Magnetofection is an efficient new physical gene transfection technology. Despite its effective gene delivery capability, till now relatively little work has been conducted on the mechanism of magnetofection, especially the intracellular fates of the components of magnetofectins and their effects on magnetofection. In this study, we investigated the mechanism of magnetofection using magnetofectins that were prepared via electrostatic self-assembly of the three components: polyethyleneimine (PEI)-coated magnetic nanoparticles (MNPs-PEI), plasmid DNA (pDNA) and PEI in the free form (free PEI). TEM observation and agarose gel electrophoresis assays have indicated MNPs play the role of driving magnetofectins to the cell surface without entering into the nucleus. Confocal microscopic tracking of fluorescence-labeled PEI has shown that the free PEI (green) can be found in the nucleus but almost all of the MNPs-PEI (red) are confined in the cytoplasm in COS-7 cells 30 min post-transfection or in SPC-A1 cells 90 min post-transfection, implying that the pDNA/PEI complex must separate from MNPs-PEI before entering into the nucleus. In addition, reporter gene assays showed the magnetofectins, in which the free PEI was absent, failed to transfect SPC-A1 or COS-7 cell lines; and there was an optimal ratio of the constituents of magnectofectins to achieve optimal transfection efficiency by balancing stable complex formation and facile release of PEI/pDNA from the complex. In summary, our findings further the knowledge of magnetofection and can be helpful for the design and preparation of gene delivery vehicles for effective magnetofection.
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