Epidrugs in the immunotherapy of cutaneous and uveal melanoma

Epigenetic modifications can affect numerous mechanisms used by neoplastic cells to evade immune control. In melanoma epigenetic defects, caused by dysregulations in the expression of genome writers, erasers, or readers, play a significant role in the reduced expression of molecules required for efficient immune recognition as well as antigen presentation and processing. Alterations in gene expression were identified in tumor-associated antigens (TAAs), human leukocyte antigen (HLA) complex, co-stimulatory/accessory molecules, antigen processing machinery (APM), and NKG2D ligands that have been shown to be silenced or down-regulated in melanoma. In agreement with the inherent reversibility of epigenetic silencing, epigenetic drugs such as inhibitors of DNA methyltransferases (DNMTs), histone deacetylases (HDACs), histone methyltransferase enhancer of Zeste homolog 2 (EZH2), and modifiers of microRNA (miRNA) dysregulation or antagomirs can restore the expression of these molecules, favouring the recognition of cancer cells by immune responses, reducing the resistance to Natural Killer (NK) and cytotoxic T cells (CTL), and enhancing the functions of antigen presenting cells. Moreover, inhibitors of reader proteins seem to preferentially affect the NF-kB-induced activation of pro-inflammatory cytokine genes. At present an increasing interest is shown toward new combined therapeutic approaches employing epidrugs or new molecular inhibitors and in vivo immunotherapies, such as vaccines and adoptive T-cell transfer (ACT). This review summarizes the current understanding of the role of epidrugs in the modulation of molecules involved in the melanoma immune response and focuses on their future clinical use in new therapeutic combinations for melanoma treatment.