Category: Assay Development and Screening
Mixed lineage leukemia protein 1 (MLL1) is one of six human histone H3 lysine 4 (H3K4) specific methyl-transferases. MLL1 translocations occur in 10% of adult and 15-20% of pediatric acute myeloid leukemia (AML), where it is associated with transcriptional activation of oncogenic gene expression. MLL1 functions as part of a multi-subunit complex with WDR5, RbBP5, Ash2L, and DPY30 dimer, collectively referred to as WRAD2.
Like most methyltransferases, the MLL1-WRAD2 complex exhibits weak activity in vitro; MLL1 alone is several hundred times slower than the full complex. Others have exploited this property to design inhibitors that bind to WDR5 and disrupt a key MLL1-WDR5 interaction, evicting MLL1 from the complex (1). To date there are no reports of inhibitors that bind to the active site of the MLL1 SET domain. Building on an earlier report from others (2), we have optimized the assay allowing us to show that the MLL1-WRAD2 complex can be very tight (EC50 < 10 nM), and that MLL1 and WRAD2 concentrations can be fine-tuned to make the assay selective for one or both modes of inhibition.
Nico Cantone– Principal Research Associate, Constellation Pharmaceuticals, Inc., Cambridge, MA