SB-505124 is a selective inhibitor of transforming growth factor-beta type I receptor ALK5 and as well as being a selective inhibitor of ALK4 but with less potency. SB-505124 blocks TGF-β–induced apoptosis of FaO cells and NRP 154 cells in a concentration-dependent manner. SB-505124 has been shown to suppress the migration and invasion of breast cancer MCF-7-M5 cells.