Expi293 cells were cultured in a 1:1 mixture of Expi293:Freestyle media. At a cell density of ∼2.5 × 106 cells/mL, 250 mL of cells was transfected using 200 μL FectoPRO (Polyplus Transfection) reagent mixed with 100 μg of PRMT5 and 100 μg HA-tagged WDR77 plasmids. One day after transfection, 3 mM valproic acid and 0.4% w/v glucose were added to the culture. Two days after transfection, cells were split into multiple flasks with 30 mL cells each and treated with compound or DMSO at a final 0.2% DMSO concentration. Cell sample was collected after 6 h, pelleted, and washed 3 times with ice-cold PBS. Additional aliquots were analyzed for viability and cell number using a Vi-Cell XR Cell Counter, and all samples were determined to have >98% viability based on trypan blue exclusion. Each sample was lysed in buffer 50 mM HEPES pH 7.5, 300 mM NaCl, 1 mM TCEP, 1% v/v Tween-20, and 2 mM reduced GSH. The PRMT5:WDR77 complex was immunoprecipitated by anti-HA agarose resin and then eluted by 50 μM 3X-HA peptide. Each eluate was measured by intact mass LC-MS to determine the percentage of complex with compound adduct.