Profile of anticonvulsant activity and minimal toxicity of methyl 4-[(p-chlorophenyl)amino]-6-methyl-2-oxo-cyclohex-3-en-1-oate and some prototype antiepileptic drugs in mice and rats

Evaluation of the antinociceptive activities of enaminone compounds on the formalin and hot plate tests in mice

Recently, we found that methyl 4-(4′-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate (E139), an anticonvulsant enaminone, has antinociceptive activity in the hot plate test. In this study we evaluated the antinociceptive activity of five anilino enaminones E139, ethyl 4-(4′-chlorophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E121), ethyl 4-(4′-bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E122), methyl 4-(4′-chlorophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E138) and ethyl 4-(4′-fluorophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (BRG 19) using the formalin and hot plate tests. E139 has been reported to exert its effects via enhancement of extracellular GABA levels, thus tiagabine, a GABA transporter inhibitor, was evaluated as a control together with indomethacin. Tiagabine had antinociceptive activity in both phase 1 (neurogenic pain) and phase 2 (inflammatory pain) of the formalin test, whereas indomethacin had activity only in phase 2. E139 and E138 had antinociceptive activity in both phases of the formalin test, whereas E121 had activity only in phase 1 and BRG 19 had activity only in phase 2. E122 had no significant activity in either phase. In the hot plate test only E139 had antinociceptive activity. Administration of either bicuculline, a GABA_A receptor antagonist, or CGP 35348, a GABA_B receptor antagonist, blocked the antinociceptive activity of E139. In conclusion our results indicate that E139 has antinociceptive activity in the formalin and hot plate tests that are dependent on GABA receptors.

Allosteric Modulation of GABAA Receptors by an Anilino Enaminone in an Olfactory Center of the Mouse Brain

In an ongoing effort to identify novel drugs that can be used as neurotherapeutic compounds, we have focused on anilino enaminones as potential anticonvulsant agents. Enaminones are organic compounds containing a conjugated system of an amine, an alkene and a ketone. Here, we review the effects of a small library of anilino enaminones on neuronal activity. Our experimental approach employs an olfactory bulb brain slice preparation using whole-cell patch-clamp recording from mitral cells in the main olfactory bulb. The main olfactory bulb is a key integrative center in the olfactory pathway. Mitral cells are the principal output neurons of the main olfactory bulb, receiving olfactory receptor neuron input at their dendrites within glomeruli, and projecting glutamatergic axons through the lateral olfactory tract to the olfactory cortex. The compounds tested are known to be effective in attenuating pentylenetetrazol (PTZ) induced convulsions in rodent models. One compound in particular, KRS-5Me-4-OCF₃, evokes potent inhibition of mitral cell activity. Experiments aimed at understanding the cellular mechanism underlying the inhibitory effect revealed that KRS-5Me-4-OCF₃ shifts the concentration-response curve for GABA to the left. KRS-5Me-4-OCF₃ enhances GABA affinity and acts as a positive allosteric modulator of GABA_A receptors. Application of a benzodiazepine site antagonist blocks the effect of KRS-5Me-4-OCF₃ indicating that KRS-5Me-4-OCF₃ binds at the classical benzodiazepine site to exert its pharmacological action. This anilino enaminone KRS-5Me-4-OCF₃ emerges as a candidate for clinical use as an anticonvulsant agent in the battle against epileptic seizures.

Evaluation of anticonvulsant actions of dibromophenyl enaminones using in vitro and in vivo seizure models

Epilepsy and other seizure disorders are not adequately managed with currently available drugs. We recently synthesized a series of dibromophenyl enaminones and demonstrated that AK6 and E249 were equipotent to previous analogs but more efficacious in suppressing neuronal excitation. Here we examined the actions of these lead compounds on in vitro and in vivo seizure models. In vitro seizures were induced in the hippocampal slice chemically (zero Mg2+ buffer and picrotoxin) and electrically using patterned high frequency stimulation (HFS) of afferents. In vivo seizures were induced in rats using the 6 Hz and the maximal electroshock models. AK6 (10 µM) and E249 (10 µM) depressed the amplitude of population spikes recorded in area CA1 of the hippocampus by -50.5±4.3% and -40.1±3.1% respectively, with partial recovery after washout. In the zero Mg2+ model, AK6 (10 µM) depressed multiple population spiking (mPS) by -59.3±6.9% and spontaneous bursts (SBs) by -65.9±7.2% and in the picrotoxin-model by -43.3±7.2% and -50.0±8.3%, respectively. Likewise, E249 (10 µM) depressed the zero-Mg2+-induced mPS by -48.8±9.5% and SBs by -55.8±15.5%, and in the picrotoxin model by -37.1±5.5% and -56.5±11.4%, respectively. They both suppressed post-HFS induced afterdischarges and SBs. AK6 and E249 dose-dependently protected rats in maximal electroshock and 6 Hz models of in vivo seizures after 30 min pretreatment. Their level of protection in both models was similar to that obtained with phenytoin Finally, while AK6 had no effect on locomotion in rats, phenytoin significantly decreased locomotion. AK6 and E249, suppressed in vitro and in vivo seizures to a similar extent. Their in vivo activities are comparable with but not superior to phenytoin. The most efficacious, AK6 produced no locomotor suppression while phenytoin did. Thus, AK6 and E249 may be excellent candidates for further investigation as potential agents for the treatment of epilepsy syndromes with possibly less CNS side effects.

