Labeling and preliminary in vivo evaluation of the 5-HT7 receptor selective agonist [11C]E-55888

E-55888 has been identified as a selective serotonin 7 (5-HT7) receptor agonist. In this study, we describe the synthesis, radiolabeling and in vivo evaluation of [11C]E-55888 as a radioligand for positron emission tomography (PET) imaging. [11C]E-55888 was obtained by N-methylation of an appropriate precursor using [11C]MeOTf in acetone at 60 °C giving isolated quantities in the range of 1.7–2.4 GBq. Studies in Danish Landrace pigs demonstrated that [11C]E-55888 has good brain uptake, however, the distribution in the brain tissue was dominated by non-specific binding, as binding could neither be displaced by the structurally different 5-HT7 receptor ligand SB-269970 nor by self-block with unlabeled E-55888. Based on these data, [11C]E-55888 does not show promise as a PET radioligand for imaging the 5-HT7 receptor in vivo.

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