Navacaprant, a novel and selective kappa opioid receptor antagonist, has no agonist properties implicated in opioid-related abuse.

Kappa opioid receptors (KORs) are implicated in the pathophysiology of various psychiatric and neurological disorders creating interest in targeting the KOR system for therapeutic purposes. Accordingly, navacaprant (NMRA-140) is a potent, selective KOR antagonist being evaluated as a treatment for major depressive disorder. In the present report, we have extended the pharmacological characterization of navacaprant by further demonstrating its selective KOR antagonist properties and confirming its lack of agonist activity at KORs and related targets involved in opioid-related abuse. Using CHO-K1 cells expressing human KOR, mu (MOR), or delta (DOR) opioid receptors, navacaprant demonstrated selective antagonist properties at KOR (IC50 = 0.029 µM) versus MOR (IC50 = 3.3 µM) and DOR (IC50 > 10 µM) in vitro. In vivo, navacaprant (10-30 mg/kg, i.p.) dose-dependently abolished KOR-agonist induced analgesia in the mouse tail-flick assay. Additionally, navacaprant (10, 30 mg/kg, p.o.) significantly reduced KOR agonist-stimulated prolactin release in mice and rats, confirming KOR antagonism in vivo. Navacaprant showed no agonist activity at any opioid receptor subtype (EC50 > 10 µM) in vitro and exhibited no analgesic effect in the tail-flick assays at doses ≤100 mg/kg, p.o. thereby confirming a lack of opioid receptor agonist activity in vivo. Importantly, navacaprant did not alter extracellular dopamine concentrations in the nucleus accumbens shell of freely-moving rats following doses ≤100 mg/kg, p.o., whereas morphine (10, 20 mg/kg, i.p.) significantly increased dopamine levels. These results demonstrate that navacaprant is a KOR-selective antagonist with no pharmacological properties implicated in opioid-related abuse.

Kappa opioid receptor antagonism protects working memory performance from mild stress exposure in Rhesus macaques.

Extensive preclinical and emerging clinical evidence point to an involvement of the kappa opioid receptor (KOR) in brain networks that promotes neurobehavioral stability. KOR expression in mesolimbic and mesocortical pathways has been the basis for characterizing the role of this receptor system in regulating motivation and emotion; however, the involvement of the KOR system in higher-order executive processes such as working memory (WM) is not well-understood. WM is readily impaired with uncontrollable stress exposure and is dysregulated in many neurobehavioral disorders. To empirically evaluate the role of the KOR system on WM performance, we administered a selective KOR antagonist, NMRA-140 (0, 0.1, 0.3, 1.0 mg/kg, intramuscular) to monkeys under both stress and non-stress conditions. In this study, NMRA-140 was co-administered with FG7142, a benzodiazepine inverse agonist, known to produce a mild stress response and to impair WM function in monkeys. NMRA-140 protected WM performance from the detrimental effects of FG7142-induced stress and exhibited no significant effect under non-stress conditions. Collectively, these data highlight the functional influence of the KOR system in mediating stress-induced dysfunction of executive processes and suggest that modulating KOR activity could offer therapeutic benefit in stress-related neurobehavioral disorders.

Basmisanil, a highly selective GABAA-α5 negative allosteric modulator: preclinical pharmacology and demonstration of functional target engagement in man.

