Abstracts

Rationale: Imbalances of neuronal excitation and inhibition are considered a significant pathological feature of many seizure disorders. Many anticonvulsant medications such as barbiturates, benzodiazepines, and gabapentin markedly increase inhibitory transmission, thus generating therapeutic benefit along with sedative side effects. NeuroTherapeutics Pharma (NTP) has developed compounds with novel mechanisms that are hypothesized to enhance presynaptic inhibition. Specifically, these compounds increase spontaneous release of GABA in hippocampus, leading to robust anti-seizure activity. Methods: Patch-clamp recording of hippocampal CA1 pyramidal cells was conducted to assess the ability of NTP compounds to increase the frequency of miniature inhibitory post-synaptic currents (mIPSCs). Excitatory synaptic transmission and Na+-dependent action potentials were blocked by kynurenic acid and TTX respectively. NTP compounds were also assessed for their ability to decrease epileptiform discharges in a mouse model of mesial temporal lobe epilepsy. Results: The NTP compound, NP260 (30 μM) significantly increased the frequency of mIPSCs from 4.85 ± 0.72 Hz to 5.94 ± 0.88 Hz (Mean ± SEM, n = 12 cells, p < 0.01 compared to pre-drug baseline, paired t-test). NP260 also showed robust activity after intra-hippocampal injection of kainate, a mouse model of refractory mesial temporal lobe epilepsy (MTLE) (Riban et al, 2002 Neuroscience 112(1):101-111; Langlois et al, 2010 J. Neurosci 30(49):16523-35). Single acute intraperitoneal (IP) doses of NP260 inhibited both the frequency and total duration of epileptiform discharges when measured for 60 minutes after administration. The effect of NP260 was dose-dependent, with 15 mg/kg reducing the frequency of epileptiform discharges by 52% and 30 mg/kg by 86% in these animals. NP260 showed no sedative effects based on rotarod performance or modified Irwin Test (CNS behavioral battery) at these IP doses and oral doses up to and including 1000 mg/kg. Conclusions: Tests of NP260 and a series of structural analogs demonstrated a correlation between increased mIPSC frequency and decreased epileptiform discharges in the MTLE model, suggesting that the increased spontaneous release of GABA may be a critical component of the compounds' mechanism of action. The novel mechanism(s) combined with the robust in vivo efficacy of NP260 suggests that modulating GABA release with NTP compounds may represent a promising strategy for treating seizure disorders.