Abstract A059: Small molecule microarray lysate screen identifies bromodomain ligands that target the MYC transcription regulatory network

Abstract

Abstract MYC is the most frequently amplified gene in human cancers and one of the most sought-after drug targets for cancer therapy. Its function as a transcription factor is essential for its oncogenic potential. However, development of small molecules that target oncogenic MYC function in cells has been intractable due to its lack of known ligand binding sites. To overcome these structural challenges, we leveraged Kronos Bio’s small molecule microarray (SMM) screening platform to identify small molecules that can bind to MYC transcriptional complexes in cell lysates from cancer cells with deregulated MYC function. Unbiased transcriptional signature-based profiling identified multiple SMM hits that modulated the MYC transcription regulatory network (TRN) in MYC-dependent cancer cell lines. One of the SMM hits mimicked signature changes due to MYC loss of function, which were also similar to signature changes effected by BET bromodomain inhibitors. Biochemical, biophysical, and structural analyses found that the SMM hit could directly engage with BET bromodomains in purified systems. Cell-based proximity labeling demonstrated binding to BET proteins in live cells, and comparative pharmacology approaches suggested that the BET protein engagement was likely driving the observed gene expression changes. These results demonstrate the utility of the SMM platform in identifying ligands that modulate transcription factor TRNs through binding to critical cofactors. Citation Format: Emily B Cohen, Zhihua Ma, Wayne L Glore, Oleg A Volkov, Tong Liang, Nikolaus D Obholzer, Andrew C Clay, Mulini Reddy Pingili, Yupeng Zheng, Jun Li, Shi Yun Wang, Tom Chen, David B Freeman, Hua Gao, Minyun Zhou, Priscilla Cheung, Tamara D Hopkins, Marius S Pop, Christopher J Dinsmore, B. Wesley Trotter, Charles Y Lin, Peter B Rahl. Small molecule microarray lysate screen identifies bromodomain ligands that target the MYC transcription regulatory network [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A059.