N-{4-Chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}-2-hydroxybenzamide (CPPHA) Acts through a Novel Site as a Positive Allosteric Modulator of Group 1 Metabotropic Glutamate Receptors

Recent studies suggest that a novel positive allosteric modulator (PAM) of the metabotropic glutamate receptor (mGluRs), mGluR5, termed 4-nitro-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (VU-29), potentiates mGluR5 responses by actions at a site that is overlapping with the binding site of 2-methyl-6-(phenylethynyl)pyridine (MPEP), a previously identified negative allosteric modulator of this receptor. It is interesting that a structurally distinct PAM, N-{4-Chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}-2-hydroxybenzamide (CPPHA), does not to bind to the MPEP site. We now report that CPPHA potentiates mGluR5 responses by a mechanism that is distinct from that of VU-29. VU-29- and CPPHA-induced potentiation of mGluR5 responses are blocked by a neutral ligand at the MPEP allosteric site termed 5-methyl-2-(phenylethynyl)pyridine (5MPEP). However, increasing concentrations of 5MPEP induce parallel rightward shifts in the VU-29 concentration-response curve, whereas 5MPEP inhibits CPPHA potentiation in a noncompetitive manner. Consistent with this, a mutation (A809V/mGluR5) that reduces binding of ligands to the MPEP site eliminates the effect of VU-29 but has no effect on the response to CPPHA. On the other hand, a mutation (F585I/mGluRs) that eliminates the effect of CPPHA does not alter the response to VU-29. CPPHA is also a PAM at mGluR1. It is interesting that the corresponding mutation of F585I/mGluR5 in mGluR1 (F599I/mGluR1) eliminates CPPHA's effect without altering the potentiation of a known PAM of mGluR1, (S)-2-(4-fluorophenyl)-1-(toluene-4-sulfonyl)pyrrolidine (Ro 67-7476). Likewise, another mutation (V757L/mGluR1) that abolishes potentiation of Ro 67-7476 has no effect on CPPHA. Finally, CPPHA does not displace binding of a radioligand for the mGluR1 allosteric antagonist characterized previously. Together, these data suggest that CPPHA acts at a novel allosteric site on both mGluR1 and -5 to potentiate responses to activation of these receptors.

[1]  F. Gasparini,et al.  The Non-competitive Antagonists 2-Methyl-6-(phenylethynyl)pyridine and 7-Hydroxyiminocyclopropan[b]chromen-1a-carboxylic Acid Ethyl Ester Interact with Overlapping Binding Pockets in the Transmembrane Region of Group I Metabotropic Glutamate Receptors* , 2000, The Journal of Biological Chemistry.

[2]  P. Conn,et al.  A close structural analog of MPEP acts as a neutral allosteric site ligand on metabotropic glutamate receptor subtype 5 and blocks the effects of multiple allosteric modulators , 2005 .

[3]  Bita Moghaddam,et al.  Targeting metabotropic glutamate receptors for treatment of the cognitive symptoms of schizophrenia , 2004, Psychopharmacology.

[4]  Andreas Mühlemann,et al.  Determination of key amino acids implicated in the actions of allosteric modulation by 3,3'-difluorobenzaldazine on rat mGlu5 receptors. , 2006, European journal of pharmacology.

[5]  P. Conn,et al.  Metabotropic Glutamate Receptor 5-Induced Phosphorylation of Extracellular Signal-Regulated Kinase in Astrocytes Depends on Transactivation of the Epidermal Growth Factor Receptor , 2001, The Journal of Neuroscience.

[6]  Xavier Langlois,et al.  [3H]R214127: a novel high-affinity radioligand for the mGlu1 receptor reveals a common binding site shared by multiple allosteric antagonists. , 2003, Molecular pharmacology.

[7]  P. Conn,et al.  Biphenyl-indanone A, a Positive Allosteric Modulator of the Metabotropic Glutamate Receptor Subtype 2, Has Antipsychotic- and Anxiolytic-Like Effects in Mice , 2006, Journal of Pharmacology and Experimental Therapeutics.

[8]  P. Conn,et al.  Direct and indirect modulation of the N-methyl D-aspartate receptor. , 2002, Current drug targets. CNS and neurological disorders.

[9]  F. Gasparini,et al.  CPCCOEt, a noncompetitive metabotropic glutamate receptor 1 antagonist, inhibits receptor signaling without affecting glutamate binding. , 1999, Molecular pharmacology.

[10]  R. Neubig,et al.  Agonist-directed trafficking of porcine alpha(2A)-adrenergic receptor signaling in Chinese hamster ovary cells: l-isoproterenol selectively activates G(s). , 2000, The Journal of pharmacology and experimental therapeutics.

[11]  J. Pin,et al.  Interaction of Novel Positive Allosteric Modulators of Metabotropic Glutamate Receptor 5 with the Negative Allosteric Antagonist Site Is Required for Potentiation of Receptor Responses , 2007, Molecular Pharmacology.

