Improved Delivery of Gene Therapies to the Central Nervous System by Focused Ultrasound-Mediated Disruption of the Blood-Brain Barrier

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Project Summary: A major challenge faced by all gene therapies directed to the central nervous system is delivering the therapy across the blood-brain barrier (BBB) in a way that achieves adequate central exposure while minimizing toxicity in non-targeted tissues. The two most common routes of administration for delivering adeno-associated viral (AAV) vectors, the only FDA-approved gene transfer platform for neurological applications, suffer from complimentary limitations. Intravenous (IV) injection can achieve widespread distribution throughout the brain but only at low concentration levels, while intraparenchymal (IPa) injections supply a high concentration of therapy but only near the site of injection. As most neurological disorders manifest in multiple brain regions, successful gene therapy treatments will require an improved approach to AAV delivery that can achieve high therapy concentration and large volume coverage. To address this critical bottleneck, we aim to develop and validate delivery strategies using the technology of focused ultrasound (FUS)-mediated disruption of the BBB to significantly improve the concentration and brain coverage of AAV-packaged gene therapies. In this project we will investigate the application of delivering an AAV-packaged micro-RNA therapy targeting suppression of mutant Huntingtin, the gene implicated in Huntington’s disease (HD). Our preliminary work demonstrates that FUS-BBB opening enhances the delivery of IV-injected AAV1 and AAV9 vectors to targeted brain regions in wild-type and HD model mice. We additionally have experience using our human clinical FUS system to achieve large-volume BBB disruption in rats, monkeys and humans. Building off this preliminary data, Aim 1 will determine the optimal FUS parameters and AAV dose for maximizing AAV concentration at the FUS-targeted site in HD model mice. The safety profile of each treatment will be characterized in terms of markers of neuroinflammation and signs of trauma-like damage to tissue. To maximize brain coverage, we will characterize the safety profile and AAV delivery efficacy as a function of BBB opening volume in HD model mice. Aim 2 will incorporate the information gained in Aim 1 to devise an optimal treatment strategy that balances high AAV concentration, large volume coverage and safety. We will assess the safety and therapeutic efficacy of delivering an AAV-packaged microRNA to HD model mice at 1-, 3- , 6- and 12-month time points in terms of mHTT lowering and functional markers of disease progression. In Aim 3, all of the mice data will be used to devise a treatment strategy for AAV delivery in rhesus macaque monkeys. A safety and biodistribution study will be carried out in these non-human primates using our human clinical FUS system. If successful, the strategies developed here would enable AAV delivery to the brain with a more favorable safety and efficacy profile than existing alternatives and unlock the clinical promise of these transformative therapies.