Technetium-99M Labeled SPECT Agents for Imaging B-amyloid in Alzheimer's Disease

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DESCRIPTION (provided by applicant): A noninvasive method for detection and quantification of ¿-amyloid plaques (A¿) in vivo would have wide utility for premortem diagnosis of Alzheimer's Disease (AD) and monitoring anti-amyloid therapy. While several PET-based agents are under development, an easily accessible, efficient, and highly specific technetium-99m-based SPECT imaging agent would be highly desirable. While exploring peptide-based agents for biomedical applications, we have discovered a small peptide that accommodates technetium-99m, the most commonly used isotope in medical imaging. Our lead 99mTc-peptide binds specifically to A¿ in a concentration-dependent and saturable manner. The agent remains nonmetabolized and a fluorescent analogue of the lead agent shows staining of A¿ plaques in brain sections of APPsw+/- transgenic mice compared with none in their age-matched WT controls. Importantly, 2 hr following tail-vein injection of the 99mTc-peptide, phosphorimaging of frozen brain sections of APPsw+/- transgenic mice and age-matched controls demonstrates a selective retention of radiotracer in APPsw+/- mice and only background binding in controls. We now propose to evaluate the impact of various chelating cores on the targeting properties of our lead agent to define structure-activity relationships in guiding the design of second-generation agents, and evaluate their potential as noninvasive diagnostic agents in biochemical systems, mouse models, and human tissues. We also propose to critically evaluate the potential of these 99m Tc-peptides to detect in vivo A¿ plaques in APPsw+/- transgenic mice versus control mice using our multiplexed multi-pinhole NanoSPECT/CT imaging system; perform complete pharmacokinetic analysis in animal models; and investigate mechanism(s) involved in uptake of our agent into the brain via multiple bioassays. These novel imaging agents may enable noninvasive SPECT imaging of A¿ in patients and assist analysis of the efficacy of new molecular-targeted therapies in AD. . Discovery of diagnostic agents capable of detecting early stages of Alzheimer's Disease (AD) would assist in disease management as well as aid in the evaluation of therapeutics under development to inhibit or reverse formation of A¿ plaques in patients. Towards this objective, the proposed project involves further characterization of a lead agent in diseased and control animal models and is based upon a strategy with potential for widespread deployment of a cost- efficient test for early diagnosis of AD.