Pharmacological Profile of the Novel Antiepileptic Drug Candidate Padsevonil: Interactions with Synaptic Vesicle 2 Proteins and the GABAA Receptor.

Padsevonil is an antiepileptic drug (AED) candidate synthesized in a medicinal chemistry program initiated to rationally design compounds with high affinity for synaptic vesicle 2 (SV2) proteins and low-to-moderate affinity for the benzodiazepine binding site on GABAA receptors. The pharmacological profile of padsevonil was characterized in binding and electrophysiological experiments. At recombinant SV2 proteins, padsevonil's affinity for SV2A was greater than that of levetiracetam and brivaracetam (pKi 8.5, 5.2, and 6.6, respectively). Unlike the latter AEDs, both selective SV2A ligands, padsevonil also displayed high affinity for the SV2B and SV2C isoforms (pKi 7.9 and 8.5, respectively). Padsevonil's interaction with SV2A differed from that of levetiracetam and brivaracetam; it exhibited slower binding kinetics: dissociation t 1/2 30 minutes from the human protein at 37°C compared with <0.5 minute for levetiracetam and brivaracetam. In addition, its binding was not potentiated by the allosteric modulator UCB1244283. At recombinant GABAA receptors, padsevonil displayed low to moderate affinity (pIC50≤6.1) for the benzodiazepine site, and in electrophysiological studies, its relative efficacy compared with zolpidem (full-agonist reference drug) was 40%, indicating partial agonist properties. In in vivo (mice) receptor occupancy studies, padsevonil exhibited SV2A occupancy at low ED50 (0.2 mg/kg) and benzodiazepine site occupancy at higher doses (ED50 36 mg/kg), supporting in vitro results. Padsevonil's selectivity for its intended targets was confirmed in profiling studies, where it lacked significant effects on a wide variety of ion channels, receptors, transporters, and enzymes. Padsevonil is a first-in-class AED candidate with a unique target profile allowing for presynaptic and postsynaptic activity. SIGNIFICANCE STATEMENT: Padsevonil is an antiepileptic drug candidate developed as a single molecular entity interacting with both presynaptic and postsynaptic targets. Results of in vitro and in vivo radioligand binding assays confirmed this target profile: padsevonil displayed nanomolar affinity for the three synaptic vesicle 2 protein isoforms (SV2A, B, and C) and micromolar affinity for the benzodiazepine binding site on GABAA receptors. Furthermore, padsevonil showed greater affinity for and slower binding kinetics at SV2A than the selective SV2A ligands, levetiracetam, and brivaracetam.

Synthesis of C-14 labeled GABAA α2/α3 selective partial agonists and the investigation of late-occurring and long-circulating metabolites of GABAA receptor modulator AZD7325.

Anxiolytic activity has been associated with GABAA α2 and α3 subunits. Several target compounds were identified and required in C-14 labeled form to enable a better understanding of their drug metabolism and pharmacokinetic properties. AZD7325 is a selective GABAA α2 and α3 receptor modulator intended for the treatment of anxiety through oral administration. A great number of AZD7325 metabolites were observed across species in vivo, whose identification was aided by [14 C]AZD7325. An interesting metabolic cyclization and aromatization pathway leading to the tricyclic core of M9 and the oxidative pathways to M10 and M42 are presented.

Multi-kinetics and site-specific release of gabapentin and flurbiprofen from oral fixed-dose combination: in vitro release and in vivo food effect.

In this work, a fixed-dose combination of gabapentin and flurbiprofen formulated as multilayer tablets has been designed, developed and studied in vitro and in vivo. The aim was to construct a single dosage form of the two drugs, able to perform a therapeutic program involving three release kinetics and two delivery sites, i.e., immediate release of gabapentin, intra-gastric prolonged release of gabapentin and intestinal (delayed) release of flurbiprofen. An oblong three-layer tablet was manufactured having as top layer a floating hydrophilic polymeric matrix for gastric release of gabapentin, as middle layer a disintegrating formulation for immediate release of a gabapentin loading dose and as bottom layer, an uncoated hydrophilic polymeric matrix, swellable but insoluble in gastric fluids, for delayed and prolonged release of flurbiprofen in intestinal environment. The formulations were studied in vitro and in vivo in healthy volunteers. The in vitro release rate assessment confirmed the programmed delivery design. A significant higher bioavailability of gabapentin administered 30min after meal, compared to fasting conditions or to dose administration 10min before meal, argued in favor of the gastro-retention of gabapentin prolonged release layer. The two drugs were delivered at different anatomical sites, since the food presence prolonged the gastric absorption of gabapentin from the floating layer and delayed the flurbiprofen absorption. The attainment of a successful delayed release of flurbiprofen was realized by a matrix based on a polymers' combination. The combined use of three hydrophilic polymers with different pH sensitivity provided the dosage form layer containing flurbiprofen with gastro-resistant characteristics without the use of film coating.

