Nanatinostat, also known as Tractinostat, CHR-3996 and VRx-3996, is an orally bioavailable, second-generation hydroxamic acid-based inhibitor of histone deacetylase (HDAC) with potential antineoplastic activity. HDAC inhibitor CHR-3996 inhibits HDAC, resulting in an accumulation of highly acetylated histones, the induction of chromatin remodeling, and the selective transcription of tumor suppressor genes; these events may result in the inhibition of tumor cell division and the induction of tumor cell apoptosis. This agent may upregulate HSP70 and downregulate anti-apoptotic Bcl-2 proteins more substantially than some first-generation HDAC inhibitors. HDACs, upregulated in many tumor cell types, are a family of metalloenzymes responsible for the deacetylation of chromatin histone proteins.