Synthesis and anticonvulsant activity of novel and potent 2,3-benzodiazepine AMPA/kainate receptor antagonists

A Proteomic Platform Unveils the Brain Glycogen Phosphorylase as a Potential Therapeutic Target for Glioblastoma Multiforme

In the last few years, several efforts have been made to identify original strategies against glioblastoma multiforme (GBM): this requires a more detailed investigation of the molecular mechanism of GBM so that novel targets can be identified for new possible therapeutic agents. Here, using a combined biochemical and proteomic approach, we evaluated the ability of a blood–brain barrier-permeable 2,3-benzodiazepin-4-one, called 1g, to interfere with the activity and the expression of brain glycogen phosphorylase (PYGB) on U87MG cell line in parallel with the capability of this compound to inhibit the cell growth and cycle. Thus, our results highlighted PYGB as a potential therapeutic target in GBM prompting 1g as a capable anticancer drug thanks to its ability to negatively modulate the uptake and metabolism of glucose, the so-called “Warburg effect”, whose increase is considered a common feature of cancer cells in respect of their normal counterparts.

Synthesis of new tricyclic imidazotriazepine derivatives condensed with various heterocycles

Previously synthesized 9-aryl-5H-imidazo[2,1-d][1,2,5]triazepin-6(7H)-ones have been used as starting materials for the synthesis of three new tricyclic ring systems, where an imidazotriazepine is condensed with an imidazole, triazole or tetrazole ring. These novel compounds could be potential drug candidates for central nervous system diseases because of their closely related structure to known tricyclic derivatives with anticonvulsant activity.

Development of novel N-3-bromoisoxazolin-5-yl substituted 2,3-benzodiazepines as noncompetitive AMPAR antagonists

In this work, we designed and synthesized novel N-3-bromoisoxazolin-5-yl substituted 2,3-benzodiazepines as noncompetitive AMPAR antagonists, with the aim that this heterocycle could establish favourable interactions with a putative binding pocket of the receptor, like the thiadiazole nucleus of GYKI 47409 does. Within this investigation, we identified some active molecules and, among these 2,3-benzodiazepines, 4c showed a much improved inhibitory potency as compared with unsubstituted 2,3-benzodiazepines.

Structural Bases of Noncompetitive Inhibition of AMPA-Subtype Ionotropic Glutamate Receptors by Antiepileptic Drugs

Excitatory neurotransmission plays a key role in epileptogenesis. Correspondingly, AMPA-subtype ionotropic glutamate receptors, which mediate the majority of excitatory neurotransmission and contribute to seizure generation and spread, have emerged as promising targets for epilepsy therapy. The most potent and well-tolerated AMPA receptor inhibitors act via a noncompetitive mechanism, but many of them produce adverse side effects. The design of better drugs is hampered by the lack of a structural understanding of noncompetitive inhibition. Here, we report crystal structures of the rat AMPA-subtype GluA2 receptor in complex with three noncompetitive inhibitors. The inhibitors bind to a novel binding site, completely conserved between rat and human, at the interface between the ion channel and linkers connecting it to the ligand-binding domains. We propose that the inhibitors stabilize the AMPA receptor closed state by acting as wedges between the transmembrane segments, thereby preventing gating rearrangements that are necessary for ion channel opening.

Mechanism-based design of 2,3-benzodiazepine inhibitors for AMPA receptors

2,3-Benzodiazepine (2,3-BDZ) compounds represent a group of structurally diverse, small-molecule antagonists of (R, S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptors. Antagonists of AMPA receptors are drug candidates for potential treatment of a number of neurological disorders such as epilepsy, stroke and amyotrophic lateral sclerosis (ALS). How to make better inhibitors, such as 2,3-BDZs, has been an enduring quest in drug discovery. Among a few available tools to address this specific question for making better 2,3-BDZs, perhaps the best one is to use mechanistic clues from studies of the existing antagonists to design and discover more selective and more potent antagonists. Here I review recent work in this area, and propose some ideas in the continuing effort of developing newer 2,3-BDZs for tighter control of AMPA receptor activities in vivo.

