Synthesis and Pharmacological Characterization of C4ß-Amide-Substituted 2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylates. Identification of (1 S,2 S,4 S,5 R,6 S)-2-Amino-4-[(3-methoxybenzoyl)amino]bicyclo[3.1.0]hexane-2,6-dicarboxylic Acid (LY2794193), a Highly Potent and Selective mGlu3 Receptor Agonist.

Multiple therapeutic opportunities have been suggested for compounds capable of selective activation of metabotropic glutamate 3 (mGlu3) receptors, but small molecule tools are lacking. As part of our ongoing efforts to identify potent, selective, and systemically bioavailable agonists for mGlu2 and mGlu3 receptor subtypes, a series of C4ß-N-linked variants of (1 S,2 S,5 R,6 S)-2-amino-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 1 (LY354740) were prepared and evaluated for both mGlu2 and mGlu3 receptor binding affinity and functional cellular responses. From this investigation we identified (1 S,2 S,4 S,5 R,6 S)-2-amino-4-[(3-methoxybenzoyl)amino]bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 8p (LY2794193), a molecule that demonstrates remarkable mGlu3 receptor selectivity. Crystallization of 8p with the amino terminal domain of hmGlu3 revealed critical binding interactions for this ligand with residues adjacent to the glutamate binding site, while pharmacokinetic assessment of 8p combined with its effect in an mGlu2 receptor-dependent behavioral model provides estimates for doses of this compound that would be expected to selectively engage and activate central mGlu3 receptors in vivo.

Synthesis and Pharmacological Characterization of C4-(Thiotriazolyl)-substituted-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylates. Identification of (1R,2S,4R,5R,6R)-2-Amino-4-(1H-1,2,4-triazol-3-ylsulfanyl)bicyclo[3.1.0]hexane-2,6-dicarboxylic Acid (LY2812223), a Highly Potent, Functionally Selective mGlu2 Receptor Agonist.

Identification of orthosteric mGlu(2/3) receptor agonists capable of discriminating between individual mGlu2 and mGlu3 subtypes has been highly challenging owing to the glutamate-site sequence homology between these proteins. Herein we detail the preparation and characterization of a series of molecules related to (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate 1 (LY354740) bearing C4-thiotriazole substituents. On the basis of second messenger responses in cells expressing other recombinant human mGlu2/3 subtypes, a number of high potency and efficacy mGlu2 receptor agonists exhibiting low potency mGlu3 partial agonist/antagonist activity were identified. From this, (1R,2S,4R,5R,6R)-2-amino-4-(1H-1,2,4-triazol-3-ylsulfanyl)bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 14a (LY2812223) was further characterized. Cocrystallization of 14a with the amino terminal domains of hmGlu2 and hmGlu3 combined with site-directed mutation studies has clarified the underlying molecular basis of this unique pharmacology. Evaluation of 14a in a rat model responsive to mGlu2 receptor activation coupled with a measure of central drug disposition provides evidence that this molecule engages and activates central mGlu2 receptors in vivo.

Synthesis and pharmacological characterization of C4-disubstituted analogs of 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate: identification of a potent, selective metabotropic glutamate receptor agonist and determination of agonist-bound human mGlu2 and mGlu3 amino terminal domain structures.

As part of our ongoing research to identify novel agents acting at metabotropic glutamate 2 (mGlu2) and 3 (mGlu3) receptors, we have previously reported the identification of the C4α-methyl analog of mGlu2/3 receptor agonist 1 (LY354740). This molecule, 1S,2S,4R,5R,6S-2-amino-4-methylbicyclo[3.1.0]hexane-2,6-dicarboxylate 2 (LY541850), exhibited an unexpected mGlu2 agonist/mGlu3 antagonist pharmacological profile, whereas the C4ß-methyl diastereomer (3) possessed dual mGlu2/3 receptor agonist activity. We have now further explored this structure-activity relationship through the preparation of cyclic and acyclic C4-disubstituted analogs of 1, leading to the identification of C4-spirocyclopropane 5 (LY2934747), a novel, potent, and systemically bioavailable mGlu2/3 receptor agonist which exhibits both antipsychotic and analgesic properties in vivo. In addition, through the combined use of protein-ligand X-ray crystallography employing recombinant human mGlu2/3 receptor amino terminal domains, molecular modeling, and site-directed mutagenesis, a molecular basis for the observed pharmacological profile of compound 2 is proposed.

