Bivalent ligands as a new universal chemotype of BCL6 degrader by inducing aggregation

Abstract BCL6 naturally exists as a homodimer to exert its transcriptional repressive function. Previous studies shown that molecular glue BI3802 can induce BCL6 dimer polymerization and thus degradation by ubiquitin-proteasome system. In this study we proposed a new strategy to degrade BCL6 by its homo-bivalent ligands, which can be rationally designed by assemble two BCL6 BTB ligands via linker. These homo-bivalent degraders (HBiDs) can induce polymerization of BCL6 dimer through chain assembly and ultimately lead to its ubiquitination and degradation. Since HBiD does not require a fragment to interact with components of protein degradation system, it could exhibit better target selectivity than traditional protein degraders while avoid drug resistance caused by mutations in protein degradation components. Here we will provide the proof-of-concept evidences for HBiD as BCL6 degrader. Most HBiDs synthesized in this study could degrade BCL6 regardless of the chemotype of BCL6 ligands, with extraordinary target selectivity. The degradation of BCL6 depends on the aggregation of BCL6 dimer induced by HBiD and the recruitment of SIAH1, the natural E3 ligase of BCL6. As protein dimerization is a common phenomenon in cells, HBiD may provide us with a powerful strategy for designing protein degraders as drug candidates or molecular probes.