Homologous recombination mediates cellular resistance and fraction size sensitivity to radiation therapy

TY - JOUR

T1 - Homologous recombination mediates cellular resistance and fraction size sensitivity to radiation therapy

AU - Somaiah, Navita

AU - Yarnold, John

AU - Lagerqvist, Anne

AU - Rothkamm, Kai

AU - Helleday, Thomas

N1 - Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

PY - 2013/7

Y1 - 2013/7

N2 - PURPOSE: Cellular sensitivity to radiotherapy total dose and fraction size is strongly influenced by DNA double strand break (DSB) repair. Here, we investigate response to radiotherapy fraction size using CHO cell lines deficient in specific DNA repair pathways in response to radiation induced DNA double strand breaks (DSB).EXPERIMENTAL DESIGN: We irradiated CHO cell lines, AA8 (WT), irs1SF (XRCC3-), V3-3 (DNA-PKcs-) and EM9 (XRCC1-) with 16 Gy in 1 Gy daily fractions over 3 weeks or 16 Gy in 4 Gy daily fractions over 4 days, and studied clonogenic survival, DNA DSB repair kinetics (RAD51 and 53BP1 foci staining) and cell cycle profiles (flow cytometry).RESULTS: In response to fractionated radiotherapy, wild-type and DNA repair defective cells accumulated in late S/G2 phase. In cells proficient in homologous recombination (HR), accumulation in S/G2 resulted in reduced sensitivity to fraction size and increased cellular resistance (clonogenic survival). Sensitivity to fraction size was also lost in NHEJ-defective V3-3 cells, which likely rely on functional HR. By contrast, HR-defective irs1SF cells, with functional NHEJ, remained equally sensitive to fractionation throughout the 3-week treatment.CONCLUSIONS: The high fidelity of HR, which is independent of induced DNA damage level, is postulated to explain the low fractionation sensitivity and cellular resistance of cells in S/G2 phase. In conclusion, our results suggest that HR mediates resistance to fractionated radiotherapy, an observation that may help future efforts to improve radiotherapy outcome.

AB - PURPOSE: Cellular sensitivity to radiotherapy total dose and fraction size is strongly influenced by DNA double strand break (DSB) repair. Here, we investigate response to radiotherapy fraction size using CHO cell lines deficient in specific DNA repair pathways in response to radiation induced DNA double strand breaks (DSB).EXPERIMENTAL DESIGN: We irradiated CHO cell lines, AA8 (WT), irs1SF (XRCC3-), V3-3 (DNA-PKcs-) and EM9 (XRCC1-) with 16 Gy in 1 Gy daily fractions over 3 weeks or 16 Gy in 4 Gy daily fractions over 4 days, and studied clonogenic survival, DNA DSB repair kinetics (RAD51 and 53BP1 foci staining) and cell cycle profiles (flow cytometry).RESULTS: In response to fractionated radiotherapy, wild-type and DNA repair defective cells accumulated in late S/G2 phase. In cells proficient in homologous recombination (HR), accumulation in S/G2 resulted in reduced sensitivity to fraction size and increased cellular resistance (clonogenic survival). Sensitivity to fraction size was also lost in NHEJ-defective V3-3 cells, which likely rely on functional HR. By contrast, HR-defective irs1SF cells, with functional NHEJ, remained equally sensitive to fractionation throughout the 3-week treatment.CONCLUSIONS: The high fidelity of HR, which is independent of induced DNA damage level, is postulated to explain the low fractionation sensitivity and cellular resistance of cells in S/G2 phase. In conclusion, our results suggest that HR mediates resistance to fractionated radiotherapy, an observation that may help future efforts to improve radiotherapy outcome.

KW - Animals

KW - CHO Cells

KW - Cricetinae

KW - Cricetulus

KW - DNA Breaks, Double-Stranded

KW - DNA End-Joining Repair

KW - Dose Fractionation, Radiation

KW - G2 Phase

KW - Homologous Recombination

KW - Radiation Tolerance

KW - S Phase

U2 - 10.1016/j.radonc.2013.05.012

DO - 10.1016/j.radonc.2013.05.012

M3 - SCORING: Journal article

C2 - 23746696

VL - 108

SP - 155

EP - 161

JO - RADIOTHER ONCOL

JF - RADIOTHER ONCOL

SN - 0167-8140

IS - 1

ER -