Notes: The authors used bioluminescence resonance energy transfer (BRET) to test the ability of a bromodomain 9 ligand to disrupt binding to histone. HEK 293 cells were cotransfected with a histone H3.3-HaloTag® fusion vector and either NanoLuc®-BRD9 bromodomain or NanoLuc®-full-length BRD4 fusion vector. After 24 hours, the transfected cells were trypsinized, diluted in phenol red-free DMEM with or without 10nM of HaloTag® NanoBRET™ 618 Ligand and dispensed into a 96-well plate. One of two potential BRD-disrupting compounds, 7d or 11, was adding to a final concentration of 0.005–33μM, cells were incubated for 18 hours and NanoBRET™ Nano-Glo® Substrate (final concentration 10µM) was added. Fluorescence was measured and a corrected BRET ratio calculated. Cytotoxicity was assessed after the NanoBRET™ assay by incubating the cells with the CellTiter-Glo® Reagent for 30 minutes and measuring luminescence. To examine histone H3.3 localization, HEK 293 cells were transfected with the histone H3.3-HaloTag® fusion vector using FuGENE® HD Transfection Reagent. After 24 hours, cells were labeled with 5μM HaloTag® TMR ligand for 15 minutes before washing with complete medium, incubated for 30 minutes and imaged with a confocal microscope. (4568)

Notes: To characterize the effectiveness of LP99, a potential bromodomain inhibitor, BRD7 and BRD9 were fused with NanoLuc® luciferase and histones H3.3 and H4 were fused with HaloTag® protein for use in BRET. The two proteins were expressed in HEK 293 cells, and the histone-HaloTag® fusions were fluorescently labeled with the HaloTag® NanoBRET™ 618 Ligand. Once the NanoBRET™ Nano-Glo® Substrate was added, NanoBRET™ ratios were assessed in the presence of varying concentrations of LP99. (4567)