VU0477573: Partial Negative Allosteric Modulator of the Subtype 5 Metabotropic Glutamate Receptor with In Vivo Efficacy.

Negative allosteric modulators (NAMs) of metabotropic glutamate receptor subtype 5 (mGlu5) have potential applications in the treatment of fragile X syndrome, levodopa-induced dyskinesia in Parkinson disease, Alzheimer disease, addiction, and anxiety; however, clinical and preclinical studies raise concerns that complete blockade of mGlu5 and inverse agonist activity of current mGlu5 NAMs contribute to adverse effects that limit the therapeutic use of these compounds. We report the discovery and characterization of a novel mGlu5 NAM, N,N-diethyl-5-((3-fluorophenyl)ethynyl)picolinamide (VU0477573) that binds to the same allosteric site as the prototypical mGlu5 NAM MPEP but displays weak negative cooperativity. Because of this weak cooperativity, VU0477573 acts as a "partial NAM" so that full occupancy of the MPEP site does not completely inhibit maximal effects of mGlu5 agonists on intracellular calcium mobilization, inositol phosphate (IP) accumulation, or inhibition of synaptic transmission at the hippocampal Schaffer collateral-CA1 synapse. Unlike previous mGlu5 NAMs, VU0477573 displays no inverse agonist activity assessed using measures of effects on basal [(3)H]inositol phosphate (IP) accumulation. VU0477573 acts as a full NAM when measuring effects on mGlu5-mediated extracellular signal-related kinases 1/2 phosphorylation, which may indicate functional bias. VU0477573 exhibits an excellent pharmacokinetic profile and good brain penetration in rodents and provides dose-dependent full mGlu5 occupancy in the central nervous system (CNS) with systemic administration. Interestingly, VU0477573 shows robust efficacy, comparable to the mGlu5 NAM MTEP, in models of anxiolytic activity at doses that provide full CNS occupancy of mGlu5 and demonstrate an excellent CNS occupancy-efficacy relationship. VU0477573 provides an exciting new tool to investigate the efficacy of partial NAMs in animal models.

Pharmacokinetics and pharmacodynamics of γ-hydroxybutyrate in healthy subjects.

AIMS: γ-Hydroxybutyrate (GHB) is used as a treatment for narcolepsy and alcohol withdrawal and as a recreational substance. Nevertheless, there are limited data on the pharmacokinetics and pharmacokinetic-pharmacodynamic relationships of GHB in humans. We characterized the pharmacokinetic profile and exposure-psychotropic effect relationship of GHB in humans. METHODS: Two oral doses of GHB (25 and 35 mg kg(-1) ) were administered to 32 healthy male subjects (16 for each dose) using a randomized, placebo-controlled, cross-over design. RESULTS: Maximal concentrations of GHB were (geometric mean and 95% CI): 218 (176-270) nmol ml(-1) and 453 (374-549) nmol ml(-1) for the 25 and 35 mg kg(-1) GHB doses, respectively. The elimination half-lives (mean ± SD) were 36 ± 9 and 39 ± 7 min and the AUC∞ values (geometric mean and 95% CI) were 15 747 (12 854-19 290) and 40 113 (33 093-48 622) nmol∙min ml(-1) for the 20 and 35 mg kg(-1) GHB doses, respectively. Thus, plasma GHB exposure (AUC0-∞ ) rose disproportionally (+40%) with the higher dose. γ-Hydroxybutyrate produced mixed stimulant-sedative effects, with a dose-dependent increase in sedation and dizziness. It did not alter heart rate or blood pressure. A close relationship between plasma GHB exposure and its psychotropic effects was found, with higher GHB concentrations associated with higher subjective stimulation, sedation, and dizziness. No clockwise hysteresis was observed in the GHB concentration effect plot over time (i.e., no acute pharmacological tolerance). CONCLUSION: Evidence was found of a nonlinear dose-exposure relationship (i.e., no dose proportionality) at moderate doses of GHB. The effects of GHB on consciousness were closely linked to its plasma exposure and exhibited no acute tolerance.

