The Thermal Dose of Photothermal Therapy Generates Differential Immunogenicity in Human Neuroblastoma Cells

SIMPLE SUMMARY: Photothermal therapy (PTT) is an effective thermal therapy for treating tumors. PTT has been combined with immunotherapy in various preclinical cancer models showing promising treatment outcomes. However, in these studies, PTT has primarily been utilized for maximizing tumor cell death. Previously, we observed that based on the “thermal dose” applied, PTT can generate dramatically different responses from the immune system when tested in cellular and animal models. Here, we sought to provide a framework to systematically assess the effect of PTT-based thermal doses on the immunogenic correlates of treated tumors as a measure of the effectiveness of PTT in eliciting an antitumor immune response. In human neuroblastoma tumor cells in vitro, we determined specific phenotypic markers, which demonstrated that SH-SY5Y cells were more responsive to PTT-based thermal dose compared with LAN-1 cells, which possess a high-risk phenotype. Our findings suggest the importance of conducting tumor thermal dose-responsiveness studies in vitro as an early measure of PTT effectiveness against a specific tumor. ABSTRACT: Photothermal therapy (PTT) is an effective method for tumor eradication and has been successfully combined with immunotherapy. However, besides its cytotoxic effects, little is known about the effect of the PTT thermal dose on the immunogenicity of treated tumor cells. Therefore, we administered a range of thermal doses using Prussian blue nanoparticle-based photothermal therapy (PBNP-PTT) and assessed their effects on tumor cell death and concomitant immunogenicity correlates in two human neuroblastoma cell lines: SH-SY5Y (MYCN-non-amplified) and LAN-1 (MYCN-amplified). PBNP-PTT generated thermal dose-dependent tumor cell killing and immunogenic cell death (ICD) in both tumor lines in vitro. However, the effect of the thermal dose on ICD and the expression of costimulatory molecules, immune checkpoint molecules, major histocompatibility complexes, an NK cell-activating ligand, and a neuroblastoma-associated antigen were significantly more pronounced in SH-SY5Y cells compared with LAN-1 cells, consistent with the high-risk phenotype of LAN-1 cells. In functional co-culture studies in vitro, T cells exhibited significantly higher cytotoxicity toward SH-SY5Y cells relative to LAN-1 cells at equivalent thermal doses. This preliminary report suggests the importance of moving past the traditional focus of using PTT solely for tumor eradication to one that considers the immunogenic effects of PTT thermal dose to facilitate its success in cancer immunotherapy.