Chimeric peptide-engineered immunostimulant for endoplasmic reticulum targeted photodynamic immunotherapy against metastatic tumor.

The combination of therapy-induced immunogenic cell death (ICD) and immune checkpoint blockade can provide a mutually reinforced strategy to reverse the poor immunogenicity and immune escape behavior of tumors. In this work, a chimeric peptide-engineered immunostimulant (ER-PPB) is fabricated for endoplasmic reticulum (ER)-targeted photodynamic immunotherapy against metastatic tumors. Among which, the amphiphilic chimeric peptide (ER-PP) is composed of ER-targeting peptide FFKDEL, hydrophilic PEG linker and photosensitizer protoporphyrin IX (PpIX), which could be assembled with a PD-1/PD-L1 blocker (BMS-1) to prepare ER-PPB. After passively targeting at tumor tissues, ER-PPB will selectively accumulate in the ER. Next, the localized PDT of ER-PPB will produce a lot of ROS to destroy the primary tumor cells, while increasing the ER stress to initiate a robust ICD cascade. Moreover, the concomitant delivery of BMS-1 can impede the immune escape of tumor cells through PD-1/PD-L1 blockade, thus synergistically activating the immune system to combat metastatic tumors. In vitro and in vivo results demonstrate the robust immune activation and metastatic tumor inhibition characteristics of ER-PPB, which may offer a promising strategy for spatiotemporally controlled metastatic tumor therapy.