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.