Anticonvulsant activity and interactions with neuronal voltage-dependent sodium channel of analogues of ameltolide

Fifteen compounds related to ameltolide (LY 201116) were studied for (i) anticonvulsant potential in the maximal electroshock-induced seizures (MES) and the subcutaneous pentylenetetrazol (sc Ptz) tests in mice and rats and (ii) interactions with neuronal voltage-dependent sodium channels. Compounds were chosen ranging in anticonvulsant activity in mice from very active to inactive. The active compounds were defined as those protecting 50% of the animals at doses between 10 and 50 mu mol/kg and inactive compounds as those protecting 50% of the animals at doses greater than 1 mmol/kg. The series studied included three N-(2,6-dimethylphenyl)benzamides (compounds 1, 2 (ameltolide), and 3), three N-(2,2,6,6-tetramethyl)piperidinyl-4-benzamides (compounds 4, 5, 6), one phenylthiourea (compound 7), five N-(2,6-dimethylphenyl)phthalimides (compounds 8, 9, 10, 13, and 14), two N-phenylphthalimide derivatives (compounds 11 and 12), and one N-(2,2,6,6-tetramethyl)piperidinyl-4-phtalimide (compound 15). Phenytoin (PHT) was employed as the reference prototype antiepileptic drug. After inital screening in mice, compounds 1, 2, 3, 5, 8, 9, 10, 13, and 14 were selected for further testing in rats. Anticonvulsant ED(50)s (effective doses in at least 50% of animals tested) of compounds in the MES test were determined in rats dosed orally and amounted to 52 (1), 135 (2), 284 (3), 31 (8), 131 (9), 25 (10), 369 (13), 354 (14), and 121 (PHT) mu mol/kg, compound 5 presenting with an ED50 value higher than 650 mu mol/kg. In our hands, the apparent IC(50)s (inhibitory concentrations 50) of compounds toward binding to rat brain synaptosomes of [H-3]batrachotoxinin-A-20 alpha-benzoate were 0.25 (1), 0.97 (2), 0.35 (3), 25.8 (5), 161.3 (8), 183.5 (9), 0.11 (10), 1.86 (13), 47.8 (14), and 0.86 (PHT) mu M. The relationship between the activity in the MES test and the capacity to interact in vitro with neuronal voltage-dependent sodium channels and the fact that the IC50 values obtained in the in vitro test are close to the brain concentrations at which anticonvulsant activities are reported to occur for ameltolide strongly suggest that the anticonvulsant properties of most compounds tested could be a direct result of their interaction with the neuronal voltage-dependent sodium channel.