Background: The high rates of women's death from breast cancer occur due to acquired resistance by
patients to certain treatments, enabling the recurrence and/or tumor growth, invasion and metastasis. It has been
demonstrated that the presence of cancer stem cells in human tumors, as responsible for recurrence and resistance
to therapy. Studies have identified OCT4 as responsible for self-renewal and maintenance of pluripotency of stem
cells. Thus, it is interesting to study potential drugs that target this specific population in breast cancer.
Melatonin, appears to have oncostatic effects on cancer cells, however, little is known about its therapeutic effect
on cancer stem cells.
Objective: Evaluate the viability and the expression of OCT4 in breast cancer stem cells, MCF-7 and MDA-MB-
231, after melatonin treatment.
Method: The cells were grown in a 3-dimensional model of mammospheres, representing the breast cancer stem
cell population and treated or not with melatonin. The cell viability of mammospheres were evaluated by MTT
assay and the OCT4 expression, a cancer stem cells marker, was verified by immunocitochemistry.
Results: Our results demonstrated that the melatonin treatment decreased the cell viability of MCF-7 and MDAMB-
231 mammospheres. Furthermore, it was observed that in both cell lines, the expression of OCT4 was
decreased in melatonin-treated cells compared to the control group.
Conclusions: This fact suggests that melatonin is effective against breast cancer stem cells inhibiting the cell
viability via OCT 4. Based on that, we believe that melatonin has a high potential to be used as an alternative
treatment for breast cancer.