Targeted Degradation of Kinases as a Novel Therapeutic Approach

Abstract

In the last 20 years Targeted Protein Degradation (TPD) has emerged as a powerful new therapeutic modality with the potential to “drug the undruggable” and overcome the shortcomings of traditional inhibitors. By recruiting E3 ligases, PROteolysis TArgeting Chimeras (PROTACs) target a protein of interest for degradation via the proteasome which results in complete removal of the protein and its associated activity. This thesis describes our efforts to develop PROTACs targeting three disease-associated kinases. RIPK3 is a key mediator of necroptosis, a pro-inflammatory form of cell death which has been indicated in numerous inflammatory and auto-immune diseases. Significant efforts have been invested in developing RIPK3 inhibitors, however these are limited by significant toxicity due to a resulting scaffolding effect of the inactivated kinase which induces apoptosis. While RIPK3 degradation was ultimately not achieved, the discovery of highly potent RIPK2 degraders validated the design and screening platform. Following this, we develop PROTACs targeting the pseudokinase MLKL – the final executor of necroptosis – and demonstrate their ability to completely block necroptosis in cells, unlike the ligands used as chemical starting points. Subsequent hypothesisdriven optimisation generated potent MLKL PROTACs, suitable for future in vivo studies. Finally, we tackled the lipid kinase PI3KC2α, a promising target for both novel anti-cancer and anti-thrombotic therapies, as a potential target for the development of PROTACs. While E3 ligase recruiting PROTACs were unable to modulate PI3KC2α activity, adopting the recently reported strategy of recruiting HSP90 we generate PROTACs with robust PI3KC2α degradation activity which are currently being further characterised. Taken together, these efforts demonstrate the rational design and optimisation of PROTACs, and further highlight their potential for improved disease-modulating activity over classical inhibitors.