XiaofangWang, Xiaomao Guo

Department of RadiationOncology, Fudan University Shanghai Cancer Center

Objective: The study aims at investigating the radiosensitivity induced byMLN4924, a specific Nedd8-activating enzyme inhibitor, and the underlyingradiosensitizing mechanisms in prostate cancer cells. Method: The IC50 ofMLN4924 was first examined by clonogenic assay in DU145 and PC3 cells. We thendetermined the radiosensitizing effect of MLN4924 and carried out clonogenicsurvival as well. To elucidate the underlying mechanisms for theradiosensitizing effect of MLN4924, fluorescence-activated cell sortinganalysis and immunoblotting were conducted. Result: MLN4924 effectivelyinhibited neddylation pathway, inactivated Cullin-RING E3 ligases (CRLs), andsensitized prostate cancer cells to radiation with a sensitivity enhancementratio (SER) of 1.39 in PC3 cells and 1.23 in DU145 cells. Mechanistically,MLN4924 stimulated an accumulation of several CRL substrates, including WEE1,p21 and p27, in parallel with an enhancement of radiation-induced G2/M phasecell cycle arrest. Importantly, knockdown of WEE1/p21/p27 by siRNA partiallyabrogated MLN4924-induced G2/M arrest, indicating a causal role ofWEE1/p21/p27. Conclusion: Our study revealed that MLN4924 was a potentradiosensitizer in prostate cancer cells by triggering G2/M arrest. Among otherregulators, WEE1, p21 and p27, three kinases regulating cell cycle progression,were contributed to G2/M arrest. Our findings lay the foundation for future applicationof MLN4924 as a radiosensitizer in prostate cancer.

Key Words: Prostate cancer, MLN4924, Radiosensitivity