The stability of breast cancer progenitor cells during cryopreservation: Maintenance of proliferation, self-renewal, and senescence characteristics.

Cancer stem cells are believed to be the driving force behind tumor progression and development. Despite extensive studies on the effects of cryopreservation on embryonic and hematopoietic stem cells there is only limited data that directly deals with in the cryopreservation of cancer stem cells. In this study, we looked at the effect of cryopreservation on breast cancer progenitor cells known as mammospheres, which are derived from the MCF7 breast carcinoma cell line. We focused on the effect of cryopreservation on the cell biology and function of tumor-initiating cells using a standard method of cryopreservation with 15% dimethyl sulfoxide (Me(2)SO). Cell proliferation and survival was analyzed by alamarBlue solution on cryopreserved cells stored for 1-12 weeks and also by the expression of Ki-67. To assess self-renewal, single cells were harvested by limiting dilution procedure and wells were scored once a week. In order to investigate senescence, the activity of beta-galactosidase was detected by histochemical staining. Our results indicate that cryopreservation of breast cancer initiating cells will not reduce the ability of the cells to proliferate following cryopreservation storage for up to 12 months. Similarly, self-renewal, a unique property of stem cells, was shown to be maintained during cryopreservation. In contrast, cryopreservation of the mammospheres significantly increases the rate of senescence-mediated pathways. These data suggest that although cryopreservation of tumor-initiating cells is feasible but further studies are necessary to achieve a trustable repository of tumor-initiating cells and the design of new therapeutic measures to specifically target these cells.