Gene delivery barriers

Plank C, Mechtler K, Szoka FC Jr, Wagner E (1996) Activation of the complement system by synthetic DNA complexes a potential barrier for intravenous gene delivery. Hum Gene Ther 7 1437-1446... 

Burke RS, Pun SH (2008) Extracellular barriers to in vivo PEI and PEGylated PEI polyplex-mediated gene delivery to the liver. Bioconjug Chem 19 693-704... 

Schaffer DV, Fidelman NA, Dan N, Lauffenburger DA (2000) Vector unpacking as a potential barrier for receptor-mediated polyplex gene delivery. Biotechnol Bioeng 67 598-606... 

No matter what their composition, such synthetic gene delivery systems also meet various biological barriers to efficient cellular gene delivery. Viral vector-based systems are far less prone to such problems, as the viral carrier has evolved in nature to overcome such obstacles. Obstacles relate to ... 

D. P. McIntosh, X.-Y. Tan, P. Oh, and J. E. Schnitzer. Targeting endothelium and its dynamic caveolae for tissue-specific transcytosis in vivo A pathway to overcome cell barriers to drug and gene delivery. Proc. Natl. Acad. Sci. USA 99 1996-2001 (2002). 

Opsonization by complement components also represents a potential barrier for intravenous gene delivery. Cationic charges of the particles activate the complement, which then takes part in particle elimination. This hurdle is possibly limited by using short hydrophobic chains, reducing the particle size, and eventually PEG insertion into lipoplexes (18). The interaction effect between the lipoplex and the complement might not be such a limitation. Indeed, it was reported that depletion of complement by injection of cobra venom factor and anti-C3 antibodies in mice indicated no differences upon intravenous injection of lipoplexes, neither in terms of tissue distribution nor in lipofection efficiency (19). 

Figure 2.6. Strategies for drug delivery across the blood-brain barrier (BBB). The physical, pharmacological and physiological approaches are discussed in the text. Present experimental attempts at viral gene delivery would also be classified as invasive because of the intracerebral administration of the vector.

Several major barriers need to be overcome for the development of nonviral gene delivery systems into true therapeutic products for use in humans. These barriers fall into three classes manufacturing, formulation, and stability (extracellular barriers and intracellular barriers) (85). Cationic lipids and cationic polymers self-assemble with DNA to form small particles that are suitable for cellular uptake. At the therapeutic doses positively charged particles readily aggregate as their concentration increases, and are quickly precipitated above their critical flocculation concentration. 

In this chapter, a brief overview of the cellular barriers to gene delivery is presented. Special emphasis is given to those events that compromise the translocation process of plasmid DNA from the cytosol into the nucleus. In addition, the strategies developed by viruses to efficiently bypass these cellular barriers and target their genomic DNA into the nucleus of infected cells will be discussed. 

Figure 12.1 Cellular barriers to gene delivery. Extracellular DNA, delivered to cells in either viral particles, liposomes, or other vehicles, must traverse the plasma, endosomal, and nuclear membranes before any transcription, replication, or integration can occur.

Gene delivery into eukaryotic cells is commonly performed for research purposes as well as in gene therapy procedures. Cellular membranes do not spontaneously take up ectopic nucleic acid because of the polar nature of the phospholipid bilayer [1] which functions as a natural barrier that prevents entry of most water-soluble molecules such as nucleic acids. In studies of gene or protein function and regulation, manipulation of the intracellular expression level is a fundamental approach. For this reason, multiple methods for delivery of nucleic acids through membranes using chemical, physical, or biological systems have been established in the last 40 years. 

Wiethoff CM, Middaugh CR (2003) Barriers to nonviral gene delivery. J Pharm Sci 92... 

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