[18F]fluoroethoxy-benzovesamicol, a PET radiotracer for the vesicular acetylcholine transporter and cholinergic synapses.

Loss of cholinergic transmission in the cortex and hippocampus is a characteristic feature of Alzheimer's disease, and visualization of functional cholinergic synapses in the brain with PET could be a useful method for studying this degenerative condition in living humans. We investigated [18F]fluoroethoxybenzovesamicol, (-)-[18F] FEOBV,(-)-(2R,3R)-trans-2-hydroxy-3-(4-phenylpiperidino)-5-(2-[18F ]fluoroethoxy)-1,2,3,4-tetralin, a high affinity positron emitting ligand for the vesicular acetylcholine transporter, as a potential in vivo cholinergic synapse mapping agent. Rodent biodistribution, dosimetry, stereospecificity of biological effects, pharmacologic blocking studies, in vivo rodent brain autoradiography and metabolites were examined. (-)-[18F]FEOBV brain uptake following intravenous injection was robust, with 2.65% dose/brain in mice at 5 min, and the regional localization matched the known distributions of presynaptic cholinergic markers at later times. Both the cholinergic localization and curare-like effects of FEOBV were associated with the "(-)"-enantiomer exclusively. (-)-[18F]FEOBV regional brain distribution in rodents was changed little by pretreatment with haloperidol, (+)-3-PPP, or E-2020, indicating FEOBV, unlike other vesamicol analogs, did not interact in vivo with dopamine or sigma receptor systems. Autoradiography of rat brain 3 h following i.v. injection of (-)-[18F]FEOBV showed high localization in brain areas rich in presynaptic cholinergic elements. Metabolic defluorination in rodents was modest, and analysis of brain tissue following tracer administration found FEOBV as the only extractable radioactive species. (-)-[18F]FEOBV dosimetry calculated from rat data estimate 10 mCi doses can be given to humans. These studies show FEOBV maps cholinergic areas with high specificity in vivo, and may provide a noninvasive means to safely and accurately gauge the functional integrity of cholinergic synapses in man using PET.