The anticonvulsant enaminone E139 attenuates paclitaxel-induced neuropathic pain in rodents

The enaminone methyl 4-(4′-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate (E139) has anticonvulsant activities. It has been reported to have a better safety profile than some anticonvulsant drugs. Since some anticonvulsant drugs are used in the management of neuropathic pain, we evaluated the effects of E139 in rodent models of acute pain and paclitaxel-induced neuropathic pain. The reaction latency to thermal stimuli (hot-plate test) of BALB/c mice was recorded before and after intraperitoneal treatment with paclitaxel (2 mg/kg, i.p. for 5 consecutive days), and after treatment with E139 (0.1–40 mg/kg), amitriptyline (10 mg/kg), and gabapentin (10 and 30 mg/kg). Mechanical allodynia in paclitaxel-treated Sprague Dawley (SD) rats was measured using a dynamic plantar aesthesiometer before and after treatment with E139 (10 and 20 mg/kg) or its vehicle for four consecutive days from day 7 after first administration of paclitaxel (16 mg/kg on two alternate days). Administration of E139 (10–40 mg/kg) produced antinociceptive activity against thermal nociception in naïve mice. Treatment with E139, amitriptyline, or gabapentin reduced paclitaxel-induced thermal hyperalgesia. E139 reduced paclitaxel-induced mechanical allodynia, with the effects lasting longer (24 h) after repetitive dosing. Our results indicate that E139 has antinociceptive activity and attenuates paclitaxel-induced neuropathic pain in rodents.

Synthesis, biological activity and molecular modelling studies of tricyclic alkylimidazo-, pyrimido- and diazepinopurinediones

Syntheses and biological activities of imidazo-, pyrimido- and diazepino[2,1-f]purinediones containing N-alkyl substituents (with straight, branched or unsaturated chains) are described. Tricyclic derivatives were synthesized by the cyclization of 8-bromo-substituted 7-(2-bromoethyl)-, 7-(3-chloropropyl)- or 7-(4-bromobutyl)-theophylline with primary amines under various conditions. Compound 22 with an ethenyl substituent was synthesized by dehydrohalogenation of 9-(2-bromoethyl)-1,3-dimethyltetrahydropyrimido[2,1-f]purinedione. The obtained derivatives (5-35) were initially evaluated for their affinity at rat A1 and A2A adenosine receptors (AR), showing moderate affinity for both adenosine receptor subtypes. The best ligands were diazepinopurinedione 28 (K i = 0.28 μM) with fivefold A2A selectivity and the non-selective A1/A2A AR ligand pyrimidopurinedione 35 (K i A1 = 0.28 μM and K i A2A = 0.30 μM). The compounds were also evaluated for their affinity at human A1, A2A, A2B and A3 ARs. All of the obtained compounds were docked to the A2A AR X-ray structure in complex with the xanthine-based, potent adenosine receptor antagonist-XAC. The likely interactions of imidazo-, pyrimido- and diazepino[2,1-f]purinediones with the residues forming the A2A binding pocket were discussed. Furthermore, the new compounds were tested in vivo as anticonvulsants in maximal electroshock, subcutaneous pentylenetetrazole (ScMet) and TOX tests in mice (i.p.). Pyrimidopurinediones showed anticonvulsant activity mainly in the ScMet test. The best derivative was compound 11, showing 100 % protection at a dose of 100 mg/kg without symptoms of neurotoxicity. Compounds 6, 7, 8 and 14 with short substituents showed neurotoxicity and caused death. In rat tests (p.o.), 9 was characterized by a high protection index (>13.3). AR affinity did not apparently correlate with the antiepileptic potency of the compounds.

