Identification of cancer stem-like CD44+ cells in human nasopharyngeal carcinoma cell line

Abstract

Background and aims: Recent studies suggest that cancer stem cells (CSC) may be responsible for tumorigenesis and contribute to some individuals' resistance to cancer therapy. Although research is rapidly advancing in this field, to our knowledge there are few published reports about the CSC in human nasopharyngeal carcinoma (NPC). We undertook this study to separate, expand, and explore the biological features of CD44+ stem-like cancer cells from the human NPC SUNE-1 5-8F cell line.

Methods: Immunocytochemistry and flow cytometry were used to detect the expression of CD44 in SUNE-1 5-8F. Fluorescence-activated cell sorting was applied to purify CD44+ cells. MTT assay or clone formation assay was used to detect the differences of CD44+ and CD44- cells in proliferation, differentiation, radiosensitivity and chemosensitivity in vitro. The expression of stem cell markers Oct-4 and Bmi-1 was examined by reverse transcriptase polymerase chain reaction (RT-PCR).

Results: CD44 was positively expressed in ∼52.5% of NPC SUNE-1 5-8F cell line. Regardless of serum-free medium and serum medium culture conditions, freshly sorted CD44+ cells showed stronger proliferative capacity than CD44- and unsorted cells. The expression levels of Bmi-1 and Oct-4 mRNA in CD44+ cells were significantly higher than CD44- cells. After 2 Gy radiation, the average clone formation efficiency for CD44+ and CD44- cells was 22.17 ± 6.65% and 11.50 ± 5.00%, respectively (p <0.05). After cisplatin and docetaxel treatment with the same drug concentration, CD44+ cells showed a higher survival rate compared with CD44- cells.

Conclusions: CD44+ cells have the biological characteristics of tumor stem cell and may be assumed as one of the markers of NPC tumor stem cells.