Figure 3.

JQ1 synergizes with CX-4945 in killing T-cell acute lymphoblastic leukemia (T-ALL) cells. (A) Combination treatment of CX-4945 and JQ1 depicted as normalized isobolograms shows strong synergism between the two drugs in JURKAT and ALL-SIL cell lines [combination index (CI)=0.31 and 0.16, respectively] but weaker synergism in RPMI-8402 and MOLT-3 cell lines (CI=0.49 and 0.75, respectively). CalcuSyn software was used to analyze combination data to produce the isobolograms normalized to the IC50 of each drug. The black diagonal line connects x- and y-axes of the normalized isobologram. Red dots on the black line represent additive dose combinations. Red dots below the black line represent synergistic drug combinations. Red dots above the black line represent antagonism. The T-ALL cell lines were treated with the following combination doses of CX-4945 and JQ1 for 72 hours, respectively: CX-4945 from 1.0 to 10 μM and JQ1 from 0.1 to 10 μM. (B) Cell viability upon combination treatment with CX-4945 2.5 μM and JQ1 1 μM is significantly reduced in all cell lines (except in MOLT-3 for JQ1 treatment vs. combination treatment), compared with those by single-agent treatment. Cell viability was determined with CellTiter-Blue after 72 hours of treatment for all four T-ALL cell lines treated with DMSO, CX-4945 (2.5 μM), JQ1 (1 μM) and both drugs in combination (CX-4945: 2.5 μM; JQ1: 1 μM). (C) Apoptosis analysis was performed on JURKAT, ALL-SIL, RPMI-8402 and MOLT-3 cells stained with Annexin V and PI after 48 hours of treatment with DMSO, CX-4945 (2.5 μM), JQ1 (1 μM) and both drugs in combination (CX-4945: 2.5 μM; JQ1: 1 μM). Cells were examined by flow cytometry to determine early apoptosis (PI-, Annexin V+) and late apoptosis (PI+, Annexin V+). Values in (B and C) are means±standard deviation (SD), and represent three biological replicates. Statistical significance was determined by two-tailed t-test.