Fluorescence Polarization Assay for Representative BET Bromodomains. All fluorescence anisotropy (FA) experiments were run in a black 384 well plate in a buffer consisting of 50 mM HEPES, 100 mM NaCl, pH=7.4. Measurements were made using a Tecan Infinite 500 with an excitation frequency of 485 nm, an emission frequency of 535 nm, and a fluorescence polarization filter. All FA experiments (direct binding and competition) used a 10 mM stock of fluorescent tracer Fl-JQ1 diluted to a final concentration of 15 nM within each well. For the direct binding experiment, the protein of interest was serially diluted across the plate (25 μM maximum protein concentration) and allowed to incubate in the presence of the fluorescent tracer for 30 minutes. After incubating, anisotropy values were recorded and fit using equation In Vitro Toxicity: XTT Cell Viability Assay. TSECs were cultured in Human EC Growth Medium and seeded in a 96-well plate (Falcon 353219) at a density of 31,000 cells/cm 2 . Following 2 hours of starvation in Endothelial cell basal media, cells were treated with various concentrations of the indicated BET inhibitor using serial dilutions with 1% DMSO as a vehicle. XTT reagent (Cell Signaling Technology 9095) was added according to the manufacturer's protocol. At 4 hours following XTT reagent addition, absorbance at 450 nm was read using a Molecular Devices Spectra max plus 384 UV-Vis spectrometer. The absorbance at 620 nm was used for background subtraction from 450 nm. The absorbance was normalized to vehicletreated cells. IC50 values determined using Graph Pad Prism 10.