Streamlined DNA-encoded small molecule library screening and validation for the discovery of novel chemotypes targeting BET proteins (ChIP-seq)
Targeting aberrant epigenetic programs that drive tumorigenesis is a promising approach to cancer therapy. DNA-encoded small-molecule 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 computational modeling and biological characterization revealed that BBC1115 binds to BET protein BRD4 and suppresses aberrant cell fate programs. Phenotypically, BBC1115-mediated BET inhibition impaired proliferation in acute myeloid leukemia, pancreatic, and colorectal cancer cells in vitro. Moreover, intravenous administration of BBC1115 inhibited subcutaneous pancreatic and colorectal cancer xenograft growth with minimal toxicity and favorable pharmacokinetic properties in vivo. Since epigenetic regulations are ubiquitously employed across normal and malignant cells, it will be critical to evaluate whether BBC1115 interferes with normal cellular functions. Nonetheless, our study implicates that 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. Overall design: H3K27ac, BRD4, and RNA Polymerase II (phosphorylated Ser 5) ChIP-seq of murine leukemia cells (RN2) treated with indicated drugs