Pharmacodynamic and pharmacokinetic effects of MK-0343, a GABA(A) alpha2,3 subtype selective agonist, compared to lorazepam and placebo in healthy male volunteers

Nonsedating anxiolytics

Anxiety disorders are the most prevalent psychiatric pathology with substantial cost to society, but the existing treatments are often inadequate. This has rekindled the interest in the GABAA-receptor (GABAAR) positive allosteric modulator (PAM) compounds, which have a long history in treatment of anxiety beginning with diazepam, chlordiazepoxide, and alprazolam. While the GABAAR PAMs possess remarkable anxiolytic efficacy, they have fallen out of favor due to a host of adverse effects including sedation, motor impairment, addictive potential and tolerance development. A substantial effort was thus devoted to the design of GABAAR PAMs as anxiolytics with reduced sedative liabilities. Several non-benzodiazepine (BZD) GABAAPAMs progressed to clinical trials (bretazenil, abecarnil, alpidem, and ocinaplon) with alpidem obtaining regulatory approval as anxiolytic, but later withdrawn from market due to hepatotoxicity. Advances in molecular biology gave birth to a host of subtype selective GABAAR-PAMs which suffered from signs of sedation and motor impairment and only three compounds progressed to proof-of-concept studies (TPA-023, AZD7325 and PF-06372865). TPA-023 was terminated due to toxicity in preclinical species while AZD7325 and PF-06372865 did not achieve efficacy endpoints in patients. We highlight a new compound, KRM-II-81, that is an imidazodiazepine selective for GABAAR containing α2/3 and β3 proteins. In preclinical studies KRM-II-81 produced anxiolytic-like effects but with minimal sedation, respiratory depression, and abuse liability. Thus, KRM-II-81 is a newly discovered, non- BZD anxiolytic compound, which targets a selective population of GABAAR for improved therapeutic gain and reduced side effects.

The interactive walkway provides fit-for-purpose fall-risk biomarkers in the elderly: Comparison of zolpidem and suvorexant

Dynamic balance assessments such as walking adaptability may yield a more realistic prediction of drug-induced falls compared with postural stability measurements, as falls often result from limited gait adjustments when walking. The Interactive Walkway (IWW) measures walking adaptability but sensitivity to medication effects is unknown. If proven sensitive and specific, IWW could serve as a biomarker for targeted fall-risk assessments in early clinical drug development. In this three-way crossover study, 18 healthy elderly (age: 65-80 years) subjects received 5 mg zolpidem, 10 mg suvorexant, or placebo in the morning. Assessments were performed pre-dose and approximately hourly until 9 h post-dose. IWW assessments included an 8-meter walking test, goal-directed stepping, obstacle-avoidance, and tandem-walking. Other pharmacodynamic measurements were the Timed-Up-and-Go (TUG) test at a comfortable and fast pace, adaptive tracking, and body sway. A decline in performance was observed for zolpidem compared with placebo for 3 h post-dose in IWW walking adaptability outcome measures, TUG, adaptive tracking, and body sway. For the IWW tasks, a decrease in walking speed (among others) was observed. IWW parameters were not affected by suvorexant compared with placebo at any timepoint. However, an increase of 9.8% (95%CI: 1.8%, 18.5%) in body sway was observed for suvorexant compared with placebo up to 3 h post-dose. The IWW successfully quantified drug effects of two hypnotic drugs and distinguished between zolpidem and suvorexant regarding their effects on walking. As a biomarker, the IWW demonstrated sensitivity in assessing dynamic balance and potential fall risk in early phase clinical drug development.

Effects of psychotropic drugs on ocular parameters relevant to traffic safety: A systematic review

Driving is a complex neurobehavioural task necessitating the rapid selection, uptake, and processing of visual information. Eye movements that are critical for the execution of visually guided behaviour such as driving are also sensitive to the effects of psychotropic substances. The Embase (via Ovid), EBSCOHost, Psynet, Pubmed, Scopus and Web of Science databases were examined from January 01st, 2000 to December 31st, 2021. Study selection, data extraction and Cochrane Risk of Bias (RoB2) assessments were conducted according to PRISMA guidelines. The review was prospectively registered (CRD42021267554). In total, 36 full-text articles examined the effects of six principal psychotropic drug classes on measures of oculomotor parameters relevant to driving. Centrally depressing substances affect oculomotor responses in a dose-dependent manner. Psychostimulants improve maximal speed, but not accuracy, of visual search behaviours. Inhaled Δ-9-tetrahydrocannabinol (THC) increases inattention (saccadic inaccuracy) but does not consistently affect other oculomotor parameters. Alterations to composite ocular parameters due to psychoactive substance usage likely differently compromises performance precision during driving through impaired ability to select and process dynamic visual information.

Central nervous system effects of TAK-653, an investigational alpha-amino-3-hydroxy-5-methyl-4-isoxazole receptor (AMPAR) positive allosteric modulator in healthy volunteers

TAK-653 is a novel AMPA receptor positive allosteric modulator in clinical development for the treatment of major depressive disorder (MDD). This study aimed to measure the functional pharmacodynamic central nervous system (CNS) effects of TAK-653. A randomised, double-blind, placebo-controlled, three-way crossover (placebo, TAK-653 0.5 mg and 6 mg) study with 24 healthy volunteers was performed. NeuroCart tests consisting of body sway (BS), saccadic peak velocity (SPV), smooth pursuit eye movements (SP), adaptive tracking (AT), Bowdle and Bond and Lader Visual Analogue Scales (B-VAS and BL-VAS) and Stroop test were performed pre-dose and 3.5 and 4 h post-dose. Data were analysed using a mixed model analysis of covariance with baseline as covariate. It was found that TAK-653 did not affect BS and subjective drug effects as measured by B-VAS and BL-VAS at either dose level. TAK-653 0.5 mg increased SPV (degrees/second) (19.49 [5.98, 32.99], P = 0.02) and affected Stroop difference in reaction time between correct congruent and correct incongruent answers and number of correct responses in incongruent trials (22.0 [4.0, 40.0], P = 0.05 and -0.3 [-0.5, -0.1], P = 0.02, respectively). TAK-653 6 mg improved AT (%) (1.68 [0.51, 2.84], P = 0.02) and increased SPV (degrees/s) (15.40 [1.91, 28.90], P = 0.06) and SP (%) (2.32 [0.37, 4.27], P = 0.05). Based on these findings it can be concluded that TAK-653 demonstrated a psychostimulant-like pharmacodynamic profile on the NeuroCart consistent with previously reported increase of cortical excitability following Transcranial Magnetic Stimulation (TMS) of the human motor cortex.

The imidazodiazepine, KRM-II-81: An example of a newly emerging generation of GABAkines for neurological and psychiatric disorders

GABAkines, or positive allosteric modulators of γ-aminobutyric acid-A (GABA_A) receptors, are used for the treatment of anxiety, epilepsy, sleep, and other disorders. The search for improved GABAkines, with reduced safety liabilities (e.g., dependence) or side-effect profiles (e.g., sedation) constituted multiple discovery and development campaigns that involved a multitude of strategies over the past century. Due to the general lack of success in the development of new GABAkines, there had been a decades-long draught in bringing new GABAkines to market. Recently, however, there has been a resurgence of efforts to bring GABAkines to patients, the FDA approval of the neuroactive steroid brexanolone for post-partum depression in 2019 being the first. Other neuroactive steroids are in various stages of clinical development (ganaxolone, zuranolone, LYT-300, Sage-324, PRAX 114, and ETX-155). These GABAkines and non-steroid compounds (GRX-917, a TSPO binding site ligand), darigabat (CVL-865), an α2/3/5-preferring GABAkine, SAN711, an α3-preferring GABAkine, and the α2/3-preferring GABAkine, KRM-II-81, bring new therapeutic promise to this highly utilized medicinal target in neurology and psychiatry. Herein, we also discuss possible conditions that have enabled the transition to a new age of GABAkines. We highlight the pharmacology of KRM-II-81 that has the most preclinical data reported. KRM-II-81 is the lead compound in a new series of orally bioavailable imidazodiazepines entering IND-enabling safety studies. KRM-II-81 has a preclinical profile predicting efficacy against pharmacoresistant epilepsies, traumatic brain injury, and neuropathic pain. KRM-II-81 also produces anxiolytic- and antidepressant-like effects in rodent models. Other key features of the pharmacology of this compound are its low sedation rate, lack of tolerance development, and the ability to prevent the development of seizure sensitization.

