BET Bromodomain as a Target of Epigenetic Therapy

Acetylation of histone is a key epigenetic modification, and contributes to many DNA-dependent cellular processes. The bromodomain structure, which consists of approximately 110 amino acid residues, serves as a 'reader' that recognizes acetylated lysine in histones, leading to recruitment of positive transcriptional elongation factor b (P-TEFb), and thereby promoting transcriptional activity and chromatin remodeling. Among bromodomain-containing proteins, members of the bromodomain and extra-terminal domain (BET) family contain tandem N-terminal bromodomains. BET proteins, especially BRD4, have attracted interest as candidate therapeutic targets due to their putative involvement in the pathogenesis of various diseases, including cancer and inflammatory diseases. Several BET inhibitors are under clinical trial for treatment of various cancers. Furthermore, polypharmacological agents such as dual kinase/BET inhibitors and dual histone deacetylase (HDAC)/BET inhibitors have recently been developed, in addition to agents that degrade BET family proteins, such as proteolysis-targeting chimeras (PROTACs). This paper reviews recent progress in epigenetic therapy targeting the BET bromodomain.