Voltage-independent, selective CFTR chloride channel blocker (Ki = 300 nM) that alters channel gating. Blocks intestinal fluid secretion induced by cholera toxin and Escherichia coli and suppresses cyst growth in animal models of polycystic kidney disease. Orally active. Inhibits mitochondrial respiration and increases reactive oxygen species (ROS) production independently of CFTR in several cell lines.