Baclofen novel gastroretentive extended release gellan gum superporous hydrogel hybrid system: in vitro and in vivo evaluation.

Baclofen is a centrally acting skeletal muscle relaxant with a short elimination half-life, which results in frequent daily dosing and subsequent poor patient compliance. The narrow absorption window of baclofen in the upper gastrointestinal tract limits its formulation as extended release dosage forms. In this study, baclofen extended release superporous hydrogel (SPH) systems, including conventional SPH, SPH composite and SPH hybrid (SPHH), were prepared aiming to increase the residence of baclofen at its absorption window. The applicability of different polymers, namely, gellan gum, guar gum, polyvinyl alcohol and gelatin, was investigated in preparation of SPHH systems. The prepared SPH systems were evaluated regarding weight and volume swelling ratio, porosity, mechanical properties, incorporation efficiency, degree of erosion and drug release. In vivo assessment was performed in dogs to evaluate gastric residence time by X-ray studies. In addition, the oral bioavailability of baclofen relative to commercially available Lioresal® immediate release tablets was also investigated. The novel baclofen gellan SPHH cross linked with calcium chloride was characterized by optimum mechanical properties, acceptable swelling properties as well as extended drug release. It also exhibited a prolonged plasma profile when compared to twice daily administered Lioresal®.

Development of Novel, CNS Penetrant Positive Allosteric Modulators for the Metabotropic Glutamate Receptor Subtype 1 (mGlu1), Based on an N-(3-Chloro-4-(1,3-dioxoisoindolin-2-yl)phenyl)-3-methylfuran-2-carboxamide Scaffold, That Potentiate Wild Type and Mutant mGlu1 Receptors Found in Schizophrenics.

The therapeutic potential of selective mGlu1 activation is vastly unexplored relative to the other group I mGlu receptor, mGlu5; therefore, our lab has focused considerable effort toward developing mGlu1 positive allosteric modulators (PAMs) suitable as in vivo proof of concept tool compounds. Optimization of a series of mGlu1 PAMs based on an N-(3-chloro-4-(1,3-dioxoisoindolin-2-yl)phenyl)-3-methylfuran-2-carboxamide scaffold provided 17e, a potent (mGlu1 EC50 = 31.8 nM) and highly CNS penetrant (brain to plasma ratio (Kp) of 1.02) mGlu1 PAM tool compound, that potentiated not only wild-type human mGlu1 but also mutant mGlu1 receptors derived from deleterious GRM1 mutations found in schizophrenic patients. Moreover, both electrophysiological and in vivo studies indicate the mGlu1 ago-PAMs/PAMs do not possess the same epileptiform adverse effect liability as mGlu5 ago-PAMs/PAMs and maintain temporal activity suggesting a broader therapeutic window.

Tonic Inhibitory Control of Dentate Gyrus Granule Cells by α5-Containing GABAA Receptors Reduces Memory Interference.

Interference between similar or overlapping memories formed at different times poses an important challenge on the hippocampal declarative memory system. Difficulties in managing interference are at the core of disabling cognitive deficits in neuropsychiatric disorders. Computational models have suggested that, in the normal brain, the sparse activation of the dentate gyrus granule cells maintained by tonic inhibitory control enables pattern separation, an orthogonalization process that allows distinct representations of memories despite interference. To test this mechanistic hypothesis, we generated mice with significantly reduced expression of the α5-containing GABAA (α5-GABAARs) receptors selectively in the granule cells of the dentate gyrus (α5DGKO mice). α5DGKO mice had reduced tonic inhibition of the granule cells without any change in fast phasic inhibition and showed increased activation in the dentate gyrus when presented with novel stimuli. α5DGKO mice showed impairments in cognitive tasks characterized by high interference, without any deficiencies in low-interference tasks, suggesting specific impairment of pattern separation. Reduction of fast phasic inhibition in the dentate gyrus through granule cell-selective knock-out of α2-GABAARs or the knock-out of the α5-GABAARs in the downstream CA3 area did not detract from pattern separation abilities, which confirms the anatomical and molecular specificity of the findings. In addition to lending empirical support to computational hypotheses, our findings have implications for the treatment of interference-related cognitive symptoms in neuropsychiatric disorders, particularly considering the availability of pharmacological agents selectively targeting α5-GABAARs. SIGNIFICANCE STATEMENT: Interference between similar memories poses a significant limitation on the hippocampal declarative memory system, and impaired interference management is a cognitive symptom in many disorders. Thus, understanding mechanisms of successful interference management or processes that can lead to interference-related memory problems has high theoretical and translational importance. This study provides empirical evidence that tonic inhibition in the dentate gyrus (DG), which maintains sparseness of neuronal activation in the DG, is essential for management of interference. The specificity of findings to tonic, but not faster, more transient types of neuronal inhibition and to the DG, but not the neighboring brain areas, is presented through control experiments. Thus, the findings link interference management to a specific mechanism, proposed previously by computational models.

