Impaired DNA Repair Fidelity in a Breast Cancer Patient With Adverse Reactions to Radiotherapy.

Ghazi Alsbeih,Michael Story,Najla Al-Harbi,Sheikh Ismail

doi:10.3389/fpubh.2021.647563

Abstract

We tested the hypothesis that differences in DNA double-strand break (DSB) repair fidelity underlies differences in individual radiosensitivity and, consequently, normal tissue reactions to radiotherapy. Fibroblast cultures derived from a radio-sensitive (RS) breast cancer patient with grade 3 adverse reactions to radiotherapy were compared with normal control (NC) and hyper-radiosensitive ataxia-telangiectasia mutated (ATM) cells. DSB repair and repair fidelity were studied by Southern blotting and hybridization to Alu repetitive sequence and to a specific 3.2-Mbp NotI restriction fragment on chromosome 21, respectively. Results for DNA repair kinetics using the NotI fidelity assay showed significant differences (P < 0.001) with higher levels of misrepaired (misrejoined and unrejoined) DSBs in RS and ATM compared with NC. At 24-h postradiation, the relative fractions of misrepaired DSBs were 10.64, 23.08, and 44.70% for NC, RS, and ATM, respectively. The Alu assay showed significant (P < 0.05) differences in unrepaired DSBs only between the ATM and both NC and RS at the time points of 12 and 24 h. At 24 h, the relative percentages of DSBs unrepaired were 1.33, 3.43, and 12.13% for NC, RS, and ATM, respectively. The comparison between the two assays indicated an average of 5-fold higher fractions of misrepaired (NotI assay) than unrepaired (Alu assay) DSBs. In conclusion, this patient with increased radiotoxicity displayed more prominent misrepaired than unrepaired DSBs, suggesting that DNA repair fidelity is a potential marker for the adverse reactions to radiotherapy. More studies are required to confirm these results and further develop DSB repair fidelity as a hallmark biomarker for interindividual differences in radiosensitivity.

Highlights

Compelling evidence suggests that adverse reactions to radiotherapy are associated with increased patient sensitivity to ionizing radiation [1]
Initial evidence for DNA double-strand break (DSB) Misrepair the heritability of radiosensitivity originated from the studies of rare genetic disorders such as ataxia-telangiectasia (A-T), Nijmegen breakage syndrome, Nijmegen breakage syndromelike disorder (RAD50 deficiency), ligase IV deficiency, A-T-like disorder, and Fanconi’s anemia [7, 8]
We examined the possibility of detecting differences in DSB misrejoining in a primary human fibroblast strain derived from a clinically radiosensitive patient with marked adverse effects to radiotherapy

Summary

Introduction

Compelling evidence suggests that adverse reactions to radiotherapy are associated with increased patient sensitivity to ionizing radiation [1]. Each syndrome has its own phenotypical characteristics, cells derived from those patients demonstrate spontaneous chromosomal instability and hypersensitivity to ionizing radiation due to mutations affecting DNA strand breaks signaling, recognition, and repair capability [9]. Cellular death mechanisms, cell cycle kinetics, and the various underlying genetic defects influence the expression and detection of chromosome damage, making qualitative cytogenetic approaches less precise as quantitative measures of cellular radiosensitivity [14]. Another method for examining the fidelity of DNA repair is to measure the ability of cells or cell extracts to reactivate plasmids containing damaged reporter genes. This approach has proven useful for examining DNA repair in some radiosensitive cell lines [15]; it is not quantitative, as there was little difference in this measure of DSB repair fidelity between some cell lines with wide differences in radiosensitivity [16]

Methods

Results

Conclusion