Synthesis, Pharmacological Characterization, and Molecular Modeling of Heterobicyclic Amino Acids Related to (+)-2-Aminobicyclo[3.1.0]hexane- 2,6-dicarboxylic Acid (LY354740):  Identification of Two New Potent, Selective, and Systemically Active Agonists for Group II Metabotropic Glutamate Receptors

Abstract

As part of our ongoing research program aimed at the identification of highly potent, selective, and systemically active agonists for group II metabotropic glutamate (mGlu) receptors, we have prepared novel heterobicyclic amino acids (-)-2-oxa-4-aminobicyclo[3.1. 0]hexane-4,6-dicarboxylate (LY379268, (-)-9) and (-)-2-thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY389795, (-)-10). Compounds (-)-9 and (-)-10 are structurally related to our previously described nanomolar potency group II mGlu receptor agonist, (+)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate (LY354740 monohydrate, 5), with the C4-methylene unit of 5 being replaced with either an oxygen atom (as in (-)-9) or a sulfur atom (as in (-)-10). Compounds (-)-9 and (-)-10 potently and stereospecifically displaced specific binding of the mGlu2/3 receptor antagonist ([3H]LY341495) in rat cerebral cortical homogenates, displaying IC50 values of 15 +/- 4 and 8.4 +/- 0.8 nM, respectively, while having no effect up to 100 000 nM on radioligand binding to the glutamate recognition site on NMDA, AMPA, or kainate receptors. Compounds (-)-9 and (-)-10 also potently displaced [3H]LY341495 binding from membranes expressing recombinant human group II mGlu receptor subtypes: (-)-9, Ki = 14.1 +/- 1.4 nM at mGlu2 and 5.8 +/- 0.64 nM at mGlu3; (-)-10, Ki = 40.6 +/- 3.7 nM at mGlu2 and 4.7 +/- 1.2 nM at mGlu3. Evaluation of the functional effects of (-)-9 and (-)-10 on second-messenger responses in nonneuronal cells expressing human mGlu receptor subtypes demonstrated each to be a highly potent agonist for group II mGlu receptors: (-)-9, EC50 = 2.69 +/- 0.26 nM at mGlu2 and 4.58 +/- 0.04 nM at mGlu3; (-)-10, EC50 = 3.91 +/- 0.81 nM at mGlu2 and 7.63 +/- 2. 08 nM at mGlu3. In contrast, neither compound (up to 10 000 nM) displayed either agonist or antagonist activity in cells expressing recombinant human mGlu1a, mGlu5a, mGlu4a, or mGlu7a receptors. The agonist effects of (-)-9 and (-)-10 at group II mGlu receptors were not totally specific, however, as mGlu6 agonist activity was observed at high nanomolar concentrations for (-)-9 (EC50 = 401 +/- 46 nM) and at micromolar concentrations (EC50 = 2 430 +/- 600 nM) for (-)-10; furthermore, each activated mGlu8 receptors at micromolar concentrations (EC50 = 1 690 +/- 130 and 7 340 +/- 2 720 nM, respectively). Intraperitoneal administration of either (-)-9 or (-)-10 in the mouse resulted in a dose-related blockade of limbic seizure activity produced by the nonselective group I/group II mGluR agonist (1S,3R)-ACPD ((-)-9 ED50 = 19 mg/kg, (-)-10 ED50 = 14 mg/kg), indicating that these molecules effectively cross the blood-brain barrier following systemic administration and suppress group I mGluR-mediated limbic excitation. Thus, heterobicyclic amino acids (-)-9 and (-)-10 are novel pharmacological tools useful for exploring the functions of mGlu receptors in vitro and in vivo.

Activation of Group II Metabotropic Glutamate Receptors Inhibits the Discriminative Stimulus Effects of Alcohol via Selective Activity Within the Amygdala

“…It could also be argued that the LY379268 doses tested were not high enough to elicit alcohol-like stimulus effects because there were no changes in behavior observed across tested doses. Indeed, the highest dose did not significantly alter response rate (Figure 2b), but acute doses of LY379268 higher than 10 mg/kg produce profound motor impairing effects (Cartmell et al, 2000) and may have nonspecific actions at other receptors (Monn et al, 1999;Seeman and Guan, 2008; but see Fell et al, 2009;Zysk et al, 2011), which would potentially complicate the interpretation of results; therefore, higher doses were not tested in this study.…”

“…(1R,4R,5S,6R)-4-amino-2-oxabicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY379268; Tocris, Ellisville, MI) and was dissolved in 0.9% saline and injected at a volume of 1 ml/kg (i.p.). LY379268 is a systemically active potent agonist of group II mGlu receptors and devoid of agonist or antagonist activity at ionotropic glutamate receptors, mGlu1a, mGlu5a, or mGlu7 receptors (Monn et al, 1999). For microinfusion studies, LY379268 was dissolved in artificial cerebral spinal fluid.…”

“…Male Long-Evans rats were trained to discriminate between a moderate dose of alcohol (1 g/kg) and water administered orally by gavage (IG) on a well-characterized two lever drug discrimination task. We first examined whether systemic pharmacological activation of mGlu2/3 receptors by LY379268, a selective mGlu2/3 receptor agonist (Monn et al, 1999), produces alcohol-like discriminative stimulus effects and/or modulates the discriminative stimulus effects of alcohol. Next, we sought to identify whether mGlu2/3 receptor activation is associated with changes in neuronal activity in specific brain regions as measured by c-Fos immunoreactivity (IR) using immunohistochemistry techniques.…”

The Metabotropic Glutamate 2/3 Receptor Agonist LY379268 Blocked Nicotine-Induced Increases in Nucleus Accumbens Shell Dopamine only in the Presence of a Nicotine-Associated Context in Rats

“…Nicotine doses are reported as base concentrations. LY379268 was custom synthesized as described previously (Monn et al, 1999) by ANAWA (Wangen, Switzerland). LY379268 (1 mg/kg, salt) was dissolved in 0.9% saline and pH-adjusted to 7.4 ( ± 0.5) with 1 M NaOH.…”

Group II Metabotropic Glutamate Receptor Modulation of DOI-induced c-fos mRNA and Excitatory Responses in the Cerebral Cortex

“…LY379268 and LY341495 were synthesized at Lilly Research Laboratories (Indianapolis, Indiana, USA) as previously described (Ornstein et al, 1998a,b;Monn et al, 1999).…”