The design of cyclodextrins for delivery of siRNA - a structure-activity relationship

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Kont, Ayse
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University College Cork
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Previously non-viral delivery of therapeutic nucleic acids (NAs) has been achieved for the treatment of liver disease and in the case of the COVID-19 vaccine. The delivery vector in both applications was a lipid-base nanoparticle (LNP). To expand the therapeutic application of NAs to treat more complex chronic diseases, such as cancer, delivery systems with wider biodistribution capable of going beyond the vaccine and the liver are required. This thesis aims to investigate the potential of modified cyclodextrins (CDs) as alternative biomaterials for siRNA delivery and to identify the optimum functional groups to maximise safety and efficacy. To help reduce the overall cationic charge and the potential for in vivo toxicity a co-formulation approach using a blend of an anionic and cationic amphiphilic CDs was investigated. The co-formulation was characterised and a reduction in the positive charge was achieved. The NPs were evaluated in vitro in HL-60, a leukaemia cell line, and results indicate that endosomal escape was a limiting factor to gene silencing with the siRNA. Structural modification of amphiphilic cationic CDs was investigated as a second approach to enhance the efficacy of CD NPs. The structural changes included varying the terminal amine, the linker, and the CD type, β versus γ. Primary amine proved to be more successful compared to tertiary amine in β- and γ-CDs. However, neither CD type was superior to the other, containing the primary amines. The exhaustive derivatisation of the secondary side of γ-CDs increased charge density and led to better transfection efficiency compared to O2-modified γ-CDs. Finally, the exchange of the linker group from triazole to thiopropyl increased the efficiency further in primary amine O2- and O3-substituted γ-CD. The optimum cellular uptake and gene silencing, in a lung cancer cell line (A549), was achieved with an O2- and O3-substituted γ-CD with a thiopropyl-linked primary amine. Finally, the potential ability of CD polymers to deliver siRNA was studied. Two cationic β-CD-polymers one functionalised with a primary amine and the other with a quaternary ammonium were used to formulate NPs containing siRNA. Both polymers formed NPs with sizes in the range of 150 to 200 nm. The primary amine functionalised polymer was taken up into the cells (A549) and produced 40% gene silencing. In contrast, the quaternary ammonium polymer failed to show any cellular uptake. The superior delivery effect achieved with the primary amine functional group agreed with the previous results from the monomer CD. In conclusion, modulation of the physicochemical characteristics of siRNA-NPs was achieved by changing the chemistry of the incorporated CD. The chemical structure significantly influenced the degree of gene knockdown. The primary amine showed superior efficiency in both monomeric amphiphilic cationic CDs and polymeric cationic CDs. Results indicate that further functionalisation of the CD is possible, and the potential exists to fine-tune the structure to achieve more specific biodistribution.
Modified cyclodextrins , siRNA delivery , Structure activity relationship , Non-viral delivery
Kont, A. 2024. The design of cyclodextrins for delivery of siRNA - a structure-activity relationship. PhD Thesis, University College Cork.
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