Epigenetic therapy of lymphoma using histone deacetylase inhibitors

In this study, we reviewed epigenetic therapy of lymphomas using histone deacetylase inhibitors (HDACi), a promising new class of antineoplastic agents. Epigenetic therapy, a new therapeutic concept, consists of the use of HDACi and or DNA methyltransferase inhibitors (DNMTi). We conducted a comprehensive review of the literature for antitumour activity of HDACi and its mechanism of action. HDACi modify the expression of several genes related to cancer development, which can result in antineoplastic activity. To elucidate the benefits of HDACi in lymphoma treatment, we discuss the crucial interplay between BCL6, p53 and STAT3. Activated B-cell (ABC) diffuse large cell lymphoma (DLCL) is increasingly being recognised as an unfavourable and frequently therapy-refractory lymphoma. We discuss the fundamental causative role of the STAT3 oncogene in ABC type DLCL. STAT3 can be effectively suppressed by several HDACi, a promising treatment for this difficult subtype of DLCL. On the other hand, various HDACi can repress the germinal-centre B Cell (GCB) type DLCL by virtue of their inhibition of the BCL6 oncogene, usually expressed in this particular subtype. We summarise the results of recent clinical trials with HDACi such as romidepsin, panobinostat, MGCD-0103, entinostat, curcumin, JAK2 inhibitor TG101348, and valproic acid that have shown preliminary activity in recurrent and refractory lymphomas. The unique mechanism of action of HDACi makes them very attractive agents to pursue in combination. Several ongoing trials are already exploring HDACi combinations in various types of cancers. Their role in front-line management remains to be determined.