Dynamic imaging analysis reveals Auger electron-emitting radio-cisplatin induces DNA damage depending on the cell cycle.

Auger electrons can induce nanoscale physiochemical damage to DNA. The present study reports a sequential and systematic evaluation of the relationship between DNA damage such as double-strand breaks (DSBs) and the cell cycle for the Auger electron-emitting agent radiolabeled cisplatin with DNA binding ability. For dynamic imaging analysis, we used U2OS-derived cancer cells expressing two fluorescent fusion proteins: tumor-suppressor p53 binding protein 1 with a green fluorescent protein (53BP1-EGFP) and proliferating cell nuclear antigen with a red fluorescent protein (PCNA-DsRed). Time-lapse images of the cells were quantitatively analyzed using the ImageJ software with the deepImageJ plugin and the Google Colaboratory platform. From the middle-to-late G1 phase, around the G1-to-S phase transition, we found increased 53BP1 foci in cells treated with the radio-cisplatin. The radio-cisplatin caused significantly more DSBs than the nonradioactive cisplatin and saline in the G1 phase but not in the other phases. These results indicate that Auger electron-induced DNA damage, including DSBs, depends on the cell cycle. The G1 phase, which is associated with low DNA repair capacity and high radiosensitivity, is a promising target; thus, combining radiolabeled cisplatin with agents that arrest cells in the G1 phase could improve the DNA-damaging effect of Auger electrons and their therapeutic efficacy.