Aroyl(aminoacyl)pyrroles, a new class of anticonvulsant agents.

2-Aroyl-4-(omega-aminoacyl)- (4) and 4-aroyl-2-(omega-aminoacyl)pyrroles (9) represent a new, structurally novel class of anticonvulsant agents. Compounds of type 4 were prepared by Friedel-Crafts acylation of a 2-aroylpyrrole with an omega-chloroacyl chloride followed by displacement of the chloro group by a primary or secondary amine. Compounds of type 9 were prepared by Friedel-Crafts aroylation of a 2-(omega-chloroacyl)pyrrole followed by displacement by an amine. These compounds were active in the mouse and rat maximal electroshock tests but not in the mouse metrazole test. The lead compound, RWJ-37868, 2-(4-chlorobenzoyl)-4-(1-piperidinyl-acetyl)-1,3,5-trimethylpyrrole++ + (4d), showed potency and therapeutic index comparable to those of phenytoin and carbamazepine and greater than those of sodium valproate. This compound blocked bicuculline induced seizures, did not elevate seizure threshold following iv infusion of metrazole, and blocked influx of Ca2+ ions into cerebellar granule cells induced by K+ or veratridine.

Analysis of anticonvulsant and neurotoxic responses to combination therapy with carbamazepine, felbamate and phenytoin by response-surface modeling.

Various combinations of carbamazepine (CAS 298-46-4), felbamate (CAS 25451-15-4), and phenytoin (CAS 57-41-0) were evaluated in mice (i.p.) for anticonvulsant activity (maximal electroshock seizure test) and minimal neurotoxicity (rotarod test). The results obtained from these studies were analyzed using response surface methodologies (RSM). The outcomes of these analyses in regard to anticonvulsant activity suggest that, under these experimental study conditions, at 0.5 h post treatment there is a significant carbamazepine/phenytoin synergism even though none of the drugs has a significant dose-response by that time when given alone, and that at 1.0 h post treatment, the combination dose-response is additive. Thus, there appears to be an important dose/time relationship. In regard to the neurotoxic response, the results suggest a significant carbamazepine/phenytoin synergism at 0.25 h post treatment and an additive neurotoxic effect due to the combination of felbamate/carbamazepine/phenytoin at 0.5, 1.0 and 2.0 h post exposure.

Anticonvulsant activity of the gamma-aminobutyric acid uptake inhibitor N-4,4-diphenyl-3-butenyl-4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol .

The N-4,4-diphenyl-3-butenyl derivative of the glial selective gamma-aminobutyric acid (GABA) uptake inhibitor 4,5,6,7-tetrahydroisoxazolo [4,5-c]pyridin-3-ol (N-DPB-THPO), was tested for its ability to block sound-induced seizures in the audiogenic seizure-susceptible Frings mouse model of epilepsy. Following intracerebroventricular (i.c.v.) administration, N-DPB-THPO blocked tonic hindlimb extension in a dose- and time-dependent manner. At the doses tested no gross behavioral effects were noted.

Characterization of the anticonvulsant properties of F-721.

