{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,22]],"date-time":"2026-04-22T11:40:36Z","timestamp":1776858036373,"version":"3.51.2"},"reference-count":49,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2026,4,21]],"date-time":"2026-04-21T00:00:00Z","timestamp":1776729600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Cells"],"abstract":"<jats:p>CDK4\/6 inhibitors such as palbociclib, ribociclib and abemaciclib are commonly used in the clinical treatment of HR-positive, HER2-negative metastatic or locally advanced breast cancer. Patients with metastatic disease often receive palliative radiotherapy for symptom control of bone metastases and\/or local lesions, typically administered in close temporal proximity to CDK4\/6 inhibitor therapy, although treatment with the inhibitors may be temporarily paused during the radiotherapy period in some cases. In this study, we investigated the extent to which senescence is induced by CDK4\/6 inhibitors, ionizing radiation, and the combination of the two, compared to other types of cell fate. Eight breast cancer cell lines with different molecular subtypes and two healthy cell lines (fibroblasts and keratinocytes) were treated with CDK inhibition using palbociclib, ribociclib or abemaciclib and with or without a single dose of 2 Gy ionizing radiation. Cellular senescence, cell death in form of apoptosis and necrosis, and the cell cycle were analyzed using flow cytometry. We focused mainly on understanding how CDK inhibition can trigger cellular senescence. Our data showed that in many cell lines \u2014but not all\u2014the use of CDK inhibitors induced senescence much more strongly than cell death. Except for one cell line, significantly more cell lines died necrotically than apoptotically. Neither apoptosis nor necrosis was responsible for a major cell fate after CDK inhibition. Combination therapy with irradiation did not show a clear additive effect. In cell lines, senescence is clearly triggered by CDK4\/6 inhibitors and even more so when in combination with ionizing radiation, which, when transferred to patients, could lead to less damage caused by cell loss, such as necrotic areas. However, it could also lead to more senescence-specific side effects, such as inflammation-induced tumors and fibrosis.<\/jats:p>","DOI":"10.3390\/cells15080734","type":"journal-article","created":{"date-parts":[[2026,4,22]],"date-time":"2026-04-22T10:38:14Z","timestamp":1776854294000},"page":"734","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Combined CDK4\/6 Inhibition and Radiation: Effects on Cellular Senescence, Cell Cycle Regulation, and Cell Death in Mammary Carcinoma Cells"],"prefix":"10.3390","volume":"15","author":[{"given":"Lisa","family":"Quarz","sequence":"first","affiliation":[{"name":"Department of Radiation Oncology, Universit\u00e4tsklinikum Erlangen, Friedrich-Alexander-Universit\u00e4t Erlangen-N\u00fcrnberg (FAU), Universit\u00e4tsstra\u00dfe 27, 91054 Erlangen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8040-3226","authenticated-orcid":false,"given":"Luitpold V.","family":"Distel","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology, Universit\u00e4tsklinikum Erlangen, Friedrich-Alexander-Universit\u00e4t Erlangen-N\u00fcrnberg (FAU), Universit\u00e4tsstra\u00dfe 27, 91054 Erlangen, Germany"},{"name":"Comprehensive Cancer Center Erlangen-Europ\u00e4ische Metropolregion N\u00fcrnberg (CCC ER-EMN), 91054 Erlangen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Stefanie","family":"Corradini","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology, Universit\u00e4tsklinikum Erlangen, Friedrich-Alexander-Universit\u00e4t Erlangen-N\u00fcrnberg (FAU), Universit\u00e4tsstra\u00dfe 27, 91054 Erlangen, Germany"},{"name":"Comprehensive Cancer Center Erlangen-Europ\u00e4ische Metropolregion N\u00fcrnberg (CCC ER-EMN), 91054 Erlangen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1522-9591","authenticated-orcid":false,"given":"Laura S.","family":"Hildebrand","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology, Universit\u00e4tsklinikum Erlangen, Friedrich-Alexander-Universit\u00e4t Erlangen-N\u00fcrnberg (FAU), Universit\u00e4tsstra\u00dfe 27, 91054 Erlangen, Germany"},{"name":"Comprehensive Cancer Center Erlangen-Europ\u00e4ische Metropolregion N\u00fcrnberg (CCC ER-EMN), 91054 Erlangen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"102586","DOI":"10.1016\/j.ctrv.2023.102586","article-title":"Safety profile of cyclin-dependent kinase (CDK) 4\/6 inhibitors with concurrent radiation therapy: A systematic review and meta-analysis","volume":"119","author":"Becherini","year":"2023","journal-title":"Cancer Treat. Rev."