Synthesis and pharmacological characterization of 4-substituted-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylates: identification of new potent and selective metabotropic glutamate 2/3 receptor agonists.

As part of our ongoing interest in identifying novel agonists acting at metabotropic glutamate (mGlu) 2/3 receptors, we have explored the effect of structural modifications of 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate (LY354740), a potent and pharmacologically balanced mGlu2/3 receptor agonist. Incorporation of relatively small substituents (e.g., F, O) at the C4 position of this molecule resulted in additional highly potent mGlu2/3 agonists that demonstrate excellent selectivity over the other mGlu receptor subtypes, while addition of larger C4-substituents (e.g., SPh) led to a loss of agonist potency and/or the appearance of weak mGlu2/3 receptor antagonist activity. Further characterization of the α-fluoro-substituted analogue (LY459477) in vivo revealed that this molecule possesses good oral bioavailability in rats and effectively suppresses phencyclidine-evoked locomotor activity at doses that do not impair neuromuscular coordination. This molecule therefore represents a valuable new addition to the arsenal of pharmacological tools competent to investigate mGlu2/3 receptor function both in vitro and in vivo.

CNS distribution of metabotropic glutamate 2 and 3 receptors: transgenic mice and [³H]LY459477 autoradiography.

Group II metabotropic glutamate (mGlu) receptor agonists were efficacious in randomized clinical research trials for schizophrenia and generalized anxiety disorder. The regional quantification of mGlu(2) and mGlu(3) receptors remains unknown. A selective and structurally novel mGlu(2/3) receptor agonist, 2-amino-4-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY459477) was tritiated and the distribution of mGlu(2) and mGlu(3) receptors was studied in transgenic mice lacking either mGlu(2), mGlu(3) or both receptors. LY459477 is an agonist with 1-2 nM potency for rodent and human mGlu(2) and mGlu(3) receptors. The functional selectivity of LY459477 was demonstrated by over 640-fold selectivity and the displacement binding selectivity was greater than 320-fold for all glutamate receptors except mGlu(6) (∼230-fold). More than 1000-fold selectivity was demonstrated for all non-glutamate receptors known to be targeted by antipsychotic drugs. Like atypical antipsychotic drugs, LY459477 reversed in vitro electrophysiological effects of a serotonergic hallucinogen and behavioral effects of phencyclidine or amphetamine. There was virtually no binding of [(3)H]LY459477 to any brain region in mice with a deletion of both mGlu(2) and mGlu(3) receptors. Regions enriched in mGlu(2) receptors included the medial prefrontal cortex, select hippocampal regions, the medial mammillary nucleus, the medial habenula, and the cerebellar granular cell layer. Regions enriched in mGlu(3) receptors were the dorsolateral entorhinal cortex, the hippocampal CA1 field, the piriform cortex, the substantia nigra, the thalamic reticular nucleus, and primary sensory thalamic nuclei. These findings suggest [(3)H]LY459477 should be a useful tool to further define the role of mGlu(2) and mGlu(3) receptors throughout the brain with respect to major neuropsychiatric syndromes. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Activation of metabotropic glutamate (mGlu)2 receptors suppresses histamine release in limbic brain regions following acute ketamine challenge.

