N-Aryl Piperazine Metabotropic Glutamate Receptor 5 Positive Allosteric Modulators Possess Efficacy in Preclinical Models of NMDA Hypofunction and Cognitive Enhancement

Abstract

Impaired transmission through glutamatergic circuits has been postulated to play a role in the underlying pathophysiology of schizophrenia. Furthermore, inhibition of the N-methyl-D-aspartate (NMDA) subtype of ionotropic glutamate receptors (NMDAR) induces a syndrome that recapitulates many of the symptoms observed in patients with schizophrenia. Selective activation of metabotropic glutamate receptor subtype 5 (mGlu 5 ) may provide a novel therapeutic approach for treatment of symptoms associated with schizophrenia through facilitation of transmission through central glutamatergic circuits. Here, we describe the characterization of two novel N-aryl piperazine mGlu 5 positive allosteric modulators (PAMs): 2-(4-(2-(benzyloxy)acetyl)piperazin-1-yl)benzonitrile (VU0364289) and 1-(4-(2,4-difluorophenyl)piperazin-1-yl)-2-((4-fluorobenzyl)oxy)ethanone (DPFE). VU0364289 and DPFE induced robust leftward shifts in the glutamate concentration-response curves for Ca 21 mobilization and extracellular signal-regulated kinases 1 and 2 phosphorylation. Both PAMs displayed micromolar affinity for the common mGlu 5 allosteric binding site and high selectivity for mGlu 5 . VU0364289 and DPFE possessed suitable pharmacokinetic properties for dosing in vivo and produced robust dose-related effects in reversing amphetamine-induced hyperlocomotion, a preclinical model predictive of antipsychotic-like activity. In addition, DPFE enhanced acquisition of contextual fear conditioning in rats and reversed behavioral deficits in a mouse model of NMDAR hypofunction. In contrast, DPFE had no effect on reversing apomorphine-induced disruptions of prepulse inhibition of the acoustic startle reflex. These mGlu 5 PAMs also increased monoamine levels in the prefrontal cortex, enhanced performance in a hippocampal-mediated memory task, and elicited changes in electroencephalogram dynamics commensurate with procognitive effects. Collectively, these data support and extend the role for the development of novel mGlu 5 PAMs for the treatment of psychosis and cognitive deficits observed in individuals with schizophrenia.

Molecular Insights into Metabotropic Glutamate Receptor Allosteric Modulation

“…Furthermore, the therapeutic relevance of biased pharmacology has yet to be realized; however, it is tempting to speculate that unappreciated bias may contribute to differential efficacy of allosteric modulators in behavioral models. For example, 1-(4-(2,4-difluorophenyl)piperazin-1-yl)-2-((4-fluorobenzyl)oxy)ethanone, an mGlu 5 PAM of glutamate, requires far lower doses for efficacy in cognitive models compared with reversing amphetamine-induced hyperlocomotion, a model for antipsychotic efficacy (Gregory et al, 2013a). Moreover, there is the potential that biased modulation may be exploited to develop therapeutics that are not only subtype selective but also pathway selective, modulating receptor responses that yield therapeutic effects and avoiding those that give rise to on-target adverse effects.…”

“…A third advantage of allosteric modulators is the potential to maintain spatial and temporal aspects of receptor activation, i.e., modulation will only occur when and where the orthosteric agonist is present. However, it is important to note that allosteric ligands may possess intrinsic efficacy (either positive or inverse) in addition to, or exclusive of, cooperativity with orthosteric ligands (Annoura et al, 1996;Litschig et al, 1999;Niswender et al, 2008;Duvoisin et al, 2010;Gregory et al, 2012Gregory et al, , 2013aNoetzel et al, 2012b;Lavreysen et al, 2013;Rook et al, 2013). The first allosteric modulator discovered for the mGlu family was CPCCOEt [7-(hydroxyimino) (Annoura et al, 1996;Litschig et al, 1999).…”

Activation of the mGlu5 Receptor for the Treatment of Schizophrenia and Cognitive-Deficit-Associated Disorders

“…, effects of 5MPEP on concentration response curves, and the impact of point mutations A809V and F585I on potentiation (decrease and no effect, respectively) [21,94]. Potentiation of glutamate-induced pERK1/2 and analysis of the foldshift data using an operational model of allosterism revealed higher affinity estimates for 72 and 74 (K B ¼ 513, 135 nM) and lower cooperativity (β ¼ 1.4,1.3) compared to effects on calcium mobilization.…”

“…10), a compound originally disclosed in an AstraZeneca patent application [93]. Functional rat mGlu 5 [94]. Partial agonism of mGlu 5 was observed at 100 μM (72) and 30 μM (74), and effects on potentiation of other mGlu receptors were not detected up to 10 μM.…”

Perirhinal Cortex mGlu5 Receptor Activation Reduces Relapse to Methamphetamine Seeking by Restoring Novelty Salience

“…With the recent advent of a more soluble, selective mGlu5 PAM, 1-(4-(2,4-difluorophenyl) piperazin-1-yl)-2-((4-fluorobenzyl)oxy)-ethanone, or DPFE (Gregory et al, 2013), a potential perirhinal locus for this effect can now be investigated using brain-site specific microinfusions. The goal of Experiment 1 was to determine whether intraperirhinal infusions of DPFE can restore novel object recognition in long-access meth rats, with the basic hypothesis that restoring glutamate receptor transmission in perirhinal cortex may be a viable strategy for restoring novel object recognition.…”