**5. Discussion**

*Translational Research in Cancer*

**148**

**Figure 4.**

**Figure 3.**

*xenografts (400 mm3*

*combination. B. Antitumor responses (tumor volumes, mm3*

their synergy, resulting in PARP hyperactivation, loss of nucleotides and increased programmed necrosis (**Figures 2** and **3**), beyond the capabilities of the single agents (IR or NQO1-bioactivatable drug) alone. Head and neck cancers, PDA and NSCLC

*in Figure 3A. C. Overall survival of animals treated as described in Figure 3A. D. PK values for plasma and subcutaneous vs. orthotopic A549-luc tumors in athymic nude mice. Note the significantly high levels of β-lap in orthotopic vs. subcutaneous A549 tumor tissue, whereas plasma levels were identical in both sets of mice.*

*β-Lap radiosensitizes subcutaneous A549-luc xenografts in athymic nude mice: A. subcutaneous A549-luc* 

*β-Lap inhibits DNA double strand break repair: A. log-phase A549 NSCLC cells were treated with or without β-lap (6 μM) and cell extracts prepared at various times during treatment to detect PAR-PARP formation, γ-H2AX (pS139), pS1981 ATM, total ATM (t-ATM) and α-tubulin steady-state levels by Western blot. A549 cells were also exposed or not to IR (8 Gy) and analyzed 1 h later. Mock, non-irradiated cells. DM, media alone. B. Graphical representation of data shown in Figure 2A. C. Representative images of A549 cells exposed or not to IR (2 Gy) alone, β-lap (3 μM, 2 h) alone, the combination [IR (2 Gy) + β-lap (3 μM, 2 h)], or the combination with DIC (50 μM, NQO1 inhibitor) and assessed for DSB breaks over time (0–120 min) using 53BP1 as the surrogate marker (in red). Cells were also stained for nuclear DNA using DAPI (in blue). Scale* 

*bar = 10 μm. D. Graphical representation of data presented in Figure 2C; \*\*\*\*p < 0.0001.*

*immediately with or without β-lap (20 mg/kg) for 5 treatments every other day. Representative antitumor responses (at day 20 post-treatment) are demonstrated for β-lap alone, IR alone, and the IR + β-lap* 

*) were generated in athymic nude mice and then treated with or without IR (2 Gy) then* 

*) over time are shown for the treatments described* 
