Discovery of 4-arylquinoline-2-carboxamides, highly potent and selective class of mGluR2 negative allosteric modulators: From HTS to activity in animal models.

Antagonism of the mGluR2 receptor has the potential to provide therapeutic benefit to cognitive disorders by elevating synaptic glutamate, the primary excitatory neurotransmitter in the brain. Selective antagonism of the mGluR2 receptor, however, has so far been elusive, given the very high homology of this receptor with mGluR3, particularly at the orthosteric binding site. Given that inhibition of mGluR3 has been implicated in undesired effects, we sought to identify selective mGluR2 negative allosteric modulators. Herein we describe the discovery of the highly potent and selective class of mGluR2 negative allosteric modulators, 4-arylquinoline-2-carboxamides, following a successful HTS campaign and medicinal chemistry optimization, showing potent in vivo efficacy in rodent.

Discovery of benzofuran propanoic acid GPR120 agonists: From uHTS hit to mechanism-based pharmacodynamic effects.

The transformation of an aryloxybutanoic acid ultra high-throughput screening (uHTS) hit into a potent and selective series of G-protein coupled receptor 120 (GPR120) agonists is reported. uHTS hit 1 demonstrated an excellent rodent pharmacokinetic profile and selectivity over the related fatty acid receptor GPR40, but only modest GPR120 potency. Optimization of the "left-hand" aryl group led to compound 6, which demonstrated a GPR120 mechanism-based pharmacodynamic effect in a mouse oral glucose tolerance test (oGTT). Further optimization gave rise to the benzofuran propanoic acid series (exemplified by compound 37), which demonstrated acute mechanism-based pharmacodynamic effects. The combination of in vivo efficacy and attractive rodent pharmacodynamic profiles suggests compounds generated from this series may afford attractive candidates for the treatment of Type 2 diabetes.

Biphasic cholinergic synaptic transmission controls action potential activity in thalamic reticular nucleus neurons.

Cholinergic neurons in the basal forebrain and the brainstem form extensive projections to a number of thalamic nuclei. Activation of cholinergic afferents during distinct behavioral states can regulate neuronal firing, transmitter release at glutamatergic and GABAergic synapses, and synchrony in thalamic networks, thereby controlling the flow of sensory information. These effects are thought to be mediated by slow and persistent increases in extracellular ACh levels, resulting in the modulation of populations of thalamic neurons over large temporal and spatial scales. However, the synaptic mechanisms underlying cholinergic signaling in the thalamus are not well understood. Here, we demonstrate highly reliable cholinergic transmission in the mouse thalamic reticular nucleus (TRN), a brain structure essential for sensory processing, arousal, and attention. We find that ACh release evoked by low-frequency stimulation leads to biphasic excitatory-inhibitory (E-I) postsynaptic responses, mediated by the activation of postsynaptic α4ß2 nicotinic ACh receptors (nAChRs) and M2 muscarinic ACh receptors (mAChRs), respectively. In addition, ACh can bind to mAChRs expressed near cholinergic release sites, resulting in autoinhibition of release. We show that the activation of postsynaptic nAChRs by transmitter release from only a small number of individual axons is sufficient to trigger action potentials in TRN neurons. Furthermore, short trains of cholinergic synaptic inputs can powerfully entrain ongoing TRN neuronal activity. Our study demonstrates fast and precise synaptic E-I signaling mediated by ACh, suggesting novel computational mechanisms for the cholinergic control of neuronal activity in thalamic circuits.

Calcineurin signaling mediates activity-dependent relocation of the axon initial segment.

