%0 Journal Article %A Yonjung Kim %A Marc O Anderson %A Jinhong Park %A Min Goo Lee %A Wan Namkung %A Alan S Verkman %T Benzopyrimido-pyrrolo-oxazine-dione (R)-BPO-27 Inhibits CFTR Chloride Channel Gating by Competition with ATP %D 2015 %R 10.1124/mol.115.098368 %J Molecular Pharmacology %P mol.115.098368 %X We previously reported that benzopyrimido-pyrrolo-oxazinedione BPO-27 inhibits the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel with low nanomolar potency and reduced cystogenesis in a model of polycystic kidney disease. Here, we used computational chemistry and patch-clamp to show that enantiomerically pure (R)-BPO-27 inhibits CFTR by competition with ATP, whereas (S)-BPO-27 is inactive. Docking computations using a homology model of CFTR structure suggested that (R)-BPO-27 binds near the canonical ATP binding site, which was supported by molecular dynamics simulations showing a lower binding energy for the (R) vs. (S) stereoisomers. Three additional lower-potency BPO-27 analogs were modeled in a similar fashion, with the binding energies predicted in the correct order. Whole-cell patch-clamp showed linear CFTR currents with a voltage-independent (R)-BPO-27 block mechanism. Single channel recordings in inside-out patches showed reduced CFTR channel open probability and increased channel closed-time by (R)-BPO-27 without altered unitary channel conductance. At a concentration of (R)-BPO-27 that inhibited CFTR chloride current by ~50%, the EC50 for ATP activation of CFTR increased from 0.27 to 1.77 mM, but was not changed by CFTRinh-172, a thiazolidinone CFTR inhibitor that acts at a site distinct from the ATP binding site. Our results suggest that (R)-BPO-27 inhibition of CFTR involves competition with ATP. %U https://molpharm.aspetjournals.org/content/molpharm/early/2015/07/14/mol.115.098368.full.pdf