The development of targeted protein degradation by recruiting a protein of interest to a ubiquitin ligase to facilitate its degradation has become a powerful therapeutic tool. The potential of this approach is limited to proteins that can be readily ubiquitinated and relies on having a ligand with the various E3 ligases. Here, we describe a new methodology for targeted protein degradation that directly recruits a protein of interest to the proteasome for degradation. We generated bifunctional molecules that incorporate a small molecule ligand into a subunit on the 26S proteasome that recruits the protein directly for degradation. ByeTAC degradation requires binding to Rpn-13, a nonessential ubiquitin receptor of the 26S proteasome, and the protein of interest and does not have to rely on the E ligase cascade for ubiquitination. The ByeTAC methodology demonstrates the application of directly recruiting a protein to the proteasome via interactions with Rpn-13 for degradation.

Immunoproteasome (iCP) is a proteasome isoform that is expressed under inflammatory conditions such as cytokine interferon-γ exposure. The iCP has different catalytic subunits other than the standard CP (standard core particle), allowing the production of major histocompatibility complex class I (MHC-I) compatible peptides for eventual T-cell activation. We have previously reported the design of a fluorescent probe that monitors iCP activity in cells called TBZ-1, and we applied TBZ-1’s iCP recognition sequence for prodrug release into iCP-active cells. Here, we demonstrate a proof-of-concept of the iCP as a prodrug release enzyme. The “payload” we utilized was a toxic moiety, doxorubicin, and a degrader for transcription factor, BRD4. Both examples show that iCP activity is required to elicit cell death or degradation of BRD4. This report highlights that the iCP is a viable prodrug target, and its activity can be used to release a variety of cargo in cells expressing the iCP.

The EFJ represents over 295,000 journalists in 44 countries.

Many human proteins lack chemical probes and are even considered undruggable. Ogasawara et al. describe diversity-oriented synthesis-inspired photoreactive small molecules (photo-stereoprobes) and the...