The axon initial segment (AIS) is a specialized neuronal subcompartment located at the beginning of the axon that is crucially involved in both the generation of action potentials and the regulation of neuronal polarity. We recently showed that prolonged neuronal depolarization produces a distal shift of the entire AIS structure away from the cell body, a change associated with a decrease in neuronal excitability. Here, we used dissociated rat hippocampal cultures, with a major focus on the dentate granule cell (DGC) population, to explore the signaling pathways underlying activity-dependent relocation of the AIS. First, a pharmacological screen of voltage-gated calcium channels (VGCCs) showed that AIS relocation is triggered by activation of L-type Cav1 VGCCs with negligible contribution from any other VGCC subtypes. Additional pharmacological analysis revealed that downstream signaling events are mediated by the calcium-sensitive phosphatase calcineurin; inhibition of calcineurin with either FK506 or cyclosporin A totally abolished both depolarization- and optogenetically-induced activity-dependent AIS relocation. Furthermore, calcineurin activation is sufficient for AIS plasticity, because expression of a constitutively active form of the phosphatase resulted in relocation of the AIS of DGCs without a depolarizing stimulus. Finally, we assessed the role of calcineurin in other forms of depolarization-induced plasticity. Neither membrane resistance changes nor spine density changes were affected by FK506 treatment, suggesting that calcineurin acts via a separate pathway to modulate AIS plasticity. Together, these results emphasize calcineurin as a vital player in the regulation of intrinsic plasticity as governed by the AIS.

Essential thalamic contribution to slow waves of natural sleep.

Slow waves represent one of the prominent EEG signatures of non-rapid eye movement (non-REM) sleep and are thought to play an important role in the cellular and network plasticity that occurs during this behavioral state. These slow waves of natural sleep are currently considered to be exclusively generated by intrinsic and synaptic mechanisms within neocortical territories, although a role for the thalamus in this key physiological rhythm has been suggested but never demonstrated. Combining neuronal ensemble recordings, microdialysis, and optogenetics, here we show that the block of the thalamic output to the neocortex markedly (up to 50%) decreases the frequency of slow waves recorded during non-REM sleep in freely moving, naturally sleeping-waking rats. A smaller volume of thalamic inactivation than during sleep is required for observing similar effects on EEG slow waves recorded during anesthesia, a condition in which both bursts and single action potentials of thalamocortical neurons are almost exclusively dependent on T-type calcium channels. Thalamic inactivation more strongly reduces spindles than slow waves during both anesthesia and natural sleep. Moreover, selective excitation of thalamocortical neurons strongly entrains EEG slow waves in a narrow frequency band (0.75-1.5 Hz) only when thalamic T-type calcium channels are functionally active. These results demonstrate that the thalamus finely tunes the frequency of slow waves during non-REM sleep and anesthesia, and thus provide the first conclusive evidence that a dynamic interplay of the neocortical and thalamic oscillators of slow waves is required for the full expression of this key physiological EEG rhythm.

Cross-modulation and molecular interaction at the Cav3.3 protein between the endogenous lipids and the T-type calcium channel antagonist TTA-A2.

T-type calcium channels (T/Ca(v)3-channels) are implicated in various physiologic and pathophysiologic processes such as epilepsy, sleep disorders, hypertension, and cancer. T-channels are the target of endogenous signaling lipids including the endocannabinoid anandamide, the ω3-fatty acids, and the lipoamino-acids. However, the precise molecular mechanism by which these molecules inhibit T-current is unknown. In this study, we provided a detailed electrophysiologic and pharmacologic analysis indicating that the effects of the major N-acyl derivatives on the Ca(v)3.3 current share many similarities with those of TTA-A2 [(R)-2-(4-cyclopropylphenyl)-N-(1-(5-(2,2,2-trifluoroethoxy)pyridin-2-yl)ethyl)acetamide], a synthetic T-channel inhibitor. Using radioactive binding assays with the TTA-A2 derivative [(3)H]TTA-A1 [(R)-2-(4-(tert-butyl)phenyl)-N-(1-(5-methoxypyridin-2-yl)ethyl)acetamide], we demonstrated that polyunsaturated lipids, which inhibit the Ca(v)3.3 current, as NAGly (N-arachidonoyl glycine), NASer (N-arachidonoyl-l-serine), anandamide, NADA (N-arachidonoyl dopamine), NATau (N-arachidonoyl taurine), and NA-5HT (N-arachidonoyl serotonin), all displaced [(3)H]TTA-A1 binding to membranes prepared from cells expressing Ca(v)3.3, with Ki in a micromolar or submicromolar range. In contrast, lipids with a saturated alkyl chain, as N-arachidoyl glycine and N-arachidoyl ethanolamine, which did not inhibit the Ca(v)3.3 current, had no effect on [(3)H]TTA-A1 binding. Accordingly, bio-active lipids occluded TTA-A2 effect on Ca(v)3.3 current. In addition, TTA-Q4 [(S)-4-(6-chloro-4-cyclopropyl-3-(2,2-difluoroethyl)-2-oxo-1,2,3,4-tetrahydroquinazolin-4-yl)benzonitrile], a positive allosteric modulator of [(3)H]TTA-A1 binding and TTA-A2 functional inhibition, acted in a synergistic manner to increase lipid-induced inhibition of the Ca(v)3.3 current. Overall, our results demonstrate a common molecular mechanism for the synthetic T-channel inhibitors and the endogenous lipids, and indicate that TTA-A2 and TTA-Q4 could be important pharmacologic tools to dissect the involvement of T-current in the physiologic effects of endogenous lipids.

