Highly potent, selective, and orally active phosphodiesterase 10A inhibitors.

The identification of highly potent and orally active phenylpyrazines for the inhibition of PDE10A is reported. The new analogues exhibit subnanomolar potency for PDE10A, demonstrate high selectivity against all other members of the PDE family, and show desired druglike properties. Employing structure-based drug design approaches, we methodically explored two key regions of the binding pocket of the PDE10A enzyme to alter the planarity of the parent compound 1 and optimize its affinity for PDE10A. Bulky substituents at the C9 position led to elimination of the mutagenicity of 1, while a crucial hydrogen bond interaction with Glu716 markedly enhanced its potency and selectivity. A systematic assessment of the ADME and PK properties of the new analogues led to druglike development candidates. One of the more potent compounds, 96, displayed an IC(50) for PDE10A of 0.7 nM and was active in predictive antipsychotic animal models.

Estrogen receptor neurobiology and its potential for translation into broad spectrum therapeutics for CNS disorders.

Estrogens are hormones that modulate a diverse array of effects during development and adulthood. The effects of estrogen are mediated by two estrogen receptor (ER) isotypes, ERalpha and ERbeta, which classically function as transcription factors to modulate specific target gene expression and in addition regulate a growing list of intracellular signaling cascades. These receptors share protein sequence homology and protein-motif organization but have distinct differences in their tissue distribution and binding affinities for their ligands. In the nervous system estrogen has been implicated to play a role in a number of processes which regulate synaptic plasticity including synaptogenesis and neurogenesis. The role for estrogen in a range of neurological and neuropsychiatric diseases is also becoming very apparent. Estrogen is able to regulate processes and behaviours relevant for both Alzheimer's disease and schizophrenia and to modulate neuroendocrine and inflammatory processes important in neuroinflammation, anxiety and depressive disorders as well as chronic pain. We will consider the rationale for estrogen-based therapies for diseases of the nervous system. In particular we will highlight the molecular mechanisms and signal transduction pathways most likely underlying the effects of estrogen in the CNS.

The orphan GPCR, GPR88, modulates function of the striatal dopamine system: a possible therapeutic target for psychiatric disorders?

In rodents, the orphan G protein-coupled receptor, Gpr88, is highly expressed in brain regions implicated in the pathophysiology of and is modulated by treatments for schizophrenia. We compared striatal function of Gpr88 knockout mice (Gpr88KOs) to wild-type mice using molecular, neurochemical and behavioral tests. Gpr88KOs lacked expression of Gpr88 in striatum, nucleus accumbens and layer IV of cortex. Gpr88KOs had normal striatal dopamine D2 receptor density and affinity and DARPP-32 expression but Gpr88KOs had higher basal striatal phosphorylated DARPP-32 Thr-34. In vivo microdialysis detected lower basal dopamine in Gpr88KOs while amphetamine-induced dopamine release was normal. Behaviorally, Gpr88KOs demonstrated disrupted prepulse inhibition of startle (PPI) and increased sensitivity to apomorphine-induced climbing and stereotypy (AICS) and amphetamine-stimulated locomotor activity. Antipsychotic administration to Gpr88KOs normalized the PPI deficit and blocked AICS. The modulatory role of Gpr88 in striatal dopamine function suggests it may be a new target for treatments for psychiatric disorders.

Activation of estrogen receptor-beta regulates hippocampal synaptic plasticity and improves memory.

Estrogens have long been implicated in influencing cognitive processes, yet the molecular mechanisms underlying these effects and the roles of the estrogen receptors alpha (ERalpha) and beta (ERbeta) remain unclear. Using pharmacological, biochemical and behavioral techniques, we demonstrate that the effects of estrogen on hippocampal synaptic plasticity and memory are mediated through ERbeta. Selective ERbeta agonists increased key synaptic proteins in vivo, including PSD-95, synaptophysin and the AMPA-receptor subunit GluR1. These effects were absent in ERbeta knockout mice. In hippocampal slices, ERbeta activation enhanced long-term potentiation, an effect that was absent in slices from ERbeta knockout mice. ERbeta activation induced morphological changes in hippocampal neurons in vivo, including increased dendritic branching and increased density of mushroom-type spines. An ERbeta agonist, but not an ERalpha agonist, also improved performance in hippocampus-dependent memory tasks. Our data suggest that activation of ERbeta can regulate hippocampal synaptic plasticity and improve hippocampus-dependent cognition.

The inhibition of glycogen synthase kinase 3beta by a metabotropic glutamate receptor 5 mediated pathway confers neuroprotection to Abeta peptides.

Activation of glycogen synthase kinase 3beta (Gsk3beta) has been shown to be a key component in signaling pathways that underlie neurodegeneration and neurodegenerative disease. Conversely, inactivation of Gsk3beta by phosphoinositide 3-kinase (PI3K)/Akt is an important neuroprotective mechanism. Previous studies have shown that agonist activation of group I metabotropic glutamate receptors (mGluRs) can increase neuronal survival and prevent apoptosis. However, little is known about the signaling pathways that couple mGluR5 to neuroprotection. In this report, we investigated whether activation of the PI3K/Akt/Gsk3beta pathway, which has been shown to have an important neuroprotective mechanism, is required for mGluR5 activation mediated neuroprotection against beta-amyloid. We found that brief incubations of mouse hippocampal slices with (R,S)-3,5-dihydroxyphenylglycine (DHPG) resulted in increased phosphorylation of Akt and Gsk3beta. The PI3K inhibitors, LY294002 and wortmannin, blocked the DHPG-induced increased phosphorylation of Akt and Gsk3beta. Similar results were observed in rat primary hippocampal cultures. Finally, we found that the PI3K inhibitor LY294002 can block (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG) mediated neuroprotection against beta-amyloid. Thus, these findings suggest that mGluR5 can modulate the PI3K/Akt/Gsk3beta pathway in the hippocampus, and that modulation of this signaling pathway can reverse beta-amyloid-induced neuronal toxicity.