In vitro activity: Specific for class I and class II HDACs, CUDC-101 does not inhibit class III Sir-type HDACs. CUDC-101 displays weak activity against other protein kinases including KDR/VEGFR2, Lyn, Lck, Abl-1, FGFR-2, Flt-3, and Ret with IC50 of 0.85 μM, 0.84 μM, 5.91 μM, 2.89 μM, 3.43 μM, 1.5 μM, abd 3.2 μM, respectively. CUDC-101 displays broad antiproliferative activity in many human cancer cell types with IC50 of 0.04-0.80 μM, exhibiting a higher potency than erlotinib, lapatinib, and combinations of vorinostat with either erlotinib or lapatinib in most cases. CUDC-101 potently inhibits lapatinib- and erlotinib-resistant cancer cell lines. CUDC-101 inhibits the erlotinib-resistant EGFR mutant T790M although its effects are incomplete with an Amax of ~60% of peak enzyme activity after inhibition. CUDC-101 treatment increases the acetylation of histone H3 and H4, as well as the acetylation of non-histone substrates of HDAC such as p53 and α-tubulin, in a dose-dependant manner in various cancer cell lines. CUDC-101 also suppresses HER3 expression, Met amplification, and AKT reactivation in tumor cells.

Kinase Assay: The activities of Class I and II HDACs are assessed using the Biomol Color de Lys system. Briefly, HeLa cell nuclear extracts are used as a source of HDACs. Different concentrations of CUDC-101 are added to HeLa cell nuclear extracts in the presence of a colorimetric artificial substrate. Developer is added at the end of the assay and enzyme activity is measured in the Wallac Victor II 1420 microplate reader at 405 nM. EGFR and HER2 kinase activity are measured using HTScan EGF receptor and HER2 kinase assay kits. Briefly, the GST-EGFR fusion protein is incubated with synthetic biotinylated peptide substrate and varying concentrations of CUDC-101 in the presence of 400 mM ATP. Phosphorylated substrate is captured with strapavidin-coated 96-well plates. The level of phosphorylation is monitored by antiphospho-tyrosine- and europium-labeled secondary antibodies. The enhancement solution is added at the end of the assay and enzyme activity is measured in the Wallac Victor II 1420 microplate reader at 615 nM.

Cell Assay: Cancer cell lines (HCC827, H358, H460, HepG2, Hep3B2, Sk-Hep-1, Capan1, BxPc3, MCF-7, MDA-MB-231, and Sk-Br-3) are plated at 5000 to 10000 cells per well in 96-well flatbottomed plates with varying concentrations of CUDC-101. The cells are incubated with CUDC-101 for 72 hours in the presence of 0.5% of fetal bovine serum. Growth inhibition is assessed by an adenosine triphosphate (ATP) content assay using the Perkin-Elmer ATPlite kit. Apoptosis is routinely assessed by measuring the activities of Caspase-3 and -7 using Apo-ONE Homogeneous Assay Kit.

J Med Chem. 2010 Mar 11;53(5):2000-9; Cancer Res. 2010 May 1;70(9):3647-56.