Magnetic Nanoparticles: Cellular Uptake And Gene Transfection

Magnetic nanoparticles (MNPs) are promising materials for variousbiomedical applications including MR imaging, stem cell tracking, gene/drugdelivery and cancer treatment.Over the last decades, extensive research has focused on the interactionbetween the MNPs with cells. However, the specific effects of MNPs size andsurface charge are a controversial subject among different researchers. Withinthe same cell type and under different conditions, various MNPs formulationsdiffering in surface modification may also use distinct endocytic machineriesfor internalization and intracellular routing pathways.To obtain additional knowledge on the internalization mechanism ofMNPs into cells, three points about cellular uptake of MNPs have beenevaluated as follows:â…°) Cytotoxicity and cellular uptake of oxidized glutathione (GSSG)modified MNPs (MNPs-GSSG) in human lung adenocarcinoma cancer cells(SPC-A1). The results showed MNPs-GSSG were well biocompatible, couldbe efficiently taken up by SPC-A1cells and the internalized MNPs-GSSGcould retain in the cells for generations. The uptake of MNPs-GSSG intoSPC-A1cells was energy-, concentration-and time-dependent. The controlledand efficient localization of MNPs-GSSG into the cytosol and their longintracellular retention provides theoretical and experimental insight into thebiomedical applications.â…±) The cellular uptake of APTES modified MNPs (MNPs-APTES) intoSPC-A1and human embryo lung cells (WI-38). The results indicated theMNPs-APTES could be greatly taken up by SPC-A1cells, but not by WI-38 cells, and the internalized MNPs-APTES could retain in the SPC-A1cells forgenerations. This may be implied for the possible future application ofMNPs-APTES in intracellular hyperthermia, drug delivery system for lungcancer therapy or MRI for cell implantation.â…²) The effects of surface modification of MNPs on internalizationmechanism. The internalization mechanism of two kinds of similar sizeparticles (MNPs-GSSG and MNPs-APTES) to SPC-A1cells were different,which mean the surface modification was more crucial to internalizationmechanism than the particle size. Therefore, we could monitor theinternalization mechanism of MNPs by adjusting their surface modification.Research efforts are currently focused on non-viral vectors that exhibitbiocompatibility and potential for large-scale production. However, non-viralvectors exhibit significantly reduced transfection efficiency as they arehindered by numerous extra-and intracellular obstacles. Magnetofectioncould greatly improve the transfection efficiency of non-viral virus. However,the assembly methods of transfection complexes (magnetofectins) are acontroversial subject among different researchers. This partly owns to theunclear magnetofection mechanism. Therefore, it is essential to elucidate theroles and the intracellular fates of the constituents of magnectofectins inmagnetofection and to gain a fundamental understanding on the design ofmagnetofectins.We prepared charged MNPs, polyethylenimine modified MNPs(MNPs-PEI), citric acid modified MNPs (MNPs-CA) andcarboxymethyldextran modified MNPs (MNPs-CMD). These charged MNPscould spontaneously form magnetofectins with plasmid DNA andPEI/liposome via electrostatic self-assembly. These magnetofectinsapparently enhanced PEI/liposome transfection efficiency and/or geneexpression level into COS-7cells with reduced transfection time from4h to15min under a magnetic field in vitro. Meanwhile, the effect ofmagnetofection was cell line-dependant.We investigated the mechanism of magnetofection using magnetofectins that were prepared via electrostatic self-assembly of the three components:MNPs-PEI, pDNA and free PEI. Our results showed MNPs play the role ofdriving magnetofectins to the cell surface without entering into the nucleus.There was an optimal ratio of the constituents of magnectofectins to achieveoptimal transfection efficiency by balancing stable complex formation andfacile release of PEI/pDNA from the complex. Our findings further theknowledge of magnetofection and can be helpful for the design andpreparation of gene delivery vehicles for effective magnetofection.