Eupatolide inhibits the TGF-β1-induced migration of breast cancer cells via downregulation of SMAD3 phosphorylation and transcriptional repression of ALK5

The epithelial-mesenchymal transition (EMT) is a hallmark of cancer metastasis, and the associated molecular signaling pathways are regarded as therapeutic targets for cancer treatment. Thus, suppressing EMT with a natural chemical compound may be of therapeutic benefit. Eupatolide is a natural chemical compound extracted from the medicinal plant Inula britannica, which is used in Eastern Asia to treat bronchitis, disorders of the digestive system and inflammation. Besides the anti-inflammatory function of eupatolide, the present study found that eupatolide suppressed the migration and invasion of breast cancer cells, which was associated with the downregulation of vimentin in MDA-MB-231 cells and the upregulation of E-cadherin in MCF-7 cells. Treatment with eupatolide also significantly inhibited the migration and invasion of breast cancer cells that had been stimulated with transforming growth factor-β1 (TGF-β1). Eupatolide also suppressed TGF-β1-induced EMT via downregulation of mothers against decapentaplegic homolog 3 (SMAD3) phosphorylation and transcriptional repression of TGF-β receptor 1 (ALK5). In addition to this canonical pathway, the non-canonical protein kinase B (AKT) and extracellular signal-regulated kinase (ERK) pathways were also inhibited by eupatolide treatment. In summary, the results suggest that eupatolide suppresses the migration and invasion of breast cancer cells by blocking the canonical ALK5-SMAD3 signaling pathway and the non-canonical ERK and AKT signaling pathways.