Date of Award
5-6-2022
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Alzheimer’s disease (AD) is one of the most important causes of dementia in the elderly. With no effective therapies to cure or inhibit AD symptom progression, AD severely decreases patients’ quality of life and creates an enormous burden on the health care system and society. Currently, clinical AD diagnosis is based on cognition and the relative impact of impairments on daily activities. However, multiple neurodegenerative and vascular pathologies can coexist and produce cognitive and behavioral symptoms which could overlap with each other. This makes it difficult to accurately identify pathology based solely on clinical symptoms. Imaging methods including structural MRI which detects brain atrophy, and PET for assessing brain amyloid-beta (Aβ), tau, and glucose metabolism have been developed to aide AD diagnosis. However, PET images have limited resolution and expose patients to radiation. Structural MRI lacks specificity and does not allow visualization of the histological markers for AD, Aβ or Tau. There is an unmet need for developing MRI molecular imaging methods which allow direct, non-invasive, high-resolution detection and measurement of specific AD markers and many other pathologies in the brains of living patients. This dissertation developed imaging methods and mathematical models to aid the development of a novel family of brain MRI molecular contrast agents. This family of contrast agents has several modules, including an ultra-small iron oxide nanoparticle (IONP) core for T1 MRI contrast, a polyethylene glycol- based coating to prevent nonspecific fouling of the iron oxide core, a single-domain antibody fragment from camelid (VHH, also referred to as Nanobody) which targets the transferrin receptor (TfR) on brain endothelial cells for blood brain barrier transcytosis, another VHH that targets the specific pathology of interest (in this case the AD hallmark Aβ in brain parenchyma), and a near-infrared (NIR) fluorescence dye for tracking in mice. An efficient NIR imaging method was established to monitor VHH and VHH conjugated IONP kinetics in mice using a hybrid approach: kinetics in blood were assessed by direct sampling, and kinetics in kidney, liver, and brain were assessed by serial in vivo NIR imaging. Based on the hybrid approach, a five-compartment pharmacokinetic model (PK) has been constructed. This PK model fits the NIR imaging data well and could be used to understand and predict contrast agent PK during the development phase. After understanding the biodistribution and clearance of the VHHs and IONPs in vivo, a VHH screening system based on neurotensin was developed to rapidly test for blood brain barrier transcytosis. This VHH screening system identified a VHH with good blood-brain barrier crossing ability and the target engagement in brain of this VHH was further analyzed using a mouse model of AD-related Aβ pathology. The establishment of the feasibility of these methods lays a foundation for future development of the brain MRI molecular contrast agents. In the future, the family of molecular contrast agents could be used to assess many other neurological disorders and provide a direct assessment of target engagement in response to candidate therapeutics.
Language
English (en)
Chair
Dennis Barbour
Committee Members
David Brody