In the current study, we investigated the effects of high LET IR and a potent radiosensitizing agent, ANTP-SMACN7, and a synthetic peptide derived from the IAP inhibitory protein, SMAC, on cell survival and apoptotic responses in 2 NSCLC lines with upregulated XIAP expressions. The gene discussed is DIABLO; the disease is non-small cell lung carcinoma.