Assessment of seizure liability of Org 306039, a 5-HT2c agonist, using hippocampal brain slice and rodent EEG telemetry

Improved seizure liability detection by combining rat hippocampal brain slice electrophysiology with in vivo behavior observation following intracerebroventricular drug administration

An adverse effect of drug candidates, seizure is a serious issue in drug development. Improving evaluation systems for seizure liability is crucial for selecting good candidates. Firstly, in vitro electrophysiological measurement by a multielectrode array system in rat hippocampal brain slices was employed to confirm an increase in electrically evoked population spike (PS) area, the occurrence of multiple population spikes (MPSs), and thereby the seizure liability of five positive control chemicals: picrotoxin, 4-aminopyridine, pentylenetetrazole, penicillin G, and chlorpromazine. Aspirin, a negative control, did not affect PS area or generate MPSs. Furthermore, baclofen, an anticonvulsant drug, decreased PS area and inhibited the increase in PS area or occurrence of MPSs induced by picrotoxin. A comparative study of seizure liability among carbapenem antibiotics revealed that tienam > carbenin > omegacin and finibax. Despite leading to a strong decrease in PS area, physostigmine, cisplatin, and paroxetine still produced MPSs. Therefore, the increase in PS area or the occurrence of the MPS are considered significant evaluation parameters for seizure liability. In contrast, the in vitro electrophysiological measurement could not detect the seizure liability of diphenhydramine or fluvoxamine. A follow-up study of in vivo mouse behavioral change induced by intracerebroventricular administration of these drugs clearly detected convulsions. The in vitro electrophysiological study using hippocampal brain slices combined with in vivo behavior observation study of drug candidates administered by intracerebroventricular injection can implement to assess the seizure liability of even small amounts, especially in the early stages of drug development.

Sensitivity, specificity and limitation of in vitro hippocampal slice and neuron-based assays for assessment of drug-induced seizure liability

An effective in vitro screening assay to detect seizure liability in preclinical development can contribute to better lead molecule optimization prior to candidate selection, providing higher throughput and overcoming potential brain exposure limitations in animal studies. This study explored effects of 26 positive and 14 negative reference pharmacological agents acting through different mechanisms, including 18 reference agents acting on glutamate signaling pathways, in a brain slice assay (BSA) of adult rat to define the assay's sensitivity, specificity, and limitations. Evoked population spikes (PS) were recorded from CA1 pyramidal neurons of hippocampus (HPC) in the BSA. Endpoints for analysis were PS area and PS number. Most positive references (24/26) elicited a concentration-dependent increase in PS area and/or PS number. The negative references (14/14) had little effect on the PS. Moreover, we studied the effects of 15 reference agents testing positive in the BSA on spontaneous activity in E18 rat HPC neurons monitored with microelectrode arrays (MEA), and compared these effects to the BSA results. From these in vitro studies we conclude that the BSA provides 93% sensitivity and 100% specificity in prediction of drug-induced seizure liability, including detecting seizurogenicity by 3 groups of metabotropic glutamate receptor (mGluR) ligands. The MEA results seemed more variable, both quantitatively and directionally, particularly for endpoints capturing synchronized electrical activity. We discuss these results from the two models, comparing each with published results, and provide potential explanations for differences and future directions.

Seizure liability assessments using the hippocampal tissue slice: Comparison of non-clinical species

INTRODUCTION

Traditionally, rat hippocampal tissue slice models are used as an in vitro electrophysiology assay to assess seizurogenic potential in early drug development despite non-clinical species-specific differences noted during in vivo seizure studies.

METHODS

Hippocampal tissue slices were acutely isolated from rats, minipigs, dogs and nonhuman primates (NHP). Population spikes (PS) were evoked through stimulation of the CA3 Schaffer collateral pathway and recorded using in vitro electrophysiological techniques via an extracellular electrode placed within the CA1 stratum pyramidale cell body layer.