The anticonvulsant properties of F-721 (3-diethylamino-2,2-dimethylpropyl-5-[p-trifluoromethylphenyl]-2-f uroate hydrochloride) were investigated in a battery of in vivo and in vitro anticonvulsant model systems. After intraperitoneal (ip) administration in mice, F-721 was effective in nontoxic doses against maximal electroshock (MES), subcutaneous picrotoxin clonic, intracerebroventricular (icv) N-methyl-D-aspartate (NMDA) tonic, icv NMDA clonic and icv quisqualic acid tonic seizures (ED50s: 11.1, 28.4, 1.76, 3.4, and 4.4 mg/kg, respectively). F-721 exhibited only partial activity against clonic seizures induced in the subcutaneous Metrazol and subcutaneous bicuculline test in mice and was inactive in this species against tonic seizures induced in the subcutaneous strychnine test. F-721 was effective against MES seizures following oral administration to mice (ED50: 31.3 mg/kg) and only partially effective by this route against clonic seizures induced by subcutaneous Metrazol. In rats, F-721 was a potent anticonvulsant in the maximal electroshock model following oral administration (ED50: 9.9 mg/kg). F-721 was also effective against corneal-kindled and amygdaloid-kindled seizures in rats. F-721 suppressed stage 5 seizures in corneal-kindled rats with an ED50 of 15 mg/kg, ip. In addition, it also decreased the afterdischarge duration and behavioral seizure stage in amygdaloid-kindled rats at doses that did not cause sedation or ataxia. At 40 mg/kg, F-721 reduced afterdischarge duration by 83.2% and reduced the seizure severity score to 1.7. The ED50 for 50% reduction of afterdischarge duration was 16.3 mg/kg, ip. In cultured mouse spinal cord neurons, F-721 suppressed sustained repetitive firing in response to a depolarizing current with a median inhibitory concentration (IC50) of 1.9 microM. F-721 had no effect on adenosine uptake, gamma-aminobutyric acid or NMDA receptor binding. Comparative data from previous studies with clinically established antiepileptic agents reveal that F-721's profile of activity most closely resembles that of phenytoin and carbamazepine. However, F-721 was notably more efficacious in suppressing amygdaloid-kindled seizures in rats and was a more potent antagonist of icv NMDA clonic seizures. Our studies indicate that F-721 is a potent, orally active anticonvulsant with a favorable margin of safety. The profile of anticonvulsant activity of F-721 suggests potential utility in the management of generalized tonic-clonic, simple and complex partial seizures.

A neuropharmacological evaluation of felbamate as a novel anticonvulsant.

Felbamate (2-phenyl-1,3-propanediol dicarbamate, FBM) was subjected to a series of carefully selected in vivo and in vitro tests to provide additional insight into mechanism of action, margin of safety, and clinical potential. FBM was effective against intracerebroventricular (i.c.v.) N-methyl-D-aspartate (NMDA)-induced clonus and i.c.v. NMDA- and quisqualic acid (quis)-induced forelimb tonic extension in mice and ineffective against i.c.v. quis-induced clonus in mice. FBM was also effective in preventing the expression of Stage 5 kindled seizures in corneal-kindled rats. The calculated protective indices (rotorod median toxic dose divided by anticonvulsant median effective dose) ranged from 28 to 146 for those tests in which FBM displayed activity. With the in vitro tests, FBM did not significantly displace [3H]MK-801 from its binding site. In contrast, FBM was effective in blocking sustained repetitive firing in mouse spinal cord neurons grown in tissue culture (median inhibitory concentration 67 micrograms/ml). This effect on repetitive firing suggests indirectly that FBM modulates sodium channel conductance. The results, when compared to similar data for phenytoin, carbamazepine, valproate, and ethosuximide, support the concept that FBM is a relatively nontoxic agent with a unique profile of anticonvulsant action, a broad margin of safety, and a clinical potential that includes at least generalized tonic-clonic and complex partial seizures.

Anticonvulsant profiles of the potent and orally active GABA uptake inhibitors SK&F 89976-A and SK&F 100330-A and four prototype antiepileptic drugs in mice and rats.

