| The identification of genes involved in a variety of diseases has given rise to renewed optimism that gene therapy breakthroughs leading to cures may follow. This thesis focuses on the synthesis and characterization of improved non-viral gene delivery systems; specifically high-density nanocomplexes composed of numerous copies of plasmid DNA and the cationic polymer polyethylenimine (PEI).; Encapsulation of PEI/DNA nanocomplexes within biodegradable polymer microspheres provided long-term delivery of viable DNA and enhanced gene expression by cells for over 75 days. Subsequently, time resolved multi-angle laser light scattering (TR-MALLS) was used to identify nanocomplex density (related to number of DNA plasmids per complex) as a critical design parameter for achieving high transfection efficiency with non-viral vectors. Importantly, both high and low DNA density gene vectors entered and trafficked within cells in an identical fashion and accumulate near the cell nucleus within 30 minutes post-addition to cell media. However, high DNA density vectors yielded higher overall transfection efficiency (based on total production) than low DNA density vectors. As a result, DNA loading density was studied extensively by varying formulation parameters of PEI/DNA nanocomplexes such as PEI molecular weight (MW), nitrogen (on PEI) to phosphate (on DNA) ratio (N/P), and the solvent in which the nanocomplexes were made to verify the correlation between high DNE loading density and high transfection efficiency in vitro. Stability of the PEI/DNA nanocomplexes was assessed in conditions mimicking in vitro, in vivo, and storage environments. Lastly, PEGylation of nanocomplexes reduced protein binding and provided enhanced DNA protection from DNase degradation. Reduced protein binding is expected to decrease in vivo clearance rates by the reticuloendothelial system (RES). PEGylated nanocomplexes maintained gene expression upon exposure to serum.; Collectively, the studies presented here should lead to improved design and characterization of more effective non-viral gene carriers. |
