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A comparative study of cationic formulations for the delivery of siRNA and DNA

Kwok, N.P.A.; (2009) A comparative study of cationic formulations for the delivery of siRNA and DNA. Doctoral thesis, UCL (University College London). Green open access

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Abstract

RNA interference (RNAi) provides a specific and efficient way to silence gene expression; therefore, it is an attractive tool to be used in basic research on gene function as well as gene therapy. Despite the enormous potential of RNAi, delivering the small interfering RNA (siRNA) to the cells is one of the main hurdles. Previously there have been reports showing effective plasmid DNA delivery to cells and such systems could be used to deliver siRNA to cells due to the similarity of the delivery criteria between plasmid DNA and siRNA. Therefore, I hypothesise that a successful siRNA delivery system will have similar biophysical characteristics as a successful DNA delivery system. The aim of this study is to identify the important criteria to establish a promising siRNA delivery system by comparing the criteria of successful DNA delivery systems such as linear and branched polylysines and linear and branched PEIs. In order to deliver nucleic acid to a cell, a vector system should be able to bind and form a positively surface-charged nano-sized complex with the nucleic acid for cellular binding and uptake. Inside the cell, the vector should be able to dissociate from the nucleic acid for gene expression or silencing. Therefore, the important parameters to investigate are the binding and dissociation properties of the vector components to the nucleic acid and the size and surface charge of the complex. From the results, generally all the polylysines and PEIs can bind, dissociate and form a positively charged nano-particle with plasmid DNA, which can mediate gene expression. Despite the ability of all the polylysines and PEIs to bind to and dissociate from siRNA, only branched polylysines, linear and branched PEI, but not linear polylysines can form positively charged nano-particles with siRNA. Indeed, branched PEI behaves similarly towards siRNA and DNA biophysically. Interestingly, only branched PEI and siRNA complexes can mediate cellular uptake and 60% target gene knockdown. Branched polylysines or linear PEI siRNA complexes cannot mediate gene silencing in spite of the formation of positively charged nano-particles. This could be due to poor cellular uptake of these complexes or degradation of siRNA upon uptake. Therefore, to improve the design of the siRNA vector system, there is a need to research the cellular binding and uptake of siRNA complexes in the future.

Type:Thesis (Doctoral)
Title:A comparative study of cationic formulations for the delivery of siRNA and DNA
Open access status:An open access version is available from UCL Discovery
Language:English
UCL classification:UCL > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Child Health

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