These studies provided an unbiased identification of the most frequent and important genetic and epigenetic alterations among the 20�C25,000 genes of the human genome. They revealed intriguing associations among genes and clinical covariates, but were unable to directly demonstrate cause-and-effect relationships between alterations and therapeutic outcomes. In contrast, RNA interference can directly demonstrate the effects of reduced gene expression on cell physiology and survival. Pooled short hairpin RNA screens, in which cancer cells are exposed to several thousand different shRNA sequences, averaging one gene knockdown per cell, have several compelling features. First, the effect of stable shRNA knockdown over several cell doublings can be explored, compared to transient transfection of small interfering RNA sequences with short-lived effects. Accordingly, shRNA expression mimics drug TWS119 GSK-3 inhibitor treatments that are typically given over several weeks rather than days. Also, cells harboring different shRNA sequences effectively compete with each other within the pool as they proliferate, giving rise to hits that yield more Tasocitinib pronounced effects on proliferation. Because radiotherapy is the mainstay of NSCLC treatment, gene silencings that result in synergistic cytotoxicity when combined with ionizing radiation are desirable. Many cancer treatments are additive in nature, and are combined because they result in differential side effect profiles. Synergistic treatments that result in greater effects when administered concurrently, compared to the additive effects of each treatment given individually, may serve particularly well as radiosensitizers, since RT delivery may be constrained to a limited volume, and side effects may be less pronounced outside the irradiated volume. Demonstrating the mechanism of a radiosensitizing shRNA may also reveal biomarkers for patient selection and treatment assessment. DNA double strand breaks are among the effects of IR that best correlate with its cytotoxicity. A single unrepaired DSB is sufficient to result in reproductive cell death via G2 arrest or mitotic catastrophe. DSBs are predominately repaired through two pathways, homologous recombination and non-homologous end-joining. Gene silencings or small molecule inhibitors of either pathway may promote radiosensitization. Here we examine proteasome inhibition as a strategy for NSCLC radiosensitization via inhibition of DNA DSB repair. Proteasome inhibition has been explored in multiple clinical trials enrolling NSCLC patients, with variable results.