Transformable prodrug nanoplatform via tumor microenvironment modulation and immune checkpoint blockade potentiates immunogenic cell death mediated cancer immunotherapy

Rationale: Chemoimmunotherapy is a promising approach in cancer immunotherapy. However, its therapeutic efficacy is restricted by high reactive oxygen species (ROS) levels, an abundance of cancer-associated fibroblasts (CAFs) in tumor microenvironment (TME) as well as immune checkpoints for escaping immunosurveillance. Methods: Herein, a new type of TME and reduction dual-responsive polymersomal prodrug (TRPP) nanoplatform was constructed when the D-peptide antagonist ( D PPA-1) of programmed death ligand-1 was conjugated onto the surface, and talabostat mesylate (Tab, a fibroblast activation protein inhibitor) was encapsulated in the watery core ( D PPA-TRPP/Tab). Doxorubicin (DOX) conjugation in the chain served as an immunogenic cell death (ICD) inducer and hydrophobic part. Results: D PPA-TRPP/Tab reassembled into a micellar structure in vivo with TME modulation by Tab, ROS consumption by 2, 2'-diselanediylbis(ethan-1-ol), immune checkpoint blockade by D PPA-1 and ICD generation by DOX. This resolved the dilemma between a hydrophilic Tab release in the TME for CAF inhibition and intracellular hydrophobic DOX release for ICD via re-assembly in weakly acidic TME with polymersome-micelle transformation. In vivo results indicated that D PPA-TRPP/Tab could improve tumor accumulation, suppress CAF formation, downregulate regulatory T cells and promote T lymphocyte infiltration. In mice, it gave a 60% complete tumor regression ratio and a long-term immune memory response.