James P. Stables

Anticonvulsant activity of hydrazones, Schiff and Mannich bases of isatin derivatives

In the present study, anticonvulsant activity of hydrazones, Schiff and Mannich bases of isatin were evaluated by maximal electroshock method (MES) and metrazol-induced convulsions (MET) at 30, 100 and 300 mg/kg dose levels. Neurotoxicity of the compounds was also assessed at the same dose levels. Eight compounds of the series exhibited significant anticonvulsant activity at 30 mg/kg dose level. 3-(4-chloro-phenylimino)-5-methyl-1,3-dihydro-indol-2-one (compound 10) was found to be the most potent compound of the series with 87% protection at 100 mg/kg and an ED(50) of 53.61 mg/kg (MET). All the compounds exhibited lesser neurotoxicity compared to phenytoin. All the active compounds showed greater protection than sodium valproate. The essential structural features responsible for interaction with receptor site are established within a suggested pharmacophore.

Anticonvulsant properties of various acetylhydrazones, oxamoylhydrazones and semicarbazones derived from aromatic and unsaturated carbonyl compounds.

Various acetylhydrazones, oxamoylhydrazones and semicarbazones were prepared as candidate anticonvulsants with a view to examining the viability of a putative binding site hypothesis. Atomic charge calculations were undertaken to determine the hydrogen bonding capacities of various molecules. The biological results obtained revealed that in general the acetylhydrazones and semicarbazones afforded good protection against convulsions while the oxamoylhydrazones were significantly less active. These data suggest that terminal electron-donating groups enhanced the hydrogen bonding capabilities and anticonvulsant properties of these molecules.

Therapy Discovery for Pharmacoresistant Epilepsy and for Disease-modifying Therapeutics: Summary of the NIH/NINDS/AES Models II Workshop

The National Institutes of Health (NIH), through the Antiepileptic Screening Project (formerly known as the Antiepileptic Drug Development Program), has been a key element in the discovery and introduction of new pharmacologic therapies since the institution of the program more than 25 years ago. The program was established with the goals of facilitating the identification of new drugs that were safer and more efficacious epilepsy treatments. Through these efforts and leadership, the program has been highly successful, with the introduction of many new antiepileptic compounds, providing new and welcomed treatment options to epilepsy patients worldwide. In spite of these successes, these new drugs have yet to make a significant impact in the most difficult to treat conditions, or for those patients who are incompletely responsive to available pharmacologic treatments. It is estimated that more than one third of patients with epilepsy (∼750,000 Americans) belong in this pharmacoresistant category. Because of this large number of pharmacoresistant patients with epilepsy, a developing consensus mandates that the current process of therapy discovery and development must be reevaluated and enhanced in light of the evolution of available models and our understanding of epilepsy. Several large meetings (notably the White House–initiated conference, “Curing Epilepsy: Focus on the Future,” which was held in March 2000, and the NIH Workshop for Models for Epilepsy and Epileptogenesis, held in March 2001) started the process. One of the primary recommendations of these conferences was that the existing process of therapy discovery and development should be enhanced with a focus on developing preclinical models that would be more predictive of clinical success in stopping the seizures of patients currently incompletely controlled with existing therapies. In addition, strong recommendations were made to develop mechanisms to identify treatments that will prevent the development of epilepsy (epileptogenesis). A key element in this latter recommendation is the identification of appropriate models for epileptogenesis and the creation of a process that will use these models for antiepileptogenic therapy discovery. In response to these recommendations, a workshop was held in September 2002 to identify useful models for therapy discovery for treatment of resistant epilepsy and the actual prevention of the disease. The first goal of this conference focused on recommendations of models to identify potential new therapies and to predict the clinical efficacy of these therapies. The second was the development of a process that can be used to evaluate and add new and promising models as they come along. The following paragraphs are a summary of the meeting with an emphasis on the recommendations that were made regarding therapy resistance and epileptogenesis. Two working groups were created for the meeting: one to concentrate on issues of therapy-resistant epilepsy, and the other to focus on disease-modifying therapeutics (DzM). The two focus groups were asked to consider the potential of candidate models in predicting clinical success of any particular treatment. Other major considerations required in the evaluations were the relative ease of use and the potential parallels among the different human epilepsies. An important point of emphasis was that the evaluation and eventual recommendations must be focused on the potential for the models to be predictive for clinical success, not for the relative value of the models for basic epilepsy research, while acknowledging the critical need for the latter. This process of evaluation should at no time be considered a general ranking system of epilepsy models. The many models, in vitro and in vivo, possess important scientific value for our understanding of the mechanisms of epilepsy. Therefore the overall goal of this workshop was to apply these criteria toward model evaluation to identify the most scientifically feasible screening

Identification of new epilepsy treatments: issues in preclinical methodology.

