Altered distribution of mGlu2 receptors in ß-amyloid-affected brain regions of Alzheimer cases and aged PS2APP mice.

Altered glutamatergic synaptic transmission is among the key events defining the course of Alzheimer's disease (AD). mGlu2 receptors, a subtype of group II metabotropic glutamate receptors, regulate (as autoreceptors) fast synaptic transmission in the CNS via the controlled release of the excitatory amino acid glutamate. Since their pharmacological manipulation in rodents has been reported to affect cognition, they are potential drug targets for AD therapy. We examined the fate of these receptors in cases of AD as well as in aging PS2APP mice--a proposed model of the disease. In vitro binding of [(3)H]LY354740, a selective group II agonist (with selective affinity for mGlu2 receptors, under the assay conditions used) and quantitative radioautography revealed a partial, but highly significant, loss of receptors in amyloid-affected discrete brain regions of AD cases and PS2APP mice. Among the mouse brain regions affected were, above all, the subiculum but also frontolateral cortex, dentate gyrus, lacunosum moleculare and caudate putamen. In AD, significant receptor losses were registered in entorhinal cortex and lacunosum moleculare (40% and 35%, respectively). These findings have implications for the development of selective ligands for symptomatic therapy in AD and for its diagnosis.

Discovery of potent, balanced and orally active dual NK1/NK3 receptor ligands.

During a program directed at selective NK(1) receptor antagonists, we serendipitously discovered an NK(1) receptor ligand with additional affinity for the NK(3) receptor. Recognising an opportunity for a drug discovery program aiming for dual NK(1)/NK(3) receptor antagonists, we prepared a series of analogues from a novel, versatile building block. From this series emerged compounds with high and balanced affinities for the NK(1) and the NK(3) receptors. Typical representatives of this series were active in the gerbil foot tapping assay after oral administration.

Discovery of the imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepine scaffold as a novel, potent and selective GABA(A) alpha5 inverse agonist series.

Through iterative design cycles we have discovered a number of novel new classes where the imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepine was deemed the most promising GABA(A) alpha5 inverse agonist class with potential for cognitive enhancement. This class combines a modest subtype binding selectivity with inverse agonism and has the most favourable molecular properties for further lead optimisation towards a central nervous system (CNS) acting medicine.

The discovery and unique pharmacological profile of RO4938581 and RO4882224 as potent and selective GABAA alpha5 inverse agonists for the treatment of cognitive dysfunction.

Lead optimisation of the imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepine class led to the identification of two clinical leads [RO4882224 (11) and RO4938581 (44)] functioning as novel potent and selective GABAA alpha5 inverse agonists. The unique pharmacological profiles and optimal pharmacokinetic profiles resulted in in vivo activity in selected cognition models.

Imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepines as potent and highly selective GABAA alpha5 inverse agonists with potential for the treatment of cognitive dysfunction.

In a search for GABAA alpha5 ligands that combine high subtype binding selectivity with a marked inverse agonism imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepines were identified as a promising class. A short tandem reaction allowed rapid access to this chemical series, thereby facilitating rapid SAR generation which guided the optimization process. Two compounds (10e and 11f) were found to be active in an in vivo paradigm for cognitive improvement.

Design and synthesis of a novel, achiral class of highly potent and selective, orally active neurokinin-1 receptor antagonists.

The discovery of a novel, achiral pyridine class of potent and orally active neurokinin-1 (NK(1)) receptor antagonists is described. The evaluation of this class is briefly outlined, leading to the identification of netupitant 21 and befetupitant 29, two new proprietary chemical entities with high affinity and excellent CNS penetration.

Distribution and abundance of metabotropic glutamate receptor subtype 2 in rat brain revealed by [3H]LY354740 binding in vitro and quantitative radioautography: correlation with the sites of synthesis, expression, and agonist stimulation of [35S]GTPgammas binding.

Until recently, there was a lack of selective radioligands for the subtypes of metabotropic glutamate (mGlu) receptors. [(3)H]LY354740 ((+)-2-aminobicyclo[3,1,0]hexane-2,6-dicarboxylic acid), a selective agonist for group II receptors (mGlu2 and -3, which are negatively coupled to cAMP production), has now been used to map their brain distribution and abundance by in vitro binding and quantitative radioautography. The selective cation dependence of its binding allowed the discrimination between mGlu2 and mGlu3 receptor labeling. Thus, in the presence of Ca(2+) and Mg(2+) ions, the agonist bound selectively to mGlu2 receptors as evidenced by: 1) the correlative distribution and abundance of binding sites (highest in the lacunosum moleculare of the hippocampus and lowest in white matter) with mGlu2 receptor mRNA and protein revealed by in situ hybridization histochemistry and immunohistochemistry, respectively; 2) its selective pharmacology; and 3) the distribution of LY354740-stimulated [(35)S]GTPgammaS binding (25-97% above basal, according to the brain region), revealing G protein-coupled receptor coupling to G(i) proteins. Nonspecific binding (in the presence of 10 muM DCG-IV, a group II-selective, mGlu2-preferring, receptor agonist) was <10% of total. In adjacent sections, the distribution of binding sites for [(3)H]DCG-IV was very similar. This extensive study paves the way for investigations of the regional expression and regulation of mGlu2 receptors in human CNS diseases, such as Alzheimer's disease, which may reveal their functional roles and identify potential therapeutic drug targets. Indeed, it has recently been demonstrated (Higgins et al. [2004] Neuropharmacology 46:907-917) that pharmacological manipulation of mGlu2 receptors influences cognitive performance in the rodent.

Effects of the mGluR2/3 agonist LY354740 on computerized tasks of attention and working memory in marmoset monkeys.

RATIONALE: LY354740 is a recently developed metabotropic glutamatergic receptor 2 and 3 (mGluR2/3) agonist. A high density of mGluR2 has been reported in terminal fields of the perforant path in rodents and humans, suggesting its involvement in cognitive functions mediated by the temporal lobe, including memory. A small number of in vivo studies in rodents have assessed the effects of LY354740 on memory tasks, reporting the induction of impaired memory for spatial orientation in a water maze task and for delayed match and non-match to position in an operant version of these tasks. OBJECTIVE: In the present primate study, we used radioautography to describe the distribution and intensity of (3)H-LY354740 binding in the hippocampal formation of the common marmoset monkey (Callithrix jacchus) relative to the rat. In the major, in vivo part of the study, the effects of systemic LY354740 on computerized tasks of attention and memory were investigated. METHODS: Adult common marmosets were trained to perform a five-choice serial reaction time (5-CSRT) task and a concurrent delayed match-to-position (CDMP) task from the Cambridge Neuropsychological Automated test Battery (CANTAB). Filter tests of LY354740 effects on motor dexterity and motivation for reward revealed high inter-individual variation in sensitivity; therefore, on the 5-CSRT, subjects were tested at a dose range of 3--10 mg/kg, and on the CDMP, subjects were tested at 1--3 or 3--10 mg/kg. RESULTS: Radioautography revealed a relatively low level of (3)H-LY354740 binding in the marmoset hippocampal formation compared to the rat. Despite low binding, LY354740 reduced sustained-attention accuracy in the 5-CSRT, and reduced accuracy in two stages of the CDMP. CONCLUSIONS: The current study provides novel evidence for the importance of mGluR2/3 in the regulation of primate cognitive functioning.