Cannabidiol in the treatment of epilepsy: Current evidence and perspectives for further research.

The therapeutic potential of cannabidiol (CBD) in seizure disorders has been known for many years, but it is only in the last decade that major progress has been made in characterizing its preclinical and clinical properties as an antiseizure medication. The mechanisms responsible for protection against seizures are not fully understood, but they are likely to be multifactorial and to include, among others, antagonism of G protein-coupled receptor, desensitization of transient receptor potential vanilloid type 1 channels, potentiation of adenosine-mediated signaling, and enhancement of GABAergic transmission. CBD has a low and highly variable oral bioavailability, and can be a victim and perpetrator of many drug-drug interactions. A pharmaceutical-grade formulation of purified CBD derived from Cannabis sativa has been evaluated in several randomized placebo-controlled adjunctive-therapy trials, which resulted in its regulatory approval for the treatment of seizures associated with Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex. Interpretation of results of these trials, however, has been complicated by the occurrence of an interaction with clobazam, which leads to a prominent increase in the plasma concentration of the active metabolite N-desmethylclobazam in CBD-treated patients. Despite impressive advances, significant gaps in knowledge still remain. Areas that require further investigation include the mechanisms underlying the antiseizure activity of CBD in different syndromes, its pharmacokinetic profile in infants and children, potential relationships between plasma drug concentration and clinical response, interactions with other co-administered medications, potential efficacy in other epilepsy syndromes, and magnitude of antiseizure effects independent from interactions with clobazam. This article is part of the special issue on 'Cannabinoids'.

Teratogenicity of valproic acid and its constitutional isomer, amide derivative valnoctamide in mice.

OBJECTIVES: The anticonvulsant valproic acid (VPA) has a known teratogenic effect capable of inducing major congenital malformations and developmental disorders. A comparative teratogenicity study of VPA and its analog valnoctamide (VCD), which is a new generation candidate antiepileptic drug, was carried out using Swiss Vancouver (SWV) mice. METHODS: Pregnant SWV dams were treated with either a single intraperitoneal injection of VPA (1.8 and 2.7 mmol/kg), VCD (1.8 and 2.7 mmol/kg), or vehicle on E8:12 (gestational day:hour). The numbers of implantation and resorption, viable and dead fetuses, and the presence of gross fetal visceral and skeletal abnormalities were determined (E18). Real-time Polymerase chain reaction (RT-PCR) arrays were used to analyze the expression of 84 genes related to the processes of neurogenesis and neural stem cell differentiation. RESULTS: Significant decreases in pregnancy weight gain and the number of live fetuses were observed when VPA was administered at the high dose, whereas the percentage of exencephalic fetuses was significantly increased in VPA treated compared with an equivalent VCD dosage group. There was a dose-related increase in visceral defects in the VPA-exposed fetuses. Missing skull bones and fused vertebrae in fetuses occurred at the high dose of VPA. Three genes (Mtap2, Bmp8b, and Stat3) were significantly upregulated and one (Heyl) was downregulated in samples from VPA-treated dams. CONCLUSIONS: The study demonstrates that the teratogenicity of VPA was significantly greater than that of an equimolar dose of VCD. Four genes (Mtap2, Bmp8b, Stat3, and Heyl) represent candidate target genes for the underlying teratogenic mechanism responsible for VPA-induced malformations.

Design and Comparative Evaluation of the Anticonvulsant Profile, Carbonic-Anhydrate Inhibition and Teratogenicity of Novel Carbamate Derivatives of Branched Aliphatic Carboxylic Acids with 4-Aminobenzensulfonamide.

