Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 150

3. complexation of pDNA without condensation/noncondensation of pDNA, and
4. enhancement of intracellular uptake of pDNA.
Molecular modelling confirmed that PVP was located in the major groove of DNA,
where it binds to the base pairs through simple hydrogen bonding. Unlike PLGA,
the complex formed between PVP and pDNA is neither particulate nor DNA encap-
sulated. These polymers may interact with DNA via hydrogen bonding and/or Van
der Waals interactions. PVP is supposed to act by different mechanisms. The vinyl
backbone of PVP provides hydrophobicity and charge shielding, effectively thereby
reducing the accessibility of degradative enzymes to the active sites of pDNA. The
shielding of the pDNA negative charge by PVP should decrease charge-based repul-
sion between the pDNA and the anionic cellular membrane, which in turn would
increase the interaction and internalization. PVP improves intracellular uptake by
interactions between the hydrophobic surface of polyplexes and the cell membrane.
PVP increases availability of pDNA in cytoplasm by inhibiting fusion of pinocytotic
vesicles and endosomes with lysosomes, known sites of degradation within cells. PVP
reduces hydrogen bonding of water with pDNA, thereby facilitating pDNA partitioning
into hydrophobic membranes.
Fourier-transformed infrared (FT-IR) and molecular modeling studies conclude
that PVP is able to bind to plasmid by hydrogen bonding. Zeta potential decreases
with an increase in the amount of PVP because of the shielding effect. A dynamic
dialysis study demonstrated that hydrophobic interactions between PVP and plas-
mid may contribute to the complexation in 150 mM NaCl [172] . The findings pro-
posed here for interactions between PVP and plasmid are also supported by Kabanov
et al. [175] , who anticipated that the complexes that formed between polyvinylpyri-
dinium-based polymers and plasmid resulted in improved hydrophobicity of the
plasmid surface, which could both shield plasmid from enzymatic degradation and
facilitate plasmid uptake into cells via hydrophobic interactions.
The study was performed in rats, using different formulation with varying PVP
concentration, pH, and salt concentration to evaluate its effect on uptake of pDNA
encoding the -galactosidase gene [172,176] . -galactosidase activity was measured
after IM delivery of complexes to determine relative amounts of pDNA uptake. It was
observed that PVP-pDNA complexes were effectively taken up by muscle cells with
a 10-fold higher uptake than naked DNA. The optimized formulation was at pH 4
with DNA-PVP ratio of approximately 1:17. The effect of muscle-specific IGF-I
expression plasmid, complexed to PVP (1:17 w/w) and formulated in 150 mM NaCl,
was evaluated in nerve regeneration in mice following sciatic nerve crush. It was
observed that IGF-I gene medicine can provide an improvement in both sciatic nerve
conduction velocity and wave amplitude up to at least 56 days postsciatic nerve
crush. A significant increase in the growth rate was observed for hypophysectomized
rats over 21 days as compared to the control, after single IM injection of a muscle-
specific growth hormone expression plasmid, complexed with PVP [177] . Over
21 days,the average daily weight gain increased from 0.29  0.09 to 0.61  0.08 g.
The antitumoral effect of PVP formulated with pDNA-encoding human cyto-
kines, specifically interleukin-12 (IL-12) or alpha-interferon (-IFN) was evaluated