Finally, to further evaluate both the on-and off-target impact of 27, we performed an unbiased mass spectrometry proteomics experiment by treating HEK293 cells with 27, using cis-neg-AB3067 (95) and DMSO as negative and vehicle control, respectively. Of the 7276 proteins detected in this experiment, all three BET proteins, BRD2, BRD3 and BRD4, were significantly depleted upon 27 treatment, with no detectable induced degradation of CRBN observed (Figure ). Another protein that was significantly downregulated by 27 treatment was EP300 interacting inhibitor protein of differentiation 2 (EID2). EID2 is a 28-kDa protein associated with inhibiting the acetyltransferase activity of p300. 42 We speculate that EID2 Dashed line on the y-axis indicates boundary line for proteins to be considered statically significant; any proteins with a -log10(P value) ≥ 1.5 to have a P value ≤ 0.03.