Design, synthesis and anticonvulsant activity of new hybrid compounds derived from N-phenyl-2-(2,5-dioxopyrrolidin-1-yl)-propanamides and -butanamides

Identification of New Antiseizure Medication Candidates in Preclinical Animal Studies

Epilepsy is a multifactorial neurologic disease that often leads to many devastating disabilities and an enormous burden on the healthcare system. Until now, drug-resistant epilepsy has presented a major challenge for approximately 30% of the epileptic population. The present article summarizes the validated rodent models of seizures employed in pharmacological researches and comprehensively reviews updated advances of novel antiseizure candidates in the preclinical phase. Newly discovered compounds that demonstrate antiseizure efficacy in preclinical trials will be discussed in the review. It is inspiring that several candidates exert promising antiseizure activities in drug-resistant seizure models. The representative compounds consist of derivatives of hybrid compounds that integrate multiple approved antiseizure medications, novel positive allosteric modulators targeting subtype-selective γ-Aminobutyric acid type A receptors, and a derivative of cinnamamide. Although the precise molecular mechanism, pharmacokinetic properties, and safety are not yet fully clear in every novel antiseizure candidate, the adapted approaches to design novel antiseizure medications provide new insights to overcome drug-resistant epilepsy.

Reactive metabolites of the anticonvulsant drugs and approaches to minimize the adverse drug reaction

Several generations of antiepileptic drugs (AEDs) are available in the market for the treatment of seizures, but these are amalgamated with acute to chronic side effects. The most common side effects of AEDs are dose-related, but some are idiosyncratic adverse drug reactions (ADRs) that transpire due to the formation of reactive metabolite (RM) after the bioactivation process. Because of the adverse reactions patients usually discontinue the medication in between the treatment. The AEDs such as valproic acid, lamotrigine, phenytoin etc., can be categorized under such types because they form the RM which may prevail with life-threatening adverse effects or immune-mediated reactions. Hepatotoxicity, teratogenicity, cutaneous hypersensitivity, dizziness, addiction, serum sickness reaction, renal calculi, metabolic acidosis are associated with the metabolites of drugs such as arene oxide, N-desmethyldiazepam, 2-(1-hydroxyethyl)-2-methylsuccinimide, 2-(sulphamoy1acetyl)-phenol, E-2-en-VPA and 4-en-VPA and carbamazepine-10,11-epoxide, etc. The major toxicities are associated with the moieties that are either capable of forming RM or the functional groups may itself be too reactive prior to the metabolism. These functional groups or fragment structures are typically known as structural alerts or toxicophores. Therefore, minimizing the bioactivation potential of lead structures in the early phases of drug discovery by a modification to low-risk drug molecules is a priority for the pharmaceutical companies. Additionally, excellent potency and pharmacokinetic (PK) behaviour help in ensuring that appropriate (low dose) candidate drugs progress into the development phase. The current review discusses about RMs in the anticonvulsant drugs along with their mechanism vis-a-vis research efforts that have been taken to minimize the toxic effects of AEDs therapy.

Research progress in biological activities of succinimide derivatives

Succinimides are well recognized heterocyclic compounds in drug discovery which produce diverse therapeutically related applications in pharmacological practices. Researches in medicinal chemistry field have isolated and synthesized succinimide derivatives with multiple medicinal properties including anticonvulsant, anti-inflammatory, antitumor and antimicrobial agents, 5-HT receptor ligands and enzyme inhibitors. Simultaneously, SAR (Structure-Activity Relationship) analysis has been gradually possessed, along with a great deal of derivatives have been derived for potential targets. In this article, we comprehensively summarize the biological activities and SAR for succinimide derivatives, along with the featuring bioactive molecules reported in patents, wishing to provide an overall retrospect and prospect on the succinimide analogues.