Epilepsy is one of the most common neurological diseases, with between 34 and 76 per 100,000 people developing epilepsy annually. Epilepsy therapy for the past 100+ years is based on the use of antiepileptic drugs (AEDs). Despite the availability of more than twenty old and new AEDs, approximately 30% of patients with epilepsy are not seizure-free with the existing medications. In addition, the clinical use of the existing AEDs is restricted by their side-effects, including the teratogenicity associated with valproic acid that restricts its use in women of child-bearing age. Thus, there is an unmet clinical need to develop new, effective AEDs. In the present study, a novel class of carbamates incorporating phenethyl or branched aliphatic chains with 6-9 carbons in their side-chain, and 4-benzenesulfonamide-carbamate moieties were synthesized and evaluated for their anticonvulsant activity, teratogenicity and carbonic anhydrase (CA) inhibition. Three of the ten newly synthesized carbamates showed anticonvulsant activity in the maximal-electroshock (MES) and 6 Hz tests in rodents. In mice, 3-methyl-2-propylpentyl(4-sulfamoylphenyl)carbamate(1), 3-methyl-pentan-2-yl-(4-sulfamoylphenyl)carbamate (9) and 3-methylpentyl, (4-sulfamoylphenyl)carbamate (10) had ED50 values of 136, 31 and 14 mg/kg (MES) and 74, 53, and 80 mg/kg (6 Hz), respectively. Compound (10) had rat-MES-ED50 = 13 mg/kg and ED50 of 59 mg/kg at the mouse-corneal-kindling test. These potent carbamates (1,9,10) induced neural tube defects only at doses markedly exceeding their anticonvuslnat-ED50 values. None of these compounds were potent inhibitors of CA IV, but inhibited CA isoforms I, II and VII. The anticonvulsant properties of these compounds and particularly compound 10 make them potential candidates for further evaluation and development as new AEDs.

Progress report on new antiepileptic drugs: A summary of the Thirteenth Eilat Conference on New Antiepileptic Drugs and Devices (EILAT XIII).

The Thirteenth Eilat Conference on New Antiepileptic Drugs and Devices (EILAT XIII) took place in Madrid, Spain, on June 26-29, 2016, and was attended by >200 delegates from 31 countries. The present Progress Report provides an update on experimental and clinical results for drugs presented at the Conference. Compounds for which summary data are presented include an AED approved in 2016 (brivaracetam), 12 drugs in phase I-III clinical development (adenosine, allopregnanolone, bumetanide, cannabidiol, cannabidivarin, 2-deoxy-d-glucose, everolimus, fenfluramine, huperzine A, minocycline, SAGE-217, and valnoctamide) and 6 compounds or classes of compounds for which only preclinical data are available (bumetanide derivatives, sec-butylpropylacetamide, FV-082, 1OP-2198, NAX 810-2, and SAGE-689). Overall, the results presented at the Conference show that considerable efforts are ongoing into discovery and development of AEDs with potentially improved therapeutic profiles compared with existing agents. Many of the drugs discussed in this report show innovative mechanisms of action and many have shown promising results in patients with pharmacoresistant epilepsies, including previously neglected rare and severe epilepsy syndromes.

Progress report on new antiepileptic drugs: A summary of the Twelfth Eilat Conference (EILAT XII).

The Twelfth Eilat Conference on New Antiepileptic Drugs (AEDs) - EILAT XII, took place in Madrid, Spain from August 31st to September 3rd 2014. About 130 basic scientists, clinical pharmacologists and neurologists from 22 countries attended the conference, whose main themes included "Conquering pharmacoresistant epilepsy", "Innovative emergency treatments", "Progress report on second-generation treatment" and "New methods and formulations". Consistent with previous formats of this conference, a large part of the program was devoted to a review of AEDs in development, as well as updates on AEDs introduced since 2004. Like the EILAT X and EILAT XI reports, the current article focuses on the preclinical and clinical pharmacology of AEDs that are currently in development. These include adenosine-releasing silk, allopregnanolone (SAGE-547), AMP-X-0079, brivaracetam, bumetanide, cannabidiol, cannabidivarin, 2-deoxy-glucose, everolimus, ganaxolone, huperzine A, imepitoin, minocycline, NAX 801-2, pitolisant, PRX 0023, SAGE-217, valnoctamide and its homologue sec-butyl-propylacetamide (SPD), and VLB-01. Since the previous Eilat conference, perampanel has been introduced into the market and twelve novel potential epilepsy treatments are presented for the first time.

