MYCN and neuroblastoma: Synergistic cytotoxicity as calculated by the Chou-Talalay Combination Index (CI) (22), was observed when YKL-5-124 was combined with inhibitors targeting Bromo- and Extra-Terminal domain proteins (BETis) in MYCN-amplified and nonamplified NB cells (Figure 3A, Supplementary Figures 2, 3A and Supplementary Table 3).