Fig 1: The effect of idasanutlin alone and in combination with temozolomide in parental and luciferase transduced neuroblastoma cell lines. (a) 72 h GI50 concentrations of parental and luciferase‐tagged cell lines to idasanutlin and temozolomide. Values represent the mean of n = 3 ± SEM. * as previously reported in Ref. 10. Western analysis for activation of the p53 pathway in (b) SHSY5Y and SHSY5Y‐Luc cells, and (c) NB1691 and NB1691‐Luc cells treated for 24 h with 1× and 10× their respective idasanutlin GI50 concentrations. D, DMSO treated control cells. Primary antibodies: p53 1:1000 (DO7, Leica Biosystems Ltd), MYCN 1:500 (sc‐53,993, Santa Cruz Biotechnology Inc., Dallas, TX, USA), MDM2 1:200 (OP46, Merck), p21WAF1 1:200 (OP64, Merck), and GAPDH 1:500 (sc‐25,778, Santa Cruz Biotechnology Inc). Growth inhibition curves of (d) SHSY5Y‐Luc and (e) NB1691‐Luc exposed to idasanutlin and temozolomide alone and in combination at the indicated constant 1:1 ratios relative to their respective GI50 concentrations for 72 h. Data are shown as the average of at least 3 independent experiments and error bars represent SEM. CI values are shown for each constant ratio combination and also at ED50, ED75, and ED90. CI range: < 0.1 very strong synergism; 0.1–0.3 strong synergism; 0.3–0.7 synergism; 0.7–0.85 moderate synergism; 0.85–0.9 slight synergism; 0.9–1.1 nearly additive; 1.1–1.2 slight antagonism; 1.2–1.45 moderate antagonism; 1.45–3.3 antagonism; 3.3–10 strong antagonism; > 10 very strong antagonism. RG, idasanutlin; TMZ, temozolomide; RG + TMZ, idasanutlin and temozolomide.