Focused ultrasound for neuronal applications
The development of treatments for central nervous system disorders has been limited because of difficulties in translating positive preclinical findings in small animal models to clinical studies. One major limit in preclinical studies is that it is difficult to directly correlate biomarker expression to cognitive/behavioral results in longitudinal studies. Animals are generally sacrificed to evaluate biomarker expression. Therefore, there is a need for a morphological, functional, and cellular/molecular neuroimaging technique capable of longitudinal assessment of brain tissue in vivo, non-invasively, and in real time. The goal of our research program is to develop a preclinical neuroimaging system based on ultrasound and photoacoustic (USPA) imaging and using gas microbubble-assisted focused ultrasound (FUS) disruption of the blood brain barrier (BBB) and delivery of targeted contrast agents. We believe that this system would improve the ability of neuroscientists to study the underlying mechanisms of diseases and to develop and evaluate potential treatments. The underlying hypothesis of this project is that non-invasive, high-resolution, high-sensitivity, in vivo imaging of the brain is possible and will provide marked advantages over existing imaging tools available to neuroscientists. USPA imaging, in combination with FUS and molecular probes, is of interest because it is non-invasive, cost-effective, and could be portable while also capable of imaging the whole rodent brain in vivo. The main goal of this exploratory R21 application is to develop and test a laboratory prototype of the USPA neuroimaging system and address known concerns in order to proceed with broader development efforts in the future. We will develop an FUS-mediated USPA imaging system to non-invasively visualize protein biomarkers in vivo in preclinical models of Alzheimer’s disease (AD). AD is a progressive neurodegenerative disease, which causes significant morbidity and mortality, characterized by pathogenic protein plaques composed of β-amyloid. In order to visualize plaques, β-amyloid-targeted gold nanorods (AuNRs) will be developed. AuNRs have been shown to be strong optical absorbers and good photoacoustic contrast agents that can be tuned to absorb in the NIR region. Specifically, anti-β-amyloid antibodies will be conjugated to AuNRs and tested in AD tissue samples as well as via surface plasmon resonance assays. After confirming targeting of the rods, an FUS positioning system will be developed for targeting the hippocampus of mice. The ability of this system to target the hippocampus will be confirmed with Evans Blue leakage as well as delivery of PEGylated AuNRs (visualized with USPA imaging). The distribution of AuNRs and clearance mechanisms and timeline will be assessed acutely and longitudinally. Finally, targeted AuNRs will be delivered to the hippocampus of AD and wild type mice using FUS and visualized with USPA in vivo acutely and longitudinally. The ability to visualize β-amyloid in the hippocampus with USPA in vivo longitudinally would prove the utility of our system. If successful, these studies will demonstrate that USPA imaging is a valuable neuroimaging tool that will help to translate the result of preclinical studies and facilitate the clinical success of disease diagnosis and therapy.