Acute response to cholinergic challenge predicts long-term response to galantamine treatment in patients with Alzheimer's Disease

BACKGROUND

Cholinesterase inhibitors (CEIs) have been shown to improve cognitive functioning in Alzheimer's Disease (AD) patients, but are associated with multiple side effects and only 20-40% of the patients clinically improve. In this study, we aimed to investigate the acute pharmacodynamic (PD) effects of a single dose administration of galantamine on CNS functioning in mild to moderate AD patients and its potential to predict long-term treatment response.

METHODS

This study consisted of a challenge and treatment phase. In the challenge phase, a single dose of 16 mg galantamine was administered to 50 mild to moderate AD patients in a double-blind, placebo-controlled cross-over fashion. Acute PD effects were monitored up to 5 hours after administration with use of the NeuroCart CNS test battery and safety and pharmacokinetics were assessed. In the treatment phase, patients were treated with open-label galantamine according to regular clinical care. After 6 months of galantamine treatment, patients were categorized as either responder or as non-responder based on their MMSE, NPI and DAD scores. An analysis of covariance was performed to study the difference in acute PD effects during the challenge phase between responders and non-responders.

RESULTS

A single dose of galantamine significantly reduced saccadic reaction time (-0.0099; 95%CI=-0.0195,-0.0003; p=.0430), absolute frontal EEG parameters in alpha (-14.9; 95%CI=-21.0,-8.3; p=.0002), beta (-12.6; 95%CI=-19.4,-5.3; p=.0019) and theta (-17.9; 95%CI=-25.0,-10.0; p=.0001) frequencies. Relative frontal (-1.669; 95%CI=-2.999,-0.339; p=.0156) and occipital (-1.856; 95%CI=-3.339,-0.372; p=.0166) EEG power in theta frequency and relative occipital EEG power in the gamma frequency (1.316; 95%CI=0.158,2.475; p=.0273) also increased significantly compared to placebo. Acute decreases of absolute frontal alpha (-20.4; 95%CI=-31.6,-7.47; p=.0046), beta (-15.7; 95% CI=-28.3,-0.93; p=.0390) and theta (-25.9; 95%CI=-38.4,-10.9; p=.0024) EEG parameters and of relative frontal theta power (-3.27%; 95%CI=-5.96,-0.58; p=.0187) on EEG significantly distinguished responders (n=11) from non-responders (n=32) after 6 months.

CONCLUSIONS

This study demonstrates that acute PD effects after single dose of galantamine are correlated with long-term treatment effects and that patients who demonstrate a reduction in EEG power in the alpha and theta frequency after a single administration of galantamine 16 mg will most likely respond to treatment.

Multiple-dose clinical pharmacology of the selective orexin-1 receptor antagonist ACT-539313

AIMS

Compounds that selectively target orexin-1 receptors may be beneficial for the treatment of various disorders. The role of selective orexin-1 receptor antagonists (1-SORAs) in addictive behavior and stress/anxiety-related disturbances has been demonstrated in animals. ACT-539313, an orally active, potent 1-SORA, has been assessed in a clinical single-ascending dose study and exhibited good safety and tolerability. In the two reported studies on ACT-539313, multiple-dose pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability were investigated and in a proof-of-mechanism study a CO₂ challenge was applied as pharmacological model for induction of anxiety and panic symptoms (sequential inhalation of air, 7.5% CO₂, and 35% CO₂).

METHODS

Two double-blind, placebo-controlled, randomized, multiple-dose studies included 58 healthy male and female subjects. In Study 1, multiple-ascending oral doses of 30, 100, and 200 mg twice daily (b.i.d.) ACT-539313 were investigated in 3 dose groups of 8 or 12 subjects (of whom 2 received placebo per dose group). Study 2 was conducted as a randomized two-way crossover design, enrolling 21 male and 9 female subjects who received 200 mg ACT-539313 or matching placebo b.i.d. for 2.5 days followed by a CO₂ challenge, with a washout period in between. PK, PD (objective and subjective measures of sedation, alertness, effects on central nervous system (CNS), and anxiety/panic symptoms), safety, and tolerability were assessed.

RESULTS

At steady state, ACT-539313 was rapidly absorbed with a median time to maximum plasma concentration of 1.8-2.3 h and eliminated with a mean half-life of 3.8-6.5 h. Overall exposure increased dose-proportionally. In Study 1, PD effects confirmed activity of ACT-539313 on the CNS, without consistent or marked effects of sedation, reduced alertness or visuo-motor impairment. In the CO₂ challenge, cortisol concentrations were lower during initial air inhalation after treatment with ACT-539313 compared to placebo, while no difference was detected after CO₂ inhalation. Trends for lower scores in subjective anxiety assessments were observed for ACT-539313. Besides reports of stress related to the challenge, the most frequently reported adverse events were somnolence and headache. No clinically relevant effects in other safety assessments were observed.

CONCLUSIONS

Multiple-dose administration of ACT-539313 was safe and well tolerated up to multiple doses of 200 mg b.i.d. The drug's PK properties as well as the pattern of a decrease in stress-related symptoms after the CO₂ challenge support further investigations of ACT-539313.

Safety, Tolerability, and Pharmacokinetics of Multiple Repeated Oral Doses of the α2/3/5-Subtype Selective GABAA -Positive Allosteric Modulator PF-06372865 in Healthy Volunteers

Multiple‐dose pharmacokinetics (PK) and safety were investigated in this phase 1 study of PF‐06372865, a positive allosteric modulator of α2/3/5 subunit‐containing γ‐aminobutyric acid A receptors (NCT03351751). In 2 cohorts (7‐8 PF‐06372865 and 2 placebo in each cohort), healthy adult subjects received twice‐daily oral doses of PF‐06372865 for 21 days, which included titration in the first 7 days, followed by a maintenance dose of 25 mg twice daily (Cohort 1) and 42.5 mg twice daily (Cohort 2) for 14 days. Serial PK samples were collected on days 1 and 21. Nineteen subjects were assigned to study treatments; 18 completed the study. Approximate dose‐proportional increases in maximum plasma concentratin and area under the plasma concentration–time curve over the dosing interval were observed. PF‐06372865 was rapidly absorbed with a median time to maximum concentration of 1 to 2 hours following both single‐ and multiple‐dose administration. Mean terminal elimination half‐life on day 21 was approximately 11 hours in both cohorts. All adverse events were mild; the most frequently reported was dizziness. After titration, there were no reports of somnolence. There were no clinically significant safety findings, including a lack of withdrawal symptoms on discontinuation of treatment. These results demonstrate that PF‐06372865 is safe and well tolerated at doses estimated to achieve high receptor occupancy (>80%), a profile differentiated from nonselective benzodiazepines.

Molecular docking analysis of α2-containing GABAA receptors with benzimidazoles derivatives

It is of interest to study the binding capacity of "3-[2-(2-Amino-1H-benzo[d]imidazol-1-yl)ethyl]-1,3-oxazolidin-2-one" (OXB2) with the active site of gamma-aminobutyric acid (GABA) located in the GABA type A receptor (GABAAR) in comparison with different GABAA subtypes. Optimal binding features were observed with the α2β2γ2 isoform (-8 kcal/mol). This is similar (-7.3 and -7.2 kcal/mol, respectively) for subtypes (α3β2γ2 and α1β2γ2). This implies that OXB2 binds preferentially to subtypes associated with anxiety (α2- and/or α3-containing receptors) linked molecules than with the subtype associated with sedation (α1-containing receptors). It is further noted that molecular dynamics simulation data of the complex (OXB2-GABAAR) shows adequate structural stability in aqueous environment. Moreover, relevant ADMET data is found adequate for further consideration.

