{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T06:08:50Z","timestamp":1790662130243,"version":"4.1.0"},"reference-count":37,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2022,8,4]],"date-time":"2022-08-04T00:00:00Z","timestamp":1659571200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"UKRI","award":["MR\/T021721\/1"],"award-info":[{"award-number":["MR\/T021721\/1"]}]},{"name":"Queen\u2019s University Belfast","award":["MR\/T021721\/1"],"award-info":[{"award-number":["MR\/T021721\/1"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Cancers"],"abstract":"<jats:p>Pharmacological inhibitors of DNA damage response (DDR) proteins, such as the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia and Rad3-related (ATR) kinases and poly (ADP-ribose) polymerase (PARP), have been developed to overcome tumor radioresistance. Despite demonstrating radiosensitization preclinically, they have performed suboptimally in clinical trials, possibly due to an incomplete understanding of the influence of DDR inhibition on ionizing radiation (IR) dose fractionation and sublethal damage repair. Hence, this study aimed to evaluate the radiosensitizing ability under fractionation of ATM inhibitor AZD0156, ATR inhibitor AZD6738 and PARP inhibitor AZD2281 (olaparib), utilizing MDA-MB-231 and MCF-7 human breast cancer cells. Clonogenic assays were performed to assess cell survival and sublethal damage repair after treatment with DDR inhibitors and either single-dose or fractionated IR. Immunofluorescence microscopy was utilized to evaluate DNA double-strand break repair kinetics. Cell cycle distributions were investigated using flow cytometry. All inhibitors showed significant radiosensitization, which was significantly greater following fractionated IR than single-dose IR. They also led to more unrepaired DNA double-strand breaks at 24 h post-IR. This study provides preclinical evidence for the role of AZD0156, AZD6738 and olaparib as radiosensitizing agents. Still, it highlights the need to evaluate these drugs in fractionated settings mirroring clinical practice to optimize the trial design.<\/jats:p>","DOI":"10.3390\/cancers14153794","type":"journal-article","created":{"date-parts":[[2022,8,4]],"date-time":"2022-08-04T21:52:48Z","timestamp":1659649968000},"page":"3794","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":17,"title":["DNA Repair Inhibitors Potentiate Fractionated Radiotherapy More Than Single-Dose Radiotherapy in Breast Cancer Cells"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3170-6300","authenticated-orcid":false,"given":"Wen-Kyle","family":"Wong","sequence":"first","affiliation":[{"name":"The Patrick G Johnston Centre for Cancer Research, Queen\u2019s University Belfast, 97 Lisburn Road, Belfast BT9 7AE, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7917-8578","authenticated-orcid":false,"given":"Francisco D. C.","family":"Guerra Liberal","sequence":"additional","affiliation":[{"name":"The Patrick G Johnston Centre for Cancer Research, Queen\u2019s University Belfast, 97 Lisburn Road, Belfast BT9 7AE, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5980-6728","authenticated-orcid":false,"given":"Stephen J.","family":"McMahon","sequence":"additional","affiliation":[{"name":"The Patrick G Johnston Centre for Cancer Research, Queen\u2019s University Belfast, 97 Lisburn Road, Belfast BT9 7AE, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,8,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"527","DOI":"10.1038\/nrclinonc.2015.120","article-title":"Opportunities and challenges of radiotherapy for treating cancer","volume":"12","author":"Schaue","year":"2015","journal-title":"Nat. Rev. Clin. Oncol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"287","DOI":"10.1038\/nature10760","article-title":"The DNA damage response and cancer therapy","volume":"481","author":"Lord","year":"2012","journal-title":"Nature"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1009","DOI":"10.3389\/fonc.2019.01009","article-title":"Altering DNA repair to improve radiation therapy: Specific and multiple pathway targeting","volume":"9","author":"Biau","year":"2019","journal-title":"Front. Oncol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1071","DOI":"10.1038\/nature08467","article-title":"The DNA-damage response in human biology and disease","volume":"461","author":"Jackson","year":"2009","journal-title":"Nature"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"237","DOI":"10.1016\/j.canlet.2012.01.007","article-title":"DNA damage-induced cell death: From specific DNA lesions to the DNA damage response and apoptosis","volume":"332","author":"Roos","year":"2013","journal-title":"Cancer Lett."