In vitro activity: In normal (HFS) and transformed (LNCaP, A549, and U87) cells, HPOB induces acetylation of α-tubulin, however, not histones, and inhibits cell growth, however, not viability. In HFS cells, HPOB enhances transformed cell death induced by etoposide, doxorubicin, or SAHA. HPOB also enhancing etoposide-induced transformed cell death via the apoptotic pathway in transformed cells.

Kinase Assay: In vitro activities of the 11 recombinant human zinc-dependent HDAC enzymes are detected by fluorigenic release of 7-amino-4-methylcoumarin from substrate upon deacetylase enzymatic activity. A series of dilutions of the unique HDAC6 compound, tubacin, and SAHA are prepared with 10% DMSO in HDAC assay buffer, and 5 μL of the dilution was added to a 50-μL reaction so that the final concentration of DMSO is 1% in all of the reactions. The enzymatic reactions are conducted in duplicate at 37 °C for 30 min in a 50-μL mixture containing HDAC assay buffer, 5 μg BSA, an HDAC substrate, an HDAC enzyme, and a test compound. After enzymatic reactions, 50 μL of 2× HDAC developer is added to each well, and the plate is incubated at room temperature for an additional 15 min. Fluorescence intensity is measured at an excitation of 360 nm and an emission of 460 nm using a Synergy microplate reader. Negative (no enzyme, no inhibitor, a drug with no HDAC inhibition activity) and positive controls (known HDAC inhibitor SAHA) are included in the assays. IC50 is determined at the drug concentration that results in 50% reduction of HDAC activity compared with the control.

Cell Assay: Normal (HFS) and transformed (LNCaP, A549, and U87) cells are cultured with indicated doses of HPOB for 72 h. Five micromolars SAHA is a positive control.Graphs were constructed using Prism 5.

Proc Natl Acad Sci U S A. 2013 Sep 24;110(39):15704-9.