NI-57 is an inhibitor of proteins of bromodomain and plant homeodomain finger-containing (BRPF) family, with IC50s of 3.1, 46 and 140 nM for BRPF1, BRPF2 (BRD1) and BRPF3, respectively.

NI-57 binds the BRD of BRPF1 with a Kd of 31 nM, BRD1 with a Kd of 110 nM, and BRPF3 with a Kd of 410 nM, whereas binding to BRD9 is weaker (Kd 1000 nM) measured by isothermal titration calorimetry. NI-57 shows less active effect on BRD9 (IC50, 520 nM) and BRD4 (BD1) (IC50, 3700 nM), TRIM24 (IC50, 1600 nM). NI-57 also inhibits BRPF BRDs in the nucleus but shows little effect on the proliferation of many cancer cell lines with GI50s of 10.4 μM (NCI-H1703 cells), 14.7 μM (DMS114), 15.6 μM (HRA-19), and 16.6 μM (RERF-LC-Sq1). Furthermore, Inhibition on BRPF1 of NI-57 (10 μM) reduces the gene expression of CCL-22 by 27.7%.

All reagents are diluted in the recommended buffer (50 mM HEPES, 100 mM NaCl, 0.1% BSA; pH = 7.4) supplemented with 0.05% CHAPS and allowed to equilibrate to room temperature prior to addition to plates. 4 mL of HIS-tagged protein is added to low-volume 384-well plates, followed by 4 mL of either buffer, non-biotinylated peptide, solvent or compounds (NI-57, etc.). Plates are sealed and incubated at room temperature for 30 minutes, before the addition of 4 mL biotinylated peptide, resealing and incubation for a further 30 minutes. 4 mL of streptavidin-coated donor beads (25 μg/mL) and 4 μL of nickel chelate acceptor beads (25 μg/mL) are then added under low light conditions. Plates are foil-sealed to protect from light, incubated at room temperature for 60 minutes and read on a PHERAstar FS plate reader using an AlphaScreenTM 680 excitation/570 emission filter set. IC50s are calculated in GraphPad Prism 5. Results for compounds (NI-57, etc.) dissolved in DMSO are normalized against corresponding DMSO controls prior to IC50 determination, which is given as the final concentration of the compound in the 20 μL reaction volume.