A novel approach applying a chemical biology strategy in phenotypic screening reveals pathway-selective regulators of histone 3 K27 tri-methylation.

Epigenetic regulation by histone methylation is crucial for proper programming of the genome during development. Homeostasis of histone methylation is balanced by the activities of histone methyltransferases and demethylases. Although these methyltransferases and demethylases represent logical targets for potential drug discovery, the activities of methyltransferases and demethylases regulated in response to a complex biological stimulus are also important and not yet clear. To manipulate and study histone methylation in biological systems, we screened a Biologically Diverse Compound Set (BDCS) utilizing a phenotypic assay system that directly measures the Histone 3 K27 tri-methylation (H3K27me3) level in cells. The BDCS is a unique set of target-annotated chemical probes, containing a total of 5853 compounds targeting 736 unique proteins with multiple maximally selective compounds for each target. A number of targets, with multiple hits against each target, were identified in the screen. This gave us confidence that these targets and pathways may be relevant, and included the identification of non-methyltransferase/demethylase targets as potential upstream regulators of H3K27me3. Our study suggests that a systematically designed chemical probe library can serve as a powerful drug discovery tool when combined with phenotypic screening. Follow-up studies using these findings may reveal novel therapeutically useful pathways and targets of H3K27me3 regulation.

Development of a high-throughput screen to detect inhibitors of TRPS1 sumoylation.

Small ubiquitin-like modifier (SUMO) belongs to the family of ubiquitin-like proteins (Ubls) that can be reversibly conjugated to target-specific lysines on substrate proteins. Although covalently sumoylated products are readily detectible in gel-based assays, there has been little progress toward the development of robust quantitative sumoylation assay formats for the evaluation of large compound libraries. In an effort to identify inhibitors of ubiquitin carrier protein 9 (Ubc9)-dependent sumoylation, a high-throughput fluorescence polarization assay was developed, which allows detection of Lys-1201 sumoylation, corresponding to the major site of functional sumoylation within the transcriptional repressor trichorhino-phalangeal syndrome type I protein (TRPS1). A minimal hexapeptide substrate peptide, TMR-VVK1201TEK, was used in this assay format to afford high-throughput screening of the GlaxoSmithKline diversity compound collection. A total of 728 hits were confirmed but no specific noncovalent inhibitors of Ubc9 dependent trans-sumoylation were found. However, several diaminopyrimidine compounds were identified as inhibitors in the assay with IC50 values of 12.5 µM. These were further characterized to be competent substrates which were subject to sumoylation by SUMO-Ubc9 and which were competitive with the sumoylation of the TRPS1 peptide substrates.