Biodistribution and tissue expression kinetics of plasmid DNA complexed with polyethylenimines of different molecular weight and structure.

Polyethylenimine (PEI) has been studied as an efficient and versatile in vitro and in vivo gene delivery agent. Here, we report the in vivo fate, tissue expression duration, and safety after the intravenous injection of plasmid DNA complexed to various PEIs under different conditions. Murine interleukin-2 plasmid DNA was complexed with branched PEI2Kd, 25Kd, or linear PEI25Kd at different N/P ratios. The mean residence time of plasmid DNA was found to be prolonged after delivery in PEI, evidencing the highest values in branched PEI25Kd. As compared to branched PEI25Kd, linear PEI25Kd at the same N/P ratio provided mRNA expression levels orders of magnitude higher in the lung over an 8-day period. In the branched PEI2Kd/DNA complexes, the N/P ratio of 80:1 evidenced higher gene expression efficiency in the kidney and spleen than the normal N/P ratio of 10:1. The generation of proinflammatory chemokine receptors was induced by branched PEI25Kd, but not by other PEIs. The complexes of DNA with linear 25Kd PEI or branched PEI2Kd exhibited no histological changes after repeated administrations. These results indicate that the structure, molecular weight, and N/P ratios of PEIs must be collectively considered and modulated for organ-targeted plasmid DNA delivery.