First, we tested the inhibitory activity of the CDK9 inhibitors AT751932,33 and BE-09-LN53 (referred to as i-CDK9 in ref. 34) on a panel of AML cell lines with (MOLM-13, MV4–11 and MLL-AF9 murine leukaemia) or without (HL-60 and U937) MLL rearrangements, since CDK9 inhibition was expected to affect expression of MYB and several other genes important for cell growth/viability. Here, KMT2A is linked to acute myeloid leukemia.