A Structure-based Design Approach for Generating High Affinity BRD4 D1-Selective Chemical Probes.

Area of Science:

• Epigenetics and Chemical Biology
• Molecular Mechanisms of Gene Regulation
• Drug Discovery and Development

Background:

• Bromodomain and extra-terminal (BET) proteins are key regulators of transcription.
• Developing selective inhibitors for individual BET bromodomains is challenging due to high protein similarity.
• Chemical probes are vital for studying epigenetic mechanisms and advancing therapeutics.

Purpose of the Study:

• To design and synthesize selective small molecule inhibitors targeting a single bromodomain of BET proteins.
• To investigate the structure-activity relationships of 1,4,5-trisubstituted imidazoles against BRD4 N-terminal bromodomain (D1).
• To evaluate the selectivity and biological activity of novel inhibitor compounds.

Main Methods:

• Structure-activity relationship (SAR) study of imidazole derivatives.
• Isothermal titration calorimetry (ITC) for binding affinity measurements.
• Fluorescence anisotropy, thermal shift assays, and Cellular Thermal Shift Assay (CETSA) for selectivity profiling.

Main Results:

• Compounds 26 and 30 demonstrated potent affinity (15 and 18 nM) for BRD4 D1.
• Exhibited over 500-fold selectivity against BRD2 D1 and BRD4 D2.
• Demonstrated target engagement and differential effects on gene expression (e.g., IL-8 downregulation) in cellular models.

Conclusions:

• Established design principles for achieving high selectivity for individual BET bromodomains.
• Validated the potential of selective BET bromodomain inhibitors in modulating specific cellular pathways.
• Provided valuable chemical tools for further research in epigenetics and therapeutic development.