Biomedical Engineering Reference
In-Depth Information
plasmid DNA (pDNA) localized in the liver and with nondetectable localization of
pDNA in other tissues.
When PEG was added as a spacer between PLL and lactose or galactose, conju-
gation increased the availability of the target ligand on the surface of the complex.
Lactose-PEG- g -PLL conjugate (Lac-PEG-PLL) with different ratios (6, 12, 22, and
30 mol%) of lactose was synthesized and evaluated for transfection to HepG2 cells
[35] . It was observed that 30 mol% showed the highest transfection efficiency, with
a significant decrease in cytotoxicity as compared to PLL. Also, the stability and
solubility under physiological conditions were higher than those achieved by PLL.
Thus, transfection assays proved the targeting capabilities of galactose moiety to the
hepatocytes cells of the liver.
4.2.1.1.2 The Terplex System
The terplex system was developed for receptor-mediated gene delivery using low-
density lipoprotein (LDL) wherein the LDL specifically interacts with the LDL
receptors on the cell surface [36,37] . LDL receptors are membrane-bound proteins
present in many types of cells like hepatocytes [38] , myocytes [39] , and endothelial
cells [40] . LDL specifically interacts with the LDL receptors on the cell surfaces by
means of the LDL-mediated targeting system. The terplex system consists of pDNA,
low-density lipoprotein, and hydropholized PLL. The pDNA, when formulated with
stearyl-PLL and LDL, forms a stable and hydrophobicity/charge-balanced terplex sys-
tem of optimal size for efficient cellular uptake [36] . The stearyl-PLL conjugate syn-
thesized by N-alkylation of PLL with stearyl bromide binds via a charge interaction
with pDNA, while stearyl-PLL could then bind to LDL via hydrophobic interaction.
LDL incorporation enhances the transfection efficiency of the system by receptor-
mediated endocytosis.
The terplex system showed proficient transfection into many kinds of cells, includ-
ing murine smooth muscle cells (A7R5), primary endothelial cells, primary smooth
muscle cells, and human lung fibroblast cells (CCD-32 Lu) [37] . Biodistribution was
studied in mice after IV administration of the terplex system [41] . The terplex system
showed prolonged circulation time compared to naked DNA. A biodistribution study
revealed that the terplex system was localized in the lungs at earlier stages (1 h) and
in the liver at later stages (24 h).
The terplex system also exhibited significantly higher gene expression of lucif-
erase than naked DNA after myocardial injection of luciferase plasmid in rat or rab-
bit [42] . The luciferase activity was sustained for 30 days as compared to 6 days
by naked DNA. The superior and sustained gene expression by terplex DNA was
because of higher gene transfection by LDL-receptor-mediated endocytosis and pro-
tection of DNA from nucleases.
4.2.1.2 PEI and Copolymers
PEI has been used in various products, including shampoos, water purification,
and mineral extraction, for the last 60 years. The PEI is a cationic polymer composed
of several 43 Da CH 2 -CH 2 -NH ethyleneimines as a basic moiety ( Fig. 4.3 ). It is
Search WWH ::




Custom Search