Plexium’s Platform for Ultra-High-Throughput Screening of Large-Scale Chemical Libraries

Targeted protein degradation (TPD) using the endogenous Ubiquitin Proteasome System (UPS) represents a fundamentally new approach to drug discovery. This potentially allows proteins that cannot be modulated by conventional small molecule inhibitors to be brought under therapeutic control. Plexium has developed an ultra-high-throughput platform for screening solid phase synthesized DNA encoded libraries (DELs) in phenotypic cell-based assays in custom nanoliter scale microfluidic devices. This platform enables the efficient identification of novel monovalent or molecular glue degraders utilizing highly diverse chemical libraries and various high content assays in intact cells.

             The platform was conceived to bridge the throughput and novel chemical diversity of DELs with more biologically relevant readouts, and is particularly suited to discovery of protein degraders. By using direct phenotypic readouts in cells, Plexium’s platform enables the identification of compounds that are cell permeable and active in situ. It also allows for detection of hits that rely on complex multi protein interactions or are based only on weak binding, all of which are expected in TPD. The platform leverages the power of combinatorial chemistry to create large solid-phase libraries, where compounds are attached to the solid phase by a photo-cleavable linker. High quality redundant DNA encoding attached to the solid support, but not the screening compound, is used for structural deconvolution of hit compounds. The same DNA encoding can also be used to capture mRNA and identify transcriptomic responses of cells to compound treatment.

            We will discuss the foundations of this transformative technology and its use in the discovery of a novel specific BRD4 degrader through large-scale immunofluorescence screening, as well as its potential for a new type of ultra-high content screening through whole transcriptome RNAseq. The latter allows for the unbiased discovery of new molecular glues and generating rich SAR datasets early in the stage of screening. The combination of rationally designed and diverse chemical libraries with robust and detailed readouts can be leveraged to greatly accelerate pre-clinical optimization of hits to timely address unmet medical needs.