Human pharmacology of positive GABA-A subtype-selective receptor modulators for the treatment of anxiety

Anxiety disorders arise from disruptions among the highly interconnected circuits that normally serve to process the streams of potentially threatening stimuli. The resulting imbalance among these circuits can cause a fundamental misinterpretation of neural sensory information as threatening and can lead to the inappropriate emotional and behavioral responses observed in anxiety disorders. There is considerable preclinical evidence that the GABAergic system, in general, and its α2- and/or α5-subunit-containing GABA(A) receptor subtypes, in particular, are involved in the pathophysiology of anxiety disorders. However, the clinical efficacy of GABA-A α2-selective agonists for the treatment of anxiety disorders has not been unequivocally demonstrated. In this review, we present several human pharmacological studies that have been performed with the aim of identifying the pharmacologically active doses/exposure levels of several GABA-A subtype-selective novel compounds with potential anxiolytic effects. The pharmacological selectivity of novel α2-subtype-selective GABA(A) receptor partial agonists has been demonstrated by their distinct effect profiles on the neurophysiological and neuropsychological measurements that reflect the functions of multiple CNS domains compared with those of benzodiazepines, which are nonselective, full GABA(A) agonists. Normalizing the undesired pharmacodynamic side effects against the desired on-target effects on the saccadic peak velocity is a useful approach for presenting the pharmacological features of GABA(A)-ergic modulators. Moreover, combining the anxiogenic symptom provocation paradigm with validated neurophysiological and neuropsychological biomarkers may provide further construct validity for the clinical effects of novel anxiolytic agents. In addition, the observed drug effects on serum prolactin levels support the use of serum prolactin levels as a complementary neuroendocrine biomarker to further validate the pharmacodynamic measurements used during the clinical pharmacological study of novel anxiolytic agents.

Effects of lorazepam on saccadic eye movements: the role of sex, task characteristics and baseline traits

BACKGROUND

Saccadic eye movements are controlled by a network of parietal, frontal, striatal, cerebellar and brainstem regions. The saccadic peak velocity is an established biomarker of benzodiazepine effects, with benzodiazepines reliably reducing the peak velocity.

AIMS

In this study, we aimed to replicate the effects of benzodiazepines on peak velocity and we investigated effects on previously less studied measures of saccades. We also explored the roles of sex, task characteristics and the baseline variables age, intelligence and trait anxiety in these effects.

METHOD

Healthy adults ( N = 34) performed a horizontal step prosaccade task under 1 mg lorazepam, 2 mg lorazepam and placebo in a double-blind, within-subjects design.

RESULTS

We replicated the dose-dependent reduction in peak velocity with lorazepam and showed that this effect is stronger for saccades to targets at smaller eccentricities. We also demonstrated that this effect is independent of sex and other baseline variables. Lorazepam effects were widespread, however, occurring on mean and variability measures of most saccadic variables. Additionally, there were sex-dependent lorazepam effects on spatial consistency of saccades, indicating more adverse effects in females.

CONCLUSIONS

We conclude that saccadic peak velocity is a sensitive and robust biomarker of benzodiazepine effects. However, lorazepam has pronounced effects also on other parameters of horizontal saccades. Sex-dependent drug effects on spatial consistency may reflect cerebellar mechanisms, given the role of the cerebellum in saccadic spatial accuracy.

Pharmacology in translation: the preclinical and early clinical profile of the novel α2/3 functionally selective GABAA receptor positive allosteric modulator PF-06372865

BACKGROUND AND PURPOSE

Benzodiazepines, non-selective positive allosteric modulators (PAMs) of GABA_A receptors, have significant side effects that limit their clinical utility. As many of these side effects are mediated by the α1 subunit, there has been a concerted effort to develop α2/3 subtype-selective PAMs.

EXPERIMENTAL APPROACH

In vitro screening assays were used to identify molecules with functional selectivity for receptors containing α2/3 subunits over those containing α1 subunits. In vivo receptor occupancy (RO) was conducted, prior to confirmation of in vivo α2/3 and α1 pharmacology through quantitative EEG (qEEG) beta frequency and zolpidem drug discrimination in rats respectively. PF-06372865 was then progressed to Phase 1 clinical trials.

KEY RESULTS

PF-06372865 exhibited functional selectivity for those receptors containing α2/3/5 subunits, with significant positive allosteric modulation (90-140%) but negligible activity (≤20%) at GABA_A receptors containing α1 subunits. PF-06372865 exhibited concentration-dependent occupancy of GABA_A receptors in preclinical species. There was an occupancy-dependent increase in qEEG beta frequency and no generalization to a GABA_A α1 cue in the drug-discrimination assay, clearly demonstrating the lack of modulation at the GABA_A receptors containing an α1 subtype. In a Phase 1 single ascending dose study in healthy volunteers, evaluation of the pharmacodynamics of PF-06372865 demonstrated a robust increase in saccadic peak velocity (a marker of α2/3 pharmacology), increases in beta frequency qEEG and a slight saturating increase in body sway.

CONCLUSIONS AND IMPLICATIONS

PF-06372865 has a unique clinical pharmacology profile and a highly predictive translational data package from preclinical species to the clinical setting.

Amygdala Lesions Reduce Anxiety-like Behavior in a Human Benzodiazepine-Sensitive Approach-Avoidance Conflict Test

BACKGROUND

Rodent approach-avoidance conflict tests are common preclinical models of human anxiety disorder. Their translational validity mainly rests on the observation that anxiolytic drugs reduce rodent anxiety-like behavior. Here, we capitalized on a recently developed approach-avoidance conflict computer game to investigate the impact of benzodiazepines and of amygdala lesions on putative human anxiety-like behavior. In successive epochs of this game, participants collect monetary tokens on a spatial grid while under threat of virtual predation.

METHODS

In a preregistered, randomized, double-blind, placebo-controlled trial, we tested the effect of a single dose (1 mg) of lorazepam (n = 59). We then compared 2 patients with bilateral amygdala lesions due to Urbach-Wiethe syndrome with age- and gender-matched control participants (n = 17). Based on a previous report, the primary outcome measure was the effect of intra-epoch time (i.e., an adaptation to increasing potential loss) on presence in the safe quadrant of the spatial grid. We hypothesized reduced loss adaptation in this measure under lorazepam and in patients with amygdala lesions.

RESULTS

Lorazepam and amygdala lesions reduced loss adaptation in the primary outcome measure. We found similar results in several secondary outcome measures. The relative reduction of anxiety-like behavior in patients with amygdala lesions was qualitatively and quantitatively indistinguishable from an impact of anterior hippocampus lesions found in a previous report.

CONCLUSIONS

Our results establish the translational validity of human approach-avoidance conflict tests in terms of anxiolytic drug action. We identified the amygdala, in addition to the hippocampus, as a critical structure in human anxiety-like behavior.

Pharmacodynamic response profiles of anxiolytic and sedative drugs

AIM

Centrally-acting acutely anxiolytic drugs, such as benzodiazepines, barbiturates and gabapentinoids, affect various central nervous system (CNS) functions, which reflects not only their anxiolytic effects but also neuropsychological side-effects. To validate the pharmacodynamic biomarkers for GABA-ergic anxiolytics, this study determined the pharmacodynamics of two anxiolytics and a nonanxiolytic control, and linked them to their anxiolytic and sedative effects, during an anxiety-challenge study day.

METHODS

Twenty healthy volunteers were randomized in this placebo-controlled, double-blind, four-way cross-over study with single-dose alprazolam (1 mg), diphenhydramine (50 mg), pregabalin (200 mg) or placebo. The Neurocart was used between repeated fear-potentiated startle assessments. Thus, the potential influence of anxiety on CNS pharmacodynamic markers could be examined.

