FN1 and breast cancer: Next, to investigate whether MDA-MB-231 was inhibited by TMD123-Fc through the binding of β1 integrin to fibronectin, we evaluated binding of the β1 integrin to fibronectin by adding a divalent ion (1 mM Mg2+ and Ca2+) to immobilized fibronectin and activating the integrin by applying shear stress to the β1 integrin from human breast cancer-derived cell lines.