3-(Pyridin-2-yl-ethynyl)benzamide metabotropic glutamate receptor 5 negative allosteric modulators: hit to lead studies.

A series of 3-(pyridin-2-yl-ethynyl)benzamide negative allosteric modulators of the metabotropic glutamate receptor 5 (mGluR5 NAMs) have been prepared. Starting from HTS hit 1 (IC(50): 926 nM), potent mGluR5 NAMs showing excellent potencies (IC(50)s<50 nM) and good physicochemical profiles were prepared by monitoring LipE values. One compound 26 showed excellent mGluR5 binding (K(i): 21 nM) and antagonism (IC(50): 8 nM), an excellent rat PK profile (CL: 12 mL/min/kg, %F: 85) and showed oral activity in a mouse 4-Plate Behavioral model of anxiety (MED: 30 mpk) and a mouse Stress Induced Hyperthermia model of anxiety (MED 17.8 mpk).

Differentiating antidepressants of the future: efficacy and safety.

There have been significant advances in the treatment of depression since the serendipitous discovery that modulating monoaminergic neurotransmission may be a pathological underpinning of the disease. Despite these advances, particularly over the last 15years with the introduction of selective serotonin and/or norepinephrine reuptake inhibitors (SNRI), there still remain multiple unmet clinical needs that would represent substantial improvements to current treatment regimens. In terms of efficacy there have been improvements in the percentage of patients achieving remission but this can still be dramatically improved and, in fact, issues still remain with relapse. Furthermore, advances are still required in terms of improving the onset of efficacy as well as addressing the large proportion of patients who remain treatment resistant. While this is not well understood, collective research in the area suggests the disease is heterogeneous in terms of the multiple parameters related to etiology, pathology and response to pharmacological agents. In addition to efficacy further therapeutic advances will also need to address such issues as cognitive impairment, pain, sexual dysfunction, nausea and emesis, weight gain and potential cardiovascular effects. With these unmet needs in mind, the next generation of antidepressants will need to differentiate themselves from the current array of therapeutics for depression. There are multiple strategies for addressing unmet needs that are currently being investigated. These range from combination monoaminergic approaches to subtype selective agents to novel targets that include mechanisms to modulate neuropeptides and excitatory amino acids (EAA). This review will discuss the many facets of differentiation and potential strategies for the development of novel antidepressants.

ADX47273 [S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]-oxadiazol-5-yl]-piperidin-1-yl}-methanone]: a novel metabotropic glutamate receptor 5-selective positive allosteric modulator with preclinical antipsychotic-like and procognitive activities.

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(2+) assays (EC(50) = 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 microM) and competed for binding of [(3)H]2-methyl-6-(phenylethynyl)pyridine (K(i) = 4.3 microM), but not [(3)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) = 30 mg/kg i.p.] and decreased mouse apomorphine-induced climbing (MED = 100 mg/kg i.p.), with little effect on stereotypy or catalepsy. Furthermore, ADX47273 blocked phencyclidine, apomorphine, and amphetamine-induced locomotor activities (MED = 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 = 1 mg/kg i.p.) and reduced impulsivity in the five-choice serial reaction time test (MED = 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.

Antidepressant-like behavioral effects of IGF-I produced by enhanced serotonin transmission.

Previous research has suggested that mobilization of neurotrophic factors, such as insulin-like growth factor I (IGF-I), can be involved in the effects of antidepressant treatments. The current experiments showed that IGF-I leads to antidepressant-like effects in the modified rat forced swim test when tested 3 days, but not 1 day, after i.c.v. administration. These effects were sustained longer than the antidepressants paroxetine and desipramine. In addition, blockade of the IGF-I receptor with the IGF-I antagonist JB1 30 min before IGF-I administration prevented the antidepressant-like effects of IGF-I. However, when JB1 was administered 3 days after IGF-I administration and 30 min prior to testing, the antidepressant-like effects of IGF-I were still present suggesting that IGF-1 produces a long-term activation of neural systems involved in the antidepressant response. Because the pattern of antidepressant-like effects of IGF-I resembled those of selective serotonin reuptake inhibitors, the role of serotonin in the behavioral effects of IGF-I was studied. Depletion of serotonin, by the tryptophan hydroxylase inhibitor para-chlorophenylalanine, blocked the antidepressant-like effects of IGF-I. Administration of IGF-I increased basal serotonin levels in the ventral hippocampus and altered the effects of acute citalopram. IGF-I administration did not change hippocampal cell proliferation at the 3-day timepoint when behavioral effects were seen. In addition, IGF-I did not alter the expression of mRNA levels of tryptophan hydroxylase or SERT in the brain stem, or [3H] citalopram binding in the hippocampus or cortex. Thus, IGF-I administration initiates a long-lasting cascade of neurochemical effects involving increased serotonin levels that results in antidepressant-like behavioral effects.