RESULTS

Compared to placebo, VAS_calmness increased with alprazolam (2.0 mm) and pregabalin (2.5 mm) but not with diphenhydramine. Saccadic peak velocity (SPV) declined after alprazolam (-57 ° s^-1 ) and pregabalin (-28 ° s^-1 ), more than with diphenhydramine (-14 ° s^-1 ); so did smooth pursuit. The average responses of SPV and smooth pursuit were significantly correlated with the drug-induced increases in VAS_calmness . The SPV-relative responses of VAS_alertness , body-sway and adaptive-tracking also differed among alprazolam, pregabalin and diphenhydramine.

CONCLUSIONS

Compared with the antihistaminergic sedative diphenhydramine, alprazolam and pregabalin caused larger SPV reduction, which was correlated with simultaneous improvement of subjective calmness, during a study day in which anxiety was stimulated repeatedly. The different effect profiles of the three drugs are in line with their pharmacological distinctions. These findings corroborate the profiling of CNS effects to demonstrate pharmacological selectivity, and further support SPV as biomarker for anxiolysis involving GABA-ergic neurons. The study also supports the use of prolonged mild threat to demonstrate anxiolytic effects in healthy volunteers.

Pharmacokinetics and pharmacodynamics of oral mecamylamine - development of a nicotinic acetylcholine receptor antagonist cognitive challenge test using modelling and simulation

A pharmacologic challenge model with a nicotinic antagonist could be an important tool not only to understand the complex role of the nicotinic cholinergic system in cognition, but also to develop novel compounds acting on the nicotinic acetylcholine receptor. The objective was to develop a pharmacokinetic-pharmacodynamic (PKPD) model using nonlinear mixed effects (NLME) methods to quantitate the pharmacokinetics of three oral mecamylamine doses (10, 20 and 30 mg) and correlate the plasma concentrations to the pharmacodynamic effects on a cognitive and neurophysiologic battery of tests in healthy subjects. A one-compartment linear kinetic model best described the plasma concentrations of mecamylamine. Mecamylamine's estimated clearance was 0.28 ± 0.015 L min^-1. The peripheral volume of distribution (291 ± 5.15 L) was directly related to total body weight. Mecamylamine impaired the accuracy and increased the reaction time in tests evaluating short term working memory with a steep increase in the concentration-effect relationship at plasma concentrations below 100 μg L^-1. On the other hand, mecamylamine induced a decrease in performance of tests evaluating visual and fine motor coordination at higher plasma concentrations (EC₅₀ 97 μg L^-1). Systolic and diastolic blood pressure decreased exponentially after a plasma mecamylamine concentration of 80 μg L^-1, a known effect previously poorly studied in healthy subjects. The developed mecamylamine PKPD model was used to quantify the effects of nicotinic blockade in a set of neurophysiological tests in humans with the goal to provide insight into the physiology and pharmacology of the nicotinic system in humans and the possibility to optimize future trials that use mecamylamine as a pharmacological challenge.

To what extent is it possible to dissociate the anxiolytic and sedative/hypnotic properties of GABAA receptors modulators?

The relatively common view indicates a possible dissociation between the anxiolytic and sedative/hypnotic properties of benzodiazepines (BZs). Indeed, GABAA receptor (GABAAR) subtypes have specific cerebral distribution in distinct neural circuits. Thus, GABAAR subtype-selective drugs may be expected to perform distinct functions. However, standard behavioral test assays provide limited direction towards highlighting new action mechanisms of ligands targeting GABAARs. Automated behavioral tests, lack sensitivity as some behavioral characteristics or subtle behavioral changes of drug effects or that are not considered in the overall analysis (Ohl et al., 2001) and observation-based analyses are not always performed. In addition, despite the use of genetically engineered mice, any possible dissociation between the anxiolytic and sedative properties of BZs remains controversial. Moreover, the involvement the different subtypes of GABAAR subtypes in the anxious behavior and the mechanism of action of anxiolytic agents remains unclear since there has been little success in the pharmacological investigations so far. This raises the question of the involvement of the different subunits in anxiolytic-like and/or sedative effects; and the actual implication of these subunits, particularly, α-subunits in the modulation of sedation and/or anxiety-related disorders. This present review was prompted by several conflicting studies on the degree of involvement of these subunits in anxiolytic-like and/or sedative effects. To this end, we explored the GABAergic system, particularly, the role of different subunits containing synaptic GABAARs. We report herein the targeting gene encoding the different subunits and their contribution in anxiolytic-like and/or sedative actions, as well as, the mechanism underlying tolerance to BZs.

NS11821, a partial subtype-selective GABAA agonist, elicits selective effects on the central nervous system in randomized controlled trial with healthy subjects

NS11821 is a partial GABAA agonist with relatively dominant α2,3 and α5 subtype efficacy but negligible α1 agonism. This first-in-human study was performed in healthy male subjects using a single-dose, parallel, double blind, placebo-controlled, randomized, dose-escalation study design. In total six cohorts (N=48) were enrolled. The eight subjects of each cohort received NS11821 (10 mg, 30 mg, 75 mg, 150 mg, 300 mg or 600 mg) or placebo in a 6:2 ratio. At low dose levels, NS11821 had a relatively low exposure and a more-than-proportional increase of the area under the curve and maximum plasma concentrations, probably due to poor solubility. Saccadic peak velocity decreased in a dose-related manner while limited impairments were seen on body sway and the visual analogue scale for alertness. The most common adverse events were somnolence and dizziness, which were more prominent with the higher doses. Although no positive control was used in this study, the results were compared post hoc with a Centre for Human Drug Research dataset for lorazepam 2 mg. The maximum saccadic peak velocity effects seemed comparable to the typical effects of lorazepam, whereas the other central nervous system effects were smaller. These results support the pharmacological selectivity of NS11821 and show that pharmacodynamic effective doses of NS11821 were safe and well tolerated in healthy subjects.

The central nervous system effects of the partial GABA-Aα2,3 -selective receptor modulator AZD7325 in comparison with lorazepam in healthy males

AIMS

AZD7325 is a novel α2,3 -subtype-selective partial GABA-A-receptor modulator. This study investigated the pharmacodynamics of single oral doses of AZD7325 2 mg and 10 mg on the central nervous system (CNS) compared with placebo and lorazepam 2 mg.

METHODS

This double-blind, randomized, four way crossover study enrolled 16 healthy males and administered two validated CNS test batteries to measure drug effects on cognitive, neurophysiologic and psychomotor function and subjective feelings. The pharmacological selectivity of AZD7325 was compared with lorazepam by plotting saccadic peak velocity change from baseline (ΔSPV) against body sway (ΔSway) and visual analogue scale for alertness(ΔVASalertness ). This analysis has previously been used to identify α2,3 -subtype-selectivity.

RESULTS

In contrast with the robust impairment caused by lorazepam (all P < 0.05 vs. placebo), neither dose of AZD7325 induced statistically significant effects on any pharmacodynamic measurements. Lorazepam-induced SPV-reduction was linearly related to changes in other neurophysiologic biomarkers. In contrast, the slopes of the regression lines were flatter for AZD7325, particularly for the Δlog(Sway) -ΔSPV relation (estimate slope, AZD7325 10 mg vs. lorazepam, difference [95% confidence interval], P value -0.00036 vs. -0.00206, 0.001704 [0.000639, 0.002768], P = 0.0018) and the ΔVASalertness -ΔSPV relationship (0.01855 vs. 0.08216, -0.06360 [-0.1046, -0.02257], P = 0.0024). AZD7325 10 mg and lorazepam induced different response patterns on VAS 'feeling high' and electro-encephalography.

CONCLUSION

The characteristic ΔSPV-relative effect profiles of AZD7325 vs. lorazepam suggest anxio-selectivity related to α2,3 -selective GABAA agonism. However, exploration of higher doses may be warranted. The paucity of effects on most CNS-PD parameters also indicates a mitigated side effect pattern, with potentially lower cognitive and neurophysiological side effect burden than non-selective benzodiazepines.

AZD6280, a novel partial γ-aminobutyric acid A receptor modulator, demonstrates a pharmacodynamically selective effect profile in healthy male volunteers

OBJECTIVE

AZD6280 is a novel γ-aminobutyric acid A receptor modulator with higher in vitro efficacy at the α2,3 subtypes as compared to the α1 and α5 subtypes. This study compared the pharmacodynamic effects of single oral dose AZD6280 10 mg and 40 mg on the central nervous system with 2 mg of lorazepam.