Alleviation of glutamate mediated neuronal insult by piroxicam in rodent model of focal cerebral ischemia: a possible mechanism of GABA agonism

Neurotransmitter imbalance is an inevitable outcome in cerebral ischemia that leads to neuronal death. In the present study, we evaluated the effects of piroxicam, a nonsteroidal anti-inflammatory drug (NSAID), on extracellular brain glutamate and Gamma-aminobutyric acid (GABA) release, survival time, and neuronal cell death. Transient focal cerebral ischemia in male Charles Foster rat led to neuronal infarction and compromised intrinsic antioxidant status. Thirty-minute preadministration of piroxicam (10 mg/kg b.w.) showed a significant (P < 0.01) reduction in cerebral infarct volume and potentiation of the intrinsic antioxidant status. High-performance liquid chromatography of brain cortex and striatum revealed changes in extracellular concentrations of neurotransmitters which were found to be 0.519 ± 0.44 pmole/mg (GABA); 1.18 ± 0.28 pmole/mg (glutamate), and 0.63 ± 0.21 pmole/mg (serotonin), respectively. Hydroxyl radical (·OH) adduct of salicylate in the frontal cortex and striatum in control, untreated, and treated groups was found to be 0.261 ± 0.06, 0.68 ± 0.52, and 0.401 ± 0.68 pmole/mg, respectively. After stroke, the extracellular level of glutamate in rat brain increases continuously as compared to that of control group. However, piroxicam administration in stroke rat significantly reduced (P < 0.05) elevated extracellular cerebral glutamate. This indicates that piroxicam attenuates extracellular glutamate release and also reduces neuronal cell death due to reduction in oxidative stress in cerebral ischemia. Our results also indicate a consequent increase of extracellular GABA in brain regions administered with piroxicam, which hints that piroxicam alleviates glutamate excitotoxicity possibly by GABA agonism

High variability in the exposure of baclofen in alcohol-dependent patients.

BACKGROUND: Baclofen is a GABA-B receptor agonist used in the treatment of spasticity. Recently, baclofen is used out of its label to decrease craving of alcoholic patients. Its optimal use in these patients requires further pharmacokinetic information. The objective of this study was to characterize the pharmacokinetics of baclofen in alcohol-dependent patients. Randomized clinical trials are ongoing to evaluate the efficacy for this new indication. METHODS: Thirty-seven outpatients (weight: 74.0 kg [42.0 to 104.0]; age: 49 years [31 to 68]) followed in the addictology unit were studied. Total mean dose of 77.9 mg (30 to 240) per day was administered by oral route. Therapeutic drug monitoring allowed the measurement of 139 plasma concentrations. The following covariates were evaluated: demographic data (age, body weight, height, sex), biological data (creatinine, urea, AST, ALT, albumin, PR, VGM, PAL, CDT, GGT), and tobacco consumption (number of cigarettes and Fagerstrom test). Pharmacokinetic analysis was performed by using a nonlinear mixed-effect population model (NONMEM 7.2 software). RESULTS: Data were modeled with a 1-compartment pharmacokinetic model. The population typical mean (95% confidence interval [95% CI]) values for clearance (CL), apparent volume of distribution (V), and rate constant of absorption (Ka) were 9.9 l/h (9.0 to 11.1), 80.7 l (63.6 to 96.9), and 4.6/h (1.5 to 19.9), respectively. The interindividual variability of CL (95% CI) and V (95% CI), and residual variability (95% CI) were 56.0% (47.9 to 60.7), 68.3% (48.7 to 80.1), and 0.096 mg/l (0.079 to 0.107), respectively. CONCLUSIONS: Baclofen exhibited a linear pharmacokinetics with a proportional relationship from 30 to 240 mg per day, the dose range currently used in alcoholic patients. A wide interpatient variability was observed which could not be explained by the covariates. This high variation of baclofen exposure may explain the lack of response observed for some patients.

