Epigenetic plasticity in metastatic dormancy: mechanisms and therapeutic implications

The overwhelming majority of cancer-associated morbidity and mortality can be ascribed to metastasis. Metastatic disease frequently presents in a delayed fashion following initial diagnosis and treatment, requiring that disseminated cancer cells (DCCs) spread early in tumor progression and persist in a dormant state at metastatic sites. To accomplish this feat, DCCs exhibit substantial phenotypic plasticity that is mediated by the epigenetic regulation of dormancy programs in response to intrinsic (i.e., cellular) and extrinsic (i.e., microenvironmental) cues. The epigenome is a dynamic landscape that encompasses transcriptional regulation via alteration of chromatin architecture, posttranscriptional RNA processing, and the diverse functions carried out by noncoding RNAs. Signals converging on DCCs are transduced through epigenetic effectors. Conversely, epigenetic regulation of gene expression controls the crosstalk between DCCs and cells of the metastatic niche, a phenomenon that is essential for the institution of dormant phenotypes. Importantly, epigenetic effectors can be targeted therapeutically, and the development of novel epigenetic therapies may provide new inroads to combating recurrent metastatic disease. Here we provide an overview of the dynamics of metastatic dormancy and summarize our current understanding of the intersections between dormancy and the epigenome, both mechanistically and therapeutically.