In vitro activity: MC1568 is a selective class II (IIa) histone deacetylas (HDAC II) inhibitor with IC50 of 220 nM and 176-fold class II selectivity (against class I). In human breast cancer ZR-75.1 cell lysates, MC1568 (5 μM) shows no inhibitory activity against HDAC1 but is able to inhibit HDAC4. In MCF-7 cells, MC1568 (20 μM) increases the accumulation of acetylated H3 and H4 histones, as well as the levels of acetyl-tubulin, which indicates a inhibitory effect of MC1568 on HDAC6. In C2C12 cells, MC1568 (5 μM) arrests myogenesis by decreasing myocyte enhancer factor 2D (MEF2D) expression, stabilizing the HDAC4-HDAC3-MEF2D complex, and by inhibiting differentiation-induced MEF2D acetylation. MC1568 (5 or 10 μM) interferes with the RAR- and PPARγ-mediated differentiation-inducing signaling pathways. In F9 cells, MC1568 specifically blocks endodermal differentiation despite not affecting retinoic acid-induced maturation of promyelocytic NB4 cells. In 3T3-L1 cells, MC1568 attenuates PPARγ-induced adipogenesis.

Kinase Assay: The enzyme liberats tritiated acetic acid from the substrate, which is quantified by scintillation counting. IC50 values are results of triple determinations. A 50 μL sample of maize enzyme (at 30 °C) is incubated (30 min) with 10 μL of total [3H]acetate-prelabeled chicken reticulocyte histones (2 mg/mL). Reaction is stopped by addition of 50 μL of 1 M HCl/0.4 M acetate and 800 μL of ethyl acetate. After centrifugation (1×104 g, 5 min), an aliquot of 600 μL of the upper phase is counted for radioactivity in 3 mL of liquid scintillation cocktail. MC1568 is tested at a starting concentration of 40 μM, and active substances are diluted further. NaB, VPA, TSA, SAHA, 85 TPX, HC-toxin, and tubacin are used as the reference compounds, and blank solvents are used as negative controls.

Cell Assay: The 3T3-L1 cells are propagated and differentiated using a cocktail of isobutylmethylxanthine, dexamethasone, and insulin. From the second day post-confluence and throughout the differentiation period of 8 days, the 3T3-L1 cells are induced by: (1) no induction: at post-confluence and throughout the differentiation period of 8 days, the cells are incubated with DMSO or MC1568. (2) troglitazone: at post-confluence and throughout the differentiation period of 8 days, the cells are induced with 5 μM troglitazone, MC1568, or both. (3) rosiglitazone: at post-confluence and throughout the differentiation period of 8 days, the cells are incubated with 1 μM rosiglitazone and either DMSO or MC1568. (4) rosiglitazone and dexamethasone: at post-confluence, the cells received 1 μM of rosiglitazone and 390 ng/mL dexamethasone. Throughout the differentiation period of 8 days, the cells are induced with 1 μM of rosiglitazone and either DMSO or MC1568. All medium is renewed every second day.