[Hepatoduodenal circulation and excretion of the new GABA derivative citrocard].

Pharmacokinetic investigation of a new gamma-aminobutyric acid (GABA) derivative cirtocard showed that, upon the intravenous introduction, the drug is determined in high concentrations in organs of elimination--the liver and kidneys. The tissue accessibility amounts to 1.341 for the liver and 4.053 for the kidneys and the separation factor is 1.041 for the liver and 4.486 for the kidneys. The study of drug excretion showed that cirtocard is determined in the urine for 48 h, its nephritic clearance being 0.047 L/h and extra-nephritic clearance, 0.33 L/h. For the unchanged substance, a large significance ofhepatoduodenal circulation is low probable, since no more than 1 - 2% of the introduced dose was isolated with bile over entire experiment. It is established that the removal of the unchanged substance does not exceed 10% of the introduced dose. There is high probability of hepatoduodenal circulation and excretion of the preparation in the form of metabolites.

Dual hypocretin receptor antagonism is more effective for sleep promotion than antagonism of either receptor alone.

The hypocretin (orexin) system is involved in sleep/wake regulation, and antagonists of both hypocretin receptor type 1 (HCRTR1) and/or HCRTR2 are considered to be potential hypnotic medications. It is currently unclear whether blockade of either or both receptors is more effective for promoting sleep with minimal side effects. Accordingly, we compared the properties of selective HCRTR1 (SB-408124 and SB-334867) and HCRTR2 (EMPA) antagonists with that of the dual HCRTR1/R2 antagonist almorexant in the rat. All 4 antagonists bound to their respective receptors with high affinity and selectivity in vitro. Since in vivo pharmacokinetic experiments revealed poor brain penetration for SB-408124, SB-334867 was selected for subsequent in vivo studies. When injected in the mid-active phase, SB-334867 produced small increases in rapid-eye-movement (REM) and non-REM (NR) sleep. EMPA produced a significant increase in NR only at the highest dose studied. In contrast, almorexant decreased NR latency and increased both NR and REM proportionally throughout the subsequent 6 h without rebound wakefulness. The increased NR was due to a greater number of NR bouts; NR bout duration was unchanged. At the highest dose tested (100 mg/kg), almorexant fragmented sleep architecture by increasing the number of waking and REM bouts. No evidence of cataplexy was observed. HCRTR1 occupancy by almorexant declined 4-6 h post-administration while HCRTR2 occupancy was still elevated after 12 h, revealing a complex relationship between occupancy of HCRT receptors and sleep promotion. We conclude that dual HCRTR1/R2 blockade is more effective in promoting sleep than blockade of either HCRTR alone. In contrast to GABA receptor agonists which induce sleep by generalized inhibition, HCRTR antagonists seem to facilitate sleep by reducing waking "drive".

Effect of food on the bioavailability of lesogaberan given as an oral solution or as modified-release capsules in healthy male volunteers.

The novel Type B gamma-aminobutyric acid (GABAB)-receptor agonist lesogaberan (AZD3355) has been evaluated as an add-on to proton pump inhibitor treatment for gastroesophageal reflux disease, but the effect of food on the bioavailability of this compound has not been assessed. In this openlabel crossover study, healthy males received single 100 mg doses of lesogaberan (oral solution (A) or oral modified release (MR) capsules with a dissolution rate of 50% (B) or 100% (C) over 4 h) with and without food. Blood plasma concentrations of lesogaberan were assessed over 48 h. A log-transformed geometric mean Cmax and AUC ratio within the 90% confidence interval (CI) range (0.80 - 1.25) was defined as excluding a clinically relevant food effect. Overall, 57 subjects completed the study. Only the oral lesogaberan solution had a fed/fasting Cmax ratio outside the 90% CI range (Cmax ratio: 0.76). AUC ratios were within the 90% CI limits for all three lesogaberan formulations. The only substantial change in tmax associated with food intake was observed for the oral solution (1.0 h without food, 1.8 h with food). In conclusion, a clinically relevant food effect could be excluded for the lesogaberan MR formulations, but not for the oral lesogaberan solution.

