Condensation of DNA for Gene Delivery: Studies on Vector-Nucleic Acid Interactions and Transfection Efficiency
Abstract: This thesis concerns the delivery of nucleic acids into cells and tissues with the aim to change or correct gene expression. The field of gene delivery has the ultimate goal of producing genetic drugs for clinical applications, and the activity in this area is intense although so far the use is limited to research purposes. The main bottleneck is the lack of suitable delivery vectors. Viral vectors have undisputed efficiency but have shown to impose large safety risks, why non-viral methods are being increasingly explored. In this work, two classes of non-viral vectors, dendrimers and cell-penetrating peptides (CPPs), have been investigated for their interactions with DNA and their ability to mediate gene delivery into cultured cells with the aim of deducing relations between vector structure and biological activity. In addition, methods allowing biophysical characterization of vector-DNA complexes with focus on their dynamic nature have been developed. For dendrimeric vectors, the effect of surface-modifications aiming to increase their biocompatibility was studied. The results showed that although these modifications render dendrimers completely non-toxic, they also abolish the ability to mediate transfection. By biophysical studies, this could be related to a decreased DNA binding capacity of the modified dendrimers, which highlights a previously largely neclected issue in the dendrimer field. CPPs are promising vectors given their inherent ability to stimulate uptake into mammalian cells and deliver macromolecular cargo. Here, peptides with varying content of arginines and lysines were examined and it was found that arginine residues enhance the uptake efficiency compared to lysines. Arginines also showed to promote more efficient condensation of DNA, and the arginine-enriched variant of the peptide was the only one that displayed successful gene delivery. However, arginines alone were not sufficient since other CPPs with equal numbers of arginines were non-active in this respect. Hydrophobic residues in the peptide were found to be equally important, with one possible mechanism being to provide stability upon interaction with negatively charged cell surface residues. In conclusion, the thesis contributes with biophysical insights into the complicated process of gene delivery and gives clues for future development of new and more efficient vectors.
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