Selective degradation of BRD9 by a DCAF16-recruiting targeted glue: mode of action elucidation and in vivo proof of concept

Prospective discovery of molecular glues degraders for a specific therapeutic target protein of interest is an emerging strategy in drug discovery. Modification of pre-existing ligands with fragments that can alter the protein surface can lead to the creation of novel compounds (‘’targeted glues’’) able to induce neo-interactions between the target and an E3 ligase, resulting in targeted protein degradation. By screening a library of potential BRD9 targeted glue compounds, we have discovered a potent and selective, reversibly covalent BRD9 degrader, AMPTX-1. Co-immunoprecipitation-mass spectrometry experiments demonstrated that cell treatment with AMPTX-1 induces selective recruitment of BRD9 to the E3 ligase DCAF16. Degradation is dependent on the engagement of the surface Cys58 of DCAF16 and formation of a covalent adduct to DCAF16 is facilitated by the ternary complex formation with BRD9. BRD9 degradation is achieved in vivo after oral dosing, demonstrating that covalent recruitment of DCAF16 is a viable strategy for targeted protein degradation and can be achieved with drug-like, orally bioavailable compounds with promising in vivo activity.