GABAA-α5 subunit-containing receptors have been shown to play a key modulatory role in cognition and represent a promising drug target for cognitive dysfunction, as well as other disorders. Here we report on the preclinical and early clinical profile of a novel GABAA-α5 selective negative allosteric modulator (NAM), basmisanil, which progressed into Phase II trials for intellectual disability in Down syndrome and cognitive impairment associated with schizophrenia. Preclinical pharmacology studies showed that basmisanil is the most selective GABAA-α5 receptor NAM described so far. Basmisanil bound to recombinant human GABAA-α5 receptors with 5 nM affinity and more than 90-fold selectivity versus α1, α2, and α3 subunit-containing receptors. Moreover, basmisanil inhibited GABA-induced currents at GABAA-α5 yet had little or no effect at the other receptor subtypes. An in vivo occupancy study in rats showed dose-dependent target engagement and was utilized to establish the plasma exposure to receptor occupancy relationship. At estimated receptor occupancies between 30 and 65% basmisanil attenuated diazepam-induced spatial learning impairment in rats (Morris water maze), improved executive function in non-human primates (object retrieval), without showing anxiogenic or proconvulsant effects in rats. During the Phase I open-label studies, basmisanil showed good safety and tolerability in healthy volunteers at maximum GABAA-α5 receptor occupancy as confirmed by PET analysis with the tracer [11C]-Ro 15-4513. An exploratory EEG study provided evidence for functional activity of basmisanil in human brain. Therefore, these preclinical and early clinical studies show that basmisanil has an ideal profile to investigate potential clinical benefits of GABAA-α5 receptor negative modulation.

Differential effects of novel kappa opioid receptor antagonists on dopamine neurons using acute brain slice electrophysiology.

Activation of the kappa opioid receptor (KOR) contributes to the aversive properties of stress, and modulates key neuronal circuits underlying many neurobehavioral disorders. KOR agonists directly inhibit ventral tegmental area (VTA) dopaminergic neurons, contributing to aversive responses (Margolis et al. 2003, 2006); therefore, selective KOR antagonists represent a novel therapeutic approach to restore circuit function. We used whole cell electrophysiology in acute rat midbrain slices to evaluate pharmacological properties of four novel KOR antagonists: BTRX-335140, BTRX-395750, PF-04455242, and JNJ-67953964. Each compound concentration-dependently reduced the outward current induced by the KOR selective agonist U-69,593. BTRX-335140 and BTRX-395750 fully blocked U-69,593 currents (IC50 = 1.2 ± 0.9 and 1.2 ± 1.3 nM, respectively). JNJ-67953964 showed an IC50 of 3.0 ± 4.6 nM. PF-04455242 exhibited partial antagonist activity asymptoting at 55% blockade (IC50 = 6.7 ± 15.1 nM). In 3/8 of neurons, 1 µM PF-04455242 generated an outward current independent of KOR activation. BTRX-335140 (10 nM) did not affect responses to saturating concentrations of the mu opioid receptor (MOR) agonist DAMGO or the delta opioid receptor (DOR) agonist DPDPE, while JNJ-67953964 (10 nM) partially blocked DAMGO and DPDPE responses. Importantly, BTRX-335140 (10 nM) rapidly washed out with complete recovery of U-69,593 responses within 10 min. Collectively, we show electrophysiological evidence of key differences amongst KOR antagonists that could impact their therapeutic potential and have not been observed using recombinant systems. The results of this study demonstrate the value of characterizing compounds in native neuronal tissue and within circuits implicated in the neurobehavioral disorders of interest.

Differential Modulation of Ventral Tegmental Area Circuits by the Nociceptin/Orphanin FQ System.

The neuropeptide nociceptin/orphanin FQ (N/OFQ) can be released by stressors and is associated with disorders of emotion regulation and reward processing. N/OFQ and its receptor, NOP, are enriched in dopaminergic pathways, and intra-ventricular agonist delivery decreases dopamine levels in the dorsal striatum, nucleus accumbens (NAc), and ventral tegmental area (VTA). We used whole-cell electrophysiology in acute rat midbrain slices to investigate synaptic actions of N/OFQ. N/OFQ was primarily inhibitory, causing outward currents in both immunocytochemically identified dopaminergic (tyrosine hydroxylase positive (TH(+))) and non-dopaminergic (TH(-)) VTA neurons; effect at 1 µm: 20 ± 4 pA. Surprisingly, this effect was mediated by augmentation of postsynaptic GABAAR currents, unlike the substantia nigra pars compacta (SNc), where the N/OFQ-induced outward currents were K+ channel dependent. A smaller population, 17% of all VTA neurons, responded to low concentrations of N/OFQ with inward currents (10 nm: -11 ± 2 pA). Following 100 nm N/OFQ, the response to a second N/OFQ application was markedly diminished in VTA neurons (14 ± 10% of first response) but not in SNc neurons (90 ± 20% of first response). N/OFQ generated outward currents in medial prefrontal cortex (mPFC)-projecting VTA neurons, but inward currents in a subset of posterior anterior cingulate cortex (pACC)-projecting VTA neurons. While N/OFQ inhibited NAc-projecting VTA cell bodies, it had little effect on electrically or optogenetically evoked terminal dopamine release in the NAc measured ex vivo with fast scan cyclic voltammetry (FSCV). These results extend our understanding of the N/OFQ system in brainstem circuits implicated in many neurobehavioral disorders.

