Pharmacological characterization of N,N-dimethyl-2-(2-amino-4-methylphenyl thio)benzylamine as a ligand of the serotonin transporter with high affinity and selectivity.
Serotonin transporter has a key-role in regulation of serotoninergic function, and is involved in numerous neurodegenerative and psychiatric disorders. To obtain an efficient radioactive ligand allowing the study of this transporter in vitro and in vivo, we synthesized a new diphenyl sulfide derivative, N,N-dimethyl-2-(2-amino-4-methylphenylthio)benzylamine or MADAM. We present here extensive pharmacological characterization of this compound. [3H]MADAM bound to serotonin transporters with a very high affinity in vitro on rat cortical membranes, at least 2 times better than the most commonly used radioactive probes (Kd, 60 pM; Bmax, 543 fmol/mg of protein). Competition studies showed few inhibitory effect of nisoxetine (Ki = 270 nM), no inhibitory effect of desipramine or 1-[2-(diphenylmethoxy) ethyl]-4-(3-phenylpropyl)piperazine (GBR 12935) (Ki >1000 nM), and strong effect of paroxetine (Ki = 0.32 nM) and citalopram (Ki = 1.57 nM). Therefore, MADAM has around 1000-fold better selectivity for the serotonin transporter than for other transporters. Autoradiographic studies both on rat and postmortem human brain slices demonstrated that the distribution of [3H]MADAM parallels the localization of serotonin transporters and is prevented by known inhibitors of them. The high affinity and selectivity of [3H]MADAM for the serotonin transporter show that it is very valuable for studies using in vitro approaches. The high selectivity and low nonspecific binding of [3H]MADAM on the postmortem human brain, together with preliminary in vivo results with [11C]MADAM, is a new argument for future use of this ligand in in vivo studies of the distribution, pharmacology, and pathophysiology of the serotonin transporter in the human brain with positron emission tomography.
Chalon
Sylvie
S
Institut National de la Santé et de la Recherche Médicale U316, Laboratoire de Biophysique médicale et pharmaceutique, Université François Rabelais, Tours, France. chalon@univ-tours.fr
Tarkiainen
Jari
J
Garreau
Lucette
L
Hall
Hakan
H
Emond
Patrick
P
Vercouillie
Johnny
J
Farde
Lars
L
Dasse
Philippe
P
Varnas
Katarina
K
Besnard
Jean-Claude
JC
Halldin
Christer
C
Guilloteau
Denis
D
D000818:Animals; D001345:Autoradiography; D001596:Benzylamines / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000187:drug effects* / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D006801:Humans; D007553:Isotope Labeling; D008024:Ligands; D008297:Male; D008562:Membrane Glycoproteins / Q000187:drug effects* / Q000378:metabolism; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D050486:Serotonin Plasma Membrane Transport Proteins; D014018:Tissue Distribution
D001596:Benzylamines; D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; C470437:N,N-dimethyl-2-(2-amino-4-methylphenylthio)benzylamine; D009419:Nerve Tissue Proteins; D019275:Radiopharmaceuticals; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat