Tumor Treating Fields (TTFields) downregulate the Fanconi Anemia-BRCA pathway and increase the efficacy of chemotherapy in malignant pleural mesothelioma preclinical models

Our plain-English summary of Tumor Treating Fields (TTFields) downregulate the Fanconi Anemia-BRCA pathway and increase the efficacy of chemotherapy in malignant pleural mesothelioma preclinical models, by H. Mumblat, A. Martinez-Conde, O. Braten, et al (Lung Cancer, 2021).

The study

• Authors: H. Mumblat, A. Martinez-Conde, O. Braten, M. Munster, E. Dor-On, R.S. Schneiderman, Y. Porat, T. Voloshin, S. Davidi, R. Blatt, A. Shteingauz, C. Tempel-Brami, E. Zeevi, C. Lajterer, Y. Shmueli, S. Danilov, A. Haber, M. Giladi, U. Weinberg, A. Kinzel, Y. Palti
• Journal: Lung Cancer
• Published: 2021;160:99-110
• Cited by: 47 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Tumor Treating Fields (TTFields) are low intensity, intermediate frequency, alternating electric fields with antimitotic effects on cancerous cells. TTFields concomitant with pemetrexed and a platinum agent are approved in the US and EU as first line therapy for unresectable, locally advanced or metastatic malignant pleural mesothelioma (MPM). The goal of the current study was to characterize the mechanism of action of TTFields in MPM cell lines and animal models.

Methods: Human MPM cell lines MSTO-211H and NCI-H2052 were treated with TTFields to determine the frequency that elicits maximal cytotoxicity. The effect of TTFields on DNA damage and repair, and the cytotoxic effect of TTFields in combination with cisplatin and/or pemetrexed were examined. Efficacy of TTFields concomitant with cisplatin and pemetrexed was evaluated in orthotopic IL-45 and subcutaneous RN5 murine models.

Results: TTFields at a frequency of 150 kHz demonstrated the highest cytotoxicity to MPM cells. Application of 150 kHz TTFields resulted in increased formation of DNA double strand breaks, elevated expression of DNA damage induced cell cycle arrest proteins, and reduced expression of Fanconi Anemia (FA)-BRCA DNA repair pathway proteins. Co-treatment of TTFields with cisplatin or pemetrexed significantly increased treatment efficacy versus each modality alone, with additivity and synergy exhibited by the TTFields-pemetrexed and TTFields-cisplatin combinations, respectively. In animal models, tumor volume was significantly lower for the TTFields-cisplatin-pemetrexed combination compared to control, accompanied by increased DNA damage within the tumor.

Conclusion: This research demonstrated that the efficacy of TTFields for the treatment of MPM is associated with reduced expression of FA-BRCA pathway proteins and increased DNA damage. This mechanism of action is consistent with the observed synergism for TTFields-cisplatin vs additivity for TTFields-pemetrexed, as cisplatin-induced DNA damage is repaired via the FA-BRCA pathway.

Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.

In plain English

This was a laboratory and animal study, not a study of people or of asbestos exposure. The authors tested Tumor Treating Fields (TTFields), which are alternating electric fields. They used two human non-epithelioid malignant pleural mesothelioma cell lines (MSTO-211H, biphasic; NCI-H2052, sarcomatoid) and rats and mice implanted with mesothelioma cells. TTFields were tested alone and with the chemotherapy drugs cisplatin and pemetrexed. Of the frequencies tested, 150 kHz produced the largest drop in cell counts. After 72 hours, cell counts fell to 56.8% (MSTO) and 75.2% (H2052) of untreated cells. Treated cells showed more DNA double-strand breaks and lower levels of FA-BRCA DNA repair proteins. Combined with pemetrexed the effect was additive; with cisplatin it was synergistic. In MSTO cells, TTFields plus both drugs reduced cell counts to 33.0% of control. In rats, only the combination significantly reduced average tumor volume (847 versus 1667 cubic millimetres in controls). In mice, tumor growth with the combination was significantly lower than with control and with chemotherapy alone. The authors concluded that TTFields' efficacy was associated with reduced FA-BRCA proteins and increased DNA damage. They called for further study in epithelioid cells.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Preclinical laboratory study (cell culture experiments and animal experiments in rats and mice) of the mechanism of action of TTFields in malignant pleural mesothelioma
• Who was studied: Two human malignant pleural mesothelioma (MPM) cell lines: MSTO-211H (biphasic histology) and NCI-H2052 (sarcomatoid histology). The animal work used 36 female Fischer 344 rats given IL-45 mesothelioma cells into the pleural cavity, and 60 male C57bl/6 mice given RN5 mesothelioma cells under the skin of the flank. No human patients were studied.
• Exposure: No asbestos exposure was studied. The treatments studied were TTFields (150 kHz; 1 V/cm RMS in cells, 1.2 V/cm RMS in animals), alone and together with cisplatin (80 nM to 10 µM) or pemetrexed (2 nM to 4 µM) in cells, or with both drugs together. Animals were assigned to four groups: sham plus saline, TTFields plus saline, sham plus cisplatin and pemetrexed, and TTFields plus cisplatin and pemetrexed.
• Main results:
  • In both cell lines, frequencies from 100 to 400 kHz were tested for 72 hours. TTFields at 150 kHz produced the greatest reduction in cell counts, which the authors described as maximal cytotoxicity.
  • After 72 hours of TTFields at 150 kHz and 1 V/cm RMS, cell counts fell significantly to 56.8 ± 5.1% of control in MSTO cells and 75.2 ± 5.4% of control in H2052 cells.
  • Both cell lines treated with TTFields for 72 hours showed high levels of gamma-H2AX foci, a marker of DNA double-strand breaks. Untreated cells showed very low levels.
  • In TTFields-treated cells, levels of the FA-BRCA DNA repair pathway proteins FANCA, FANCD2, FANCJ and BRCA1 were lower than in untreated cells.
  • In cells, TTFields combined with pemetrexed gave an additive effect, and TTFields combined with cisplatin gave a synergistic effect.
  • In MSTO cells, TTFields plus cisplatin and pemetrexed together reduced cell counts to 33.0 ± 3.5% of control.
  • In the rat model, average tumor volumes after 8 days of treatment were 1667 ± 528 mm3 for control, 1390 ± 583 mm3 for TTFields, 1065 ± 369 mm3 for cisplatin plus pemetrexed, and 847 ± 391 mm3 for the TTFields plus chemotherapy combination.
  • In the rat model, only the combined treatment produced a statistically significant reduction in tumor volume.
  • In the mouse model, tumor volume fold change for TTFields plus cisplatin and pemetrexed was 70.6 ± 17.4% relative to control. This was significantly lower than control and than chemotherapy alone.
  • In mouse tumors, gamma-H2AX (a DNA damage marker) was higher in the TTFields plus chemotherapy group than in controls.
• The authors' conclusion: The authors concluded that the efficacy of TTFields in MPM is associated with reduced expression of FA-BRCA pathway proteins and increased DNA damage.
• Limitations the authors state:
  • Only non-epithelioid cell lines were tested. The authors stated that further studies are needed in epithelioid MPM cells.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Tumor Treating Fields (TTFields), Chemotherapy, Pleural Mesothelioma, Pemetrexed (Alimta), Unresectable, Cisplatin.

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