The Search for New Anticonvulsants in a Group of (2,5-Dioxopyrrolidin-1-yl)(phenyl)Acetamides with Hybrid Structure-Synthesis and In Vivo/In Vitro Studies

Epilepsy belongs to the most common and debilitating neurological disorders with multifactorial pathophysiology and a high level of drug resistance. Therefore, with the aim of searching for new, more effective, and/or safer therapeutics, we discovered a focused series of original hybrid pyrrolidine-2,5-dione derivatives with potent anticonvulsant properties. We applied an optimized coupling reaction yielding several hybrid compounds that showed broad-spectrum activity in widely accepted animal seizure models, namely, the maximal electroshock (MES) test and the psychomotor 6 Hz (32 mA) seizure model in mice. The most potent anticonvulsant activity and favorable safety profile was demonstrated for compound 30 (median effective dose (ED₅₀) MES = 45.6 mg/kg, ED₅₀ 6 Hz (32 mA) = 39.5 mg/kg, median toxic dose (TD₅₀) (rotarod test) = 162.4 mg/kg). Anticonvulsant drugs often show activity in pain models, and compound 30 was also proven effective in the formalin test of tonic pain, the capsaicin-induced pain model, and the oxaliplatin (OXPT)-induced neuropathic pain model in mice. Our studies showed that the most plausible mechanism of action of 30 involves inhibition of calcium currents mediated by Cav_1.2 (L-type) channels. Importantly, 30 revealed high metabolic stability on human liver microsomes, negligible hepatotoxicity, and relatively weak inhibition of CYP3A4, CYP2D6, and CYP2C9 isoforms of cytochrome P450, compared to reference compounds. The promising in vivo activity profile and drug-like properties of compound 30 make it an interesting candidate for further preclinical development.

Synthesis, anticonvulsant, and antinociceptive activity of new 3-(3-methyl-2,5-dioxo-3-phenylpyrrolidin-1-yl)propanamides and 3-phenyl-butanamides

A focused library of new 3-(3-methyl-2,5-dioxo-3-phenylpyrrolidin-1-yl)propanamides and their nonimide analogs were synthesized and tested for anticonvulsant activity. These compounds were obtained through the coupling reaction of the starting carboxylic acids with appropriate amines. The initial anticonvulsant screening was performed in mice (intraperitoneal administration) using the maximal electroshock seizure (MES) and the subcutaneous pentylenetetrazole (scPTZ) seizure models. The most promising compound 6 showed more potent protection in the MES and scPTZ tests than valproic acid, which is still recognized as one of the most relevant first-line anticonvulsants. The structure-activity relationship analysis revealed that the presence of the pyrrolidine-2,5-dione ring is important but not indispensable to retain anticonvulsant activity. Additionally, compound 6 showed potent antinociceptive properties in the oxaliplatin-induced neuropathic pain model in mice. The most plausible mechanism of action for compound 6 may result from its influence on the neuronal sodium channel (Site 2) and the high-voltage-activated L-type calcium channel.

N-Benzyl-(2,5-dioxopyrrolidin-1-yl)propanamide (AS-1) with Hybrid Structure as a Candidate for a Broad-Spectrum Antiepileptic Drug

In our recent studies, we identified compound N-benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide (AS-1) as a broad-spectrum hybrid anticonvulsant which showed potent protection across the most important animal acute seizure models such as the maximal electroshock (MES) test, the subcutaneous pentylenetetrazole (s.c. PTZ) test, and the 6-Hz (32 mA) test in mice. Therefore, AS-1 may be recognized as a candidate for new anticonvulsant effective in different types of human epilepsy with a favorable safety margin profile determined in the rotarod test in mice. In the aim of further pharmacological evaluation of AS-1, in the current study, we examined its activity in the 6-Hz (44 mA) test, which is known as the model of drug-resistant epilepsy. Furthermore, we determined also the antiseizure activity in the kindling model of epilepsy induced by repeated injection of pentylenetetrazole (PTZ) in mice. As a result, AS-1 revealed relatively potent protection in the 6-Hz (44 mA) test, as well as delayed the progression of kindling induced by repeated injection of PTZ in mice at doses of 15 mg/kg, 30 mg/kg, and 60 mg/kg. Importantly, the isobolographic analysis showed that a combination of AS-1 and valproic acid (VPA) at the fixed ratio of 1:1 displayed a supra-additive (synergistic) interaction against PTZ-induced seizures in mice. Thus, AS-1 may be potentially used in an add-on therapy with VPA. Moreover, incubation of zebrafish larvae with AS-1 substantially decreased the number, cumulative but not the mean duration of epileptiform-like events in electroencephalographic assay. Finally, the in vitro ADME-Tox studies revealed that AS-1 is characterized by a very good permeability in the parallel artificial membrane permeability assay test, excellent metabolic stability on human liver microsomes (HLMs), no significant influence on CYP3A4/CYP2D6 activity, and moderate inhibition of CYP2C9 in a concentration of 10 μM, as well as no hepatotoxic properties in HepG2 cells (concentration of 10 μM).

