The antitumor activity of alternating electric fields (TTFields) in combination with immune checkpoint inhibitors.

Abstract

e14570 Background: Tumor Treating Fields (TTFields) are an effective anti-neoplastic treatment modality delivered via application of low intensity, intermediate frequency, alternating electric fields. This therapy is approved for the treatment of patients with glioblastoma. Previous investigations have shown that some of the outcomes of mitosis under TTFields application include abnormal chromosome segregation and ER stress which trigger different forms of cell death. In this study we evaluated whether TTFields induced cancer cell death can be perceived as immunogenic by the immune system, and explored the possibility of combining TTFields with immune-modulating drugs. Methods: Murine Lewis lung carcinoma (LLC) and ovarian surface epithelial (MOSE) cells were treated with TTFields using the inovitro system. The exposure of calreticulin (CRT) on the surface of treated cells was evaluated using flow cytometry. HMGB1 secretion was measured using ELISA assay. For in-vivo experiments, mice were implanted with LLC cells, and treated with TTFields, anti-PD-1 or combination of the two modalities. Changes in tumor volume were monitored and flow cytometry analysis was performed for phenotypic characterization of tumor infiltrating immune cells. Results: We demonstrate that application of TTFields leads to surface exposure of CRT and also promotes release of HMGB1. In vivo, the combined treatment of TTFields and anti-PD-1 led to a significant decrease in tumor volume compared to control group and to animals treated with anti-PD-1 alone. Significant increase in CD45+ tumor infiltrating cells was observed in the TTFields+anti-PD-1 combination treatment group. This cell population demonstrated a significant upregulation of PD-L1 expression on the cell surface. Specifically, this upregulation was observed in both F4/80+CD11b+ cells and CD11c+ cells whereas no effect on the infiltration pattern of these immune cell populations was noted. Conclusions: Our results demonstrate that TTFields application potentiates immunogenic cell death in cancer cells and that combining TTFields with specific immunotherapies such as anti-PD-1 might achieve tumor control by further enhancing antitumor immunity.