HDAC9 and neoplasm: A new collection of N-(6-mercaptohexyl)-3-substituted-1H-pyrazole-5-carboxamide HDAC inhibitors was developed by Wen et al. The disulfide compound 287 was found to be potent cytotoxic agent against a panel of seven tumor cells, causing hyperacetylation of histone and non-histone proteins in cellular level, and demonstrated a notable in vivo anti-tumor activity in HCT-116 xeno-grafted model [192].