After profiling all heterotrivalent and heterotetravalent (86) compounds in various biological assays, we established AB3067 ( ) as the most suitable hetero-multivalent compound to take forward for further study. We wanted to further assess the relative contribution of both VHL and CRBN to degrade BET proteins with 27. To this end, we investigated live cell kinetic degradation of endogenous HiBiT-BRD4 in the presence of either a VHL or CRBN KO (Figure ). In each VHL and CRBN KO HiBiT-BRD4 cell line, the Dmax 50 values for the degradation of BRD4