Preclinical research has facilitated the discovery of valuable drugs for the symptomatic treatment of epilepsy. Yet, despite these therapies, seizures are not adequately controlled in a third of all affected individuals, and comorbidities still impose a major burden on quality of life. The introduction of multiple new therapies into clinical use over the past two decades has done little to change this. There is an urgent demand to address the unmet clinical needs for: (1) new symptomatic antiseizure treatments for drug‐resistant seizures with improved efficacy/tolerability profiles, (2) disease‐modifying treatments that prevent or ameliorate the process of epileptogenesis, and (3) treatments for the common comorbidities that contribute to disability in people with epilepsy. New therapies also need to address the special needs of certain subpopulations, that is, age‐ or gender‐specific treatments. Preclinical development in these treatment areas is complex due to heterogeneity in presentation and etiology, and may need to be formulated with a specific seizure, epilepsy syndrome, or comorbidity in mind. The aim of this report is to provide a framework that will help define future guidelines that improve and standardize the design, reporting, and validation of data across preclinical antiepilepsy therapy development studies targeting drug‐resistant seizures, epileptogenesis, and comorbidities.

Lacosamide, a novel anti-convulsant drug, shows efficacy with a wide safety margin in rodent models for epilepsy.

This paper comprises a series of experiments in rodent models of partial and generalized epilepsy which were designed to describe the anti-convulsant profile of the functionalized amino acid lacosamide. Lacosamide was effective against sound-induced seizures in the genetically susceptible Frings mouse, against maximal electroshock test (MES)-induced seizures in rats and mice, in the rat hippocampal kindling model of partial seizures, and in the 6Hz model of psychomotor seizures in mice. The activity in the MES test in both mice (4.5mg/kg i.p.) and rats (3.9 mg/kg p.o.) fell within the ranges previously reported for most clinically available anti-epileptic drugs. At both the median effective dose for MES protection, as well as the median toxic dose for rotorod impairment, lacosamide elevated the seizure threshold in the i.v. pentylenetetrazol seizure test, suggesting that it is unlikely to be pro-convulsant at high doses. Lacosamide was inactive against clonic seizures induced by subcutaneous administration of the chemoconvulsants pentylenetetrazol, bicuculline, and picrotoxin, but it did inhibit NMDA-induced seizures in mice and showed full efficacy in the homocysteine model of epilepsy. In summary, the overall anti-convulsant profile of lacosamide appeared to be unique, and the drug displayed a good margin of safety in those tests in which it was effective. These results suggest that lacosamide may have the potential to be clinically useful for at least the treatment of generalized tonic-clonic and partial-onset epilepsies, and support ongoing clinical trials in these indications.

Synthesis and structure-activity relationships of potential anticonvulsants based on 2-piperidinecarboxylic acid and related pharmacophores.

Using N-(2,6-dimethyl)phenyl-2-piperidinecarboxamide (1) and N-(alpha-methylbenzyl)-2-piperidinecarboxamide (2) as structural leads, a variety of analogues were synthesised and evaluated for anticonvulsant activity in the MES test in mice. In the N-benzyl series, introduction of 3-Cl, 4-Cl, 3,4-Cl2, or 3-CF3 groups on the aromatic ring led to an increase in MES activity. Replacement of the alpha-methyl group by either i-Pr or benzyl groups enhanced MES activity with no increase in neurotoxicity. Substitution on the piperidine ring nitrogen led to a decrease in MES activity and neurotoxicity, while reduction of the amide carbonyl led to a complete loss of activity. Movement of the carboxamide group to either the 3- or 4-positions of the piperidine ring decreased MES activity and neurotoxicity. Incorporation of the piperidine ring into a tetrahydroisoquinoline or diazahydrinone nucleus led to increased neurotoxicity. In the N-(2,6-dimethyl)phenyl series, opening of the piperidine ring between the 1- and 6-positions gave the active norleucine derivative 75 (ED50=5.8 mgkg(-1), TD50 =36.4 mgkg(-1), PI=6.3). Replacement of the piperidine ring of 1 by cycloalkane (cyclohexane, cyclopentane, and cyclobutane) resulted in compounds with decreased MES activity and neurotoxicity, whereas replacement of the piperidine ring by a 4-pyridyl group led to a retention of MES activity with a comparable PI. Simplification of the 2-piperidinecarboxamide nucleus of 1 into a glycinecarboxamide nucleus led to about a six-fold decrease in MES activity. The 2,6-dimethylanilides were the most potent compounds in the MES test in each group of compounds evaluated, and compounds 50 and 75 should be useful leads in the development of agents for the treatment of tonic-clonic and partial seizures in man.

