Evaluation of [C-11]RTI-121 as a selective radioligand for PET studies of the dopamine transporter

The cocaine analogue RTI-121 (3 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid isopropyl ester), when labeled with carbon-11, was evaluated in rats as a potential PET ligand for the dopamine transporter. The compound gave in vivo striatum:cerebellum ratios that were similar to those obtained with the related ligand [C-11]RTI-55 (2 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid methyl ester) but showed a much greater selectivity for the dopamine compared with the 5-HT uptake site, The results indicate that [C-11]RTI-121 could be used in preference to [C-11]RTI-55 in man. Experimentally, [C-11]RTI-121 has potential in the quantification of dopamine terminal function in rat models of disease, using a combination of autoradiography, postmortem sampling, and in vivo tomography.