(191u) DNA Release Dynamics Induced by Inter-Polyelectrolyte Exchange

Synthetic delivery vectors based on self-assembly of DNA and polycations (polyplexes) continue to gain strength as viable alternatives to viral vectors. But the low transfection efficiency inhibits the application of polymeric gene delivery vectors. One of the critical barriers is the premature release of DNA by interpolyelectrolyte exchange reaction with polyanions including heparin and albumin. AFM was used to study DNA release dynamics from bioreducible hyperbranched poly(amido amine) (PAA) polyplexes in simulated physiologic conditions with heparin as releasing agent. DNA release is induced by inter-polyelectrolyte exchange reaction. Since heparin has stronger negative charge density, polycation tends to bind with heparin instead of DNA. Once DNA molecules are not bound and protected by polycation, they will get destroyed by DNAse and lose their bioactivity in the physiological environment. It is found the DNA release on solid/liquid interphase is different from bulk reaction in solution and maybe more close to the realistic situation.  Real-time in situ AFM revealed morphological pathway for such DNA release process at single molecule level. The morphological milestones include core-shell, toroid, nanoparticle decorated toroid, and loose chains held by a compact core structure. In addition, PEG and hyaluronic acid modification on PAA could reduce the interaction between polyplex and heparin, which can improve the polyplex stability. This study contributes to basic understanding of interpolyelectrolyte interaction at the solid/liquid interface and its effect on polyplex stability.