Synthesis and anticonvulsant activity of trans- and cis-2-(2,6-dimethylphenoxy)-N-(2- or 4-hydroxycyclohexyl)acetamides and their amine analogs

A group of trans- and cis-2-(2,6-dimethylphenoxy)-N-(2-hydroxycyclohexyl)acetamides (1-7) and -ethylamines (8-9) have been synthesized and investigated for their anticonvulsant activity. One of them, racemic trans-2-(2,6-dimethylphenoxy)-N-(2-hydroxycyclohexyl)acetamide proved to be the most effective in MES (mice, ip), exhibiting ED(50)=42.97 mg/kg b.w. and TD(50)=105.67 mg/kg b.w. It also proved protection in focal seizures (electric kindling, rats, ip) and it raises seizure threshold. The mechanism of action is inhibition of voltage-gated sodium currents and enhancement of GABA effect. Safety pharmacology assay on threshold tonic extension revealed no lowering of the seizure threshold.

Anti-tussive and bronchodilator mechanisms of action for the enaminone E121

AIMS

In this study, we investigated whether the enaminone, E121, has anti-tussive effects in a guinea pig model of cough, and if so, whether this effect is mediated via a central or peripheral site of action. We also assessed whether E121 has bronchodilator effects and the molecular mechanisms underlying any anti-tussive and/or bronchodilator effects.

MAIN METHODS

Whole body plethysmography was used to assess both cough and airway obstruction. A stereotaxic apparatus was used to administer drugs intracerebroventricularly (i.c.v.). Effects of E121 were examined in vitro on contractile effects in guinea pig bronchioles.

KEY FINDINGS

Pre-treatment of animals with E121 resulted in a significant inhibition in the citric acid-induced cough and airway obstruction compared to vehicle-pretreated animals. The K(ATP) antagonist, glibenclamide, significantly inhibited the anti-tussive and bronchoprotective effects of E121. Also, intra-tracheal administration of E121 resulted in a significant inhibition of both the citric acid-induced cough response and airway obstruction compared to vehicle-pretreated animals. By contrast, i.c.v. administration had no effect. Finally, E121 significantly inhibited carbachol-induced airway smooth muscle contractions, an effect that was reduced by both glibenclamide and propranolol. Interestingly, E121 enhanced histamine-induced cAMP release in human eosinophils although it did not directly elevate cAMP levels.

SIGNIFICANCE

The enaminone, E121, has anti-tussive and bronchodilatory effects and is topically, but not centrally, active. The anti-tussive mechanism of action of E121 seems to be K(ATP) channel dependent, whereas its bronchodilatory effects appear to be mediated via activation of both K(ATP) channels and β(2) receptors. Therefore, E121 may potentially represent a novel therapy for cough, particularly cough associated with airway obstruction.

The study of the lipophilicity of some aminoalkanol derivatives with anticonvulsant activity

A series of new (phenoxyethyl)aminoalkanol derivatives were synthesized and evaluated for their anticonvulsant activity. The most promising compound seemed to be (R,S)-1N-[(2,6-dimethyl)phenoxyethyl]amino-2-butanol, which displayed anti-MES activity (in mice, i.p.) with protective index (TD(50) /ED(50) ) of 5.712, corresponding to that of phenytoin (6.6), carbamazepine (4.9) and valproate (1.7). The lipophilicity of compounds 1-17 exhibiting anticonvulsant activity was investigated. Their lipophilicities (R(M0) ) were determined using reversed-phase thin-layer chromatography (RP-TLC) with a mixture of acetone and water as mobile phases. The partition coefficients of 1-17 (logP) were also calculated using two computer programs (Pallas and ALOGPS) and compared with R(M0) . The relationship between anticonvulsant activity and lipophilicity of the tested substances was estimated.

A substituted anilino enaminone acts as a novel positive allosteric modulator of GABA(A) receptors in the mouse brain

