Pharmaceutical aspects of polymer-based non-viral gene delivery systems: experience with p(DMAEMA)-pCMV-lacZ polyplexes

The cationic acid and water-soluble polymer poly(2-(dimethylamino)ethyl met hacrylate), p(DMAEMA), is able to condense plasmid DNA by electrostatic int eractions. The ability of the thus formed polyplexes to transfect cells gre atly depends on their characteristics: small (< 0.15 <mu>m), positively cha rged particles showed the highest transfectivity. We therefore systematical ly investigated the effect of formulation parameters on the polyplex charac teristics. The polymer/plasmid ratio was seen to dominate the size of the p olyplexes. Furthermore, a low pH and ionic strength enhanced the formation of small-sized polyplexes, especially in the presence of sucrose. Once comp lexed with p(DMAEMA), linear forms of DNA showed lower transfection activit ies than circular topoisomers. The polyplexes preserved almost their full t ransfection potential after aging for 10 months at 4 and 20 degreesC, but n ot at 40 degreesC. After storage, conformational changes in the secondary a nd tertiary structure of DNA were observed. Freeze-dried polyplexes with su crose as lyoprotectant almost fully retained their transfection efficiency, even when aged for 10 months at 40 degreesC.