Salinomycin inhibits canine mammary carcinoma in vitro by targeting cancer stem cells

Salinomycin (SAL), a polyether ionophore antibiotic, has been demonstrated to selectively kill cancer stem cells (CSCs) in various types of human tumor. The aim of the present study was to investigate the effects of SAL on canine mammary CSCs. CSCs in canine mammary carcinoma cell lines (CMT7364 and CIPp) were identified using a sphere formation assay and flow cytometry. The chemoresistance, invasive potential and expression of stem cell-associated proteins of these spheres was then analyzed. This demonstrated that the spheres exhibited characteristics of CSCs, including a cluster of differentiation (CD)44(+)/CD24(-/low) phenotype, upregulation of Wnt/beta-catenin signaling pathway-associated proteins and chemoresistance. The viability of the spheres was decreased in a concentration- and time-dependent manner following treatment with SAL, and the spheres did not exhibit increased resistance to SAL compared with their parental cells. In addition, exposure to SAL inhibited sphere-formation and invasive potential in canine mammary CSCs in a dose-dependent manner. Furthermore, SAL decreased the CD44(+)/CD24(-/low) population and downregulated the expression of Wnt/beta-catenin signaling-associated proteins (beta-catenin, Cyclin D1 and octamer-binding transcription factor 4) in the spheres. In conclusion, the present study demonstrated that SAL is an effective inhibitor of canine mammary CSCs in vitro, indicating that SAL is a promising chemotherapeutic agent for the treatment of canine mammary carcinoma.