A 211At-labelled mGluR1 inhibitor induces cancer senescence to elicit long-lasting anti-tumor efficacy.

Metabotropic glutamate receptor 1 (mGluR1), a key mediator of glutamatergic signaling, is frequently overexpressed in tumor cells and is an attractive drug target for most cancers. Here, we present a targeted radiopharmaceutical therapy strategy that antagonistically recognizes mGluR1 and eradicates mGluR1+ human tumors by harnessing a small-molecule alpha (α)-emitting radiopharmaceutical, 211At-AITM. A single dose of 211At-AITM (2.96 MBq) in mGluR1+ cancers exhibits long-lasting in vivo antitumor efficacy across seven subtypes of four of the most common tumors, namely, breast cancer, pancreatic cancer, melanoma, and colon cancers, with little toxicity. Moreover, complete regression of mGluR1+ breast cancer and pancreatic cancer is observed in approximate 50% of tumor-bearing mice. Mechanistically, the functions of 211At-AITM are uncovered in downregulating mGluR1 oncoprotein and inducing senescence of tumor cells with a reprogrammed senescence-associated secretory phenotype. Our findings suggest α-radiopharmaceutical therapy with 211At-AITM can be a useful strategy for mGluR1+ pan-cancers, regardless of their tissue of origin.

mGlu2/3 receptor antagonists for depression: overview of underlying mechanisms and clinical development.

Triggered by the ground-breaking finding that ketamine exerts robust and rapid-acting antidepressant effects in patients with treatment-resistant depression, glutamatergic systems have attracted attention as targets for the development of novel antidepressants. Among glutamatergic systems, group II metabotropic glutamate (mGlu) receptors, consisting of mGlu2 and mGlu3 receptors, are of interest because of their modulatory roles in glutamatergic transmission. Accumulating evidence has indicated that mGlu2/3 receptor antagonists have antidepressant-like effects in rodent models that mirror those of ketamine and that mGlu2/3 receptor antagonists also share underlying mechanisms with ketamine that are responsible for these antidepressant-like actions. Importantly, contrary to their antidepressant-like profile, preclinical studies have revealed that mGlu2/3 receptor antagonists are devoid of ketamine-like adverse effects, such as psychotomimetic-like behavior, abuse potential and neurotoxicity. Despite some discouraging results for an mGlu2/3 receptor antagonist decoglurant (classified as a negative allosteric modulator [NAM]) in patients with major depressive disorder, clinical trials of two mGlu2/3 receptor antagonists, a phase 2 trial of TS-161 (an orthosteric antagonist) and a phase 1 trial of DSP-3456 (a NAM), are presently on-going. mGlu2/3 receptors still hold promise for the development of safer and more efficacious antidepressants.

Early treatment with JNJ-46356479, a mGluR2 modulator, improves behavioral and neuropathological deficits in a postnatal ketamine mouse model of schizophrenia.

Positive allosteric modulators of the metabotropic glutamate receptor 2 (mGluR2), such as JNJ-46356479 (JNJ), may mitigate the glutamate storm during the early stages of schizophrenia (SZ), which could be especially useful in the treatment of cognitive and negative symptoms. We evaluated the efficacy of early treatment with JNJ or clozapine (CLZ) in reversing behavioral and neuropathological deficits induced in a postnatal ketamine (KET) mouse model of SZ. Mice exposed to KET (30 mg/kg) on postnatal days (PND) 7, 9, and 11 received JNJ or CLZ (10 mg/kg) daily in the adolescent period (PND 35-60). Mice exposed to KET did not show the expected preference for a novel object or for social novelty, but they recovered this preference with JNJ treatment. Similarly, KET group did not show the expected dishabituation in the fifth trial, but mice treated with JNJ or CLZ recovered an interest in the novel animal. Neuronal immunoreactivity also differed between treatment groups with mice exposed to KET showing a reduction in parvalbumin positive cells in the prefrontal cortex and decreased c-Fos expression in the hippocampus, which was normalized with the pharmacological treatment. JNJ-46356479 treatment in early stages may help improve the cognitive and negative symptoms, as well as certain neuropathological deficits, and may even obtain a better response than CLZ treatment. This may have relevant clinical translational applications since early treatment with mGluR2 modulators that inhibit glutamate release at the onset of critical phases of SZ may prevent or slow down the clinical deterioration of the disease.

