Previous studies have demonstrated that the natural product isotoosendanin (ITSN) inhibited triple-negative breast cancer (TNBC) metastasis by preventing epithelial-mesenchymal transition (EMT) and lamellipodia formation regulated by the TGF-β–Smad2/3 signaling pathway in TNBC cells through directly binding to TGF-β receptor type 1 (TGF-βR1).