Tetramethylcyclopropyl analogue of the leading antiepileptic drug, valproic acid: evaluation of the teratogenic effects of its amide derivatives in NMRI mice.

BACKGROUND: Although valproic acid (VPA) is used extensively for treating various kinds of epilepsy, it causes hepatotoxicity and teratogenicity. In an attempt to develop a more potent and safer second generation to VPA drug, the amide derivatives of the tetramethylcyclopropyl VPA analogue, 2,2,3,3-tetramethylcyclopropanecarboxamide (TMCD), N-methyl-TMCD (MTMCD), 4-(2,2,3,3-tetramethylcyclopropanecarboxamide)-benzenesulfonamide (TMCD-benzenesulfonamide), and 5-(TMCD)-1,3,4-thiadiazole-2-sulfonamide (TMCD-thiadiazolesulfonamide) were synthesized and shown to have more potent anticonvulsant activity than VPA. Teratogenic effects of these CNS-active compounds were evaluated in Naval Medical Research Institute (NMRI) mice susceptible to VPA-induced teratogenicity by comparing them to those of VPA. METHODS: Pregnant NMRI mice were given a single sc injection of either VPA or TMC-amide derivatives on gestation day 8.5, and then the live fetuses were examined to detect any external malformations on gestation day 18. After double-staining for bone and cartilage, their skeletons were examined. RESULTS: In contrast to VPA, which induced NTDs in a high number of fetuses at 2.4-4.8 mmol/kg, TMCD, TMCD-benzenesulfonamide, and TMCD-thiadiazolesulfonamide at 4.8 mmol/kg and MTMCD at 3.6 mmol/kg did not induce a significant number of NTDs. TMCD-thiadiazolesulfonamide exhibited a potential to induce limb defects in fetuses. Skeletal examination also revealed that fetuses exposed to all four of the tetramethylcyclopropanecarboxamide derivatives developed vertebral and rib abnormalities less frequently than those exposed to VPA. Our results established that TMCD, MTMCD, and TMCD-benzenesulfonamide are distinctly less teratogenic than VPA in NMRI mice. CONCLUSIONS: The CNS-active amides containing a tetramethylcyclopropanecarbonyl moiety demonstrated better anticonvulsant potency compared to VPA and a lack of teratogenicity, which makes these compounds good second-generation VPA antiepileptic drug candidates.

Development of new antiepileptic drugs: challenges, incentives, and recent advances.

Despite the introduction of many second-generation antiepileptic drugs (AEDs) in the past 15 years, a third of patients with epilepsy remain refractory to available treatments, and newer and more effective therapies are needed. Although our understanding of the mechanisms of drug resistance is fragmented, novel AED targets have been identified, and models of refractory epilepsy have been developed that can help to select candidate compounds for development. There are more than 20 compounds with potential antiepileptic activity in various stages of clinical development, and for many of these promising clinical trial results are already available. Several incentives justify further investment into the discovery of newer and more effective AEDs. Moreover, developments in clinical trial methodology enable easier completion of proof-of-concept studies, earlier definition of the therapeutic potential of candidate compounds, and more efficient completion of trials for various epilepsy indications.

Preclinical evaluation of 2,2,3,3-tetramethylcyclopropanecarbonyl-urea, a novel, second generation to valproic acid, antiepileptic drug.

