DNA methyltransferase (DNMT) inhibitors are epigenetic compounds that block the activity of DNA methyltransferases, the enzymes responsible for adding methyl groups to cytosine residues in DNA. By reducing DNA methylation, these inhibitors can reactivate genes that are abnormally silenced, particularly tumor suppressor genes in cancer cells. They are widely investigated as therapeutic agents in oncology and in diseases associated with epigenetic dysregulation.

Mechanism of Action

DNMT inhibitors interfere with the enzymatic transfer of methyl groups onto DNA. Nucleoside analogs such as azacytidine and decitabine are incorporated into DNA during replication, where they form covalent complexes with DNMTs, leading to enzyme trapping, depletion, and progressive passive demethylation across cell divisions.

Non-nucleoside inhibitors, such as RG108, act through direct binding to the DNMT active site or regulatory regions without being incorporated into DNA, thereby inhibiting catalytic activity through a different molecular mechanism.

Major Classes of Inhibitors

DNMT inhibitors are generally classified into nucleoside analogs and non-nucleoside inhibitors:

• Nucleoside analogs: Azacytidine and decitabine are the most established compounds in clinical use and remain key epigenetic drugs in hematological malignancies.
• Zebularine: A cytidine analog characterized by increased chemical stability and reduced toxicity, although its clinical development remains limited compared to first-generation agents.
• Non-nucleoside inhibitors: Compounds such as RG108 inhibit DNMT activity without DNA incorporation, offering an alternative pharmacological strategy.

Therapeutic Applications

DNMT inhibitors are primarily used in the treatment of hematologic malignancies, where aberrant DNA methylation contributes to oncogenic progression. They are also under investigation in solid tumors, including breast cancer, where epigenetic reprogramming may restore tumor suppressor gene expression and enhance therapeutic response.

In addition, DNMT inhibition is being evaluated in combination with immunotherapy and other anticancer strategies to improve clinical outcomes through epigenetic modulation of tumor and immune cell interactions.