Pyroxamide is a potent histone deacetylase (HDAC) inhibitor with IC50 of 100nM. Pyroxamide induced terminal differentiation in murine erythroleukemia (MEL) cells, and inhibited the growth by cell cycle arrest or apoptosis in a variety of tumor cells^1-4. An accumulation of acetylated histones and increased levels of p21/WAF1 expression were detected in cancer cells and in prostate xenografts treated with pyroxamide^1,2.