2,2,3,3-Tetramethylcyclopropanecarbonylurea (TMCU) is an amide derivative of a tetramethylcyclopropyl analogue of valproic acid (VPA), one of the leading antiepileptic drugs. Structural considerations used in the design of TMCU aimed to enhance the anticonvulsant potency of VPA and to prevent its two life-threatening side effects; i.e., teratogenicity and hepatotoxicity. The anticonvulsant activity of TMCU was evaluated in the MES, scMet, 6-Hz, scBic and scPic tests, and also in the hippocampal kindling model of partial seizures and lamotrigine-resistant amygdala kindling model of therapy-resistant seizures. Minimal motor impairment was determined using the rotorod test in mice and the positional sense test, muscle tone test, and gait and stance test in rats. The antinociceptive effect of TMCU was evaluated in the mouse formalin model of acute-tonic pain. The molecular mechanisms of action of TMCU were investigated in electrophysiological studies using the whole-cell patch-clamp technique. Teratogenicity studies were performed in a SWV/Fnn-mouse model of VPA-induced teratogenicity. TMCU hepatotoxicity was evaluated following 1-week intraperitoneal and oral administration of 50, 250 and 500 mg/kg doses to rats. In the hepatotoxicity study the blood levels of TMCU were evaluated at day 1 and day 7 of the treatment. TMCU mutagenicity was evaluated in the Ames test.

New antiepileptic drugs that are second generation to existing antiepileptic drugs.

In the last decade, 10 new antiepileptic drugs (AEDs) have been introduced that offer appreciable advantages in terms of their favourable pharmacokinetics, improved tolerability and lower potential for drug interactions. However, despite the large therapeutic range of old and new AEDs, approximately 30% of the patients with epilepsy are still not seizure free and, consequently, there is a substantial need to develop new AEDs. The new AEDs currently in development can be divided into two categories: drugs with completely new chemical structures such as lacosamide (formally harkoseride), retigabine, rufinamide and talampanel; and drugs that are derivatives or analogues of existing AEDs that can be regarded as second-generation or follow-up compounds of established AEDs. This article focuses on the second category and thus critically reviews the following second-generation compounds: eslicarbazepine acetate or BIA-2-093 and 10-hydroxy carbazepine (carbamazepine derivatives); valrocemide and NPS 1776 (isovaleramide; valproic acid derivatives); pregabalin and XP13512 (gabapentin derivatives); brivaracetam (ucb 34714) and seletracetam (ucb 44212; levetiracetam derivatives); and fluorofelbamate (a felbamate derivative). In addition, a series of valproic acid derivatives that are currently in preclinical stage has also been evaluated because some lead compounds of this series have a promising potential to become new antiepileptics and CNS drugs. For any of these follow-up compounds to become a successful second generation to an existing AED, it has to be more potent, safer and possess favourable pharmacokinetics, including low potential for pharmacokinetic and pharmacodynamic drug interactions.

Correlation analysis between anticonvulsant ED50 values of antiepileptic drugs in mice and rats and their therapeutic doses and plasma levels.

OBJECTIVE: Although there are several animal models of epilepsy, the extrapolation of antiepileptic drug (AEDs) performance to epileptic patients from anticonvulsant activity results in animals is not straightforward. Consequently, the aim of this work was to perform a correlation analysis between therapeutic daily doses (D) and average steady-state plasma concentrations (Css,av) of AEDs and their activity in common anticonvulsant animal models. METHODS: AED activity in anticonvulsant animal models was expressed as maximal electroshock seizure (MES) test ED50 values in mice and rats and ED50 values in audiogenic seizure-susceptible mice (AGS ED50). Data were examined, by use of linear and logarithmic approaches, for an association between Css,av (mg/L or micromol/L) and D (mg or mmol) for each AED in epileptic patients as the dependent variable (Y) and its MES ED50 in mice and rats and AGS ED50 in mice (mg/kg or micromol/kg) as the independent variable (X). RESULTS: Linear correlation analyses between Css,av (mg/L) and ED50 (mg/kg) for 11 AEDs gave the following correlation coefficients (R2): 0.68 (mice, MES); 0.73 (rat, MES); 0.64 (AGS). Switching the units from milligrams to micromoles improved the correlation significantly and gave the following R2 values: 0.88 (mice, MES); 0.90 (rat, MES); 0.76 (AGS). The linear correlation between Css,av and ED50 was better than that between D and ED50. CONCLUSIONS: The results of this analysis suggest that the relationship between Css,av and ED50 is useful in predicting target concentration ranges in humans. The Y intercepts of the Css,av-versus-ED50 and D-versus- ED50 plots were similar in all three animal models and ranged between 12 and 17 mg/L and between 570 and 890 mg, respectively, indicating that for all AEDs analyzed except valproic acid and ethosuximide, the therapeutic plasma concentration is in the range 10-20 mg/L.

