Abstract 4398: In vitro Tumor Treating Fields (TTFields) alter proliferation and morphology of patient-derived high-grade meningioma cell lines

Introduction: Meningiomas are the most common neoplasm of the central nervous system (CNS), accounting for 37% of primary CNS tumors. Though derived from the arachnoid cap cells within the meninges, high-grade meningiomas (WHO grades II and III) invade into the normal brain tissue, and have a high rate of recurrence. As there are no efficacious chemotherapies for these high-grade meningiomas, standard of care is currently limited to maximal surgical resection followed by radiotherapy, with a median overall survival of only 2.5-3 years. Clinical trials with TTFields therapy are under way for patients with high-grade meningiomas. In this study, in vitro experiments comparing TTFields to untreated controls were performed on two patient-derived anaplastic (WHO grade III) meningioma cell lines to determine the effects of TTFields on cell proliferation and clonogenicity. Methods: Studies utilizing patient tumor specimens were approved by the Wayne State University Institutional Review Board and written informed consent was obtained from participants. Meningioma tumor specimens were collected immediately following microsurgical resection. Single-cell suspensions from the tumor tissues were prepared by enzymatic and mechanical disruption. Cells were plated on plastic coverslips (10,000 each) in DMEM/F12 media supplemented with 10% fetal bovine serum. TTFields were applied at ~1.6 V/cm at 100, 200, 300, or 400 kHz (groups n=4-5) with one control group. Culture media were replaced every day. After 12 days of treatment, cell proliferation was assessed with the XTT assay and cells were harvested and replated for clonogenic assays (500 cells/well), which were stained with crystal violet and counted with an automated colony counter. Harvested cells were also fixed and immunostained with the diagnostic meningioma cytoplasmic marker vimentin to observe the cell morphology in control vs. TTFields-treated cells. Control vs. TTFields-treated groups were compared by one- or two-tailed t-tests. Results: The 12-day TTFields treatment significantly reduced cell proliferation, with the greatest decrease found in the 200 kHz group (0.508±0.21; mean±SEM) compared to the control (1.515±0.08; two-tailed t test p=0.0019). Similar results were found in the clonogenic assay, with control cell counts of 4219±793 compared to the 200kHz treated cells 1793±444 (one-tailed t test p=0.0279). In the vimentin-stained cells, the control cells displayed a typical meningioma spindle morphology, while the TTFields-treated cells demonstrated pleomorphic and irregular morphologies. Conclusions: Application of TTFields in vitro reduced proliferation and clonogenicity and altered morphology of patient-derived anaplastic meningioma cell lines. This is the first report on the in vitro effects of TTFields on meningioma. Citation Format: Sharon K. Michelhaugh, Sam Kiousis, Sam A. Michelhaugh, Neil V. Klinger, Sandeep Mittal. In vitro Tumor Treating Fields (TTFields) alter proliferation and morphology of patient-derived high-grade meningioma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4398.