MYCN and neuroblastoma: Since BCL-xL levels are relatively low in neuroblastoma (Figure 3A) and MYCN-amplified neuroblastoma cells and tumors have high levels of the MCL-1 inhibitor NOXA (Figures 1C–1E, S1D, S1G, and S1H), we hypothesized that the further induction of apoptosis seen when MLN8237 was combined with ABT-199 could be due to reduction of MCL-1 levels, effectively decreasing the apoptotic threshold even lower in these cancers.