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Background: Radiation therapy is one of the most effective therapeutic tools for brain metastasis. However, it is inevitable that some cancer cells become resistant to radiation. This study is focused on the identification of genes associated with radioresistance in metastatic brain tumor from lung cancer and the functional examination of the selected genes with regards to altered sensitivity of cancer cells to radiation. Methods: After establishing radioresistant cells from the xenograft model, we explored the significant transcriptional changes by performing DNA microarray profiling. Functional analyses in vitro and in vivo performed to validate the gene responsible for radioresistance. Results: Transcriptional changes induced by radiation therapy are much more extensive in H460 cells than in PC14PE6 cells. The expression levels of TopBP1 and Claspin were increased in the cancer cells that survived radiation therapy. Depletion of TopBP1 or Claspin using shRNA showed an enhancement of sensitivity to radiation in radioresistant lung cancer cells (PC14PE6). Moreover, increased levels of TopBP1 or Claspin endowed cells a higher resistance to radiation. In xenograft models, the knock-down of TopBP1 or Claspin significantly prolonged the median survival time post radiation therapy. Conclusions: We analyzed the gene expression profiles of the radiosensitive cells and the radioresistant cells to define a set of genes that may be involved in endowing lung cancer cells radioresistance post brain metastasis. Functional analyses indicated that the expression TopBP1 and Claspin positively affects the survival of cancer cells and thus negatively the xenograft metastasis model animals in response to radiation. These results show that TopBP1 and Claspin can be potential targets for the enhanced efficacy of radiotherapy. [ABSTRACT FROM AUTHOR]