Spatially constrained tandem bromodomain inhibition bolsters sustained repression of BRD4 transcriptional activity for TNBC cell growth

Abstract

The importance of BET protein BRD4 in gene transcription is well recognized through the study of chemical modulation of its characteristic tandem bromodomain (BrD) binding to lysine-acetylated histones and transcription factors. However, while monovalent inhibition of BRD4 by BET BrD inhibitors such as JQ1 blocks growth of hematopoietic cancers, it is much less effective generally in solid tumors. Here, we report a thienodiazepine-based bivalent BrD inhibitor, MS645, that affords spatially constrained tandem BrD inhibition and consequently sustained repression of BRD4 transcriptional activity in blocking proliferation of solid-tumor cells including a panel of triple-negative breast cancer (TNBC) cells. MS645 blocks BRD4 binding to transcription enhancer/mediator proteins MED1 and YY1 with potency superior to monovalent BET inhibitors, resulting in down-regulation of proinflammatory cytokines and genes for cell-cycle control and DNA damage repair that are largely unaffected by monovalent BrD inhibition. Our study suggests a therapeutic strategy to maximally control BRD4 activity for rapid growth of solid-tumor TNBC cells.

Nucleosome scaffolding by Brd4 tandem bromodomains in acetylation-dependent chromatin compartmentalization

“…Our SAXS-guided Rosetta modeling indicated that the Brd4 tandem bromodomains may access conformations in which the two acetyl-lysine binding sites reside as little as 15 Å apart, perhaps allowing for bivalent binding toward adjacent acetylation sites on individual histone tails. These results are consistent with the known ability of bivalent BET bromodomain inhibitors to simultaneously engage both acetyl-lysine binding sites (59, 74, 75). Previous studies of the Taf1 tandem bromodomains demonstrated 8-to 29-fold tighter binding affinity toward diacetylated ( K d = 1.4 to 5.3 µ M) relative to monoacetylated histone H4 tail mimic peptides ( K d ∼40 µ M) and proposed a model in which the two Taf1 bromodomains bivalently engage separate acetyl-lysine residues on a single peptide.…”

Fli-1 Activation through Targeted Promoter Activity Regulation Using a Novel 3’, 5’-diprenylated Chalcone Inhibits Growth and Metastasis of Prostate Cancer Cells

“…The experiment was performed as previously described [44]. Briefly, PC3 cells were treated with an increasing amount of C10 and DMSO for 1 h at 37 • C. Following this, the cells were washed with PBS, heated at 49 • C for 5 min, placed at room temperature for 3 min, and treated with liquid nitrogen (−37 • C) water-bath cycles three times.…”

ZMYND11-MBTD1 induces leukemogenesis through hijacking NuA4/TIP60 acetyltransferase complex and a PWWP-mediated chromatin association mechanism

“…But it is noteworthy to mention that the currently available BET inhibitors as single agents, despite their promising anti-cancer activity in animal models, seem to only exhibit limited efficacy in clinical trials 53 . To address potential issues of low potency, next-generation BET-inhibiting compounds are being developed, such as bivalent BET inhibitors that bind to tandem bromodomains simultaneously and PROTAC-based BET degraders, which offer superior therapeutic effects in preclinical studies 54 – 57 . In addition, combination therapy with other synergistic anti-cancer drugs was reported to greatly boost the efficacy of BET inhibition and prevent emergency of drug resistance 58 , 59 .…”