ALDEFLUOR-positive populations in breast cell lines: evidence for cancer stem cells properties and gene expression profile (GEP)

1307 Evidence for the cancer stem cell concept has emerged recently in many fields of cancerous pathology. As in leukemia, myeloma, melanoma, brain, colon and prostate malignancies, it was shown that breast tumors derive from and are driven by a small population of cancer stem cells. The extension of this concept to different kinds of tumors suggests that some same markers will identify cancer stem cells in different malignancies. One approach to find these “universal” markers is to rely on conserved stem or progenitor cells functions. Aldehyde dehydrogenase1 (ALDH1), a detoxifying enzyme implicated in retinoic acid metabolism, fits this description is enzymatic activity has been associated with the identification of cancer stem cells in multiple myeloma and leukemia. Here, we have aimed at characterizing in breast cell lines, a population of cells sorted by flow cytometry using an enzymatic fluorescent assay, ALDEFLUOR, based on ALDH activity. First, we showed that the presence of ALDEFLUOR-positive cells was more frequent and higher in the 15 basal-like breast cell lines than in the 13 luminal ones in which only 5 cell lines contained ALDEFLUOR-positive cells. We had previously established the subtype of the 29 cell lines using DNA microarrays. Second, we demonstrated the ability of the ALDEFLUOR-positive to form much more spheres in suspension cultures compared to the negative populations in the same cell lines. Third, we proved the tumorigenic properties of the ALDEFLUOR-positive population compared to ALDEFLUOR-negative and whole cell line, by injecting orthotopically limiting dilution of each population in cleared and humanized NOD/SCID mice fat pads. These in vitro and in vivo analyses confirmed the cancer stem cell properties of the ALDEFLUOR-positive population.Finally, we profiled the ALDEFLUOR-positive and negative cells from ten cell lines with Affymetrix U133 Plus 2.0 human oligonucleotide microarrays. We compared the gene expression profile (GEP) of the ALDEFLUOR-positive population with previously established stem cell signatures, and determined the molecular subtype by comparison to the ALDELFUOR-negative or the whole cell line population. The GEP of ALDEFLUOR-positive cells will help discover other potential cancer stem cell markers and develop the field of new targeted therapies for breast cancers.