Design, synthesis, and structure-activity relationship of 5,7- dimethylbenzo[d]thiazoles as novel Kv7.2/7.3 activators with antiepileptic effects

Abstract

The activation of neuronal Kv7 channels has emerged as an important therapeutic strategy for epilepsy due to their role in regulating neuronal excitability. Retigabine (RTG), a Kv7.2/7.3 channel activator, was previously approved for epilepsy treatment but was withdrawn in 2017 because of its side effects of ophthalmological and dermatological pigmentation. Despite this setback, Kv7.2/7.3 channel remains a promising target for the development of antiepileptic drugs (AEDs). Previous studies have attributed the toxic metabolic quinone/azaquinone diimines and associated blue discoloration of RTG to its electron-rich tri-amine aromatic scaffold. A common strategy to mitigate this toxicity involves removing the ortho-aniline moiety of RTG. In this study, we designed and synthesized a series of compounds based on dimethylbenzene heterocyclic scaffolds as Kv7.2/7.3 activators. Among them, compound 2c demonstrated improved efficacy in Rb⁺ efflux assays and exhibited comparable activity in whole-cell patch clamp recordings on Kv7.2/7.3 channels. Moreover, compound 2c was effective in both maximal electroshock seizure (MES) and subcutaneous pentylenetetrazol (sc-PTZ) mouse models, with ED₅₀ values of 4.02 mg/kg and 43.17 mg/kg, respectively. The LD₅₀ value of 2c in acute toxicity experiments was 340.35 mg/kg (95 % CI: 293.68–394.45) in mice. Additionally, 2c exhibited locomotor impairment with at TD₅₀ of 48.93 mg/kg in an open field test and 49.25 mg/kg in a rotarod test. Compound 2c also demonstrated reasonable pharmacokinetic (PK) properties and blood-brain barrier (BBB) penetration, along with good photostability. Site-directed mutagenesis, combined with molecular docking, confirmed that 2c interacted with key residues (W236, F305, and L299) in the Kv7.2 channel. Our findings suggest that compound 2c is a promising lead compound with a novel scaffold as a Kv7.2/7.3 activator for the management of epilepsy.