Abstract
Metabotropic glutamate receptor type 1 (mGluR1) is thought to play important roles in the neurotransmission and pathogenesis of several neurological disorders. Here, we describe the radioligand binding properties and pharmacological effects of a newly synthesized, high-affinity, selective, and noncompetitive mGluR1 antagonist, 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-298198). YM-298198 inhibited glutamate-induced inositol phosphate production in mGluR1-NIH3T3 cells with an IC50 of 16 ± 5.8 nM in a noncompetitive manner. Its radiolabeled form, [3H]YM-298198, bound to mGluR1-NIH3T3 cell membranes with a KD of 32 ± 8.5 nM and a Bmax of 2297 ± 291 fmol/mg protein. In ligand displacement experiments using rat cerebellum membrane, an existing noncompetitive mGluR1 antagonist 7-(hydroxyimino)cyclo-propa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) competitively displaced [3H]YM-298198 binding, although glutamate and other mGluR1 ligands acting on a glutamate site failed to inhibit [3H]YM-298198 binding, suggesting that YM-298198 binds to CPCCOEt (allosteric) binding sites but not to glutamate (agonist) binding sites. Specificity was demonstrated for mGluR1 over mGluR subtypes 2 to 7, ionotropic glutamate receptors, and other receptor, transporter, and ion channel targets. In in vivo experiments, orally administered YM-298198 showed a significant analgesic effect in streptozotocin-induced hyperalgesic mice at doses (30 mg/kg) that did not cause Rotarod performance impairment, indicating that it is also useful even for in vivo experiments. In conclusion, YM-298198 is a newly synthesized, high-affinity, selective, and noncompetitive antagonist of mGluR1 that will be a useful pharmacological tool due to its highly active properties in vitro and in vivo. Its radiolabeled form [3H]YM-298198 will also be a valuable tool for future investigation of the mGluR1.
Footnotes
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doi:10.1124/jpet.105.087171.
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ABBREVIATIONS: mGluR, metabotropic glutamate receptor; CPCCOEt, 7-(hydroxyimino)cyclo-propa[b]chromen-1a-carboxylate ethyl ester; BAY 36-7620, (3aS,6aS)-6a-naphtalan-2-ylmethyl-5-methyliden-hexahydro-cyclopenta[c]furan-1-on; R214127, 1-(3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-2-phenyl-1-ethanone; YM-298198, 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide; YM-193167, 6-{[(2-methoxyethyl)amino]methyl}-N-methyl-N-neopentylthiazolo[3,2-a]benzoimidazole-2-carboxamide dihydrochloride; (RS)-AMPA, (R,S)-a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; l-AP4, l-(+)-2-amino-4-phosphonobutylic acid; (1S,3R)-ACPD, (1S,3R)-1-aminocyclopentane-trans-1,3-dicarboxylic acid; (S)-4C3HPG, (S)-4-carboxy-3-hydroxyphenylglycine; l-CCG-I, (2S,1′S,2′S)-2-(carboxycyclopropyl)glycine; (S)-3,5-DHPG, (S)-3,5-dihydroxyphenylglycine; GYKI 52466, 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-[5H-2,3]-benzodiazepine; (+)-MK-801, dizocilpine; NMDA, N-methyl-d-aspartic acid; HEK, human embryonic kidney; IP, inositol phosphate; PBS, phosphate-buffered saline.
- Received March 31, 2005.
- Accepted June 14, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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