(451b) The Role of Polyelectrolyte Exchange On DNA Release Dynamics From Polyplexes

Nonviral gene carriers, especially polycations, are attractive alternatives to viral carriers because they show lower safety risks and can be tailored to specific therapeutic needs. A major problem of nonviral gene carriers is low transfection efficiency. The timing, location, and extent of DNA release is a limiting step to the overall gene delivery efficiency. One of the critical barriers is the premature release of DNA by interpolyelectrolyte exchange reaction with polyanions including heparin and albumin. We carried out a mechanistic study of DNA release by polyelectrolyte exchange with heparin at the single polyplex level using real-time atomic force microscopy (AFM) imaging. Bioreducible poly(amido amine) and non-bioreducible polyethylenimine polyplexes were studied. The AFM results are correlated with gel electrophoresis data. The release rate was determined and fitted to a first order reaction. DNA release rate using free heparin in solution is compared to heparin adsorbed at the solid/liquid interface. The extent of DNA release is a function of heparin concentration. A critical heparin concentration above which significant DNA release occurs was determined. The critical concentration was found to be a function of polycation charge density, chain architecture, and amine to phosphate (N/P) ratio. AFM captured distinct polyplex structures with partial DNA release that include the core-shell, toroid, nanoparticle decorated toroid, and loose chains held by a compact core structure. This study contributes to basic understanding of interpolyelectrolyte interaction at the solid/liquid interface and its effect on polyplex stability.