Mechanism and site of inhibition of AMPA receptors: pairing a thiadiazole with a 2,3-benzodiazepine scaffold

2,3-Benzodiazepine compounds are synthesized as drug candidates for treatment of various neurological disorders involving excessive activity of AMPA receptors. Here we report that pairing a thiadiazole moiety with a 2,3-benzodiazepine scaffold via the N-3 position yields an inhibitor type with >28-fold better potency and selectivity on AMPA receptors than the 2,3-benzodiazepine scaffold alone. Using whole-cell recording, we characterized two thiadiazolyl compounds, that is, one contains a 1,3,4-thiadiazole moiety and the other contains a 1,2,4-thiadiazole-3-one moiety. These compounds exhibit potent, equal inhibition of both the closed-channel and the open-channel conformations of all four homomeric AMPA receptor channels and two GluA2R-containing complex AMPA receptor channels. Furthermore, these compounds bind to the same receptor site as GYKI 52466 does, a site we previously termed as the "M" site. A thiadiazole moiety is thought to occupy more fully the side pocket of the receptor site or the "M" site, thereby generating a stronger, multivalent interaction between the inhibitor and the receptor binding site. We suggest that, as a heterocycle, a thiadiazole can be further modified chemically to produce a new class of even more potent, noncompetitive inhibitors of AMPA receptors.

Mechanism of inhibition of the GluA2 AMPA receptor channel opening by talampanel and its enantiomer: the stereochemistry of the 4-methyl group on the diazepine ring of 2,3-benzodiazepine derivatives

Stereoselectivity of 2,3-benzodiazepine compounds provides a unique way for the design of stereoisomers as more selective and more potent inhibitors as drug candidates for treatment of the neurological diseases involving excessive activity of AMPA receptors. Here we investigate a pair of enantiomers known as Talampanel and its (+) counterpart about their mechanism of inhibition and selectivity toward four AMPA receptor subunits or GluA1-4. We show that Talampanel is the eutomer with the endismic ratio being 14 for the closed-channel and 10 for the open-channel state of GluA2. Kinetic evidence supports that Talampanel is a noncompetitive inhibitor and it binds to the same site for those 2,3-benzodiazepine compounds with the C-4 methyl group on the diazepine ring. This site, which we term as the "M" site, recognizes preferentially those 2,3-benzodiazepine compounds with the C-4 methyl group being in the R configuration, as in the chemical structure of Talampanel. Given that Talampanel inhibits GluA1 and GluA2, but is virtually ineffective on the GluA3 and GluA4 AMPA receptor subunits, we hypothesize that the "M" site(s) on GluA1 and GluA2 to which Talampanel binds is different from that on GluA3 and GluA4. If the molecular properties of the AMPA receptors and Talampanel are used for selecting an inhibitor as a single drug candidate for controlling the activity of all AMPA receptors in vivo, Talampanel is not ideal. Our results further suggest that addition of longer acyl groups to the N-3 position should produce more potent 2,3-benzodiazepine inhibitors for the "M" site.

A series of structurally novel heterotricyclic alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor-selective antagonists

BACKGROUND AND PURPOSE

A new class of heterotricyclic glutamate analogues recently was generated by incorporating structural elements of two excitotoxic marine compounds, kainic acid and neodysiherbaine A. Rather than acting as convulsants, several of these 'IKM' compounds markedly depressed CNS activity in mice. Here, we characterize the pharmacological profile of the series with a focus on the most potent of these molecules, IKM-159.

EXPERIMENTAL APPROACH

The pharmacological activity and specificity of IKM compounds were characterized using whole-cell patch clamp recording from neurons and heterologous receptor expression systems, in combination with radioligand binding techniques.

