Potent CysLT1 (LTD4) leukotriene receptor inverse agonist (EC50 = 1.3 nM). Antagonizes LTD4-induced contractions of guinea pig trachea and ileum (pA2 values are 9.4 and 10.5 respectively). Also inhibitor of multidrug resistance protein-1 (MRP1) mediated transport; in vitro augments the effects of cytotoxic agents on malignant cells.