In the present study we demonstrated that ketamine, an NMDA antagonist and possible psychotomimetic, increases extracellular histamine (HA) in the rat brain. We then examined the ability of the group II mGlu receptor agonist LY379268 to modulate the ketamine evoked increases in HA release in three limbic brain regions. Ketamine (25 mg/kg) increased HA in the medial prefrontal cortex (mPFC), ventral hippocampus (vHipp) and the nucleus accumbens (NAc) shell. LY379268 administered alone was without effect on basal HA efflux in the mPFC or vHipp but modestly decreased HA efflux in the NAc shell. Administration of LY379268 (3 and 10 mg/kg) prior to ketamine significantly attenuated the HA response in the mPFC, vHipp and the NAc shell. The inhibitory effects of LY379268 in the mPFC were mimicked by the systemic administration of the mGlu2 receptor positive allosteric modulator CBiPES (60 mg/kg). Finally, local perfusion experiments revealed that the effects of LY379268 on ketamine evoked HA efflux appear to be mediated by mGlu2 receptors outside the PFC as the intra-mPFC perfusion of LY379268 (100 microM or 300 microM) failed to attenuate ketamine evoked increases in HA efflux. Together, these novel observations reveal an effect of ketamine on histaminergic transmission in limbic brain areas and provide further insight into the possible antipsychotic mechanism of action of mGlu2/3 receptor agonists.

In vitro and in vivo evidence for a lack of interaction with dopamine D2 receptors by the metabotropic glutamate 2/3 receptor agonists 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicaroxylate monohydrate (LY354740) and (-)-2-oxa-4-aminobicyclo[3.1.0] Hexane-4,6-dicarboxylic acid (LY379268).

Some recently published in vitro studies with two metabotropic glutamate 2/3 receptor (mGluR(2/3)) agonists [(-)-2-oxa-4-aminobicyclo[3.1.0] hexane-4,6-dicarboxylic acid (LY379268) and 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicaroxylate monohydrate (LY354740)] suggest that these compounds may also directly interact with dopamine (DA) D(2) receptors. The current in vitro and in vivo studies were undertaken to further explore this potential interaction with D(2) receptors. LY379268 and LY354740 failed to inhibit D(2) binding in both native striatal tissue homogenates and cloned receptors at concentrations up to 10 microM. LY379268 and LY354740 (up to 10 microM) also failed to stimulate [(35)S]GTPgammaS binding in D(2L)- and D(2S)-expressing clones in the presence of NaCl or N-methyl-d-glucamine. In an in vivo striatal D(2) receptor occupancy assay, LY379268 (3-30 mg/kg) or LY354740 (1-10 mg/kg) failed to displace raclopride (3 microg/kg i.v.), whereas aripiprazole (10-60 mg/kg) showed up to 90% striatal D(2) receptor occupancy. LY379268 (10 mg/kg) and raclopride (3 mg/kg) blocked d-amphetamine and phencyclidine (PCP)-induced hyperactivity in wild-type mice. However, the effects of LY379268 were lost in mGlu(2/3) receptor knockout mice. In DA D(2) receptor-deficient mice, LY379268 but not raclopride blocked both PCP and d-amphetamine-evoked hyperactivity. In the striatum and nucleus accumbens, LY379268 (3 and 10 mg/kg) was without effect on the DA synthesis rate in reserpinized rats and also failed to prevent S-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine-induced reductions in DA synthesis rate. Taken together, the current data fail to show evidence of direct DA D(2) receptor interactions of LY379268 and LY354740 in vitro or in vivo. Instead, these results provide further evidence for a novel antipsychotic mechanism of action for mGluR(2/3) agonists.

Evidence for the role of metabotropic glutamate (mGlu)2 not mGlu3 receptors in the preclinical antipsychotic pharmacology of the mGlu2/3 receptor agonist (-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY404039).