KEY RESULTS

The majority of the IKM compounds tested reduced excitatory synaptic transmission in neuronal cultures, and IKM-159 inhibited synaptic currents from CA1 pyramidal neurons in hippocampal slices. IKM-159 inhibited glutamate-evoked whole-cell currents from recombinant GluA2- and GluA4-containing alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptors most potently, whereas kainate and NMDA receptor currents were not reduced by IKM-159. Antagonism of steady-state currents was agonist concentration dependent, suggesting that its mechanism of action was competitive, although it paradoxically did not displace [(3)H]-AMPA from receptor binding sites. IKM-159 reduced spontaneous action potential firing in both cultured hippocampal neurons in control conditions and during hyperactive states in an in vitro model of status epilepticus.

CONCLUSIONS AND IMPLICATIONS

IKM-159 is an AMPA receptor-selective antagonist. IKM-159 and related nitrogen heterocycles represent structurally novel AMPA receptor antagonists with accessible synthetic pathways and potentially unique pharmacology, which could be of use in exploring the role of specific populations of receptors in neurophysiological and neuropathological processes.

Neuroprotective and anticonvulsant effects of EGIS-8332, a non-competitive AMPA receptor antagonist, in a range of animal models

BACKGROUND AND PURPOSE

Blockade of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors is a good treatment option for a variety of central nervous system disorders. The present study evaluated the neuroprotective and anticonvulsant effects of EGIS-8332, a non-competitive AMPA receptor antagonist, as a potential drug candidate.

EXPERIMENTAL APPROACH

AMPA antagonist effects of EGIS-8332 were measured using patch-clamp techniques. Neuroprotective and anticonvulsant effects of EGIS-8332 were evaluated in various experimental models, relative to those of GYKI 53405.

KEY RESULTS

EGIS-8332 inhibited AMPA currents in rat cerebellar Purkinje cells and inhibited the AMPA- and quisqualate-induced excitotoxicity in primary cultures of telencephalon neurons (IC(50)=5.1-9.0 microM), in vitro. Good anticonvulsant actions were obtained in maximal electroshock-, sound- and chemically-induced seizures (range of ED(50)=1.4-14.0 mg kg(-1) i.p.) in mice. Four days after transient global cerebral ischaemia, EGIS-8332 decreased neuronal loss in the hippocampal CA1 area in gerbils and rats. EGIS-8332 dose-dependently reduced cerebral infarct size after permanent middle cerebral artery occlusion in mice and rats (minimum effective dose=3 mg kg(-1) i.p.). Side effects of EGIS-8332 emerged much above its pharmacologically active doses. A tendency for better efficacy of GYKI 53405 than that of EGIS-8332 was observed in anticonvulsant tests that reached statistical significance in few cases, while the contrary was perceived in cerebral ischaemia tests.

CONCLUSIONS AND IMPLICATIONS

EGIS-8332 seems suitable for further development for the treatment of epilepsy, ischaemia and stroke based on its efficacy in a variety of experimental disease models, and on its low side effect potential.

Synthesis of novel 3-(alkylcarbamoyl)-2-aryl-1,2-dihydro-6,7-(methylenedioxy)-3H-quinazolin-4-ones as anticonvulsant agents

A series of 3-(alkylcarbamoyl)-2-aryl-1,2-dihydro-6,7-(methylenedioxy)-3H-quinazolin-4-ones, compounds 3-6, were synthesized, and screened as anticonvulsant agents in DBA/2 mice against sound-induced seizure (Table). The new compounds were found to display anticonvulsant properties inferior to those of the known dehydro congeners 1 and 2. The binding affinities of 1-6 at the AMPA and NMDA receptors were also evaluated.

New 7,8-ethylenedioxy-2,3-benzodiazepines as noncompetitive AMPA receptor antagonists

A series of 1-aryl-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-ones 2a-f, were synthesized and screened as anticonvulsant agents in DBA/2 mice against sound-induced seizures. The new compounds display anticonvulsant properties although the ED(50) values are higher than those of prototypes 1-aryl-3,5-dihydro-7,8-methylenedioxy-4H-2,3-benzodiazepin-4-ones (1) and GYKI 52466, well-known noncompetitive AMPA receptor antagonists. Functional tests were performed to evaluate the antagonistic activity at the AMPA and kainate receptors.

