Synthetic Polymer and Microbubble Systems for Gene Delivery to the Brain

Abstract

The natural neurogenesis after neuron death in cases like traumatic brain injury and neurological diseases is sparse. Increasing the replenishment of functional neurons can improve patient outcome and prognosis. One way to encourage neurogenesis is by selective differentiation of neural progenitor cells and neural stem cells in the brain. Gene delivery has emerged as a promising strategy to accomplish this due to the development of effective gene transfer vehicles and the identification of factors that can modulate neural differentiation. The first half of this thesis focuses on improving the efficacy of synthetic gene delivery vehicles. Typically, negative-charged DNA is condensed and protected from degradation by complexing it with positively charged materials. These cationic materials improve gene transfection efficiency by enabling for endosomal uptake and escape from the lysosomal degradation pathway. However, the cationic nature of the materials also brings about deleterious effects such as cell cytotoxicity. Therefore, a there is a balance between transfection efficiency and cytotoxicity with cationic vectors. Strategies to reduce cytotoxicity and improve upon transfection efficiency are explored in this section. Even with the most effective transfection agents, a major hurdle is reaching the neural progenitor cells and neural stem cells in the subventricular zone of the brain. The blood-brain barrier and the blood-cerebrospinal fluid barrier effectively block substances from reaching the brain parenchyma after systemic and intraventricular injection. Recently, the use of microbubbles and ultrasound have been shown to transiently disrupt the blood-brain barrier and allow the permeation of larger molecular drugs into the brain parenchyma. Microbubbles and ultrasound will be investigated as a way to disrupt the brain-cerebrospinal fluid barrier and increase the permeation of our gene delivery vehicles into the brain in the second half of this thesis.