Abstract
Phenotypic studies of mice lacking metabotropic glutamate receptor subtype 7 (mGluR7) suggest that antagonists of this receptor may be promising for the treatment of central nervous system disorders such as anxiety and depression. Suzuki et al. (J Pharmacol Exp Ther 323:147–156, 2007) recently reported the in vitro characterization of a novel mGluR7 antagonist called 6-(4-methoxyphenyl)-5-methyl-3-(4-pyridinyl)-isoxazolo[ 4,5-c]pyridin-4(5H)-one (MMPIP), which noncompetitively inhibited the activity of orthosteric and allosteric agonists at mGluR7. We describe that MMPIP acts as a noncompetitive antagonist in calcium mobilization assays in cells coexpressing mGluR7 and the promiscuous G protein Gα15. Assessment of the activity of a small library of MMPIP-derived compounds using this assay reveals that, despite similar potencies, compounds exhibit differences in negative cooperativity for agonist-mediated calcium mobilization. Examination of the inhibitory activity of MMPIP and analogs using endogenous Gi/o-coupled assay readouts indicates that the pharmacology of these ligands seems to be context-dependent, and MMPIP exhibits differences in negative cooperativity in certain cellular backgrounds. Electrophysiological studies reveal that, in contrast to the orthosteric antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxyclycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495), MMPIP is unable to block agonist-mediated responses at the Schaffer collateral-CA1 synapse, a location at which neurotransmission has been shown to be modulated by mGluR7 activity. Thus, MMPIP and related compounds differentially inhibit coupling of mGluR7 in different cellular backgrounds and may not antagonize the coupling of this receptor to native Gi/o signaling pathways in all cellular contexts. The pharmacology of this compound represents a striking example of the potential for context-dependent blockade of receptor responses by negative allosteric modulators.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grants NS053536, NS031373, NS048334] and the Michael J. Fox Foundation.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.058768
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ABBREVIATIONS:
- GPCR
- G protein-coupled receptor
- GIRK
- G protein-regulated inwardly rectifying potassium channel
- mGluR
- metabotropic glutamate receptor
- HEK
- human embryonic kidney
- DMSO
- dimethyl sulfoxide
- l-AP4
- l-(+)-amino-4-phosphonobutyric acid
- LY341495
- (2S)-2-amino-2-[(1S,2S)-2-carboxyclycloprop-1-yl]-3-(xanth-9-yl) propanoic acid
- MMPIP
- 6-(4-methoxyphenyl)-5-methyl-3-(4-pyridinyl)-isoxazolo[ 4,5-c]pyridin-4(5H)-one
- AMN082
- N,N′-dibenzhydrylethane-1,2-diamine dihydrochloride
- PAM
- positive allosteric modulator
- NAM
- negative allosteric modulator
- CNS
- central nervous system
- DMEM
- Dulbecco's modified Eagle's medium
- ACSF
- artificial cerebrospinal fluid
- BHK
- baby hamster kidney
- fEPSP
- field excitatory postsynaptic potential
- PICK1
- protein interacting with C kinase 1
- SC-CA1
- Schaffer collateral-CA1
- VUSC001
- 6-(4-methoxyphenyl)-5-methyl-3-phenylisoxazolo[4,5-c]pyrdin-4(5H)-one
- VUSC027
- 6-(3-methoxyphenyl)-5-methyl-3-phenylisoxazolo[4,5-c]pyridine-4(5H)-one.
- Received June 22, 2009.
- Accepted December 18, 2009.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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