Synthesis and Structure-Activity-Relationship Study of 1,4-Acylthiazepanes as BD2-Selective BET Bromodomain Inhibitors
Epigenetic dysregulation involving bromodomain and extra-terminal domain (BET) proteins, BRD2, 3, 4 and T plays a crucial role in inflammation and cancer, including alcoholic hepatitis, an inflammatory liver disease. BET proteins recognize and bind to N-ε-acetylated lysine residues on histone proteins. A disruption of this interaction triggers inflammation, highlighting the therapeutic potential of BET bromodomain inhibitors. Current non-selective inhibitors targeting both bromodomains (BD1 and BD2) exhibit dose-limiting toxicity. Selective BD2 inhibitors attenuate undesirable side effects in clinical settings, underscoring the need for selective inhibitors. The Pomerantz lab identified a 1,4-acylthiazepane scaffold, demonstrating BD2 inhibition in BET proteins. The high 3D-character of 1,4-acylthizepanes allows for conformational diversity, mimicking the acetylated lysine on the histone tail, and allows the ring system to potentially engage a non-conserved histidine residue in BET BD2 domains. This research focuses on synthesizing 1,4-acylthizepane analogs with diverse substituents to study the histidine interaction. Biophysical analysis of the acyl group and enantiomeric forms of 1,4-acylthiazepanones have been completed by other lab members, further supporting ongoing development. The synthetic steps involve cyclization of α,β-unsaturated esters with 1,2-aminothiols, yielding 1,4-thiazepanones, followed by reduction and acylation to yield the final product. Using a competitive AlphaScreen assay, we assessed the binding affinity and selectivity of 1,4-acylthiazepanes for BD2. Electron-donating substituents depicted a 2–3 fold increase in affinity for BRD2-BD2 compared to electron-withdrawing groups, suggesting potential noncovalent interactions of the ring system with the histidine residue of BRD2-BD2. This ongoing work contributes to the development of novel BET BD2 selective inhibitors, allowing for further studies in inflammation models at the Mayo Clinic for targeted therapeutics for alcoholic hepatitis.