A Review of the Cholinergic System and Therapeutic Approaches to Treat Brain Disorders.

Since its identification over a hundred years ago, the neurotransmitter acetylcholine (ACh) has proven to play an essential role in supporting many diverse functions. Some well-characterized functions include: chemical transmission at the neuromuscular junction; autonomic function in the peripheral nervous system; and, sustained attention, sleep/wake regulation, and learning and memory within the central nervous system. Within the brain, major cholinergic projection pathways from the basal forebrain and the brainstem support these centrally mediated processes, and dysregulation of the cholinergic system is implicated in cognitive decline associated with aging and dementias including Alzheimer's disease. ACh exerts its effects by binding to two different membrane-bound receptor classes: (1) G­protein coupled muscarinic acetylcholine receptors (mAChRs), and (2) ligand-gated nicotinic acetylcholine receptors (nAChRs). These receptor systems are described in detail within this chapter along with discussion on the successes and failures of synthetic ligands designed to selectively target receptor subtypes for treating brain disorders. New molecular approaches and advances in our understanding of the target biology combined with opportunities to re-purpose existing cholinergic drugs for new indications continue to highlight the exciting opportunities for modulating this system for therapeutic purposes.

Electrophysiological characterization of sleep/wake, activity and the response to caffeine in adult cynomolgus macaques.

Most preclinical sleep studies are conducted in nocturnal rodents that have fragmented sleep in comparison to humans who are primarily diurnal, typically with a consolidated sleep period. Consequently, we sought to define basal sleep characteristics, sleep/wake architecture and electroencephalographic (EEG) activity in a diurnal non-human primate (NHP) to evaluate the utility of this species for pharmacological manipulation of the sleep/wake cycle. Adult, 9-11 y.o. male cynomolgus macaques (n = 6) were implanted with telemetry transmitters to record EEG and electromyogram (EMG) activity and Acticals to assess locomotor activity under baseline conditions and following injections either with vehicle or the caffeine (CAF; 10 mg/kg, i.m.) prior to the 12 h dark phase. EEG/EMG recordings (12-36 h in duration) were analyzed for sleep/wake states and EEG spectral composition. Macaques exhibited a sleep state distribution and architecture similar to previous NHP and human sleep studies. Acute administration of CAF prior to light offset enhanced wakefulness nearly 4-fold during the dark phase with consequent reductions in both NREM and REM sleep, decreased slow wave activity during wakefulness, and increased higher EEG frequency activity during NREM sleep. Despite the large increase in wakefulness and profound reduction in sleep during the dark phase, no sleep rebound was observed during the 24 h light and dark phases following caffeine administration. Cynomolgus macaques show sleep characteristics, EEG spectral structure, and respond to CAF in a similar manner to humans. Consequently, monitoring EEG/EMG by telemetry in this species may be useful both for basic sleep/wake studies and for pre-clinical assessments of drug-induced effects on sleep/wake.

Trace amine-associated receptor 1 agonism promotes wakefulness without impairment of cognition in Cynomolgus macaques.