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Joiner, M., and Kogel, A.v.d. (2018). Irradiation-induced damage and the DNA damage response. Basic Clinical Radiobiology, CRC Press.","DOI":"10.1201\/9780429490606"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"3682","DOI":"10.1016\/j.febslet.2010.07.029","article-title":"The MRN complex in double-strand break repair and telomere maintenance","volume":"584","author":"Lamarche","year":"2010","journal-title":"FEBS Lett."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"409","DOI":"10.1101\/gad.2021311","article-title":"Dynamics of DNA damage response proteins at DNA breaks: A focus on protein modifications","volume":"25","author":"Polo","year":"2011","journal-title":"Genes Dev."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"107391","DOI":"10.1016\/j.pharmthera.2019.07.002","article-title":"ATM in DNA repair in cancer","volume":"203","author":"Jin","year":"2019","journal-title":"Pharmacol. Ther."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"177","DOI":"10.1016\/j.dnarep.2018.08.022","article-title":"The comings and goings of PARP-1 in response to DNA damage","volume":"71","author":"Pascal","year":"2018","journal-title":"DNA Repair"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"622","DOI":"10.1038\/nrm.2017.67","article-title":"The essential kinase ATR: Ensuring faithful duplication of a challenging genome","volume":"18","author":"Saldivar","year":"2017","journal-title":"Nat. Rev. Mol. Cell Biol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"251","DOI":"10.1089\/ars.2013.5668","article-title":"Ionizing radiation-induced DNA damage, response, and repair","volume":"21","author":"Santivasi","year":"2014","journal-title":"Antioxid. Redox Signal."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1285","DOI":"10.1002\/cam4.1318","article-title":"PARP inhibitor olaparib sensitizes cholangiocarcinoma cells to radiation","volume":"7","author":"Mao","year":"2018","journal-title":"Cancer Med."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1158\/1535-7163.MCT-18-1394","article-title":"Pharmacology of the ATM inhibitor AZD0156: Potentiation of irradiation and olaparib responses preclinically","volume":"19","author":"Riches","year":"2020","journal-title":"Mol. Cancer Ther."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"2462","DOI":"10.1158\/1535-7163.MCT-18-0470","article-title":"ATR inhibition is a promising radiosensitizing strategy for triple-negative breast cancer","volume":"17","author":"Tu","year":"2018","journal-title":"Mol. Cancer Ther."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"105","DOI":"10.1007\/s11060-016-2275-x","article-title":"Veliparib in combination with whole-brain radiation therapy for patients with brain metastases from non-small cell lung cancer: Results of a randomized, global, placebo-controlled study","volume":"131","author":"Chabot","year":"2017","journal-title":"J. Neurooncol."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Joiner, M., and Kogel, A.v.d. (2018). Modified fractionation. Basic Clinical Radiobiology, CRC Press.","DOI":"10.1201\/9780429490606"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1419","DOI":"10.1200\/JCO.2007.14.5565","article-title":"Estrogen receptor, progesterone receptor, HER-2, and response to postmastectomy radiotherapy in high-risk breast cancer: The Danish Breast Cancer Cooperative Group","volume":"26","author":"Kyndi","year":"2008","journal-title":"J. Clin. Oncol."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1002\/ijc.30373","article-title":"Anti-tumor activity of the ATR inhibitor AZD6738 in HER2 positive breast cancer cells","volume":"140","author":"Kim","year":"2017","journal-title":"Int. J. Cancer Res."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1158\/1535-7163.MCT-16-0239","article-title":"Radiosensitization by the ATR inhibitor AZD6738 through generation of acentric micronuclei","volume":"16","author":"Dillon","year":"2017","journal-title":"Mol. Cancer Ther."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Jang, N.Y., Kim, D.H., Cho, B.J., Choi, E.J., Lee, J.-S., Wu, H.-G., Chie, E.K., and Kim, I.A. (2015). Radiosensitization with combined use of olaparib and PI-103 in triple-negative breast cancer. BMC Cancer, 15.","DOI":"10.1186\/s12885-015-1090-7"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"2315","DOI":"10.1038\/nprot.2006.339","article-title":"Clonogenic assay of cells in vitro","volume":"1","author":"Franken","year":"2006","journal-title":"Nat. Protoc."