Pharmacoepigenetics and Toxicoepigenetics: Novel Mechanistic Insights and Therapeutic Opportunities

Pharmacological treatment and exposure to xenobiotics can cause substantial changes in epigenetic signatures. The majority of these epigenetic changes, caused by the compounds in question, occur downstream of transcriptional activation mechanisms, whereby the epigenetic alterations can create a transcriptional memory and stably modulate cell function. The increasing understanding of epigenetic mechanisms and their importance in disease has prompted the development of therapeutic interventions that target epigenetic modulatory mechanisms, particularly in oncology where inhibitors of epigenetic-modifying proteins (epidrugs) have been successfully used in treatment, mostly in combination with standard-of-care chemotherapy, either provoking direct cytotoxicity or inhibiting resistance to anticancer drugs. In addition, emerging methods for detecting epigenetically modified DNA in bodily fluids may provide information about tumor phenotype or drug treatment success. However, it is important to note that many technical pitfalls, such as the nondeconvolution of methylcytosine and hydroxymethylcytosine, compromise epigenetic analyses and the interpretation of results. In this review, we provide an update on the field, with an emphasis on the novel therapeutic opportunities made possible by epidrugs.