To assess whether the trivalent PROTAC induced also a more sustained degradation of BET proteins in cells compared to MZ1 or (R,S)-SIM1, degradation washout experiments were performed. CRISPR HiBiT-BET HEK293 cells were treated with equivalent concentration (100nM) of SIM1, (R,S)-SIM1 and MZ1 compounds for 3.5h, then media was removed and replaced with media lacking compounds. We also tested SIM1 at 10x lower concentration (10nM) to account for its higher potency of degradation across BET proteins. The HiBiT-BET protein levels were continuously monitored from the initial addition of the compounds and immediately after the wash for a total time of 50h. At the 100nM treatment, degradation of all BET family members by SIM1 remained at constant low levels after washout over the time course, while at the 10nM SIM1 treatment partial recovery was observed for BRD2, BRD3, and BRD4 after washout (Fig. ). Recovery of all BET family members following washout for cells treated with 100nM (R,S)-SIM1 or 100nM MZ1 was greater and occurred faster than those observed with SIM1 (Fig. ).