METHODS

Sixteen healthy males were enrolled into the double-blind, randomized, 4-way crossover study. Two validated central nervous system test batteries, Neurocart and CogState, were administered to measure drug effects on cognition, neurophysiologic function, and psychomotor and subjective feelings. Statistical analysis was performed using mixed model analysis of variance, with fixed factors of treatment, period, time and treatment by time, and random factors of subject, subject by treatment and subject by time, and the average prevalue as covariate.

RESULTS

Most pharmacodynamic parameters were affected by lorazepam. AZD6280 induced dose-dependent smaller-than-lorazepam effects on saccadic peak velocity (SPV) (AZD6280, 10 mg vs. AZD6280, 40 mg vs. lorazepam [deg/s]: -22.6 vs. -50.0 vs. -62.9, P < 0.001), whereas the impacts on adaptive-tracking, body-sway, smooth-pursuit, and the one-card-learning tests were significant but much smaller than lorazepam. Thus, the slopes of regression lines for the ΔLog(Sway)-ΔSPV, ΔTracking-ΔSPV, and ΔSmooth-ΔSPV relations were flatter with AZD6280 than with lorazepam. AZD6280 caused a distinct electroencephalography signature from that of lorazepam.

CONCLUSIONS

The SPV responses to AZD6280 suggest potential concentration-related anxiolytic effects, whereas the smaller SPV-normalized effects of AZD6280 on various non-SPV pharmacodynamic parameters suggest a more favorable side effect profile compared to lorazepam. Overall, the pharmacodynamic profile of AZD6280 matches the pharmacological specificity and selectivity of this compound at the α2,3 γ-aminobutyric acid A receptor subtypes.

Discontinued anxiolytic drugs (2009 - 2014)

INTRODUCTION

Anxiety is a complex psychiatric disorder with an unknown aetiology and involving several neurotransmitter systems. These constraints have meant that researchers have looked to develop drugs, which target a variety of molecular targets, with the aim of creating safer and more effective anxiolytic drugs. Apart from the 'traditional' GABAergic and serotonergic systems, the endocannabinoid, opioidergic, glutamatergic, neurokinin, and even cholinergic systems have been (and are being) considered as preferred targets for prospective new drugs.

AREAS COVERED

This review presents candidate drugs that were investigated for the treatment of anxiety-spectrum disorders and then discontinued between the 2009 and 2014 period.

EXPERT OPINION

Despite the large variety of molecular targets, and the considerable financial and R&D resources dedicated to finding treatment solutions for anxiety-spectrum disorders, a great number of candidates have failed to reach the market. Indeed, there is still an unmet need for more effective anxiolytics that give patients a better quality of life. Although there are inherent problems with psychiatric drug development, it is thought that repurposed drugs may provide some benefit in the future.

GABAA receptor subtypes: Therapeutic potential in Down syndrome, affective disorders, schizophrenia, and autism

The γ-aminobutyric acid (GABA) system plays a pivotal role in orchestrating the synchronicity of local networks and the functional coupling of different brain regions. Here we review the impact of the GABAA receptor subtypes on cognitive and emotional behavior, paying particular attention to five disease states: cognitive dysfunction and Down syndrome, anxiety disorders, depression, schizophrenia, and autism. Through the bidirectional modulation of tonic inhibition, α5-subunit-containing GABAA receptors permit the bidirectional modulation of cognitive processes, and a partial inverse agonist acting at the α5-subunit-containing GABAA receptor is in a clinical trial in individuals with Down syndrome. With regard to anxiety disorders, the viability of nonsedative anxiolytics based on the modulation of α2- and α3-subunit-containing GABAA receptors has been established in clinical proof-of-concept trials. Regarding the remaining three disease states, the GABA hypothesis of depression offers new options for antidepressant drug development; cognitive symptoms in schizophrenia are attributed to a cortical GABAergic deficit, and dysfunctional GABAergic inhibition is increasingly understood to contribute to the pathophysiology of autism spectrum disorders.

Ion channels as drug targets in central nervous system disorders

Ion channel targeted drugs have always been related with either the central nervous system (CNS), the peripheral nervous system, or the cardiovascular system. Within the CNS, basic indications of drugs are: sleep disorders, anxiety, epilepsy, pain, etc. However, traditional channel blockers have multiple adverse events, mainly due to low specificity of mechanism of action. Lately, novel ion channel subtypes have been discovered, which gives premises to drug discovery process led towards specific channel subtypes. An example is Na(+) channels, whose subtypes 1.3 and 1.7-1.9 are responsible for pain, and 1.1 and 1.2 - for epilepsy. Moreover, new drug candidates have been recognized. This review is focusing on ion channels subtypes, which play a significant role in current drug discovery and development process. The knowledge on channel subtypes has developed rapidly, giving new nomenclatures of ion channels. For example, Ca(2+)s channels are not any more divided to T, L, N, P/Q, and R, but they are described as Ca(v)1.1-Ca(v)3.3, with even newer nomenclature α1A-α1I and α1S. Moreover, new channels such as P2X1-P2X7, as well as TRPA1-TRPV1 have been discovered, giving premises for new types of analgesic drugs.

Anxioselective anxiolytics: on a quest for the Holy Grail

The discovery of benzodiazepine receptors provided the impetus to discover and develop anxioselective anxiolytics ('Valium without the side effects'). The market potential for an anxioselective based on the γ-aminobutyric acid A (GABA(A)) receptor resulted in clinical trials of multiple compounds. In contrast to the anxioselective profile displayed in preclinical models, compounds such as bretazenil, TPA023, and MRK 409 produced benzodiazepine-like side effects (sedation, dizziness) in Phase I studies, whereas alpidem and ocinaplon exhibited many of the characteristics of an anxioselective in the clinic. Alpidem was briefly marketed for the treatment of anxiety, but was withdrawn because of liver toxicity. Reversible elevations in liver enzymes halted development of ocinaplon in Phase III. The clinical profiles of these two molecules demonstrate that it is possible to develop GABA(A) receptor-based anxioselectives. However, despite the formidable molecular toolbox at our disposal, we are no better informed about the GABA(A) receptors responsible for an anxioselective profile in the clinic. Here, I discuss the evolution of a quest, spanning four decades, for molecules that retain the rapid and robust anti-anxiety actions of benzodiazepines without the side effects that limit their usefulness.

Chronic pain states: pharmacological strategies to restore diminished inhibitory spinal pain control

Potentially noxious stimuli are sensed by specialized nerve cells named nociceptors, which convey nociceptive signals from peripheral tissues to the central nervous system. The spinal dorsal horn and the trigeminal nucleus serve as first relay stations for incoming nociceptive signals. At these sites, nociceptor terminals contact a local neuronal network consisting of excitatory and inhibitory interneurons as well as of projection neurons. Blockade of neuronal inhibition in this network causes an increased sensitivity to noxious stimuli (hyperalgesia), painful sensations occurring after activation of non-nociceptive fibers (allodynia), and spontaneous pain felt in the absence of any sensory stimulation. It thus mimics the major characteristics of chronic pain states. Diminished inhibitory pain control in the spinal dorsal horn occurs naturally, e.g., through changes in the function of inhibitory neurotransmitter receptors or through altered chloride homeo-stasis in the course of inflammation or nerve damage. This review summarizes our current knowledge about endogenous mechanisms leading to diminished spinal pain control and discusses possible ways that could restore proper inhibition through facilitation of fast inhibitory neurotransmission.

