SIB-1757 and SIB-1893: Selective, Noncompetitive Antagonists of Metabotropic Glutamate Receptor Type 5

• Published in: The Journal of pharmacology and experimental therapeutics 1999-07, Vol.290 (1), p.170-181
• Main Authors: Varney, M A, Cosford, N D, Jachec, C, Rao, S P, Sacaan, A, Lin, F F, Bleicher, L, Santori, E M, Flor, P J, Allgeier, H, Gasparini, F, Kuhn, R, Hess, S D, Veliçelebi, G, Johnson, E C
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Binding, Competitive; Brain - cytology; Brain - drug effects; Brain - metabolism; Calcium - metabolism; Cells, Cultured; CHO Cells; Cricetinae; Excitatory Amino Acid Antagonists - chemistry; Excitatory Amino Acid Antagonists - pharmacology; Humans; In Vitro Techniques; Inositol Phosphates - metabolism; Methoxyhydroxyphenylglycol - analogs & derivatives; Methoxyhydroxyphenylglycol - antagonists & inhibitors; Neurons - drug effects; Phenazopyridine - analogs & derivatives; Phenazopyridine - chemistry; Phenazopyridine - pharmacology; Pyridines - chemistry; Pyridines - pharmacology; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate - antagonists & inhibitors; Recombinant Proteins - metabolism; Structure-Activity Relationship
• ISSN: 0022-3565; 1521-0103

Cell lines expressing the human metabotropic glutamate receptor subtype 5a (hmGluR5a) and hmGluR1b were used as targets in an automated high-throughput screening (HTS) system that measures changes in intracellular Ca 2+ ([Ca 2+ ] i ) using fluorescence detection. This functional screen was used to identify the mGluR5-selective antagonist, SIB-1757 [6-methyl-2-(phenylazo)-3-pyridinol], which inhibited the glutamate-induced [Ca 2+ ] i responses at hmGluR5 with an IC 50 of 0.37 μM compared with an IC 50 of >100 μM at hmGluR1. Schild analysis demonstrated a noncompetitive mechanism of inhibition. Pharmacophore mapping was used to identify an additional compound, SIB-1893 [( E )-2-methyl-6-(2-phenylethenyl)pyridine], which was also shown to block glutamate-induced increases in [Ca 2+ ] i at hmGluR5 with an IC 50 of 0.29 μM compared with an IC 50 of >100 μM at hmGluR1. SIB-1757 and SIB-1893 showed little or no activity when tested for agonist and antagonist activity at the other recombinant human mGluR subtypes, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, and N -methyl- d -aspartate receptors. In rat neonatal brain slices, SIB-1757 and SIB-1893 inhibited ( S )-3,5-dihydroxyphenylglycine (DHPG)-evoked inositol phosphate accumulation in hippocampus and striatum by 60% to 80%, with a potency similar to that observed on recombinant mGluR5. However, in the cerebellum, a brain region with low mGluR5 expression, SIB-1757 failed to inhibit DHPG-evoked inositol phosphate accumulation. In cultured rat cortical neurons, SIB-1757 and SIB-1893 largely inhibited DHPG-evoked [Ca 2+ ] i signals, revealing a population of neurons that were less sensitive to SIB-1757 and SIB-1893. This is the first description of highly selective, noncompetitive mGluR5 antagonists. These compounds will be useful tools in evaluating the role of mGluR5 in normal physiology and in animal models of disease.