Trace amine-associated receptor 1 (TAAR1) is a G-protein coupled receptor with affinity for the trace amines. TAAR1 agonists have pro-cognitive, antidepressant-, and antipsychotic-like properties in both rodents and non-human primates (NHPs). TAAR1 agonism also increases wakefulness and suppresses rapid-eye movement (REM) sleep in mice and rats and reduces cataplexy in two mouse models of narcolepsy. We investigated the effects of TAAR1 agonism in Cynomolgus macaques, a diurnal species that exhibits consolidated night-time sleep, and evaluated the effects of TAAR1 agonists on cognition using a working memory (WM) paradigm in this species. Adult male Cynomolgus macaques (n = 6) were surgically implanted to record the electroencephalogram (EEG), electromyogram, and locomotor activity (LMA) and the efficacy of the TAAR1 partial agonist RO5263397 (0.1,1,10 mg/kg, p.o.) on sleep/wake, EEG spectra, and LMA was determined. In a second experiment, the acute effects of RO5263397 (0.1,1,10 mg/kg, p.o.) were assessed on a delayed-match-to-sample test of WM in adult male macaques (n = 7). RO5263397 (10 mg/kg) administered at lights off, when sleep pressure was high, promoted wakefulness and reduced both REM and non-REM sleep without inducing hyperlocomotion. RO5263397 (10 mg/kg) also increased delta/theta activity during all vigilance states. RO5263397 had no effect on WM at either short (2 sec) or long (10 sec) delay intervals. The wake-enhancing and REM-suppressing effects of R05263397 shown here in a diurnal primate are consistent with previous results in nocturnal rodents. These effects and the associated alterations in EEG spectra occurred without inducing hyperlocomotion or affecting WM, encouraging further study of TAAR1 agonists as potential narcolepsy therapeutics.

Therapeutic Approaches for NOP Receptor Antagonists in Neurobehavioral Disorders: Clinical Studies in Major Depressive Disorder and Alcohol Use Disorder with BTRX-246040 (LY2940094).

Conventional antidepressants increase the efflux of biogenic amine neurotransmitters (the monoamine hypothesis of depression) in the central nervous system (CNS) and are the principle drugs used to treat major depressive disorder (MDD). However, the lack of efficacy in some patients, the slow onset of action, and the side effect profiles of existing antidepressants necessitate the exploration of additional treatment options. The discovery of the nociceptin/orphanin FQ peptide NOP receptor (N/OFQ-NOP receptor) system and its characterization in preclinical biological and pharmacological stress-related conditions supports the potential antidepressant and anti-stress properties of a NOP receptor antagonist for the treatment of neurobehavioral disorders. BTRX-246040 (formerly LY2940094) was designed to test this hypothesis in the clinic. A small clinical proof of concept study demonstrated efficacy of BTRX-246040 in MDD patients. In this study, BTRX-246040 (40 mg, p.o.) significantly reduced negative bias as assessed by the facial recognition test within 1 week of treatment and decreased depression symptoms after 8 weeks. BTRX-246040 also reduced depression symptoms in a second trial with heavy alcohol drinkers. Given the comorbidity of MDD and alcohol use disorder, a compound with such effects in patients could be a valuable addition to the medications available. A proof of concept study showed efficacy of BTRX-246040 in reducing heavy drinking and increasing the probability of abstinence in individuals diagnosed with alcohol dependence. In addition, plasma levels of gamma-glutamyl transferase were decreased by BTRX-246040 compared to placebo control implying improvement in liver function. Collectively, the clinical data reviewed within this chapter suggest that BTRX-264040 functions to normalize dysfunction in reward circuits. The overall efficacy and safety of this compound with a novel mechanism of action are encouraging of further clinical development. BTRX-246040 is currently under development for MDD by BlackThorn Therapeutics.

Peripheral complement interactions with amyloid ß peptide in Alzheimer's disease: 2. Relationship to amyloid ß immunotherapy.

