Discovery of HN37 as a Potent and Chemically Stable Antiepileptic Drug Candidate.

We previously reported that P-retigabine (P-RTG), a retigabine (RTG) analogue bearing a propargyl group at the nitrogen atom in the linker of RTG, displayed moderate anticonvulsant efficacy. Recently, our further efforts led to the discovery of HN37 (pynegabine), which demonstrated satisfactory chemical stability upon deleting the ortho liable -NH2 group and installing two adjacent methyl groups to the carbamate motif. HN37 exhibited enhanced activation potency toward neuronal Kv7 channels and high in vivo efficacy in a range of pre-clinical seizure models, including the maximal electroshock test and a 6 Hz model of pharmacoresistant limbic seizures. With its improved chemical stability, strong efficacy, and better safety margin, HN37 has progressed to clinical trial in China for epilepsy treatment.

A Small-Molecule Compound Selectively Activates K2P Channel TASK-3 by Acting at Two Distant Clusters of Residues.

The TASK-3 channel is a member of the K2P family that is important for the maintenance of the resting membrane potential. Previous studies have demonstrated that the TASK-3 channel is involved in several physiologic and pathologic processes, including sleep/wake control, cognition, and epilepsy. However, there is still a lack of selective pharmacological tools for TASK-3, which limits further research on channel function. In this work, using a high-throughput screen, we discovered that N-(2-((4-nitro-2-(trifluoromethyl)phenyl)amino)ethyl)benzamide (NPBA) showed excellent potency and selectivity as a novel TASK-3 activator. The molecular determinants of NPBA activation were then investigated by combining chimera and mutagenesis analysis. Two distant clusters of residues located at the extracellular end of the second transmembrane domain (A105 and A108) and the intracellular end of the third transmembrane domain (E157) were found to be critical for NPBA activation. We then compared the essentials of the actions of NPBA with inhalation anesthetics that nonselectively activate TASK-3 and found that they may activate TASK-3 channels through different mechanisms. Finally, we transplanted the three residues A105, A108, and E157 into the TASK-1 channel, which resists NPBA activation, and the constructed mutant TASK-1(G105A, V108A, A157E) showed dramatically increased activation by NPBA, confirming the importance of these two distant clusters of residues. SIGNIFICANCE STATEMENT: TASK-3 channels conduct potassium and are involved in various physiological and pathological processes. However, the lack of selective modulators has hindered efforts to increase our understanding of the physiological roles of TASK-3 channels. By using a high-throughput screen, we identified NPBA as a potent and selective TASK-3 activator, and we show that NPBA is a more potent activator than terbinafine, the only reported TASK-3 selective activator to date. We also show here that NPBA has outstanding selectivity for TAS-3 channels. These characteristics make NPBA a promising pharmacological probe for research focused on defining TASK-3 channel function(s). In addition, we identified two distant clusters of residues as determinants of NPBA activation providing new molecular clues for the understanding of the gating mechanism of K2P channels.