A small library of anilino enaminones was analyzed for potential anticonvulsant agents. We examined the effects of three anilino enaminones on neuronal activity of output neurons, mitral cells (MC), in an olfactory bulb brain slice preparation using whole-cell patch-clamp recording. These compounds are known to be effective in attenuating pentylenetetrazol-induced convulsions. Among the three compounds tested, 5-methyl-3-(4-trifluoromethoxy-phenylamino)-cyclohex-2-enone (KRS-5Me-4-OCF₃) showed potent inhibition of MC activity with an EC₅₀ of 24.5 μM. It hyperpolarized the membrane potential of MCs accompanied by suppression of spontaneous firing. Neither ionotropic glutamate receptor blockers nor a GABA(B) receptor blocker prevented the KRS-5Me-4-OCF(3)-evoked inhibitory effects. In the presence of GABA(A) receptor antagonists, KRS-5Me-4-OCF(3) completely failed to evoke inhibition of MC spiking activity, suggesting that KRS-5Me-4-OCF₃-induced inhibition may be mediated by direct action on GABA(A) receptors or indirect action through the elevation of tissue GABA levels. Neither vigabatrin (a selective GABA-T inhibitor) nor 1,2,5,6-tetrahydro-1-[2-[[(diphenylmethylene)amino]oxy]ethyl]-3-pyridinecarboxylic acid hydrochloride (NNC-711) (a selective inhibitor of GABA uptake by GABA transporter 1) eliminated the effect of KRS-5ME-4-OCF₃ on neuronal excitability, indicating that the inhibitory effect of the enaminone resulted from direct activation of GABA(A) receptors. The concentration-response curves for GABA are left-shifted by KRS-5Me-4-OCF₃, demonstrating that KRS-5Me-4-OCF₃ enhanced GABA affinity and acted as a positive allosteric modulator of GABA(A) receptors. The effect of KRS-5Me-4-OCF₃ was blocked by applying a benzodiazepine site antagonist, suggesting that KRS-5Me-4-OCF₃ binds at the classic benzodiazepine site to exert its pharmacological action. The results suggest clinical use of enaminones as anticonvulsants in seizures and as a potential anxiolytic in mental disorders.

Synthesis, Reactions and Antitumour Screening of new Enaminones

A new series of enaminones derived from 3-acetyl-1-aryl-4-benzoyl-5-phenyl-1 H-pyrazoles has been obtained and their reactions with hydrazine hydrate, guanidine hydrochloride, 3-amino-1,2,4-triazole, 2-aminobenzimidazole and active methylenenitriles are described. The mechanisms and regioselectivity of the studied reactions are discussed. The results of screening of the antitumor activity of the enaminones against the human breast cancer cell line MCF-7 revealed that the compounds showed less activity than that of the reference drug doxorubicin. Their activity was found to depend on the nature of the substituent group on the 1-aryl moiety. The order of activity of the series is: H > 4–Cl > 4-MeO > 4-Me > 4-NO2.

Evaluation of mutagenic and antimutagenic properties of some bioactive xanthone derivatives using Vibrio harveyi test

AIMS

Drug safety evaluation plays an important role in the early phase of drug development, especially in the preclinical identification of compounds' biological activity. The Vibrio harveyi assay was used to assess mutagenic and antimutagenic activity of some aminoalkanolic derivatives of xanthone (1-5), which were synthesized and evaluated for their anticonvulsant and hemodynamic activities.

METHODS AND RESULTS

A novel V. harveyi assay was used to assess mutagenic and antimutagenic activity of derivatives of xanthone 1-5. Two V. harveyi strains were used: BB7 (natural isolate) and BB7M (BB7 derivative containing mucA and mucB genes on a plasmid pAB91273, products of these genes enhance error-prone DNA repair). According to the results obtained, the most beneficial mutagenic and antimutagenic profiles were observed for compounds 2 and 3. A modification of the chemical structure of compound 2 by the replacement of the hydroxy group by a chloride improved considerably the antimutagenic activity of the compound. Thus, antimutagenic potency reached a maximum with the presence of tertiary amine and chloride atom in the side chain.

CONCLUSIONS

Among the newly synthesized aminoalkanolic derivatives of xanthone with potential anticonvulsant properties, there are some compounds exhibiting in vitro antimutagenic activity. In addition, it appears that the V. harveyi assay can be applied for primary mutagenicity and antimutagenicity assessment of compounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

The obtained preliminary mutagenicity and antimutagenicity results encourage further search in the group of amino derivatives of xanthone as the potential antiepileptic drugs also presenting some antimutagenic potential. Furthermore, V. harveyi test may be a useful tool for compounds safety evaluation.

Enaminones 8: CoMFA and CoMSIA studies on some anticonvulsant enaminones

3D-QSAR studies comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were carried out on 26 structurally diverse subcutaneous pentylenetetrazol (scPTZ) active enaminone analogues, previously synthesized in our laboratory. CoMFA and CoMSIA were employed to generate models to define the specific structural and electrostatic features essential for enhanced binding to the putative GABA receptor. The 3D-QSAR models demonstrated a reliable ability to predict the CLogP of the active anticonvulsant enaminones, resulting in a q(2) of 0.558 for CoMFA, and a q(2) of 0.698 for CoMSIA. The outcomes of the contour maps for both models provide detailed insight for the structural design of novel enaminone derivatives as potential anticonvulsant agents.

