GABAA receptors are a family of ligand-gated ion channels which are essential for the regulation of central nervous system function. Benzodiazepines – which target GABAA receptors containing the α1, α2, α3, or α5 subunits non-selectively – have been in clinical use for decades and are still among the most widely prescribed drugs for the treatment of insomnia and anxiety disorders. However, their use is limited by side effects and the risk of drug dependence. In the past decade, the identification of separable key functions of GABAA receptor subtypes suggests that receptor subtype-selective compounds could overcome the limitations of classical benzodiazepines and, furthermore, might be valuable for novel indications, such as analgesia, depression, schizophrenia, cognitive enhancement and stroke.

The amyloid-β lowering capacity of anti-Aβ antibodies has been demonstrated in transgenic models of Alzheimer's disease (AD) and in AD patients. While the mechanism of immunotherapeutic amyloid-β removal is controversial, antibody-mediated sequestration of peripheral Aβ versus microglial phagocytic activity and disassembly of cerebral amyloid (or a combination thereof) has been proposed. For successful Aβ immunotherapy, we hypothesized that high affinity antibody binding to amyloid-β plaques and recruitment of brain effector cells is required for most efficient amyloid clearance. Here we report the generation of a novel fully human anti-Aβ antibody, gantenerumab, optimized in vitro for binding with sub-nanomolar affinity to a conformational epitope expressed on amyloid-β fibrils using HuCAL(®) phage display technologies. In peptide maps, both N-terminal and central portions of Aβ were recognized by gantenerumab. Remarkably, a novel orientation of N-terminal Aβ bound to the complementarity determining regions was identified by x-ray analysis of a gantenerumab Fab-Aβ(1-11) complex. In functional assays gantenerumab induced cellular phagocytosis of human amyloid-β deposits in AD brain slices when co-cultured with primary human macrophages and neutralized oligomeric Aβ42-mediated inhibitory effects on long-term potentiation in rat brain. In APP751(swedish)xPS2(N141I) transgenic mice, gantenerumab showed sustained binding to cerebral amyloid-β and, upon chronic treatment, significantly reduced small amyloid-β plaques by recruiting microglia and prevented new plaque formation. Unlike other Aβ antibodies, gantenerumab did not alter plasma Aβ suggesting undisturbed systemic clearance of soluble Aβ. These studies demonstrated that gantenerumab preferentially interacts with aggregated Aβ in the brain and lowers amyloid-β by eliciting effector cell-mediated clearance.

Vigilance, anxiety, epileptic activity, and muscle tone can be modulated by drugs acting at the benzo- (Fig. la) was constructed containing a 6.4-kb genomic region including exons 7, 9, and 10 of the y2 subunit gene isolated from a 129SV mouse genomic library. A 1.2-kb genomic Pvu II-Nco I fragment including exon 8 (coding for amino acids 306-375 of the y2 polypeptide) was replaced with the phosphoglycerate kinase (PGK)-neo cassette (11), and a tk expression cassette (12) was added at the 3' end of the y2 sequence. Splicing from exon 7 to exon 9 would result in a stop of the translational reading frame and prohibit expression of sequences downstream of exon 7. Before electroporation into E14 ES cells (13), the plasmid was linearized at a polylinker site adjacent to the 5' end of the 7y2 genomic sequence. E14 ES cells were cultured on irradiated G418-resistant feeder cells obtained from CD1-M-TKneo2 mouse embryos [BRL, Fullinsdorf (Basel)] in GMEM (Glasgow modification of Eagle's medium; Flow Laboratories) containing 10% total calf serum and leukemia inhibitory factor (103 units/ml, Life Technologies). The cells were transfected and screened for homologous recombinants (14) by using PCR and the primers y2.19 (5'-CATCT CCATC GCTAA GAATG TTCGG derived from 7y2 sequences upstream of the targeting vector and Y2.20 (5'-ATGCT CCAGA CTGCC TTGGG AAAAG C-3') derived from PGK promoter sequences (11). Chimeric mice were generated (15) and mated to C57BL/6 females, and the offspring were genotyped by PtR amplification of tail DNAs. Reactions specific for the disrupted y2 allele [(0) Abbreviations: BZ, benzodiazepine; GABA, y-aminobutyric acid; DRG, dorsal root ganglion (ganglia); ES, embryonic stem; E, embryonic day; P, postnatal day.§To whom reprint requests should be addressed. 7749The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

We have identified two chemical series of compounds acting as selective positive allosteric modulators (enhancers) of native and recombinant metabotropic glutamate 1 (mGlu1) receptors. These compounds did not directly activate mGlu1 receptors but markedly potentiated agonist-stimulated responses, increasing potency and maximum efficacy. Binding of these compounds increased the affinity of a radiolabeled glutamate-site agonist at its extracellular N-terminal binding site. Chimeric and mutated receptors were used to localize amino acids in the receptor transmembrane region critical for these enhancing properties. Finally, the compounds potentiated synaptically evoked mGlu1 receptor responses in rat brain slices. The discovery of selective positive allosteric modulators of mGlu1 receptors opens up the possibility to develop a similar class of compounds for other family 3 G protein-coupled receptors.

