Discovery of a VHL molecular glue degrader of GEMIN3 by Picowell RNA-seq

Abstract

Targeted protein degradation (TPD) is an emerging therapeutic modality in which small molecules are used to recruit targets to the natural protein degradation machinery of the cell. Molecular glue degraders (MGD) are monovalent small molecules that accomplish this by redirecting E3 ubiquitin ligases to target proteins, offering the potential to degrade previously unliganded and "undruggable" proteins in cancer, neurodegenerative, and other diseases. While attractive due to their drug-like properties, MGDs are exceptionally hard to discover and have largely been identified serendipitously. The Von Hippel-Lindau (VHL) E3 ligase is the second most widely used effector for TPD, though current VHL-based degraders are primarily large heterobifunctional PROTACs (proteolysis-targeting chimeras) designed using target-based ligands. Here, we have instead pursued target-agnostic discovery of VHL MGDs leveraging proprietary ultra-miniaturized microfluidics devices (Picowells) to facilitate unbiased RNA-seq screening of a biased E3-focused library. This resulted in dGEM3, a novel VHL molecular glue that targets the survival of motor neuron (SMN) complex member GEMIN3 for degradation. Through a combination of cellular, biochemical, and biophysical assays, we have characterized the GEMIN3 degron within its helicase ATP-binding domain, and how the kinetics of ternary complex formation impact degradation. These findings provide insights on the re-programmability of VHL for novel targets using drug-like molecular glues.