INTRODUCTION: Our previous studies have shown that amyloid ß peptide (Aß) is subject to complement-mediated clearance from the peripheral circulation, and that this mechanism is deficient in Alzheimer's disease. The mechanism should be enhanced by Aß antibodies that form immune complexes (ICs) with Aß, and therefore may be relevant to current Aß immunotherapy approaches. METHODS: Multidisciplinary methods were employed to demonstrate enhanced complement-mediated capture of Aß antibody immune complexes compared with Aß alone in both erythrocytes and THP1-derived macrophages. RESULTS: Aß antibodies dramatically increased complement activation and opsonization of Aß, followed by commensurately enhanced Aß capture by human erythrocytes and macrophages. These in vitro findings were consistent with enhanced peripheral clearance of intravenously administered Aß antibody immune complexes in nonhuman primates. DISCUSSION: Together with our previous results, showing significant Alzheimer's disease deficits in peripheral Aß clearance, the present findings strongly suggest that peripheral mechanisms should not be ignored as contributors to the effects of Aß immunotherapy.

Peripheral complement interactions with amyloid ß peptide: Erythrocyte clearance mechanisms.

INTRODUCTION: Although amyloid ß peptide (Aß) is cleared from the brain to cerebrospinal fluid and the peripheral circulation, mechanisms for its removal from blood remain unresolved. Primates have uniquely evolved a highly effective peripheral clearance mechanism for pathogens, immune adherence, in which erythrocyte complement receptor 1 (CR1) plays a major role. METHODS: Multidisciplinary methods were used to demonstrate immune adherence capture of Aß by erythrocytes and its deficiency in Alzheimer's disease (AD). RESULTS: Aß was shown to be subject to immune adherence at every step in the pathway. Aß dose-dependently activated serum complement. Complement-opsonized Aß was captured by erythrocytes via CR1. Erythrocytes, Aß, and hepatic Kupffer cells were colocalized in the human liver. Significant deficits in erythrocyte Aß levels were found in AD and mild cognitive impairment patients. DISCUSSION: CR1 polymorphisms elevate AD risk, and >80% of human CR1 is vested in erythrocytes to subserve immune adherence. The present results suggest that this pathway is pathophysiologically relevant in AD.

Alterations in High-Frequency Neuronal Oscillations in a Cynomolgus Macaque Test of Sustained Attention Following NMDA Receptor Antagonism.

A growing body of evidence indicates that neuronal oscillations in the gamma frequency range (30-80 Hz) are disturbed in schizophrenic patients during cognitive processes and may represent an endophenotype of the disease. N-methyl-D-aspartate (NMDA) receptor antagonists have been used experimentally to induce schizophrenia-like symptoms including cognitive deficits in animals and humans. Here we characterized neuronal oscillations and event-related potentials (ERPs) in Cynomolgus macaques fully trained to perform a continuous performance test (CPT) in the presence and absence of the NMDA antagonist phencyclidine (PCP). Macaques (n=8) were trained to touch 'target' stimuli and ignore 'distractor' stimuli presented randomly on a touchscreen. Subsequently, all subjects were implanted with epidural EEG electrodes over frontal (FC) and parietal cortices (PC) and later tested under vehicle (saline, i.m.) or acute PCP (0.1-0.3 mg/kg, i.m.) conditions. Compared with vehicle treatment, PCP produced a significant dose-dependent decrease in CPT performance accuracy and increased reaction times. Furthermore, PCP elevated the amplitudes of 'low' (30-50 Hz) and 'high' (51-80 Hz) gamma oscillations in FC and PC around target presentations for all correct responses. The CPT accuracy was inversely correlated with the gamma band amplitude in the presence of PCP. Additionally, PCP delayed the N100 peak latency in FC, and prolonged and suppressed the cognitively relevant P300 component of mean ERPs in FC and PC, respectively. The NMDA receptor antagonist-induced alteration in neuronal oscillations and ERPs may contribute to the observed cognitive deficits in macaques, and enhance our understanding of EEG recordings as a translatable biomarker.

Neuronal α7 Nicotinic Receptors as a Target for the Treatment of Schizophrenia.