Anticonvulsant activity of some xanthone derivatives

A series of appropriate alkanolamine and amide derivatives of xanthone were prepared and evaluated for anticonvulsant activity using maximal electroshock (MES) and subcutaneous pentylenetetrazole (scMet) induced seizures, and for neurotoxicity (TOX) using the rotorod test on mice and rats. The most promising compounds seem to be the appropriate aminoalkanolic derivatives of 6-chloroxanthone, among which the R-(-) and S-(+)-2amino-1-propanol derivatives of 6-chloro-2-methylxanthone (2(a) and 2(b)) displayed anti-MES activity (in mice) with a protective index (TD(50)/ED(50)) of 6.23<6.85, corresponding to that of phenytoin, carbamazepine and valproate. The most active compound, 2(b), was determined to have an affinity to the benzodiazepine (BDZ) receptor and voltage-dependent Ca(2+) channel (VDCC) by using radioligand binding assays. The enantiomeric purities of 2(a) and 2(b) were determined using an analytical liquid chromatography-mass spectrometry method.

Enaminones: Exploring Additional Therapeutic Activities

Enaminones, enamines of beta-dicarbonyl compounds, have been known for many years. Their early use has been relegated to serving as synthetic intermediates in organic synthesis and of late, in pharmaceutical development. Recently, the therapeutic potential of these entities has been realized. This review provides the background and current research in this area with emphasis of these agents as potential anticonvulsants, their proposed mechanisms of action, and as potential modulators of multidrug resistance (MDR).

Anticonvulsant enaminone E139 suppresses epileptiform activity in rat hippocampal slices

Some enaminones are reported to have in vivo anticonvulsant activity. We asked if methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate (E139), one of such enaminones produced in vitro effects that may underlie or explain these in vivo anticonvulsant actions by testing if E139 suppressed in vitro seizures. In vitro seizures were generated chemically in hippocampal slices using picrotoxin and zero Mg(2+) buffer and electrically by high frequency stimulation (HFS). E139 (10 microM) depressed evoked field population spike (PS) amplitude by -28.6+/-4.5% (n=5), an effect that was blocked by 1 microM CGP55845 (2.7+/-5.5%, n=6). Picrotoxin (100 microM) transformed single PS into multiple PS (4.5+/-0.2, n=5) and E139 reversibly reduced the number of these multiple PS by -23.4+/-1.8% (n=5). Similarly, zero Mg(2+) buffer produced multiple spikes (3.6+/-0.6, n=5) that were suppressed by E139 (-54.8+/-9.7%, n=5). This effect was also blocked by CGP55845 (2.3+/-5.7%, n=6). Furthermore, E139 suppressed the frequency of spontaneous bursts (SB) that were recorded in zero Mg(2+) by -65.8+/-10.5% (n=12). CGP55845 significantly reduced this E139-induced SB suppression (-21.7+/-9.6%, n=6). In the electrical model, afterdischarges (AD) and SB recorded in area CA3 after a pattern of HFS (100Hz) were suppressed by E139 (-48.6+/-14.3% and -66.7+/-6.7%, respectively, n=6). These E139 effects on AD and SB were reduced, but not completely blocked, by CGP55845 (-32.1+/-5.3% and -44.4+/-9.7%, respectively, n=7). Finally, pretreatment of slices with E139 did not prevent zero Mg(2+)-induced multiple spikes and SB. We conclude that E139 suppresses in vitro seizures in the hippocampus by synaptic and non-synaptic mechanisms. These actions on network activity may underlie their reported in vivo anticonvulsant effects.

Enaminones and norepinephrine employ convergent mechanisms to depress excitatory synaptic transmission in the rat nucleus accumbensin vitro

