Activating Antitumor Immunity and Antimetastatic Effect Through Polydopamine‐Encapsulated Core–Shell Upconversion Nanoparticles

: Synergistic phototherapy has the potential to conquer the extreme heterogeneity and complexity of difficult tumors and result in better cancer treatment outcomes than monomodal photodynamic therapy (PDT) or photothermal therapy (PTT). However, the previous approaches to combining PDT and PTT are mainly focused on primary tumor obliteration while neglecting tumor metastasis, which is responsible for about 90% of cancer deaths. It is shown that a combined PDT/PTT approach, based on upconversion-polymer hybrid nanoparticles with surface-loaded chlorin e6 photosensitizer, can enhance primary tumor elimination and elicit antitumor immunity against disseminated tumors. The specifical arrangement of an external upconversion coating over the polymer core ensures adequate photoabsorption by the upconversion nanoparticles for the generation of reactive oxygen species upon single near-infrared light irradiation. Furthermore, it is found that synergistic phototherapy can elicit robust systemic and humoral antitumor immune responses. When combined with immune checkpoint blockades, it can inhibit tumor relapse and metastasis as well as prolong the survival of tumor-bearing mice in two types of tumor metastasis models. This study may establish a new modality for enhancing immunogenic cell death through a synergistic phototherapeutic nanoplatform and extend this strategy to overcome tumor metastasis with an augmented antitumor immune response.