DASB -in vitro binding characteristics on human recombinant monoamine transporters with regard to its potential as positron emission tomography (PET) tracer.
The efficiency of serotonergic signal transduction is controlled by the density of serotonegic synapses and by the activity of the serotonin transporter (SERT), which selectively clears the synaptic cleft of the neurotransmitter. SERT is located in axons, where it is concentrated in varicosities and terminal boutons and thus is an exquisite marker for serotonergic synapses. This finding has been taken advantage of for neuroimaging serotonergic synaptic contact sites. Previous positron emission tomography (PET) and single photon emission computed tomography (SPECT) studies were often carried out using radioligands that bind with high affinity to SERTs in the brainstem but also exhibit high affinity for dopamine and norepinephrine transporters and therefore did not allow quantification of serotonergic innervations in brain regions also containing dopaminergic or noradrenergic terminals. In order to visualize SERT availability more selectively, in recent years new tracers have been developed, one of which is [11C]DASB (N,N-dimethyl-2-2-amino-4-cyanophenylthiobenzylamine). Here, we have performed a detailed pharmacological characterization of unlabelled as well as radioactive DASB on recombinant human monoamine transporter proteins. Our results show that DASB selectively binds to SERT with high affinity (KD = 3.5 nm) to a site distinct from the serotonin (5-HT) recognition/translocation site. 5-HT inhibits DASB binding to SERT with more than one order of magnitude lower affinity than that of DASB binding (IC50 = 82.4 nm). These findings suggest DASB to be a highly selective PET tracer to visualize the density of serotonergic synapses in human brain.
Biochemical Laboratory, Central Institute of Mental Health, Mannheim, Germany.
René
R
Hummerich
Gerald
G
Reischl
Walter
W
Ehrlichmann
Hans-Jürgen
HJ
Machulla
Andreas
A
Heinz
Patrick
P
Schloss
D018759:Adrenergic Uptake Inhibitors / Q000493:pharmacokinetics; D001596:Benzylamines / Q000737:chemistry / Q000493:pharmacokinetics*; D001667:Binding, Competitive; D002247:Carbon Isotopes / Q000493:pharmacokinetics; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D015283:Citalopram / Q000493:pharmacokinetics; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian; D006801:Humans; D007099:Imipramine / Q000493:pharmacokinetics; D020128:Inhibitory Concentration 50; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012044:Regression Analysis; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors / Q000493:pharmacokinetics; D013997:Time Factors; D014055:Tomography, Emission-Computed / Q000379:methods*; D014316:Tritium / Q000493:pharmacokinetics
D018759:Adrenergic Uptake Inhibitors; D001596:Benzylamines; D002247:Carbon Isotopes; D002352:Carrier Proteins; D015283:Citalopram; D004298:Dopamine; D007099:Imipramine; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009638:Norepinephrine; D011994:Recombinant Proteins; D012701:Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; D014316:Tritium; C420885:N,N-dimethyl-2-(2-amino-4-cyanophenylthio)benzylamine; C493230:SLC6A4 protein, human