In vitro and in vivo metabolism of the antianxiolytic agent fenobam in the rat

Sleep and diurnal rest-activity rhythm disturbances in a mouse model of Alzheimer's disease

STUDY OBJECTIVES

Accumulating evidence suggests a strong association between sleep, amyloid-beta (Aβ) deposition, and Alzheimer's disease (AD). We sought to determine if (1) deficits in rest-activity rhythms and sleep are significant phenotypes in J20 AD mice, (2) metabotropic glutamate receptor 5 inhibitors (mGluR5) could rescue deficits in rest-activity rhythms and sleep, and (3) Aβ levels are responsive to treatment with mGluR5 inhibitors.

METHODS

Diurnal rest-activity levels were measured by actigraphy and sleep-wake patterns by electroencephalography, while animals were chronically treated with mGluR5 inhibitors. Behavioral tests were performed, and Aβ levels measured in brain lysates.

RESULTS

J20 mice exhibited a 4.5-h delay in the acrophase of activity levels compared to wild-type littermates and spent less time in rapid eye movement (REM) sleep during the second half of the light period. J20 mice also exhibited decreased non-rapid eye movement (NREM) delta power but increased NREM sigma power. The mGluR5 inhibitor CTEP rescued the REM sleep deficit and improved NREM delta and sigma power but did not correct rest-activity rhythms. No statistically significant differences were observed in Aβ levels, rotarod performance, or the passive avoidance task following chronic mGluR5 inhibitor treatment.

CONCLUSIONS

J20 mice have disruptions in rest-activity rhythms and reduced homeostatic sleep pressure (reduced NREM delta power). NREM delta power was increased following treatment with a mGluR5 inhibitor. Drug bioavailability was poor. Further work is necessary to determine if mGluR5 is a viable target for treating sleep phenotypes in AD.

Effect of Novel Allosteric Modulators of Metabotropic Glutamate Receptors on Drug Self-administration and Relapse: A Review of Preclinical Studies and Their Clinical Implications

Results from preclinical rodent studies during the last 20 years implicated glutamate neurotransmission in different brain regions in drug self-administration and rodent models of relapse. These results, along with evidence for drug-induced neuroadaptations in glutamatergic neurons and receptors, suggested that addiction might be treatable by medications that inhibit glutamatergic responses to drugs of abuse, drug-associated cues, and stressors. This idea is supported by findings in rodent and primate models that drug self-administration and relapse are reduced by systemic injections of antagonists of ionotropic glutamate receptors or metabotropic glutamate receptors (mGluRs) or orthosteric agonists of mGluR2/3. However, these compounds have not advanced to clinical use because of potential side effects and other factors. This state of affairs has led to the development of positive allosteric modulators (PAMs) and negative allosteric modulators (NAMs) of mGluRs. PAMs and NAMs of mGluRs, either of which can inhibit evoked glutamate release, may be suitable for testing in humans. We reviewed results from recent studies of systemically injected PAMs and NAMs of mGluRs in rodents and monkeys, focusing on whether they reduce drug self-administration, reinstatement of drug seeking, and incubation of drug craving. We also review results from rat studies in which PAMs or NAMs of mGluRs were injected intracranially to reduce drug self-administration and reinstatement. We conclude that PAMs and NAMs of mGluRs should be considered for clinical trials.

Gastroretentive carrier systems in the delivery of therapeutic actives: an updated patent review

Gastroretentive drug-delivery systems have the potential to prolong the gastric retention time and provide controlled/sustained release of a drug at the absorption site, thereby improving the bioavailability. Advantageous features include reduction in dose, side effects and dosing frequency. Research inputs have led to exploration of novel gastroretentive systems. The present review explores various patents issued on gastroretentive drug delivery on the basis of the therapeutic category of drugs. It traces US, EP and WIPO patents issued in the last 10 years. Various patents have revealed that gastrocarriers can effectively enhance therapeutic activity of a drug. Drugs acting on the CNS have been prominently investigated, followed by antimicrobials and locally acting drugs. Areas of future research can be drugs acting on the cardiovascular system.

