Formulation and characterization of DNA-polyethylenimine-dextran sulfate nanoparticles

Polyethylenimine (PEI) is a promising non-viral gene delivery polymer that produces high transfection efficiency both in vitro and in vivo. The use of PEI, however, is hindered by its toxicity, reflecting its polycationic nature. In an attempt to decrease this charge-dependent cytotoxicity, a polyanionic polymer, dextran sulfate (DS), has been incorporated into self-assembling PEI-DNA complexes with zinc as stabilizing agent. Spherical particles with a mean particle size of approximately 200 nm and a polydispersity index of 0.2 were achieved using the following optimal conditions: PEI solutions at pH 8, PEI/DS mass ratios of >or=2, and 25 microM zinc sulfate. Plasmid DNA was completely condensed within the nanoparticles as confirmed by an ethidium bromide accessibility assay. This result correlates well with DNase protection studies which find partial protection of the DNA nanoparticles from degradation by the enzyme. The DNA was incorporated into the PEI-DS particles with a high efficiency (>95%) and maintained a primarily supercoiled B-form as determined by gel electrophoresis and circular dichroism. The cytotoxicity of the DNA nanoparticles appeared to decrease as the amount of DS in the formulation was increased and they produced moderate transfection activities that were only modestly inhibited by the presence of serum.