Kv7(KCNQ) potassium channels influence neuronal excitability, and are promising targets for development of analgesic and anti-epileptic drugs. Kv7-targeted inhibitors such as XE-991 are frequently used to validate the molecular target of candidate Kv7 activator drugs. However, there is uncertainty in terms of the binding site, mechanism, and Kv7 subtype specificity of XE-991. This study was motivated by our observation of strong subtype specificity of XE-991 for Kv7.2 over other Kv7 channel types. Among the neuronal Kv7 subtypes (Kv7.2-Kv7.5), homomeric Kv7.2 exhibits the highest sensitivity and fastest rate of XE-991 inhibition, while Kv7.3 is significantly less sensitive. In addition, XE991 exhibits properties of an allosteric inhibitor rather than a simple blocker, because XE-991 effects are markedly attenuated if it is applied in combination with the pore-targeted potentiator ML213. We generated chimeric rearrangements of Kv7.2 and Kv7.3 to investigate channel motifs that contribute to drug binding and subtype specificity. These experiments highlighted the S4-S5 linker and the pore region as critical determinants of XE-991 sensitivity. This contrasts with recent structural studies indicating binding of the closely related compound linopirdine to the C-terminal extension of S6. Overall, our study suggests a complex molecular mechanism of XE-991 inhibition with functional outcomes that are incongruent with current structural models of XE-991/linopirdine binding.
Kanyo et al. (Sun,) studied this question.