Pracinostat, also known as SB939, is a potent and orally available inhibitor of histone deacetylase (HDAC) with a relatively stronger selectivity (more than 1000-fold) for class I, class II and class IV HDACs rather than class III HDACs. Pracinostat potently suppresses proliferation in a wide range of cancer cell lines, including colon cancer, ovarian cancer, prostate carcinomas, acute myeloid leukaemia (AML) and B cell lymphoma. Recent study results have shown that SB939 induces the accumulation of acetylated histone H3 (AcH3) and acetylated α-tubulin and increases the expression of the cyclin dependent kinase inhibitor p21 in cancer cells.