CD44+/CD24- breast cancer cells isolated from MCF-7 cultures exhibit enhanced angiogenic properties

Recent studies suggest that the relationship between cancer stem cells (CSCs) and the vascular niche may be bidirectional; the niche can support the growth and renewal of CSCs, and CSCs may contribute to the maintenance of the niche. There is little knowledge concerning the role of breast cancer stem cells in promoting tumor angiogenesis. For human breast cancers, CSCs have been shown to be associated with a CD44(+)/CD24 (-) phenotype. We investigated the potential activities of CD44(+)/CD24 (-) breast cancer stem cells in promoting tumor angiogenesis. The expression of pro-angiogenic genes was determined by quantitative real-time RT-PCR. Endothelial cell migration assays were employed to evaluate effects of conditioned media from CD44(+)/CD24 (-) on human umbilical vein endothelial cells. A chorioallantoic membrane (CAM) assay was used to study the potential of CD44(+)/CD24 (-) cells to promote angiogenesis. In our study, CD44(+)/CD24 (-) cells expressed elevated levels of pro-angiogenic factors compared with CD44(+)/CD24(+) cells. CD44(+)/CD24 (-) cell-conditioned media significantly increased endothelial cell migration. Breast cancer cell lines enriched with CD44(+)/CD24 (-) cells were more pro-angiogenic in the CAM assay than those lacking a CD44(+)/CD24 (-) subpopulation. CD44(+)/CD24 (-) cells sorted from MCF-7 cell lines were more pro-angiogenic in a CAM assay than CD44(+)/CD24(+) cells. Furthermore, the VEGF concentration was significantly higher in CD44(+)/CD24 (-) cell-conditioned media than in CD44(+)/CD24(+) cell-conditioned media. The pro-angiogenic effect of CD44(+)/CD24 (-) cells on endothelial cells was abolished by bevacizumab. Our findings demonstrate that CD44(+)/CD24 (-) breast cancer stem cells have substantial pro-angiogenic potential and activity. This provides new insights to explore in the development of targeted therapies.