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408 Non-Viral Gene Therapy

Reproduced from (Alatorre-Meda et al., 2010a) by permission of the PCCP Owner Societies. Fig. 11. Typical TEM (A and B) and AFM (C and D) images obtained for DNA-MEP

lipoplexes with an average size of 135 nm that were stable within at least 7 days.

**3. General conclusions and forthcoming work** 

endosomal escape not occurring during polyplex transfection.

scattered by samples marks (L/D)c ~ 600 as the zone from which lipoplexes exist, validating the mass ratio recommended for transfection of (L/D) ~ 700. Finally, DLS results reveal

In general, the DNA-chitosan and DNA-pDADMAC systems revealed good colloidal properties and similar physicochemical features as compared one to each other. They were able to condense DNA plasmids to form particles small and positive enough so as to be taken up to cells by endocytosis; however, the transfection efficiency they rendered was markedly lower than that of the DNA-MEP lipoplex. With the experimental results here presented it appears that this low transfection efficiency relies on the high DNA-polycation binding affinity coupled with the structural conformation the polyplexes adopt in solution. Additionally, repulsive membrane acidolysis processes and different conformational transitions adopted by DOPE upon pH changes confer the MEP lipoplex a successful

In light of the obtained results a deeper understanding of both the complex internalization to cells and DNA release from complexes to the cytoplasm must, in our opinion, be achieved

lipoplexes at L/D = 1000.


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**17** 

*Korea* 

**Medical Polymer-Based Gene Therapy** 

*2Department of Agricultural Biotechnology and Research Institute for Agriculture and Life* 

Gene therapy provides great opportunities for treatment of diseases resulting from genetic disorders, infections, and cancer (Park, et al., 2006). Gene therapy has also been regarded as a suitable substitute for conventional protein therapy, since it can overcome inherent problems associated with administration of protein drugs in terms of bioavailability, systemic toxicity, *in vivo* clearance rate, and manufacturing cost (Ledley, 1996). Gene therapy refers to local or systemic administration of a nucleic acid construct capable of prevention, treatment, and even cure of disease through change of expression of genes responsible for the pathological condition (Bhavsar & Amiji, 2007). In theory, gene therapy is a simple concept that holds great promise as a cure for disease. However, in practice, considerable obstacles need to be overcome, including problems associated with safe and efficient gene delivery and stable gene expression. Many problems need to be solved in development of any gene therapy approach, including definition of cells that constitute the target, entry of DNA into those cells, expression of useful levels of gene product over an appropriate time period, and avoidance of the almost inevitable response of the host to the

Current gene therapy consists of two key factors: a gene that encodes a specific therapeutic protein, and a gene delivery system that controls delivery of gene expression plasmids to specific locations within the body (Mahato, et al., 1999, Park, et al., 2006). Due to several problems, including their instability in body fluids, non-specificity to target cells, degradation by enzymes, and low transfection efficiency, the lack of effective vectors is a major barrier to progress in gene therapy. Therefore, the ideal gene delivery method will be capable of high efficiency transfection of genes to a specific cell type; delivery to the nucleus, where it will become integrated into the host genome in a non-mutagenic fashion and be expressed or regulated; efficient transduction of cells, independent of the mitotic potential of the recipient; be non-infectious, non-toxic, and non-immunogenic; and be easy to

introduced materials, and so on (Grosshans, 2000, Smith, 1995).

manufacture and apply clinically (Chaum & Hatton, 2002).

**1. Introduction** 

*Graduate School of Convergence Science and Technology, Seoul National University* 

*4Advanced Institute of Convergence Technology, Seoul National University* 

Hu-Lin Jiang1, You-Kyoung Kim2, Chong-Su Cho2

*1College of Veterinary Medicine, Seoul National University* 

*5Graduate Group of Tumor Biology, Seoul National University 6Center for Food Safety and Toxicology, Seoul National University* 

and Myung-Haing Cho1,3,4,5,6

*Sciences, Seoul National University 3Department of Nanofusion Technology* 

