Streamlined DNA-encoded small molecule library screening and validation for the discovery of novel chemotypes targeting BET proteins.

Targeting aberrant epigenetic programs that drive tumorigenesis is a promising approach to cancer therapy. DNA-encoded library (DEL) screening is a core platform technology increasingly used to identify drugs that bind to protein targets. Here, we use DEL screening against bromodomain and extra-terminal motif (BET) proteins to identify inhibitors with new chemotypes, and successfully identified BBC1115 as a selective BET inhibitor. While BBC1115 does not structurally resemble OTX-015, a clinically active pan-BET inhibitor, our intensive biological characterization revealed that BBC1115 binds to BET proteins, including BRD4, and suppresses aberrant cell fate programs. Phenotypically, BBC1115-mediated BET inhibition impaired proliferation in acute myeloid leukemia, pancreatic, colorectal, and ovarian cancer cells . Moreover, intravenous administration of BBC1115 inhibited subcutaneous tumor xenograft growth with minimal toxicity and favorable pharmacokinetic properties . Since epigenetic regulations are ubiquitously distributed across normal and malignant cells, it will be critical to evaluate if BBC1115 affects normal cell function. Nonetheless, our study shows integrating DEL-based small-molecule compound screening and multi-step biological validation represents a reliable strategy to discover new chemotypes with selectivity, efficacy, and safety profiles for targeting proteins involved in epigenetic regulation in human malignancies.