Novel α-Amino-3-hydroxy-5-methyl-4-isoxazole Propionate (AMPA) Receptor Antagonists of 2,3-Benzodiazepine Type: Chemical Synthesis, in Vitro Characterization, and in Vivo Prevention of Acute Neurodegeneration

Under pathophysiological conditions, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor activation is considered to play a key role in several disorders of the central nervous system. In the search for AMPA receptor antagonists, the synthesis and pharmacological characterization of a series of novel compounds that are structurally related to GYKI 52466 (1), a well-known selective noncompetitive AMPA receptor antagonist, was performed. In vitro, 2,3-dimethyl-6-phenyl-12H-[1,3]dioxolo[4,5-h]imidazo[1,2-c][2,3]benzodiazepine (ZK 187638, 14a) antagonized the kainate-induced currents in cultured hippocampal neurons with an IC(50) of 3.4 microM in a noncompetitive fashion. When tested in a clinically predictive rat model of acute ischemic stroke, this noncompetitive AMPA receptor antagonist significantly reduced brain infarction, indicating that it is neuroprotective after permanent focal cerebral ischemia.

Design of 1-substituted 2-arylmethyl-4,5-methylenedioxybenzene derivatives as antiseizure agents

A series of 1-substituted 2-[(4-aryl)-methyl]-4,5-methylenedioxybenzene derivatives (13-25), structurally related to model compound 5 (2-[(4-aminophenyl)-(4-methylsemicarbazono)-methyl]-4,5-methylenedioxyphenylacetic acid methyl ester), were synthesized and tested as anticonvulsant agents in DBA/2 mice against sound-induced seizures. The new compounds possess anticonvulsant properties lower than those of prototype 5 but, in some instances, comparable to that of GYKI 52466, a well-known noncompetitive AMPA receptor antagonist.

QSAR Study of Anticonvulsant Negative Allosteric Modulators of the AMPA Receptor

A quantitative structure-activity relationship (QSAR) study was performed on a set of 49 negative allosteric modulators of AMPA receptor, acting as anticonvulsant agents, using multiple linear regression. The predictive ability of the resulting model was evaluated against a set of 12 compounds; the results showed good statistics in regression and revealed high correlation between anticonvulsant activity and some electrotopological descriptors.

1-Aryl-6,7-methylenedioxy-3 H -quinazolin-4-ones as anticonvulsant agents

A set of novel 1-aryl-6,7-methylenedioxy-3H-quinazolin-4-(thi)ones (3a-f) has been designed and screened as anticonvulsant agents in DBA/2 mice. The new compounds are provided with anticonvulsant properties comparable to those of GYKI 52466. To clarify the mode of action, their affinity for the quinazolinone/2,3-benzodiazepine site of the AMPA receptor complex has been assayed.

Design and synthesis of 4H-3-(2-phenoxy)phenyl-1,2,4-triazole derivatives as benzodiazepine receptor agonists

A series of new 5-substituted analogues of 4H-3-(2-phenoxy)phenyl-1,2,4-triazole and its chlorinated derivatives was designed and prepared. Conformational analysis and superimposition of energy minima conformers of the compounds on estazolam, a known benzodiazepine receptor agonist, revealed that the main proposed benzodiazepine pharmacophores were well matched. Rotarod and pentylenetetrazole-induced lethal convulsion tests showed that the introduction of an amino group in position 5 of 1,2,4-triazole ring especially in chlorinated derivatives had the best effect which was comparable with diazepam.

