ROS-responsive resiquimod prodrug nanoparticles for macrophage reprogramming and enhanced immune checkpoint inhibitor therapy in bladder cancer.

Bladder cancer remains a formidable challenge, especially for patients who fail to respond adequately to immune checkpoint inhibitors (ICIs). The suboptimal efficacy of current treatments underscores an urgent need for more effective immunomodulatory strategies. Here, we propose a ROS-responsive resiquimod (R848) prodrug (R-P) that improves drug delivery and reshapes the immunosuppressive tumor microenvironment. Clinical data from The Cancer Genome Atlas and patient samples underscore the therapeutic value of targeting CD206 and TLR7/8 to repolarize tumor-associated macrophages. The prodrug R-P is created by conjugating a phenylboronic acid pinacol ester moiety to R848 via a succinic anhydride linker, enabling the prodrug to remain stable in systemic circulation while releasing its parent compound in the oxidative tumor microenvironment, thereby minimizing off-target effects. Further, mannose-functionalized nanoparticles (R-P@APM-DPs) achieve an impressive loading capacity of R848 (34.3 %) and exhibit robust ROS-responsive release. In a murine MB49 bladder cancer model, R-P@APM-DPs significantly reduce tumor growth, enhance M1 macrophages, and increase CD8 and CD4 T cells, while decreasing the number of immunosuppressive cells. Notably, combination therapy with anti-PD-1 leads to a potent anticancer response in both MB49-bearing mice and patient-derived organoids. This synergy highlights the translational potential of a ROS-responsive prodrug approach for enhancing ICI-based immunotherapies.