(-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY404039) is a potent and selective group II metabotropic glutamate [(mGlu)2 and mGlu3] receptor agonist for which its prodrug LY2140023 [(1R,4S,5S,6S)-2-thiabicyclo[3.1.0]-hexane-4,6-dicarboxylic acid,4-[(2S)-2-amino-4-(methylthio)-1-oxobutyl]amino-, 2,2-dioxide monohydrate] has recently been shown to have efficacy in the treatment of the positive and negative symptoms of schizophrenia. In this article, we use mGlu receptor-deficient mice to investigate the relative contribution of mGlu2 and mGlu3 receptors in mediating the antipsychotic profile of LY404039 in the phencyclidine (PCP) and d-amphetamine (AMP) models of psychosis. To further explore the mechanism of action of LY404039, we compared the drugs' ability to block PCP-induced hyperlocomotion to that of atypical antipsychotics in wild-type and mice lacking mGlu2/3 receptors. In wild-type animals, LY404039 (3-30 mg/kg i.p.) significantly reversed AMP (5 mg/kg, i.p.)-induced increases in ambulations, distance traveled, and reduced time spent at rest. LY404039 reversed PCP (7.5 mg/kg i.p.)-evoked behaviors at 10 mg/kg. The antipsychotic-like effects of LY404039 (10 mg/kg i.p.) on PCP and AMP-evoked behavioral activation were absent in mGlu2 and mGlu2/3 but not in mGlu3 receptor-deficient mice, indicating that the activation of mGlu2 and not mGlu3 receptors is responsible for the antipsychotic-like effects of the mGlu2/3 receptor agonist LY404039. In contrast, the atypical antipsychotic drugs clozapine and risperidone inhibited PCP-evoked behaviors in both wild-type and mGlu2/3 receptor-deficient mice. These data demonstrate that the antipsychotic-like effects of the mGlu2/3 receptor agonist LY404039 in psychostimulant models of psychosis are mechanistically distinct from those of atypical antipsychotic drugs and are dependent on functional mGlu2 and not mGlu3 receptors.

Activation of mGlu2/3 receptors as a new approach to treat schizophrenia: a randomized Phase 2 clinical trial.

Schizophrenia is a chronic, complex and heterogeneous mental disorder, with pathological features of disrupted neuronal excitability and plasticity within limbic structures of the brain. These pathological features manifest behaviorally as positive symptoms (including hallucinations, delusions and thought disorder), negative symptoms (such as social withdrawal, apathy and emotional blunting) and other psychopathological symptoms (such as psychomotor retardation, lack of insight, poor attention and impulse control). Altered glutamate neurotransmission has for decades been linked to schizophrenia, but all commonly prescribed antipsychotics act on dopamine receptors. LY404039 is a selective agonist for metabotropic glutamate 2/3 (mGlu2/3) receptors and has shown antipsychotic potential in animal studies. With data from rodents, we provide new evidence that mGlu2/3 receptor agonists work by a distinct mechanism different from that of olanzapine. To clinically test this mechanism, an oral prodrug of LY404039 (LY2140023) was evaluated in schizophrenic patients with olanzapine as an active control in a randomized, three-armed, double-blind, placebo-controlled study. Treatment with LY2140023, like treatment with olanzapine, was safe and well-tolerated; treated patients showed statistically significant improvements in both positive and negative symptoms of schizophrenia compared to placebo (P < 0.001 at week 4). Notably, patients treated with LY2140023 did not differ from placebo-treated patients with respect to prolactin elevation, extrapyramidal symptoms or weight gain. These data suggest that mGlu2/3 receptor agonists have antipsychotic properties and may provide a new alternative for the treatment of schizophrenia.

The orexin-1 antagonist SB-334867 blocks antipsychotic treatment emergent catalepsy: implications for the treatment of extrapyramidal symptoms.

