Appel, Lieuwe2; Bergström, Mats3; Buus Lassen, Jørgen4; Roland Långström, Bengt5
1 Clinical Physiology and Nuclear Medicine, Department of Clinical Research, Det Sundhedsvidenskabelige Fakultet, SDU2 PET Centre, Department of Medical Imaging, Uppsala University Hospital, S-751 85 Uppsala, Sweden; Section of Nuclear Medicine and PET, Department of Radiology, Oncology, and Radiation Sciences, Uppsala University, Uppsala, Sweden. Electronic address: firstname.lastname@example.org Uppsala University4 NeuroSearch A/S, Pederstrupvej 93, DK-2750 Ballerup, Denmark.5 Clinical Physiology and Nuclear Medicine, Department of Clinical Research, Det Sundhedsvidenskabelige Fakultet, SDU
dopamine transporter occupancy as measured by PET
Tesofensine (TE) is a novel triple monoamine re-uptake inhibitor inducing a potent inhibition of the re-uptake process in the synaptic cleft of the neurotransmitters dopamine, norepinephrine, and serotonin. In recent preclinical and clinical evaluations TE showed a robust anti-obesity effect, but the specific mechanism of this triple monoamine re-uptake inhibitor still needs to be further elucidated. This positron emission tomography (PET) study, using [¹¹C]βCIT-FE, aimed to assess the degree of the dopamine transporter (DAT) occupancy, at constant TE plasma levels, following different oral, multiple doses of TE during totally 8-12 days. In addition, the relationships between DAT occupancy and TE plasma concentrations, or doses, were investigated to enable assessment of DAT occupancies in subsequent clinical trials. The results demonstrated that TE induced a dose-dependent blockade of DAT following multiple doses of 0.125-1 mg TE at anticipated steady-state conditions. The mean striatal DAT occupancy varied dose-dependently between 18% and 77%. A sigmoid E(max) model well described the relationship between striatal DAT occupancy and TE plasma concentrations or doses. It was estimated that the maximum achievable DAT occupancy was about 80% and that half of this effect was accomplished by approximately 0.25 mg TE and a plasma drug concentration of 4 ng/ml. The results indicated an important mechanism of action of TE on DAT. Further, these results suggest that the previously reported dose-dependent weight loss, in TE treated subjects, was in part mediated by an up-regulation of dopaminergic pathways due to enhanced amounts of synaptic dopamine after blockade of DAT.
European Neuropsychopharmacology, 2014, Vol 24, Issue 2, p. 251-61