[Radiation-induced G2 phase arrest may contribute to the radioresistance of breast cancer stem cells].

OBJECTIVE: To investigate radiation-induced cell cycle changes of human breast cancer stem cells enriched by suspension culture.

METHODS: The tumorigenicity of human breast cancer stem cell line MCF-7 cultured in serum-free media was confirmed in NOD/SCID mice, and the radiosensitivity of the cells was tested by clone formation assay following radiation exposure. Flow cytometry was performed to evaluate radiation-induced cell cycle changes, and the protein expression of pCDC25C (ser216) was measured by Western blotting.

RESULTS: After the exposure to 2 Gy radiation, the survived fraction of the cells in suspension culture and those in adherent culture was 0.856 ∓ 0.061 and 0.783 ∓ 0.097, respectively, and the cells in suspension culture showed an obviously greater capacity of tumorigenicity in NOD/SCID mice. The radiation exposure resulted in an obvious increase in the proportion of G2 phase cells from (22.03 ∓ 2.12)% to (45.83 ∓ 2.25)% and significantly increased the expression of pCDC25C (ser216).

CONCLUSION: Radiation- induced G2 phase arrest may contribute to the resistance of the breast cancer stem cells to radiotherapy.