An inhibitor of histone deacetylase (HDAC) enzymes, with potential antineoplastic activity. Upon administration, OBP-801 inhibits the activity of HDACs; this results in an accumulation of highly acetylated chromatin histones, the induction of chromatin remodeling and an altered pattern of gene expression. This leads to selective transcription of tumor suppressor genes, tumor suppressor protein-mediated inhibition of tumor cell division and induction of tumor cell apoptosis. This may inhibit proliferation of susceptible tumor cells. HDAC, which is upregulated in many tumor cell types, deacetylates chromatin histone proteins.