Halwani, Abdulrahman Ali; (2019) Designing an Efficient and Biocompatible Polymer for the Oral Delivery of Nucleic Acids. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Our work is concerned with the discovery of delivery systems that are safe as well as efficacious for gene therapeutics by being biocompatible and stabilising nucleic acids from degradation after oral administration. We have designed an efficient, synthetic nucleic acid vector, which is relatively non-toxic compared to lipofectamine. [N-(2-ethylamino-palmitoyl)-6-O-glycol chitosan – EAGCP] was able to increase the stability of the polyplexes due to the presence of the palmitoyl group in the chemical structure of the polymer. Increasing the level of amine groups in EAGC and EAGCP has enhanced the stability of the polyplexes. Additionally, the endosomal escape capability of the polyplexes is associated with the buffer capacity of the polymers as an ​endosomal escape is necessary for transfection. Our results showed that increasing the incubation time required to form a complex plays a critical role in elevating transfection efficiency at low polymer, DNA mass ratio. EAGC polymers with a low degree of ethylamino substitution have maximum transfection at high polymer, DNA mass ratio compared to those with a high degree of substitution. Accordingly, we have found the complexation time, and degree of substitution are critical factors that may be manipulated to decrease the polymer content of polyplexes and in turn make efficient, biocompatible complexes. Furthermore, the results show that modification of the chemical structure of the EAGC polymer through adding palmitoyl group decreases the cytotoxicity of the polyplex. In contrast, the transfection efficiency of the polyplex was decreased as the degree of palmitoylation increased due to the strong stability that restricted the release of DNA inside the cells. The polyplexes stability against gastrointestinal enzymes has been investigated, and the results showed that EAGC and EAGCP have the ability to protect DNA against pancreatin enzyme for 2 hours while the polymers did not protect DNA against pepsin due to the presence of anions such as chloride in SGF that are able to destabilize the polyplex. EAGCP showed its ability to improve the opening of in vitro MDCK cells tight junctions and increase paracellular permeability of 4kDa dextran when compared to sodium caprate (C10). A promising result of an in vivo transfection has been observed with EAGCP and EAGC after oral administration; however, the results were not reproducible.

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