Purpose:Radiation therapy continues to be an important therapeutic strategy for providing definitive local/regional control of human cancer. However, oncogenes that harbor driver mutations and/or amplifications can compromise therapeutic efficacy. Thus, there is a need for novel approaches that enhance the DNA damage produced by ionizing radiation. Experimental Design:A forward chemical genetic approach coupled with cell-based phenotypic screening of several tumor cell lines was used to identify a novel chemical entity (NCE) that functioned as a radiation sensitizer. Proteomics, comet assays, confocal microscopy and immunoblotting were used to identify the biological target. Results:The screening process identified a 5-((N-benzyl-1H-indol-3-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)trione as a NCE that radiosensitized cancer cells expressing amplified and/or mutated RAS, ErbB, PIK3CA, and/or BRAF oncogenes. Affinity-based solid phase resin capture followed by LC/MS/MS analysis identified the chaperone nucleophosmin as the NCE target. SiRNA suppression of nucleophosmin abrogated radiosensitization by the NCE. Confocal microscopy demonstrated that the NCE inhibited nucleophosmin shuttling to radiation-induced DNA damage repair foci and analysis of comet assays indicated a diminished rate of DNA double strand break repair. Conclusions:These data support the hypothesis that inhibition of DNA repair due to inhibition of nucleophosmin shuttling increases the efficacy of DNA damaging therapeutic strategies
- Received April 20, 2011.
- Revision received July 13, 2011.
- Accepted July 30, 2011.
- Copyright © 2011, American Association for Cancer Research.