In vitro activity: I-BET151 exhibits potent selectivity over an extensive range of diverse protein types such as COX-2, P450, Aurora B, GSK3β, PI3K-γ, GPCR, ion channels, and transporters. Similar to I-BET762 (GSK525762A), I-BET151 displays potent binding affinity to BRD2, BRD3 and BRD4 with KD of 0.02-0.1 μM, and significantly inhibits lipopolysaccharide-stimulated IL-6 cytokine production in human peripheral blood mononuclear cells (PBMC) and whole blood (WB) as well as rat WB with IC50 of 0.16 μM, 1.26 μM, and 1.26 μM, respectively. I-BET151 (0.5 or 5 μM) inhibits the binding of BETs (BRD2, BRD3, BRD4, and BRD9) but not the binding of 23 other bromodomain proteins in HL60 nuclear extract to acetylated histone peptides. I-BET151 has potent efficacy against cell lines harboring different MLL-fusions such as MV4;11, RS4;11, MOLM13, and NOMO1 cells with IC50 of 15-192 nM. Consistently, I-BET151 completely ablates the colony-forming potential of MLL-fusion-driven leukaemias (MOLM13) but not leukaemias driven by tyrosine kinase activation (K562). I-BET151 also displays potent efficacy in both liquid culture and clonogenic assays using primary murine progenitors transformed with either MLL-ENL or MLL-AF9. I-BET151 treatment significantly induces apoptosis and prominent G0/G1 arrest in MLL-fusion cell lines driven by distinct MLL fusions (MOLM13 and MV4;11 containing MLL-AF9 and MLL-AF4, respectively) but not the K562 cells, probably due to the inhibition of transcription of BCL2, C-MYC and CDK6 by blocking the recruitment of BRD3/4, PAFc and SEC components into transcriptional start site (TSS).

Kinase Assay: All components are dissolved in buffer of composition 50 mM HEPES pH 7.4, 150 mM NaCl and 0.5 mM CHAPS with final concentrations of BRD 2/3/4 75 nM, fluorescent ligand 5 nM. 10 μL of this reaction mixture is added using a micro multidrop to wells containing 100 nL of various concentrations of I-BET151 or DMSO vehicle (1% final) in Greiner 384 well Black low volume microtitre plate and equilibrated in the dark for 60 minutes at room temperature. Fluorescence anisotropy is read in Envision (lex = 485 nm, lEM = 530 nm; Dichroic = 505 nM).

Cell Assay: Cells are exposed to various concentrations of I-BET151 for 24 or 72 hours in 384-well or 96-well plates. For cell growth inhibition assays, plates are added with CellTiter-Glo reagent using a volume equivalent to the cell culture volume in the wells, shaken for approximately 2 minutes and chemiluminescent signal is read on the Analyst GT or EnVision Plate Reader. For cell proliferation assays, CellTiter-Aqueous One is added to each well and plates are incubated for 4 hours at 37 °C. Absorbance is read at 490 nm on a SpectraMax Gemini reader.

Nature. 2011 Oct 2;478(7370):529-33.