Discovery of a novel potent GABA(B) receptor agonist.

Structure-activity studies have led to a discovery of 3-(4-pyridyl)methyl ether derivative 9d that has 25- to 50-fold greater functional potency than R-baclofen at human and rodent GABA(B) receptors in vitro. Mouse hypothermia studies confirm that this compound crosses the blood-brain barrier and is approximately 50-fold more potent after systemic administration.

Molecular basis for the high THIP/gaboxadol sensitivity of extrasynaptic GABA(A) receptors.

Extrasynaptic GABA(A) receptors (eGABARs) allow ambient GABA to tonically regulate neuronal excitability and are implicated as targets for ethanol and anesthetics. These receptors are thought to be heteropentameric proteins made up of two α subunits-either α4 or α6-two ß2 or ß3 subunits, and one δ subunit. The GABA analog 4,5,6,7-tetrahydroisoxazolo (5,4-c)pyridin-3(-ol) (THIP) has been proposed as a selective ligand for eGABARs. Behavioral and in vitro studies suggest that eGABARs have nanomolar affinity for THIP; however, all published studies on recombinant versions of eGABARs report micromolar affinities. Here, we examine THIP sensitivity of native eGABARs on cerebellar neurons and on reconstituted GABARs in heterologous systems. Concentration-response data for THIP, obtained from cerebellar granule cells and molecular layer interneurons in wild-type and δ subunit knockout slices, confirm that submicromolar THIP sensitivity requires δ subunits. In recombinant experiments, we find that δ subunit coexpression leads to receptors activated by nanomolar THIP concentrations (EC(50) of 30-50 nM for α4ß3δ and α6ß3δ), a sensitivity almost 1,000-fold higher than receptors formed by α4/6 and ß3 subunits. In contrast, γ2 subunit expression significantly reduces THIP sensitivity. Even when δ subunit cDNA or cRNA was supplied in excess, high- and low-sensitivity THIP responses were often apparent, indicative of variable mixtures of low-affinity αß and high-affinity αßδ receptors. We conclude that δ subunit incorporation into GABARs leads to a dramatic increase in THIP sensitivity, a defining feature that accounts for the unique behavioral and neurophysiological properties of THIP.

Targeting γ-aminobutyric acid (GABA) carriers to the brain: potential relevance as antiepileptic pro-drugs.

The search for antiepileptic compounds with more selective activity continues to be an area of intensive investigation in medicinal chemistry. 3,5-Disubstituted tetrahydro-2H-1,3,5-thiadiazine-2-thione (THTT) derivatives, 3a-g, potential prodrugs incorporating the neurotransmitter GABA were synthesized and studied for crossing the blood-brain barrier (BBB). Compounds were prepared from primary amines and carbon disulfide to give dithiocarbamates 2a-g which upon reaction in situ with formaldehyde provided the intermediates Ia-g. Addition of Ia-g onto GABA furnished the title compounds 3a-g. The structures were verified by spectral data and the amounts of the compounds in the brain were investigated by using HPLC. The concentration profiles of the tested compounds in mice brain were determined and the in vivo anticonvulsant activity was measured.

Effect of lesogaberan, a novel GABA(B)-receptor agonist, on transient lower oesophageal sphincter relaxations in male subjects.

BACKGROUND: Transient lower oesophageal sphincter relaxations (TLESRs) are a major mechanism behind gastro-oesophageal reflux disease (GERD). AIM: To assess the effect of lesogaberan (AZD3355) - a novel peripherally active GABA(B) receptor agonist - on TLESRs. METHODS: Twenty-four healthy men were enrolled in this single-blind, placebo-controlled, randomized, single-centre, three-period crossover phase 1 study. Subjects were randomized to receive single oral doses of lesogaberan (0.8 mg/kg), baclofen (40 mg) and placebo, separated by washout periods of < or = 7 days. Subjects finished a meal 1 h after the dose. Oesophageal manometry and pH-metry measurements were taken during the 3 h after the meal. RESULTS: Twenty-one subjects completed the study. Compared with placebo, lesogaberan 0.8 mg/kg significantly reduced the number of TLESRs by 36% [geometric mean ratio (GMR): 0.64; 95% confidence interval (CI): 0.51-0.82] and significantly reduced the number of acid reflux episodes (mean reduction: 1.6; 95% CI: 0.34-2.9). Lesogaberan also significantly increased lower oesophageal sphincter (LES) pressure by 39% compared with placebo (GMR: 1.39; 95% CI: 1.18-1.64). Comparable results were observed with baclofen. Similar numbers of adverse events were reported by subjects taking lesogaberan and placebo. CONCLUSION: Compared with placebo, lesogaberan significantly reduced TLESRs and acid reflux episodes and increased LES pressure.

