Consistent with its higher affinity, C16 is ~20 times more potent than C6 in inhibiting MV4;11 (MLL–AF4) and MOLM13 (MLL–AF9) leukemia lines (Figure 1—figure supplement 1B and C): in MV4;11 cells, for example, the GI50 for C6 is 1 μM compared to 46 nM for C16. This evidence concerns the gene AFF1 and leukemia.