CTEP: a novel, potent, long-acting, and orally bioavailable metabotropic glutamate receptor 5 inhibitor

The metabotropic glutamate receptor 5 (mGlu5) is a glutamate-activated class C G protein-coupled receptor widely expressed in the central nervous system and clinically investigated as a drug target for a range of indications, including depression, Parkinson's disease, and fragile X syndrome. Here, we present the novel potent, selective, and orally bioavailable mGlu5 negative allosteric modulator with inverse agonist properties 2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazol-4-yl)ethynyl)pyridine (CTEP). CTEP binds mGlu5 with low nanomolar affinity and shows >1000-fold selectivity when tested against 103 targets, including all known mGlu receptors. CTEP penetrates the brain with a brain/plasma ratio of 2.6 and displaces the tracer [(3)H]3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-O-methyl-oxime (ABP688) in vivo in mice from brain regions expressing mGlu5 with an average ED(50) equivalent to a drug concentration of 77.5 ng/g in brain tissue. This novel mGlu5 inhibitor is active in the stress-induced hyperthermia procedure in mice and the Vogel conflict drinking test in rats with minimal effective doses of 0.1 and 0.3 mg/kg, respectively, reflecting a 30- to 100-fold higher in vivo potency compared with 2-methyl-6-(phenylethynyl)pyridine (MPEP) and fenobam. CTEP is the first reported mGlu5 inhibitor with both long half-life of approximately 18 h and high oral bioavailability allowing chronic treatment with continuous receptor blockade with one dose every 48 h in adult and newborn animals. By enabling long-term treatment through a wide age range, CTEP allows the exploration of the full therapeutic potential of mGlu5 inhibitors for indications requiring chronic receptor inhibition.

Metabotropic glutamate receptors: their therapeutic potential in anxiety

Psychiatric and neurological disorders are linked to changes in synaptic excitatory processes with a key role for glutamate, that is, the most abundant excitatory amino-acid. Molecular cloning of the metabotropic glutamate (mGlu) receptors has led to the identification of eight mGlu receptors, which, in contrast to ligand-gated ion channels (responsible for fast excitatory transmission), modulate and fine-tune the efficacy of synaptic transmission. mGlu receptors are G protein-coupled and constitute a new group of "drugable" targets for the treatment of various CNS disorders. The recent discovery of small molecules that selectively bind to receptors of Groups I (mGlu1 and mGlu5) and II (mGlu2 and mGlu3) allowed significant advances in our understanding of the roles of these receptors in brain function and dysfunction including anxiety. Although investigation of the role of the Group III (mGlu4, 6, 7, and 8) receptors is less advanced, the generation of genetically manipulated animals and recent advances in the identification of subtype-selective compounds have revealed some first insights into the therapeutic potential of this group of receptors.

The anxiolytic and analgesic properties of fenobam, a potent mGlu5 receptor antagonist, in relation to the impairment of learning

Fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl)urea] was suggested to possess anxiolytic actions 30 years ago. Hoffmann-La Roche researchers recently reported that it is a selective and potent mGlu5 receptor antagonist, acting as a negative allosteric modulator. In the present study, we show that fenobam readily penetrates to the brain, reaching concentrations over 600 nM, clearly above the affinity for mGluR5 receptors. Fenobam (at 10, 30, and 100 mg/kg) did not affect horizontal locomotor activity in the open field test. Anxiolytic-like activity in the context freezing test was seen at 30 mg/kg, while fenobam was not active in the elevated plus maze test at the tested concentrations. Fenobam had antinociceptive actions in the formalin test at 10 and 30 mg/kg, but failed to attenuate mechanical allodynia in the chronic constriction injury model. Impairment of learning was revealed in the passive avoidance test at 30 mg/kg. Fenobam also impaired performance in both the Morris water maze and in the contextual fear conditioning test at the doses of 30 and 10 mg/kg, respectively. Prepulse inhibition, used as a model of psychomimetic activity, was not affected by fenobam at doses of up to 60 mg/kg. Our results indicate that the beneficial effects of fenobam occur in a similar dose range as the potential side-effects.

