BET bromodomain proteins (e.g. BRD4)

Class

Small molecule BET inhibitor

Pathway

MYC-driven transcriptional regulation

BET bromodomain proteins, including BRD4, are 'reader' proteins that recognize a chemical mark called acetylation on histones, the proteins around which DNA is packaged. By binding these marks, BRD4 anchors itself at active gene regions and helps recruit the machinery that copies DNA into RNA, a step called transcription. It is especially important at clusters of DNA control elements known as super-enhancers, which drive very high expression of certain genes, including the growth-promoting gene MYC. Many cancers become dependent on sustained, elevated MYC or related oncogenic programs maintained through this super-enhancer activity. Small molecule BET inhibitors occupy the same pocket that normally binds acetylated histones, displacing BRD4 from chromatin and reducing transcription of these dependency genes. This can slow proliferation or trigger cell death in susceptible tumor cells. The mechanism is broadly relevant across blood cancers such as leukemia, lymphoma, and myeloma, as well as certain solid tumors and rare cancers defined by structural rearrangements involving BRD4 itself. Because the mechanism acts upstream on gene expression rather than on a single downstream protein, it can affect multiple oncogenic pathways simultaneously, which is part of its appeal as a therapeutic strategy.