We have previously shown that the orexin-1 antagonist SB-334867 blocks the electrophysiological effects of haloperidol and olanzapine on the activity of A9 and A10 dopamine neurons. To evaluate if orexin-1 antagonists might block other effects of antipsychotic drugs in animals, we examined the effects of SB-334867 on behavioral, neurochemical, and neuroendocrine effects of antipsychotic drugs. Pretreatment with SB-334867 (0.01-10 mg/kg, intraperitoneal [IP]) significantly decreased the catalepsy produced by the administration of haloperidol (1 mg/kg, subcutaneous [SC]), risperidone (2 mg/kg, SC), and olanzapine (10 mg/kg, SC). Administration of SB-334467 also reversed catalepsy after it had been established in animals pretreated 2 hours earlier with haloperidol. However, pretreatment with SB-334867 (1-10 mg/kg, IP) did not block the decreases in exploratory locomotor activity produced by administration of haloperidol (0.1 mg/kg, SC) or risperidone (0.3 mg/kg, SC). In addition, pretreatment with SB-334867 (1-10 mg/kg, IP) neither blocked the increased levels of dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens or striatum nor the elevation in serum prolactin produced by administration of haloperidol (0.1 mg/kg, SC) and risperidone (1 mg/kg, SC). Administration of SB-334867 alone neither changed locomotor activity and DOPAC or prolactin levels nor produced catalepsy. These results show that orexin-1 antagonists block the catoleptogenic effects of antipsychotics but do not block other locomotor, neurochemical, or neuroendocrine effects of antipsychotics. Because catalepsy is thought to be a good predictor of extrapyramidal symptoms in humans, treatment with orexin-1 antagonists might decrease the occurrence or severity of antipsychotic treatment-emergent extrapyramidal symptoms in humans.

Metabotropic glutamate receptors in the control of mood disorders.

Current treatments for depression are less than optimal in terms of onset of action, response and remission rates, and side-effect profiles. Glutamate is the major excitatory neurotransmitter controlling synaptic excitability and plasticity in most brain circuits, including limbic pathways involved in depression. Thus, drugs that target glutamate neuronal transmission offer novel approaches to treat depression. Recently, the NMDA receptor antagonist ketamine has demonstrated clinical efficacy in a randomized clinical trial of depressed patients. Metabotropic glutamate (mGlu) receptors function to regulate glutamate neuronal transmission by altering the release of neurotransmitter or modulating the post-synaptic responses to glutamate. Accumulating evidence from biochemical and behavioral studies support the idea that the regulation of glutamatergic neurotransmission via mGlu receptors is linked to mood disorders and that these receptors may serve as novel targets for the discovery of small molecule modulators with unique antidepressant properties. For example, mGlu receptor modulation can facilitate neuronal stem cell proliferation (neurogenesis) and the release of neurotransmitters that are associated with treatment response to depression in humans (serotonin, norepinephrine, dopamine). In particular, compounds that antagonize mGlu2, mGlu3 and/or mGlu5 receptors (e.g. LY341495, MSG0039, MPEP) have been linked to the above pharmacology and have also shown in vivo activity in animal models predictive of antidepressant efficacy such as the forced-swim test. The in vivo actions of these agents can be antagonized by compounds that block AMPA receptors, suggesting that their actions are direct downstream consequences of the enhancement of glutamate neuronal transmission in brain regions involved in depression. These data provide new approaches to finding mechanistically distinct drugs for depression that may have advantages over current therapies for some patients. Moreover, since the mood disorders encompase a non-homogenous set of symptoms, comorbid disorders, and potential etiologies, the rich arsensel that exists within the mGlu receptor families provides an opportunity for both broad and customized therapeutics.

In vivo pharmacological characterization of the structurally novel, potent, selective mGlu2/3 receptor agonist LY404039 in animal models of psychiatric disorders.

