Endothelin 1 (ET-1) is overexpressed in cancer, contributing to disease progression. We previously showed that ET-1 stimulated proliferative, migratory, and contractile tumorigenic effects via the ET A receptor. Here, for the first time, we evaluate zibotentan, a specific ET A receptor antagonist, in the setting of colorectal cancer, in cellular models. Pharmacologic characteristics were further determined in patient tissues. Colorectal cancer lines (n ¼ 4) and fibroblast strains (n ¼ 6), isolated from uninvolved areas of colorectal cancer specimens, were exposed to ET-1 and/or ET A/B receptor antagonists. Proliferation (methylene blue), migration (scratch wounds), and contraction (gel lattices) were assessed. Receptor distribution and binding characteristics (K d , B max ) were determined using autoradiography on tissue sections and homogenates and cytospun cells, supported by immunohistochemistry. Proliferation was inhibited by ET A (zibotentan > BQ123; P < 0.