(-)-Xanthatin as a Killer of Human Breast Cancer MCF-7 Mammosphere Cells: A Comparative Study with Salinomycin.

Experimental evidence accumulated by our research group and others strongly suggests that (-)-xanthatin, a xanthanolide sesquiterpene lactone, exhibits anti-proliferative effects on human breast cancer cells (in vitro) as well as anti-tumor effects in experimental animals (in vivo). In cancer biology, it is now critically important for anti-cancer agents to selectively target cancer stem cells (CSCs) in order to overcome cancer therapeutic resistance and recurrence. However, it has not yet been established whether (-)-xanthatin abrogates the formation of breast CSCs. In the present study, we utilized chemically synthesized pure (-)-xanthatin and a culture system to obtain mammospheres from human breast cancer MCF-7 cells, which are a CSC-enriched population. We herein demonstrated for the first time that (-)-xanthatin exhibited the ability to kill mammospheres, similar to salinomycin, an established selective killer of CSCs. A possible anti-proliferative mechanism toward mammospheres by (-)-xanthatin is discussed.