Transcriptional regulation of NRF1 on metabotropic glutamate receptors in a neonatal hypoxic­ischemic encephalopathy rat model.

BACKGROUND: Neonatal hypoxic-ischemic encephalopathy (HIE) is a kind of brain injury that causes severe neurological disorders in newborns. Metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs) are significantly associated with HIE and are involved in ischemia-induced excitotoxicity. This study aimed to investigate the upstream mechanisms of mGluRs and the transcriptional regulation by nuclear respiratory factor 1 (NRF1). METHODS: The rat model of neonatal HIE was created using unilateral carotid artery ligation and in vitro oxygen-glucose deprivation paradigm. We used western blot, immunofluorescence, Nissl staining, and Morris water maze to investigate the impact of NRF1 on brain damage and learning memory deficit by HIE. We performed ChIP and luciferase activities to identify the transcriptional regulation of NRF1 on mGluRs. RESULTS: The neuronal NRF1 and some glutamatergic genes expression synchronously declined in infarcted tissues. The NRF1 overexpression effectively restored the expression of some glutamatergic genes and improved cognitive performance. NRF1 regulated some members of mGluRs and iGluRs in hypoxic-ischemic neurons. Finally, NRF1 is bound to the promoter regions of Grm1, Grm2, and Grm8 to activate their transcription. CONCLUSIONS: NRF1 is involved in the pathology of the neonatal HIE rat model, suggesting a novel therapeutic approach to neonatal HIE. IMPACT: NRF1 and some glutamatergic genes were synchronously downregulated in the infarcted brain of the neonatal HIE rat model. NRF1 overexpression could rescue cognitive impairment caused by the neonatal HIE rat model. NRF1 regulated the expressions of Grm1, Grm2, and Grm8, which activated their transcription by binding to the promoter regions.

Characterization of the novel positive allosteric modulator of the metabotropic glutamate receptor 4 ADX88178 in rodent models of neuropsychiatric disorders.

There is growing evidence that activation of metabotropic glutamate receptor 4 (mGlu4) leads to anxiolytic- and antipsychotic-like efficacy in rodent models, yet its relevance to depression-like reactivity remains unclear. Here, we present the pharmacological evaluation of ADX88178 [5-methyl-N-(4-methylpyrimidin-2-yl)-4-(1H-pyrazol-4-yl)thiazol-2-amine], a novel potent, selective, and brain-penetrant positive allosteric modulator of the mGlu4 receptor in rodent models of anxiety, obsessive compulsive disorder (OCD), fear, depression, and psychosis. ADX88178 dose-dependently reduced the number of buried marbles in the marble burying test and increased open-arm exploration in the elevated plus maze (EPM) test, indicative of anxiolytic-like efficacy. Target specificity of the effect in the EPM test was confirmed using male and female mGlu4 receptor knockout mice. In mice, ADX88178 reduced the likelihood of conditioned freezing in the acquisition phase of the fear conditioning test, yet had no carryover effect in the expression phase. Also, ADX88178 dose-dependently reduced duration of immobility in the forced swim test, indicative of antidepressant-like efficacy. ADX88178 reduced DOI (2,5-dimethoxy-4-iodoamphetamine)-mediated head twitches (albeit with no dose-dependency), and MK-801 [(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine]-induced locomotor hyperactivity in mice, but was inactive in the conditioned avoidance response test in rats. The compound showed good specificity as it had no effect on locomotor activity in mice and rats at efficacious doses. Thus, allosteric activation of mGlu4 receptors can be a promising new therapeutic approach for treatment of anxiety, OCD, fear-related disorders, and psychosis.

[Effects of chronic, systemic treatment with metabotropic glutamate receptor 5 antagonist on behavioral activity and neuroprotection in a preclinical rat model of Parkinson's disease].