Presynaptic Cav3.2 channels regulate excitatory neurotransmission in nociceptive dorsal horn neurons.

It is generally accepted that presynaptic transmitter release is mainly regulated by subtypes of neuronal high-voltage-activated Ca(2+) channels. Here for the first time, we examined the role of T-type Ca(2+) channels (T-channels) in synaptic transmission in the dorsal horn (DH) of the spinal cord using patch-clamp recordings from acute spinal cord preparations from both rat and mouse. We found that selective pharmacological antagonism of T-channels inhibited spontaneous synaptic release of glutamate in superficial laminae I-II of the DH, while GABA release was spared. We found similar effect in identified nociceptive projection neurons of lamina I of the DH, but not in inhibitory DH interneurons. In comparison, antagonism of T-channels did not affect excitatory transmission in deeper non-nociceptive DH laminae. Furthermore, we used isoform-specific agents, knock-out mice and immunohistochemistry to specifically implicate presynaptic Ca(V)3.2 channels. We also used an animal model of painful diabetic neuropathy to demonstrate that blocking T-channels in superficial DH neurons suppressed spontaneous excitatory synaptic transmission in diabetic rats in greater degree than in healthy age-matched animals. These studies provide previously unknown information regarding the role of presynaptic T-channels in nociceptive signaling in the spinal cord.

GABAergic synaptic transmission triggers action potentials in thalamic reticular nucleus neurons.

GABAergic neurons in the thalamic reticular nucleus (TRN) form powerful inhibitory connections with several dorsal thalamic nuclei, thereby controlling attention, sensory processing, and synchronous oscillations in the thalamocortical system. TRN neurons are interconnected by a network of GABAergic synapses, but their properties and their role in shaping TRN neuronal activity are not well understood. Using recording techniques aimed to minimize changes in the intracellular milieu, we show that synaptic GABA(A) receptor activation triggers postsynaptic depolarizations in mouse TRN neurons. Immunohistochemical data indicate that TRN neurons express very low levels of the Cl(-) transporter KCC2. In agreement, perforated-patch recordings show that intracellular Cl(-) levels are high in TRN neurons, resulting in a Cl(-) reversal potential (E(Cl)) significantly depolarized from rest. Additionally, we find that GABA(A) receptor-evoked depolarizations are amplified by the activation of postsynaptic T-type Ca(2+) channels, leading to dendritic Ca(2+) increases and the generation of burst firing in TRN neurons. In turn, GABA-evoked burst firing results in delayed and long-lasting feedforward inhibition in thalamic relay cells. Our results show that GABA-evoked depolarizations can interact with T-type Ca(2+) channels to powerfully control spike generation in TRN neurons.

T-type calcium channels consolidate tonic action potential output of thalamic neurons to neocortex.

