DNA double-strand break repair and induction of apoptosis in ex vivo irradiated blood lymphocytes in relation to late normal tissue reactions following breast radiotherapy

Melvin Lee Kiang Chua, Simon Horn, Navita Somaiah, Sue Davies, Lone Gothard, Roger A'Hern, John Yarnold, Kai Rothkamm*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Citations (Scopus)


This study aimed to test whether induction of apoptosis following ex vivo X-irradiation of unstimulated blood lymphocytes correlated with clinical radiosensitivity and DNA double-strand break (DSB) repair in breast radiotherapy patients and healthy volunteers. Using small molecule inhibitors, the relationship between DSB repair and radiation-induced apoptosis was examined. Sixteen breast cancer patients with minimal (controls, n = 8) or extremely marked late radiation-induced change (cases, n = 8) and eight healthy volunteers were selected. DSBs were quantified by γH2AX/53BP1 immunofluorescence, and apoptosis was measured using a fluorogenic inhibitor of caspases assay. Mean γH2AX/53BP1 focus levels 24 h after exposure to 4 Gy were higher in cases (12.7 foci per cell) than in controls (10.3 foci per cell, p = 0.002). In contrast, the mean apoptotic fraction 48 h after 8 Gy was comparable, 37.2 % in cases and 34.7 % in controls (p = 0.442). Residual focus and apoptosis levels were not correlated within individuals (Spearman's R = -0.0059, p = 0.785). However, cells treated with DNA-PK inhibitor Nu7441 had higher focus and apoptosis levels 48 h after 1 Gy compared to mock-treated cells, suggesting that apoptosis induction following irradiation is modulated by DSB repair. This effect required functional ATM since cells treated simultaneously with Nu7441 and the ATM inhibitor Ku55933 were resistant to apoptosis despite high levels of residual foci. One clinical case displayed an impaired DNA-PK-dependent end-joining cellular phenotype. In summary, clinical radiosensitivity may be associated with impaired DSB repair in some patients. Although pharmaceutical inhibition of ATM and DNA-PK affected apoptosis induction and DSB repair, no association was observed between apoptosis and residual focus levels in patients and volunteers.

Original languageEnglish
Pages (from-to)355-364
Number of pages10
JournalRadiation and Environmental Biophysics
Issue number2
Publication statusPublished - May 2014

Bibliographical note

Funding Information:
Acknowledgments This study was funded by The Royal Marsden National Health Service (NHS) Foundation Trust Charity Panel (grant number 06048) and the National Institute for Health Research (NIHR). The authors would also like to acknowledge NHS funding to the NIHR Biomedical Research Centre. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.


  • DNA double-strand break repair
  • Gamma-H2AX foci
  • Late normal tissue damage
  • Radiation-induced apoptosis
  • Radiotherapy


Dive into the research topics of 'DNA double-strand break repair and induction of apoptosis in ex vivo irradiated blood lymphocytes in relation to late normal tissue reactions following breast radiotherapy'. Together they form a unique fingerprint.

Cite this