Cytotoxic activities of sesquiterpenoids from the aerial parts of Petasites japonicus against cancer stem cells

From the methanolic extract of the aerial parts of Petasites japonicus, six new eremophilane-type sesquiterpenoids, petasitesterpenes I-VI were isolated together with eight known compounds including S-japonin and eremophilenolide. The chemical structures of the isolated new compounds were elucidated based on chemical/physicochemical evidence. For petasitesterpenes I and II, the absolute configurations were established by comparison of experimental and predicted electronic circular dichroism (ECD) data. Among the isolated compounds, petasitesterpenes I, II, VI, and S-japonin showed cytotoxic activity against both human astrocytoma U-251MG cancer cells (non-CSCs) and their cancer stem cells (CSCs) isolated by sphere formation. In addition, cytotoxic activities of these compounds against breast cancer MDA-MB-231 were evaluated, supporting that petasitesterpene II has more effective than other isolated compounds.