Following several recent reports that suggest that dual cAMP and cGMP phosphodiesterase 10A (PDE10A) inhibitors may present a novel mechanism to treat positive symptoms of schizophrenia, we sought to extend the preclinical characterization of two such compounds, papaverine [1-(3,4-dimethoxybenzyl)-6,7-dimethoxyisoquinoline] and MP-10 [2-{[4-(1-methyl-4-pyridin-4-yl-1H-pyrazol-3-yl)phenoxy]methyl}quino-line], in a variety of in vivo and in vitro assays. Both of these compounds were active in a range of antipsychotic models, antagonizing apomorphine-induced climbing in mice, inhibiting conditioned avoidance responding in both rats and mice, and blocking N-methyl-D-aspartate antagonist-induced deficits in prepulse inhibition of acoustic startle response in rats, while improving baseline sensory gating in mice, all of which strengthen previously reported observations. These compounds also demonstrated activity in several assays intended to probe negative symptoms and cognitive deficits, two disease domains that are underserved by current treatments, with both compounds showing an ability to increase sociality in BALB/cJ mice in the social approach/social avoidance assay, enhance social odor recognition in mice and, in the case of papaverine, improve novel object recognition in rats. Biochemical characterization of these compounds has shown that PDE10A inhibitors modulate both the dopamine D1-direct and D2-indirect striatal pathways and regulate the phosphorylation status of a panel of glutamate receptor subunits in the striatum. It is striking that PDE10A inhibition increased the phosphorylation of the (Ϯ)-␣-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptor GluR1 subunit at residue serine 845 at the cell surface. Together, our results suggest that PDE10A inhibitors alleviate both dopaminergic and glutamatergic dysfunction thought to underlie schizophrenia, which may contribute to the broad-spectrum efficacy.Phosphodiesterase 10A (PDE10A) inhibition has generated much excitement as a potential novel mechanism for the treatment of the positive symptoms of schizophrenia (Menniti et al., 2007;Siuciak, 2008 ABBREVIATIONS: PDE10A, phosphodiesterase 10A; MP-10, 2-[4-(1-methyl-4-pyridin-4-yl-1H-pyrazol-3-yl)-phenoxymethy]-quinoline; TP-10, 2-{4-[pyridin-4-yl-1-(2,2,2-trifluoroethyl)-1H-pyrazol-3-yl]-phenoxymethyl}-quinoline; MK-801, dizocilpine maleate; CREB, cAMP-response element-binding protein; pCREB, phospho-cAMP-response element-binding protein; DARPP-32, dopamine and cAMP-regulated phosphoprotein of 32-kDa molecular mass; pDARPP-32, phosphodopamine and cAMP-regulated phosphoprotein of 32-kDa molecular mass; PKA, protein kinase A; cGKII, cGMP-dependent kinase type II; D1, dopamine receptor subtype 1; D2, dopamine receptor subtype 2; GluR1, glutamate receptor subunit 1; pGluR1, phosphoglutamate receptor subunit 1; GluR2/3, glutamate receptor subunit 2/glutamate receptor subunit 3; pGluR2/3, phosphoglutamate receptor subunit 2/phosphoglutamate receptor subunit 3; NMDA, N-methyl-D-aspartate; NR2B, NMDA ...

No abstract

Positive allosteric modulators (PAMs) of metabotropic glutamate receptor subtype 5 (mGlu5) enhance N-methyl-D-aspartate receptor function and may represent a novel approach for the treatment of schizophrenia. ADX47273 [S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone], a recently identified potent and selective mGlu5 PAM, increased (9-fold) the response to threshold concentration of glutamate (50 nM) in fluorometric Ca 2ϩ assays (EC 50 ϭ 170 nM) in human embryonic kidney 293 cells expressing rat mGlu5. In the same system, ADX47273 dose-dependently shifted mGlu5 receptor glutamate response curve to the left (9-fold at 1 M) and competed for binding of3 H]quisqualate. In vivo, ADX47273 increased extracellular signal-regulated kinase and cAMP-responsive element-binding protein phosphorylation in hippocampus and prefrontal cortex, both of which are critical for glutamate-mediated signal transduction mechanisms. In models sensitive to antipsychotic drug treatment, ADX47273 reduced rat-conditioned avoidance responding [minimal effective dose (MED) ϭ 30 mg/kg i.p.] and decreased mouse apomorphine-induced climbing (MED ϭ 100 mg/kg i.p.), with little effect on stereotypy or catalepsy. Furthermore, ADX47273 blocked phencyclidine, apomorphine, and amphetamine-induced locomotor activities (MED ϭ 100 mg/kg i.p.) in mice and decreased extracellular levels of dopamine in the nucleus accumbens, but not in the striatum, in rats. In cognition models, ADX47273 increased novel object recognition (MED ϭ 1 mg/kg i.p.) and reduced impulsivity in the fivechoice serial reaction time test (MED ϭ 10 mg/kg i.p.) in rats. Taken together, these effects are consistent with the hypothesis that allosteric potentiation of mGlu5 may provide a novel approach for development of antipsychotic and procognitive agents.The metabotropic glutamate receptor (mGlu) receptor family includes eight G-protein-coupled receptor (GPCR) subtypes classified on the basis of structural homology, Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.108.136580.ABBREVIATIONS: mGlu, metabotropic glutamate receptor; GPCR, G-protein-coupled receptor; PAM, positive allosteric modulator; CPPHA, 2, NMDA, MPEP,

No abstract

No abstract