The anticonvulsant profiles of two potent and orally active gamma-aminobutyric acid (GABA) uptake inhibitors, 1-(4,4-diphenyl-3-butenyl)-3-piperidine-carboxylic acid hydrochloride (SK&F 89976-A) and 1-(4,4-diphenyl-3-butenyl)-1,2,5,6-tetrahydro-3-pyridine-carboxylic acid hydrochloride (SK&F 100330-A), were determined with a battery of well-standardized tests in mice and rats and compared with the profiles of phenytoin (PHT), carbamazepine (CBZ), valproate (VPA) and clonazepam (CZP) when subjected to the same tests. ED50 values were calculated and compared with TD50 values for minimal motor impairment to provide protective indexes (PI = TD50/ED50). The anticonvulsant profiles of SK&F 89976-A and SK&F 100330-A were similar and suggest that these compounds raise the threshold for seizure initiation rather than inhibit seizure spread. Like intraperitoneal (i.p.) PHT, CBZ, VPA, and CZP, SK&F 89976-A and SK&F 100330-A inhibited seizures in corneally kindled rats. The profiles of SK&F 89976-A and SK&F 100330-A were most similar to that of CZP and virtually opposite to that of PHT. Intraperitoneal SK&F 100330-A provided complete protection against pentylenetetrazol-induced seizures [subcutaneous (s.c.) PTZ] in mice but was ineffective against seizures induced by maximal electroshock (MES) at doses slightly greater than its TD50. SK&F 100330-A provided complete protection against picrotoxin-induced seizures (s.c. Pic) and against both clonus and forelimb tonic extension induced by NMDA N-methyl-D-aspartate [intracerebral ventricular (i.c.v.)-NMDA] in mice; however, SK&F 100330-A was ineffective against seizures induced by bicuculline (s.c. Bic) and strychnine (s.c. Strych) at doses slightly greater than its TD50. SK&F 89976-A was similar but provided partial protection against NMDA-induced clonus.(ABSTRACT TRUNCATED AT 250 WORDS)

AHR-12245: a potential anti-absence drug.

AHR-12245, 2-(4-chlorophenyl)-3H-imadazo[4,5-b]pyridine-3-acetamid, ethosuximide, Na valproate, phenytoin, and clonazepam were evaluated in mice and rats with a battery of well-standardized anticonvulsant test procedures. The results obtained indicate that the anticonvulsant profile of AHR-12245 is similar to that for ethosuximide and clonazepam. AHR-12245 is effective in nontoxic intraperitoneal doses in mice by the maximal electroshock seizure (MES), pentylenetatrazol (s.c. PTZ), bicuculline, and picrotoxin tests but ineffective against strychnine-induced seizures; it is effective after nontoxic oral doses in both mice and rats by the s.c. PTZ test and ineffective by the MES test. The candidate antiepileptic substance was also ineffective against seizures induced in amygdala and corneally kindled rats. The PIs for AHR-12245 by the s.c. PTZ test were 4.5 to 12 times higher than those for the prototype agents, except that for clonazepam when administered orally in mice. The in vitro studies indicate that AHR-12245 is a weak inhibitor of benzodiazepine (BDZ) receptor binding but does inhibit adenosine uptake. These results indicate that AHR-12245 is a relatively nontoxic agent with a profile of anticonvulsant action which suggests it should be useful in generalized absence seizures.

Preclinical profile of stereoisomers of the anticonvulsant remacemide in mice.

Stereoisomers of remacemide (racemate form) were compared for anticonvulsant efficacy and safety in mice. In the maximal electroshock seizure (MES) test for oral efficacy, the (-) stereoisomer, FPL 14145, was more potent than the racemate or the (+) stereoisomer, FPL 14144. Respective ED50 values (expressed as mg/kg) were: remacemide, 58; FPL 14145, 45; FPL 14144, 79. In 2 of 3 tests for neural impairment, FPL 14145 yielded significantly better therapeutic indices (toxic dose 50/ED50) than the racemate. The margin of safety (estimated median lethal dose ED50) was more favorable for FPL 14144: remacemide, 15.1; FPL 14144, 18.9; FPL 14145, 15.7. The duration of protection against MES indicated the stereoisomers were longer acting than the racemate. After intravenous administration the order of potency against MES was similar: FPL 14145 greater than remacemide greater than FPL 14144. Following daily administration of the oral ED98 for 4 days, with a dose response curve run on day 5, the MES ED50 values for all compounds were increased. The test indicates tolerance. In the pentylenetetrazol infusion test the racemate and FPL 14144 demonstrated more proconvulsant properties than FPL 14145. Intraperitoneal administration of 50 mg/kg or more produced changes in behavior with all compounds. At higher doses the racemate and FPL 14145 elicited more severe symptoms with death at 200 mg/kg.