An Overview of the CNS-Pharmacodynamic Profiles of Nonselective and Selective GABA Agonists

Various α_2,3 subtype selective partial GABA-A agonists are in development to treat anxiety disorders. These compounds are expected to be anxiolytic with fewer undesirable side effects, compared to nonselective GABA-A agonists like benzodiazepines. Several α_2,3 subtype selective and nonselective GABA-A agonists have been examined in healthy volunteers, using a battery addressing different brain domains. Data from five placebo-controlled double-blind studies were pooled. Lorazepam 2 mg was the comparator in three studies. Three α_2,3-selective GABAA agonists (i.e., TPA023, TPACMP2, SL65.1498), one α₁-selective GABAA agonists (zolpidem), and another full agonist (alprazolam) were examined. Pharmacological selectivity was assessed by determination of regression lines for the change from baseline of saccadic-peak-velocity- (ΔSPV-) relative effect, relative to changes in different pharmacodynamic endpoints (ΔPD). SPV was chosen for its sensitivity to the anxiolysis of benzodiazepines. Slopes of the ΔSPV-ΔPD relations were consistently lower with the α_2,3 selective GABA-A agonists than with lorazepam, indicating that their PD effects are less than their SPV-effects. The ΔSPV-ΔPD relations of lorazepam were comparable to alprazolam. Zolpidem showed relatively higher impairments in ΔPD relative to ΔSPV, but did not significantly differ from lorazepam. These PD results support the pharmacological selectivity of the α_2,3-selective GABA-A agonists, implying an improved therapeutic window.

Pharmacokinetic-pharmacodynamic relationships of central nervous system effects of scopolamine in healthy subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The cholinergic system is important for different central nervous system functions, including memory, learning and attention. Scopolamine, a centrally active muscarinic antagonist, has been used to model dementia and to demonstrate the pharmacological effects of cholinergic drugs, but for most effects the concentration-effect relationships are unknown.

WHAT THIS STUDY ADDS

• We determined the pharmacokinetic-pharmacodynamic relationships of scopolamine using a multidimensional central nervous system test battery in a large group of healthy volunteers. The results suggested there are various functional cholinergic systems with different pharmacological characteristics, which can be used to study the effects of drugs that directly or indirectly modify cholinergic systems. The design of such studies should take the different concentration-effect relationships into account. AIM(S) Although scopolamine is a frequently used memory impairment model, the relationships between exposure and corresponding central nervous system (CNS) effects are mostly unknown. The aim of our study was to characterize these using pharmacokinetic-pharmacodynamic (PK-PD) modelling.

METHODS

In two double-blind, placebo-controlled, four-way crossover studies, 0.5-mg scopolamine was administered i.v. to 90 healthy male subjects. PK and PD/safety measures were monitored pre-dose and up to 8.5 h after administration. PK-PD relationships were modelled using non-linear mixed-effect modelling.

RESULTS

Most PD responses following scopolamine administration in 85 subjects differed significantly from placebo. As PD measures lagged behind the plasma PK profile, PK-PD relationships were modelled using an effect compartment and arbitrarily categorized according to their equilibration half-lives (t(1/2) k(eo) ; hysteresis measure). t(1/2) k(eo) for heart rate was 17 min, saccadic eye movements and adaptive tracking 1-1.5 h, body sway, smooth pursuit, visual analogue scales alertness and psychedelic 2.5-3.5 h, pupil size, finger tapping and visual analogue scales feeling high more than 8 h.

CONCLUSIONS

Scopolamine affected different CNS functions in a concentration-dependent manner, which based on their distinct PK-PD characteristics seemed to reflect multiple distinct functional pathways of the cholinergic system. All PD effects showed considerable albeit variable delays compared with plasma concentrations. The t(1/2) k(eo) of the central effects was longer than of the peripheral effects on heart rate, which at least partly reflects the long CNS retention of scopolamine, but possibly also the triggering of independent secondary mechanisms. PK-PD analysis can optimize scopolamine administration regimens for future research and give insight into the physiology and pharmacology of human cholinergic systems.

Insights into the structure and pharmacology of GABA(A) receptors

GABA is the major inhibitory neurotransmitter in the adult mammalian CNS. The ionotropic GABA type A receptors (GABA(A)Rs) belong to the Cys-loop family of receptors. Each member of the family is a large pentameric protein in which each subunit traverses the cell membrane four times. Within this family, the GABA type A receptors are particularly important for their rich pharmacology as they are targets for a range of therapeutically important drugs, including the benzodiazepines, barbiturates, neuroactive steroids and anesthetics. This review discusses new insights into receptor properties that allow us to begin to relate the structure of an individual receptor to its functional and pharmacological properties.

MRK-409 (MK-0343), a GABAA receptor subtype-selective partial agonist, is a non-sedating anxiolytic in preclinical species but causes sedation in humans

MRK-409 binds to α1-, α2-, α3- and α5-containing human recombinant GABA(A) receptors with comparable high affinity (0.21-0.40 nM). However, MRK-409 has greater agonist efficacy at the α3 compared with α1 subtypes (respective efficacies relative to the full agonist chlordiazepoxide of 0.45 and 0.18). This compound readily penetrates the brain in rats and occupies the benzodiazepine site of GABA(A) receptors, measured using an in vivo [(3)H]flumazenil binding assay, with an Occ(50) of 2.2 mg/kg p.o. and a corresponding plasma EC(50) of 115 ng/mL. Behaviourally, the α3-preferring agonist efficacy profile of MRK-409 produced anxiolytic-like activity in rodent and primate unconditioned and conditioned models of anxiety with minimum effective doses corresponding to occupancies, depending on the particular model, ranging from ∼35% to 65% yet there were minimal overt signs of sedation at occupancies greater than 90%. In humans, however, safety and tolerability studies showed that there was pronounced sedation at a dose of 2 mg, resulting in a maximal tolerated dose of 1 mg. This 2 mg dose corresponded to a C(max) plasma concentration of 28 ng/mL, which, based on the rodent plasma EC(50) for occupancy of 115 ng/mL, suggested that sedation in humans occurs at low levels of occupancy. This was confirmed in human positron emission tomography studies, in which [(11)C]flumazenil uptake following a single dose of 1 mg MRK-409 was comparable to that of placebo, indicating that occupancy of GABA(A) receptor benzodiazepine binding sites by MRK-409 was below the limits of detection (i.e. <10%). Taken together, these data show that MRK-409 causes sedation in humans at a dose (2 mg) corresponding to levels of occupancy considerably less than those predicted from rodent models to be required for anxiolytic efficacy (∼35-65%). Thus, the preclinical non-sedating anxiolytic profile of MRK-409 did not translate into humans and further development of this compound was halted.

Preclinical and clinical pharmacology of TPA023B, a GABAA receptor &alpha;2/&alpha;3 subtype-selective partial agonist

In the accompanying paper we describe how MRK-409 unexpectedly produced sedation in man at relatively low levels of GABA(A) receptor occupancy (∼10%). Since it was not clear whether this sedation was mediated via the α2/α3 or α1 GABA(A) subtype(s), we characterized the properties of TPA023B, a high-affinity imidazotriazine which, like MRK-409, has partial agonist efficacy at the α2 and α3 subtype but is an antagonist at the α1 subtype, at which MRK-409 has weak partial agonism. TPA023B gave dose- and time-dependent occupancy of rat brain GABA(A) receptors as measured using an in vivo [(3)H]flumazenil binding assay, with 50% occupancy corresponding to a respective dose and plasma drug concentration of 0.09 mg/kg and 19 ng/mL, the latter of which was similar to that observed in mice (25 ng/mL) and comparable to values obtained in baboon and man using [(11)C]flumazenil PET (10 and 5.8 ng/mL, respectively). TPA023B was anxiolytic in rodent and primate (squirrel monkey) models of anxiety (elevated plus maze, fear-potentiated startle, conditioned suppression of drinking, conditioned emotional response) yet had no significant effects in rodent or primate assays of ataxia and/or myorelaxation (rotarod, chain-pulling, lever pressing), up to doses (10 mg/kg) corresponding to occupancy of greater than 99%. In man, TPA023B was well tolerated at a dose (1.5 mg) that produced occupancy of >50%, suggesting that the sedation previously seen with MRK-409 is due to the partial agonist efficacy of that compound at the α1 subtype, and highlighting the importance of antagonist efficacy at this particular GABA(A) receptor population for avoiding sedation in man.

