A Novel Class of Positive Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 1 Interact with a Site Distinct from That of Negative Allosteric Modulators

Abstract

We recently reported a novel class of compounds, represented by 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CD-PPB), that act as positive allosteric modulators (potentiators) of metabotropic glutamate receptor (mGluR) subtype 5. Studies of CDPPB analogs revealed that some compounds in this series serve also as positive allosteric modulators of mGluR1. Although CDPPB is selective for mGluR5 relative to other mGluR subtypes, several CDPPB analogs also showed 2.5-fold potentiation of glutamate-induced calcium transients in cells expressing mGluR1 at 10 M, with 4-nitro-N-(1,4-diphenyl-1H-pyrazol-5-yl)benzamide (VU-71) being selective for mGluR1. In previous studies, we found that two structural classes of mGluR5-selective allosteric potentiators, including CDPPB, share a common binding site with the allosteric mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine. Negative allosteric modulators of mGluR1, regardless of structural class, have been reported to bind to a common allosteric antagonist site on this receptor. However, neither the novel CDPPB analogs nor previously identified allosteric mGluR1 potentiators [e.g., (S)-2-(4-fluorophenyl)-1-(toluene-4-sulfonyl)pyrrolidine (Ro 67-7476), ethyl diphenylacetylcarbamate (Ro 01-6128), and butyl (9H-xanthene-9-carbonyl)carbamate (Ro 67-4853)] displaced the binding of [, a high-affinity radioligand for the allosteric antagonist site on mGluR1 at concentrations several orders of magnitude higher than those required to induce allosteric potentiation of mGluR1 responses. These data suggest that allosteric potentiators of mGluR1 act at a site that is distinct from that of allosteric antagonists of mGluR1. Sitedirected mutagenesis revealed that valine at position 757 in transmembrane V of mGluR1a is crucial for the activity of multiple classes of allosteric mGluR1 potentiators.In the mammalian central nervous system, glutamate is the major excitatory neurotransmitter, exerting its effects through activation of two major classes of glutamate receptors. These include cation channels, termed ionotropic glutamate receptors, and G protein-coupled receptors, termed metabotropic glutamate receptors (mGluRs) (Conn and Pin, 1997). The mGluRs are members of G protein-coupled receptor family 3, which consist of a large bilobed N-terminal extracellular domain containing the orthosteric agonist binding site, a seven-transmembrane domain, and a C-terminal intracellular domain (Gasparini et al

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

“…10A). However, F599I/mGluR1, the homologous mutation of F585I/mGluR5, eliminated the potentiation of mGluR1 responses by CPPHA but not a mGluR1 PAM characterized previously, Ro 67-7476 (Knoflach et al, 2001;Hemstapat et al, 2006) (Fig. 10B).…”

“…Radioactivity was counted using a Wallac 1450 Microbeta scintillation and luminescence counter (PerkinElmer Life and Analytical Sciences). Results Hemstapat et al (2006). Compounds were dissolved in dimethyl sulfoxide (DMSO) as stocks kept in Ϫ20°C.…”

Metabotropic Receptors for Glutamate and GABA

“…These data suggest that mGlu 1 possesses multiple allosteric binding sites, in addition to its orthosteric ligand-binding site. Similar to mGlu 1 , mGlu 5 PAMs have also been discovered, such as DFB, CPPHA, CDPPB, VU29, and ADX47273, with CDPPB also having some PAM activity at mGlu 1 (Conn et al, 2009b;Hemstapat et al, 2006).…”

“…As with nearly all orthosteric mGlu pharmacological agents there is the underlying issue of selectivity. DCG-IV and LY379268 are reference Group II mGlu agonists, BINA and LY487379 are highly potent PAMs and the recently discovered MNI series of compounds (MNI-135, MNI-136 and MNI-137) are potent negative allosteric modulators (Galici et al, 2006;Hemstapat et al, 2006;Johnson et al, 2003;Linden et al, 2005;Schweitzer et al, 2000). Despite the large array of pharmacological tools available for Group II mGlu receptors, there remains a paucity of ligands that selectively differentiate between mGlu 2 and mGlu 3 , which is due to the high degree of sequence homology between the two.…”

Structure and ligand recognition of class C GPCRs

“…For the mGlu5 receptor, most PAMs and NAMs share an overlapping binding pocket that is composed of TM3, 5, 6, and 7 [73] , except for a small number of distinct sites [74] . For the mGlu1 receptor, however, the PAMs and NAMs bind to distinct sites in the 7TM [64,65,[75][76][77] , except for a shared site that consists of Val757 in TM3 [65,77] . Removed from the conserved binding pocket, there is a distinct allosteric site located in TM1.…”