LAQ824- and LBH589-mediated apoptosis and therapeutic efficacy are independent of the p53 pathway. (A) Eμ-myc/p53^−/− and Eμ-myc/arf^−/− lymphoma cells were incubated for 24 hours with the indicated concentrations of LAQ824 or LBH589. Cell viability was determined by staining with PI and FACS analysis. (B) Whole cell lysates were prepared from Eμ-myc/p53^−/− and Eμ-myc/arf^−/− lymphomas that had been treated for 2 hours with vehicle, LAQ824 (25 nM), or LBH589 (4 nM). Western blot analysis was performed with antibodies specific to acetylated histone H3. Equivalent protein loading was confirmed by probing for β-actin. (C-D) Eμ-myc/p53^−/− and Eμ-myc/arf^−/− lymphomas were treated for 24 hours with vehicle (■), LAQ824 (25 nM; □), or LBH589 (4 nM; ▩). The extent of apoptosis was measured by flow cytometric analysis of Δψm, exposure of phosphatidylserine on the cell surface (annexin V staining), and presence of cells with less than 2n DNA content (PI staining of fixed/permeabilized cells). Each dose or time point represents the mean value of 3 individual experiments ± SE. (E) C57BL/6 mice bearing palpable Eμ-myc/p53^−/− lymphomas were treated intravenously with LAQ824 (75 mg/kg) or LBH589 (80 mg/kg), and lymph nodes were harvested at the indicated times. Histologic sections were assessed by hematoxylin and eosin staining (top panel), immunohistochemistry using antibodies to acetyl histone H3 (middle panel), and TUNEL staining (bottom panel). Each time point is of an individual mouse. (F) C57BL/6 mice bearing an Eμ-myc/p53^−/− lymphoma were treated with vehicle (200 μL 10% lactic acid/D5W; n = 10), LAQ824 (75 mg/kg; n = 10), or LBH589 (80 mg/kg; n = 10). Kaplan-Meier survival curves of mice treated with vehicle (black line), LAQ824 (blue line), and LBH589 (red line) are shown. (G) WBC counts of mice bearing an Eμ-myc/p53^−/− lymphoma (n = 3) were taken 3 days after treatment with vehicle, LAQ824, or LBH589. Each point represents the mean value of 3 individual mice ± SE (*P = .06, #P = .002).