RESULTS

Hippocampal slices, across all species, displayed a concentration-dependent increase in PS area and number with the pro-convulsant pentylenetetrazol (PTZ; 0.1-10mM). Beagle dogs exhibited higher sensitivities to PTZ-induced changes in PS area and number compared to both rats and NHPs which presented nuanced differences in their responsiveness to PTZ modulation. Minipigs were comparatively resistant to PTZ-induced changes in both PS area and number. Rat and NHP hippocampal tissues were further characterized with the pro-convulsant agents 4-aminopyradine (4-AP; 1-100μM) and cefazolin (0.001-10mM). Rats possessed higher sensitivities to 4-AP- and cefazolin-induced changes to both PS area and number whereas NHP displayed greater modulation in PS duration. The anti-convulsant agents, diazepam (10-500μM) and lidocaine (1-500μM), were also tested on either rat and/or NHP tissue with both drugs repressing PS activation at high concentrations.

DISCUSSION

Hippocampal tissue slices, across all species, possessed distinct sensitivities to pro- and anti-convulsant agents which may benefit the design of non-clinical seizure liability studies and their associated data interpretation.

Agomelatine protects against neuronal damage without preventing epileptogenesis in the kainate model of temporal lobe epilepsy

Recent studies about the novel antidepressant agomelatine, which is a mixed MT₁ and MT₂ melatonin receptor agonist and 5HT_2C serotonin receptor antagonist possessing an anticonvulsant and neuroprotective action, suggest that it may have potential to contribute against epileptogenesis and epilepsy-induced memory impairment. In order to ascertain whether protection of some brain structures could suppress epileptogenesis, in the present study, we evaluated the effect of chronic post-status treatment with agomelatine on epileptogenesis, behavioral and neuronal damage induced by kainate acid (KA) status epilepticus (SE). Agomelatine/vehicle treatment (40mg/kg, i.p.) started one hour after SE and continued up to 10weeks in Wistar rats. Latency for onset of spontaneous motor seizures (SMS) and their frequency was detected by a 24-h video-recording. Locomotor activity, anxiety and hippocampus-dependent spatial memory in open field (OF), elevated plus maze (EPM), light-dark test (LDT) and radial arm maze (RAM) test, respectively, were evaluated during the last two weeks after SE. Agomelatine significantly decreased the latency for onset of SMS and increased the seizure frequency during the 2nd and the 3rd week of treatment. The MT₁ and MT₂ receptor agonist and serotonin 5HT_2C receptor antagonist exacerbated the KA-induced hyperlocomotion and impulsive behavior and it was unable to prevent spatial memory impairment of epileptic rats. However, agomelatine induced a neuroprotection in the dorsal hippocampus, specifically in the CA1, septal CA2 and partially in the CA3c region, the hilus of the dentate gyrus, piriform cortex and septo-temporal and temporal basolateral amygdala. Our findings suggest that the beneficial impact against SE-induced neuronal loss exerted by agomelatine is not crucial for the suppression of epileptogenesis and its deleterious consequences in KA model of temporal lobe epilepsy.

EEG in non-clinical drug safety assessments: Current and emerging considerations

Electroencephalogram (EEG) data in nonclinical species can play a critical role in the successful evaluation of a compound during drug development, particularly in the evaluation of seizure potential and for monitoring changes in sleep. Yet, while non-invasive electrocardiogram (ECG) monitoring is commonly included in preclinical safety studies, pre-dose or post-dose EEG assessments are not. Industry practices as they relate to preclinical seizure liability and sleep assessments are not well characterized and the extent of preclinical EEG testing varies between organizations. In the current paper, we discuss the various aspects of preclinical EEG to characterize drug-induced seizure risk and sleep disturbances, as well as describe the use of these data in a regulatory context. An overview of EEG technology-its correct application and its limitations, as well as best practices for setting up the animal models is presented. Sleep and seizure detection are discussed in detail. A regulatory perspective on the use of EEG data is provided and, tying together the previous topics is a discussion of the translational aspects of EEG.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

