DNA damage responses in cell cycle G2 phase and mitosis--tracking and targeting.

Background: In order to determine temporal responses of cell cycle populations to DNA damage, a rational combination of cell cycle analyses is critical. Moreover, the targeting of cell cycle checkpoint responses may modify the cytotoxic effect of DNA damage.

Materials And Methods: The characteristics of cell cycle populations (DNA content, cell cycle transitioning of S phase cells and size of mitotic cell fraction within the total G2/M phase population) in HeLa cells exposed to ionizing radiation were analyzed using three individual flow cytometry-based assays. The potential radiosensitization from inhibiting DNA damage responses was assessed by the colony formation assay.

Results: Irradiation resulted in an initial accumulation of S phase cells in G2 phase, from which the arrested cells were subsequently released to enter mitosis. Upon drug inhibition of G2 checkpoint signaling or mitotic progression, the cytotoxic effect of ionizing radiation on the HeLa cells was amplified.

Conclusion: DNA damage-induced cell cycle responses, analyzed by selected cytometry assays and modified by specific targeting, might contribute to an understanding of how to improve radiotherapy outcome.