RATIONALE: Data from both preclinical and clinical studies have provided proof of concept that modulation of limbic and forebrain glutamate, via mGlu2/3 receptor agonists, might provide therapeutic benefits in many psychiatric disorders including schizophrenia and anxiety. OBJECTIVE: The aim of this study was to assess the efficacy of a structurally novel, potent, selective mGlu2/3 receptor agonist with improved bioavailability (LY404039) in animal models predictive of antipsychotic and anxiolytic efficacy. MATERIALS AND METHODS: LY404039 was assessed in amphetamine- and phencyclidine-induced hyperlocomotion, conditioned avoidance responding, fear-potentiated startle, marble burying, and rotarod behavioral tests. Monoamine release and turnover were assessed using microdialysis and ex vivo tissue levels. RESULTS: LY404039 attenuated amphetamine- and phencyclidine-induced hyperlocomotion (3-30 and 10 mg/kg, respectively). LY404039 (3-10 mg/kg) inhibited conditioned avoidance responding. LY404039 also reduced fear-potentiated startle in rats (3-30 microg/kg) and marble burying in mice (3-10 mg/kg), indicating anxiolytic-like effects. Importantly, LY404039 did not produce sedative effects or motor impairment as measured by rotarod performance and lack of escape failures in the conditioned avoidance task (at doses up to 30 and 10 mg/kg, respectively). LY404039 (10 mg/kg) also increased dopamine and serotonin release/turnover in the prefrontal cortex. CONCLUSIONS: These results demonstrate the broad preclinical efficacy of LY404039 across multiple animal models of antipsychotic and anxiolytic efficacy. Additionally, this compound modulates mesocortical neurotransmission and provides a novel mechanism for the treatment of psychiatric disorders that may be associated with improved efficacy and reduced incidence of undesirable side effects. As glutamatergic dysfunction has been linked to the etiology of schizophrenia, clinical studies with more potent mGlu2/3 agonists, such as LY404039, may be useful to explore the validity of this hypothesis.

Pharmacological and pharmacokinetic properties of a structurally novel, potent, and selective metabotropic glutamate 2/3 receptor agonist: in vitro characterization of agonist (-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]-hexane-4,6-dicarboxylic acid (LY404039).

Group II metabotropic glutamate (mGlu) receptor agonists, including (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate (LY354740) and (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268), have demonstrated efficacy in animal models of anxiety and schizophrenia, and LY354740 decreased anxiety in human subjects. Herein, we report the in vitro pharmacological profile and pharmacokinetic properties of another potent, selective, and structurally novel mGlu2/3 receptor agonist, (-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY404039) and provide comparisons with LY354740. Similar to LY354740, LY404039 is a nanomolar potent agonist at recombinant human mGlu2 and mGlu3 receptors (K(i) = 149 and 92, respectively) and in rat neurons expressing native mGlu2/3 receptors (Ki = 88). LY404039 is highly selective for mGlu2/3 receptors, showing more than 100-fold selectivity for these receptors, versus ionotropic glutamate receptors, glutamate transporters, and other receptors targeted by known anxiolytic and antipsychotic medications. Functionally, LY404039 potently inhibited forskolin-stimulated cAMP formation in cells expressing human mGlu2 and mGlu3 receptors. Electrophysiological studies indicated that LY404039 suppressed electrically evoked excitatory activity in the striatum, and serotonin-induced l-glutamate release in the prefrontal cortex; effects reversed by LY341495. These characteristics suggest LY404039 modulates glutamatergic activity in limbic and forebrain areas relevant to psychiatric disorders; and that, similar to LY354740, it works through a mechanism that may be devoid of negative side effects associated with current antipsychotics and anxiolytics. Interestingly, despite the slightly lower potency (approximately 2-5-fold) of LY404039 versus LY354740 in binding, functional, and electrophysiological assays, LY404039 demonstrated higher plasma exposure and better oral bioavailability in pharmacokinetic experiments. Collectively, the current data indicate that LY404039 may be valuable in the treatment of neuropsychiatric disorders, including anxiety and psychosis.

Synthesis and metabotropic glutamate receptor activity of S-oxidized variants of (-)-4-amino-2-thiabicyclo-[3.1.0]hexane-4,6-dicarboxylate: identification of potent, selective, and orally bioavailable agonists for mGlu2/3 receptors.

