ATPS-25p53 STATUS DEPENDENCE OF TUMOR TREATING FIELDS (TTFIELDS) EFFICACY AGAINST GLIOMA CANCER CELLS

Abstract

TTFields are an effective anticancer treatment modality delivered via continuous, noninvasive application of low intensity, intermediate frequency, alternating electric fields. This innovative treatment approach is approved for the treatment of patients with recurrent glioblastoma and a recent phase 3 study demonstrated superior progression free and overall survival in newly diagnosed glioblastoma patients when TTFields were added to standard of care. The goal of this study was to evaluate the therapeutic responsiveness of genetically defined glioma cells, specifically the status of p53 tumor suppressor gene as a determinant of tumor response to TTFields. For in vitro studies, TTFields (1.75 V/cm RMS, 200 kHz) were applied for 72 hours using the inovitro™ system (Novocure, Haifa, Israel). The surviving fractions of glioma cell lines expressing either wild-type (wt) p53 (A-172 and U-87 MG) or mutant p53 (U-118 MG and F-98 rat glioma) were determined using cell counts and clonogenic assays. Induction of apoptosis was examined using flow cytometry based on Annexin V and 7-AminoactinomycinD (7-AAD) staining. Detection of caspase activity was conducted using a poly caspase assay kit. The effect of caspase inhibition was explored using the Z-VAD-FMK pan-caspase inhibitor. Application of TTFields in-vitro led to a significant reduction in cell count and clonogenic potential as compared to untreated cells in both p53 wt and p53 mutant cell lines. Flow cytometry analysis of Annexin V and Propidium Iodide staining revealed that TTFields-induced apoptosis is independent of p53 status. Caspase activity was increased in wt p53 cells following TTFields application, however no increase was observed in mutant p53 cells. Treatment of wt p53 cells with Z-VAD-FMK partially impaired cytotoxicity induced by TTFields treatment and completely abrogated apoptosis. In summary, our results suggest that TTFields exposure induces apoptosis by both p53-dependent and p53-independent pathways.