KA-11, a Novel Pyrrolidine-2,5-dione Derived Broad-Spectrum Anticonvulsant: Its Antiepileptogenic, Antinociceptive Properties and in Vitro Characterization

Recently, compound KA-11 was identified as a promising candidate for a new broad-spectrum anticonvulsant. This compound revealed wide protective activity across the most important animal models of seizures such as the maximal electroshock test (MES), the subcutaneous pentylenetetrazole test ( scPTZ), and the six-hertz test (6 Hz, 32 mA). Importantly, KA-11 was devoid of acute neurological activity, which was assessed by applying the chimney test (TD₅₀ value higher than 1500 mg/kg). The preliminary in vivo results confirmed favorable anticonvulsant and safety properties of KA-11. With the aim of further biological characterization of KA-11, in the current studies we evaluated its antiepileptogenic activity in the kindling model of epilepsy induced by repeated injection of PTZ in mice. Furthermore, we assessed the antinociceptive activity of KA-11 in several animal pain models. As a result, KA-11 (at all doses applied: 25, 50, and 100 mg/kg) significantly delayed the progression of kindling induced by repeated injection of PTZ in mice. Additionally, KA-11 revealed potent antinociceptive activity in the formalin-induced tonic pain and, importantly, in the oxaliplatin-induced neuropathic pain model in mice. Moreover, KA-11 did not induce motor deficits in the rotarod test. Patch-clamp experiments revealed that one of the mechanisms of action of KA-11 is inhibition of voltage-gated sodium currents. Compound KA-11 appeared to be safe in relation to hepatotoxic properties as no phospholipidosis induction was determined in HepG2 cells at 50 μM, and a small, statistically significant decrease of cell viability was observed only at the highest used dose of 100 μM. Moreover, KA-11 did not affect the function of CYP2D6. The aforementioned hybrid substance proved to penetrate the biological membranes in the in vitro permeability assays.

Evaluation of anticonvulsant and analgesic activity of new hybrid compounds derived from N-phenyl-2-(2,5-dioxopyrrolidin-1-yl)-propanamides and -butanamides

Epilepsy is a chronic neurological disorder that is associated with various types of recurrent seizures, which are drug-resistant in about one third of patients. Moreover, anticonvulsant drugs are used to treat a wide range of non-epileptic conditions, including chronic pain. Here, we investigated the anticonvulsant activity of six new hybrid compounds based on the pyrrolidine-2,5-dione scaffold in the 6 Hz corneal stimulation test with 44 mA stimulus intensity in mice, which is the model of pharmacoresistant seizures. We demonstrated that two molecules, DK-10 (11) and DK-14 (14) show higher anticonvulsant activity and similar safety profile in comparison with valproic acid and much higher in comparison with levetiracetam in the aforementioned test. The second aim of this study was to examine analgesic activity of these compounds. For this purpose, the hot plate test, the formalin test, and the oxaliplatin-induced peripheral neuropathy model were performed. Among tested agents DK-11 (12) revealed prominent antinociceptive activity at non-sedative doses in the second (inflammatory) phase of the formalin test, which is the model of tonic pain and antiallodynic activity in the oxaliplatin-induced neuropathic pain, the model of painful chemotherapy-induced peripheral neuropathy. No cytotoxic effect on hepatoma cells was observed. Compound DK-10 (11) had high affinity for voltage-gated sodium channels, whereas compound DK-11 (12) showed weak binding toward sodium and calcium voltage-gated channels and the NMDA receptor. As a result, hybrid compounds reported herein seem to be very promising broad spectrum anticonvulsant molecules with collateral analgesic activity.