The thalamic output during different behavioral states is strictly controlled by the firing modes of thalamocortical neurons. During sleep, their hyperpolarized membrane potential allows activation of the T-type calcium channels, promoting rhythmic high-frequency burst firing that reduces sensory information transfer. In contrast, in the waking state thalamic neurons mostly exhibit action potentials at low frequency (i.e., tonic firing), enabling the reliable transfer of incoming sensory inputs to cortex. Because of their nearly complete inactivation at the depolarized potentials that are experienced during the wake state, T-channels are not believed to modulate tonic action potential discharges. Here, we demonstrate using mice brain slices that activation of T-channels in thalamocortical neurons maintained in the depolarized/wake-like state is critical for the reliable expression of tonic firing, securing their excitability over changes in membrane potential that occur in the depolarized state. Our results establish a novel mechanism for the integration of sensory information by thalamocortical neurons and point to an unexpected role for T-channels in the early stage of information processing.

Randomized controlled study of the T-type calcium channel antagonist MK-8998 for the treatment of acute psychosis in patients with schizophrenia.

OBJECTIVE: This study aimed to evaluate whether the T-type calcium channel antagonist MK-8998 was effective in treating acute psychosis in patients with schizophrenia. METHODS: This was a randomized, double-blind, parallel-group study. After a placebo lead-in, acutely psychotic inpatients with schizophrenia were randomized to 4 weeks of MK-8998 12/16 mg daily (N = 86), olanzapine 10/15 mg daily (N = 47), or placebo (N = 83). The primary efficacy measure was score on the Positive and Negative Syndrome Scale (PANSS). RESULTS: Out of 216 randomized patients, 158 completed the 4-week study: MK-8998 = 58 (67.4%), olanzapine = 38 (80.9%), and placebo = 62 (74.7%). The mean changes from baseline in PANSS score at week 4 for MK-8998 and olanzapine were not significantly different from placebo: MK-8998-placebo difference = -0.6 [95% confidence interval (CI): -7.0, 5.8], p = 0.9; olanzapine-placebo difference = -4.3 [95% CI: -11.7, 3.1), p = 0.3. A responder rate analysis (≥20% improvement from baseline in PANSS score) suggested an advantage of olanzapine over placebo (odds ratio = 2.20 [95% CI: 0.95, 5.09], p = 0.07) but no effect of MK-8998 over placebo (odds ratio = 1.28 [95% CI: 0.62, 2.64], p = 0.5). Treatments were generally well tolerated, but more patients reported adverse events for MK-8998 (47.7%) and olanzapine (48.9%) than placebo (37.3%). CONCLUSIONS: MK-8998 was not effective in treating acutely psychotic inpatients with schizophrenia, as measured by PANSS score at week 4. Because of the limited efficacy of the active comparator, we cannot exclude the possibility that T-type calcium channel antagonists could prove to be effective in schizophrenia.

Discovery of MK-8768, a Potent and Selective mGluR2 Negative Allosteric Modulator.

Glutamate plays a key role in cognition and mood, and it has been shown that inhibiting ionotropic glutamate receptors disrupts cognition, while enhancing ionotropic receptor activity is pro-cognitive. One approach to elevating glutamatergic tone has been to antagonize presynaptic metabotropic glutamate receptor 2 (mGluR2). A desire for selectivity over the largely homologous mGluR3 motivated a strategy to achieve selectivity through the identification of mGluR2 negative allosteric modulators (NAMs). Extensive screening and optimization efforts led to the identification of a novel series of 4-arylquinoline-2-carboxamides. This series was optimized for mGluR2 NAM potency, clean off-target activity, and desirable physical properties, which resulted in the identification of improved C4 and C7 substituents. The initial lead compound from this series was Ames-positive in a single strain with metabolic activation, indicating that a reactive metabolite was likely responsible for the genetic toxicity. Metabolic profiling and Ames assessment across multiple analogs identified key structure-activity relationships associated with Ames positivity. Further optimization led to the Ames-negative mGluR2 negative allosteric modulator MK-8768.

