A Novel Family of Negative and Positive Allosteric Modulators of NMDA Receptors

Abstract

The N-methyl-D-aspartate (NMDA) receptor family regulates various central nervous system functions, such as synaptic plasticity. However, hypo-or hyperactivation of NMDA receptors is critically involved in many neurological and psychiatric conditions, such as pain, stroke, epilepsy, neurodegeneration, schizophrenia, and depression. Consequently, subtype-selective positive and negative modulators of NMDA receptor function have many potential therapeutic applications not addressed by currently available compounds. We have identified allosteric modulators with several novel patterns of NMDA receptor subtype selectivity that have a novel mechanism of action. In a series of carboxylated naphthalene and phenanthrene derivatives, compounds were identified that selectively potentiate responses at GluN1/GluN2A [e.g., 9-iodophenanthrene-3-carboxylic acid (UBP512)]; GluN1/GluN2A and GluN1/GluN2B [9-cyclopropylphenanthrene-3-carboxylic acid (UBP710)]; GluN1/GluN2D [3,5-dihydroxynaphthalene-2-carboxylic acid (UBP551)]; or GluN1/GluN2C and GluN1/GluN2D receptors [6-, 7-, 8-, and 9-nitro isomers of naphth[1,2-c][1,2,5]oxadiazole-5-sulfonic acid (NSC339614)] and have no effect or inhibit responses at the other NMDA receptors. Selective inhibition was also observed; UBP512 inhibits only GluN1/GluN2C and GluN1/GluN2D receptors, whereas 6-bromo-2-oxo-2H-chromene-3-carboxylic acid (UBP608) inhibits GluN1/ GluN2A receptors with a 23-fold selectivity compared with GluN1/ GluN2D receptors. The actions of these compounds were not competitive with the agonists L-glutamate or glycine and were not voltage-dependent. Whereas the N-terminal regulatory domain was not necessary for activity of either potentiators or inhibitors, segment 2 of the agonist ligand-binding domain was important for potentiating activity, whereas subtype-specific inhibitory activity was dependent upon segment 1. In terms of chemical structure, activity profile, and mechanism of action, these modulators represent a new class of pharmacological agents for the study of NMDA receptor subtype function and provide novel lead compounds for a variety of neurological disorders.

Inhibition of GluN2A-Containing N-Methyl-d-Aspartate Receptors by 2-Naphthoic Acid

“…1). This IC 50 value is larger than previously measured in Xenopus oocytes (Costa et al, 2010), where 0.1 mM NPA produced 30% inhibition. We attribute this discrepancy to differences in experimental conditions because these previous measurements were done at pH 5 7.4, where 2A receptors are tonically ∼50% inhibited (Traynelis and Cull-Candy, 1990) and in the absence of chelators, when trace zinc and magnesium ions further inhibit 2A currents (Nowak et al, 1984;Paoletti et al, 1997).…”

“…Importantly, the compounds in this family have distinct patterns of selectivity at NMDA receptors containing different N2 subunits. Experiments with NMDA receptors containing N2 subunit chimeras suggested that the effect may be mediated by residues located in the LBD, at the interface between the N1 and N2 subunits (Costa et al, 2010), implying that this class of modulators may have a mode of action that is separate from other characterized NMDA receptor allosteric modulators and thus currently unknown. Their ability to discriminate between A/B and C/D subtypes makes NPA derivatives attractive both as possible therapeutics and research tools.…”

“…The adverse effects have been attributed to the lack of selectivity of firstgeneration inhibitors, thus pointing to the need for isoform-or function-selective antagonists (Popescu, 2005;Wyllie et al, 2013). Recently, 2-naphthoic acid (NPA) has been identified as the parent compound of a new family of NMDA receptor allosteric modulators (Costa et al, 2010). Importantly, the compounds in this family have distinct patterns of selectivity at NMDA receptors containing different N2 subunits.…”

A Multifaceted GABAAReceptor Modulator: Functional Properties and Mechanism of Action of the Sedative-Hypnotic and Recreational Drug Methaqualone (Quaalude)

“…We will refrain from further speculations about this, however, not having investigated the basis for the lack of modulation at this subtype. Analogously to the notion of methaqualone exerting its multifaceted pharmacology through a uniform site in the GABA A Rs, some benzodiazepine-site ligands display functional selectivity at a 1,2,3,5 bg 2 receptors (Dawson et al, 2006;de Lucas et al, 2015), and allosteric modulators of other receptor types have also been shown to mediate subtype-specific modulation (Mathiesen et al, 2003;Marlo et al, 2009;Costa et al, 2010).…”

Structural basis of subunit selectivity for competitive NMDA receptor antagonists with preference for GluN2A over GluN2B subunits

“…Considerable progress has been made in the development of subunit-selective allosteric modulators (7)(8)(9)(10)(11)(12)(13), but the development of subtype-selective competitive NMDA receptor antagonists has been less successful. The competitive glutamate-site antagonist NVP-AAM077 (hereafter NVP) was originally reported to have 100-fold preference for GluN1/2A over GluN1/2B (14).…”