| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 92 === In this study, we used dextran of molecular weight 1500 and 1000 and folate to modify branched polyethylenimine, and investigated how the grafting degree of the modified PEI affected trasfection efficiency. Because of the over-expression of the folate receptor on many cancer cells, folate can be used to selectively transfect the cancer cells. The modified PEI was mixed with plasmid pEGFP-C1 to form complexes, which was used to transfect KB cells, a folate-receptor-positive cell line. The transfection efficiency was calculated by dividing the number of green cells by the number of the total cell as measured by flow cytometry.
When N/P ratio increased, the transfection efficiency was increased. When EMA labeled plasmid was used to examine plasmid delivery, it was found that the intracellular amounts of the delivered plasmid within KB cell decreased for using the modified PEI. The cytotoxicity of the modified PEI was slightly reduced. In addition, as the titration experiments revealed, the buffer capacity of the modified PEI was lower than that of unmodified PEI, and increased as the grafting degree decreased. The buffer capacity of the PEI modified by the dextran molecular weight of 10000 was lower than that modified by the dextran of molecular weight of 1500. The size and zeta potential of the polymer/DNA complex were examined using a salt-free buffer and DMEM. When the grafting degree increased, the size of complex was increased, and the zeta of the complex was decreased. When the complexes were exposed to heparin to examine the percentage of uncondensed DNA. The modified PEI was dissociated from complexes more easily than unmodified PEI, especially for the PEI modified with dextran of molecular weight that have steric hindrance. In conclusion, the PEI modified by low level of dextran grafting decreased the transfection efficiency, and then modified by folate releaved it can increase efficiency. In future, we can design shorter spacer and low modified level to achieve optimal design.
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