Kinase experiment:

Forty microliter enzyme buffer (15 mM Tris HCl pH 8.1, 0.25 mM EDTA, 250 mM NaCl, 10% v:v glycerol) containing HDAC1, 3, 6 or 8 activity, 29 μL enzyme buffer and 1 μL resminostat [HCl] at different concentrations are added to a 96-well microtitre plate and the reaction started by the addition of 30 μL substrate peptide Ac-NH-GGK(Ac)-AMC (HDAC1, 3 and 6 assays, final concentrations 6 μM for HDAC1, 10 μM for HDAC6 and 25 μM for HDAC3/DAD) or Ac-RHK(Ac)K(Ac)-AMC (HDAC8 assay, final concentration 50 μM). After incubation for 180 min (HDAC1, HDAC6, HDAC8) or 120 min (HDAC3) at 30℃, the reaction is terminated by the addition of 25 μL stop solution (50 mM Tris HCl pH 8, 100 mM NaCl, 0.5 mg/mL trypsin and 2 μM trichostatin A [TSA]). After incubation at room temperature for further 40 min, fluorescence is measured using a Wallac Victor2 1420 multilabel counter (extinction 355 nm, emission 460 nm) for quantification of AMC generated by tryptic cleavage of the deacetylated peptide. For the calculation of the 50% inhibitory concentration (IC50) values the fluorescence in wells without test compound (1% DMSO, negative control) is set as 100% enzymatic activity and the fluorescence in wells with 2 μM TSA (positive control) are set at 0% enzymatic activity (background fluorescence substracted)[1].

Cell experiment:

A CCK-8 cell proliferation assay is used to investigate the antiproliferative effect of resminostat on HNSCC cells. Cells are seeded into 96-well plates at a density of 3 × 105/well. After 24 hours of growth, the cells are treated with resminostat and cisplatin, either alone or in combination and incubated for 72 hours. Untreated cells maintained in RPMI and equal concentrations of dimethylsulfoxide served as control. After 72 hours, cell proliferation is measured by CCK-8. Experiments are carried out in triplicate 3 times[2].

Resminostat is an inhibitor of histone deacetylase (HDAC) with IC50 values of 42.5nM, 50.1nM and 71.8nM, respectively against HDAC1, 3 and 6 [1].

As an inhibitor of HDACs, resminostat also inhibits HDAC8 with a weak activity (IC50=877nM). 5μM resminostat induces the acetylation of histone H4 in U266 myeloma cells. 10μM resminostat completely suppresses the cell growth in human myeloma cell lines, such as OPM-2, RPMI-8226 and U266. This inhibition is proved to be caused by the induction of apoptosis. In primary myeloma cells, resminostat also induces apoptosis of cells. Besides that, resminostat is proved to downregulate the expression of cell cycle proteins, including phosphorylated Rb, cdc25a, cyclin D1, Cdk4 and p53. In addition, resminostat is reported to be well tolerated, have no unexpected toxicities and do not cause clinically significant myelosuppression in the first-human study [1, 2].

References:
[1] Mandl-Weber S, Meinel FG, Jankowsky R, Oduncu F, Schmidmaier R, Baumann P. The novel inhibitor of histone deacetylase resminostat (RAS2410) inhibits proliferation and induces apoptosis in multiple myeloma (MM) cells. Br J Haematol. 2010 May;149(4):518-28.
[2] Brunetto AT, Ang JE, Lal R, Olmos D, Molife LR, Kristeleit R, Parker A, Casamayor I, Olaleye M, Mais A, Hauns B, Strobel V, Hentsch B, de Bono JS. First-in-human, pharmacokinetic and pharmacodynamic phase I study of Resminostat, an oral histone deacetylase inhibitor, in patients with advanced solid tumors. Clin Cancer Res. 2013 Oct 1;19(19):5494-504.