Design, Synthesis, and Biological Evaluation of Selective TBL1X Degraders.

Transducin β-like protein 1 X-linked (TBL1X) is an essential scaffold protein involved in multiple signaling pathways, such as the Wnt/β-catenin pathway, where it protects β-catenin from ubiquitination and proteasomal degradation. Recent studies, however, suggest that TBL1X might modulate Wnt-regulated genes independently of β-catenin in diffuse large B-cell lymphoma (DLBCL). Here, we developed selective TBL1X degraders against DLBCL using the Proteolysis Targeting Chimeras (PROTACs) strategy as a proof-of-concept. Eight PROTACs showed strong cytotoxic activity. Interestingly, N-linked PROTACs exhibited minimal TBL1X degradation, while most O-linked PROTACs significantly reduced TBL1X levels, suggesting the crucial role of the linker attachment site in successful TBL1X degradation. Our mechanistic study revealed that TBL1X degradation induced by TD11 relied on the formation of the ternary complex and was dependent on the proteasome. The TBL1X degraders developed in this study could be a valuable chemical tool for investigating TBL1X-related pathways.