},{"key":"ref_2","first-page":"79","article-title":"CDK 4\/6 inhibitors combined with radiotherapy: A review of literature","volume":"26","author":"Bosacki","year":"2021","journal-title":"Clin. Transl. Radiat. Oncol."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Kubeczko, M., Gabrys, D., Gawkowska, M., Polakiewicz-Gilowska, A., Cortez, A.J., Krzywon, A., Wozniak, G., Latusek, T., Lesniak, A., and Swiderska, K. (2023). Safety and Feasibility of Radiation Therapy Combined with CDK 4\/6 Inhibitors in the Management of Advanced Breast Cancer. Cancers, 15.","DOI":"10.3390\/cancers15030690"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"10","DOI":"10.1186\/1747-1028-8-10","article-title":"Silencing CDK4 radiosensitizes breast cancer cells by promoting apoptosis","volume":"8","author":"Hagen","year":"2013","journal-title":"Cell Div."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"213","DOI":"10.1186\/s12943-025-02419-2","article-title":"Cellular senescence in cancer: From mechanism paradoxes to precision therapeutics","volume":"24","author":"Feng","year":"2025","journal-title":"Mol. Cancer"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"177475","DOI":"10.1016\/j.ejphar.2025.177475","article-title":"Pharmacological modulation of cellular senescence: Implications for breast cancer progression and therapeutic strategies","volume":"997","author":"Xie","year":"2025","journal-title":"Eur. J. Pharmacol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"3131","DOI":"10.7150\/jca.18457","article-title":"Breast Cancer Cell Line Classification and Its Relevance with Breast Tumor Subtyping","volume":"8","author":"Dai","year":"2017","journal-title":"J. Cancer"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Witt, B.L., and Tollefsbol, T.O. (2023). Molecular, Cellular, and Technical Aspects of Breast Cancer Cell Lines as a Foundational Tool in Cancer Research. Life, 13.","DOI":"10.3390\/life13122311"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"317","DOI":"10.1007\/s40265-020-01461-2","article-title":"Inhibiting CDK4\/6 in Breast Cancer with Palbociclib, Ribociclib, and Abemaciclib: Similarities and Differences","volume":"81","author":"Braal","year":"2021","journal-title":"Drugs"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"23","DOI":"10.4137\/CPath.S31563","article-title":"Diversity of Breast Carcinoma: Histological Subtypes and Clinical Relevance","volume":"8","author":"Makki","year":"2015","journal-title":"Clin. Med. Insights Pathol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"755","DOI":"10.1111\/cas.12932","article-title":"Phase I study of palbociclib, a cyclin-dependent kinase 4\/6 inhibitor, in Japanese patients","volume":"107","author":"Tamura","year":"2016","journal-title":"Cancer Sci."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1016\/j.jpba.2019.01.017","article-title":"Determination of total and unbound ribociclib in human plasma and brain tumor tissues using liquid chromatography coupled with tandem mass spectrometry","volume":"166","author":"Bao","year":"2019","journal-title":"J. Pharm. Biomed. Anal."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"740","DOI":"10.1158\/2159-8290.CD-16-0095","article-title":"Efficacy and Safety of Abemaciclib, an Inhibitor of CDK4 and CDK6, for Patients with Breast Cancer, Non-Small Cell Lung Cancer, and Other Solid Tumors","volume":"6","author":"Patnaik","year":"2016","journal-title":"Cancer Discov."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"483","DOI":"10.1634\/theoncologist.2014-0443","article-title":"The Role of CDK4\/6 Inhibition in Breast Cancer","volume":"20","author":"Murphy","year":"2015","journal-title":"Oncologist"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1798","DOI":"10.1038\/nprot.2009.191","article-title":"Protocols to detect senescence-associated beta-galactosidase (SA-betagal) activity, a biomarker of senescent cells in culture and in vivo","volume":"4","author":"Erusalimsky","year":"2009","journal-title":"Nat. Protoc."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"128","DOI":"10.3892\/ijmm.2022.5184","article-title":"CDK4\/6 inhibitor resistance mechanisms and treatment strategies (Review)","volume":"50","author":"Huang","year":"2022","journal-title":"Int. J. Mol. Med."