Demethylating Agents as Epigenetic Anticancer Therapeutics

DNA methylation is an epigenetic phenomenon, which has major effects on gene expression. Increased methylation generally inhibits transcription while hypomethylation is primarily associated with increased transcription. Hypermethylation of tumor suppressor genes occurs frequently in cancer leading to silencing of these growth inhibitory genes. Demethylating agents are a class of anti-cancer drugs which reduce cytosine methylation, promoting transcriptional activation of genes by virtue of reducing methylation in their promoter regions. Most compounds that inhibit methylation are inhibitors of DNA methyltransferases (DNMTs) that are responsible for methylating cytosine residues on DNA. Azacitidine and Decitabine are two such demethylating agents that are approved for use in myelodysplastic syndromes. In this review, we describe the pharmacology of demethylating agents and their use in recent clinical studies. The current literature describing the efficacy of combining these agents with other chemotherapeutics in various types of cancer is also reviewed.