...................................................................................................... 185 8.3.1Intramuscular Injection ............................................................................................. 185 8.3.2Mucosal Administration ........................................................................................... 186
8.3.2.1 Oral Route .................................................................................................. 186 8.3.2.2 Nasal Route ................................................................................................ 187 8.3.2.3Pulmonary Route ....................................................................................... 188
8.4Concluding Remarks ............................................................................................................ 188 Abbreviations ................................................................................................................................. 189 References ...................................................................................................................................... 189
of synthetic vectors based on nonviral systems. Deoxyribonucleic acid (DNA) has the potential to lead a new generation of reverse engineered biopharmaceuticals as it has inherent advantages over other biomolecules such as protein and ribonucleic acid (RNA) in terms of simplicity in production and its high thermal stability. Plasmid-based approaches to gene therapy often termed “nonviral” involve the recombination of gene sequence, encoding a therapeutic protein into closed circular piece of DNA, and administered directly to patients to induce gene expression (Figure 8.1). The ability of genetic DNA vaccines to generate both B-cell and T-cell responses has been identied as a promising technique to prevent cancer, and intracellular bacterial and viral infections. Effective gene therapy requires that the DNA successfully gets access to the target cell, is taken up for internalization into the cell, is trafcked through the cell after escaping the degradative pathway to the nucleus, and is subsequently transcribed and translated to produce the desired gene product (Ledley 1996). Due to the size and charge of naked DNA and the enzymatic and membrane barriers imposed by the cell, the entry of DNA molecules into cells and subsequent expression is a very wasteful process (Liu 2003). This is proved by the fact that the progress of naked plasmid DNA in clinical trials from phase I to phase III was highly unsuccessful (Figure 8.2) (Edelstein 2009). The rapidly rising demand for therapeutic grade DNA molecules requires associated improvements in encapsulation and delivery technologies. This includes the formulation of DNA molecules into synthetic delivery systems for enhanced cellular transformation efciencies.
