Molecular glue degraders for LRRK2

Hijacking the ubiquitin proteasome system (UPS) to degrade undruggable proteins has launched a new era of
targeted protein degradation (TPD). Two main drug modalities in TPD field are PROTACs (PROteolysis
TArgeting Chimeras) and MGs (Molecular Glues). MGs and PROTACs both function by inducing proximity
between an E3 ligase and target protein for event driven proteolysis. While PROTACs are heterobifunctional
molecules with a distinct ligand that target a specific E3 ligase linked to another ligand specific for the target
protein, MGs function by inducing target-ligase interactions by bridging protein-protein interfaces. Molecular
glues have significant advantage over PROTACs as they adhere more closely to conventional small molecule
design principles making them suitable for many therapeutic applications including CNS diseases. Unlike
conventional small molecule inhibitors, MGs are not ‘occupancy driven’ they function at sub-stoichiometric levels
for degradation efficiency at exceptionally low doses. Because ubiquitin proteasome system is a complex multi-
step process that involves multiple enzymes, development of molecular glues by structure-based design or
monitoring proximity of proteins or analyzing degradation of target has been challenging and full of artifacts. Over
past few years multiple studies suggest that protein degradability is heavily influenced by protein-intrinsic
features, especially the protein’s endogenous “ubiquitination potential”. Novel approaches that identify chemical
modulators to induce not only proximity but also induce ubiquitination of native endogenous protein targets will
be a game changer in the field of TPD. The current proposal describes simple and high-throughput ubiquitination
assay, that can be applied invitro and in cells to expand drug discovery enterprise to rationally design molecular
glues. The proposed approach will rely on monitoring true function of a molecular glue i.e., compound mediated
ubiquitination of target protein without need for adding external tags to target proteins. We propose to integrate
split luciferase approach with LifeSensors’ TUBEs (tandem ubiquitin binding entities) technology to accurately
monitor ubiquitination of target proteins without the need for external tags on target proteins that might render
false positives. Our ability to understand nature and type of compound mediated poly-ubiquitination will provide
mechanistic information, enabling medicinal chemists to rationally design reliable SAR. Development of the
technology platforms will dramatically speed up the discovery and clinical development of this class of protein
degraders.

Grant Number: 1R43GM156150-01
NIH Institute/Center: NIH
Principal Investigator: Tauseef Butt