Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 180

The same group proposed a PEG modified, transferrin-conjugated CD-based gene
delivery system to increase stability in biological fluids using PEG and to target can-
cer cells that express the transferrin receptor using transferrin as ligand [370] . The
nanoparticles of said system displayed superior stability in physiological saline and
improved transfection efficiency against K562 cells. However, the increase in trans-
fection is abolished when transfections are conducted in the presence of excess free
transferrin.
In another approach, oligocationic CDs modified at six-positions of the glucose
units with pyridylamino, alkylimidazole, methoxyethylamino, or primary amine
groups were prepared [371] . The oligocationic -CDs form stable nanoparticulate
polyplexes via charge neutralization. The transfection efficiency of these -CDs
varied, with substituents present at the six-position, among which amino, pyridyl-
amino, or butylimidazole derivative demonstrated higher transfection efficiency. The
transfection efficiency of heptakis-pyridylamino -CD was 4000-fold higher than
that observed by DNA alone. Further, use of the endosomolytic agent chloroquine
enhanced the transfection efficiency by 10 times which is comparable to DOTAP.
Uptake of the polycationic -CDs was mediated by proteoglycan binding to cells.
4.7.3 Dextran
Diethylaminoethyl (DEAE)-dextran was the very first chemical vector used for DNA
delivery ( Fig. 4.19 ). Initially in 1965, Vaheri and Pagano reported use of DEAE-dextran
to enhance the viral infectivity of cells [372] . DEAE-dextran-mediated transfection
method has gained much attention in the early to mid-1980s because of the simplic-
ity, efficiency, and reproducibility of the procedure [373-375] . Similar to cationic
polymers, DEAE-dextran forms complexes with DNA through electrostatic inter-
action. Owing to their net positive charge, these complexes are assumed to bind
negatively charged plasma membrane and then are internalized through endocyto-
sis. DEAE-dextran exhibited higher transfection efficiency than calcium phosphate;
however, it varies with the type of cells and other experimental conditions. One of
the major issues of concern is cellular cytotoxicity, as the method requires exposing
the cells to dimethyl sulfoxide (DMSO). Also, DEAE-dextran itself is toxic to cells
at high concentration. Because of these reasons, DEAE-dextran had lost the focus as
a transfection vector.
Several dextran derivatives are synthesized for improved transfection efficiency.
Dextran-spermine polycations exhibited comparable transfection efficiency to
Transfect and DOTAP [376] . The optimized branched polymeric structure with
6000-8000 Da molecular weight and 25-30% of the spermine groups conjugated at
both ends displayed the highest in vitro gene transfer [377] . Surprisingly, quaternary
ammonium derivatives of dextran-spermine conjugates displayed lower transfection
efficiency, probably due to the hindered release of DNA from a too strongly bound
complex [378] . Incorporation of PEG significantly enhances in vivo transfection effi-
ciency of dextran-spermine conjugates administered either intramuscularly or intra-
venously at a polycation to DNA weight ratio of 5 [379] .