In vitro HDAC assay. (A) In vitro assay of HDAC1, HDAC2, and HDAC3 isolated by immunoprecipitation from K562 cells. HDACs were assayed in the presence of control (C), AB (arginine butyrate, 2.5 mM), SAHA (suberoylanilide hydroxamic acid, 10 μM), BHA (butyryl hydroxamic acid, 2.5 mM), TSA (trichostatin A, 1 μM), ST-20 (1 mM), RB7 (200 μM), and RB25 (200 μM). For each enzyme assayed, the values represented are relative to the control reaction. Values are a mean of 3 independent experiments; error bars indicate the standard errors of the mean. (B) RB7 dose-response curve of immunoprecipitated HDAC1, HDAC2, and HDAC3 activity. Activity was assayed at RB7 concentrations of 10, 100, and 200 μM. Values reported are relative to the control reaction and are an average of 2 independent experiments.