Schizophrenia is a lifelong disease, the burden of which is often underestimated. Characterized by positive (e.g., hallucinations) and negative (e.g., avolition, amotivation) symptoms, schizophrenia is also accompanied with profound impairments in cognitive function that progress throughout the development of the disease. Although treatment with antipsychotic medications can effectively dampen some of the positive symptoms, these medications largely fail to reverse cognitive deficits or to mitigate negative symptoms. With a worldwide prevalence of approximately 1%, schizophrenia remains a large unmet medical need that stands to benefit greatly from (1) continued research to better understand the biological underpinnings of the disease and (2) the targeted development of novel therapeutics to improve the lives of those affected individuals. Improvements in our understanding of the neuronal networks associated with schizophrenia as well as progress in identifying genetic risk factors and environmental conditions that may predispose individuals to developing the disease are advancing new strategies to study and treat it. Herein, we review the evidence that supports the role of α7 nicotinic acetylcholine receptors in the central nervous system and why these receptors constitute a promising target to treat some of the prominent symptoms of schizophrenia.

Animal paradigms to assess cognition with translation to humans.

Cognition is a complex brain function that represents processes such as learning and memory, attention, working memory, and executive functions amongst others. Impairments in cognition are prevalent in many neuropsychiatric and neurological disorders with few viable treatment options. The development of new therapies is challenging, and poor efficacy in clinical development continues to be one of the most consistent reasons compounds fail to advance, suggesting that traditional animal models are not predictive of human conditions and behavior. An effort to improve the construct validity of neuropsychological testing across species with the intent of facilitating therapeutic development has been strengthening over recent years. With an emphasis on understanding the underlying biology, optimizing the use of appropriate systems (e.g., transgenic animals) to model targeted disease states, and incorporating non-rodent species (e.g., non-human primates) that may enable a closer comparison to humans, an improvement in the translatability of the results will be possible. This chapter focuses on some promising translational cognitive paradigms for use in rodents, non-human primates, and humans.

Effect of bitopertin, a glycine reuptake inhibitor, on negative symptoms of schizophrenia: a randomized, double-blind, proof-of-concept study.

IMPORTANCE: In schizophrenia, the severity of negative symptoms is a key predictor of long-term disability. Deficient signaling through the N-methyl-D-aspartate receptor is hypothesized to underlie many signs and symptoms associated with schizophrenia in particular negative symptoms. Glycine acts as an N-methyl-D-aspartate receptor coagonist. Blockade of the glycine transporter type 1 to inhibit glycine reuptake and elevate synaptic glycine concentrations represents an effective strategy to enhance N-methyl-D-aspartate receptor transmission. OBJECTIVE: To determine the efficacy and safety of bitopertin (RG1678), a glycine reuptake inhibitor, in patients with schizophrenia and predominant negative symptoms who were stable while taking an antipsychotic treatment. DESIGN, SETTING, AND PARTICIPANTS: This randomized, double-blind, placebo-controlled, phase 2 proof-of-concept trial involved 323 patients with schizophrenia and predominant negative symptoms across 66 sites worldwide. INTERVENTIONS: Bitopertin (10, 30, or 60 mg/d) or placebo added to standard antipsychotic therapy for a treatment duration of 8 weeks. MAIN OUTCOMES AND MEASURES: Change from baseline in the Positive and Negative Syndrome Scale negative factor score. RESULTS: In the per-protocol population, 8 weeks of treatment with bitopertin was associated with a significant reduction of negative symptoms in the 10-mg/d (mean [SE] reduction in negative symptoms score, -25% [2%]; P = .049) and 30-mg/d (mean [SE], -25% [2%]; P = .03) bitopertin groups, a significantly higher response rate and a trend toward improved functioning in the 10-mg/d group when compared with placebo (mean [SE], -19% [2%]). Results reached trend-level significance in the intent-to-treat population. Estimates of bitopertin binding to glycine transporter type 1 showed that low to medium levels of occupancy yielded optimal efficacy in patients, consistent with findings in preclinical assays. CONCLUSIONS AND RELEVANCE: Bitopertin-mediated glycine reuptake inhibition may represent a novel treatment option for schizophrenia, with the potential to address negative symptoms. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00616798.

