Therefore, drugs that inhibit DNA methylation and those that inhibit histone deacetylase can reactivate silenced genes in combination better than they can individually. Decitabine (5 aza-2'deoxycytidine), a drug that produces marked DNA hypomethylator, has demonstrated antileukemic activity at low doses. There are several drugs that have been shown to have histone acetylase activity. One of these is valproic acid that has been used safely for many years as an anti-seizure medication.