The present invention relates to compositions and methods for treating a disease in an animal, which disease is responsive to inhibiting of functional cystic fibrosis transmembrane conductance regulator (CFTR) polypeptide by administering to a mammal in need thereof an effective amount of a compound defined herein (including those compounds set forth in Tables 1-2 or encompassed by formulas I-IV) or compositions thereof, thereby treating the disease. The present invention particularly, relates to a method of treating diarrhea and polycystic kidney disease.