| Background:Umbilical cord mesenchymal stem cells (UCMSCs) are a type of stem cell that are present in the Wharton’s jelly of the umbilical cord and the tissues surrounding blood vessels with multiple differentiation and self-renewal potential. UCMSCs were found to target a variety of primary solid tumors and their metastases. When these cells are engineered to secrete a cytokine interferon beta(IFN-β), are capable of reducing growth of MDA231human breast carcinoma cells by inducing apoptosis.It was reported that stem cells without genetic modification inhibited the growth of a variety of tumors, such as Kaposi’s sarcoma and glioma. UCMSCs have many advantages, including easy in vitro isolation and propagation, wide sources,easily obtained samples, low immunogenicity.Therefore, UCMSCs could have a wide range of clinical applications, provided that UCMSCs without genetic modification can suppress tumor growth.Objective:The purpose of the study was to detect the effect and possible mechanism of human umbilical cord mesenchymal stem cells (hUCMSCs) on the human breast cancer stem cells and to develop the basis of a novel treatment strategy for breast tumors. The specific aims are:(1) to isolated ESA+CD44+CD24-/low phenotype cells from primary human breast cancer cells and cell lines MDA-MB-231and MCF-7.(2) to detect the effect and possible mechanism of human umbilical cord mesenchymal stem cells (hUCMSCs) on the growth of stem cells in vitro.(3) to detect the effect and possible mechanism of human umbilical cord mesenchymal stem cells (hUCMSCs) on the growth of stem cells in vivo.Methods:1.Primary human breast cancer cells and MDA-MB-231and MCF-7cells were sorted in vitro using flow cytometry, and the ESA+CD44+CD24-/low cells were isolated as breast cancer stem cells (CSCs).Compare the colony forming ability of ESA+CD44+CD24-/low cells and the unsorted cells in vitro2.The inhibitory effect of hUCMSCs on CSCs was examined using the Cell Counting Kit-8(CCK8) cell proliferation and soft agar colony formation assay. CSCs were co-cultured with hUCMSCs, then examination of cell cycle and apoptotic cells by a flow cytometer.3.In vivo tumor inhibition was studied using a severe combined immunodeficient (SCID) xenograft mouse model transplanted with MDA-MB-231breast cancer stem cells. The expression of phosphoinositide3-kinase (PI3K) and AKT was examined in the xenograft tumors using immunohistochemistry.Results:1. The percentage of stem cells in breast cancer cell lines MDA-MB-231MCF-7and primary breast cancer cells is1.83%±0.28%;1.53%±0.16%;0.55%±0.17%. The number of colonies of sorted CSCs were higher than the unsorted groups (p<0.001).2. The results of the CCK-8assay and soft agar colony formation assay showed that the hUCMSCs inhibited the growth of MDA-MB-231, MCF-7and primary breast cancer stem cells in a dose-dependent manner in vitro. The ratios of the G2/M phase for the MDA-MB-231, MCF-7and primary breast cancer stem cells that were cocultured with hUCMSCs were significant increases (p<0.05), the apoptotic rates of these MDA-MB-231, MCF-7and primary breast cancer stem cells were significantly higher than that of the control (p<0.01).3. The tumor weights in the medium-and high-concentration hUCMSC groups were significantly lower than that of the control group, with statistically significant differences (p<0.05, p<0.01), and the average inhibition rates were21.4%and29.6%, respectively. The expression levels of PI3K and Akt proteins in the groups treated with increasing concentrations of hUCMSCs were significantly lower than that of the control group(P<0.001).Conclusions:1. The ESA+CD44+CD24-/low phenotype cells have the similar characteristics as cancer stem cells in aspect of unlimited self-renewal and reconstruction of tumor.2. hUCMSCs have certain inhibitory effects on the growth of breast cancer stem cells in vivo. The underlying mechanism is likely related to cell cycle arrest, induction of tumor cell apoptosis.3. hUCMSC significantly inhibited the growth of breast cancer stem cells in vivo. The underlying mechanism is likely related to suppressed activities of PI3K and Akt protein kinases. |
