MM-102

The HMT assay is performed in 50 mM HEPES pH 7.8, 100 mM NaCl, 1.0 mM EDTA, and 5% glycerol at 22 °C. Each reaction contains 1.5 μCi of the co-factor, ³H-S-adenosylmethionine. H3 10-residue peptide is used as the substrate at 50 μM. Compounds are added at concentrations ranging from 0.125 to 128 μM and incubated with the pre-assembled WDR5/RbBP5/ASH2L complex at a final concentration of 0.5 μM for each protein for 2–5 min. Reactions are initiated by addition of the MLL1 protein at a final concentration of 0.5 μM and allowed to proceed for 30 min before preparing scintillation counting. To count samples, reactions are spotted on separate squares of P81 filter paper and precipitated by submerging in freshly prepared 50 mM sodium bicarbonate buffer with pH 9.0. After washing and drying, samples are vortexed in Ultima Gold scintillation fluid and counted. As a negative control, assays are performed using 0.5 μM MLL1/WDR5/RbBP5/ASH2L complex assembled with the non-interacting mutant, WDR5D107A.

MV4;11, KOPN8, and K562 cells are cultured in RPMI 1640 medium (ATCC) supplemented with 10% fetal bovine serum and 100 U/L penicillin-streptomycin and incubated at 37 °C under 5% CO₂. Cells are seeded into 12-well plates for suspension at a density of 5 × 10⁵ per well (1 mL) and treated with either vehicle control (DMSO, 0.2%) or MM-102 for 7 days. The medium is changed every 2 days, and compounds are resupplied. The CellTiter-Glo Luminescent Cell Viability Assay kit is used following the manufacturer’s instruction. First, 100 μL of the assay reagent is added into each well, and the content is mixed for 2 min on an orbital shaker to induce cell lysis. After 10 min incubation at room temperature, the luminescence is read on a microplate reader.