Deuterated 18F-9-O-hexadeutero-3-fluoropropoxyl-(+)-dihydrotetrabenazine (D6-FP-(+)-DTBZ): A vesicular monoamine transporter 2 (VMAT2) imaging agent

Abstract

IntroductionVesicular monoamine transporters 2 (VMAT2) in the brain serve as transporter for packaging monoamine in vesicles for normal CNS neurotransmission. Several VMAT2 imaging agents, [11C]-(+)-DTBZ, dihydrotetrabenazine and [18F]FP-(+)-DTBZ (9-O-fluoropropyl-(+)-dihydro tetrabenazine, a.k.a. [18F]AV-133), are useful for studying the changes in brain function related to monoamine transmission by in vivo imaging. Deuterated analogs have been reported targeting VMAT2 binding sites. MethodsA novel deuterated [18F]9-O-hexaduterofluoropropyl-(+)-dihydrotetrabenazine, [18F]D6-FP-(+)-DTBZ, [18F]1, was prepared as a VMAT2 imaging agent. This 18F agent which targeted VMAT2 was evaluated by in vitro binding, in vivo biodistribution and microPET imaging studies in rodents. ResultsThe one step radiolabeling reaction led to the desired [18F]D6-FP-(+)-DTBZ, [18F]1, which showed excellent binding affinity to VMAT2 (Ki=0.32±0.07nM) comparable to that of FP-(+)-DTBZ (Ki=0.33±0.02nM) using [18F]FP-(+)-DTBZ and rat striatum membrane homogenates. In vivo biodistribution in normal rats showed that 1, exhibited excellent brain uptake and comparable high ratio of striatum to cerebellum (target/background) ratio at 1h after injection (ratio of 6.05±0.43 vs 5.66±0.72 for [18F]FP-(+)-DTBZ vs [18F]1, respectively). MicroPET imaging studies in rats further confirm that the striatum with high VMAT2 concentration was clearly delineated in normal rat brain after iv injection of [18F]1. We observed minor changes of metabolism in rat plasma between these two agents; however, the changes showed little effect on regional brain uptake and retention. ConclusionsThe results reported here lend support for using [18F]D6-FP-(+)-DTBZ, [18F]1, as in vivo PET imaging agent for VMAT2 binding in the brain.