Correlation between DNA double strand breaks and cell death in peripheral blood lymphocytes from breast cancer patients

Abstract

Purpose: Radiotherapy affects both cancer and healthy cells, potentially causing side effects. Factors like total dose administered or patient individual characteristics, such as genetic variability, influence radiotoxicity. Several biomarkers have been proposed to predict radiotoxicity, especially those based on apoptosis or DNA damage, like γ-H2AX, which correlates with DNA breaks. Our aim is to analyze how apoptosis and γ-H2AX correlate to each other and to link these results with selected SNPs associated with apoptosis.

Material and methods: Blood samples from 60 breast cancer patients in remission were collected. Mononucleated cells were isolated and γ-H2AX kinetics was evaluated at 1, 2, 4 and 24 h after 2 Gy irradiation. Apoptosis in CD8+ lymphocytes was assessed at 24 and 48 h after 8 Gy irradiation. SNP genotyping was performed for 27 apoptosis-related SNPs.

Results: Individual basal levels of γ-H2AX and apoptosis correlated positively with those observed at different post-irradiation times. High interindividual variability was observed in both γ-H2AX and apoptosis under all tested conditions. When both biomarkers were analyzed together, a negative correlation was observed between basal and residual γ-H2AX levels and apoptosis at 48 h post-irradiation. SNP analysis identified two apoptosis-associated SNPs located at TP53 and FAS genes.

Conclusions: These findings support previous studies done in cancer patients showing a negative correlation between apoptosis and γ-H2AX. Overall, our results seem to indicate that individuals with less efficiency in removing damaged cells, probably due to genetic polymorphisms, presented more basal and residual levels of DNA damage.

Keywords: DNA damage response; Radiosensitivity; polymorphisms; radioinduced apoptosis; radioinduced y-H2AX.