Belinostat (also known as PXD101) is a novel and potent hydroxamate-type inhibitor of histone deacetylase (HDAC) that inhibits the activity of HDAC in Hela cell extracts with 50% inhibition concentration IC50 value of 27 nM. Belinostat has been found to significantly increase the acetylation of histones H3 and H4 and exerts cytotoxicity in a wide range of tumor cell lines. In the treatment of urothelial carcinoma cell lines, belinostat dose-dependently inhibits proliferation in 5637, T24, J82 and RT4 cells with IC50 values of 1.0 μM, 3.5 μM, 6.0 μM and 10 μM respectively; while, in prostate cancer cell lines, it inhibits cancer cell growth with IC50 values ranging from 0.5 to 2.5 μM.