Characterization of the mechanism of anticonvulsant activity for a selected set of putative AMPA receptor antagonists

A selected set of 1-aryl-7,8-methylenedioxy-2,3-benzodiazepin-4-ones and their analogues were evaluated for their ability to bind the competitive and noncompetitive sites of the AMPA receptors complex as well as to the glycine site of the NMDA receptors. The results put in evidence that most of the test compounds, despite a close structural similarity with GYKI 52466, possess a significantly different pharmacological profile.

One-pot synthesis of 2,4-benzodiazepin-1-ones using benzotriazole methodology

2, 4-Benzodiazepin-1-ones were prepared in moderate to good yields by reaction of bis(benzotriazolylmethyl)amines with ortho-metalated N-substituted benzamides.

Novel potent AMPA/kainate receptor antagonists: synthesis and anticonvulsant activity of a series of 2-[(4-alkylsemicarbazono)-(4-amino-phenyl)methyl]-4,5-methylenedioxyphenylacetic acid alkyl esters

In this paper we describe the synthesis of a series of novel 2-[(4-alkylsemicarbazono)-(4-aminophenyl)-methyl]-4,5-methylenedioxyphenylacetic acid alkyl esters (10-19) carrying an alkylsemicarbazono moiety at a benzylic site. The influence of this group on the biological activity was evaluated by testing the corresponding derivatives 20-22 in which the 4-alkylsemicarbazono moiety was removed (compound 20) or its alkylureido portion shifted at position 1 (compounds 21-22). Furthermore, the involvement of the 4-aminobenzyl moiety in the anticonvulsant activity was evaluated by testing derivative 23. The anticonvulsant activity of all compounds was assayed against audiogenic seizures induced in DBA/2 mice. Within this series of derivatives, 2-[(4-aminophenyl)-(4-methylsemicarbazono)-methyl]-4,5-methylenedioxyphenylacetic acid methyl ester (10) proved to be the most active compound. It displayed a potency 5-fold higher than that shown by 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (1, GYKI 52466), a well-known noncompetitive 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptor antagonist. Compound 10 was also effective in suppressing seizures induced in Swiss mice by maximal electroshock (MES) or pentylenetetrazole (PTZ). Furthermore, it antagonized in vivo seizures induced by icv administration of AMPA or kainate (KA). Using the patch-clamp technique in primary cultures of granule neurons we tested compounds 10 and 21 for their ability to modulate currents evoked by KA and 2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propionic acid (ATPA). These two derivatives reduced KA and ATPA currents to a larger extent than that shown by reference compound 1. Compounds 10 and 21 were also able to reduce neuronal cell death induced by the application of KA (100 microM).

Synthesis and anticonvulsant activity of novel and potent 1-aryl-7,8-methylenedioxy-1,2,3,5-tetrahydro-4H-2,3-benzodiazepin-4-ones

The synthesis and anticonvulsant activity of 1-aryl-7,8-methylenedioxy-1,2,3,5-tetrahydro-4H-2,3-benzodiazepin-4-(thi)ones (4a-d) and their 3-N-alkylcarbamoyl derivatives (4e-h) are reported. The new compounds possess marked anticonvulsant properties, comparable to those of the dehydro analogues 3 and higher than that of GYKI 52466 (1). Noteworthy, compound 4c shows a longer-lasting anticonvulsant activity. Electrophysiological experiments show that derivative 4c is less effective than 1 and 3c to reduce the KA-evoked currents in cerebellar granule neurons.

Synthesis and evaluation of pharmacological and pharmacokinetic properties of 11H-[1,2,4]triazolo[4,5-c][2,3]benzodiazepin-3(2H)-ones