We recently reported that anticonvulsant anilino enaminones depress excitatory postsynaptic currents (EPSCs) in the nucleus accumbens (NAc) indirectly via gamma-aminobutyric acid (GABA) acting on GABA(B) receptors [S.B. Kombian et al. (2005)Br. J. Pharmacol., 145, 945-953]. Norepinephrine (NE) and dopamine (DA), both known to be involved in seizure disorders, also depress EPSCs in this nucleus. The current study explored a possible interaction between enaminones and adrenergic and/or dopaminergic mechanisms that may contribute to their synaptic depression and anticonvulsant effect. Using whole-cell recording in rat forebrain slices containing the NAc, we show that NE-induced, but not DA-induced, EPSC depression occludes E139-induced EPSC depressant effect. UK14,304, a selective alpha(2) receptor agonist, mimicked the synaptic effect of NE and also occluded E139 effects. Phentolamine, a non-selective alpha-adrenergic antagonist that blocked NE-induced EPSC depression, also blocked the E139-induced EPSC depression. Furthermore, yohimbine, an alpha(2)-adrenoceptor antagonist, also blocked the E139-induced EPSC depression, while prazosin, a selective alpha(1)-adrenergic antagonist, and propranolol, a non-selective beta-adrenoceptor antagonist, did not block the E139 effect. Similar to the E139-induced EPSC depression, the NE-induced EPSC depression was also blocked by the GABA(B) receptor antagonist, CGP55845. By contrast, however, neither SCH23390 nor sulpiride, D1-like and D2-like DA receptor antagonists, respectively, blocked the E139-induced synaptic depression. These results suggest that NE and E139, but not DA, employ a similar mechanism to depress EPSCs in the NAc, and support the hypothesis that E139, like NE, may act on alpha(2)-adrenoceptors to cause the release of GABA, which then mediates synaptic depression via GABA(B) receptors.

Concentration-dependent effects of anticonvulsant enaminone methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate on neuronal excitability in vitro

Enaminones are a novel group of compounds some of which possess anticonvulsant activity in in vivo animal models of seizures. We recently reported that some enaminones, including methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate, depress glutamate-mediated excitatory synaptic transmission and that this may contribute to their anticonvulsant activity [Kombian SB, Edafiogho IO, Ananthalakshmi KVV (2005) Anticonvulsant enaminones depress excitatory synaptic transmission in the rat brain by enhancing extracellular GABA levels. Br J Pharmacol 145:945-953]. Here we studied the effects of methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate, on the excitability of male rat (Sprague-Dawley) nucleus accumbens and hippocampal cells in vitro using whole-cell patch clamp recording techniques. At low, therapeutically relevant concentrations (0.3-10 microM), methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate reversibly suppressed action potential firing rate in a concentration-dependent manner. This action potential suppression was present when GABA(A), GABA(B) and glutamate receptors were blocked with their antagonists. Furthermore, methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate suppressed tetrodotoxin-sensitive sodium currents in these cells. At concentrations >/=100 microM, it induced inward currents and increased action potential firing frequency. The inward currents were without changes in input resistance and did not reverse polarity between -120 and -40 mV. These currents were independent of extracellular potassium, but were absent when extracellular sodium was replaced by choline and finally, were occluded by pretreatment with ouabain (200 microM). We conclude that methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate directly inhibits action potential firing at therapeutically relevant concentrations by suppressing tetrodotoxin-sensitive sodium currents, while inducing an ouabain-sensitive current at high concentrations to excite neurons. These two actions of methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate on neuronal excitability would have therapeutic implications in future clinical use of enaminones as anticonvulsants in seizure disorders.

Anticonvulsant enaminones depress excitatory synaptic transmission in the rat brain by enhancing extracellular GABA levels

Enaminones are a novel group of compounds that have been shown to possess anticonvulsant activity in in vivo animal models of seizures. The cellular mechanism by which these compounds produce their anticonvulsant effects is not yet known. This study examined the effects of enaminones on excitatory synaptic transmission. We studied the effects of 3-(4'-chlorophenyl)aminocyclohex-2-enone (E118), methyl 4-(4'-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate (E139) and ethyl 4-(4'-hydroxyphenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate (E169) on isolated evoked, glutamate-mediated excitatory synaptic responses by recording whole-cell currents and potentials in cells of the nucleus accumbens (NAc) contained in forebrain slices. The anticonvulsant enaminones (E118 and E139), but not E169, depressed NMDA and non-NMDA receptor-mediated synaptic responses. The inhibition of the non-NMDA response was concentration-dependent (1.0-100 microM) with a maximal depression of approximately -30%. E118 and E139 had similar potencies (EC(50)=3.0 and 3.5 microM, respectively) in depressing this response but E139 was more efficacious (E(max)=-31.3+/-3.8%) than E118 (E(max)=-22.6+/-1.6%). The excitatory postsynaptic current (EPSC) depression caused by 10 microM E139 (-27.7+/-3.8%) was blocked by 1 microM CGP55845 (6.3+/-8.1%), a potent GABA(B) receptor antagonist. Pretreatment of slices with gamma-vinylGABA and 1-(2-(((diphenylmethylene)imino)oxy)ethyl)-1,2,5,6-tetrahydro-3-pyridine-carboxylic acid (NO-711), an irreversible GABA transaminase (GABA-T) inhibitor and a GABA reuptake blocker, respectively, like the anticonvulsant enaminones, also caused a depression of the evoked EPSC (-38.1+/-14.1 and -24.1+/-8.9%, respectively). In the presence of these compounds, E139 did not cause a further depression of the EPSC. Our data suggest that anticonvulsant enaminones cause EPSC depression by enhancing extracellular GABA levels possibly through the inhibition of either GABA reuptake or GABA-T enzyme, or both.