[12]  T. Kenakin,et al.  G Protein-Coupled Receptor Allosterism and Complexing , 2002, Pharmacological Reviews.

[13]  Y. Smith,et al.  Activation of Group I Metabotropic Glutamate Receptors Produces a Direct Excitation and Disinhibition of GABAergic Projection Neurons in the Substantia Nigra Pars Reticulata , 2001, The Journal of Neuroscience.

[14]  P. Conn,et al.  Distinct physiological roles of the Gq‐coupled metabotropic glutamate receptors co‐expressed in the same neuronal populations , 2002, Journal of cellular physiology.

[15]  P. Conn,et al.  Allosteric Potentiators of Metabotropic Glutamate Receptor Subtype 5 Have Differential Effects on Different Signaling Pathways in Cortical Astrocytes , 2005, Journal of Pharmacology and Experimental Therapeutics.

[16]  P. Conn,et al.  Differential regulation of metabotropic glutamate receptor 5‐mediated phosphoinositide hydrolysis and extracellular signal‐regulated kinase responses by protein kinase C in cultured astrocytes , 2002, Journal of neurochemistry.

[17]  S. Nickolls,et al.  Functional coupling of the human dopamine D2 receptor with Gαi1, Gαi2, Gαi3 and Gαo G proteins: evidence for agonist regulation of G protein selectivity , 2003 .

[18]  F. Gasparini,et al.  SIB-1757 and SIB-1893: selective, noncompetitive antagonists of metabotropic glutamate receptor type 5. , 1999, The Journal of pharmacology and experimental therapeutics.

[19]  Roland Heckendorn,et al.  2-Methyl-6-(phenylethynyl)-pyridine (MPEP), a potent, selective and systemically active mGlu5 receptor antagonist , 1999, Neuropharmacology.

[20]  P. Leff,et al.  Effector pathway-dependent relative efficacy at serotonin type 2A and 2C receptors: evidence for agonist-directed trafficking of receptor stimulus. , 1998, Molecular pharmacology.

[21]  R. Baldwin,et al.  Substituent effects of N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamides on positive allosteric modulation of the metabotropic glutamate-5 receptor in rat cortical astrocytes. , 2006, Journal of medicinal chemistry.

[22]  C. Lindsley,et al.  A Novel Selective Positive Allosteric Modulator of Metabotropic Glutamate Receptor Subtype 5 Has in Vivo Activity and Antipsychotic-Like Effects in Rat Behavioral Models , 2005, Journal of Pharmacology and Experimental Therapeutics.

[23]  P Jeffrey Conn,et al.  A Novel Selective Allosteric Modulator Potentiates the Activity of Native Metabotropic Glutamate Receptor Subtype 5 in Rat Forebrain , 2004, Journal of Pharmacology and Experimental Therapeutics.

[24]  J. Pin,et al.  Pharmacology and functions of metabotropic glutamate receptors. , 1997, Annual review of pharmacology and toxicology.

[25]  J. Kemp,et al.  Positive allosteric modulators of metabotropic glutamate 1 receptor: Characterization, mechanism of action, and binding site , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[26]  R. Anwyl.  Metabotropic glutamate receptors: electrophysiological properties and role in plasticity , 1999, Brain Research Reviews.

[27]  P. Conn,et al.  The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) potentiates PCP-induced cognitive deficits in rats , 2004, Psychopharmacology.

[28]  P. Malherbe,et al.  Mutational analysis and molecular modeling of the binding pocket of the metabotropic glutamate 5 receptor negative modulator 2-methyl-6-(phenylethynyl)-pyridine. , 2003, Molecular pharmacology.

[29]  Francine Acher,et al.  Heptahelical domain of metabotropic glutamate receptor 5 behaves like rhodopsin-like receptors , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[30]  Thomas Knöpfel,et al.  Book Review: Metabotropic Glutamate Receptors: Electrical and Chemical Signaling Properties , 2002, The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry.

[31]  F. Spinella,et al.  Opposite influence of the metabotropic glutamate receptor subtypes mGlu3 and ‐5 on astrocyte proliferation in culture , 1997, Glia.

[32]  P Jeffrey Conn,et al.  A family of highly selective allosteric modulators of the metabotropic glutamate receptor subtype 5. , 2003, Molecular pharmacology.

[33]  P. Conn,et al.  A Novel Class of Positive Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 1 Interact with a Site Distinct from That of Negative Allosteric Modulators , 2006, Molecular Pharmacology.

[34]  D. Jane,et al.  Pharmacological agents acting at subtypes of metabotropic glutamate receptors , 1999, Neuropharmacology.

[35]  P. Jeffrey Conn,et al.  A Close Structural Analog of 2-Methyl-6-(phenylethynyl)-pyridine Acts as a Neutral Allosteric Site Ligand on Metabotropic Glutamate Receptor Subtype 5 and Blocks the Effects of Multiple Allosteric Modulators , 2005, Molecular Pharmacology.