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Joiner, M., and Kogel, A.v.d. (2018). Quantifying cell kill and cell survival. Basic Clinical Radiobiology, CRC Press.","DOI":"10.1201\/9780429490606"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1651","DOI":"10.7150\/thno.15019","article-title":"Standards and methodologies for characterizing radiobiological impact of high-Z nanoparticles","volume":"6","author":"Subiel","year":"2016","journal-title":"Theranostics"},{"key":"ref_25","first-page":"e56617","article-title":"Immunofluorescence Microscopy of \u03b3H2AX and 53BP1 for Analyzing the Formation and Repair of DNA Double-strand Breaks","volume":"129","author":"Popp","year":"2017","journal-title":"J. Vis. Exp."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"534","DOI":"10.1016\/j.ygyno.2018.07.002","article-title":"Radiosensitization by the PARP inhibitor olaparib in BRCA1-proficient and deficient high-grade serous ovarian carcinomas","volume":"150","author":"Bi","year":"2018","journal-title":"Gynecol. Oncol."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"327","DOI":"10.1534\/g3.111.000554","article-title":"Replication stress-induced chromosome breakage is correlated with replication fork progression and is preceded by single-stranded DNA formation","volume":"1","author":"Feng","year":"2011","journal-title":"G3 Genes Genomes Genet."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"6170","DOI":"10.1093\/nar\/gkl840","article-title":"PARP-1 and Ku compete for repair of DNA double strand breaks by distinct NHEJ pathways","volume":"34","author":"Wang","year":"2006","journal-title":"Nucleic Acids Res."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"3320","DOI":"10.1158\/0008-5472.CAN-09-3800","article-title":"Coordination of centrosome homeostasis and DNA repair is intact in MCF-7 and disrupted in MDA-MB 231 breast cancer cells","volume":"70","author":"Acu","year":"2010","journal-title":"Cancer Res."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"128","DOI":"10.1016\/j.euprot.2015.05.002","article-title":"Pathway-centric analysis of the DNA damage response to chemotherapeutic agents in two breast cell lines","volume":"8","author":"Antberg","year":"2015","journal-title":"EuPA Open Proteom."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"803","DOI":"10.1093\/jrr\/rrx030","article-title":"Equivalency of the quality of sublethal lesions after photons and high-linear energy transfer ion beams","volume":"58","author":"Furusawa","year":"2017","journal-title":"J. Radiat. Res."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"557","DOI":"10.1016\/0360-3016(87)90071-X","article-title":"Is the rate of repair of radiation-induced sublethal damage in rat spinal cord dependent on the size of dose per fraction?","volume":"13","author":"Ang","year":"1987","journal-title":"Int. J. Radiat. Oncol. Biol. Phys."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Joiner, M., and Kogel, A.v.d. (2018). Tumour growth and response to radiation. Basic Clinical Radiobiology, CRC Press.","DOI":"10.1201\/9780429490606"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"928","DOI":"10.1016\/j.ijrobp.2004.03.005","article-title":"Role of cell cycle in mediating sensitivity to radiotherapy","volume":"59","author":"Pawlik","year":"2004","journal-title":"Int. J. Radiat. Oncol. Biol. Phys."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"47","DOI":"10.1007\/s10549-013-2785-6","article-title":"DNA-PK inhibition by NU7441 sensitizes breast cancer cells to ionizing radiation and doxorubicin","volume":"143","author":"Ciszewski","year":"2014","journal-title":"Breast Cancer Res. Treat."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"409","DOI":"10.1038\/nrc3958","article-title":"The tumour microenvironment after radiotherapy: Mechanisms of resistance and recurrence","volume":"15","author":"Barker","year":"2015","journal-title":"Nat. Rev. Cancer"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"917","DOI":"10.1038\/nature03445","article-title":"Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy","volume":"434","author":"Farmer","year":"2005","journal-title":"Nature"}],"container-title":["Cancers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-6694\/14\/15\/3794\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T00:04:00Z","timestamp":1760141040000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-6694\/14\/15\/3794"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,8,4]]},"references-count":37,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2022,8]]}},"alternative-id":["cancers14153794"],"URL":"https:\/\/doi.org\/10.3390\/cancers14153794","relation":{},"ISSN":["2072-6694"],"issn-type":[{"value":"2072-6694","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,8,4]]}}}