Radioligand binding properties and pharmacological characterization of 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-298198), a high-affinity, selective, and noncompetitive antagonist of metabotropic glutamate receptor type 1.
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.
Kohara
Atsuyuki
A
Neuroscience Research, Pharmacology Laboratories, Institute for Drug Discovery Research, Yamanouchi Pharmaceutical Co., Ltd., 21 Miyukigaoka, Tsukuba, 305-8585, Japan.
Toya
Takashi
T
Tamura
Seiji
S
Watabiki
Tomonari
T
Nagakura
Yukinori
Y
Shitaka
Yoshitsugu
Y
Hayashibe
Satoshi
S
Kawabata
Shigeki
S
Okada
Masamichi
M
D000698:Analgesia; D000818:Animals; D001562:Benzimidazoles / Q000378:metabolism* / Q000494:pharmacology; D002531:Cerebellum / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D051379:Mice; D041681:NIH 3T3 Cells; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000032:analysis / Q000037:antagonists & inhibitors*; D013844:Thiazoles / Q000378:metabolism* / Q000494:pharmacology
C505455:6-amino-N-cyclohexyl-N,3-dimethylthiazolo(3,2-a)benzimidazole-2-carboxamide; D001562:Benzimidazoles; D018691:Excitatory Amino Acid Antagonists; D018094:Receptors, Metabotropic Glutamate; D013844:Thiazoles; C104077:metabotropic glutamate receptor type 1