Abstract 1692: A novel immunoregulatory role of tumor treating fields (TTFields) on macrophage polarization

Abstract

Abstract Introduction: Tumor Treating Fields (TTFields) therapy is a clinically applied anti-neoplastic treatment modality delivered via noninvasive application of low intensity (1-3 V/cm), intermediate frequency (100-500 kHz), alternating electric fields. In this study we investigated the potential of TTFields for regulating macrophage phenotype skewing, with or without lipopolysaccharide (LPS) and interferon-γ (IFN-γ) or IL-4 activation. Methods: Bone marrow cells were flushed from the femurs and tibias of 5-8 week old Balb\C mice to generate bone marrow-derived macrophages (BMDMs). To study individual macrophage responses to TTFields, we profiled macrophages that were stimulated with LPS+IFN-γ (M1 polarization) or IL-4 (M2 polarization), followed by treatment with TTFields (150 kHz) for 24 hours. Flow cytometry was used to assess surface expression of F4/80 (a macrophage biomarker) and the activation markers that included major histocompatibility complex class II (MHC II), CD80, and inducible nitric oxide synthase (iNOS). A multiplexed secretion assay was used to measure the heterogeneity of the stimulated macrophages. We captured the secretion of 13 different proteins including CXCL1 (KC), IL-18, IL-23, IL-12p70, IL6, TNF-α, IL-12p40, free active TGF-β1, CCL22 (MDC), IL-10, IL-6, G-CSF, CCL17 (TARC) and IL-1β. Results: TTFields treatment polarized IL-4 stimulated M2 macrophages to the M1 phenotype, as indicated by a significant increase in the percentage of CD80+MHC IIhigh cells. Treatment with TTFields of BMDMs that were either stimulated with IFN-γ and LPS (M1 phenotype) or had remained unstimulated increased the percentage of CD80+MHC IIhigh cells to a lesser degree. Moreover, treatment with TTFields significantly increased intracellular iNOS levels in M1 polarized BMDMs. In unstimulated BMDMs, application of TTFields resulted in significant increases in secretion of the pro-inflammatory cytokines CXCL1, IL-18, IL-23, IL-12p70, TNF-α, IL-12p40, CCL22, G-CSF, CCL17 and IL-1β. Also, a similar pattern was observed in cell supernatants of M1 and M2 stimulated BMDMs after TTFields application. Conclusions: These results elucidate a novel immunoregulatory role of TTFields on macrophage polarization. Future studies will aim to focus on the mechanism governing phenotypic skewing of macrophages treated with TTFields and to explore the effect of TTFields on macrophage in the tumor microenvironment. Citation Format: Boris Brant, Tali Voloshin, Alexandra Volodin, Lilach Koren, Anat Klein-Goldberg, Efrat Zemer-Tov, Rom Paz, Moshe Giladi, Uri Weinberg, Yoram Palti. A novel immunoregulatory role of tumor treating fields (TTFields) on macrophage polarization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1692.