Biodistribution of nonviral cationic vector/DNA complexes was studied after systemic or intratracheal administration to the lungs and correlated with transgene expression. Intravenous injection in C57Bl/6 mice gave maximal and significant luciferase expression in the lungs with the cationic polymer PEI 22K/DNA complexes at the highest ratios of positive/negative charges versus DNA alone. While DOTAP/DNA complexes with high charge ratio determined lower but still significant luciferase activity versus uncomplexed DNA, GL-67A and PEI 25K mediated negligible luciferase expression. Labelled PEI 22K and DOTAP complexes were evenly distributed in the alveolar region, where GFP expression was revealed, while PEI 25K and GL-67A complexes were not detected, suggesting a different interaction of these complexes with the plasma membrane of endothelial cells. Following an intratracheal injection, the highest and significant levels of transfection were obtained with

We investigated the cell association and intracellular pathway to the nucleus of complexes formed between DNA and cationic lipid DOTAP (lipoplexes) or cationic polymer polyethylenimine (polyplexes). Flow cytometry and confocal microscope analysis showed that lipoplexes presented higher affinity for cell membrane than polyplexes. Electron microscopy demonstrated that both types of complexes followed an endocytic pathway and were metabolized but did not enter the nucleus. However, by in situ PCR and FISH it was possible to show that the plasmid localized to the nuclei, indicating that DNA must be dissociated from the vectors to be delivered to the nucleus. Our results identify a different behaviour in the interaction of polyplexes and lipoplexes with the cell, indicating that a combination of advantageous properties of the two kinds of cationic molecules could further ameliorate efficiency of nonviral gene transfer vectors.