Background: Tumor treating fields (TTFields) are FDA-approved for treatment of newly diagnosed and recurrent glioblastoma and are typically initiated after patients have undergone surgical resection, temozolomide, (TMZ) and radiotherapy. In this study, GBM cells generated from a tumor resected from a newly diagnosed glioblastoma patient were treated in vitro with TTFields ± TMZ or treated with in vitro TTFields followed by irradiation to determine if TTFields alter the response to the standard-of-care treatment modalities.
Methods: Single-cell suspensions generated from tumor tissue obtained from a newly diagnosed patient were cultured in DMEM/F12 media with 10% fetal bovine serum and gentamicin. For the TMZ experiment, cells were plated on plastic coverslips (1 × 104cells/coverslip; n=4-6/group) and incubated overnight. TTFields (200 kHz; field intensity of ~1.6 V/cm). were applied with or without 50 µM TMZ for 5 days, followed by the XTT proliferation assay. For the radiation experiment, cells were plated on plastic coverslips (5 × 104cells/coverslip; n=3/group) and incubated overnight. TTFields (200 kHz; field intensity of ~1.6 V/cm). were applied for 3 days followed by irradiation with 0, 2, 4, or 6 Gy. Cells were harvested and plated to assess clonogenic potential. After 3 days, cells were stained with crystal violet and plates were scanned to determine cell counts. Data were analyzed by one-way ANOVA with Tukey's post-hoc test.
Results: In the TTFields/TMZ experiment, control XTT values were 0.665 ± 0.052, TMZ only were 0.480±0.024, TTFields only were 0.550±0.080 and TTFields + TMZ were 0.164 ± 0.062 (mean ± SD; ANOVA p<0.0001). In the TTFields/radiation experiment, there was no statistical difference in cell counts across the radiation doses in the control cells. In the TTFields treated groups, the mean cell counts were 62146, 53324, 41070 and 28680 in the control, 2 Gy, 4Gy, and 6 Gy groups (ANOVA p=0.002).
Conclusions: In GBM cells generated from a newly diagnosed patient's tumor. TTFields application in combination with TMZ reduced cell proliferation by 75%, compared to only 20-30% for either treatment alone. Also, TTFields application prior to radiation significantly reduced cell counts. These results suggest that newly diagnosed patients would benefit from TTFields therapy earlier in the course of treatment.
Citation Format: Sharon K. Michelhaugh, Sandeep Mittal. In vitro TTFields enhance the response to temozolomide or radiation in GBM cells from a newly diagnosed patient [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 574.