The effect of PARP1 inhibitor BMN 673 with or without cytotoxic drugs against MLL-AF9 leukemia in mice. (A-C) mBMCs expressing MLL-AF9 (MLL-AF9, green bars) or empty plasmid (wt, purple bars) were untreated (C) or treated with 10 nM doxorubicin plus 15 nM cytarabine (DA), 5 μM or 1 μM olaparib (O in B and C, respectively), and doxorubicin plus cytarabine plus olaparib (DAO) for 24 and 72 hours (A-B and C, respectively. (A) Real-time quantitative PCR analysis of PARP1 messenger RNA expression (top); western blot analysis of PARP1 and lamin (loading control) in nuclear cell lysates (bottom). (B) γ-H2AX fluorescence intensity (left) and percentage of dead cells (right). Results represent mean ± SD from 3 independent experiments. *P < .001 and **P ≤ .002 when compared with control and single treatment, respectively, using Student t test. (C) Mean number of colonies per 10⁴ cells ± SD in methylcellulose (triplicate experiment). *P < .02 and ** P < .002 in comparison with control and individual treatment, respectively, using Student t test. (D) Experimental design: syngeneic mice were injected with 1 × 10⁵ GFP+MLL-AF9 leukemia cells and were treated 10 days later with vehicle (Control), DA, BMN 673, or DA plus BMN 673. GFP⁺ leukemia cells in peripheral blood leukocytes and median survival time were scored. (E) GFP+MLL-AF9 leukemia cells (green dots) in representative plots (n = 3-4 per group). Results represent the mean percentage of GFP+MLL-AF9 leukemia cells ± SD. *P = .02 in comparison with other groups using the response additivity approach. (F) Survival curves and MST (7-9 mice/group). * P < .04 and ** P < .03 in comparison with Control and other groups, respectively, using Kaplan-Meier log-rank test.