A novel proteolysis-targeting chimera strategy targeting multiple immune checkpoints containing ITIMs enhances antitumor immunity.

Immune checkpoint inhibitors (ICIs) have significantly advanced and revolutionized cancer treatment over the past decade; however, their clinical benefits have been limited to a subset of cancer patients. While ICI-based combinations have emerged as promising strategies, they risk broader toxicities and significant cost burdens. This highlights the critical need for the development of inhibitors that target multiple immune checkpoints. In this study, we developed a peptide that emulates the conserved sequence of the Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2) C-terminal Src homology 2 (C-SH2) domain, which is capable of binding to immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in the cytoplasmic tails of multiple immune inhibitory receptors. By utilizing this peptide as the protein of interest (POI) ligand and coupling it with the von Hippel‒Lindau (VHL) ligand via a peptide linker, a proteolytic targeting chimera (PROTAC) named PROTAC of ITIM-targeting inhibitory peptide (PITIP) was constructed. PITIP effectively induced the degradation of multiple immune inhibitory receptors in a proteasome-dependent manner, thereby attenuating immunosuppressive signaling within T cells, natural killer (NK) cells, and macrophages.