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Improving gene delivery efficiency by lipid modification of cationic polymers Open Access


Other title
Bone marrow stromal cells
Non viral vectors
Cationic polymers
Lipid-modified polymer
Gene delivery
Type of item
Degree grantor
University of Alberta
Author or creator
Incani Ramirez, Vanessa
Supervisor and department
Lavasanifar, Afsaneh (Pharmacy and Pharmaceutical Sciences)
Uludag, Hasan (Chemical and Materials Engineering)
Examining committee member and department
Ijeoma Uchegbu (Pharmaceutics)
Ravin Narain (Chemical and Material Engineering)
Robert Campbell (Chemistry)
Kamaljit, Kaur (Pharmacy and Pharmaceutical Sciences)
Faculty of Pharmacy and Pharmaceutical Sciences

Date accepted
Graduation date
Doctor of Philosophy
Degree level
This thesis explores the capabilities of cationic polymers modified with lipids of different carbon chain length to deliver DNA molecules to primary cells and transformed cell lines. Our studies focus on two different polymers: polyethylenimine (PEI) and poly(L-lysine) (PLL). Firstly, PEI and PLL were conjugated to palmitic acid (C16). The delivery of plasmid DNA to rat bone marrow stromal cells (rat-BMSC) was evaluated by using a Green Fluorescent Protein gene expressing plasmid (pEGFP-N2) as a reporter system. The rationale for lipid substitution is to give the polymer an amphiphilic character so as to improve the transfection efficiency of native polymers by improving the DNA/polymer translocation through the phospholipid-rich cell membranes. In the case of PLL-C16, transfection efficiency was significantly increased (5 fold) as compared to native PLL, and it was significantly higher than commercially available cationic lipids (LipofectamineTM 2000 and FugeneTM). We further explore the use of other lipids with variable chain lengths (carbon chain length ranging from 8 to 18 saturated and unsaturated) in order to identify other candidates to enhance the gene delivery properties of the PLL. Lipid-modified PLL of high molecular weight (25 vs. 4 kDa) was found to be more effective in delivering plasmid DNA in rat-BMSC. We noted that C14-, C16- and C18-substituted PLL gave the most effective DNA delivery. Moreover, a correlation between the extent of lipid substitution and the plasmid DNA delivery efficiency was found Additionally, transgene expression by BMSC significantly increased when amphiphilic PLLs were used as compared to native PLL. The modified polymers were able to transfect the cells up to 7 days, after which the expression decreased. Encouraged by the successful transgene expression agents obtained by modifying low molecular weight PEI with the same series of lipids described above, we explored the possibility of modifying low molecular weight PEI (2 kDa) with longer lipids; saturated fatty acid (C22), trans fat (C18:1T) and essential fatty acids (C22:1, C22:6 and C18:3). Transfection efficiency proved to be cell dependent. Only the transformed 293T cells were able to express GFP compared to human-derived BMSC. The highest transfection efficiency was found with highly unsaturated lipid-substituted PEI (C18:3 and C22:6) and were able to increase transgene expression overtime (6 days). Furthermore, internalization studies indicated that effective transfection of these carries do not follow any known endocytosis pathway instead the DNA/carrier penetrates the plasma membrane directly.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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