Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 137

(PEG-PEI-FabV-DNA) revealed higher cellular association and higher transgene
expression (luciferase) in OA3 antigen-expressing OVCAR-3 cells compared to
unmodified PEI-DNA complexes. Besides, the enhanced activity of PEG-PEI-FabV-
DNA complexes was absent in OA3 negative cells. This confirms the role of anti-
body-mediated targeting. PEG-PEI-FabV-DNA complexes showed a size of 150 nm,
with almost neutral surface charge.
Pancreatic  cell overexpresses GAD, which was one of the major auto antigens
expressed. The FabV fragment of a monoclonal antibody against GAD was conju-
gated to PEI via a PEG linkage (FabV-PEG-PEI) for targeting pancreatic  cells [62] .
FabV-PEG-PEI-DNA complexes exhibited enhanced cellular association and trans-
fection efficiency in GAD-expressing mouse insulinoma cells (MIN6).
4.2.1.2.1.4 Peptide- and Protein-Conjugated PEIs Transferrin conjugated PEI-DNA
complex (Tf-PEI-DNA) and PEGylated transferrin conjugated PEI-DNA (Tf-PEG-
PEI-DNA) complex were evaluated for systemically target subcutaneous tumor
(murine neuroblastoma [neuro2A]) after application of complexes in the tail vein of
syngenic A/J mice [63,64] . The complexes were preferentially target tumor cells, and
luciferase gene expression was reduced in other organs (liver, lung, heart, spleen, and
kidney) as compared to unconjugated complexes. The targeting by Tf-PEG-PEI-DNA
polyplexes was the first demonstration of tumor-specific targeted gene expression
after systemic application.
There were two justifications proposed for this enhanced expression. The first was
passive targeting due to the shielding of the complexes (PEG or transferrin) from non-
specific interactions, which leads to increases in blood circulation time, thereby allow-
ing the complexes to reach the tumor. The second approach was active targeting via
receptor-mediated uptake of the transferrin receptor overexpressed on the tumor cell.
The angiogenic endothelial cells in solid tumors exhibit arh3/arh5 integrins on the
cell membrane [65,66] . The RGD peptide (ACDCRGDCFC) contains two disulfide
bridges that restrict the peptide conformation and show much higher affinity to the
arh3/arh5 integrins than similar peptides with one disulfide linkage, or linear RGD
peptide [67] . An angiogenic endothelial cell targeted gene delivery system (PEI- g -
PEG-RGD) comprised of arh3/arh5 integrin-binding RGD peptide was developed.
The PEI- g -PEG-RGD-DNA complexes demonstrated fivefold higher transfection
efficiency and lower cytotoxicity in VEGF-stimulated angiogenic human dermal
microvascular endothelial cells (HDMEC) than unconjugated complexes [68] .
4.2.1.3 Poly(  -Amino Esters)
Despite recent advances in conventional polymeric vectors such as PEI, vectors
suffer from a substantial drawback of cytotoxicity and poor transfection efficiency
[48,63] . It requires modification of the chemical structure of the polymer to achieve
the desirable attribute, such as biodegradability, minimal cytotoxicity, and improved
transfection efficiency. Structure-function relationships play a role in the synthesis
of the new polymeric vector. Langer's research group has worked in that direction
and come up with one such polymer library approach to define the structure-function
relationships of polymer-based DNA delivery [69] . These polymer libraries have