Photothermal-Triggered Extracellular Matrix Clearance and Dendritic Cell Maturation for Enhanced Osteosarcoma Immunotherapy

Osteosarcoma, a predominant malignant tumor among adolescents, exhibits high mortality and suboptimal immunotherapy efficacy due to a collagen-dense extracellular matrix (ECM) that hinders cytotoxic T lymphocyte (CTL) infiltration. Herein, we developed mesoporous polydopamine (MPDA) nanoparticles encapsulating bromelain and the immune adjuvant R848 (M@B/R), aimed at enhancing photothermal immunotherapy. These nanoparticles efficiently accumulate at the tumor site following injection. Upon near-infrared (NIR) light irradiation, photothermal therapy (PTT) induces immunogenic cell death in tumor cells and, with the aid of R848, efficiently promotes dendritic cell maturation, activating antitumor immunity and leading to CTL infiltration into the tumor. Concurrently, NIR-induced heating activates bromelain, resulting in ECM degradation and improved CTL penetration into the tumor. Our <i>in vivo</i> evaluations demonstrate potent antitumor effects in osteosarcoma-bearing mice. This integrated approach offers a promising strategy for overcoming physical barriers in ECM-rich tumors, marking a significant advancement in the treatment of osteosarcoma.