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Introduction: The cancer stem cells are the small population of cells in tumor tissue with the ability of self-renew and differentiation into other tumor cells. Targeting these cells has great importance in the treatment of cancer and prevent cancer recurrence. Milk thistle is the plant of the Asteraceae with the scientific name of Silybum Marianum. However there is no report about the effect of Silibilin on mammospheres. So, the aim of this study was to evaluate the effect of silibinin on the ability of self-renewal, growth and stemness genes expression and markers of MCF-7 cell line derived mammospheres.

Methods: In this study, the viability of the MCF7 derived mammospheres were treated with silibinin for 72h using MTS test and 50% lethal dose (IC50) have been evaluated, respectively. Next, untreated and treated mammospheres with silibinin were investigated for the ability of invasion, colony and sphere formation, expression of stemness genes expression includes Oct4 and KLF by real time PCR.

Results: Our data showed that silibinin decreased the MCF-7 cells in the mamospheres with a dose dependent manner. Silibinin at dose of 150 µM (IC50) reduced 4.6 and 11.2 fold the ability of sphere and colony formation respectively. Also invasion and expression of stemness genes significantly decreased.

Conclusion: Due to reduction of growth, colony and sphere formation, as well as reduction of invasion and expression of stemness genes, Silibinin can be a good candidate for targeting of cancer stem cells.