Aberrant RNA m 6 A modification in gastrointestinal malignancies: versatile regulators of cancer hallmarks and novel therapeutic opportunities.

Gastrointestinal (GI) cancer is one of the most common malignancies, and a leading cause of cancer-related death worldwide. However, molecular targeted therapies are still lacking, leading to poor treatment efficacies. As an important layer of epigenetic regulation, RNA N6-Methyladenosine (m 6 A) modification is recently linked to various biological hallmarks of cancer by orchestrating RNA metabolism, including RNA splicing, export, translation, and decay, which is partially involved in a novel biological process termed phase separation. Through these regulatory mechanisms, m 6 A dictates gene expression in a dynamic and reversible manner and may play oncogenic, tumor suppressive or context-dependent roles in GI tumorigenesis. Therefore, regulators and effectors of m 6 A, as well as their modified substrates, represent a novel class of molecular targets for cancer treatments. In this review, we comprehensively summarize recent advances in this field and highlight research findings that documented key roles of RNA m 6 A modification in governing hallmarks of GI cancers. From a historical perspective, milestone findings in m 6 A machinery are integrated with a timeline of developing m 6 A targeting compounds. These available chemical compounds, as well as other approaches that target core components of the RNA m 6 A pathway hold promises for clinical translational to treat human GI cancers. Further investigation on several outstanding issues, e.g. how oncogenic insults may disrupt m 6 A homeostasis, and how m 6 A modification impacts on the tumor microenvironment, may dissect novel mechanisms underlying human tumorigenesis and identifies next-generation anti-cancer therapeutics. In this review, we discuss advances in our understanding of m 6 A RNA modification since its discovery in the 1970s to the latest progress in defining its potential clinic relevance. We summarize the molecular basis and roles of m 6 A regulators in the hallmarks of GI cancer and discuss their context-dependent functions. Furthermore, the identification and characterization of inhibitors or activators of m 6 A regulators and their potential anti-cancer effects are discussed. With the rapid growth in this field there is significant potential for developing m 6 A targeted therapy in GI cancers.