Prediction of radiosensitivity using phosphorylation of histone H2AX and apoptosis in human tumor cell lines

We examined the relationship between radiosensitivity, histone H2AX (γH2AX) phosphorylation, and apoptosis to develop a new predictive assay for radiosensitivity.

Seven human tumor cell lines, including one fibrosarcoma (HT1080), four oesophageal carcinomas (TE-9, KYSE30, KYSE150, and KYSE220), and two breast carcinomas (HCC70, and ZR75-1) were used. Cellular radiosensitivity was assessed using a standard colony-forming assay. To measure the frequency of γH2AX foci, we counted the number of foci per cell under fluorescence microscopy following immunofluorescence staining. DNA content was determined by a flow cytometric assay. To assess the frequency of apoptosis, we enumerated apoptotic cells by fluorescence microscopy 24 hours after irradiation.

All seven cell lines showed dose (0-9 Gy)-dependent increases in the number of γH2AX foci per cell 24 h after irradiation. When both the frequency of γH2AX foci normalized by DNA content and the frequency of apoptosis were used, a better correlation was observed between the actual cell survivals and the predicted ones.

Our study shows that the number of γH2AX foci after normalization of the DNA content and apoptotic cell frequency can be used as a new predictive assay for cell survival.