The purpose of this study was to evaluate the effects of tumor-treating fields (TTFields) on tunneling nanotubes (TNTs) in malignant mesothelioma. TTFields have emerged as a therapeutic modality for the treatment of glioblastoma, through application of alternating electric fields, which exert dipole alignment and dielectrophoretic force. The dielectrophoretic force is intensified in cellular compartments that are non-uniform in size and shape such as the mitotic furrow. TNTs are filamentous actin protrusions that are conduits for intercellular communication and transport of vital cell signals that stimulate cell growth, invasion, and resistance to treatment. TNTs are highly prevalent in malignant pleural mesothelioma. We hypothesized that by creating dielectrophoretic force, TTFields may disrupt or prevent the formation of mesothelioma TNTs and thus sensitize these cells to the cytotoxic effect of chemotherapy and TTFields. TTFields (1.1-1.6 V/cm; 150-200 kHz) were applied using the inovitro system to VAMT and MSTO malignant mesothelioma cell lines. TNT index (average # of TNTs/cell) was determined at 24, 48, and 72 hours of TTFields application. Cell viability assessment using evaluation of cell count and colony formation assays were performed to determine effects of TTFields either alone or in combination with varying concentrations of cisplatin (range 0-10 µM) or pemetrexed (0-512 nM). In separate experiments, we examined the effects of cell cycle inhibition on TNTs using the compound AZD 5438 (Tocris Biosciences). Application of continuous TTFields suppressed TNT formation by 60% over a 72-hour period. This suppression was achieved by the 24-hour timepoint, and maintained over the 72 hours. Assessment of cell viability showed high rate of cell death at the stated frequencies and intensities. The addition of cisplatin or pemetrexed to TTFields application significantly decreased the cell count. The combination of TTFields and low concentration cisplatin (0.1-1 µM) resulted in enhanced treatment efficacy as evaluated using the colony formation assay. Complete inhibition of the cell cycle paradoxically stimulated a significantly higher number of TNTs. Here, we show that TTFields application suppresses TNTs formation in malignant mesothelioma cell lines. Treatment with TTFields leads to enhanced treatment efficacy when combined with standard of care chemotherapeutic drugs cisplatin and pemetrexed. Additional optimization of the applied TTFields intensities and frequencies may further improve treatment efficacy. The sharp rise in TNTs seen following cell cycle inhibition is a potential cellular stress response to cancer-directed treatment. Suppression of TNT formation, and thus TNT-mediated intercellular communication networks in tumors, is a potential mechanism of TTF efficacy in treatment of mesothelioma, glioblastoma, and other invasive cancers.

Citation Format: Akshat Sarkari, Michal Munster, Einav Zeevi, Moshe Giladi, Emil Lou. In vitro application of tumor-treating fields to suppress tunneling nanotubes in mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5156.