OBJECTIVE: To study the effects of chronic, systemic treatment with 2-methyl-6-(phenylethynyl)-pyridine (MPEP) on behavioral activity and neuroprotection in the rat with partial lesion of the nigrostriatal pathway. METHODS: A total of 37 male SD rats were randomly divided into sham (n=11), PD+ saline (n=15) and PD+MPEP group (n=11). Rat model of Parkinson's disease was established by injection of 6-OHDA into medial forebrain bundle. PD+vehicle rats and PD+MPEP rats were injected with NS (0.1 mL) and MPEP (3 mg/kg) per day respectively. Changes in the spontaneous and induced behaviors and the degree of dopamimnergic neurons loss in the substantia nigra pars compacta (SNpc) were observed by behavioral and immunocytochemical methods in partially lesioned and MPEP-treated rats. RESULTS: Unilateral injection of 6-hydrodopamine (6-OHDA) into medial forebrain bundle resulted in the moderate loss (39%) of dopaminergic neurons in the SNpc, and MPEP treatment decreased the number of neurons loss compared with PD+saline rats (P < 0.01). In this model, the lesioned rats did not show obviously abnormal posture. However, apomorphine (APO) induced significant rotation behavior, which increases in a time-dependent manner. Chronic, systemic treatment with MPEP could against the toxicity of 6-OHDA, and reduced the loss of SNpc dopaminergic neurons. In addition, MPEP ameliorated significantly the rotation behaviour induced by APO, which is strengthened in a time-dependent manner. CONCLUSION: MPEP treatment has anti-parkinsonian and neuroprotective effects in the rat with partial lesion of the nigrostriatal pathway, and the efficacy gradually increase with the treatment time.

Metabotropic glutamate receptors: physiology, pharmacology, and disease.

The metabotropic glutamate receptors (mGluRs) are family C G-protein-coupled receptors that participate in the modulation of synaptic transmission and neuronal excitability throughout the central nervous system. The mGluRs bind glutamate within a large extracellular domain and transmit signals through the receptor protein to intracellular signaling partners. A great deal of progress has been made in determining the mechanisms by which mGluRs are activated, proteins with which they interact, and orthosteric and allosteric ligands that can modulate receptor activity. The widespread expression of mGluRs makes these receptors particularly attractive drug targets, and recent studies continue to validate the therapeutic utility of mGluR ligands in neurological and psychiatric disorders such as Alzheimer's disease, Parkinson's disease, anxiety, depression, and schizophrenia.

Structure, pharmacology and therapeutic prospects of family C G-protein coupled receptors.

Family C of G-protein coupled receptors (GPCRs) from humans is constituted by eight metabotropic glutamate (mGlu(1-8)) receptors, two heterodimeric gamma-aminobutyric acid(B) (GABA(B)) receptors, a calcium-sensing receptor (CaR), three taste (T1R) receptors, a promiscuous L-alpha-amino acid receptor (GPRC6A), and five orphan receptors. Aside from the orphan receptors, the family C GPCRs are characterised by a large amino-terminal domain, which bind the endogenous orthosteric agonists. Recently, a number of allosteric modulators binding to the seven transmembrane domains of the receptors have also been reported. Family C GPCRs regulate a number of important physiological functions and are thus intensively pursued as drug targets. So far, two drugs acting at family C receptors (the GABA(B) agonist baclofen and the positive allosteric CaR modulator cinacalcet) have been marketed. Cinacalcet is the first allosteric GPCR modulator to enter the market, which demonstrates that the therapeutic principle of allosteric modulation can also be extended to this important drug target class. In this review we outline the structure and function of family C GPCRs with particular focus on the ligand binding sites, and we present the most important pharmacological agents and the therapeutic prospects of the receptors.

Metabotropic glutamate receptors as a strategic target for the treatment of epilepsy.

