Exploring the Metabolism of (+)-[F]Flubatine in Vitro and in Vivo: LC-MS/MS Aided Identification of Radiometabolites in a Clinical PET Study.

Both (+)-[F]flubatine and its enantiomer (-)-[F]flubatine are radioligands for the neuroimaging of α4β2 nicotinic acetylcholine receptors (nAChRs) by positron emission tomography (PET). In a clinical study in patients with early Alzheimer's disease, (+)-[F]flubatine ((+)-[F]) was examined regarding its metabolic fate, in particular by identification of degradation products detected in plasma and urine. The investigations included an in vivo study of (+)-flubatine ((+)-) in pigs and structural elucidation of formed metabolites by LC-MS/MS. Incubations of (+)- and (+)-[F] with human liver microsomes were performed to generate in vitro metabolites, as well as radiometabolites, which enabled an assignment of their structures by comparison of LC-MS/MS and radio-HPLC data. Plasma and urine samples taken after administration of (+)-[F] in humans were examined by radio-HPLC and, on the basis of results obtained in vitro and in vivo, formed radiometabolites were identified.