Cell cycle and growth response of CHO cells to X-irradiation: threshold-free repair at low doses

• Published in: International journal of radiation oncology, biology, physics Vol. 50; no. 1; p. 221
• Main Authors: Bartkowiak, D, Högner, S, Nothdurft, W, Röttinger, E M
• Format: Journal Article
• Language: English
• Published: United States 01-05-2001
• Subjects: Animals; Cell Cycle - radiation effects; Cell Division - radiation effects; Cell Survival - radiation effects; CHO Cells - cytology; CHO Cells - physiology; CHO Cells - radiation effects; Colony-Forming Units Assay; Cricetinae; DNA - radiation effects; DNA Damage; DNA Repair - physiology; Dose-Response Relationship, Radiation; Linear Models; Models, Biological; Radiation Tolerance
• ISSN: 0360-3016
• DOI: 10.1016/S0360-3016(01)01455-9

To test the hypothesis of a threshold for induced repair of DNA damage (IR) and, secondarily, of hyperradiosensitivity (HRS) to low-dose X-irradiation.
Exponentially growing Chinese hamster ovary cells (CHO) were X-irradiated with doses from 0.2 to 8 Gy. Survival data were established by conventional colony-forming assay and flow-cytometric population counting. The early cell cycle response to radiation was studied based on DNA-profiles and bromodeoxyuridine pulse-labeling experiments.
Colony-forming data were consistent with HRS. However, these data were of low statistic significance. Population counting provided highly reproducible survival curves that were in perfect accord with the linear-quadratic (LQ) model. The dominant cell cycle reaction was a dose-dependent delay of G2 M and late S-phase.
There was no evidence for a threshold of IR and for low-dose HRS in X-irradiated CHO cells. It is suggested that DNA damage repair activity is constitutively expressed during S-phase and is additionally induced in a dose-dependent and threshold-free manner in late S-phase and G2. The resulting survival is precisely described by the LQ model.