Metabotropic glutamate receptor (mGluR) subtypes (mGluR1 to mGluR8) act as important pre-and postsynaptic regulators of neurotransmission in the CNS. These receptors consist of two domains, an extracellular region containing the orthosteric agonist site and a transmembrane heptahelical domain involved in G protein activation and recognition of several recently synthesized pharmacological modulators. The presynaptic receptor mGluR7 shows the highest evolutionary conservation within the family, but no selective pharmacological tool was known. Here we characterize an mGluR7-selective agonist, N,N-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082), which directly activates receptor signaling via an allosteric site in the transmembrane domain. At transfected mammalian cells expressing mGluR7, AMN082 potently inhibits cAMP accumulation and stimulates GTP␥S binding (EC50-values, 64 -290 nM) with agonist efficacies comparable with those of L-2-amino-4-phosphonobutyrate (L-AP4) and superior to those of L-glutamate. AMN082 (<10 M) failed to show appreciable activating or inhibitory effects at other mGluR subtypes and selected ionotropic GluRs. Chimeric receptor studies position the binding site of AMN082 in the transmembrane region of mGluR7, and we demonstrate that this allosteric agonist has little, if any, effect on the potency of orthosteric ligands. Here we provide evidence for full agonist activity mediated by the heptahelical domain of family 3 G protein-coupled receptors (which have mGluR-like structure) that may lead to drug development opportunities. Further, AMN082 is orally active, penetrates the bloodbrain barrier, and elevates the plasma stress hormones corticosterone and corticotropin in an mGluR7-dependent fashion. Therefore, AMN082 is a valuable tool for unraveling the role of mGluR7 in stress-related CNS disorders.G protein ͉ mGluR G protein-coupled receptors in vertebrates constitute a superfamily of 1,000-2,000 transmembrane heptahelical proteins that can be activated by a large number of extracellular signals such as photons, hormones, neurotransmitters, and growth and development factors. These receptors transduce and amplify cellular signals by the activation of G proteins, which in turn modulates cytoplasmic second-messenger and ion levels (1). Sequence comparison among the different G protein-coupled receptors revealed the existence of at least six receptor families (2). One of them, family 3, comprises receptors for extracellular calcium, pheromones, GABA, and L-glutamate. This receptor family is characterized by a large N-terminal extracellular domain that has been demonstrated by site-directed mutagenesis and x-ray crystallography to contain the binding site for orthosteric agonists (3-5). Metabotropic glutamate receptors (mGluRs) are members of family 3 and are activated by the major excitatory neurotransmitter of the mammalian brain, L-glutamate. The mGluRs act as important pre-and postsynaptic regulators of neurotransmission in the CNS, and there are at least eight subtypes (mGluR1 to m...

Dual orexin receptor (OXR) antagonists (DORAs) such as almorexant, 1 (SB-649868), or suvorexant have shown promise for the treatment of insomnias and sleep disorders in several recent clinical trials in volunteers and primary insomnia patients. The relative contribution of antagonism of OX1R and OX2R for sleep induction is still a matter of debate. We therefore initiated a drug discovery project with the aim of creating both OX2R selective antagonists and DORAs. Here we report that the OX2R selective antagonist 26 induced sleep in mice primarily by increasing NREM sleep, whereas the DORA suvorexant induced sleep largely by increasing REM sleep. Thus, OX2R selective antagonists may also be beneficial for the treatment of insomnia.

Background: Behavioral genetics identified mGlu7 as a key regulator of brain emotion circuits. Results: An mGlu7-selective, Venus flytrap domain (VFTD)-directed antagonist inhibits fear, synaptic plasticity, stress, and anxiety in rodents. Conclusion: Pharmacological blockers of mGlu7 may represent promising future anxiolytics and antidepressants in man. Significance: The VFTD region of class C GPCRs provides a promising target for computer-assisted drug design.

Dual orexin receptor (OXR) antagonists (DORAs) such as almorexant, SB-649868, suvorexant (MK-4305), and filorexant (MK-6096), have shown promise for the treatment of insomnias and sleep disorders. Whether antagonism of both OX1R and OX2R is necessary for sleep induction has been a matter of some debate. Experiments using knockout mice suggest that it may be sufficient to antagonize only OX2R. The recent identification of an orally bioavailable, brain penetrant OX2R preferring antagonist 2-((1H-Indol-3-yl)methyl)-9-(4-methoxypyrimidin-2-yl)-2,9-diazaspiro[5.5]undecan-1-one (IPSU) has allowed us to test whether selective antagonism of OX2R may also be a viable strategy for induction of sleep. We previously demonstrated that IPSU and suvorexant increase sleep when dosed during the mouse active phase (lights off); IPSU inducing sleep primarily by increasing NREM sleep, suvorexant primarily by increasing REM sleep. Here, our goal was to determine whether suvorexant and IPSU affect sleep architecture independently of overall sleep induction. We therefore tested suvorexant (25 mg/kg) and IPSU (50 mg/kg) in mice during the inactive phase (lights on) when sleep is naturally more prevalent and when orexin levels are normally low. Whereas IPSU was devoid of effects on the time spent in NREM or REM, suvorexant substantially disturbed the sleep architecture by selectively increasing REM during the first 4 h after dosing. At the doses tested, suvorexant significantly decreased wake only during the first hour and IPSU did not affect wake time. These data suggest that OX2R preferring antagonists may have a reduced tendency for perturbing NREM/REM architecture in comparison with DORAs. Whether this effect will prove to be a general feature of OX2R antagonists vs. DORAs remains to be seen.

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