Tricyclic oxazolo[2,3-f]purinediones: potency as adenosine receptor ligands and anticonvulsants

Synthesis and physicochemical properties of 7-mono- and 6,7-disubstituted dihydrooxazolo-[3,2-f]purinediones are described. Oxazolo[2,3-f]purinediones were synthesized by cyclization of 8-bromotheophylline with oxiranes. The obtained compounds (1-22) were evaluated for their affinity at adenosine A(1) and A(2A) receptors. They showed mainly adenosine A(2A) receptor affinity at low micromolar concentrations and A(2A) selectivity, for example, compound 9 with an octyl substituent at the oxazole ring displayed adenosine A(2A) receptor affinity (K(i)=0.998 microM) and at least 25-fold A(2A) versus A(1) selectivity. This compound was less selective (5-fold) towards human recombinant A(2B) and A(3) adenosine receptors. In this group of compounds active adenosine A(1) receptor antagonists were also identified. Oxazolopurinediones were evaluated in vivo as anticonvulsants in MES and ScMet tests and examined for neurotoxicity in mice (ip). Compounds with long alkyl chains showed anticonvulsant activity in both tests (in 100 and 300 mg/kg doses), accompanied by significant neurotoxicity. The anticonvulsant activity in rats (po) was higher and without signs of neurotoxicity. SAR and QSAR studies stressed the importance of lipophilic 7-substituents for both types of pharmacological activity. The volume of the substituent is, however, limited at the A(2A) AR, an n-octyl group being optimal.

A base-catalyzed solution-phase parallel synthesis of substituted vinylic benzamides from 3-amino-2-cyclohexanones

An improved method for the synthesis of benzamides from 3-amino-2-cyclohexenones is presented. Using sodium hydride, a base-catalyzed N-benzoylation provided significantly higher yields (71-79%) for the reported compounds. This novel protocol was applied in the solution-phase parallel synthesis of a 12-member library of vinylic benzamide derivatives of 3-amino-2-cyclohexenones in 63-90% yield, using a Radley's Carousel Reaction Station.

Shared mechanisms of antidepressant and antiepileptic treatments: drugs and devices

Many treatments for the epilepsies and affective disorder share the properties of seizure suppression and mood stabilization. Moreover, affective disorders and the epilepsies appear to share partially similar pathogenic mechanisms. A component of the shared predisposition appears to arise from noradrenergic and serotonergic deficits. Increasing evidence supports the hypothesis that noradrenergic and/or serotonergic elevation is a mechanism of therapeutic benefit shared by most antidepressants and many antiepileptic medications. Medication induced alterations in GABAergic, glutamatergic, and CRH (corticotropin releasing hormone) containing neurons may also contribute to the shared therapeutic properties of antidepressant and antiepileptic medications.

Preclinical evaluation of the pharmacokinetics, brain uptake and metabolism of E121, an antiepileptic enaminone ester, in rats

The present study describes the brain uptake, pharmacokinetics and metabolism of an anticonvulsant enaminone ester E121, which belongs to a new and active series of compounds with potential in vivo anticonvulsant activity in rodent models, in rats. A single dose of E121 was administered i.p. to male Sprague Dawley rats at 10 mg E121/kg body weight. Cohorts of animals (n=3) were killed at varying times over 0-24 h to collect plasma and brain samples. Urinary excretion of E121 was studied in a separate group of five rats at the same dose. A validated HPLC method was used to quantify E121 and its metabolites in plasma, brain and urine. LC-MS/MS was used to characterize the metabolites. The plasma and brain Cmax of 11.0+/-3.0 mg/l and 10.4+/-1.4 mg/kg, respectively, were observed for E121 at 15 min post dose and they declined in a mono-exponential fashion. The plasma Cl/F and t1/2 were 0.57 l/h/kg and 0.75 h, respectively. The brain uptake ratio of E121 was 0.9. Mass spectral analysis of urine showed two major metabolites (m/z 280) and one minor metabolite (m/z 236) that were consistent with initial hydrolysis of the compound to the acid followed by further decarboxylation and appears to be the major route of elimination of E121. The rapid and moderate brain uptake of E121 correlates well with its potential anticonvulsant activity (ED50 3.0 mg/kg p.o. in rats). The brain uptake, pharmacokinetic and metabolic profile of E121 supports the need to further evaluate this compound for its potential as an antiepileptic.

