Metabolism and autoradiographic evaluation of [18F]FE@CIT: a Comparison with [123I]β-CIT and [123I]FP-CIT

Fluorine-18 Radiolabeled PET Tracers for Imaging Monoamine Transporters: Dopamine, Serotonin, and Norepinephrine

This review focuses on the development of fluorine-18 radiolabeled PET tracers for imaging the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET). All successful DAT PET tracers reported to date are members of the 3β-phenyl tropane class and are synthesized from cocaine. Currently available carbon-11 SERT PET tracers come from both the diphenylsulfide and 3β-phenyl nortropane class, but so far only the nortropanes have found success with fluorine-18 derivatives. NET imaging has so far employed carbon-11 and fluorine-18 derivatives of reboxetine but due to defluorination of the fluorine-18 derivatives further research is still necessary.

Comparison of 2beta-carbomethoxy-3beta-(4-[18F]fluorophenyl)tropane and N-(3-[18F]fluoropropyl)-2beta-carbomethoxy-3beta-(4-fluorophenyl)nortropane, tracers for imaging dopamine transporter in rat

PURPOSE

This study compares 2beta-carbomethoxy-3beta-(4-[(18)F]fluorophenyl)tropane ([(18)F]beta-CFT) and N-(3-[(18)F]fluoropropyl)-2beta-carbomethoxy-3beta-(4-fluorophenyl)nortropane ([(18)F]beta-CFT-FP) as radiotracers for imaging the dopamine transporter (DAT) in rat.

PROCEDURES

Biodistribution, specificity and selectivity of the radiotracers were studied ex vivo in rats pre-treated with specific antagonists for DAT, serotonin transporter (SERT) and noradrenalin transporter (NET) and in control rats. Positron emission tomography (PET) studies were performed using an HRRT scanner. Radiolabelled metabolites were analyzed with thin-layer chromatography.

RESULTS

[(18)F]beta-CFT showed slow kinetics with a maximum striatum/cerebellum uptake ratio of 9.2 at 120 min. [(18)F]beta-CFT-FP showed fast kinetics with a maximum ratio of 3.1 at 5 min. Both tracers bound to DAT. [(18)F]beta-CFT also bound to NET. [(18)F]beta-CFT was more resistant to metabolism than [(18)F]beta-CFT-FP.

CONCLUSIONS

Structural modifications of [(18)F]beta-CFT significantly changed its biological properties, as shown by [(18)F]beta-CFT-FP. [(18)F]beta-CFT is a suitable tracer for both preclinical and human PET studies, but [(18)F]beta-CFT-FP is less suitable as a PET tracer.