The Design, Synthesis and in vitro Evaluation of Proteolysis Targeting Chimeras (PROTACs) for the Degradation of Protein Arginine Methyltransferase 1
Protein arginine methyltransferase 1 (PRMT1) is a protein responsible for the asymmetric dimethylation of arginine. PRMT1 is upregulated in a wide range of cancers and the reduction of PRMT1 activity reduces cell proliferation and tumour growth in cell and animal models of cancer. A reduction in PRMT1 can also sensitise cancer cells to other treatments. Therefore, targeting PRMT1 is a promising therapeutic strategy in cancer treatment. Published inhibitors for PRMT1 show poor selectivity and dose-limiting toxicities that have precluded their translation to the clinic. The degradation of PRMT1 using a PROTAC may be superior to inhibition as PROTACs can act catalytically at a low dose. PROTACs can also exhibit high selectivity and cause a more pronounced functional outcome compared to inhibition. In this thesis, PRMT1 is explored as a target protein for PROTAC-induced degradation. The endogenous properties of PRMT1 were evaluated and PRMT1 was determined to be amenable to degradation by a PROTAC. PROTACs were designed that comprised a PRMT1 ligand, a linker and an E3-ligase ligand. Ten PROTACs that recruit the VHL E3-ligase and six PROTACs that recruit the CRBN E3-ligase were synthesised. The degradation of PRMT1 was assessed by Western blot and degradation was not observed for the PROTACs synthesised. Suitable pharmacokinetic properties and target engagement have been shown for selected candidates by the detection of the downstream effects of PRMT1 inhibition and by a NanoBRET assay for E3-ligase binding. Regioselectivity challenges in the synthesis of the CRBN-recruiting PROTACs led to the isolation of a heterobifunctional molecule with the linker attached to the binding pharmacophore of the CRBN ligand. This molecule was found to degrade PRMT1 and is proposed to be a monomeric degrader that destabilises the structure of PRMT1 upon binding. This thesis details a novel approach to degrade PRMT1 using a PROTAC and provides insights that may assist the rational design of PROTACs that target PRMT1 in the future.
Degradation, E3-ligase, Heterobifunctional Molecule, Methyltransferase, Monomeric Degrader, Organic Synthesis, PRMT1, PROTAC, Protein Arginine Methyltransferase 1, Proteolysis Targeting Chimera, Targeted Protein Degradation, Type I PRMT, Ubiquitin Proteasome System
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