Stable expression of adenylyl cyclase 2 leads to the functional rescue of human 5-HT6 receptor in a CHODUKX cell line.

INTRODUCTION: The generation and selection of recombinant cell lines specifically designed to express high picomolar levels of heterologous G-protein-coupled receptors can lead to loss of ligand-dependent functional activity. As a result, the clonal selection of a suitable host model and/or lower receptor expression levels within the same cell system becomes important especially when a functional assay is necessary to evaluate the pharmacological potencies of ligands at the receptor site. To address this question, we examined the utility of various signal transducers to restore the functional capacity of a high expressing human 5-HT(6) receptor CHODUKX system. METHODS: The plasmids for human 5-HT(6) receptor and full-length human G(s), G(olf) and rat adenylyl cyclase isoforms 2 (rAC2) and 5 were obtained by PCR. The h5-HT(6) receptor pHTop plasmid was stably transfected into a CHODUKX cell line to generate an h5-HT(6) expressing clone. h5-HT(6) CHODUKX cells were transfected with signaling components and functional cAMP responses measured. rAC2 was selected to generate a double stable h5-HT(6) receptor/rAC2 pHTop CHODUKX line. RESULTS: The h5-HT(6) receptor CHODUKX line was a high receptor expressor (>2 pmol/mg protein) but an extremely poor ligand-dependent functional responder, failing to produce the appropriate cAMP signal upon addition of selective agonists. We found that stable co-expression of rAC2 with h5-HT(6) receptor in the CHODUKX cell line displayed dose-dependent cAMP accumulation following agonist treatment. The pharmacological profile of several agonists in the h5-HT(6) receptor/rAC2 cell line was consistent with an h5-HT(6)-like receptor-mediated event. DISCUSSION: We provide evidence for restoration of functional capacity in a heterologous G(s)-coupled 5-HT(6)/AC2 CHODUKX expression system. We discuss the broader value of a stable AC2-expressing CHODUKX cell line in which the generation of high expressing GPCR receptor/AC2 lines can retain their functional responsiveness and provide pharmacological drug comparisons between the same host line for screening purposes and measurement of multiple cellular parameters.

Basal adrenocorticotropin (ACTH) secretion is negatively modulated by protein phosphatase 5 in mouse pituitary corticotropin AtT20 cells.

siRNA oligonucleotides for protein phosphatase 5 (PP5) were designed and transfected into mouse corticotroph AtT20 cells to induce lower PP5 expression levels. PP5-siRNA transfections (at 3 days) produced a approximately 50% down-regulation in targeted protein levels. PP5-underexpressing cells released significantly more ir-ACTH (10-12-fold) relative to baseline levels and promoted POMC release into the media. Neither CRF-mediated ACTH release nor dexamethasone-induced ACTH repression were affected in PP5-siRNA transfected cells. In summary, our observations suggest that endogenous PP5 can exert a negative modulatory effect on basal ACTH release in neurosecretion-competent AtT20 cells through a mechanism as yet unknown but which does not directly involve regulated CRF or glucocorticoid receptor-dependent pathways. However, PP5 may cause mis-sorting of POMC and POMC-derived peptides at the constitutive-like secretory pathway level in an unregulated manner. Such a missorting could lead to impaired processing of POMC.

High-throughput confirmation of differential display PCR results using reverse Northern blotting.

Nylon filter arrays spotted with differential display PCR (DD-PCR) clones and hybridized with radiolabeled cRNA generated from the source RNA pool (reverse Northern blot) provide a high-throughput means to screen clones for artifacts. Reverse Northern blots also confirm differential gene expression in parallel and require modest quantities of the source RNA pool. We describe a strategy to screen multiple candidates from DD-PCR by high-throughput ligation and transformation, followed by reverse Northern blotting. Purification of re-amplified DD-PCR clones and fabrication of nylon arrays was facilitated by a batch-processing protocol using the widely available Biomek laboratory robot and Bioworks scripts (available from the authors). A strategy to screen out DD-PCR product artifacts of an inappropriate size was also employed. Using these approaches, we identified several mRNAs that are differentially expressed in response to venlafaxine, fluoxetine or desipramine antidepressant treatment in rat C6 glioma cell lines and are candidates for full length clone isolation using 5'-RACE. Such an approach provides a rapid means to eliminate the high percentage of false positive clones from DD-PCR and enables independent confirmation of differential gene expression patterns generated by various experimental conditions.