Progress report on new antiepileptic drugs: a summary of the Seventh Eilat Conference (EILAT VII).

The Seventh Eilat Conference on New Antiepileptic Drugs (AEDs) (EILAT VII) took place in Villasimius, Sardinia, Italy from the 9th to 13th May 2004. Basic scientists, clinical pharmacologists and neurologists from 24 countries attended the conference,whose main themes included advances in pathophysiology of drug resistance, new AEDs in pediatric epilepsy syndromes, modes of AED action and spectrum of adverse effects and a re-appraisal of comparative responses to AED combinations. Consistent with previous formats of this conference, the central part of the conference was devoted to a review of AEDs in development, as well as updates on second-generation AEDs. This article summarizes the information presented on drugs in development, including atipamezole, BIA-2-093, fluorofelbamate, NPS 1776, pregabalin, retigabine, safinamide, SPM 927, stiripentol, talampanel,ucb 34714 and valrocemide (TV 1901). Updates on felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine,topiramate, vigabatrin, zonisamide, new oral and parenteral formulations of valproic acid and SPM 927 and the antiepileptic vagal stimulator device are also presented.

Anticonvulsant activity, teratogenicity and pharmacokinetics of novel valproyltaurinamide derivatives in mice.

1 The purpose of this study was to synthesize novel valproyltaurine (VTA) derivatives including valproyltaurinamide (VTD), N-methyl-valproyltaurinamide (M-VTD), N,N-dimethyl-valproyltaurinamide (DM-VTD) and N-isopropyl-valproyltaurinamide (I-VTD) and evaluate their structure-pharmacokinetic-pharmacodynamic relationships with respect to anticonvulsant activity and teratogenic potential. However, their hepatotoxic potential could not be evaluated. The metabolism and pharmacokinetics of these derivatives in mice were also studied. 2 VTA lacked anticonvulsant activity, but VTD, DM-VTD and I-VTD possessed anticonvulsant activity in the Frings audiogenic seizure susceptible mice (ED(50) values of 52, 134 and 126 mg kg(-1), respectively). 3 VTA did not have any adverse effect on the reproductive outcome in the Swiss Vancouver/Fnn mice following a single i.p. injection of 600 mg kg(-1) on gestational day (GD) 8.5. VTD (600 mg kg(-1) at GD 8.5) produced an increase in embryolethality, but unlike valproic acid, it did not induce congenital malformations. DM-VTD and I-VTD (600 mg kg(-1) at GD 8.5) produced a significant increase in the incidence of gross malformations. The incidence of birth defects increased when the length of the alkyl substituent or the degree of N-alkylation increased. 4 In mice, N-alkylated VTDs underwent metabolic N-dealkylation to VTD. DM-VTD was first biotransformed to M-VTD and subsequently to VTD. I-VTD's fraction metabolized to VTD was 29%. The observed metabolic pathways suggest that active metabolites may contribute to the anticonvulsant activity of the N-alkylated VTDs and reactive intermediates may be formed during their metabolism. In mice, VTD had five to 10 times lower clearance (CL), and three times longer half-life than I-VTD and DM-VTD, making it a more attractive compound than DM-VTD and I-VTD for further development. VTD's extent of brain penetration was only half that observed for the N-alkylated taurinamides suggesting that it has a higher intrinsic activity that DM-VTD and I-VTD. 5 In conclusion, from this series of compounds, although VTD caused embryolethality, this compound emerged as the most promising new antiepileptic drug, having a preclinical spectrum characterized by the highest anticonvulsant potential, lowest potential for teratogenicity and favorable pharmacokinetics.