Epilepsy is a chronic neurological disorder that has many known types, including generalized epilepsies that involve cortical and subcortical structures. A proportion of patients have seizures that are resistant to traditional anti-epilepsy drugs, which mainly target ion channels or postsynaptic receptors. This resistance to conventional therapies makes it important to identify novel targets for the treatment of epilepsy. Given the involvement of the neurotransmitter glutamate in the etiology of epilepsy, targets that control glutamatergic neurotransmission are of special interest. The metabotropic glutamate receptors (mGluRs) are of a family of eight G-protein-coupled receptors that serve unique regulatory functions at synapses that use the neurotransmitter glutamate. Their distribution within the central nervous system provides a platform for both presynaptic control of glutamate release, as well as postsynaptic control of neuronal responses to glutamate. In recent years, substantial efforts have been made towards developing selective agonists and antagonists which may be useful for targeting specific receptor subtypes in an attempt to harness the therapeutic potential of these receptors. We examine the possibility of intervening at these receptors by considering the specific example of absence seizures, a form of generalized, non-convulsive seizure that involves the thalamus. Views of the etiology of absence seizures have evolved over time from the "centrencephalic" concept of a diffuse subcortical pacemaker toward the "cortical focus" theory in which cortical hyperexcitability leads the thalamus into the 3-4 Hz rhythms that are characteristic of absence seizures. Since the cortex communicates with the thalamus via a massive glutamatergic projection, ionotropic glutamate receptor (iGluR) blockade has held promise, but the global nature of iGluR intervention has precluded the clinical effectiveness of drugs that block iGluRs. In contrast, mGluRs, because they modulate iGluRs at glutamatergic synapses only under certain conditions, may quell seizure activity by selectively reducing hyperactive glutamatergic synaptic communication within the cortex and thalamus without significantly affecting normal response rates. In this article, we review the circuitry and events leading to absence seizure generation within the corticothalamic network, we present a comprehensive review of the synaptic location and function of mGluRs within the thalamus and cerebral cortex, and review the current knowledge of mGluR modulation and seizure generation. We conclude by reviewing the potential advantages of Group II mGluRs, specifically mGluR2, in the treatment of both convulsive and non-convulsive seizures.

Metabotropic glutamate receptors as novel targets for anxiety and stress disorders.

Anxiety and stress disorders are the most commonly occurring of all mental illnesses, and current treatments are less than satisfactory. So, the discovery of novel approaches to treat anxiety disorders remains an important area of neuroscience research. Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system, and G-protein-coupled metabotropic glutamate (mGlu) receptors function to regulate excitability via pre- and postsynaptic mechanisms. Various mGlu receptor subtypes, including group I (mGlu(1) and mGlu(5)), group II (mGlu(2) and mGlu(3)), and group III (mGlu(4), mGlu(7) and mGlu(8)) receptors, specifically modulate excitability within crucial brain structures involved in anxiety states. In addition, agonists for group II (mGlu(2/3)) receptors and antagonists for group I (in particular mGlu(5)) receptors have shown activity in animal and/or human conditions of fear, anxiety or stress. These studies indicate that metabotropic glutamate receptors are interesting new targets to treat anxiety disorders in humans.

Positive and negative allosteric modulation of metabotropic glutamate receptors: emerging therapeutic potential.

Metabotropic glutamate receptors (mGluRs) modulate neuronal activity in the central and peripheral nervous systems, and since their discovery have attracted considerable attention as putative therapeutic targets for a range of neurological and psychiatric disorders. A number of competitive agonists and antagonists acting at the N-terminal glutamate binding site have been identified, the majority of which are conformationally constrained or substituted amino acid analogues. These ligands have greatly facilitated investigation of the physiological and pathological roles of the receptor family. However, their utility and therapeutic potential has been restricted by relatively poor bioavailability and central nervous system (CNS) penetration, as well as limited chemical tractability and, generally, a lack of selectivity for individual mGluRs. Recently, a number of non-competitive mGluR ligands have been identified which bind within the receptor transmembrane heptahelical domain. These include both positive and negative allosteric modulators. Positive allosteric modulators do not exhibit intrinsic agonism but facilitate agonist-mediated receptor activity. Negative allosteric modulators include both non-competitive antagonists and inverse agonists. Allosteric modulation offers the potential for improved selectivity, particularly for individual receptors within the mGluR family, and enhanced chemical tractability relative to competitive agonists/antagonists. In addition, positive allosteric modulation provides a distinct, and perhaps superior, profile to receptor agonism, offering the potential for facilitation of physiologically appropriate receptor activation with reduced liability for receptor desensitisation and/or tolerance. Thus, the emerging field of positive and negative allosteric modulation of the mGluR family offers considerable promise for the development of novel therapeutics.