Effects of venlafaxine on p90Rsk activity in rat C6-gliomas and brain.

The intracellular actions of the antidepressant, venlafaxine, were studied in C6-gliomas using a phosphoproteomics approach. Long-term pre-treatment of C6-gliomas with venlafaxine followed by an acute challenge with isoproterenol (a beta-adrenoceptor agonist), resulted in increased p90Rsk phosphorylation (three-fold) versus control levels (isoproterenol alone). The effect of venlafaxine pre-treatment on p90Rsk activity was dose-dependent (EC(50)=3.75nM) in C6 gliomas. In rat brain sections, intense immunoreactive phospho-p90Rsk labeling was observed for both neurons and glia, especially in cortical layers II/III and hippocampal formations. In vivo studies demonstrated an intense but similar distribution pattern of phospho-p90Rsk staining after chronic venlafaxine dosing of rats compared to naives and no region-specific drug effect was observed in vivo. In conclusion, our findings suggest that some of the centrally-mediated benefits of venlafaxine in depression may be due to its intracellular properties especially on the neuro-glial circuitry and MAPK/p90Rsk-dependent pathways at an early stage.

The role of melanin-concentrating hormone in energy homeostasis and mood disorders.

The melanin-concentrating hormone (MCH) is a cyclic peptide exerting its actions through two G-protein-coupled receptors, MCHR1 and MCHR2. MCH is implicated in the regulation of different physiological functions, including energy homeostasis and mood that is supported by the distribution of MCH and MCHR1 in the hypothalamus as well as corticolimbic structures. Genetic manipulation of MCH and MCHR1 results in a lean phenotype with increased resting energy expenditure as well as anxiolytic and antidepressant phenotypes. Similar observations have been demonstrated pharmacologically using different classes of selective MCHR1 antagonists. Here, we summarize the reported genetic and pharmacological evidence for the role played by the MCH system in the regulation of both energy homeostasis and mood disorders. We also comment on the utility of small-molecule MCHR1 antagonists for the treatment of obesity and affective disorders compared to existing therapies and provide a critical overview of the potential risks.

Scintillation proximity assay in lead discovery.

BACKGROUND: Scintillation proximity assay (SPA) is a homogeneous scintillant bead-based platform for the measurement of biological processes and plays an important role in the identification of active chemical entities in drug discovery. OBJECTIVE: The design and development of solid-phase SPA approaches are examined and compared with alternative non-radiometric fluorescence-based technologies. METHODS: This review provides background on the principle of SPA and its application to biomolecular interactions from a variety of biological sources. CONCLUSION: The SPA approach is well suited to the demands of commercial high volume automation and assay miniaturization for target-based high-throughput screening campaigns on synthetic and natural product libraries as well as for benchtop characterization and confirmation studies. In the near future, innovations in the way SPA and fluorescence-based screening strategies are multiplexed will improve our comprehensive understanding of cellular system biology and dramatically advance the lead discovery process for the treatment of complex target-related disorders.

WAY-100635 antagonist-induced plasticity of 5-HT receptors: regulatory differences between a stable cell line and an in vivo native system.

We present evidence that the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor antagonist, N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl}-N-(2-pyridinyl)cyclohexanecarboxamide (WAY-100635), can induce receptor internalization in a human (h)5-HT(1A) receptor Chinese hamster ovary (CHO-K1) cell system. Exposure of h5-HT(1A) CHO cells to WAY-100635 decreased the cell-surface h5-HT(1A) receptor density in a way that was both time (24-72 h) and concentration (1-100 nm) dependent.[(3)H]WAY-100635 and [(3)H]8-hydroxy-dipropylaminotetralin ([(3)H]8-OH-DPAT) saturation analyses demonstrated a significant reduction (50-60%) in total h5-HT(1A) receptor number in the WAY-100635-treated (100 nm; 72 h) compared with control cells. In WAY-100635-treated cells, the 8-OH-DPAT-mediated inhibition of forskolin (FSK)-stimulated cAMP accumulation was right-shifted and the maximal inhibitory response of 8-OH-DPAT was impaired compared with control cells. Similar results were obtained for 8-OH-DPAT-mediated Ca(2+) mobilization after WAY-100635 treatment. h5-HT(1A) receptors labeled with [(3)H]WAY-100635, as well as [(3)H]4-(2'-Methoxy)-phenyl-1-[2'-(N-2''-pyridinyl)-p-fluorobenzamido]ethyl-piperazine (MPPF), exhibited a time-dependent rate of cellular internalization that was blocked by endocytotic suppressors and was pertussis-toxin insensitive. In contrast, quantitative autoradiographic studies demonstrated that chronic treatment of rats with WAY-100635 for two weeks produced a region-specific increase in the 5-HT(1A) receptor density. In conclusion, prolonged exposure of an h5-HT(1A) cell-based system to the 5-HT(1A) antagonist, WAY-100635, induced a paradoxical internalization of cell surface receptor resulting in depressed functional activity. This suggests that an antagonist can influence 5-HT(1A) receptor recycling in vitro differently to in vivo regulatory conditions.

