Ani 9 is an inhibitor of the calcium-activated chloride channel (CaCC) anoctamin 1 (ANO1) that blocks ATP-induced apical membrane chloride currents in ANO1-expressing Fischer rat thyroid (FRT) cells (IC50 = 77 nM). It is selective for ANO1 over ANO2 at 10 μM and the cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial sodium channel (ENaC) at 30 μM. Ani 9 inhibits ATP-induced quenching of a fluorescent intracellular halide sensor in PC3 prostate cancer cells and Capan-1 pancreatic carcinoma cells in a concentration-dependent manner.