Pol I inhibition activates ATM/ATR-dependent signaling and alters cell-cycle progression in human AML cell lines. (A) Cell-cycle analysis by BrdU incorporation after 24 hours of Pol I inhibition (n = 4). (B) Western blot analysis of CHK1 S345, CHK2 T68, and pp53 S15 phosphorylation, and total p53 abundance in 6 human AML cell lines with varied p53 status after treatment with 500 nM CX-5461 for the times indicated (n = 2). (C) Quantitation of cell-cycle distribution by BrdU incorporation in SHI-1, KG-1, and THP-1 after 30 minutes of pre-treatment with either ATMi (5 μM KU-5593), ATRi (5 μM VE-821), or both ATMi/ATRi (5 μM) in combination with CX-5461 (100 nM) treatment of 24 hours (n = 3). (D) Analysis of CHK1 S345, and CHK2 T68 phosphorylation in THP-1 and SHI-1 after 30 minutes pre-treatment with either ATMi (5 μM KU-5593), ATRi (5 μM VE-821), or both ATMi/ATRi (5 μM) in combination with 100 nM or 1000 nM CX-5461 for 1 hour by western blotting (n = 2). Graphs represent mean ± SEM.