Chemical Synthesis of a Highly Selective Probe of the Renal Outer Medullary Potassium Channel (ROMK)

Abstract

The renal outer medullary potassium channel, ROMK, critically regulates salt and water balance and may be a drug target for a novel class of diuretic. However, the molecular pharmacology of the inward rectifier potassium channel family is virtually undeveloped, precluding assessment of ROMK's therapeutic potential. We therefore performed a high-throughput screen of approximately 225,000 small molecules for modulators of ROMK function, from which several novel antagonists were identified. One compound, termed VU590, inhibits ROMK with a half-inhibition concentration (IC50) of 300 nM, has no effect on Kir2.1 or Kir4.1, but inhibits Kir7.1 at low micromolar concentrations. Two structurally related compounds were identified in the screen, but were found to be comparatively weak ROMK inhibitors. Using a molecular mechanics-based knowledge of VU590, medicinal chemistry was employed to improve the potency of one compound 33-fold (IC50 from 8 μM to 240 nM). This novel probe, termed VU591, is highly selective for ROMK over Kir2.1, Kir2.3, Kir4.1, Kir6.2/SUR1B, Kir7.1 and a panel of more than 65 other potential off-targets, including voltage-gated sodium and calcium channels and hERG. Functional studies suggest the VU591 binding site is located in the cytoplasmic pore of ROMK. VU591 will be instrumental in mapping the location and topographical features of this selective binding site and could pave the way for animal studies assessing the therapeutic potential of ROMK.