Down syndrome (DS) is associated with neurological complications, including cognitive deficits that lead to impairment in intellectual

A model of the rmGlu1 seven-transmembrane domain complexed with a negative allosteric modulator, 1-ethyl-2-methyl-6-oxo-4-(1,2,4,5-tetrahydro-benzo[d]azepin-3-yl)-1,6-dihydro-pyrimidine-5-carbonitrile (EM-TBPC) was constructed. Although the mGlu receptors belong to the family 3 G-protein-coupled receptors with a low primary sequence similarity to rhodopsin-like receptors, the high resolution crystal structure of rhodopsin was successfully applied as a template in this model and used to select residues for site-directed mutagenesis. The mGlu 1 receptor family currently comprises eight receptors that are divided into three classes on the basis of their sequence similarities, signal transduction, and agonist rank order of potency. Group I (mGlu1 and -5) receptors are coupled to the stimulation of phosphoinositide hydrolysis; group II (mGlu2 and -3) and group III receptors (mGlu4, -6, -7, and -8) are negatively coupled to cAMP production (1-3). Many studies have demonstrated the involvement of mGlu receptors in the modulation of synaptic transmission, ion channel activity, and synaptic plasticity (4, 5), and dysfunction of these receptors has been implicated in psychiatric and neurological diseases (6). The mGlu receptors belong to the family 3 of G-protein-coupled receptors (GPCRs). Other members of this family include the GABA B , Ca 2ϩ -sensing, vomeronasal, pheromone, and putative taste receptors (7). The family 3 GPCRs shares a low sequence similarity with the other families. In contrast to family 1, the family 3 receptors are characterized by two distinctly separated topological domains: an exceptionally long extracellular amino-terminal domain (500 -600 amino acids), which forms the agonistbinding pocket (8 -10), and the 7TM helical segments involved in receptor activation and G-protein coupling (11).Compounds acting at group I mGlu receptors can be grouped into two categories. Category one comprises competitive agonists and antagonists. These compounds are phenylglycine derivatives or rigidified analogs of glutamate (12), which logically bind to the glutamate-binding domain. Competitive group I ligands have achieved only limited subtype selectivity and potency, perhaps due to the high sequence homology of the mGlu receptor family agonist-binding site supported by the threedimensional structure of mGlu1 amino-terminal domain (10). However, recent development of more sensitive technologies for functional screening of GPCRs has resulted in the discovery of a second category of compounds. These novel compounds, which interact within the 7TMD of group I mGlu receptor, act as positive or negative allosteric modulators (13). CPCCOEt was the first non-amino acid derivative, subtype-selective antagonist of the mGlu1 receptor (IC 50 ϭ 6.5 M at hmGlu1b) to

The data further support the potential of GABAA alpha5 receptors as a target for cognition-enhancing drugs. The dual binding and functional selectivity offers an ideal profile for cognition-enhancing effects without the unwanted side effects associated with activity at other GABAA receptor subtypes.

IMPORTANCE In schizophrenia, the severity of negative symptoms is a key predictor of long-term disability. Deficient signaling through the N-methyl-D-aspartate receptor is hypothesized to underlie many signs and symptoms associated with schizophrenia in particular negative symptoms. Glycine acts as an N-methyl-D-aspartate receptor coagonist. Blockade of the glycine transporter type 1 to inhibit glycine reuptake and elevate synaptic glycine concentrations represents an effective strategy to enhance N-methyl-D-aspartate receptor transmission. OBJECTIVE To determine the efficacy and safety of bitopertin (RG1678), a glycine reuptake inhibitor, in patients with schizophrenia and predominant negative symptoms who were stable while taking an antipsychotic treatment. DESIGN, SETTING, AND PARTICIPANTS This randomized, double-blind, placebo-controlled, phase 2 proof-of-concept trial involved 323 patients with schizophrenia and predominant negative symptoms across 66 sites worldwide. INTERVENTIONS Bitopertin (10, 30, or 60 mg/d) or placebo added to standard antipsychotic therapy for a treatment duration of 8 weeks. MAIN OUTCOMES AND MEASURES Change from baseline in the Positive and Negative Syndrome Scale negative factor score. RESULTS In the per-protocol population, 8 weeks of treatment with bitopertin was associated with a significant reduction of negative symptoms in the 10-mg/d (mean [SE] reduction in negative symptoms score, −25% [2%]; P = .049) and 30-mg/d (mean [SE], −25% [2%]; P = .03) bitopertin groups, a significantly higher response rate and a trend toward improved functioning in the 10-mg/d group when compared with placebo (mean [SE], −19% [2%]). Results reached trend-level significance in the intent-to-treat population. Estimates of bitopertin binding to glycine transporter type 1 showed that low to medium levels of occupancy yielded optimal efficacy in patients, consistent with findings in preclinical assays. CONCLUSIONS AND RELEVANCE Bitopertin-mediated glycine reuptake inhibition may represent a novel treatment option for schizophrenia, with the potential to address negative symptoms.