From Classification to Regression Multitasking QSAR Modeling Using a Novel Modular Neural Network: Simultaneous Prediction of Anticonvulsant Activity and Neurotoxicity of Succinimides

Succinimides, which contain a pharmacophore responsible for anticonvulsant activity, are frequently used antiepileptic drugs and the synthesis of their new derivatives with improved efficacy and tolerability presents an important task. Nowadays, multitarget/tasking methodologies focused on quantitative-structure activity relationships (mt-QSAR/mtk-QSAR) have an important role in the rational design of drugs since they enable simultaneous prediction of several standard measures of biological activities at diverse experimental conditions and against different biological targets. Relating to this very topic, the mt-QSAR/mtk-QSAR methodology can give only binary classification models, and as such, in this study a regression mtk-QSAR (rmtk-QSAR) model based on a novel modular neural network (MNN) has been proposed. The MNN uses standard classification mtk-QSAR models as input modules, while the regression is performed by the output module. The rmtk-QSAR model has been successfully developed for the simultaneous prediction of anticonvulsant activity and neurotoxicity of succinimides, with a satisfactory accuracy in testing (R² = 0.87). Thus, the proposed mtk-QSAR regression method can be regarded as a viable alternative to the standard QSAR methodology.

Synthesis, Anticonvulsant Activity, and SAR Study of Novel 4-Quinazolinone Derivatives

Series of N-(4-substitutedphenyl)-4-(1-methyl (or 1,2-dimethyl)-4-oxo-1,2-dihydroquinazolin-3(4H)-yl)-alkanamides (5a-j) and 4-chloro-N'-((1-methyl (or 1,2-dimethyl)-4-oxo-1,2-dihydroquinazolin-3(4H)-yl)-alkaloyl)benzohydrazides (6a-f) were designed based on the previously reported essential structural features for anticonvulsant activity. Several amino acids were incorporated within the synthesized quinazolin-4(3H)-ones to improve their bioavailability and the anticonvulsant activity. Synthesis of the target compounds was accomplished in four steps starting from the reaction between N-methyl isatoic anhydride and the appropriate amino acid. Then, the carboxylic acid group was utilized to synthesize the required final structures. The new quinazolinone derivatives were evaluated for their anticonvulsant activity according to the Anticonvulsant Drug Development (ADD) Program protocol. All the 16 new quinazolinones exhibited good anticonvulsant activity; especially 5f, 5b, and 5c showed superior anticonvulsant activities in comparison to the reference drug, with ED₅₀ values of 28.90, 47.38, and 56.40 mg/kg, respectively.

Analgesic, antiallodynic, and anticonvulsant activity of novel hybrid molecules derived from N-benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide and 2-(2,5-dioxopyrrolidin-1-yl)butanamide in animal models of pain and epilepsy

The purpose of the present study was to examine the analgesic activity of six novel hybrid molecules, which demonstrated in the previous research anticonvulsant activity in the maximal electroshock seizure (MES) and subcutaneous pentylenetetrazole seizure (scPTZ) tests in mice. The antinociceptive properties were estimated in three models of pain in mice—the hot plate test, the formalin test, and in the oxaliplatin-induced neuropathy. Moreover, extended anticonvulsant studies were carried out and the antiseizure activity was investigated in the 6-Hz test. Considering drug safety evaluation, the influence of compounds on locomotor activity and contextual memory were checked. Furthermore, chosen molecules were tested in vitro for potential hepatotoxicity. To explain the probable mechanism of action, the radioligand binding assays were performed. In both phases of formalin test, analgesic activity demonstrated compounds 4, 8, and 9. These agents relieved also mechanical allodynia in oxaliplatin-induced model of neuropathic pain. At active doses, they did not influence locomotor activity of mice. Moreover, for compounds 8 and 9, no deleterious effect on memory was observed, but compound 4 might induce memory deficits. All tested compounds (4, 5, 8, 9, 15, and 16) inhibited psychomotor seizures with the ED₅₀ values = 24.66–47.21 mg/kg. The binding studies showed that compound 4 only at the high concentrations revealed the effective binding to the neuronal sodium channels and moderately binding to the L-type calcium (verapamil site) channels and NMDA receptors. The present preclinical results proved that novel hybrid molecules demonstrate very promising anticonvulsant and analgesic activity.