BRD4 and breast cancer: ABBV-744 did not significantly alter the levels of BRD2 or BRD3 (Supplementary Figure S2D); however, a significant downregulation in BRD4 levels was evident at both 75 nM and 100 nM (Supplementary Figure S2D), indicating the potential selectivity of ABBV-744 towards BRD4 in ER+ breast cancer cells.