Exogenous c-Myc expression partially rescues cell-cycle arrest and apoptosis of murine T-ALL cells treated with JQ1. Murine T-ALL cell lines were transduced with a MSCV2.2 IRES-GFP retrovirus or with one expressing mouse c-Myc. Murine stem cell virus– or c-Myc–expressing cells were treated with JQ1 (250 nM) or with the GSI (Compound E, 1 μM), unless otherwise noted. (A-B) c-Myc expression rescues JQ1 effects on cell-cycle progression at 24 hours. Murine T-ALL cell lines were left untreated or treated with JQ1 or Compound E for 24 hours and then stained with propidium iodide followed by flow cytometry. Mouse T-ALL cell line 5059 was analyzed; shown are 1 representative histogram overlay of DNA content (A) and collated data for the percentage of cells in S phase (B). The results are averages of 3 independent experiments and error bars represent SEM. *P < .05, **P < .01. (C) Mouse T-ALL cell line 5059 was treated with DMSO, JQ1 or GSI for 10 days and the total number of viable cells was calculated via trypan blue exclusion assay. The results are averages of 3 independent experiments and error bars represent SEM. **P < .01. (D) JQ1 induces apoptosis of mouse T-ALL cells. T-ALL cell lines were treated with vehicle, JQ1, or GSI for 10 days and the percentage of GFP-positive cells were determined by flow cytometry. The results are averages of 3 independent experiments and error bars represent SEM. *P < .05, **P < .001.