Abstract
Metabotropic glutamate receptor subtype 5 (mGluR5) is a potential drug target in neurological and psychiatric disorders, and subtype-selective allosteric modulators have attracted much attention as potential drug candidates. In this study, the binding sites of three novel 2-methyl-6-(phenylethynyl)pyridine (MPEP)-derived negative allosteric modulators, 2-, 3-, and 4-BisPEB, have been characterized. 2-, 3-, and 4-BisPEB are 1,3-bis(pyridinylethynyl)-benzenes and differ only by the position of the nitrogen atoms in the pyridine rings. Despite their high structural similarity, 2-BisPEB [1,3-bis(pyridin-2-ylethynyl)-benzene, nitrogen atoms in ortho positions], with an IC50 value in the nanomolar range, is significantly more potent than the 3- and 4-pyridyl analogs. Mutational analysis, directed by a previously published mGluR5 homology model, was used to determine key residues for the ligand-receptor interactions that may explain the potency differences of 2-, 3-, and 4-BisPEB. Residues Ile651, Pro655, Tyr659, Asn747, Trp785, Phe788, Tyr792, Ser809, and Ala810 were found to have critical roles for the activity of one or more of the three BisPEBs and the reference compound MPEP. The mutagenesis data suggest that the higher potency of 2-BisPEB is due to hydrogen bonding to Ser809 because the S809A mutation made 2-BisPEB equipotent to 3- and 4-BisPEB (IC50, 1–2.5 μM). The potency of MPEP was also greatly affected by S809A (52-fold), suggesting that a Ser809-mediated hydrogen bond is also a key interaction between MPEP and mGluR5. Potential binding modes of 2-, 3-, and 4-BisPEB obtained by molecular docking to the mGluR5 homology model provide a structural context for the reported major mutational effects.
Footnotes
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the Drug Research Academy, the A. P. Møller Foundation for the Advancement of Medical Sciences, Brødrene Hartmanns Fond, the Danish Council for Independent Research/Medical Sciences, the Carlsberg Foundation, the Lundbeck Foundation, and H. Lundbeck A/S.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- mGluR
- metabotropic glutamate receptor
- GPCR
- G protein-coupled receptor
- mGluR5
- metabotropic glutamate receptor subtype 5
- 7TMD
- 7-transmembrane domain
- MPEP
- 2-methyl-6-(phenylethynyl)pyridine
- NAM
- negative allosteric modulator
- BisPEB
- 1,3-bis(pyridinylethynyl)benzene
- BHK cells
- baby hamster kidney
- ELISA
- enzyme-linked immunosorbent assay
- ANOVA
- analysis of variance
- TMH
- transmembrane helix.
- Received March 31, 2012.
- Accepted August 16, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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