Histone deacetylase(HDAC)inhibitors contain a functional group,which mimics lysine side chain that interacts with the critical HDAC Zinc atom.They are able to up-regulate histone acetylation and down- regulate deacetylation via competitive inhibition to modulate the gene transcription and expression,inhibit cell proliferation,stimulate cell differentiation,and provocate cell apoptosis.Many HDAC inhibitors have been found or synthesized as new potent anticancer drugs.