Immunogenic Cell Death Induced by Tumor Treating Fields (TTFields) Enhances Efficacy When Combined with Anti-PD-1 Therapy in Lung and Colon Cancer Animal Models

Abstract

Tumor Treating Fields (TTFields) therapy is an FDA approved anti-neoplastic treatment modality delivered via noninvasive application of low-intensity, intermediate-frequency, non-ionizing alternating electric fields. Previously it was shown that TTFields induce immunogenic cell death. In this study we evaluated whether TTFields-induced cell death can be further enhanced by the combination with anti-PD-1 therapy in murine models. Bone marrow derived dendritic cells (DCs) were co-incubated with TTFields treated cells and phagocytosis by DCs and DCs maturation were evaluated. The combination of TTFields and anti-PD-1 was evaluated in short duration treatment protocol in orthotopic lung cancer model and long duration treatment protocol in heterotopic subcutaneous colon cancer model. Tumor volume was monitored and analysis was performed for phenotypic characterization of infiltrating immune cells. We demonstrate that TTFields treated cells promote phagocytosis by DCs, DCs maturation in vitro, and promote immune cells recruitment in vivo. We also show that the combined treatment of lung tumor-bearing mice with TTFields plus anti-PD-1 led to a significant decrease in tumor volume compared to the other treatment groups. Significant increases in CD45+ tumor infiltrating cells were observed in the TTFields plus anti-PD-1 group in both models. In the orthotopic lung tumors, the CD45+ infiltrating cells, specifically macrophages and DCs, demonstrated upregulation of surface PD-L1 expression following short treatment duration. Correspondingly, cytotoxic T-cells isolated from these tumors have shown higher levels of IFN-γ production relative to untreated mice. In the heterotopic subcutaneous colon cancer tumors, significant increases in T-cell infiltration was observed following long treatment duration of heterotopic subcutaneous colon cancer tumors with TTFields plus anti-PD-1. These results demonstrate robust efficacy with concurrent application of TTFields and anti PD-1 therapy in mouse models of lung and colon cancers. These data suggest that combining TTFields with anti-PD-1 may achieve tumor control by further enhancing antitumor immunity.