SBE 13 HCl is a potent and selective inhibitor of activin receptor-like kinase 5 (ALK5, TGF-β receptor type I), with an IC50 of 140 nM for inhibiting TGF-β-induced Smad2/3 phosphorylation. It is primarily used in biomedical research to study TGF-β signaling pathways, particularly in models of fibrosis (e.g., idiopathic pulmonary fibrosis), epithelial-mesenchymal transition (EMT), cancer progression, metastasis, and other TGF-β-related pathologies. As a tool compound, it helps dissect receptor-mediated cellular signaling, evaluate pathway modulation, and screen for therapeutic candidates targeting these mechanisms.