| Summary: | <p>CREBBP and p300 are multidomain paralogues involved in numerous cellular pathways, including epigenetic regulation and the mediation of target gene expression. They share high sequence and structure homologies and perform distinct, but overlapping, cellular functions. Mutations in both CREBBP and p300 have been implicated in a range of cancers and in Rubinstein-Taybi syndrome.</p>
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<p>The work in this dissertation describes the synthesis and biological evaluation of proteolysis targeting chimeras (PROTACs) and hydrophobic tags (HyTs) targeting CREBBP and p300 for proteasomal degradation. Such molecules enable the overall cellular functions of the proteins to be studied and provide starting points for therapeutic development.</p>
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<p>PROTACs and HyTs are bifunctional molecules comprising a POI ligand and an E3 ubiquitin ligase ligand, joined by a linker. PROTACs were designed to recruit the E3 ligases VHL and cereblon, while HyTs used an adamantane group for non-specific E3 ligase recruitment. Initially, PROTACs and HyTs
used the CREBBP/p300 ligand <strong>(<i>R</i>)-OXFBD05</strong> and four PEG linker lengths were evaluated. The resultant compounds had low synthetic throughput, lacked potency, had poor physicochemical properties, and the VHL-targeting PROTACs and the HyTs exhibited off-target cytotoxicity. HyTs were abandoned and the next series of PROTACs was designed to enhance synthetic throughput and physicochemical properties.</p>
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<p>CREBBP/p300 bromodomain ligands were functionalised with amine groups to enable one-step derivatisation to the final PROTACs in amide coupling reactions. Three CREBBP and p300 ligands were investigated based on <strong>(<i>R</i>)-OXFBD05</strong> and <strong>Inobrodib</strong>, and a variety of linker lengths, linker
composition, and E3 ligase ligands were used. A total of 42 novel PROTACs were synthesised and their ability to degrade CREBBP and p300 was assessed using an optimised capillary electrophoresis immunoassay. PROTAC <strong>144</strong> is a potent degrader of both CREBBP and p300 and subsequent investigation into the mechanism of action confirmed protein degradation was using the proteasomal degradation pathway.</p>
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