Consideration of species differences in developing novel molecules as cognition enhancers.

The NIH-funded CNTRICS initiative has coordinated efforts to promote the vertical translation of novel procognitive molecules from testing in mice, rats and non-human primates, to clinical efficacy in patients with schizophrenia. CNTRICS highlighted improving construct validation of tasks across species to increase the likelihood that the translation of a candidate molecule to humans will be successful. Other aspects of cross-species behaviors remain important however. This review describes cognitive tasks utilized across species, providing examples of differences and similarities of innate behavior between species, as well as convergent construct and predictive validity. Tests of attention, olfactory discrimination, reversal learning, and paired associate learning are discussed. Moreover, information on the practical implication of species differences in drug development research is also provided. The issues covered here will aid in task development and utilization across species as well as reinforcing the positive role preclinical research can have in developing procognitive treatments for psychiatric disorders.

Alpha7 neuronal nicotinic receptors as a drug target in schizophrenia.

INTRODUCTION: Schizophrenia is a profoundly debilitating disease that represents not only an individual, but a societal problem. Once characterized solely by the hyperactivity of the dopaminergic system, therapies directed to dampen dopaminergic neurotransmission were developed. However, these drugs do not address the significant impairments in cognition and the negative symptoms of the disease, and it is now apparent that disequilibrium of many neurotransmitter systems is involved. Despite enormous efforts, minimal progress has been made toward the development of safer, more effective therapies to date. AREAS COVERED: The high preponderance of smoking in schizophrenics suggests that nicotine may provide symptomatic improvement, which has led to investigation for selective molecules targeted to individual nicotinic receptor (nAChR) subtypes. Of special interest is activation of the homomeric α7nAChR, which is widely distributed in the brain and has been implicated in the pathophysiology of schizophrenia through numerous approaches. EXPERT OPINION: Preclinical and clinical data suggest that neuronal α7nAChRs play an important role in cognitive functions. Moreover, some, but not all, early clinical trials conducted with α7nAChR agonists show cognitive benefits in schizophrenics. These encouraging results suggest that development of compounds targeting α7nAChRs will represent a valuable tool to mitigate symptoms associated with schizophrenia, and open new strategies for better pharmacological treatment of these patients.

Trace amine-associated receptor 1 partial agonism reveals novel paradigm for neuropsychiatric therapeutics.

BACKGROUND: Trace amines, compounds structurally related to classical biogenic amines, represent endogenous ligands of the trace amine-associated receptor 1 (TAAR1). Because trace amines also influence the activity of other targets, selective ligands are needed for the elucidation of TAAR1 function. Here we report on the identification and characterization of the first selective and potent TAAR1 partial agonist. METHODS: The TAAR1 partial agonist RO5203648 was evaluated for its binding affinity and functional activity at rodent and primate TAAR1 receptors stably expressed in HEK293 cells, for its physicochemical and pharmacokinetic properties, for its effects on the firing frequency of monoaminergic neurons ex vivo, and for its properties in vivo with genetic and pharmacological models of central nervous system disorders. RESULTS: RO5203648 showed high affinity and potency at TAAR1, high selectivity versus other targets, and favorable pharmacokinetic properties. In mouse brain slices, RO5203648 increased the firing frequency of dopaminergic and serotonergic neurons in the ventral tegmental area and the dorsal raphe nucleus, respectively. In various behavioral paradigms in rodents and monkeys, RO5203648 demonstrated clear antipsychotic- and antidepressant-like activities as well as potential anxiolytic-like properties. Furthermore, it attenuated drug-taking behavior and was highly effective in promoting attention, cognitive performance, and wakefulness. CONCLUSIONS: With the first potent and selective TAAR1 partial agonist, RO5203648, we show that TAAR1 is implicated in a broad range of relevant physiological, behavioral, and cognitive neuropsychiatric dimensions. Collectively, these data uncover important neuromodulatory roles for TAAR1 and suggest that agonists at this receptor might have therapeutic potential in one or more neuropsychiatric domains.