Background: The blood-brain barrier (BBB) may impede application of drugs to the brain for treatment of malignant brain tumors, in particular glioblastoma multiforme (GBM). Alternating electric fields with intermediate frequency and low intensity, called Tumor Treating Fields (TTFields), are an established novel adjuvant treatment modality for GBM. Here, the effect of TTFields on BBB permeability is analyzed.

Material and Methods: After TTFields treatment with a frequency of 100-300 kHz for up to 72 h, immortalized murine brain capillary endothelial cells (cerebEND) grown on cover slips and transwell inserts were stained for immunofluorescent assessment of the tight junction proteins Claudin-5 and ZO-1. Transendothelial electrical resistance (TEER) was applied to investigate BBB integrity. Moreover, BBB permeability was determined by fluorescein isothiocyanate (FITC) staining followed by flow cytometry. For in vivo analysis, the increase in vessel permeability was quantified by utilizing i.v. injected Evans Blue (EB) in rats during TTFields application to the brain (100 kHz, 72 h).

Results: The BBB was disturbed by treatment with TTFields as tight junction proteins were delocalized from the cell boundaries to the cytoplasm with maximal effects at 100 kHz. TTFields application significantly reduced the BBB integrity by 65% and significantly increased the BBB permeability for 4 kDa large molecules. Initial recovery of the cell morphology was observed 48 h post-treatment and a complete recovery could be detected after 96 h, indicating a reversibility of the TTFields effect on the BBB. Average accumulation of EB in the rat brain was significantly increased by TTFields application to the rats head.

Conclusion: In the future, TTFields could be utilized to deliver drugs generally unable to cross the BBB to the central nervous system as TTFields at a frequency of 100 kHz are potentially able to disrupt the BBB. The data presented on in vitro and in vivo application of TTFields to permeabilize the BBB may be a rationale for a phase I clinical trial and clinical application in the future.

Citation Format: Almuth F. Kessler, Clara M. Schaeffer, Malgorzata Burek, Ursula Ruschig, Catherine Tempel-Brami, Tali Voloshin, Moshe Giladi, Ellaine Salvador, Ralf-Ingo Ernestus, Mario Löhr, Carola Förster, Carsten Hagemann. Tumor treating fields (TTFields) affect blood brain barrier (BBB) integrity in vitro and in vivo [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 252.