Analysis of spontaneous hippocampal activity allows sensitive detection of acetylcholine-mediated effects

INTRODUCTION

Excitation of Acetylcholine-mediated (Ach) transmission (especially if irreversible) may pose life-threatening adverse events by increasing neuronal network activity. Unfortunately, adequate detection of this liability during early drug development is hampered, because published ex vivo electrophysiological models are very insensitive to this regard. For example, Eserine, which reversibly inhibits acetylcholinesterase (AchE) in the double digit nM range, affects electrically evoked potentials in hippocampal slices only at ≥10μM. Here, a significantly more sensitive method for detecting Ach-mediated alternations is presented by analyzing spontaneous neuronal network activity in hippocampal slices.

METHODS

The microelectrode array (MEA) technique with an 8×8 electrode grid was applied to analyze evoked and spontaneous extracellular field recordings in parallel from acute rat hippocampal slices. For evoked potentials, the Schaffer collateral CA3-CA1 pathway was electrically stimulated and the resulting field potential analyzed at the CA1 pyramidal layer. Spontaneous spike activity was detected as negative inflections from the 100Hz high pass filtered signal. Spike frequency was analyzed within the whole CA1 region.

RESULTS

Modification of Ach-mediated neuronal transmission via carbachol, Eserine, or Diisopropylfluorophosphate (DFP) does not induce any effects on evoked field potentials at physiologically relevant concentrations. Similar to previous reports, subtle effects were detectable at very high concentrations. By contrast, spontaneous spike frequency was already increased within the expected concentration range. Eserine-induced effects can also be reversed by atropine and washout. On the contrary, effects by the irreversible AchE-blocker DFP could not be washed out.

DISCUSSION

Compared to evoked field potentials, spontaneous spike activity in the hippocampal CA1 region appears to be a significantly more sensitive parameter for functional electrophysiological analysis of drug induced Ach-mediated effects. This finding may supplement existing models for detection and prediction of drug-related adverse effects like seizure liability already during early development stages.

Reprint of "Safety pharmacology in 2014: New focus on non-cardiac methods and models"

"What do you know about Safety Pharmacology?" This is the question that was asked in 2000 with the inception of the Safety Pharmacology Society (SPS). There is now a widespread awareness of the role of safety pharmacology in drug discovery and increasing awareness among the wider community of methods and models used in the assessment of the core battery required set of safety studies. However, safety pharmacology does not stop with core battery studies. New methods are intensively sought in order to achieve a swifter and more reliable assessment of adverse effect liability. The dynamics of the discipline and method expansion are reflected in the content of this issue of the Journal of Pharmacological and Toxicological Methods (JPTM). We are into the second decade of publishing on safety pharmacology methods and models, reflected by the annual themed issue in JPTM, and on willingness of investigators to embrace new technologies and methodologies. This years' themed issue is derived from the annual Safety Pharmacology Society (SPS) meeting, held in Rotterdam, The Netherlands, in 2013.

Safety pharmacology in 2014: new focus on non-cardiac methods and models

"What do you know about Safety Pharmacology?" This is the question that was asked in 2000 with the inception of the Safety Pharmacology Society (SPS). There is now a widespread awareness of the role of safety pharmacology in drug discovery and increasing awareness among the wider community of methods and models used in the assessment of the core battery required set of safety studies. However, safety pharmacology does not stop with core battery studies. New methods are intensively sought in order to achieve a swifter and more reliable assessment of adverse effect liability. The dynamics of the discipline and method expansion are reflected in the content of this issue of the Journal of Pharmacological and Toxicological Methods (JPTM). We are into the second decade of publishing on safety pharmacology methods and models, reflected by the annual themed issue in JPTM, and on willingness of investigators to embrace new technologies and methodologies. This years' themed issue is derived from the annual Safety Pharmacology Society (SPS) meeting, held in Rotterdam, The Netherlands, in 2013.