Identification of novel activators of two-pore domain potassium (K2P) channels
Growing functional and genetic evidence points to an emerging role for two-pore domain potassium channels (K2Ps) in numerous pathophysiologies. K2Ps carry background (or leak) potassium current and primarily function to maintain cellular resting membrane potential. However, K2Ps have proved a challenging superfamily to modulate with small molecules and there is currently a lack of pharmacological tools which target K2Ps. This has limited the investigation of K2Ps precise physiological function and efforts to generate therapeutics which act upon K2Ps. Our initial aim was to develop a screening system which would allow the identification of small molecule K2P activators. We initially showed that the identification of channel activators can be compromised in systems in which the target (K2P) is over-expressed at high levels. To avoid this, we used baculovirus (‘BacMam’) to transduce K2P expression in mammalian cells. ‘BacMam’ allows the precise titration of expression of the gene of interest. This enabled us to develop cell systems in which we were able to intricately and robustly select a level of K2P expression (via functional studies) optimized for the identification of channel activators. An example assay development using the K2P TRAAK is described. TRAAK is known to be expressed in nociceptors and has been shown to be a genetic predictor of post-surgical neuropathic pain. An appropriate level of TRAAK channel function was chosen after ‘BacMam’ optimization and channel function measured via thallium flux. The pharmacology of previously described TRAAK activators is also shown. A representative sub-group of K2Ps (TWIK-1, THIK-1, TASK-3, TASK-2, TREK-2) was screened using the BacMam/ Thallium flux assay against the LifeArc Index set (11k compounds). This allowed us to assess which K2Ps were ‘ligandable’ or ‘activatable’ by small molecules. Multiple novel activators were identified, and development is on-going. We also screened a library of drug-like molecules against the same group of K2Ps and identified Terbinafine as a novel activator of the TASK-3 channel. The selectivity of this molecule across the K2P superfamily was assessed and structure-activity relationship studies showed that relatively small changes to the molecule had significant effects on activity and selectivity.