Novel 18F-Labeled Benzoxazole Derivatives as Potential Positron Emission Tomography Probes for Imaging of Cerebral β-Amyloid Plaques in Alzheimer's Disease

Two radiofluoro-pegylated phenylbenzoxazole derivatives, 4-(5-(2-(2-(2-[F-18]fluoroethoxy)ethoxy)ethoxy)benzo-[d]oxazol-2-yl)-N-methylaniline ([F-18]24) and 4-(5-(2-(2-[F-18]fluoroethoxy)ethoxy)ethoxy)benzo[d]oxazol-2-yl)-N,N-dimethylaniline ([F-18]32), were synthesized and evaluated as probes for imaging cerebral beta-amyloid (A beta) plaques in living brain tissue by PET. [F-18]24 and [F-18]32 displayed high affinity for A beta(1-42) aggregates (K-1 = 9.3 and 3.9 nM, respectively). In vitro autoradiography with sections of post-mortem AD brain and transgenic mouse brain confirmed the affinity of these tracers. Initial high uptake into and rapid washout from the brain in normal mice were observed. [F-18]24 also displayed excellent binding to A beta plaques in ex vivo autoradiographic experiments with Tg2576 mice. Furthermore, small-animal PET studies demonstrated significant differences in the clearance profile after the administration of [F-18]24 between Tg2576 and wild-type mice. The results suggest [F-18]24 to be a useful PET agent for detecting A beta plaques in the living human brain.