Central nervous system effects of haloperidol on THC in healthy male volunteers

In this study, the hypothesis that haloperidol would lead to an amelioration of Δ9-tetrahydrocannabinol (THC)-induced 'psychotomimetic' effects was investigated. In a double-blind, placebo-controlled, partial three-way crossover ascending dose study the effects of THC, haloperidol and their combination were investigated in 35 healthy, male mild cannabis users, measuring Positive and Negative Syndrome Scale, Visual Analogue Scales for alertness, mood, calmness and psychedelic effects, saccadic and smooth pursuit eye measurements, electroencephalography, Body Sway, Stroop test, Visual and Verbal Learning Task, hormone levels and pharmacokinetics. Compared with placebo, THC significantly decreased smooth pursuit, Visual Analogue Scales alertness, Stroop test performance, immediate and delayed word recall and prolactin concentrations, and significantly increased positive and general Positive and Negative Syndrome Scale score, Visual Analogue Scales feeling high, Body Sway and electroencephalography alpha. Haloperidol reversed the THC-induced positive Positive and Negative Syndrome Scale increase to levels observed with haloperidol alone, but not THC-induced 'high' feelings. Compared with placebo, haloperidol significantly decreased saccadic peak velocity, smooth pursuit, Visual Analogue Scales mood and immediate and delayed word recall and significantly increased Body Sway, electroencephalography theta and prolactin levels. THC-induced increases in positive Positive and Negative Syndrome Scale but not in Visual Analogue Scales feeling high were reversed by haloperidol. This indicates that psychotic-like effects induced by THC are mediated by dopaminergic systems, but that other systems are involved in 'feeling high'. Additionally, the clear reductions of psychotic-like symptoms by a clinically relevant dose of haloperidol suggest that THC administration may be a useful pharmacological cannabinoid model for psychotic effects in healthy volunteers.

Pharmacokinetics, pharmacodynamics and the pharmacokinetic/ pharmacodynamic relationship of zolpidem in healthy subjects

Zolpidem is one of the most frequently prescribed hypnotics, as it is a very short-acting compound with relatively few side effects. Zolpidem's short duration of action is partly related to its short elimination half-life, but the associations between plasma levels and pharmacodynamic (PD) effects are not precisely known. In this study, the concentration-effect relationships for zolpidem were modelled. Zolpidem (10 mg) was administered in a double-blind, randomised, placebo-controlled trial to determine PD and pharmacokinetics (PK) in 14 healthy volunteers. Zolpidem was absorbed and eliminated quickly, with a median T(max) of 0.78 h (range: 0.33-2.50) and t(1/2) of 2.2 h. Zolpidem reduced saccadic peak velocity (SPV), adaptive tracking performance, electroencephalogram (EEG) alpha power and visual analogue scale (VAS) alertness score and increased body sway, EEG beta power and VAS 'feeling high'. Short- and long-term memory was not affected. Central nervous system effects normalised more rapidly than the decrease of plasma concentrations. For most effects, zolpidem's short duration of action could be adequately described by both a sigmoid E(max) model and a transit tolerance model. For SPV and EEG alpha power, the tolerance model seemed less suitable. These PK/PD models have different implications for the mechanism underlying zolpidem's short duration of action. A sigmoid E(max) model (which is based on ligand binding theory) would imply a threshold value for the drug's effective concentrations. A transit tolerance model (in which a hypothetical factor builds up with time that antagonises the effects of the parent compound) is compatible with a rapid reversible desensitisation of GABAergic subunits.

The effects of the glycine reuptake inhibitor R213129 on the central nervous system and on scopolamine-induced impairments in psychomotor and cognitive function in healthy subjects

In this study the effects of R213129, a selective glycine transporter 1 inhibitor, on central nervous system function were investigated in healthy males in the absence and presence of scopolamine. This was a double-blind, placebo-controlled, 4-period crossover ascending dose study evaluating the following endpoints: body sway, saccadic and smooth pursuit eye movements, pupillometry, electroencephalography, visual analogue scales for alertness, mood, calmness and psychedelic effects, adaptive tracking, finger tapping, Visual and Verbal Learning Task, Stroop test, hormone levels and pharmacokinetics. R213129 dose levels were selected based on exposure levels that blocked the GlyT1 sites >50% in preclinical experiments. Forty-three of the 45 included subjects completed the study. Scopolamine significantly affected almost every central nervous system parameter measured in this study. R213129 alone compared with placebo did not elicit pharmacodynamic changes. R213129 had some small effects on scopolamine-induced central nervous system impairments. Scopolamine-induced finger tapping impairment was further enhanced by 3 mg R213129 with 2.0 taps/10 seconds (95% CI -4.0, -0.1), electroencephalography alpha power was increased by 10 mg R213129 with respectively 12.9% (0.7, 26.6%), scopolamine-induced impairment of the Stroop test was partly reversed by 10 mg R213129 with 59 milliseconds (-110, -7). Scopolamine produced robust and consistent effects in psychomotor and cognitive function in healthy volunteers. The most logical reason for the lack of R213129 effects seems to be that the central nervous system concentrations were too low. The effects of higher doses in healthy volunteers and the clinical efficacy in patients remain to be established.

GABAA receptor alpha2/alpha3 subtype-selective modulators as potential nonsedating anxiolytics

Nonselective benzodiazepines exert their pharmacological effects via GABAA receptors containing either an alpha1, alpha2, alpha3, or alpha5 subunit. The use of subtype-selective tool compounds along with transgenic mice has formed the conceptual framework for defining the requirements of subtype-selective compounds with potentially novel pharmacological profiles. More specifically, compounds which allosterically modulate the alpha2 and/or alpha3 subtypes but are devoid of, or have much reduced, effects at the alpha1 subtype are hypothesized to be anxioselective (i.e., anxiolytic but devoid of sedation). Accordingly, three compounds, MRK-409, TPA023 and TPA023B, which selectively potentiated the effects of GABA at the alpha2 and alpha3 compared to alpha1 subtypes were progressed into man. All three compounds behaved as nonsedating anxiolytics in preclinical (rodent and primate) species but, surprisingly, MRK-409 produced sedation in man at relatively low levels of occupancy (< 10%). This sedation liability of MRK-409 in man was attributed to its weak partial agonist efficacy at the alpha1 subtype since both TPA023 and TPA023B lacked any alpha1 efficacy and did not produce overt sedation even at relatively high levels of occupancy (> 50%). The anxiolytic efficacy of TPA023 was evaluated in Generalized Anxiety Disorder and although these clinical trials were terminated early due to preclinical toxicity issues, the combined data from these incomplete studies demonstrated an anxiolytic-like effect of TPA023. This compound also showed a trend to increase cognitive performance in a small group of schizophrenic subjects and is currently under further evaluation of its cognition-enhancing effects in schizophrenia as part of the TURNS initiative. In contrast, the fate of the back-up clinical candidate TPA023B has not been publicly disclosed. At the very least, these data indicate that the pharmacological profile of compounds that differentially modulate specific populations of GABAA receptors is distinct from classical benzodiazepines and should encourage further preclinical and clinical investigation of such compounds, with the caveat that, as exemplified by MRK-409, the preclinical profile might not necessarily translate into man.

The pharmacology of anxiety

Understanding the neurochemistry of anxiety is of fundamental importance in the development and use of novel anxiolytics. Through measuring peripheral markers of brain biochemistry, direct pharmacological challenges and brain neuroimaging techniques our understanding of this field has increased substantially in the past few decades. We review the four most studied neurotransmitter systems with respect to in anxiety disorders: gamma amino-butyric acid, serotonin, noradrenaline and dopamine. We have focussed upon clinical studies to highlight the current techniques used to determine brain neurochemistry in vivo. Future research in this field will greatly benefit from recent advances in neuroimaging techniques and the discovery of novel ligands targeting specific receptors.

