Heat-shrinking DNA nanoparticles for in vivo gene delivery

The particle size of a PEG-peptide DNA nanoparticle is a key determinant of biodistribution following i.v. dosing. DNA nanoparticles of <100 nm in diameter are sufficiently small to cross through fenestrated endothelial cells to target hepatocytes in the liver. In addition, DNA nanoparticles must be close to charge-neutral to avoid recognition and binding to scavenger receptors found on Kupffer cells and endothelial cells in the liver. In the present study, we demonstrate an approach to heat shrink DNA nanoparticles to reduce their size to <100 nm to target hepatocytes. An optimized protocol heated plasmid DNA at 100 degrees C for 10 min resulting in partial denaturation. The immediate addition of a polyacridine PEG-peptide followed by cooling to room temperature resulted in heat-shrunken DNA nanoparticles that were similar to 70 nm in diameter compared with 170 nm when heating was omitted. Heat shrinking resulted in the conversion of supercoiled DNA into open circular to remove strain during compaction. Heat-shrunken DNA nanoparticles were stable to freeze-drying and reconstitution in saline. Hydrodynamic dosing established that 70 nm heat-shrunken DNA nanoparticles efficiently expressed luciferase in mouse liver. Biodistribution studies revealed that 70 nm DNA nanoparticles are rapidly and transiently taken up by liver whereas 170 nm DNA nanoparticles avoid liver uptake due to their larger size. The results provide a new approach to decrease the size of polyacridine PEG-peptide DNA nanoparticles to allow penetration of the fenestrated endothelium of the liver for the purpose of transfecting hepatocytes in vivo.