Nerve terminal nicotinic acetylcholine receptors initiate quantal GABA release from perisomatic interneurons by activating axonal T-type (Cav3) Ca²âº channels and Ca²âº release from stores.

Release of conventional neurotransmitters is mainly controlled by calcium (Ca²âº) influx via high-voltage-activated (HVA), Ca(v)2, channels ("N-, P/Q-, or R-types") that are opened by action potentials. Regulation of transmission by subthreshold depolarizations does occur, but there is little evidence that low-voltage-activated, Ca(v)3 ("T-type"), channels take part. GABA release from cortical perisomatic-targeting interneurons affects numerous physiological processes, and yet its underlying control mechanisms are not fully understood. We investigated whether T-type Ca²âº channels are involved in regulating GABA transmission from these cells in rat hippocampal CA1 using a combination of whole-cell voltage-clamp, multiple-fluorescence confocal microscopy, dual-immunolabeling electron-microscopy, and optogenetic methods. We show that Ca(v)3.1, T-type Ca²âº channels can be activated by α3ß4 nicotinic acetylcholine receptors (nAChRs) that are located on the synaptic regions of the GABAergic perisomatic-targeting interneuronal axons, including the parvalbumin-expressing cells. Asynchronous, quantal GABA release can be triggered by Ca²âº influx through presynaptic T-type Ca²âº channels, augmented by Ca²âº from internal stores, following focal microiontophoretic activation of the α3ß4 nAChRs. The resulting GABA release can inhibit pyramidal cells. The T-type Ca²âº channel-dependent mechanism is not dependent on, or accompanied by, HVA channel Ca²âº influx, and is insensitive to agonists of cannabinoid, µ-opioid, or GABA(B) receptors. It may therefore operate in parallel with the normal HVA-dependent processes. The results reveal new aspects of the regulation of GABA transmission and contribute to a deeper understanding of ACh and nicotine actions in CNS.

Control of firing patterns through modulation of axon initial segment T-type calcium channels.

Spontaneously active neurons typically fire either in a regular pattern or in bursts. While much is known about the subcellular location and biophysical properties of conductances that underlie regular spontaneous activity, less is known about those that underlie bursts. Here, we show that T-type Ca(2+) channels localized to the site of action potential initiation in the axon initial segment play a pivotal role in spontaneous burst generation. In auditory brainstem interneurons, axon initial segment Ca(2+) influx is selectively downregulated by dopaminergic signalling. This regulation has marked effects on spontaneous activity, converting the predominant mode of spontaneous activity from bursts to regular spiking. Thus, the axon initial segment is a key site, and dopamine a key regulator, of spontaneous bursting activity.

State-dependent firing determines intrinsic dendritic Ca2+ signaling in thalamocortical neurons.

Activity-dependent dendritic Ca(2+) signals play a critical role in multiple forms of nonlinear cellular output and plasticity. In thalamocortical neurons, despite the well established spatial separation of sensory and cortical inputs onto proximal and distal dendrites, respectively, little is known about the spatiotemporal dynamics of intrinsic dendritic Ca(2+) signaling during the different state-dependent firing patterns that are characteristic of these neurons. Here we demonstrate that T-type Ca(2+) channels are expressed throughout the entire dendritic tree of rat thalamocortical neurons and that they mediate regenerative propagation of low threshold spikes, typical of, but not exclusive to, sleep states, resulting in global dendritic Ca(2+) influx. In contrast, actively backpropagating action potentials, typical of wakefulness, result in smaller Ca(2+) influxes that can temporally summate to produce dendritic Ca(2+) accumulations that are linearly related to firing frequency but spatially confined to proximal dendritic regions. Furthermore, dendritic Ca(2+) transients evoked by both action potentials and low-threshold spikes are shaped by Ca(2+) uptake by sarcoplasmic/endoplasmic reticulum Ca(2+) ATPases but do not rely on Ca(2+)-induced Ca(2+) release. Our data demonstrate that thalamocortical neurons are endowed with intrinsic dendritic Ca(2+) signaling properties that are spatially and temporally modified in a behavioral state-dependent manner and suggest that backpropagating action potentials faithfully inform proximal sensory but not distal corticothalamic synapses of neuronal output, whereas corticothalamic synapses only "detect" Ca(2+) signals associated with low-threshold spikes.

