(628d) AFM Study of DNA Release Dynamics From Bioreducible Polyplexes

Synthetic delivery vectors based on self-assembly of DNA and polycations (polyplexes) continue to gain strength as viable alternatives to viral vectors. Redox potential gradients have been among the most successfully employed stimuli for improving the efficacy of DNA delivery. How to correlate physiochemical attributes with transfection and toxicity data remains a major scientific challenge. AFM was used to study DNA release dynamics from bioreducible hyperbranched poly(amido amine) (PAA) polyplexes in simulated physiologic conditions with 1,4-dithiothreitol as the reducing agent. DNA release is triggered by a depolymerization of high-molecular-weight polycations into low-molecular-weight oligocations via thiol and disulfide exchange reaction. A DNA release pathway with varying rate of DNA release was found to be common among polyplexes with different disulfide content, molecular weight, and polymer architecture. The three-stage pathway begins with morphological change from metastable nanostructures into the more favorable toroid structure. Then toroids interact with each other by aggregation and fusion. Finally, DNA wormlike chains gradually unravel from the polyplex resulting in loose loops/tails that are held by a central compact core. The AFM results at the single polyplex level reveal likely connections between nanostructure and transfection efficiency of bioreducible polyplexes.