Radiotherapy is used in locally advanced pancreatic cancers in which it can 
improve survival in combination with gemcitabine. However, prognosis is still 
poor in this setting in which more effective therapies remain needed. MLN4924 is 
an investigational small molecule currently in phase I clinical trials. MLN4924 
inhibits NAE (NEDD8 Activating Enzyme), a pivotal regulator of the E3 ubiquitin 
ligase SCF (SKP1, Cullins, and F-box protein), that has been implicated recently 
in DNA damage and repair. In this study, we provide evidence that MLN4924 can be 
used as an effective radiosensitizer in pancreatic cancer. Specifically, MLN4924 
(20-100 nmol/L) effectively inhibited cullin neddylation and sensitized 
pancreatic cancer cells to ionizing radiation in vitro with a sensitivity 
enhancement ratio of approximately 1.5. Mechanistically, MLN4924 treatment 
stimulated an accumulation of several SCF substrates, including CDT1, WEE1, and 
NOXA, in parallel with an enhancement of radiation-induced DNA damage, 
aneuploidy, G(2)/M phase cell-cycle arrest, and apoptosis. RNAi-mediated 
knockdown of CDT1 and WEE1 partially abrogated MLN4924-induced aneuploidy, 
G(2)/M arrest, and radiosensitization, indicating a causal effect. Furthermore, 
MLN4924 was an effective radiosensitizer in a mouse xenograft model of human 
pancreatic cancer. Our findings offer proof-of-concept for use of MLN4924 as a 
novel class of radiosensitizer for the treatment of pancreatic cancer.