A series of 2,3-benzodiazepine derivatives has been previously described as noncompetitive AMPA-type glutamate receptor antagonists potentially useful for treatment of epilepsy. To further explore the structure-activity relationships of AMPA antagonists, a series of 11H-[1,2,4]triazolo[4,5-c][2,3]benzodiazepin-3(2H)-ones (6) was synthesized starting from the corresponding bicyclic 1-aryl-3, 5-dihydro-7,8-dimethoxy-4H-2,3-benzodiazepin-4-ones (2, CFM). The new compounds were found to possess anticonvulsant effects against seizures induced both by means of auditory stimulation in DBA/2 mice and by pentylenetetrazole or maximal electroshock in Swiss mice. In addition, they antagonize the AMPA-induced seizures, and their anticonvulsant activity is reversed by pretreatment with aniracetam, thus suggesting the involvement of AMPA receptors. The pharmacological studies revealed that the 11H-[1,2,4]triazolo[4, 5-c][2,3]benzodiazepin-3(2H)-ones (6) herein reported show anticonvulsant activity comparable to that of their bicyclic precursors. Furthermore, an HPLC study put in evidence that these tricyclic derivatives 6 were converted in vivo into the corresponding 2, the agents likely to be mainly responsible for the anticonvulsant properties observed.

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.

New non competitive AMPA antagonists

New halogen atom substituted 2,3-benzodiazepine derivatives condensed with an azole ring on the seven membered part of the ring system of type 3 and 4 as well as 5 and 6 were synthesized. It was found that chloro-, dichloro- and bromo-substitutions in the benzene ring and additionally imidazole ring condensation on the diazepine ring can successfully substitute the methylenedioxy group in the well known molecules GYKI 52466 (1) and GYKI 53773 (2) and the 3-acetyl-4-methyl structural feature in 2, respectively, preserving the highly active AMPA antagonist characteristic of the original molecules. From the most active compounds (3b,i) 3b (GYKI 47261) was chosen for detailed investigations. 3b revealed an excellent, broad spectrum anticonvulsant activity against seizures evoked by electroshock and different chemoconvulsive agents indicating a possible antiepileptic efficacy. 3b was found to be highly active in a transient model of focal ischemia predictive of a therapeutic value in human stroke. 3b also reversed the dopamine depleting effect of MPTP and antagonized the oxotremorine induced tremor in mice indicating a potential antiparkinson activity.

Synthesis and anticonvulsant activity of novel and potent 6,7-methylenedioxyphthalazin-1(2H)-ones

In this paper, we describe the synthesis of a series of novel substituted 4-aryl-6,7-methylenedioxyphthalazin-1(2H)-ones. The anticonvulsant activity of these compounds against audiogenic seizures was evaluated in DBA/2 mice after intraperitoneal (ip) injection. Most of these derivatives are more active than 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (1, GYKI 52466), a well-known noncompetitive AMPA receptor antagonist. As deduced by the rotarod test, all the compounds exhibit a toxicity lower than that of 1. Within the series of derivatives submitted to investigation, 4-(4-aminophenyl)-2-butylcarbamoyl-6,7-methylenedioxyphthalazin -1(2H)-one (21) proved to be the most active compound and is 11-fold more potent than 1 (i.e., ED50 3.25 micromol/kg for 21 versus ED50 35.8 micromol/kg for 1). When compared to 1, compound 21 as well as its analogue 4-(4-aminophenyl)-6,7-methylenedioxyphthalazin-1(2H)-one (16) show a longer lasting anticonvulsant activity. Compound 21 also effectively suppresses seizures induced in Swiss mice by maximal electroshock (MES) and pentylenetetrazole (PTZ). Furthermore, it antagonizes in vivo seizures induced by 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA), 2-amino-3-(3-hydroxy-5-tert-butyl-isoxazol-4-yl)propionic acid (ATPA), and kainate (KA), and its anticonvulsant activity is reversed by pretreatment with aniracetam. Using the patch-clamp technique, the capability of derivatives 16 and 21 to antagonize KA-evoked currents in primary cultures of granule neurons was tested. They behaved as antagonists, but they proved to be less effective than 1 and 1-(4-aminophenyl)-3,4-dihydro-4-methyl-3-N-methylcarbamoyl-7,8-met hylenedioxy-5H-2,3-benzodiazepine (2, GYKI 53655) to reduce the KA-evoked currents.