EXTH-30. TUMOR TREATING FIELDS (TTFIELDS) INDUCE AUTOPHAGY IN GLIOMA CELLS

Abstract

Tumor treating fields (TTFields) are an established anti-neoplastic treatment modality in patients with glioblastoma. TTFields are delivered via noninvasive application of low-intensity, intermediate-frequency, alternating electric fields to the region of the tumor. Previous studies have shown that TTFields lead to increased granularity which is often associated with autophagy. Autophagy has been shown to regulate cell survival and proliferation under stress conditions and to influence cellular response to cytotoxic drugs. The goal of this study was to evaluate the possible effect of TTFields on the induction of autophagy in glioma cells. Different glioma cell lines were treated with TTFields using the inovitro system. Cellular granularity was evaluated using flow cytometry. Autophagy was monitored by quantifying levels of lipidated Microtubule Associated Protein Light Chain 3 (LC3-II) using immunoblotting and immunofluorescence microscopy. Transmission Electron Microscopy (TEM) was used to visualize autophagosome-like structures. Flow cytometry analysis demonstrated that TTFields application leads to a significant increase in cellular granularity in all tested cell lines. Significant elevation in LC3-II levels was observed in treated U-87 MG cells using immunoblotting analysis. Evidence of increased autophagy following TTFields application was also detected using fluorescence microscopy, where punctate distribution of LC3-II was observed. TEM micrographs demonstrated the presence of autophagy typical, autophagosome-like structures in TTFields treated cells. Combination of TTFields with chloroquine, an autophagy inhibitor, resulted in a significant dose dependent reduction of cell growth compared with TTFields treatment alone. TTFields are known to exert anti-mitotic effects by disrupting highly dipolar structures which play critical roles in mitosis. Our results suggest that in addition, TTFields can also induce cellular autophagy. Importantly, inhibition of autophagy sensitizes tumor cells to TTFields treatment. Future studies are warranted to examine to what extent TTFields-elicited- autophagy may affect treatment outcomes, and to investigate the therapeutic implications of combining TTFields with autophagy inhibitors in vivo.