(-)-4-Amino-2-thiabicyclo-[3.1.0]hexane-4,6-dicarboxylate (LY389795, (-)-3) is a highly potent and selective agonist of metabotropic glutamate receptors 2 (mGlu2) and 3 (mGlu3). As part of our ongoing research program, we have prepared S-oxidized variants of (-)-3, compounds (-)-10, (+)-11 (LY404040), and (-)-12 (LY404039). Each of these chiral heterobicyclic amino acids displaced specific binding of the mGlu2/3 receptor antagonist 3H-2S-2-amino-2-(1S,2S-2-carboxycycloprop-1-yl)-3-(xanth-9-yl)propanoic acid (3H-LY341495) from membranes expressing recombinant human mGlu2 or mGlu3 and acted as potent agonists in cells expressing these receptor subtypes. Docking of the most potent of these derivatives, (+)-11, to mGlu2 revealed the possibility of an additional H-bond interaction between the sulfoxide oxygen of (+)-11 with tyrosine residue Y236. Pharmacokinetic analysis of mGlu active enantiomers (+)-11 and (-)-12 in rats showed each to be well absorbed following oral administration. Consistent with their mGlu2/3 agonist potency and pharmacokinetic properties, both (+)-11 and (-)-12 blocked phencyclidine-evoked ambulations in a dose-dependent manner, indicating their potential as nonclassical antipsychotic agents.

Improved bioavailability of the mGlu2/3 receptor agonist LY354740 using a prodrug strategy: in vivo pharmacology of LY544344.

Numerous studies have indicated that selective agonists of group II metabotropic glutamate (mGlu) receptors, such as LY354740 [(1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate] and LY379268 [(-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate], may be useful in the treatment of many psychiatric disorders, including psychosis, anxiety, and drug withdrawal. Although animal and human studies demonstrate potential therapeutic utility, poor oral bioavailability is a limiting factor in the clinical development of these compounds. Therefore, a novel prodrug approach is being pursued to increase exposure levels of active compound after oral administration. Here, we demonstrate a 10-fold increase in brain, plasma, and cerebrospinal fluid levels of LY354740 after oral prodrug administration. Furthermore, we compare the oral efficacy of the mGlu2/3 receptor agonist LY354740 and its prodrug LY544344 [(1S,2S,5R,6S)-2-[(2'S)-(2'-amino)propionyl]aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid hydrochloride] in rodent models of psychosis and anxiety. Phencyclidine (PCP)-induced hyperlocomotion was dose dependently inhibited in rats receiving oral administration of 30 or 100 mg/kg LY544344, whereas LY354740 did not significantly reverse PCP-mediated behaviors at doses up to 100 mg/kg. Orally administered LY544344 (30 mg/kg) and subcutaneously administered LY354740 (10 mg/kg) attenuated stress-induced hyperthermia in DBA/2 mice, with the prodrug producing anxiolytic effects at lower oral doses than the parent compound. Although oral administration of LY354740 did not significantly affect fear-induced suppression of operant responding in rats, subcutaneously administered LY354740 (10 or 20 mg/kg) and orally administered LY544344 (10 or 30 mg/kg) produced significant anxiolytic effects in this model. The present data confirm that mGlu2/3 receptor agonists produce antipsychotic and anxiolytic effects in animal behavioral models and demonstrate that oral bioavailability of LY354740 was substantially increased using a prodrug strategy.

C3'-cis-Substituted carboxycyclopropyl glycines as metabotropic glutamate 2/3 receptor agonists: synthesis and SAR studies.

The synthesis of a series of C3'-cis-substituted carboxycyclopropyl glycines bearing a wide variety of functional groups is described, and the structure-activity relationship for this series as agonists of group II metabotropic glutamate receptors is reported.

Methyl substitution of 2-aminobicyclo[3.1.0]hexane 2,6-dicarboxylate (LY354740) determines functional activity at metabotropic glutamate receptors: identification of a subtype selective mGlu2 receptor agonist.

