Objectives: Breast cancer stem cells (BCSCs) contribute to breast cancer progression, relapse, and treatmentresistance. Identification of the natural inhibitory components of BCSCs is therefore critical for clinical treat-ment. Here, we investigated whether isoharringtonine (IHT) had inhibitory effects on BCSCs in breast cancer celllines.

Methods: HCC1806, HCC1937, and MCF7 cells were treated with IHT. The proliferation and the migration ofcells were detected by MTS assay and wound healing migration assay, respectively. The proportions of BCSCswere determined by flow cytometry and tumor sphere formation assay. Using real-time quantitative polymerasechain reaction (qRT-PCR) and Western blotting, the expression of Nanog and activation of STAT3 were detected,respectively.

Results: Results showed that IHT inhibited the proliferation of HCC1806, HCC1937, and MCF-7 cells, andsuppressed the migration of HCC1806 and HCC1937 cells in a dose-dependent manner. IHT treatment decreasedthe proportion of BCSCs in MCF-7, HCC1806, and HCC1937 cells. In addition, the mRNA level of Nanong wassignificantly downregulated after IHT treatment. We also found an inhibitory effect of IHT on STAT3 activation.

Conclusion: IHT inhibited the proliferation, migration, and BCSC proportion of breast cancer cell lines via in-hibition of the STAT3/Nanong pathway.