Design, synthesis, anti-tumor activity and mechanism of novel PROTACs as degraders of PD-L1 and inhibitors of PD-1/PD-L1 interaction

Currently, antibody drugs targeting programmed cell death ligand 1 (PD-L1) have achieved promising results in Cancer treatment, while the development of small-molecule drugs lags behind. In this study, we designed and synthesized a series of PD-L1-degrading agents based on the PROTAC design principle, utilizing the PD-L1 inhibitor A56. Through systematic screening of ligands and linkers and investigating the structure-activity relationship of the degraders, we identified two highly active compounds, 9i and 9j. These compounds enhance levels of CD4⁺, CD8⁺, granzyme B, and perforin, demonstrating significant in vivo antitumor effects with a tumor growth inhibition (TGI) of up to 57.35 %. Both compounds facilitate the internalization of PD-L1 from the cell surface and promote its degradation through proteasomal and lysosomal pathways, while also maintaining inhibition of the PD-1/PD-L1 interaction. In summary, our findings provide a novel strategy and mechanism for developing biphenyl-based PROTAC antitumor drugs targeting and degrading PD-L1.