Selective T-type calcium channel block in thalamic neurons reveals channel redundancy and physiological impact of I(T)window.

Although it is well established that low-voltage-activated T-type Ca(2+) channels play a key role in many neurophysiological functions and pathological states, the lack of selective and potent antagonists has so far hampered a detailed analysis of the full impact these channels might have on single-cell and neuronal network excitability as well as on Ca(2+) homeostasis. Recently, a novel series of piperidine-based molecules has been shown to selectively block recombinant T-type but not high-voltage-activated (HVA) Ca(2+) channels and to affect a number of physiological and pathological T-type channel-dependent behaviors. Here we directly show that one of these compounds, 3,5-dichloro-N-[1-(2,2-dimethyl-tetrahydro-pyran-4-ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide (TTA-P2), exerts a specific, potent (IC(50) = 22 nm), and reversible inhibition of T-type Ca(2+) currents of thalamocortical and reticular thalamic neurons, without any action on HVA Ca(2+) currents, Na(+) currents, action potentials, and glutamatergic and GABAergic synaptic currents. Thus, under current-clamp conditions, the low-threshold Ca(2+) potential (LTCP)-dependent high-frequency burst firing of thalamic neurons is abolished by TTA-P2, whereas tonic firing remains unaltered. Using TTA-P2, we provide the first direct demonstration of the presence of a window component of Ca(2+) channels in neurons and its contribution to the resting membrane potential of thalamic neurons and to the Up state of their intrinsically generated slow (<1 Hz) oscillation. Moreover, we demonstrate that activation of only a small fraction of the T-type channel population is required to generate robust LTCPs, suggesting that LTCP-driven bursts of action potentials can be evoked at depolarized potentials where the vast majority of T-type channels are inactivated.

Rebound excitation triggered by synaptic inhibition in cerebellar nuclear neurons is suppressed by selective T-type calcium channel block.

Following hyperpolarizing inputs, many neurons respond with an increase in firing rate, a phenomenon known as rebound excitation. Rebound excitation has been proposed as a mechanism to encode and process inhibitory signals and transfer them to target structures. Activation of low-voltage-activated T-type calcium channels and the ensuing low-threshold calcium spikes is one of the mechanisms proposed to support rebound excitation. However, there is still not enough evidence that the hyperpolarization provided by inhibitory inputs, particularly those dependent on chloride ions, is adequate to deinactivate a sufficient number of T-type calcium channels to drive rebound excitation on return to baseline. Here, this issue was investigated in the deep cerebellar nuclear neurons (DCNs), which receive the output of the cerebellar cortex conveyed exclusively by the inhibitory Purkinje cells and are also known to display rebound excitation. Using cerebellar slices and whole cell recordings of large DCNs, we show that a novel piperidine-based compound that selectively antagonizes T-type calcium channel activity, 3,5-dichloro-N-[1-(2,2-dimethyl-tetrahydropyran-4-ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide (TTA-P2), suppressed rebound excitation elicited by current injection as well as by synaptic inhibition, whereas other electrophysiological properties of large DCNs were unaltered. Furthermore, TTA-P2 suppressed transient high-frequency rebounds found in DCNs with low-threshold spikes as well as the slow rebounds present in DCNs without low-threshold spikes. These findings demonstrate that chloride-dependent synaptic inhibition effectively triggers T-type calcium channel-mediated rebounds and that the latter channels may support slow rebound excitation in neurons without low-threshold spikes.

Pharmacological validation of candidate causal sleep genes identified in an N2 cross.

