Effect Of Tumor Treating Fields And Radiotherapy Combination On Brain Tumor And Normal Brain Cell Lines

Yalman D. , Köylü M. , Anacak Y. , Kamer E. S. , Bilge M. D. , Parlak C. , ...More

Astro 62nd Annual Meeting, Florida, United States Of America, 25 - 28 October 2020, vol.108, no.509, pp.509

  • Publication Type: Conference Paper / Summary Text
  • Volume: 108
  • Doi Number: 10.1016/j.ijrobp.2020.07.1603
  • City: Florida
  • Country: United States Of America
  • Page Numbers: pp.509


Purpose/Objective(s): To determine the effect of the combination of “Tumor-treating fields” (TTF) and radiotherapy (RT) in brain tumor and normal brain cell lines in-vitro.

Materials/Methods: Glioblastoma (U118MG and T98G), brain cancer stem cell (BCSC), brain stem cell (BSC),and brain endothelial primary cell (BEPC) lines were used. Using an arduino processor, a frequency generator and electrodes a generator capable of producing multiple electric fields with different frequency (100-200-300-400-500 kHz), voltage (1-2-3-4 V) and duration (24-48-72 hours) was developed to apply TTF. Apoptotic effect was evaluated by annexin V and caspase 3, inhibition of cell proliferation by CFSE (carboxyfluorescein diacetate N-succinimidyl ester), effect on cell cycle by flow cytometry after PI staining, effect on survival by clonogenic analysis, and effect on genotoxicity by micronucleus analysis. For each cell line efficient RT dose, efficent frequency, voltage and duration of TTF were determined. Combination index (CI) was calculated by CalcuSyn software. Linear regression method, Student’s t test and ANOVA were used for statistical analyses (p<0.05 was considered statistically significant).

Results: Inhibition of cell proliferation was prominent in T98G and BSC cell lines by RT+TTF [strongly synergistic (CI:0.072) and synergistic (CI:0.596) respectively], whereas this effect was prominent in U118MG, BCSC and BEPC cell lines by TTF+RT combination [(additive effect (CI:1.006), additive effect (CI:1.006) and synergistic effect (CI:0.476) respectively]. This effect disappeared in all cell lines if the duration of TTF was more than 48 hours. Besides proliferation was triggered in T98G and BCSC lines. Combination treatment increased apoptosis in BCSC lines both in annexin V and caspase 3 analyses (p<0.05), but this effect was detected only with annexin V in U118G cell line (p<0.05). No effect was determined for T98G and BEPC cell lines. Interestingly RT-induced apoptosis decreased with combination treatment in BSC cell lines. In cell cycle analyses none of the cell lines showed accumulation in G2/M phase with only TTF. With combined application, effect on cell cycle became prominent in tumor cell lines (U118MG and T98G), while no difference was observed in BCSC, BCS and BEPC cell lines. TTF alone did not produce genotoxicity through micronuclear level. Combined applications did not increase micronucleus rates produced by RT (p>0.05). In clonogenic analyses combined applications decreased % survival 1.72-fold in BCSC, 1.33-fold in U118MG when compared to RT alone group. Although no apoptotic effect was experienced in BSC cell line % survival decreased by 1.23-fold in clonogenic analysis.

Conclusion: Combination treatment produced synergistic effect in tumor and BCSC cell lines but this effect disappeared in normal brain cell lines indicating a therapeutic gain with combination treatment. This result should be supported by in vivo studies.