Synthesis and anticonvulsant activity of 4-bromophenyl substituted aryl semicarbazones

A number of 4-bromophenyl semicarbazones were synthesised and evaluated for anticonvulsant and sedative -hypnotic activities. After intraperitoneal injection to mice, the semicarbazone derivatives were examined in the maximal electroshock seizure (MES), subcutaneous pentylenetetrazole (scPTZ), subcutaneous strychnine (scSTY) and neurotoxicity (NT) screens. All the compounds showed anticonvulsant activity in one or more test models. Compound 12 showed greatest activity, being active in all the screens with very low neurotoxicity and no sedative-hypnotic activity. All the compounds except 7 had lower neurotoxicity compared to phenytoin. Three compounds (6, 11 and 14) showed greater protection than sodium valproate. The essential structural features responsible for interaction with receptor site are established within a suggested pharmacophore.

Models for Epilepsy and Epileptogenesis: Report from the NIH Workshop, Bethesda, Maryland

Summary:  Purpose: The workshop explored the current problems, needs, and potential usefulness of existing methods of discovery of new therapies to treat epilepsy patients. Resistance to medical therapy (pharmacoresistance) and the development of epilepsy (epileptogenesis) are recognized as two of the major problems in epilepsy treatment today. At the same time, there is growing awareness that the development of new therapies has slowed, a trend that has economic and scientific roots. To move toward new and more effective therapies, novel approaches to therapy discovery are needed.

Synthesis and anticonvulsant activity of enaminones. 4. Investigations on isoxazole derivatives

Due to the exceptional anticonvulsant activity displayed by substituted aniline enaminones, related pyridine derivatives and phenothiazines synthesised in our laboratories, the further investigation of various aromatic heterocycles was undertaken. Condensation of cyclic 1,3-diketo esters with 3-, and 5-aminoisoxazole derivatives led to a series of potent anti-maximal electroshock (MES) analogues, three of which occurred in the 3-amino series: ethyl ester (10), orally (po) active in rats [ED(50) 68.9 mg kg(-1), TD(50) > 500 mg kg(-1), protective index (PI = TD(50)/ED(50)) > 49.6]; methyl ester (9), ED(50) 68.9 mg kg(-1) intraperitoneally (ip) in mice, TD(50) > 500 mg kg(-1), PI > 7.3, and tert-butyl ester (8), ED(50) 28.1 mg kg(-1) po in rats, TD(50) > 500 mg kg(-1), PI > 17.8. Sodium channel binding studies, as well as evaluations against pentylenetetrazol, bicuculline, and picrotoxin on isoxazole 10 were all negative, leading to an unknown mechanism of action. X-ray diffraction patterns of a representative of the 3-amino series (isoxazoles 6-11) unequivocally display the existence of intramolecular hydrogen bonding of the nitrogen to the vinylic proton in the cyclohexene ring, providing a pseudo three ring structure which was also shown previously with the vinylic benzamides. Physicochemical-permeability across the BBB suggested an efflux mechanism for the previously synthesised aniline enaminones, but not with isoxazole 10.

Synthesis of some 1-(2-naphthyl)-2-(imidazole-1-yl)ethanone oxime and oxime ether derivatives and their anticonvulsant and antimicrobial activities.

In this study, oxime and oxime ether derivatives of anticonvulsant nafimidone [1-(2-naphthyl)-2-(imidozole-1-yl)ethanone] were prepared as potential anticonvulsant compounds. Nafimidone oxime was synthesized by the reaction of nafimidone and hydroxylamine hydrochloride. O-Alkylation of the oxime by various alkyl halides gave the oxime ether derivatives. Anticonvulsant activity of the compounds was determined by maximal electroshock (MES) and subcutaneous metrazole (scMet) tests in mice and rats according to procedures of the Antiepileptic Drug Development (ADD) program of the National Institutes of Health (NIH). In addition to anticonvulsant evaluation, compounds were also screened for possible antibacterial and antifungal activities because of the structural resemblance to the azole antifungals, especially to oxiconazole. All compounds were evaluated against three human pathogenic fungi and four bacteria using the microdilution method. Most of the compounds exhibited both anticonvulsant and antimicrobial activities; the O-alkyl substituted compounds (2, 3, 4 and 5) were found to be more active than the O-arylalkyl substituted compounds in both screening paradigms.