Comparison of midazolam and diazepam by the intramuscular route for the control of seizures in a mouse model of status epilepticus.

A model system is described in which sustained clonic seizures are produced by a combination of phenytoin (PHT) and pentylenetetrazol (PTZ) in the mouse, the former agent preventing the terminal tonic spasms produced by the latter. In this system, midazolam (MDL), a water-soluble benzodiazepine, was compared with diazepam (DZP), a sparingly soluble agent which is widely used to treat status epilepticus (SE) in humans. Both agents were administered intramuscularly (i.m.) in approximately equieffective doses in animals exhibiting clonic seizure activity. MDL proved to be about twice as potent as DZP. Whereas control animals convulsed for a period of approximately 90 min, those treated with DZP 0.2 and 0.4 mg/kg convulsed for 7.8 and 3.9 min, respectively; mice receiving MDL 0.1 and 0.2 mg/kg convulsed for 1.9 and 1.4 min, respectively. MDL arrested seizures substantially more rapidly than diazepam (p less than 0.05). These data suggest that MDL has sufficiently rapid anticonvulsant action to merit evaluation for control of SE in humans when a rapidly absorbed antiepileptic drug (AED) is needed and intravenous (i.v.) administration is not feasible.

Pharmacodynamics and pharmacokinetics of AHR-11748, a new antiepileptic agent, in rodents.

AHR-11748, the desmethyl metabolite of fluzinamide (an effective antiepileptic), was active in preventing maximal seizures induced in mice or rats by electroshock and threshold seizures induced in mice by Metrazol, bicuculline, and picrotoxin. The compound showed a profile of anticonvulsant activity similar to those of phenobarbital and valproic acid and different from those of phenytoin and ethosuximide. ED50s were less than those of valproic acid, but greater than those of phenobarbital. Analysis of plasma and whole brain homogenates of mice indicated that AHR-11748 has an apparent terminal half-life (t1/2, beta) of 1.0 h. The brain:plasma ratio of AHR-11748 was 3.4:1 from 0.5 h to 6 h.

Hypnotic action of pentobarbital in mice: a possible mechanism.

The effect of GABA receptor agonists (THIP and baclofen) on the hypnotic activity (loss of righting reflex and sleep time) of pentobarbital in mice was investigated. Combinations of either THIP-pentobarbital or baclofen-pentobarbital interacted synergistically by increasing hypnotic activity. The GABAa receptor antagonist, bicuculline, decreased the hypnotic effect of THIP-pentobarbital combinations but not that of baclofen-pentobarbital combinations. These results suggest that the hypnotic activity of pentobarbital involves GABAa receptor function.

The effect of chronic felbamate administration on anticonvulsant activity and hepatic drug-metabolizing enzymes in mice and rats.

The possibility of tolerance development from chronic administration of felbamate (FBM) was investigated in mice and rats. Chronic administration (15 days) of FBM (150 mg/kg i.p.) in mice had no significant effect on either intravenous pentylenetetrazol (PTZ) seizure threshold or hexobarbital sleep time; however, hexobarbital sleep time was significantly increased after a single dose. Chronic administration (5-7 days) of FBM (48 or 95 mg/kg orally) in rats also had no significant effect on either maximal electroshock seizure activity or hexobarbital sleep time. Chronic administration of FBM at 238 mg/kg slightly decreased anti-subcutaneous PTZ activity in chronically treated rats (one of eight protected) as compared with those receiving only a single dose (three of eight protected), but there was no significant change in hexobarbital sleep time. Chronic treatment of rats for 7 days with 48 mg/kg had no significant effect on any hepatic parameters. However, 95 or 238 mg/kg of FBM significantly increased p-nitroanisole O-demethylase activity. It is concluded that the increased hexobarbital sleep time induced by an acute dose of FBM reflects the CNS-depressant effect of the substance. The increased p-nitroanisole O-demethylase activity observed after chronic administration may be indicative of some liver microsomal induction. Overall, FBM in doses ranging from 48 to 238 mg/kg appears to have minimal potential for tolerance development.

