Abstract
BACKGROUND: Tumour radiosensitivity would be particularly useful in optimizing the radiation dose during radiotherapy. The aim of the current study was to evaluate the potential value of phosphorylated H2AX (γH2AX) and ATM (pATM) in assessing (12)C(6+) radiosensitivity of tumour cells. METHODS: Human cervical carcinoma HeLa cells, hepatoma HepG2 cells, and mucoepidermoid carcinoma MEC-1 cells were irradiated with different doses of (12)C(6+). The survival fraction was assayed with clonogenic survival method and the foci of γH2AX and pATM was visualized using immunocytochemical methods. Flow cytometry was used to assay γH2AX, pATM and the cell cycle. RESULTS: The survival fraction decreased immediately in dose-dependent manner, but in turn, significantly increased during 24 h after (12)C(6+) irradiation. Both γH2AX and pATM foci accumulated linearly with doses and with a maximum induction at 0.5 h for γH2AX and 0.5 or 4 h for pATM, respectively, and a fraction foci kept for 24 h. The expression of γH2AX and pATM was in relation to cell cycle. The G0/G1 phase cells had the highest expression of γH2AX after 0.5 h irradiation and then decreased to a lower level at 24 h after irradiation. An obvious increase of pATM in G2/M phase was shown after 24 h of 2 and 4 Gy irradiation. The significant G2/M phase arrest was shown. There was a close relationship between the clonogenic survival and γH2AX and pATM expression both in timing and dose in response to (12)C(6+). CONCLUSIONS: The rate of γH2AX and pATM formation and loss may be an important factor in the response of cells to (12)C(6+). pATM and γH2AX are effective radiation biomarkers in assessing the radiosensitivity of (12)C(6+) in human tumor cells.