Epigenetic therapies in patients with solid tumors: Focus on monotherapy with deoxyribonucleic acid methyltransferase inhibitors and histone deacetylase inhibitors

Epigenomics is the study of the gene expression changes due to epigenetic processes and not due to the deoxyribonucleic acid (DNA) base sequence alterations. The key mechanisms of epigenetic regulation include DNA methylation, histone modifications, and noncoding RNAs. Epigenetic alterations in cancer are predominantly linked with hypermethylation of promoters of the tumor suppressor genes, global DNA hypomethylation, and increased expression of histone deacetylases (HDAC). There is a growing need to investigate epigenetic patterns and to provide safe and effective, innovative therapeutic strategies for oncology patients, who did not improve on traditional anticancer regimens. The epi-drugs (e.g., DNA methyltransferase inhibitors, e.g., azacitidine and decitabine and HDAC inhibitors, e.g., vorinostat and romidepsin) have been approved for the clinical use. In this paper, we provide a brief overview of the mechanisms of action and targets for novel epi-drugs, focusing on their potential clinical applications in patients with solid tumors, resistant to standard oncology treatments.