Synthesis and evaluation of [11C]Cimbi-806 as a potential PET ligand for 5-HT7 receptor imaging

2-(2′,6′-Dimethoxy-[1,1′-biphenyl]-3-yl)-N,N-dimethylethanamine has been identified as a potent ligand for the serotonin 7 (5-HT7) receptor. In this study, we describe the synthesis, radiolabeling and in vivo evaluation of [11C]2-(2′,6′-dimethoxy-[1,1′-biphenyl]-3-yl)-N,N-dimethylethanamine ([11C]Cimbi-806) as a radioligand for imaging brain 5-HT7 receptors with positron emission tomography (PET). Precursor and reference compound was synthesized and subsequent 11C-labelling with [11C]methyltriflate produced [11C]Cimbi-806 in specific activities ranging from 50 to 300 GBq/μmol. Following intravenous injection, brain uptake and distribution of [11C]Cimbi-806 was assessed with PET in Danish Landrace pigs. The time–activity curves revealed high brain uptake in thalamic and striatal regions (SUV ∼2.5) and kinetic modeling resulted in distribution volumes (VT) ranging from 6 mL/cm3 in the cerebellum to 12 mL/cm3 in the thalamus. Pretreatment with the 5-HT7 receptor antagonist SB-269970 did not result in any significant changes in [11C]Cimbi-806 binding in any of the analyzed regions. Despite the high brain uptake and relevant distribution pattern, the absence of appropriate in vivo blocking with a 5-HT7 receptor selective compounds renders the conclusion that [11C]Cimbi-806 is not an appropriate PET radioligand for imaging the 5-HT7 receptor in vivo.

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