Non-viral Gene Therapy - Intracellular Delivery: Fundamentals and Applications - page 655

5 Nanomaterials as Non-viral Vectors

Nanomaterials, such as gold nanoparticles, magnetite, quantum dots, and layered
double hydroxides, carbon nanotubes, and nanostructures of calcium phosphate and
silica, are emerging as novel delivery carriers for a large number of therapeutics
varying from small molecules drugs, proteins, to nucleic acids (Bourgeat-Lami 2002 ;
Chowdhury and Akaike 2005 ; Fukumori and Ichikawa 2006 ). In addition to their
advantages of easy production and purification, controlled shape and size, and good
storage stability, these nanostructured materials have showed their special capability
to break through some tissue barriers, which is unachievable by organic materials.

5.1 Noble Metallic Nanoparticles

Gold nanoparticles with typical size of 10-20 nm can be easily taken up by the cell
(Fynan et al. 1993b ; Sandhu et al. 2002 ; Thomas and Klibanov 2003 ; Jen et al.
2004 ). It has been recently reported by Schmid et al. that Au 55 clusters could func-
tion as anticancer agents because of their effective interactions with DNA (Tsoli
et al. 2005 ). The conventional method for preparing metallic nanoparticles is to
reduce the corresponding metal salts in the presence of suitable protecting groups
that can prevent further aggregation. For gold nanoparticles, their surface can be
conveniently functionalized using citrate, amine, ODN, peptide, and antibody.
Studies by Rotello and co-workers have demonstrated that 2 nm gold nanoparticles
functionalized with a mixed monolayer containing alkanethilos and trimethylam-
monium thiols were able to bind with pDNAs and deliver them efficiently to 293T
cells (Sandhu et al. 2002 ). These nanoconjugates showed ~8% fold higher effi-
ciency than the commonly used PEI (60 kDa). The transfection efficiency was
found to be affected by the ratio of positively charged quaternary amines to nega-
tively charged phosphate groups on the DNA, as well as the length of alkyl chains.
Furthermore, the same group has recently shown that gold nanoparticles functional-
ized with lysine moieties are highly efficacious for pDNA delivery, and they per-
formed better than PLL vector by a factor of 28 (Ghosh et al. 2008 ). Klibanov et al.
synthesized gold nanoparticles conjugated with thiol-modified PEI (2 kDa) and
dodecyl-PEI (2 kDa) (Thomas and Klibanov 2003 ). These PEI-Au hybrid particles
could deliver pDNA to COS-7 cells and show 15- and 6-fold higher transfection
efficiency than PEI (2 kDa) and PEI25, respectively.
Feldheim et al. covalently conjugated various peptides to gold nanoparticles
through coupling with bovine serum albumin (BSA) (Tkachenko et al. 2003, 2004 ).
The intracellular fate of these gold-peptide nanoparticles was studied. When trans-
fected in different cell lines, these nanomaterials showed different degrees of
nuclear targeting based on the peptide and cell line studied. Only nanoparticles
conjugated with the peptides that can mediate both receptor-mediated endocytosis
and nuclear localization were able to enter the nucleus of these cells. ODN-loaded
gold nanoparticles have been reported for gene-silencing by Mirkin's group