As regulators of transcription, proteins that interpret post-translational modifications to N-terminal histone tails are essential for maintaining cellular homeostasis. When dysregulated, these ‘reader’ proteins become drivers of disease. In the case of bromodomains, which recognize N-e-acetylated-lysine, developing domain selective inhibitors has been a significant challenge to medicinal chemists. We and others have previously reported on the bromodomain inhibitory activity of kinase inhibitors, with selectivity observed for the Bromodomain and Extra Terminal (BET) family of bromodomains. We identified tri-substituted imidazole MAP kinase inhibitors (p38α, Kd = 470 pM) with &gt; 50-fold N-terminal BET bromodomain selectivity but modest affinity (e.g. BRD4-D1, Kd = 1.2 µM). These molecules displayed an unusual mode of BET bromodomain selectivity via the displacement of conserved structured waters; however, it remained unclear whether dual inhibition of BRD4-D1 and p38α was a viable approach for the regulation transcription. Here we describe a structure-based design approach to both eliminate p38α affinity, while improving BET selectivity and affinity for BRD4-D1. Using these molecules, we observe differential transcriptional effects relative to pan-D1 inhibitors. Whereas BRD4-D1 inhibition can reduce the expression of inflammatory cytokines, a weak effect on MYC regulation is only observed at concentrations when both D1 and D2 bromodomains are inhibited. We have thus identified cell-active BET inhibitor scaffolds without kinase activity and are leveraging these molecules with chemical-biology strategies to study individual BET bromodomains that play a role in cancer and inflammatory signaling.

Deciphering the role of tandem BRD4 bromodomains using selective BRD4-D1 bromodomain inhibitors

ACS Fall 2020 Virtual Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.