Correlation of the hypnotic potency of benzodiazepines with inhibition of voltage-dependent calcium uptake into mouse brain synaptosomes.

Nine benzodiazepines were tested for their ability to inhibit 45Ca2+ uptake into mouse whole brain synaptosomes and for hypnotic activity as indicated by their ability to produce loss of the righting reflex. Eight of the benzodiazepines significantly inhibited fast-phase voltage-dependent 45Ca2+ uptake and five exhibited hypnotic activity. There was a direct correlation between the hypnotic potency of these five benzodiazepines and their ability to inhibit 45Ca2+ uptake. There does not appear to be a correlation between the anticonvulsant potency of the benzodiazepines and their potency for inhibiting 45Ca2+ uptake. These results support previous findings with other sedative/hypnotic drugs and suggest that inhibition of presynaptic calcium uptake may be linked with hypnotic but not anticonvulsant actions of benzodiazepines.

Effects of gamma-aminobutyric acid (GABA) receptor agonists on the neurotoxicity and anticonvulsant activity of barbiturates in mice.

The effects of gamma-aminobutyric acid (GABA) receptor agonists [4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol THIP]; [progabide and baclofen] on the minimal neurotoxicity and anticonvulsant activity of pentobarbital and phenobarbital in mice were investigated. When either progabide, THIP or baclofen were administered with pentobarbital, the components of this combination interacted additively by the rotorod test. Combinations of pentobarbital and progabide or phenobarbital and progabide interacted additively when subjected to the pentylenetetrazol (PTZ) minimal threshold seizure (clonic) test. THIP, even at toxic doses, did not alter the anti-PTZ activity of either pentobarbital or phenobarbital. In contrast, baclofen at toxic doses potentiated the anti-PTZ activity of pentobarbital and phenobarbital. Combinations of progabide and pentobarbital or progabide and phenobarbital interacted additively by the maximal electroshock seizure (MES) test. THIP, even when given in toxic doses, had no effect on the anti-MES activity of pentobarbital and phenobarbital. However, baclofen at nontoxic doses potentiated the anti-MES activity of phenobarbital but not that of pentobarbital. These results suggest that 1) in vitro interactions between barbiturates and GABAa receptor agonists may not be the same in vivo, 2) GABAa receptors may play a minor role in the minimal neurotoxicity and anticonvulsant activity of barbiturates and 3) inhibition of glutamate-induced excitation by baclofen may be an important action in potentiating the anti-MES activity of phenobarbital.

Effect of ethosuximide alone and in combination with gamma-aminobutyric acid receptor agonists on brain gamma-aminobutyric acid concentration, anticonvulsant activity and neurotoxicity in mice.

The acute administration of an anticonvulsant dose of ethosuximide (150 mg/kg) had no effect on brain gamma-aminobutyric acid (GABA) concentration, whereas a toxic dose (400 mg/kg) increased significantly the concentration of brain GABA (1.23 +/- 0.05 vs. 1.92 +/- 0.14 mumol/g of wet tissue). The administration of 500 mg/kg/day of ethosuximide for 1, 2, 4, 6, 8 and 11 days induced neurotoxicity in 100, 100, 67, 0, 0 and 0% of animals, respectively, and increased brain GABA concentration 46, 38, 25, 14, 9 and 0%, respectively. These results imply that the tolerance that develops in response to the chronic administration of toxic doses of ethosuximide correlates well with the concentration of brain GABA. 4,5,6,7-Tetrahydroisoxazolo [5,4-c]pyridin-3-ol even in toxic doses had no effect on the anticonvulsant activity of ethosuximide. Combination studies with ethosuximide and progabide demonstrated that the antipentylenetetrazol activity of the individual components interacts additively. Likewise, combinations of either ethosuximide and 4,5,6-tetrahydroisoxazolo [5,4-c]pyridin-3-ol or ethosuximide and progabide showed an additive effect by the rotorod test. These results indicate that the antipentylenetetrazol activity of ethosuximide is unrelated to GABA function and that the increase in brain GABA concentration induced by toxic doses of ethosuximide contributes to its neurotoxicity.

