Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 139

Figure 4.5 Chemical structure of pDMAEMA.

n

O

O

N

The cell-based screening of a larger 2350-member library has been performed using
plasmid-encoding firefly luciferase (pCMV-Luc) and the COS-7 cell line [75] . The
result of transfection efficiency has shortlisted 46 new degradable polymers that mediate
higher levels of gene expression than PEI in serum-free medium. Twenty-six polymers
among them perform better than a leading lipid-based reagent. Although the 46 poly-
mers identified in this assay have quite a diverse set of structures, many of these poly-
mers have a number of structural features in common. Many polymers of the 46 efficient
polymers are derivatives of hydrophobic diacrylates and/or linear bis(secondary) amines.
Nevertheless, 12 of the 26 polymers that are identified as transfecting better than a lead-
ing lipid-based reagent are derivative of hydroxyl-functionalized amines.
The use of poly(-amino ester)s as pH-responsive biodegradable polymers for the
encapsulation of DNA within microspheres and nanospheres presents an important
approach for targeted, intracellular delivery of nucleic acid material.

4.2.1.4 Poly[2-(Dimethyalamino)Ethyl Methacrylate]
Hennink et al. have synthesized and evaluated poly[2-(dimethylamino)ethyl methac-
rylate] (pDMAEMA) for gene transfer ( Fig. 4.5 ) [76-78] . pDMAEMA is a water-
soluble cationic polymer, capable of forming compact complexes by electrostatic
interaction with DNA [77] . The size of the complex depends on molecular weight.
High-molecular-weight pDMAEMA ( 300 kDa) was capable of condensing DNA
effectively into particles of 150-200 nm, whereas low-molecular-weight pDMAEMA
forms larger particles of size 0.5-1.0 m. It was demonstrated that at pDMAEMA-
plasmid ratios above 1 (w/w) and at low ionic strengths, small and stable polyplexes
were formed. At ratios below 1, aggregation occurred, irrespective of the other
parameters investigated. Low ionic strength favors the formation of small polyplexes
because polymer-DNA interaction increases with decrease in ionic strength.
It was suggested that at the most optimal pDMAEMA-DNA ratio (3-4 w/w),
1-2% of COS-7 cells were transfected, which was eightfold greater than the effi-
ciency of PLL-plasmid complexes having the same zeta potential (30-45 mV) and
particle size (100-200 nm) [76] . In another study, pDMAEMA-DNA complex
exhibited maximum in vitro cell transfection efficiency when cell viability was only
40-70% [79] . The transfection efficiency increased with the molecular weight of
pDMAEMA. A copolymer of DMAEM with 20 mol% methyl methacrylate (MMA)
demonstrated reduced transfection efficiency and increased cytotoxicity compared to
the pDMAEMA homopolymer. Nevertheless, polyplexes of plasmid and copolymers
with low content (20 mol%) of a hydrophilic comonomer (either N -vinyl-pyrrolidone