Cancer Epigenomics

Abstract

Large-scale cancer genomic projects indicated that more than 50% of human cancers carry mutations in key chromatin proteins. Moreover, compared to normal cells cancer cells show genome-wide changes in DNA methylation, histone modifications and 3D chromatin structure. In addition, many tumors re-activate programs of fetal development, which is a sign of epigenetic reprograming. The mechanistic bases of cancer epigenomics are specific genetic, environmental and metabolic stimuli that disrupt the homeostatic balance of chromatin, which then either becomes very restrictive or permissive. Restrictive chromatin states can prevent the induction of tumor suppressor programs or block differentiation. In contrast, permissive states allow oncogene activation or non-physiologic cell fate transitions.

Many of these epigenetic changes are only “passengers,” but a few also act as “drivers” of the tumorigenesis process. In pre-malignant cells these epigenetic dys-regulations promote tumor initiation and in malignant cells they accelerate tumor evolution and adaptation. The effects of diverse oncogenic stimuli are mediated via epigenetic modulators and contribute to diverse aspects of cancer biology, such as all hallmarks of cancer. Recent drug discovery efforts targeted the epigenome and several new drugs – inhibitors of chromatin modifiers – are tested in clinical trials and some were already approved by the US Food and Drug Administration (FDA).

In this chapter, we will discuss the impact of epigenetic modifiers in the tumorigenesis process. We will present epigenetic dys-regulations as the basis for an epigenetic reprograming that can transform normal cells into tumor cells. In this context, we will understand how epigenomic changes will contribute to basically all hallmarks of cancer. Finally, we will analyze the impact of epigenetic therapy for the treatment of cancer.