Development of a peptide-based tumor-activated checkpoint inhibitor for cancer immunotherapy.

Antibody-based checkpoint inhibitors have achieved great success in cancer immunotherapy, but their uncontrollable immune-related adverse events remain a major challenge. In this study, we developed a tumor-activated nanoparticle that is specifically active in tumors but not in normal tissues. We discovered a short anti-PD-L1 peptide that blocks the PD-1/PD-L1 interaction. The peptide was modified with a PEG chain through a novel matrix metalloproteinase-2 (MMP-2)-specific cleavage linker. The modified TR3 peptide self-assembles into a micelle-like nanoparticle (TR3-M-NP), which remains inactive and unable to block the PD-1/PD-L1 interaction in its native form. However, upon cleavage by MMP-2 in tumors, it releases the active peptide. The TR3-M-NP nanoparticle was specifically activated in tumors through enzyme-mediated cleavage, leading to the inhibition of tumor growth and extended survival compared to control groups. In summary, TR3-M-NP shows great potential as a tumor-responsive immunotherapy agent with reduced toxicities. STATEMENT OF SIGNIFICANCE: In this study, we developed a bioactive peptide-based checkpoint inhibitor that is active only in tumors and not in normal tissues, thereby potentially avoiding immune-related adverse effects. We discovered a short anti-PD-L1 peptide, TR3, that blocks the PD-1/PD-L1 interaction. We chemically modified the TR3 peptide to self-assemble into a micelle-like nanoparticle (TR3-M-NP), which itself cannot block the PD-1/PD-L1 interaction but releases the active TR3 peptide in tumors upon cleavage by MMP-2. In contrast, the nanoparticle is randomly degraded in normal tissues into peptides fragments that cannot block the PD-1/PD-L1 interaction. Upon intraperitoneal injection, TR3-M-NP was activated specifically in tumors through enzyme cleavage, leading to the inhibition of tumor growth and extended survival compared to the control groups. In summary, TR3-M-NP holds significant promise as a tumor-responsive immunotherapy agent with reduced toxicities. The bioactive platform has the potential to be used for other types of checkpoint inhibitor.