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Summary

The presented method combines the quantitative analysis of DNA double-strand breaks (DSBs), cell cycle distribution and apoptosis to enable cell cycle-specific evaluation of DSB induction and repair as well as the consequences of repair failure.

Abstract

The presented method or slightly modified versions have been devised to study specific treatment responses and side effects of various anti-cancer treatments as used in clinical oncology. It enables a quantitative and longitudinal analysis of the DNA damage response after genotoxic stress, as induced by radiotherapy and a multitude of anti-cancer drugs. The method covers all stages of the DNA damage response, providing endpoints for induction and repair of DNA double-strand breaks (DSBs), cell cycle arrest and cell death by apoptosis in case of repair failure. Combining these measurements provides information about cell cycle-dependent treatment effects and thus allows an in-depth study of the interplay between cellular proliferation and coping mechanisms against DNA damage. As the effect of many cancer therapeutics including chemotherapeutic agents and ionizing radiation is limited to or strongly varies according to specific cell cycle phases, correlative analyses rely on a robust and feasible method to assess the treatment effects on the DNA in a cell cycle-specific manner. This is not possible with single-endpoint assays and an important advantage of the presented method. The method is not restricted to any particular cell line and has been thoroughly tested in a multitude of tumor and normal tissue cell lines. It can be widely applied as a comprehensive genotoxicity assay in many fields of oncology besides radio-oncology, including environmental risk factor assessment, drug screening and evaluation of genetic instability in tumor cells.

Introduction

The goal of oncology is to kill or to inactivate cancer cells without harming normal cells. Many therapies either directly or indirectly induce genotoxic stress in cancer cells, but also to some extend in normal cells. Chemotherapy or targeted drugs are often combined with radiotherapy to enhance the radiosensitivity of the irradiated tumor1,2,3,4,5, which allows for a reduction of the radiation dose to minimize normal tissue damage.

Ionizing radiation and other genotoxic agents ....

Protocol

1. Preparation

  1. Prepare ≥1 x 105 cells/sample in any type of culture vessel as starting material.
    1. For example, conduct a time-course experiment after exposure of U87 glioblastoma cells to ionizing radiation: Irradiate sub-confluent U87 cells in T25 flasks in triplicates for each time point. Choose early time-points (15 min up to 8 h after irradiation) to follow the kinetics of DSB repair (γH2AX level) and late time points (24 h up to 96 h) to assess residual D.......

Representative Results

Human U87 or LN229 glioblastoma cells were irradiated with 4 Gy of photon or carbon ion radiation. Cell cycle-specific γH2AX levels and apoptosis were measured at different time points up to 48 h after irradiation using the flow cytometric method presented here (Figure 3). In both cell lines, carbon ions induced higher γH2AX peak levels that declined slower and remained significantly elevated at 24 to 48 h compared to photon radiation at the same physical dose (

Discussion

The featured method is easy to use and offers a fast, accurate and reproducible measurement of the DNA damage response including double-strand break (DSB) induction and repair, cell cycle effects and apoptotic cell death. The combination of these endpoints provides a more complete picture of their interrelations than individual assays. The method can be widely applied as a comprehensive genotoxicity assay in the fields of radiation biology, therapy and protection, and more generally in oncology (e.g., for environmental r.......

Acknowledgements

We thank the Flow Cytometry Facility team at the German Cancer Research Center (DKFZ) for their support.

....

Materials

NameCompanyCatalog NumberComments
1000 µL filter tipsNerbe plus07-693-8300
100-1000 µL pipetteEppendorf3123000063
12 x 75 mm Tubes with Cell Strainer Cap, 35 µm mesh pore sizeBD Falcon352235
15 mL tubesBD Falcon352096
200 µL filter tipsNerbe plus07-662-8300
20-200 µL pipetteEppendorf3123000055
4’,6-Diamidin-2-phenylindol (DAPI)Sigma-AldrichD9542Dissolve in water at 200 µg/ml and store aliquots at -20 °C
Alexa Fluor 488 anti-H2A.X Phospho (Ser139) Antibody, RRID: AB_2248011BioLegend613406Dilute 1:20
Alexa Fluor 647 Rabbit Anti-Active Caspase-3 Antibody, AB_1727414BD Pharmingen560626Dilute 1:20
BD FACSClean solutionBD Biosciences340345For cytometer cleaning routine after measurement
BD FACSRinse solutionBD Biosciences340346For cytometer cleaning routine after measurement
Dulbecco’s Phosphate Buffered Saline (PBS)BiochromL 182Dissolve in water to 1x concentration
Dulbecco's Modified Eagle's Medium with stable glutaminBiochromFG 0415Routine cell culture material for the example cell line used in the protocol
Ethanol absoluteVWR20821.330
Excel softwareMicrosoft
FBS Superior (fetal bovine serum)BiochromS 0615Routine cell culture material for the example cell line used in the protocol
FlowJo v10 softwareLLConline order
Fluoromount-GSouthernBiotech0100-01Embedding medium for optional preparation of microscopic slides from stained samples
folded cellulose filters, grade 3hwNeoLab11416
LSRII or LSRFortessa cytometerBD Biosciences
MG132Calbiochem474787optional drug for apoptosis positive control
Multifuge 3SR+Heraeus
ParaformaldehydeAppliChemA3813Prepare 4.5% solution fresh. Dilute in PBS by heating to 80 °C with slow stirring under the fume hood. Cover the flask with aluminium foil to prevent heat loss. Let the solution cool to room temperature and adjust the final volume. Pass the solution through a cellulose filter.
Phospho-Histone H3 (Ser10) (D2C8) XP Rabbit mAb (Alexa Fluor® 555 Conjugate) RRID: AB_10694639Cell Signaling Technology#3475Dilute 3:200
PIPETBOY acu 2Integra Biosciences155 016
Serological pipettes, 10 mLCorning4488
Serological pipettes, 25 mLCorning4489
Serological pipettes, 5 mLCorning4487
SuperKillerTRAIL (modified TNF-related apoptosis-inducing ligand)BiomolAG-40T-0002-C020optional drug for apoptosis positive control
T25 cell culture flasksGreiner bio-one690160Routine cell culture material for the example cell line used in the protocol
Trypsin/EDTAPAN BiotechP10-025500Routine cell culture material for the example cell line used in the protocol
U87 MG glioblastoma cellsATCCATCC-HTB-14Example cell line used in the protocol

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