Mammosphere Culture of Established Cell Lines Does Not Enrich for a More Tumorigenic Breast Cancer Stem Cell Population.

Abstract

Abstract Background:The cancer stem cell model suggests that tumors arise from and are maintained by a relatively small proportion of cells, termed cancer stem cells. According to this model, only these cells have the capacity for self-renewal and the ability to repopulate the tumor bulk by giving rise to the phenotypically heterogeneous populations of cells that comprise the primary tumor. Evidence to support the cancer stem cell model has been provided by isolation of subpopulations of cells on the basis of differential expression of cell surface markers, followed by functional transplantation into animal models. These studies reveal that only a small subset of CD44+/CD24-/low cancer cells retain the ability to form new tumors after transplantation in immunodeficient mice, consistent with the cancer stem cell model. These results indicate that it may be necessary to target and eliminate cancer stem cells in order to eradicate tumors.Material and Methods:Previous studies have suggested that only breast stem cells have the capacity to proliferate in suspension as spherical colonies termed mammospheres, and that mammosphere derived breast cancer cells are CD44+/CD24-/low and able to form tumors that reproduce the heterogeneity of the original primary tumor when injected into the mammary fat pad of immunodeficient mice. This indicates that mammospheres are comprised of breast cancer stem cells. To identify and characterize breast cancer stem cells more completely, the mammosphere culture system was used to isolate and propagate breast cancer stem cells from three basal breast cancer cell lines (BT549, MDA231, MDA436) and three luminal breast cancer cell lines (MCF7, SKBR3, T47D). The tumorigenicity of the cultured mammospheres and parental cell lines was examined using dilution studies in immunodeficient mice and gene expression profiles were studied by microarray analysis.Results and Discussion:No significant differences in tumorigenicity were observed between breast cancer cells cultured as mammospheres versus standard culture conditions. Furthermore, no consistent differences in gene expression profiles were observed between mammosphere and parental cells across the panel of cancer cell lines. These results suggest that mammosphere culture is not capable of significantly enriching for a more tumorigenic breast cancer stem cell population from established breast cancer cell lines. This may indicate that cancer subpopulations that exist in primary tumors are lost during the long term culture of breast cancer cell lines and that these systems may not be a suitable model for breast cancer stem cell studies. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 502.