Activation of group III metabotropic glutamate receptors in selected regions of the basal ganglia alleviates akinesia in the reserpine-treated rat.

1. This study examined whether group III metabotropic glutamate (mGlu) receptor agonists injected into the globus pallidus (GP), substantia nigra pars reticulata (SNr) or intracerebroventricularly (i.c.v.) could reverse reserpine-induced akinesia in the rat. 2. Male Sprague-Dawley rats, cannulated above the GP, SNr or third ventricle, were rendered akinetic with reserpine (5 mg kg(-1) s.c.). 18 h later, behavioural effects of the group III mGlu receptor agonists L-serine-O-phosphate (L-SOP) or L-(+)-2-amino-4-phosphonobutyric acid (L-AP4) were examined. 3. In reserpine-treated rats, unilateral injection of L-SOP (2000 and 2500 nmol in 2.5 microl) into the GP produced a significant increase in net contraversive rotations compared to vehicle, reaching a maximum of 83+/-21 rotations 120 min(-1) (n=8). Pretreatment with the group III mGlu receptor antagonist methyl-serine-O-phosphate (M-SOP; 250 nmol in 2.5 microl) inhibited the response to L-SOP (2000 nmol) by 77%. Unilateral injection of L-SOP (250-1000 nmol in 2.5 microl) into the SNr of reserpine-treated rats produced a dose-dependent increase in net contraversive rotations, reaching a maximum of 47+/-6 rotations 30 min(-1) (n=6). M-SOP (50 nmol in 2.5 microl) inhibited the response to L-SOP (500 nmol) by 78%. 4. Following i.c.v. injection, L-SOP (2000-2500 nmol in 2.5 microl) or L-AP4 (0.5-100 nmol in 2 microl) produced a dose-dependent reversal of akinesia, attaining a maximum of 45+/-17 (n=8) and 72+/-3 (n=9) arbitrary locomotor units 30 min(-1), respectively. 6. These studies indicate that injection of group III mGlu receptor agonists into the GP, SNr or cerebral ventricles reverses reserpine-induced akinesia, the mechanism for which remains to be established.

Effects of LY379268, a selective group II metabotropic glutamate receptor agonist on EEG activity, cortical perfusion, tissue damage, and cortical glutamate, glucose, and lactate levels in brain-injured rats.

Activating presynaptic group II metabotropic glutamate (mGlu II) receptors reduces synaptic glutamate release. Attenuating glutamatergic transmission without blocking ionotropic glutamate receptors, thus avoiding unfavorable psychomimetic side effects, makes mGlu II receptor agonists a promising target in treating brain-injured patients. Neuroprotective effects of LY379268 were investigated in rats following controlled cortical impact injury (CCI). At 30 min after CCI, rats received a single intraperitoneal injection of LY379268 (10 mg/kg/body weight) or NaCl. Changes in EEG activity and pericontusional cortical perfusion were determined before trauma, at 4, 24, and 48 h, and 7 days after CCI. Brain edema and contusion volume were determined at 24 h and 7 days after CCI, respectively. Before brain removal pericontusional cortical glutamate, glucose, and lactate were measured via microdialysis. During the early period following CCI, EEG activity and cortical perfusion were significantly reduced in rats receiving LY379268. At 7 days, cortical perfusion was significantly increased in rats treated with LY379268, while EEG activity was depressed as in control rats. While brain edema remained unchanged at 24 h, cortical contusion was significantly decreased by 56% at 7 days after CCI. Cortical glutamate, glucose, and lactate were not influenced. Significant reductions in EEG activity and contusion volume by LY379268 do not appear mediated by attenuated excitotoxicity and energetic impairment. Overall, an additional decrease in cortical perfusion seems to interfere with the anti-edematous potential of LY379268 during the early period following CCI, while an increase in perfusion in LY379268-treated rats at 7 days might contribute to tissue protection.