Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 144

cancer cell line transfected with the DNA complex with the papiloma virus proteins-
PLL conjugate [102] . However, endosomolytic compounds like fusogenic pep-
tide HA2 and chloroquine had no effect on the transgene expression. This suggests
another mechanism apart from that facilitating DNA release from the endosomes.
4.2.2.1.2 Pluronic ® -Polycation Graft/Block Copolymers
The cationic copolymers were prepared to overcome the problems associated with
first-generation polyplexes. This cationic copolymer interacts with DNA to form prac-
tically uncharged hydrophilic particles, known as block ionomer complexes or poly-
ion complex micelles, that are comprised of a core of neutralized polycation and DNA
chains and a shell of water-soluble nonionic chains. Although these systems proved
effective for short DNA oligodeoxynucleotides (ODNs) in vitro and in vivo , they are
less efficient with pDNA because of its larger size. Pluronic ® block copolymers were
used as substitutes for nonionic EO chains in the block ionomer complexes [106] . It
was hypothesized that hydrophobic PO chains of the Pluronic ® in the polyplex could
facilitate membrane interactions and may act as a synthetic fusogen moiety to enhance
transport of the polyplex into the cell interior. However, the EO chains of the Pluronic ®
molecules confer solubility of polyplex in aqueous dispersions.
Block-graft copolymers, P123- g -PEI(2K), were synthesized by covalent conjuga-
tion of Pluronic ® and branched PEI. The basic components of these polyplexes are
DNA, Pluronic ® -PEI conjugate, and free Pluronic ® . The polyplexes prepared with
pDNA and ODNs give stable dispersion of the size 100-200 nm. The polyplexes effi-
ciently delivered DNA and antisense ODN in vitro and in vivo [107,108] .
It was proposed that the resulting polyplex represented mixed complexes, in which
the free Pluronic ® molecules were bound through hydrophobic interactions with the PO
chains of the Pluronic ® P123- g -PEI(2K) conjugates. The incorporation of Pluronic ®
P123 in such polyplexes was essential to prevent aggregation of the particles and
accomplish efficient transport of the plasmid into cells [106] . The P123- g -PEI(2K)-
based system demonstrated high transfection activity in vivo with superior biodistribu-
tion compared to unmodified PEI [106] . The in vivo study revealed uniform distribution
of gene expression, compared to first-generation polyplex and a lipid-based system, in
the spleen, heart, lungs, and liver, after 24 h of IV injection of this polyplex in mice.
Subsequently, IV delivery of the polyplex comprising a gene encoding the murine
ICAM-1 molecule demonstrated superior gene expression in the liver of transgenic
ICAM-1-deficient mice [107] . In another study, a similar type of graft-block copoly-
mer molecule, Pluronic ® F127 grafted to PLL, was proposed for gene delivery [105] .
4.2.2.1.3 Pluronics ® with naked DNA
Certain Pluronic ® block copolymers drastically improve expression of pDNA in
skeletal muscle in mice [109,110] . The formulation, composed of a mixture of the
block copolymers Pluronic ® L61 and Pluronic ® F127, termed SP1017, increased
expression of both reporter and therapeutic genes by 5 to 20 folds compared to naked
DNA. The maximum activity of SP1017 was found at a concentration near to CMC.
This observation concludes that Pluronic ® unimers are responsible for the activity. It
was also observed that SP1017 was more efficient than PVP. Histology experiments