Trapoxin A, a cyclotetrapeptide,is a potent histone deacetylase (HDAC) inhibitor with potential anticancer activity. It increases the level of chromatin acetylation associated with histone H3 at low nanomolar concentrations. Trapoxin irreversibly inhibits HDAC activity in crude cell lysates and
induces the accumulation of hyperacetylated core histones in a number of
mammalian cell lines and tissues.