Determination of Inhibitor IC50 Values
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EPZ004777 is serially diluted 3-fold in DMSO for a total of ten concentrations, beginning at 1 μM. A 1 μL aliquot of each inhibitor dilution is plated in a 384-well microtiter plate. The 100% inhibition control consisted of 2.5 μM final concentration of the product inhibitor S-adenosyl-L-homocysteine, (SAH). Compound is incubated for 30 min with 40 μl per well of 0.25 nM DOT1L(1-416) in assay buffer (20 mM TRIS [pH 8.0] 10 mM NaCl, 0.002% Tween 20, 0.005% Bovine Skin Gelatin, 100 mM KCl, and 0.5 mM DTT). 10 ml per well of substrate mix comprising assay buffer with 200 nM 3H-SAM (American Radiolabeled Chemicals: 80 Ci/mmol), 600 nM unlabeled SAM, and 20 nM nucleosomes are added to initiate the reaction (both substrates are present in the final reaction mixture at their respective KM values). Reactions are incubated for 120 min and quenched with 10 μl per well of 800 μM SAM. Incorporation of radioactivity into nucleosome substrate is measured in a flashplate. IC50 values for enzymes in the histone methyltransferase panel are determined under similar balanced assay conditions with both SAM and protein/peptide substrate present at concentrations equal to their respective KM values.
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References:
1Daigle, S. R., Olhava, E. J., Therkelsen, C. A., Majer, C. R., Sneeringer, C. J., Song, J., Johnston, L. D., Scott, M. P., Smith, J. J., Xiao, Y., Jin, L., Kuntz, K. W., Chesworth, R., Moyer, M. P., Bernt, K. M., Tseng, J. C., Kung, A. L., Armstrong, S. A., Copeland, R. A., Richon, V. M. and Pollock, R. M. (2011) Selective killing of mixed lineage leukemia cells by a potent small-molecule DOT1L inhibitor. Cancer Cell. 20, 53-65
2Chen, L., Deshpande, A. J., Banka, D., Bernt, K. M., Dias, S., Buske, C., Olhava, E. J., Daigle, S. R., Richon, V. M., Pollock, R. M. and Armstrong, S. A. (2013) Abrogation of MLL-AF10 and CALM-AF10-mediated transformation through genetic inactivation or pharmacological inhibition of the H3K79 methyltransferase Dot1l. Leukemia. 27, 813-822
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