Radioligands for PET imaging of the serotonin transporter

Dysfunctions of serotonergic neuro- transmission – in particular of the serotonin transporter (SERT) – are correlated with neuropsychiatric disorders such as depression, obsessive-compulsive disorders and anxiety. Studies of serotonin transporter function and density using PET can provide an important contribution to understand corresponding functional relationships.As an important milestone for such studies the fluorine-18 labelled PET tracer (+)- [18F]FMe-McN5652 has been developed and characterised in preclinical as well as clinical studies, in cooperation with the Turku PET Centre, Finland and the Department of Nuclear Medicine, University of Leipzig. All results obtained so far lead to a successful clinical applicability (Hesse et al. 2012).

Representative ex vivo digital autoradiogram (right) of a coronal rat brain section at 60 min p.i. of (+)-[18F]FMe-McN5652. Uptake of radioactivity is evident in substantia nigra, a brain region of high SERT density (red highest, blue lowest uptake). Ex vivo digital autoradiogram of a coronal rat brain section at 60 min p.i. of (+)-[18F]FMe-McN5652

Despite overall very positive evaluation results of (+)-[18F]FMe-McN5652, the radioligand has the inherent disadvantage of a relatively high non-specific binding. This leads to our developments, based on new structure classes and pharmaceuticals, such as indolylalkyl-tetrahydroisoquinolines. In-house and in close cooperation with the Hadassah University in Jerusalem, various halogen-substituted derivatives were synthesised and characterised in radioligand binding experiments regarding their SERT affinity and selectivity versus other targets. Recently, the two 11C- and 18F-labelled compounds [11C]FMI and [18F]CFPI, respectively, have been investigated in vitro and in vivo. Revealing a high non-specific binding in porcine brain and mice in vivo, these radioligands are unfortunately not suitable for SERT-selective PET imaging.

SERT radioligands
Two new SERT radioligands (left) and in vitro autoradiographs (right) obtained after incubation of sagittal rat brain slices with [18F]CFPI without (A) or with coincubation with highly SERT affine and selective Citalopram (B).


  • Department of Nuclear Medicine, Universität Leipzig, Germany

  • Turku University, Finland

  • Hebrew University Jerusalem, Israel


  • Hesse, S.; Brust, P.; Mäding, P.; Becker, G.-A.; Seese, A.; Patt, M.; Sorger, D.; Zessin, J.; Sacher, J.; Lobsien, D.; Habermann, B.; Meyer. PM.; Füchtner, F.; Luthardt, J.; Bresch, A.; Steinbach, J. & Sabri O. Imaging of the brain serotonin transporters (SERT) with the new fluorine-18 labelled fluoromethyl-McN5652 and PET in humans. Eur. J. Nucl. Med. 2012, 39, 1001-1011.

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Financial Support by

  • Deutsche Forschungsgemeinschaft - DFG
  • German Federal Ministry for Education and Research (German-Israeli cooperation in neuroscience)