Design of PROTACs utilizing the E3 ligase GID4 for targeted protein degradation

Proteolysis targeting chimeras (PROTACs) hijack E3 ligases and the ubiquitin–proteasome system to achieve selective degradation of neo-substrates. Their ability to target otherwise intractable substrates has rendered them a valuable modality in drug discovery. However, only a handful of over 600 human E3 ligases have been functionalized for PROTAC applications. Here we show that the E3 ligase GID4 (glucose-induced degradation deficient complex 4) can be leveraged for targeted protein degradation using a noncovalent small molecule. We design and synthesize GID4-based PROTACs, exemplified by NEP162, which can eliminate endogenous BRD4 in a GID4- and ubiquitin–proteasome system-dependent manner. NEP162 exhibits antiproliferative activity and inhibits tumor growth in a xenograft model, hinting toward potential anticancer applications. We further present the crystal structures of GID4–PROTAC–BRD4 ternary complexes in three distinct states, unveiling plastic interactions between GID4 and BRD4. These structural insights, combined with in vitro and in vivo data, decipher the molecular basis by which the hereby developed PROTACs recruit BRD4 to GID4 for targeted degradation and expand our arsenal of PROTAC-exploitable E3 ligases.