A nanodrug provokes antitumor immune responses via synchronous multicellular regulation for enhanced cancer immunotherapy

Hepatocellular carcinoma (HCC) exhibits a low response to immunotherapy due to the dense extracellular matrix (ECM) filled with immunosuppressive cells including dendritic cells (DCs) of blocked maturation. Herein, we develop a nanoprodrug self-assembled from polyethylene glycol-poly-4-borono-l-phenylalanine (mPEG-PBPA) conjugating with quercetin (QUE) via boronic ester bonds. In addition, an immune adjuvant of imiquimod (R837) is incorporated. The nanodrug (denoted as Q&R@NPs) is prepared from a simple mixing means with a high loading content of QUE reaching more than 30%. Owing to the acid and reactive oxygen species (ROS) sensitivities of boronic ester bonds, Q&R@NPs can respond to the tumor microenvironment (TME) and release QUE and R837 to synchronously exert multicellular regulation functions. Specifically, QUE inhibits the activation state of hepatic stellate cells and reduces highly expressed programmed death receptor ligand 1 (PD-L1) on tumor cells, meanwhile R837 exposes calreticulin on tumor cell surface as an "eat me" signal and leads to a large number of DCs maturing for enhanced antigen presentation. Consequently, the cooperative immune regulation results in a remodeled TME with high infiltration of cytotoxic T lymphocytes for enhanced HCC immunotherapy, which demonstrates an effective immunotherapy paradigm for dense ECM characterized solid tumors with high PD-L1 expression.