LY354740 (1) is a highly potent and selective agonist of metabotropic glutamate (mGlu) receptors 2 and 3. In the present study, we have prepared C3- and C4-methyl-substituted variants of rac-1, compounds 5, 9, and 13. Each of these racemic methyl-substituted analogues displaced specific binding of the mGlu2/3 receptor antagonist (3)H-2S-2-amino-2-(1S,2S-2-carboxycycloprop-1-yl)-3-(xanth-9-yl)propanoic acid ((3)H-LY341495) from membranes expressing mGlu2 or mGlu3 receptor subtypes. Evaluation of the functional effects of this series on second messenger responses in cells expressing human mGlu2 or mGlu3 receptors revealed C3beta-methyl analogue 5 to possess antagonist properties at both mGlu2 and mGlu3 receptors while C4beta-methyl analogue 9 acts as a full agonist at each of these targets. Unexpectedly, we found that incorporation of a methyl substituent at the C4alpha-position as in analogue 13 results in a mixed mGlu2 agonist/mGlu3 antagonist pharmacological profile. All of the mGlu2 agonist and mGlu3 antagonist activity of rac-13 was found to reside in its resolved (+)-isomer.

(2S,1'S,2'R,3'R)-2-(2'-Carboxy-3'-hydroxymethylcyclopropyl) glycine is a highly potent group 2 and 3 metabotropic glutamate receptor agonist with oral activity.

The asymmetric synthesis and biological activity of (2S,1'S,2'R,3'R)-2-(2'-carboxy-3'-hydroxymethylcyclopropyl) glycine ((+)-3) is described. This novel C-3' substituted carboxy cyclopropyl glycine is a highly potent group 2 and group 3 mGluR agonist that has proven to be orally active in both fear potentiated startle (animal model for anxiety) and PCP-induced motor activation (animal model for psychosis) assays in rats.

Synthesis and structure-activity relationship studies of novel 2-diarylethyl substituted (2-carboxycycloprop-1-yl)glycines as high-affinity group II metabotropic glutamate receptor ligands.

The major excitatory neurotransmitter in the central nervous system, (S)-glutamic acid , activates both ionotropic and metabotropic excitatory amino acid receptors. Its importance in connection to neurological and psychiatric disorders has directed great attention to the development of compounds that modulate the effects of this endogenous ligand. Whereas L-carboxycyclopropylglycine (L-CCG-1) is a potent agonist at, primarily, group II metabotropic glutamate receptors, alkylation of at the alpha-carbon notoriously result in group II mGluR antagonists, of which the most potent compound described so far, LY341495, displays IC(50) values of 23 and 10 nM at the group II receptor subtypes mGlu2 and mGlu3, respectively. In this study we synthesized a series of structural analogues of in which the xanthyl moiety is replaced by two substituted-phenyl groups. The pharmacological characterization shows that these novel compounds have very high affinity for group II mGluRs when tested as their racemates. The most potent analogues demonstrate K(i) values in the range of 5-12 nM, being thus comparable to LY341495.

Inhibition of group I metabotropic glutamate receptor responses in vivo in rats by a new generation of carboxyphenylglycine-like amino acid antagonists.

A series of novel group I metabotropic glutamate receptor (mGlu) antagonists have been designed on the basis of the 4-carboxyphenylglycine pharmacophore. The compounds are either mGlu1 receptor selective or equipotent for both mGlu1 and mGlu5 receptors and have IC(50) values ranging from 1 to 30 microM determined by phosphoinositide hydrolysis (PI) assay in vitro. All the compounds produced dose-dependent inhibition of group I mGlu receptor agonist (RS)-3,5-dihydroxyphenylglycine (DHPG)-induced limbic seizure responses in mice with ED(50) values ranging from 9 nmol for LY393053 to 138 nmol for LY339840 after intracerebroventricular injection and were more potent than the mGlu1 receptor antagonist 1-aminoindan-1,5-dicarboxylic acid (ED(50)=477 nmol). Further antagonist actions were also demonstrated in a model of (RS)-DHPG-induced PI hydrolysis in vivo such that LY367385 and the active cis isomer of LY393053 produced dose-dependent inhibition of PI responses in both cerebellum and hippocampus. Cis LY393053 also inhibited hippocampal PI responses when administered intraperitoneally at a dose of 30 mg/kg. These compounds define a new series of group I mGlu receptor antagonists which may serve as useful experimental tools.