Non-viral Gene Therapy - Intracellular Delivery: Fundamentals and Applications - page 657

uptake of DNA by cells after treatment with superparamagnetic iron oxide (SPIO)
particles. The SPIO particles coated with polyelectrolytes were mixed with other
gene vectors, such as DNA or recombinant viruses, in a salt-containing solution.
The gene vectors were supposed to collect around the magnetic particles owing to
the salt-induced colloid aggregation. These tagged particles could then be directed
along a magnetic field gradient to transfect appropriate cells. The researchers have
shown that their 'magnetofection' method worked for in vivo applications. But
substantial improvements are required to direct the magnetic gene vectors to spe-
cific target sites in the human body without invasive surgery.
Different cell lines show a different selectivity towards the hydrophilicity of the
particle's surface when it comes to the uptake of nanoparticles. Berry et al. investigated
the effect of naked and functionalized (either with dextran or albumin) iron oxide
nanoparticles on the uptake by fibroblasts (Berry et al. 2003 ). They found that all three
kinds of nanoparticles were well taken up by the cells, but only albumin-coated nano-
particles did not hinder cell proliferation, the other two particles caused cell death.

5.3 Carbon Nanotubes

Carbon nanotubes (CNTs) are considered to be first discovered by L. V.
Radushkevich and V. M. Lukyanovich in 1952 (Monthioux and Kuznetsov 2006 ).
There are two different types of CNTs: single-walled CNTs (SWCNTs) and multi-
walled CNTs (MWCNTs), with diameters of a few nanometers and lengths up to
1 mm (Dicks 2006 ; Balani et al. 2007 ; Grujicica et al. 2007 ). Since these carbon
structures are practically insoluble in aqueous environments, both noncovalent and
covalent functionalization techniques have been utilized to increase their solubility
(Klumpp et al. 2006 ). In the case of covalent functionalization, there are two meth-
ods: the oxidation of CNTs in acidic conditions to form acid-terminated structures
or 1, 3-dipolar cycloaddition reactions using a-amino acid derivatives and para-
formaldehyde. Noncovalent functionalization usually involves either hydrophobic
or p - p stacking interactions between CNTs and surfactants, nucleic acids, peptides,
polymers, or oligomers. Major efforts have been directed to improve the solubility
and to reduce the toxicity of CNTs to a practical delivery system.
Bianco et al. synthesized ammonium-functionalized SWCNTs and MWCNTs by
1, 3-dipolar cycloaddition reactions to afford cationic nanoplexes (f-SWNT and
f-MWNT, respectively) (Pantarotto et al. 2004 ). In HeLa cells, these nanoplexes
were taken up by a non-endocytic route, as cellular uptake was not inhibited by
sodium azide or 2, 4-dinitrophenol, which typically hinder energy-dependent cellular
processes. In CHO cell lines, the f-SWNT nanoplexes showed significant b -galacto-
sidase expression at f-SWNT/DNA ratios between 2:1 and 6:1. MWCNTs were
found to bind to DNA more tightly than the single-walled analogues due to increased
surface area. The same group also investigated the system that replaced the ammo-
nium cation with a lysine group and found the DNA binding capacity was increased,
because of the increased charge density of lysine group (Singh et al. 2005 ). Cai et al.
synthesized vertically aligned CNTs by plasma-enhanced chemical vapor deposition.