Follow-up studies enabled characterisation of potency and binding sites of hit PhABits. The direct measurement of PhABit KD values that matched those obtained in orthogonal assays is significant, as it enables hits to be prioritised without the development of secondary screens. Further, LC-MS/MS analysis enabled identification of the residue of crosslinking, from which the site of binding could be inferred. These follow-up studies will be particularly impactful in the case of emerging proteins where assays and crystallography are not available, allowing characterisation and progression of hits on the PhABit platform alone. It was anticipated that the PhABit platform could be an expedient approach to identify warheads for the development of bifunctional molecules, such as PROteolysis TArgeting Chimeras (PROTACs). PROTACs have recently emerged as a therapeutic strategy, inducing protein degradation by hijacking components of the ubiquitin-proteasome system. Three PROTACs (P1-P3), derived from PhABits 3, 4 and 8, were synthesised containing a PEG linker conjugated to a VHL-ligase binder (Fig- ; for synthesis see Supplementary Figure ). Degradation of BRD4 was subsequently measured in HEK293 cells using a HiBiT assay protocol. The higher affinity PROTACs P1 (pIC50=5.5) and P2 (pIC50=5.9) induced degradation above 1 µM (Figure ), while PROTAC P3 (pIC50=4.7), did not degrade BRD4 up to 10 µM, suggesting insufficient fragment affinity. Analysis of the cellular ATP levels indicated that the PROTAC ligands did not inhibit cell growth. Additionally, pre-treatment of the cells with epoxomicin (proteasome inhibitor) reduced degradation of BRD4, supporting degradation via the proteasome (Supplementary Figure ). The experiment thus highlights that more potent PhABits could be directly employed for the development of PROTACs, to degrade proteins by recruiting components of the ubiquitin-proteasome system. Since the PhABit platform identifies binders and not necessarily inhibitors, coupling this screening methodology with the generation of PROTACs could be an attractive strategy to enable degradation of proteins where inhibition proves challenging (e.g. protein-protein interactions (PPIs) and transcription factors).