Abstract 2981: Glioblastoma reduced sensitivity to tumor treating fields (TTFields) is associated with changes in electrical membrane properties of tumor cells

Glioblastoma (GBM) is recognized as the most aggressive type of brain tumor, and current treatments generally fail to prevent recurrence. Tumor-treating fields (TTFields) is an innovative therapy that improves patients' life expectancy. Although the initial application of TTFields slows tumor progression, it typically does not prevent tumor relapse in most patients. To model tumor recurrence after surgical intervention, we exposed patient-derived GBM primary cultures to continuous electric field stimulation. Remarkably, three days of uninterrupted TTFields stimulation completely halted the proliferation of tumor cells. However, the surviving cells eventually become less sensitive to TTFields, and rescue proliferation at their maximum rate within 8 to 10 days. In this study, we analyzed transcripts of several patients’ tumor tissues derived from primary and secondary surgical resection. Eight of these patients received TTFields treatment between the two surgical interventions. Their transcriptomic profile was compared with those who received the standard therapy but not TTFields between the surgeries. The tumor samples collected during initial surgeries and untreated GBM cells displayed significant inter-heterogeneity in their transcript profiles. These differences were less pronounced following TTFields application, which unveiled several commonly altered cytosolic pathways including inhibition of proliferation. Many of the upregulated pathways are not viable therapeutic targets, as they involve positive or negative modulations of physiological cellular functions. In addition, RNA extracts from human glioblastoma primary cultures were matched with those of patients treated with TTFields. After the TTFields application, several stemness pathways were significantly upregulated in isolated cells and human biopsies. Previous studies demonstrate that glioblastoma stem cells are enriched in transmembrane Chloride Intracellular Channel 1 (tmCLIC1) and its inhibition slows down tumor cell proliferation. CLIC1 transcript does not appear to be modulated in patients by electric field stimulation. However, following prolonged TTFields exposure in primary cell lines we observed a significant increase in the membrane protein activity. This indicates that tmCLIC1 could serve as a valuable target for a combined antitumoral therapy alongside TTFields to impair glioblastoma development.