Involvement of a GABAergic mechanism in the pharmacologic action of phenytoin.

In vivo interactions between phenytoin (PHT) and baclofen (a GABAb receptor agonist) or PHT and progabide (a GABAa receptor agonist) were investigated by the rotorod minimal neurotoxicity test and maximal electroshock seizure (MES) test. The combination of PHT and baclofen produced an additive effect by the rotorod test, whereas the combination of PHT and progabide elicited a supra-additive (synergistic) effect. The median minimal neurotoxic dose of baclofen augmented the anti-MES activity of PHT. The combination of PHT and progabide induced a supra-additive effect by the MES test. These results imply that GABAa receptors are involved in both the minimal neurotoxicity and anti-MES activity of PHT.

Benzodiazepine inhibition of [3H]flunitrazepam binding and caffeine-induced seizures in mice.

The median inhibitory and anticonvulsant potencies of seven benzodiazepine (BDZ) agonists and one BDZ antagonist (Ro15-1788) were established by two tests: inhibition of [3H]flunitrazepam receptor binding and prevention of caffeine-induced seizures in mice. The effect of Ro15-1788 on the anticonvulsant potency of diazepam against caffeine-induced seizures was also investigated. The [3H]flunitrazepam receptor binding inhibitory potencies (IC50s) of the BDZ agonists correlate well with their anticonvulsant potencies (ED50s) against caffeine-induced seizures (r = 0.831; P greater than 0.01 and less than 0.05). Ro15-1788 and clonazepam are the most potent inhibitors (IC50s: 1.72 and 1.75 nM, respectively), but differ markedly in their ability to obtund caffeine-induced seizures (ED50s: 43.2 and 0.226 mg/kg, respectively). Although both Ro15-1788 and diazepam are effective against caffeine-induced seizures, when used in combination Ro15-1788 antagonizes the anti-caffeine effect of diazepam. These data indicate that Ro15-1788 is a BDZ partial agonist with low efficacy as well as a potent antagonist.

Comparative anticonvulsant activity and neurotoxicity of felbamate and four prototype antiepileptic drugs in mice and rats.

Felbamate (2-phenyl-1,3-propanediol dicarbamate), phenytoin, phenobarbital, ethosuximide, and valproate were evaluated in mice and rats with a battery of well-standardized anticonvulsant test procedures. The results obtained indicate that felbamate exhibits a wider range of experimental anticonvulsant activity than either phenytoin or ethosuximide and a somewhat more restricted range than either phenobarbital or valproate. Felbamate is effective in nontoxic intraperitoneal doses in mice by the maximal electroshock seizure (MES), pentylenetetrazol (s.c. PTZ), and picrotoxin (s.c. Pic) tests but ineffective against bicuculline- and strychnine-induced seizures; it is effective after nontoxic oral doses in both mice and rats by the MES and s.c. PTZ tests. When compared on the basis of protective indices (PI = TD50/ED50) calculated from the intraperitoneal data in mice, the PIs for felbamate were from 1.05 to 2.37 times higher than those of the prototype antiepileptics. Overall, except for the s.c. PTZ test in mice and rats after oral administration, the PIs were equal to or higher than those of the prototype agents. The PIs for the s.c. PTZ test in mice and rats after oral administration were within the range of the prototype agents. These data indicate that felbamate is a relatively nontoxic agent with a unique profile of anticonvulsant action.