Image-guided convection-enhanced delivery of muscimol to the primate brain.

OBJECT: Muscimol is a potent gamma-aminobutyric acid-A receptor agonist that temporarily and selectively suppresses neurons. Targeted muscimol suppression of neuronal structures could provide insight into the pathophysiological processes and treatment of a variety of neurological disorders. To determine if muscimol delivered to the brain by convection-enhanced delivery could be monitored using a coinfused surrogate MR imaging tracer, the authors perfused the striata of primates with tritiated muscimol and Gd-diethylenetriamine pentaacetic acid (DTPA). METHODS: Three primates underwent convective coinfusion of (3)H-muscimol (0.8 microM) and Gd-DTPA (5 mM) into the bilateral striata. Primates underwent serial MR imaging during infusion, and the animals were killed immediately after infusion. Postmortem quantitative autoradiography and histological analysis was performed. RESULTS: Real-time MR imaging revealed that infusate (tritiated muscimol and Gd-DTPA) distribution was clearly discernible from the noninfused parenchyma. Real-time MR imaging of the infusion revealed the precise region of anatomical perfusion in each animal. Imaging analysis during infusion revealed that the distribution volume (Vd) of infusate linearly increased (R = 0.92) with volume of infusion (Vi). Overall, the mean (+/- SD) Vd/Vi ratio was 8.2 +/- 1.3. Autoradiographic analysis revealed that MR imaging of Gd-DTPA closely correlated with the distribution of (3)H-muscimol, and precisely estimated its Vd (mean difference in Vd, 7.4%). Quantitative autoradiograms revealed that muscimol was homogeneously distributed over the perfused region in a square-shaped concentration profile. CONCLUSIONS: Muscimol can be effectively delivered to clinically relevant volumes of the primate brain. Moreover, the distribution of muscimol can be tracked using coinfusion of Gd-DTPA and MR imaging. The ability to perform accurate monitoring and to control the anatomical extent of muscimol distribution during its convection-enhanced delivery will enhance safety, permit correlations of muscimol distribution with clinical effect, and should lead to an improved understanding of the pathophysiological processes underlying a variety of neurological disorders.

Preclinical and clinical pharmacology of the GABAA receptor alpha5 subtype-selective inverse agonist alpha5IA.

alpha5IA is a triazolophthalazine that selectively attenuates the effects of GABA at GABA(A) receptors containing an alpha5 subunit. It enhances long-term potentiation in an in vitro model of mouse hippocampal synaptic plasticity, gives good in vivo receptor occupancy and improves cognitive performance in normal rats as measured using the delayed-matching-to-place version of the Morris water maze yet, importantly, it is without anxiogenic or proconvulsant liabilities. The hydroxymethyl isoxazole metabolite, which occurs both in vitro and in vivo, has a very low aqueous solubility (0.6microg/mL) that resulted in renal toxicity (crystal formation) at very high doses in preclinical safety and toxicity studies. Although this precluded it from being dosed to humans over prolonged periods of time, alpha5IA is, nevertheless, well tolerated in young and elderly subjects up to a dose of 6mg in multiple-dose studies and gives a plasma EC(50) for alpha5IA occupancy measured using [(11)C]flumazenil PET of 10ng/mL. The compound was evaluated in experimental studies and although in elderly subjects alpha5IA does not improve performance in a paired-associate learning task (a 4-mg dose actually impairs performance), it is able to reverse the ethanol-induced impairment in performance in healthy young normal volunteers. These data demonstrate that in man an alpha5-selective inverse agonist may be effective at increasing performance under certain conditions. Whether or not such a compound has efficacy in conditions associated with cognitive deficits, such as attention-deficit hyperactivity disorder, Alzheimer's disease or schizophrenia remains to be determined.