A novel KIR-specific KATP channel opener

KATP channels have diverse roles, including regulation of insulin secretion, protection against cardiac stress responses, and blood flow regulation, and are therefore excellent therapeutic targets. Different subclasses of KATP channels exist in various tissue types due to the specific assemblies of pore-forming (Kir6.x) and accessory (SURx) subunits. The majority of pharmacological openers and blockers act by binding to SURx and are poorly selective against various KATP channel subclasses. We generated 3D models of the Kir6.2/SUR homotetramers based on existing cryo-EM structures in both the open and closed states and identified a potential agonist binding pocket in a functionally critical area of the channel in the vicinity of a palmitoylated Kir6.2-C166 residue and the PIP2 binding region. Computational docking screens of this pocket with the Chembridge Core chemical library of 492,000 drug-like compounds were performed. The top 15 ‘hits’ were tested for activity against KATP channels using patch clamping and thallium (Tl+) flux assays with a Kir6.2/SUR2A HEK-293 stable cell line. Several of the compounds increased Tl+ fluxes and of them (70862985) opened Kir6.2/SUR2A channels with a similar potency as pinacidil (EC50 respectively 5 µM and 1 µM). Remarkably, at 15-100 µM, compound 70862985 had no or minimal effects on other Kir channels, including Kir6.1/SUR2B, Kir2.1 or Kir3.1/Kir3.4 channels and at 100 µM minimally affected Na+ currents in TE671 medulloblastoma cells. We examined whether 70862985 can correct Kir6.2 mutants with a decreased open probability, which is typically associated with congenital hyperinsulinism. Each of the Kir6.2-F55L, Kir6.2-T62M and Kir6.2-R301C mutants were associated with reduced Tl+ fluxes from Kir6.2/SUR1 transfected HEK-293 cells and were relatively insensitive to diazoxide. Kir6.2-R301C, by contrast, was strongly activated by 70862985. 70862985 is a Kir6.2 opener that does not affect the structurally similar Kir6.1 channel. This, to our knowledge, is the first Kir-specific channel opener.