Sequentially pH-Responsive Drug-Delivery Nanosystem for Tumor Immunogenic Cell Death and Cooperating with Immune Checkpoint Blockade for Efficient Cancer Chemoimmunotherapy.

Chemoimmunotherapy has anchored a new blueprint for cancer management. As a burgeoning approach, immunotherapy has shifted the paradigm of traditional chemotherapy and opened up new prospects for cancer treatment. Here, a sequentially pH-responsive doxorubicin (DOX) delivery nanosystem is designed for simultaneous chemotherapy and tumor immunogenic cell death (ICD). DOX is modified into pH-sensitive cis-aconityl-doxorubicin (CAD) for being easily adsorbed by polycationic polyethylenimine (PEI), and the PEI/CAD complexes are in situ-shielded by aldehyde-modified polyethylene glycol (PEG). The PEG/PEI/CAD nanoparticles (NPs) can keep stable in neutral physiological pH during systemic circulation but will detach PEG shielding once in slightly acidic tumor extracellular pH. The exposed positive PEI/CAD complexes are endocytosed effortlessly, and CAD is then converted back to DOX by endosomal-acidity-triggered cis-aconityl cleavage. The released DOX further elicits ICD, and the moribund tumor cells will release antigens and damage-associated molecular patterns to recruit dendritic cells and activate antitumor immunity. An excellent therapeutic effect is achieved when the immune checkpoint PD-1 antibody (aPD-1) is utilized to cooperate with the PEG/PEI/CAD NPs for blocking tumor immune escape and maintaining antitumor activity of the ICD-instigated T cells. The sequentially pH-responsive DOX delivery nanosystem cooperating with immune checkpoint blockade will provide a potential strategy for cancer chemoimmunotherapy.