Tumor and Stem Cell Biology Aldehyde Dehydrogenase in Combination with CD133 Defines Angiogenic Ovarian Cancer Stem Cells That Portend Poor Patient Survival

Markers that reliably identify cancer stem cells (CSC) in ovarian cancer could assist prognosis and improve strategies for therapy. CD133 is a reported marker of ovarian CSC. Aldehyde dehydrogenase (ALDH) activity is a reported CSCmarker in several solid tumors, but it has not been studied in ovarian CSC. Here we report that dual positivity of CD133 and ALDH defines a compelling marker set in ovarian CSC. All human ovarian tumors and cell lines displayed ALDH activity. ALDHþ cells isolated from ovarian cancer cell lines were chemoresistant and preferentially grew tumors, compared with ALDH cells, validating ALDH as a marker of ovarian CSC in cell lines. Notably, as few as 1,000 ALDHþ cells isolated directly from CD133 human ovarian tumors were sufficient to generate tumors in immunocompromised mice, whereas 50,000 ALDH cells were unable to initiate tumors. Using ALDH in combination with CD133 to analyze ovarian cancer cell lines, we observed even greater growth in the ALDHþCD133þ cells compared with ALDHþCD133 cells, suggesting a further enrichment of ovarian CSC in ALDHþCD133þ cells. Strikingly, as few as 11 ALDHþCD133þ cells isolated directly from human tumors were sufficient to initiate tumors in mice. Like other CSC, ovarian CSC exhibited increased angiogenic capacity compared with bulk tumor cells. Finally, the presence of ALDHþCD133þ cells in debulked primary tumor specimens correlated with reduced disease-free and overall survival in ovarian cancer patients. Taken together, our findings define ALDH and CD133 as a functionally significant set of markers to identify ovarian CSCs. Cancer Res; 71(11); 1–11. 2011 AACR.