title: 5-Chloro-2-(2'-((dimethylamino)methyl)-4'-iodophenylthio)benzenamine: a new serotonin transporter ligand.
abstract: Two novel ligands with 4' substitution on the Phenyl Ring B of biphenylthiol, 5-chloro-2-(2'-((dimethylamino)methyl)-4'-iodophenylthio)benzenamine (7) and 2-(2'-((dimethylamino)methyl)-4'-methoxyphenylthio)-5-iodobenzenamine (8), were prepared and tested as potential serotonin transporter (SERT) imaging agents. The new ligands displayed extremely high binding affinities to SERT (K(i)=0.22+/-0.09 and 0.11+/-0.04 nM, respectively), with very low binding affinities to dopamine and norepinephrine transporters (K(i)>1000 nM). The corresponding [(125)I]7 and [(125)I]8 were successfully prepared from tri-n-butyltin derivatives. They showed good brain uptakes and prolonged retention after intravenous injection in rats (brain uptake was 1.77% and 0.98% dose/g for [(125)I]7, and 0.92% and 0.29% dose/g for [(125)I]8, at 2 and 120 min, respectively). Significantly, [(125)I]7 showed excellent uptake and prolonged retention in the hypothalamus, where SERT concentration was highest. The hypothalamus/cerebellum (HY/CB) ratios (target/background ratios) were 4.24, 7.10, 8.24 and 12.6 at 2, 4, 6 and 12 h, respectively. The HY/CB ratios for [(125)I]8 were 3.97, 5.57 and 5.06 at 1, 2 and 4 h, respectively. Adding the 4'-iodo group to the Phenyl Ring B of Compound (7) appeared to reduce the rate of clearance from the brain, and kinetics favored uptake and retention in the hypothalamus. The localization of [(125)I]7 in the hypothalamus region in the rat brain could be blocked by pretreatment with (+)McN5652, escitalopram and ADAM (2), which are all selective SERT ligands (at 2 mg/kg iv, 5 min pretreatment). Ex vivo autoradiograms of rat brain sections (at 4 h after intravenous injection of [(125)I]7) showed intense labeling in regions of the brain known to have high SERT density. The excellent selective uptake and retention in the hypothalamus region suggest that [(123)I]7 is a potential lead compound for developing new imaging agents targeting SERT-binding sites with single-photon emission computed tomography.
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Oya
authors.forename: Seok-Rye
authors.initials: SR
authors.lastname: Choi
authors.forename: Mei-Ping
authors.initials: MP
authors.lastname: Kung
authors.forename: Hank F
authors.initials: HF
authors.lastname: Kung
mesh_terms: D000814:Aniline Compounds / Q000493:pharmacokinetics*; D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D008297:Male; D008657:Metabolic Clearance Rate; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism*; D013440:Sulfides / Q000493:pharmacokinetics*; D014018:Tissue Distribution
chemical_list: C521163:5-chloro-2-(2'-((dimethylamino)methyl)-4'-iodophenylthio)benzenamine; D000814:Aniline Compounds; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D050486:Serotonin Plasma Membrane Transport Proteins; D013440:Sulfides