SB505124 is a selective inhibitor of the TGF-β (transforming growth factor-beta) type I receptor kinase, particularly ALK4, ALK5, and ALK7. It is widely used in research to block TGF-β signaling pathways, which play key roles in cell proliferation, differentiation, apoptosis, and fibrosis. Due to its ability to modulate these pathways, SB505124 is applied in studies related to cancer, where TGF-β signaling can promote tumor progression and metastasis. It helps in reversing epithelial-to-mesenchymal transition (EMT), making it valuable in investigating mechanisms of tumor invasiveness and potential therapeutic strategies. It is also used in stem cell research to support the maintenance of pluripotency in human embryonic stem cells by preventing spontaneous differentiation induced by TGF-β signaling. Additionally, SB505124 has been employed in fibrosis research, showing potential in reducing fibrotic responses in tissues by inhibiting TGF-β-mediated activation of fibroblasts. Its application spans cellular and molecular studies aiming to dissect signaling pathways and develop targeted therapies in oncology, regenerative medicine, and chronic disease models.