Non-viral Gene Therapy - Intracellular Delivery: Fundamentals and Applications - page 604

desired gene (Smith 1995 ; Breyer et al. 2001 ; Young et al. 2006 ). Despite their high
transfection efficiency, the application of viral vectors to human body is often frus-
trated by potentially serious toxicity and production problems. The death of a
patient in a gene therapy trial using adenoviral vectors has accelerated the research
on non-viral vectors (Hollon 2000 ; Glover et al. 2005 ). Compared with viral vec-
tors, non-viral systems offer a number of advantages such as low immunogenicity
and toxicity, ease in manufacturing and mass production, low cost, stability,
reduced vector size limitations, high flexibility regarding the size of the transgene
delivered, and diverse chemical designs for constructing vectors with multiple func-
tions (Li and Huang 2006 ; Wong et al. 2007 ).
A variety of effective nonviral gene delivery approaches including naked DNA
injection (Wolff et al. 1990 ), physical techniques such as electroporation or gene
gun (Yang et al. 1990 ; Mathiesen 1999 ), and synthetic vectors (Luo and Saltzman
2000 ) have been developed. Synthetic vectors are among the most extensively stud-
ied systems for gene delivery. In general, synthetic vectors are materials that can
electrostatically bind DNA or RNA, condense the genetic materials into nanostruc-
tured particles, protect the genes and mediate cellular entry. The complexes of
plasmid DNA (pDNA) or RNA with cationic lipids and polymers are known as
lipoplexes and polyplexes, respectively. The use of cationic lipids for gene delivery
was first introduced by Felgner in 1987 (Felgner et al. 1987 ). Due to their relatively
high efficiency, vectors based on cationic lipids such as 'Lipofection' have been
routinely used in both in vitro and in vivo gene delivery studies, as well as in some
clinical trials for gene therapy. Synthetic polymers, like diethylaminoethyl-dextran
(DEAE-dextran), have been used for in vitro gene transfection studies since the
1960s (Vaheri and Pagano 1965 ). Progress in polymer chemistry makes it possible
to engineer diverse polymers with a plethora of different architectures such as linear,
branched, and dendritic, for gene delivery applications. Through delicate molecular
design, chemically defined polymer carriers can be powerfully armed with multiple
functions required for efficient gene delivery while maintaining biocompatibility,
facile manufacturing, and robust and stable formulation. As a result, polymer vec-
tors have great potential for human gene therapy (Putnam 2006 ; Wagner and
Kloeckner 2006 ). Most recently, nonviral vectors based on nanomaterials, including
magnetic nanoparticles, quantum dots, gold or silica nanostructures, and other inor-
ganic/organic nano-hybrids, have gained significant attention. These nano-carriers
due to their special characters such as well-controlled size and morphology at nano-
scale, multimodal imaging, and targetability, have the potential to be developed to
new gene vectors, or elucidate the transport events involved in gene therapy from
molecular, cellular, tissue to whole body level. Furthermore, integrating the func-
tions owed by these nanostructures into one platform offers the opportunity to create
new generations of multifunctional vectors (Sanvicens and Marco 2008 ).
Nonviral vectors are generally viewed as less efficacious than the viral methods,
especially for in vivo applications. However, recent developments suggest that the
gene delivery by some synthetic vectors has reached the efficiency and expression
duration that are clinically meaningful. Indeed, some synthetic vehicles have been
developed to clinical trials. In this chapter, we reviewed most of the synthetic non-viral