Synthesis, Biological Evaluation and Preclinical Study of a Novel 99Mtc-Peptide: A Targeting Probe of Amyloid-Β Plaques As a Possible Diagnostic Agent for Alzheimer's Disease.

With respect to the main role of amyloid-beta (A beta) plaques as one of the pathological hallmarks in the brain of Alzheimer's patients, the development of new imaging probes for targeted detection of A beta plaques has attracted considerable interests. In this study, a novel cyclopentadienyl tricarbonyl Technetium-99 m (Tc-99m) agent with peptide scaffold, Tc-99m-Cp-GABA-D-(FPLIAIMA)-NH2, for binding to the A beta plaques was designed and successfully synthesized using the Fmoc solid-phase peptide synthesis method. This radiopeptide revealed a good affinity for A beta 42 aggregations (K-d = 20 mu M) in binding affinity study and this result was confirmed by binding to A beta plaques in brain sections of human Alzheimer's disease (AD) and rat models using in vitro autoradiography, fluorescent staining, and planar scintigraphy. Biodistribution studies of radiopeptide in AD and normal rats demonstrated a moderate initial brain uptake about 0.38 and 0.35% (ID/g) 2 min post-injection, respectively. Whereas, AD rats showed a notable retention time in the brain (0.23% ID/g at 30 min) in comparison with fast clearance in normal rat brains. Normal rats following treatment with cyclosporine A as a p-glycoprotein inhibitor showed a significant increase in the radiopeptide brain accumulation compared to non-treated ones. There was a good correlation between data gathered from single-photon emission computed tomography/computed tomography (SPECT/CT) imaging and biodistribution studies. Therefore, these findings showed that this novel radiopeptide could be a potential SPECT imaging agent for early detection of A beta plaques in the brain of patients with AD.C