Understanding barriers to efficient nucleic acid delivery with bioresponsive block copolymers

Abstract

The delivery of nucleic acids has the potential to revolutionize medicine by allowing previously untreatable diseases to be clinically addressed. Viral delivery systems have been held back by immunogenicity and toxicity concerns, but synthetic vectors have lagged in transfection efficiency. This thesis describes the rational design and systematic study of three classes of bioresponsive polymers for nucleic acid delivery. A central theme of the study was understanding how the structure of the polymers impacted each of the intracellular steps of delivery, rather than solely the end result. A powerful tool for efficiently quantifying endosomal escape was developed and applied to each of the material systems described. First, a linear-dendritic poly(amido amine) -poly(ethylene glycol) (PAMAM-PEG) block copolymer system previously developed in our lab was evaluated and its ability to overcome the sequential barriers of uptake, endosomal escape, and nuclear import were characterized. Next, a class of crosslinked linear polyethyleimine (xLPEI) hyperbranched polymers, which can contain disulfideresponsive linkages, were synthesized and investigated. It was demonstrated that free polymer in solution, not the presence of a functional bioresponsive domain, was responsible for the highly efficient and relatively nontoxic DNA delivery of this promising class of crosslinked polyamines. Finally, this analysis was applied to siRNA delivery by a library of amine-functionalized synthetic polypeptides. The pH-responsive secondary structure, micelle formation, and ester hydrolysis were studied prior to the discrete barrier-oriented analysis of the siRNA delivery potential of this library. It is hoped that the tools, materials, and systemic analysis of structure-function relationships in this thesis will enhance the process of discovery and development of clinically relevant gene carriers.