title: The p21-dependent radiosensitization of human breast cancer cells by MLN4924, an investigational inhibitor of NEDD8 activating enzyme.
abstract: Radiotherapy is a treatment choice for local control of breast cancer. However, intrinsic radioresistance of cancer cells limits therapeutic efficacy. We have recently validated that SCF (SKP1, Cullins, and F-box protein) E3 ubiquitin ligase is an attractive radiosensitizing target. Here we tested our hypothesis that MLN4924, a newly discovered investigational small molecule inhibitor of NAE (NEDD8 Activating Enzyme) that inactivates SCF E3 ligase, could act as a novel radiosensitizing agent in breast cancer cells. Indeed, we found that MLN4924 effectively inhibited cullin neddylation, and sensitized breast cancer cells to radiation with a sensitivity enhancement ratio (SER) of 1.75 for SK-BR-3 cells and 1.32 for MCF7 cells, respectively. Mechanistically, MLN4924 significantly enhanced radiation-induced G2/M arrest in SK-BR-3 cells, but not in MCF7 cells at early time point, and enhanced radiation-induced apoptosis in both lines at later time point. However, blockage of apoptosis by Z-VAD failed to abrogate MLN4924 radiosensitization, suggesting that apoptosis was not causally related. We further showed that MLN4924 failed to enhance radiation-induced DNA damage response, but did cause minor delay in DNA damage repair. Among a number of tested SCF E3 substrates known to regulate growth arrest, apoptosis and DNA damage response, p21 was the only one showing an enhanced accumulation in MLN4924-radiation combination group, as compared to the single treatment groups. Importantly, p21 knockdown via siRNA partialy inhibited MLN4924-induced G2/M arrest and radiosensitization, indicating a causal role played by p21. Our study suggested that MLN4924 could be further developed as a novel class of radiosensitizer for the treatment of breast cancer.
authors.affiliation: Division of Radiation and Cancer Biology, Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Dong
authors.initials: D
authors.lastname: Yang
authors.forename: Mingjia
authors.initials: M
authors.lastname: Tan
authors.forename: Gongxian
authors.initials: G
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
mesh_terms: D017209:Apoptosis; D001483:Base Sequence; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D003517:Cyclopentanes / Q000494:pharmacology*; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D000075687:NEDD8 Protein; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology*; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014452:Ubiquitins / Q000037:antagonists & inhibitors*
chemical_list: D003517:Cyclopentanes; D000075687:NEDD8 Protein; C082860:NEDD8 protein, human; D011743:Pyrimidines; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; D014452:Ubiquitins; D015689:Oncogene Protein p21(ras); C539933:pevonedistat