Epigenetic processes required DNA methylation and histone modification which are regulated by several classes of enzymes in the cells. Imbalances in histone acetylation and DNA methylation lead to an aberrant behavior of the cells in morphology, cell cycle, differentiation, and carcinogenesis. Thus, the enzymes regulating the reactions can be considered as a therapeutic target of epigenetic modification. Clinical trials designed to evaluate inhibitors of DNA methyltransferases and histone deacetylases at phase I or phase II are showing encouraging results in cancer patients. A growing number of genes that are silenced by epigenetic inactivation can be used as biomarkers to monitor the efficacy of epigentically- effective drugs. (Cancer Prev Res 10, 1-5, 2005)

Keywords: Epigenetics, DNA methylation, Histone modification, Acetylation, Deacetylation, Biomarker, Drug efficacy