Innovative approaches for the development of antidepressant drugs: current and future strategies.

Depression is a highly debilitating disorder that has been estimated to affect up to 21% of the world population. Despite the advances in the treatment of depression with selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs), there continue to be many unmet clinical needs with respect to both efficacy and side effects. These needs range from efficacy in treatment resistant patients, to improved onset, to reductions in side effects such as emesis or sexual dysfunction. To address these needs, there are numerous combination therapies and novel targets that have been identified that may demonstrate improvements in one or more areas. There is tremendous diversity in the types of targets and approaches being taken. At one end of a spectrum is combination therapies that maintain the benefits associated with SSRIs but attempt to either improve efficacy or reduce side effects by adding additional mechanisms (5-HT1A, 5-HT1B, 5-HT1D, 5-HT2C, alpha-2A). At the other end of the spectrum are more novel targets, such as neurotrophins (BDNF, IGF), based on recent findings that antidepressants induce neurogenesis. In between, there are many approaches that range from directly targeting serotonin receptors (5-HT2C, 5-HT6) to targeting the multiplicity of potential mechanisms associated with excitatory (glutamate, NMDA, mGluR2, mGluR5) or inhibitory amino acid systems (GABA) or peptidergic systems (neurokinin 1, corticotropin-releasing factor 1, melanin-concentrating hormone 1, V1b). The present review addresses the most exciting approaches and reviews the localization, neurochemical and behavioral data that provide the supporting rationale for each of these targets or target combinations.

Proteomic analysis of protein changes developing in rat hippocampus after chronic antidepressant treatment: Implications for depressive disorders and future therapies.

It is recognized that monoamine reuptake inhibitors (MARIs) exert beneficial effects in the treatment of major depression and general anxiety disorder. The aim of this study was to identify proteins regulated by this class of antidepressant using a proteome differential profiling approach. Either venlafaxine or fluoxetine was administered systemically to adult rats for 2 weeks, and protein patterns from rat hippocampal cytosolic extracts were compared by two-dimensional gel electrophoresis. Silver-stained protein spots displaying differential expression were identified by mass spectrometry. Thirty-three protein spots were modulated by both drug treatments compared to controls. The classification of several proteins that were sorted by function suggested convergent pathway activities for both MARIs at the post-receptor level. These included proteins associated with neurogenesis (insulin like growth factor 1 (IGF-1), glia maturation factor [GMF]-beta), outgrowth/maintenance of neuronal processes (hippocampal cholinergic neurostimulating peptide [HCNP], PCTAIRE-3), and with neural regeneration/axonal guidance collapsin response mediator protein (CRMP-2) systems. Other modulated proteins indicated an increase in neuronal vesicular cell trafficking and synaptic plasticity (Ras-related protein 4a (Rab4a), Ras-related protein 1b (Rab1b), heat shock protein 10 [HSP10]), as well as neurosteroidogenic (hydroxysteroid sulfotransferase A) and possible anti-apoptotic (dimethylargininase-1 L-N,N-dimethylarginine dimethylaminohydrolase-1 [DDAH-1], pyruvate dehydrogenase-E1 [PDH-E1], antioxidant protein-2 [AOP-2]) pathway-mediated regulatory events. Parallel studies to investigate further the effects of venlafaxine and fluoxetine on adult hippocampal neurogenesis in vivo by quantitative bromodeoxyuridine immunolabeling revealed a significant drug-induced increase in the proliferation rate and long-term survivability of progenitor stem cells located in the subgranular zone. These data suggest that MARIs share wide-ranging proteome changes within the hippocampal formation, beyond 5-HT/NE neurotransmission. This may reflect long-term functional adaptations required for antidepressant activity.