Antagonists at metabotropic glutamate receptor subtype 5: structure activity relationships and therapeutic potential for addiction

As a result of intensive investigation, particularly in the pharmaceutical industry, a number of potent and selective metabotropic glutamate receptor subtype 5 (mGluR5) antagonists have been discovered. The structure activity relationship studies that led to the discovery of these mGluR5 antagonists are presented in this review. Results from studies on selected mGluR5 antagonists in animal models that simulate drug reward, reinforcement, and relapse appear promising. The comorbidity between drug abuse and anxiety and depression make drugs active in these disorders of great interest. Clinical studies showed that the mGluR5 antagonist fenobam was an active anxiolytic drug. Several new mGluR5 antagonists produced anxiolytic and antidepressant-like effects in animal models of these disorders. The results from the clinical and animal studies provide information for new approaches to finding mechanistically distinct pharmacotherapies to help patients achieve and maintain abstinence from cocaine, methamphetamine, opiates, ethanol, and nicotine (smoking).

Rational design, synthesis, and structure–activity relationship of benzoxazolones: New potent mglu5 receptor antagonists based on the fenobam structure

A novel class of potent and stable mGlu5 receptor antagonists was developed by combining information from a high-throughput screening campaign with the structure of the known anxiolytic fenobam. Representative compounds from this class show favorable pharmacokinetic properties and are active in an in vivo model of anxiety.

Synthesis and biological evaluation of fenobam analogs as mGlu5 receptor antagonists

Optimization of affinity and microsomal stability led to identification of the potent, metabolically stable fenobam analog 4l. Robust in vivo efficacy of 4l was demonstrated in four different models of anxiety. Additionally, a ligand based pharmacophore alignment of fenobam and MPEP is proposed.

Phenyl ureas of creatinine as mGluR5 antagonists. A structure–activity relationship study of fenobam analogues

Fenobam (1) was developed by McNeil Laboratories as an anxiolytic agent with an unknown molecular target in the late 1970s. In a recent publication, it was revealed that fenobam is a non-competitive mGluR5 antagonist. Herein, we present the structure-activity relationship of fenobam and its analogues and similarities between the SAR of mGluR5 antagonism and the SAR of CNS properties originally reported by McNeil are discussed.

Fenobam: a clinically validated nonbenzodiazepine anxiolytic is a potent, selective, and noncompetitive mGlu5 receptor antagonist with inverse agonist activity

Fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl)urea] is an atypical anxiolytic agent with unknown molecular target that has previously been demonstrated both in rodents and human to exert anxiolytic activity. Here, we report that fenobam is a selective and potent metabotropic glutamate (mGlu)5 receptor antagonist acting at an allosteric modulatory site shared with 2-methyl-6-phenylethynyl-pyridine (MPEP), the protypical selective mGlu5 receptor antagonist. Fenobam inhibited quisqualate-evoked intracellular calcium response mediated by human mGlu5 receptor with IC(50) = 58 +/- 2 nM. It acted in a noncompetitive manner, similar to MPEP and demonstrated inverse agonist properties, blocking 66% of the mGlu5 receptor basal activity (in an over expressed cell line) with an IC(50) = 84 +/- 13 nM. [(3)H]Fenobam bound to rat and human recombinant receptors with K(d) values of 54 +/- 6 and 31 +/- 4 nM, respectively. MPEP inhibited [(3)H]fenobam binding to human mGlu5 receptors with a K(i) value of 6.7 +/- 0.7 nM, indicating a common binding site shared by both allosteric antagonists. Fenobam exhibits anxiolytic activity in the stress-induced hyperthermia model, Vogel conflict test, Geller-Seifter conflict test, and conditioned emotional response with a minimum effective dose of 10 to 30 mg/kg p.o. Furthermore, fenobam is devoid of GABAergic activity, confirming previous reports that fenobam acts by a mechanism distinct from benzodiazepines. The non-GABAergic activity of fenobam, coupled with its robust anxiolytic activity and reported efficacy in human in a double blind placebo-controlled trial, supports the potential of developing mGlu5 receptor antagonists with an improved therapeutic window over benzodiazepines as novel anxiolytic agents.