CENTRAL SEROTONERGIC S2 BINDING IN PAPIO-ANUBIS MEASURED INVIVO WITH N-OMEGA-[F-18]FLUOROETHYLKETANSERIN AND PET

N-omega-[18F]Fluoroethylketanserin ([18F]FEK), an 18F-labelled analogue of the serotonin S2 antagonist ketanserin, was evaluated for use with positron emission tomography (PET). PET imaging of a baboon brain following injection of [18F]FEK indicated that the fluorinated ligand rapidly localized in vivo within S2 receptor-rich tissues (frontal cortex/cerebellum radioactivity ratio = 2.5 after 15 min), and selective localization was retained for as long as 3 h post injection. Pretreatment with unlabeled ketanserin (15 mg/kg, i.v.) 1 h prior to [18F]FEK completely abolished selective localization of the radiotracer, whereas regional cerebral blood flow, cerebral blood volume, and the free fraction of [18F]FEK in arterial blood were unaltered. [18F]FEK has several advantages compared to previously used PET radiopharmaceuticals, and may be an excellent radioligand for non-invasive evaluation of S2 binding in vivo.