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Janostiak, R., Torres-Sanchez, A., Posas, F., and de Nadal, E. (2022). Understanding Retinoblastoma Post-Translational Regulation for the Design of Targeted Cancer Therapies. Cancers, 14.","DOI":"10.3390\/cancers14051265"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"2690","DOI":"10.1111\/cas.14116","article-title":"Different sensitivities of senescent breast cancer cells to immune cell-mediated cytotoxicity","volume":"110","author":"Inao","year":"2019","journal-title":"Cancer Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"8988","DOI":"10.1002\/cam4.4410","article-title":"Protective role of cytoplasmic p21Cip1\/Waf1 in apoptosis of CDK4\/6 inhibitor-induced senescence in breast cancer cells","volume":"10","author":"Kartika","year":"2021","journal-title":"Cancer Med."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"415","DOI":"10.1007\/s12282-019-01035-5","article-title":"Anti-cell growth and anti-cancer stem cell activity of the CDK4\/6 inhibitor palbociclib in breast cancer cells","volume":"27","author":"Kishino","year":"2020","journal-title":"Breast Cancer"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"216","DOI":"10.1002\/1878-0261.13541","article-title":"CDK4\/6 inhibitors induce breast cancer senescence with enhanced anti-tumor immunogenic properties compared with DNA-damaging agents","volume":"18","author":"Lee","year":"2024","journal-title":"Mol. Oncol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1921","DOI":"10.1038\/s44318-025-00371-x","article-title":"Pharmacological CDK4\/6 inhibition promotes vulnerability to lysosomotropic agents in breast cancer","volume":"44","author":"Nehme","year":"2025","journal-title":"EMBO J."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"15916","DOI":"10.1038\/ncomms15916","article-title":"CDK4\/6 and autophagy inhibitors synergistically induce senescence in Rb positive cytoplasmic cyclin E negative cancers","volume":"8","author":"Vijayaraghavan","year":"2017","journal-title":"Nat. Commun."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Jost, T., Heinzerling, L., Fietkau, R., Hecht, M., and Distel, L.V. (2021). Palbociclib Induces Senescence in Melanoma and Breast Cancer Cells and Leads to Additive Growth Arrest in Combination with Irradiation. Front. Oncol., 11.","DOI":"10.3389\/fonc.2021.740002"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"R77","DOI":"10.1186\/bcr2419","article-title":"PD 0332991, a selective cyclin D kinase 4\/6 inhibitor, preferentially inhibits proliferation of luminal estrogen receptor-positive human breast cancer cell lines in vitro","volume":"11","author":"Finn","year":"2009","journal-title":"Breast Cancer Res."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"101103","DOI":"10.1016\/j.drup.2024.101103","article-title":"Mechanisms of sensitivity and resistance to CDK4\/CDK6 inhibitors in hormone receptor-positive breast cancer treatment","volume":"76","author":"Glaviano","year":"2024","journal-title":"Drug Resist. Updat."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Zhai, J., Han, J., Li, C., Lv, D., Ma, F., and Xu, B. (2023). Tumor senescence leads to poor survival and therapeutic resistance in human breast cancer. Front. Oncol., 13.","DOI":"10.3389\/fonc.2023.1097513"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"5165","DOI":"10.1038\/s41388-020-1354-9","article-title":"Senescence as a therapeutically relevant response to CDK4\/6 inhibitors","volume":"39","author":"Wagner","year":"2020","journal-title":"Oncogene"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"332","DOI":"10.1007\/s11427-019-1629-6","article-title":"Cellular senescence: From anti-cancer weapon to anti-aging target","volume":"63","author":"Yuan","year":"2020","journal-title":"Sci. China Life Sci."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"6568","DOI":"10.1158\/1078-0432.CCR-20-2269","article-title":"Short-term CDK4\/6 Inhibition Radiosensitizes Estrogen Receptor-Positive Breast Cancers","volume":"26","author":"Pesch","year":"2020","journal-title":"Clin. Cancer Res."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"188","DOI":"10.1186\/s13046-020-01693-w","article-title":"CDK4\/6 inhibitors: A novel strategy for tumor radiosensitization","volume":"39","author":"Yang","year":"2020","journal-title":"J. Exp. Clin. Cancer Res."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1016\/j.canlet.2019.02.049","article-title":"P53 pathway is a major determinant in the radiosensitizing effect of Palbociclib: Implication in cancer therapy","volume":"451","author":"Roche","year":"2019","journal-title":"Cancer Lett."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1855","DOI":"10.1158\/1078-0432.CCR-20-3871","article-title":"Radiotherapy Delivered before CDK4\/6 Inhibitors Mediates Superior Therapeutic Effects in ER(+) Breast Cancer","volume":"27","author":"Petroni","year":"2021","journal-title":"Clin. Cancer Res."},{"key":"ref_34","first-page":"e1470","article-title":"Unexpected toxicity of CDK4\/6 inhibitor palbociclib and radiotherapy","volume":"5","author":"Beeker","year":"2022","journal-title":"Cancer Rep."