The p21-dependent radiosensitization of human breast cancer cells by MLN4924, an investigational inhibitor of NEDD8 activating enzyme

PLoS One. 2012;7(3):e34079. doi: 10.1371/journal.pone.0034079. Epub 2012 Mar 22.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Apoptosis
  • Base Sequence
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology*
  • Cell Cycle
  • Cell Line, Tumor
  • Cyclopentanes / pharmacology*
  • Female
  • Flow Cytometry
  • Humans
  • NEDD8 Protein
  • Oncogene Protein p21(ras) / metabolism*
  • Pyrimidines / pharmacology*
  • RNA, Small Interfering
  • Radiation-Sensitizing Agents / pharmacology*
  • Ubiquitins / antagonists & inhibitors*

Substances

  • Cyclopentanes
  • NEDD8 Protein
  • NEDD8 protein, human
  • Pyrimidines
  • RNA, Small Interfering
  • Radiation-Sensitizing Agents
  • Ubiquitins
  • Oncogene Protein p21(ras)
  • pevonedistat