Abstract 1007: Patient-derived metastatic renal carcinoma cells are highly sensitive to in vitro Tumor Treating Fields (TTFields)
Authors: Michelhaugh Sharon K. , Walker Blake C. , Coombe Susan , Mittal Sandeep 
Published: July 2021

Background: Until the advent of checkpoint inhibitor (CI) therapies, renal cell carcinoma (RCC) was clinically challenging to treat given its radio- and chemotherapy resistance. Despite the advances with CIs, patients with brain metastases derived from RCC still face challenges with treatment due to limited brain penetration of CI compounds. Anti-mitotic TTFields therapy is FDA-approved for the treatment of glioblastoma and mesothelioma, and clinical trials are underway for the application of TTFields therapy to primary lung cancer as well as lung cancer brain metastases. In this study, in vitro TTFields were applied to patient-derived brain metastasis RCC cells to determine the potential efficacy of this emerging treatment modality.

Methods: This study was approved by the Institutional Review Board. A single-cell suspension was generated from tumor tissues obtained from a patient with newly-diagnosed RCC brain metastasis (male, age 52, mutant p53). Cells were cultured in DMEM/F12 media with 10% fetal bovine serum and gentamicin. Prior to TTFields initiation, cells were plated on plastic coverslips (1×104cells/coverslip; n=8/group) and incubated overnight. Then, TTFields were applied at 200 kHz with a field intensity of ~1.6 V/cm for 14 days, with one group of coverslips maintained as untreated controls. At the conclusion of the experiment, cells were harvested, stained with acridine orange/propidium iodide and counted with a Cellometer K2 (Nexcelom Bioscience, Lawrence, MA) that provides viable cell counts and average cell diameter. Groups were compared with a two-tailed t-test (GraphPad Prism v9, GraphPad Software, San Diego, CA) with significance set at P&lt;0.05.

Results: Viable cell count per coverslip for the control group was 149,863 ± 85644 (mean ± SD; n=8) and for the TTFields (200 kHz) group was 1,426 ± 1345 (n=6, 2 coverslips had no cell recovery). Average cell diameter was 9.713 ± 0.6312 for the control group and 16.92 ± 2.903 for the TTFields group. TTFields application significantly reduced cell count (P=0.0012) and increased the average cell diameter (P&lt;0.0001) compared to the controls.

Conclusions: TTFields application (200 kHz) demonstrated efficacy by markedly reducing cell proliferation (i.e., decreased cell counts) in RCC. The increase in average cell diameter observed with TTFields is consistent with previously reported findings of other research groups also showing increases in cell volume with TTFields in multiple cancer types (brain, lung, pancreas, breast, ovarian, and cervical). This study is the first to demonstrate the efficacy of in vitro TTFields treatment in patient-derived RCC and suggests that patients with renal carcinoma brain metastases may benefit from TTFields therapy.

Citation Format: Sharon K. Michelhaugh, Blake C. Walker, Susan Coombe, Sandeep Mittal. Patient-derived metastatic renal carcinoma cells are highly sensitive to in vitro Tumor Treating Fields (TTFields) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1007.