SIS3 HCl is primarily used in research settings to study the TGF-β signaling pathway. It acts as a specific inhibitor of Smad3 phosphorylation, making it a valuable tool for investigating the role of Smad3 in cellular processes such as fibrosis, inflammation, and cancer progression. Researchers utilize SIS3 HCl to explore its potential therapeutic effects in diseases where TGF-β signaling is dysregulated, including pulmonary fibrosis, liver fibrosis, and certain types of cancer. Additionally, it is employed in in vitro and in vivo studies to better understand the mechanisms of TGF-β-mediated cellular responses and to develop targeted therapies. Its ability to selectively inhibit Smad3 makes it a key compound in the field of molecular biology and drug discovery.