TTFields reduce sensitivity in glioblastoma is associated with the functional expression of the chloride intracellular channel 1 and with voltage dependent sodium channel

Abstract Glioblastoma (GBM) is the most aggressive type of brain tumor, and existing treatments are inadequate at preventing recurrence. Tumor Treating Fields (TTFields) is a novel treatment that has been proven to extend patients' lives during the previous two decades. The antitumoral impact of TTFields involve different mechanism and is an optional add-on to standard temozolomide maintenance. Although TTFields therapy slows tumor progression initially, it does not prevent tumor relapse in most patients. We subjected patient-derived GBM primary cultures to continuous TTFields stimulation to mimic the GBM standard of care and examine the molecular pathways behind GBM sensitivity to TTFields treatment. TTFields initially limit cellular growth well. However, even under constant TTFields administration, the remaining cells regain their ability to proliferate at their own rate in long-term trials. Prolonged treatment with TTFields increases the expression of many stemness markers as well as the overexpression of different genes involved in cell cycle progression. There is also a rise in membrane ionic conductance activity. After sustained exposure to TTFields, sodium, potassium, and chloride channels are functionally increased. This influences the properties of tumor cells. Increased sodium channel functional activity, for example, promotes membrane potential depolarization. Furthermore, earlier research has shown that the membrane form of the chloride intracellular channel 1 (tmCLIC1) is important in the development of GBM. In patient-derived GBM cells exposed to TTFields, tmCLIC1 is significantly concentrated, and membrane depolarization improves its function. The evaluation of GBM tissues obtained from many patients who were treated with TTFields validates the in vitro tumor relapse model.Our findings imply that the process by which GBM cells develop a decrease in sensitivity to TTFields correlates with an increase in stemness markers and an increase in ionic channel functional expression. Citation Format: Stefania Castiglione, Gaetano Cannavale, Francesca Cianci, Ivan Verduci, Chiara Biella, Chiara Mercurio, Emanuela Pastorelli, Monica Lupi, Laura Paracchini, Laura Mannarino, Dietmar Krex, Federico Brandalise, Michele Mazzanti. TTFields reduce sensitivity in glioblastoma is associated with the functional expression of the chloride intracellular channel 1 and with voltage dependent sodium channel [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1425.