Voltage sensor targeted activation of Kv7 channels by QO-58.

Abstract

Kv7 (KCNQ) voltage-gated potassium channels are key modulators of neuronal excitability and have been a promising target for developing novel drugs to treat epilepsy and pain. Drug discovery has focused on identifying small molecules that modulate channel function and understanding their mechanisms of action. Special attention has been given to Kv7 channel activators, which may have therapeutic benefits in epilepsy or pain. In this study, we compared the effects and mechanism of a candidate Kv7 activator, QO-58, which has been previously described but has an unclear site and mechanism of action. We compared QO-58 actions with other well-characterized activators that influence either the VSD (ICA-069673) or pore domain (ML213) of Kv7 channels. QO-58 exhibits strong subtype specificity for Kv7.2 over Kv7.3, similar to VSD-targeted activators. Additionally, QO-58 exhibits prominent state-dependent actions, as it requires channels to activate before binding, and dramatically decelerates closure of Kv7.2. We also tested the effects of multiple VSD mutations on QO-58 and ICA-069673 actions. Interestingly, we found that the Kv7.2[F168L] mutation, previously shown to abolish ICA-069673 sensitivity, does not markedly affect QO-58 mediated effects. Notably, Kv7.2[I134A] and Kv7.2[I173T] weaken the effects of ICA-069673, but are hypersensitive to QO-58. This finding may suggest that dimensions of the VSD binding pocket influence the potency of smaller compounds (e.g. ICA-069673) relative to bulkier ones (e.g. QO-58), despite overlap in their binding sites. Our findings highlight that key contacts underlying sensitivity to VSD-targeted activators may vary significantly depending on the chemical and steric features of the drug. We anticipate that further investigation of VSD-targeted activators will continue to clarify the complex pharmacophore of the VSD binding pocket in Kv7 channels.