A multicenter, placebo-controlled, double-blind, randomized study of efficacy and safety of ocinaplon (DOV 273,547) in generalized anxiety disorder

Preclinical studies demonstrated that ocinaplon, a positive allosteric modulator of GABA(A) receptors, possesses anxiolytic-like actions at doses devoid of the side effects typically associated with benzodiazepines. The aim of this study was to evaluate the effects of ocinaplon in a multicenter, double-blind proof-of-concept trial of male and female outpatients who met DSM-IV criteria for GAD with no coexisting depression, and had a baseline score of > or =20 on the Hamilton Scale for Anxiety (HAM-A). Patients with <20% reduction in HAM-A to placebo in a single-blind 7-day run-in period were randomly assigned to treatment with ocinaplon 90 mg t.i.d. (n = 31) or placebo for 28 days (n = 29). Ocinaplon was more effective than placebo in reducing HAM-A scores (P= 0.009). Patients assigned to ocinaplon exhibited a mean improvement of 14.2 points (SE = 2.6) on the total score of the HAM-A scale at the conclusion of the trial, while patients assigned to placebo obtained a mean improvement of 6.3 points (SE = 2.0). A significant (P= 0.023) difference in improvement between ocinaplon and placebo was observed beginning at and continuing from 1-week after the initiation of dosing. The proportion of patients with treatment-emergent adverse events (TEAE) was not statistically significant between ocinaplon and placebo. One serious adverse event (SAE) occurred in the ocinaplon group that was considered possibly related to study medication (icterus following transaminase elevations). The patient had preexisting medical conditions that may have contributed to this SAE. A full recovery was observed with no residual effects. The overall safety profile revealed no patterns of TEAEs, including those effects typically associated with other anxiolytic and/or benzodiazepine compounds, such as sedation. Ocinaplon appears to be a well-tolerated and effective treatment for GAD. It produces a rapid onset of anxiolytic action absent the side effects (e.g., dizziness, sedation) typically reported following anxiolytic doses of benzodiazepines.

Limiting activity at beta1-subunit-containing GABAA receptor subtypes reduces ataxia

GABA(A) receptor (R) positive allosteric modulators that selectively modulate GABA(A)Rs containing beta(2)- and/or beta(3)- over beta(1)-subunits have been reported across diverse chemotypes. Examples include loreclezole, mefenamic acid, tracazolate, and etifoxine. In general,"beta(2/3)-selective" GABA(A)R positive allosteric modulators are nonbenzodiazepines (nonBZs), do not show alpha-subunit isoform selectivity, yet have anxiolytic efficacy with reduced ataxic/sedative effects in animal models and humans. Here, we report on an enantiomeric pair of nonBZ GABA(A)R positive allosteric modulators that demonstrate differential beta-subunit isoform selectivity. We have tested this enantiomeric pair along with a series of other beta(2/3)-subunit selective, alpha-subunit isoform-selective, BZ and nonBZ GABA(A) positive allosteric modulators using electrophysiological, pharmacokinetic, and behavioral assays to test the hypothesis that ataxia may be correlated with the extent of modulation at beta(1)-subunit-containing GABA(A)Rs. Our findings provide an alternative strategy for designing anxioselective allosteric modulators of the GABA(A)R with BZ-like anxiolytic efficacy by reducing or eliminating activity at beta(1)-subunit-containing GABA(A)Rs.

Benzodiazepine binding site occupancy by the novel GABAA receptor subtype-selective drug 7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (TPA023) in rats, primates, and humans

The GABA(A) receptor alpha2/alpha3 subtype-selective compound 7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (TPA023; also known as MK-0777) is a triazolopyridazine that has similar, subnanomolar affinity for the benzodiazepine binding site of alpha1-, alpha2-, alpha3-, and alpha5-containing GABA(A) receptors and has partial agonist efficacy at the alpha2 and alpha3 but not the alpha1 or alpha5 subtypes. The purpose of the present study was to define the relationship between plasma TPA023 concentrations and benzodiazepine binding site occupancy across species measured using various methods. Thus, occupancy was measured using either in vivo [(3)H]flumazenil binding or [(11)C]flumazenil small-animal positron emission tomography (microPET) in rats, [(123)I]iomazenil gamma-scintigraphy in rhesus monkeys, and [(11)C]flumazenil PET in baboons and humans. For each study, plasma-occupancy curves were derived, and the plasma concentration of TPA023 required to produce 50% occupancy (EC(50)) was calculated. The EC(50) values for rats, rhesus monkeys, and baboons were all similar and ranged from 19 to 30 ng/ml, although in humans, the EC(50) was slightly lower at 9 ng/ml. In humans, a single 2-mg dose of TPA023 produced in the region of 50 to 60% occupancy in the absence of overt sedative-like effects. Considering that nonselective full agonists are associated with sedation at occupancies of less than 30%, these data emphasize the relatively nonsedating nature of TPA023.

The pharmacokinetic and pharmacodynamic effects of SL65.1498, a GABA-A alpha2,3 selective agonist, in comparison with lorazepam in healthy volunteers

Benzodiazepines are effective short-term treatments for anxiety disorders, but their use is limited by undesirable side effects related to Central Nervous System impairment and tolerance development. SL65.1498 is a new compound that acts in vitro as a full agonist at the gamma-aminobutyric acid(A) 2 and 3 receptor and as a partial agonist at the 1 and 5 receptor subtypes. It is thought that the compound could be anxiolytic by its activation at the alpha2 and alpha3 receptor subtypes, without causing unfavourable side effects, which are believed to be mediated by the alpha1 and alpha5 subtypes. This study was a double-blind, five-way cross-over study to investigate the effects of three doses of SL65.1498 in comparison with placebo and lorazepam 2 mg in healthy volunteers. The objective was to select a dose level (expected to be therapeutically active), free of any significant deleterious effect. Psychomotor and cognitive effects were measured using a validated battery of measurements, including eye movements, body sway, memory tests, reaction-time assessments, and visual analogue scales. The highest dose of SL65.1498 showed slight effects on saccadic peak velocity and smooth pursuit performance, although to a much lesser extent than lorazepam. In contrast to lorazepam, none of the SL65.1498 doses affected body sway, visual analogue scale alertness, attention, or memory tests. This study showed that the three doses of SL65.1498 were well tolerated and induced no impairments on memory, sedation, psychomotor, and cognitive functions.

A novel operant conflict procedure using incrementing shock intensities to assess the anxiolytic and anxiogenic effects of drugs

There is a need for novel anxiolytics, which are effective, but do not cause sedation, tolerance, and rebound anxiety on discontinuation. To investigate a procedure that can be used to assess these characteristics preclinically, rats were initially trained to press a lever at a high rate to obtain food. Once trained, periods of punishment were introduced in which electric shocks were superimposed. The intensity of these electric shocks was increased every 90 s from very low (0.01 mA) to sufficiently high to stop most subjects responding (0.4 mA), so that a complete rate/intensity function was obtained during each punishment period. The benzodiazepine, chlordiazepoxide, and two novel subtype-selective gamma-aminobutyric acid-A agonists, TP003 and TPA023, significantly increased response rates mildly suppressed by intermediate levels of electric shock without any effect on unpunished response rate. Two clinically anxiogenic agents, yohimbine and flumazenil, reduced the rate of punished responding. Aripiprazole and amphetamine reduced both punished and unpunished responding. Repeated treatment with diazepam 2.5 mg/kg daily for 15 days, initially markedly reduced unpunished response rates, but also increased punished response rates, an effect which became greater with repeated treatment. Abrupt cessation of diazepam treatment produced a reduction in punished responding. Diazepam (5 mg/kg daily) produced a greater reduction in unpunished responding, a smaller increase in punished responding, and a larger and longer lasting reduction in punished rates on withdrawal. In conclusion, the procedure detected anxiolytic and anxiogenic effects of drugs, and the sedative side effects, development of tolerance, and rebound-anxiety on discontinuation of a benzodiazepine. This procedure should have utility in the characterization of novel treatments of anxiety.

Emerging therapies for sleep disorders

There has been an upsurge in interest in treatments for sleep disorders recently, as new discoveries in the physiology of sleep-related brain neurotransmitter systems have been made. New targets for therapies have been identified in the field of insomnia, and these will be described in this article.