RAD50 expression is associated with poor clinical outcomes after radiotherapy for resected non-small cell lung cancer

Purpose: Although postoperative radiotherapy is often used to maintain local control after surgical resection and chemotherapy for locally advanced non-small cell lung cancer (NSCLC), both locoregional failure and distant metastasis remain problematic. The mechanisms of therapeutic resistance remain poorly understood. Experimental Design: We used reverse-phase protein arrays (RPPA) to profile the baseline expression of 170 total and phosphorylated proteins in 70 NSCLC cell lines to categorize pathways that may contribute to radiation resistance. Significant markers identified by RPPA were further analyzed in tissue microarrays (TMA) of specimens from 127 patients with NSCLC who had received surgery before receiving postoperative radiotherapy. Cox regression analysis and log-rank tests were used to identify potential predictive factors. We then validated the biological function of the markers in NSCLC cell lines in vitro. Results: Of the 170 proteins or phospho-proteins profiled, a subset of 12 proteins was found to correlate with radiation response parameters. TMA analysis of the 12 proteins showing the greatest differences in expression in the RPPA analysis demonstrated that RAD50 had the strongest correlation with distant relapse-free survival, locoregional relapse-free survival, and disease-free survival in patients with NSCLC. We confirmed that knockdown of RAD50 sensitized NSCLC cells to radiation and that upregulation of RAD50 increased radioresistance in in vitro experiments. Conclusions: Upregulated RAD50 may be a predictor of radioresistance in patients with lung cancer who received radiotherapy. Clin Cancer Res; 24(2); 341-50.