Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 143

The micelles are used as vectors for various drugs owing to their characteristic
properties. Incorporation of drugs into the core of the Pluronic ® micelle resulted in
increased solubility, increased metabolic stability, and increased circulation time for
the drug. A ligand capable of directing site-specific drug delivery can be attached to
the surface of the EO corona, thereby effectively targeting a micelle to a specific site
in the body [96] . It was evident from literature that both polyplex and lipoplex par-
ticles possessing a strong positive charge confer poor biodistribution and a short in
vivo half-life because of preferential uptake by the liver nonparenchymal cells, mainly
Kupffer cells, via phagocytosis [97,98] . The positive charge is responsible for the
immunogenic response and their subsequent rapid clearance from circulation [99] .
Thus, second-generation polyplexes have been developed using “cationic copolymers”
to overcome problems associated with positively charged polyplexes.
Polycation-conjugated Pluronics ® were used as the vector in gene delivery. The
conjugates retained their inherent ability to self-assemble into micelle-like aggre-
gates. In presence of DNA, conjugates form mixed micelle-like aggregates exhibit-
ing two types of interaction, hydrophobic interactions of the PO chain segments and
electrostatic interactions of the polycation and DNA. The hydrophilic EO blocks of
Pluronic ® impart stability to the complex in aqueous dispersion.
Initially, Pluronics ® demonstrated increased expression of genes delivered into
cells using nonviral vectors [100-102] . Secondly, the conjugates of Pluronic ® with
polycations were used as DNA-condensing agents to form polyplexes [104-106] .
Finally, Pluronics ® demonstrated enhanced regional expression of the naked DNA
after injection into the cardiac muscles, skeletal muscles, and tumor. Pluronics ® have
been administered with different types of vectors, including naked DNA, via differ-
ent delivery routes. Thus, it was evident that Pluronic ® block copolymers, through a
broad variety of applications, can significantly enhance gene expression.
4.2.2.1.1 Pluronics ® with Polyplexes
Pluronic ® block copolymers can enhance polycation-mediated gene transfer in vitro .
When Pluronic ® P85 was administered as a 1% aqueous solution to cells simultane-
ously with the polyplex, the uptake and transfection of the polyplex formed between
pDNA and poly( N -ethyl-4-vinylpyridinium) (PEVP) were significantly enhanced in
several cell lines [100] . The probable mechanism of P85 was an increase in endocytic
uptake of the complex into eukaryotic, along with an increase in the liberation of
the macromolecules from the endocytic compartments in the cytoplasm. Moreover,
Pluronic ® may interact with the hydrophobic sites of the polyplexes, forming mixed
Pluronic ® /DNA/PEVP nanoparticles. Another report demonstrated that Pluronic ®
F127 enhances the receptor-mediated gene delivery to the HepG2 hepatic cell line,
using complexes of a pDNA with an asialo-oroso-mucoid-PLL conjugate [101] .
Subsequently, it was demonstrated that hydrophilic Pluronic ® block copolymers used
at a concentration of 1-3% w/v reduced the serum-mediated inhibition of gene trans-
fer with DNA-PEI polyplexes in NIH/3T3 cells [103] . The efficiency of the block
copolymers decreased with an increase in hydrophobicity; F68  F127  P105 
P94  L122  L61. Thus, hydrophilic EO chains of the copolymers provide steric
stabilization to the particle dispersions and prevent aggregation of the particles in the
presence of serum. Pluronic ® F127 enhanced the transgene expression in a cervical