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"4527","DOI":"10.1038\/s41467-023-40132-0","article-title":"The intensities of canonical senescence biomarkers integrate the duration of cell-cycle withdrawal","volume":"14","author":"Ashraf","year":"2023","journal-title":"Nat. Commun."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"e4612","DOI":"10.21769\/BioProtoc.4612","article-title":"Flow Cytometry-based Method for Efficient Sorting of Senescent Cells","volume":"13","author":"Goy","year":"2023","journal-title":"Bio Protoc."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1007\/978-1-4939-6670-7_3","article-title":"Cellular Model of p21-Induced Senescence","volume":"Volume 1534","author":"Shtutman","year":"2017","journal-title":"Oncogene-Induced Senescence"},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Hou, J., Wang, F., Kong, P., Yu, P.K., Wang, H., and Han, W. (2015). Gene profiling characteristics of radioadaptive response in AG01522 normal human fibroblasts. PLoS ONE, 10.","DOI":"10.1371\/journal.pone.0123316"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"71","DOI":"10.1007\/s10522-015-9593-9","article-title":"Premature aging\/senescence in cancer cells facing therapy: Good or bad?","volume":"17","author":"Gonzalez","year":"2016","journal-title":"Biogerontology"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"1834","DOI":"10.1038\/s12276-021-00717-5","article-title":"Senescent tumor cells: An overlooked adversary in the battle against cancer","volume":"53","author":"Park","year":"2021","journal-title":"Exp. Mol. Med."},{"key":"ref_41","doi-asserted-by":"crossref","unstructured":"Liu, Y., Lomeli, I., and Kron, S.J. (2024). Therapy-Induced Cellular Senescence: Potentiating Tumor Elimination or Driving Cancer Resistance and Recurrence?. Cells, 13.","DOI":"10.20944\/preprints202406.0057.v1"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"513","DOI":"10.1101\/sqb.2008.73.048","article-title":"Implications of cellular senescence in tissue damage response, tumor suppression, and stem cell biology","volume":"73","author":"Krizhanovsky","year":"2008","journal-title":"Cold Spring Harb. Symp. Quant. Biol."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1046\/j.1474-9728.2003.00031.x","article-title":"Apoptosis, necrosis and cellular senescence: Chaperone occupancy as a potential switch","volume":"2","author":"Soti","year":"2003","journal-title":"Aging Cell"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1047","DOI":"10.1152\/physrev.00020.2018","article-title":"Cellular Senescence: Aging, Cancer, and Injury","volume":"99","author":"Calcinotto","year":"2019","journal-title":"Physiol. Rev."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"181","DOI":"10.1186\/s12943-024-02096-7","article-title":"Cellular senescence and SASP in tumor progression and therapeutic opportunities","volume":"23","author":"Dong","year":"2024","journal-title":"Mol. Cancer"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"525","DOI":"10.1111\/cas.12118","article-title":"Roles and mechanisms of cellular senescence in regulation of tissue homeostasis","volume":"104","author":"Ohtani","year":"2013","journal-title":"Cancer Sci."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"902","DOI":"10.37349\/etat.2024.00254","article-title":"Therapy-induced senescence in breast cancer: An overview","volume":"5","author":"Chembukavu","year":"2024","journal-title":"Explor. Target Antitumor. Ther."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"110","DOI":"10.1186\/s12967-023-03964-4","article-title":"Cellular senescence in the response of HR(+) breast cancer to radiotherapy and CDK4\/6 inhibitors","volume":"21","author":"Klapp","year":"2023","journal-title":"J. Transl. Med."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"420","DOI":"10.1038\/s41420-022-01205-z","article-title":"Cellular senescence in ischemia\/reperfusion injury","volume":"8","author":"Chen","year":"2022","journal-title":"Cell Death Discov."}],"container-title":["Cells"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4409\/15\/8\/734\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,22]],"date-time":"2026-04-22T10:51:15Z","timestamp":1776855075000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4409\/15\/8\/734"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,21]]},"references-count":49,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2026,4]]}},"alternative-id":["cells15080734"],"URL":"https:\/\/doi.org\/10.3390\/cells15080734","relation":{},"ISSN":["2073-4409"],"issn-type":[{"value":"2073-4409","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,21]]}}}