Alzheimer's disease (AD) is a devastating and progressive disease without a cure. Neuroinflammation is now recognized as a key early event in the development of AD. Aberrant neuroinflammatory response activates immune cells that can increase oxidative stress, and oxidative stress can directly damage neurons and axons, cause demyelination, and break down the blood-brain barrier (BBB). Thus, damaging neuroinflammation is emerging to be a potential treatment target. A non-invasive imaging method to detect and assess early damaging neuroinflammation would be able to detect disease before irreversible damage occurs, and enable monitoring of disease progression and treatment response of current and emerging therapies. However, current clinical imaging technologies do not distinguish between damaging and reparative inflammation. The goal of this proposal is to develop an imaging method to detect and monitor oxidative stress and consequent damaging neuroinflammation in AD. We hypothesize that such an imaging technology will allow early detection of damaging neuroinflammation in AD patients, enable timely treatment decisions, predict progression, and allow non-invasive monitoring of treatment response, particularly for emerging anti-inflammatory therapies. We have found that myeloperoxidase (MPO) is highly expressed by pro-inflammatory cells but not by reparative cells. MPO is a key mediator of oxidative inflammation and has been found to be associated with AD. An increased number of MPO immunoreactive cells have been found in the brains of early AD patients, but not in the brains of normal patients. We have developed an activatable MPO-PET imaging agent (18F-EH301) that can cross the BBB to enable imaging of MPO activity in AD. In Phase 1 we will establish that 18F-EH301 can specifically detect oxidative stress in the brain in the 5XFAD mouse AD model. In Phase 2 we will use 18F- EH301 PET imaging to a) longitudinally track the evolution of oxidative stress in the brain in different AD models, b) compare and correlate with other AD imaging agents: 18F-FDG (glucose metabolism), 18F-florbetapir (β-amyloid), 18F-flortaucipir (tau), 11C-PBR28 (translocator protein), and c) monitor treatment changes using an MPO inhibitor (verdiperstat) with and without donezepil. Finally, to enable clinical translation of this technology, we will synthesize 18F-EH301 under cGMP conditions and perform GLP toxicology studies in rats. This proposal addresses the NIA priority of development and validation of innovative diagnostic tests and novel biomarkers to identify or predict age-related decline, dysfunction, diseases, and conditions, including Alzheimer's disease and AD-related dementias. The output of this proposal will be a translational MPO- targeting PET imaging method with demonstrated efficacy to report damaging neuroinflammation in AD for diagnosis, prognosis, and treatment monitoring. This project will directly enable first-in-man clinical trials to test MPO imaging ...