title: Ionizing radiation sensitizes breast cancer cells to Bcl-2 inhibitor, ABT-737, through regulating Mcl-1.
abstract: Breast-conserving surgery followed by radiation therapy has become the standard of care for early stage breast cancer. However, there are some patients that develop a local failure. We have previously shown that Bcl-2 overexpression was associated with an increased risk of local recurrence in patients with early stage breast cancer. The purpose of this study was to explore an approach to overcome radiation resistance by targeting pro-survival Bcl-2 family proteins in breast cancer cells. The breast cancer cell lines MCF-7, ZR-75-1 and MDA-MB231 were used in this study. siRNAs were employed to silence myeloid cell leukemia 1 (Mcl-1). A small molecule inhibitor of Bcl-2, ABT-737, was used to target anti-apoptotic Bcl-2 family proteins. Apoptosis was identified by FITC Annexin V, PI staining and Western blot analysis. The sensitivity to ionizing radiation and ABT-737 were measured by clonogenic assays. The effect of radiation and ABT-737 was also tested in a MCF-7 xenograft mouse model. Our data demonstrate that the combination of ABT-737 and radiation-induced apoptosis had an inhibitory effect on breast cancer cell proliferation. However, treatment with ABT-737 resulted in elevated Mcl-1 in breast cancer cell lines. Targeting Mcl-1 by siRNA sensitized MCF-7 cells to ABT-737. We revealed that radiation blunted Mcl-1 elevation induced by ABT-737, and that radiation downregulated Mcl-1 by promoting its degradation. Our results indicate that radiation and ABT-737 exert a synergistic effect on breast cancer cell lines through downregulating Mcl-1 and activating the bak-apoptotic pathway. These results support the combination of radiation and pro-survival Bcl-2 family inhibitor as a potential novel therapeutic strategy in the local-regional management of breast cancer.
authors.affiliation: a  Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey.
authors.forename: Hao
authors.initials: H
authors.lastname: Wu
authors.forename: Devora S
authors.initials: DS
authors.lastname: Schiff
authors.forename: Yong
authors.initials: Y
authors.lastname: Lin
authors.forename: Hanmanth J R
authors.initials: HJ
authors.lastname: Neboori
authors.forename: Sharad
authors.initials: S
authors.lastname: Goyal
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Feng
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Haffty
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D001713:Biphenyl Compounds / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D009596:Nitrophenols / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects / Q000528:radiation effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors*; D034741:RNA, Small Interfering / Q000235:genetics; D013449:Sulfonamides / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: C501332:ABT-737; D001713:Biphenyl Compounds; C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D013449:Sulfonamides