 - Methylation-mediated silencing of genes is an epigenetic mechanism implicated in carcinogenesis; agents that inhibit this mechanism are of clinical interest because of their potential to re-activate silenced tumor suppressor genes. Two DNA hypomethylating nucleosides, 5-azacytidine azacytidine and 5-aza-2-deoxycytidine decitabine have been approved by the FDA for the treatment of patients with myelodysplastic syndromes and certain leukemias. 