Aldehyde dehydrogenase activity is a cancer stem cell marker of tongue squamous cell carcinoma

Accumulating data reveal that aldehyde dehydrogenase (ALDH) activity is a cancer stem cell marker in several types of human cancers. Whether ALDH also defines cancer stem cells of tongue squamous cell carcinoma is unknown. In the present study, we performed the Aldefluor assay to detect ALDH enzymatic activity, and used flow cytometry to isolate ALDH+ and ALDH- cells based on their ALDH activity in the Tca8113 tongue squamous cell carcinoma cell line. We found that Tca8113 cells harbored 1.3% of ALDH+ cells, which exhibited higher proliferation capacity than their ALDH- counterparts and parental cells. Sorted ALDH+ cells were able to differentiate and generate ALDH- cells in vitro. Moreover, in serum-free medium, ALDH+, but not ALDH- cells, survived and formed tumorspheres. The suppression subtractive hybridization assay revealed 68 overexpressed or underexpressed genes in the ALDH+ subpopulation relative to ALDH- cells, which included a set of known cancer stem cell-related genes. Thus, our data demonstrated that a small subset of Tca8113 cells with high ALDH enzymatic activity display characteristics of cancer stem cells, suggesting that ALDH activity may be a cancer stem cell marker for tongue squamous cell carcinoma.