Synthesis and radiopharmacological characterization of 2β-carbo-2′-[18F]fluoroethoxy-3β-(4-bromo-phenyl)tropane ([18F]MCL-322) as a PET radiotracer for imaging the dopamine transporter (DAT)
摘要:
The fluoroalkyl-containing tropane derivative 2 beta-carbo-2'-fluoroethoxy-3 beta-(4-bromo-phenyl)tropane (MCL-322) is a highly potent and moderately selective ligand for the dopamine transporter (DAT). The compound was labeled with the short-lived positron emitter F-18 in a single step by nucleophilic displacement of the corresponding tosylate precursor MCL-323 with no-carrieradded [F-18]fluoride. The positron emission tomography (PET) radiotracer 20-carbo-2'-[F-18]fluoroethoxy-3p-(4-bromo-phenyl)tropane [F-18]MCL-322 was obtained in decay-corrected radiochemical yields of 30-40% at a specific radioactivity of 1.6-2.4 Ci/mu mol (60-90 GBq/mu mol) at the end-of-synthesis (EOS). Small animal PET, ex vivo and in vivo biodistribution experiments in rats demonstrated a high uptake in the striatum (3.2% ID/g) 5 min after injection, which increased to 4.2% ID/g after 60 min. The uptake in the cerebellum was 1.8% ID/g and 0.6% ID/g after 5 min and 60 min post-injection, respectively. Specific binding to DAT of [F-18]MCL-322 was confirmed by blocking experiments using the high affinity DAT ligand GBR 12909. The radiopharmacological characterization was completed with metabolite and autoradiographic studies confirming the selective uptake of [F-18]MCL-322 in the striatum. It is concluded that the simple single-step radiosynthesis of [F-18]MCL-322 and the promising radiopharmacological data make [F-18]MCL-322 an attractive candidate for the further development of a PET radiotracer potentially suitable for clinical DAT imaging in the human brain. (c) 2007 Elsevier Ltd. All rights reserved.