Despite the substantial impact of sleep disturbances on human health and the many years of study dedicated to understanding sleep pathologies, the underlying genetic mechanisms that govern sleep and wake largely remain unknown. Recently, the authors completed large-scale genetic and gene expression analyses in a segregating inbred mouse cross and identified candidate causal genes that regulate the mammalian sleep-wake cycle, across multiple traits including total sleep time, amounts of rapid eye movement (REM), non-REM, sleep bout duration, and sleep fragmentation. Here the authors describe a novel approach toward validating candidate causal genes, while also identifying potential targets for sleep-related indications. Select small-molecule antagonists and agonists were used to interrogate candidate causal gene function in rodent sleep polysomnography assays to determine impact on overall sleep architecture and to evaluate alignment with associated sleep-wake traits. Significant effects on sleep architecture were observed in validation studies using compounds targeting the muscarinic acetylcholine receptor M3 subunit (Chrm3) (wake promotion), nicotinic acetylcholine receptor alpha4 subunit (Chrna4) (wake promotion), dopamine receptor D5 subunit (Drd5) (sleep induction), serotonin 1D receptor (Htr1d) (altered REM fragmentation), glucagon-like peptide-1 receptor (Glp1r) (light sleep promotion and reduction of deep sleep), and calcium channel, voltage-dependent, T type, alpha 1I subunit (Cacna1i) (increased bout duration of slow wave sleep). Taken together, these results show the complexity of genetic components that regulate sleep-wake traits and highlight the importance of evaluating this complex behavior at a systems level. Pharmacological validation of genetically identified putative targets provides a rapid alternative to generating knock out or transgenic animal models, and may ultimately lead towards new therapeutic opportunities.

Pyridyl amides as potent inhibitors of T-type calcium channels.

A novel series of amide T-type calcium channel antagonists were prepared and evaluated using in vitro and in vivo assays. Optimization of the screening hit 3 led to identification of the potent and selective T-type antagonist 37 that displayed in vivo efficacy in rodent models of epilepsy and sleep.

In vitro characterization of T-type calcium channel antagonist TTA-A2 and in vivo effects on arousal in mice.

T-type calcium channels have been implicated in many behaviorally important neurophysiological processes, and altered channel activity has been linked to the pathophysiology of neurological disorders such as insomnia, epilepsy, Parkinson's disease, depression, schizophrenia, and pain. We have previously identified a number of potent and selective T-type channel antagonists (Barrow et al., 2007; Shipe et al., 2008; Yang et al., 2008). Here we describe the properties of the antagonist TTA-A2 [2-(4-cyclopropylphenyl)-N-((1R)-1-{5-[(2,2,2-trifluoroethyl)oxo]-pyridin-2-yl}ethyl)acetamide], assessed in patch-clamp experiments. TTA-A2 blocks T-type channels (Ca(v)3.1, 3.2, 3.3) voltage dependently and with high potency (IC(50) ∼100 nM). Stimulation at 3 Hz revealed additional use dependence of inhibition. A hyperpolarized shift of the channel availability curve and delayed channel recovery from inactivation suggest that the compound preferentially interacts with and stabilizes inactivated channels. The compound showed a ∼300-fold selectivity for Ca(v)3 channels over high-voltage activated calcium channels. Inhibitory effects on native T-type currents were confirmed in brain slice recordings from the dorsal lateral geniculate nucleus and the subthalamic nucleus. Furthermore, we demonstrate that in vivo T-type channel inhibition by TTA-A2 suppresses active wake and promotes slow-wave sleep in wild-type mice but not in mice lacking both Ca(v)3.1 and Ca(v)3.3, suggesting the selective effect of TTA-A2 on recurrent thalamocortical network activity. The discovery of the potent and selective T-type channel antagonist TTA-A2 has enabled us to study the in vivo effects of pharmacological T-channel inhibition on arousal in mice, and it will help to explore the validity of these channels as potential drug targets for sleep-related and other neurological diseases.