A potent histone deacetylase (HDAC) activity inhibitor. It inhibits HDAC activity in HeLa cell extracts with an IC₅₀ of 27 nM. Belinostat significantly increases acetylation of histones H3 and H4 and potently inhibits the growth of prostate cancer cell lines (IC₅₀ range from 0.5 to 2.5 µM) with cytotoxic activity preferentially against tumor cells.