Determination of the enaminone DM5, an anti-epileptic agent, in mouse plasma and brain tissue by high-performance liquid chromatography with ultraviolet detection

Enaminone derivatives of the 4-carbomethoxy-5-methylcyclohexane-1,3-dione series represent a new and potentially active series of compounds for the treatment of Epilepsy. Enaminone esters have been previously evaluated as compounds with potent oral anticonvulsant activity similar to class 1 anticonvulsants phenytoin, carbamazepine, and lamotrigine. DM5, a member of this class with -Cl in the para-substituted position, has been assessed to have the most potent pharmacological activity (ED50) in both the mouse and rat. A selective and specific high-performance liquid chromatography method was developed to quantitate DM5 in plasma and brain tissue in mice. Reverse phase chromatography with ultraviolet (lambda = 307 nm) detection was utilized to quantitate eluate. A C18 analytical column was used and the mobile phase consisted of acetonitrile and 0.05 M NaH2PO4 buffer (60:40; v/v). Liquid-liquid extraction with ether was used to extract the DM5 from plasma or brain homogenates. DM5 and carbamazepine (internal standard) eluted at approximately 6.0 and 9.0 min without any interfering peaks. The calibration curves were found to be linear (r > or = 0.9999) in the range of 0.1-5.0 microg/ml or microg/g. Intra-run precision's were in all in the range of 90%. The absolute recovery of the analyte in brain and plasma samples was < or = 90%. The valid method accurately quantified DM5 in plasma and brain tissue samples collected from a pharmacokinetic study consisting of an intravenous bolus in the tail vein of wild type and genetically altered mice.

Synthesis, characterization, and anticonvulsant activity of enaminones. Part 5: investigations on 3-carboalkoxy-2-methyl-2,3-dihydro-1H-phenothizin-4[10H]-one derivatives

A new series of anticonvulsant 3-carboalkoxy-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-on es is herein reported. 2-Aminothiophenols underwent cyclocondensation with 4-carboalkoxy-5-methylcyclohexane-1,3-diones in refluxing dimethylsulfoxide (DMSO) to yield 3-carboalkoxy-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-on es, 4ak. In the case of the carbo-tert-butoxy derivatives (4c and 4k) prolonged reaction times led to the isolation of the respective 3-unsubstituted-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-ones (41 and 4m) instead. Significant anticonvulsant activity was displayed by these analogues, most particularly 4k, which was active at 30 mg/kg intraperitoneally (ip) in mice in the maximal electroshock seizure (MES) evaluation, with no toxicity noted at dosages up to 300 mg/kg. Oral (p.o.) rat evaluation of 4k in the MES evaluation provided an ED50 of 17.60 mg/kg, with no toxicity noted at dosages up to 500 mg/kg, providing a protective index (PI = TD50/ED50) > 28.40. These compounds represent the first reported series of phenothiazines which possess anticonvulsant activity.

Nuclear magnetic resonance studies of anticonvulsant enaminones

1H nuclear magnetic resonance (NMR) spectra of enaminones were determined and compared to the anticonvulsant activity of the compounds. Although the precise employment of the NMR data to predict anticonvulsant activity of the enaminones could not be established, general inferences were made. The NMR data confirmed that the enaminones existed predominantly in the amino tautomer, and no evidence was found for the imino tautomer. The ketamine form of the enaminones was supported by the observed spin-spin splittings of the NH with the alpha-protons on certain enaminones. The NH of secondary enaminones was very important in conferring anticonvulsant activity to the enaminones. The peak for the NH proton which could be seen between delta (ppm) 4.50 and 9.70 was present in all of the active enaminones. The tertiary enaminones, which were devoid of the NH proton, were uniformly inactive. It appeared that a combination of steric and electronic effects, lipophilicity, and hydrogen bonding were necessary for the anticonvulsant activity of the enaminones. The cyclic enaminones existed in the trans-S-trans fixed conformation, and the NMR data supported our hypothesis that enantioselectivity is retained in synthesizing enaminones from cyclic, diasteriomeric 1,3-diketones. In addition, the AB system and many unique features were observed in some enaminones. The para, meta, and ortho substituted patterns were observed for monosubstituted phenyl protons, and the NMR patterns for di- and trisubstituted phenyl groups were elucidated.