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.
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