Development of N-[ 11C]methylamino 4-hydroxy-2(1 H)-quinolone derivatives as PET radioligands for the glycine-binding site of NMDA receptors

• Published in: Bioorganic & medicinal chemistry 2009-08, Vol.17 (15), p.5665-5675
• Main Authors: Fuchigami, Takeshi, Haradahira, Terushi, Fujimoto, Noriko, Nojiri, Yumiko, Mukai, Takahiro, Yamamoto, Fumihiko, Okauchi, Takashi, Maeda, Jun, Suzuki, Kazutoshi, Suhara, Tetsuya, Yamaguchi, Hiroshi, Ogawa, Mikako, Magata, Yasuhiro, Maeda, Minoru
• Format: Article
• Language: English
• Subjects: 4-Hydroxy-2(1 H)-quinolone; Animals; Autoradiography; Binding Sites; Biological and medical sciences; Brain - metabolism; Contrast media. Radiopharmaceuticals; Glutamatergic system (aspartate and other excitatory aminoacids); Glycine - metabolism; Glycine-binding site; Medical sciences; Mice; Molecular Structure; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; NMDA receptor; PET; Pharmacology. Drug treatments; Positron-Emission Tomography - methods; Protein Binding; Quinolones - blood; Quinolones - chemistry; Quinolones - metabolism; Quinolones - pharmacokinetics; Radiochemistry; Radiopharmaceuticals - blood; Radiopharmaceuticals - chemistry; Radiopharmaceuticals - metabolism; Radiopharmaceuticals - pharmacokinetics; Receptors, N-Methyl-D-Aspartate - analysis; Receptors, N-Methyl-D-Aspartate - metabolism; Structure-Activity Relationship
• ISSN: 0968-0896; 1464-3391
• DOI: 10.1016/j.bmc.2009.06.014

A series of amino 4-hydroxy-2-quinolone derivatives have been synthesized and evaluated in vitro and in vivo as potential PET tracers for imaging of the glycine site of the NMDA receptors. In this study, we synthesized and evaluated several amino 4-hydroxy-2(1 H)-quinolone (4HQ) derivatives as new PET radioligand candidates for the glycine site of the NMDA receptors. Among these ligands, we discovered that 7-chloro-4-hydroxy-3-{3-(4-methylaminobenzyl) phenyl}-2-(1 H)-quinolone ( 12) and 5-ethyl-7-chloro-4-hydroxy-3-(3-methylaminophenyl)-2(1 H)-quinolone ( 32) have high affinity for the glycine site ( K i values; 11.7 nM for 12 and 11.8 nM for 32). In vitro autoradiography experiments indicated that [ 11C] 12 and [ 11C] 32 showed high specific binding in the brain slices, which were strongly inhibited by both glycine agonists and antagonists. In vivo brain uptake of these 11C-labeled 4HQs were examined in normal mice. Cerebellum to blood ratio of accumulation, of both [ 11C] 12 and [ 11C] 32 at 30 min were 0.058, which were slightly higher than those of cerebrum to blood ratio (0.043 and 0.042, respectively). These results indicated that [ 11C] 12 and [ 11C] 32 have poor blood brain barrier permeability. Although the plasma protein-binding ratio of [ 11C] 32 was much lower than methoxy analogs (71% vs 94–98%, respectively), [ 11C] 32 still binds with plasma protein strongly. It is conjectured that still acidic moiety and high affinity with plasma protein of [ 11C] 32 may prevent in vivo brain uptake. In conclusion, [ 11C] 12 and [ 11C] 32 are unsuitable for imaging cerebral NMDA receptors.