Tumor treating fields affect mesothelioma cell proliferation by exerting histotype-dependent cell cycle checkpoint activations and transcriptional modulations

Our plain-English summary of Tumor treating fields affect mesothelioma cell proliferation by exerting histotype-dependent cell cycle checkpoint activations and transcriptional modulations, by L. Mannarino, F. Mirimao, N. Panini, et al (Cell Death & Disease, 2022).

The study

• Authors: L. Mannarino, F. Mirimao, N. Panini, L. Paracchini, S. Marchini, L. Beltrame, R. Amodeo, F. Grosso, R. Libener, I. De Simone, G.L. Ceresoli, P.A. Zucali, M. Lupi, M. D'Incalci
• Journal: Cell Death & Disease
• Published: 2022;13(7):612
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Although clinical antitumor activity of Tumor Treating Fields (TTFields) has been reported in malignant pleural mesothelioma (MPM) patients, the mechanisms behind the different selectivity displayed by the various MPM histotypes to this physical therapy has not been elucidated yet. Taking advantage of the development of well characterized human MPM cell lines derived from pleural effusion and/or lavages of patients' thoracic cavity, we investigated the biological effects of TTFields against these cells, representative of epithelioid, biphasic, and sarcomatoid histotypes. Growth inhibition and cell cycle perturbations caused by TTFields were investigated side by side with RNA-Seq analyses at different exposure times to identify pathways involved in cell response to treatment. We observed significant differences of response to TTFields among the cell lines. Cell cycle analysis revealed that the most sensitive cells (epithelioid CD473) were blocked in G2M phase followed by formation of polyploid cells. The least sensitive cells (sarcomatoid CD60) were only slightly affected by TTFields with a general delay in all cell cycle phases. Apoptosis was present in all samples, but while epithelioid cell death was already observed during the first 24 h of treatment, sarcomatoid cells needed longer times before they engaged apoptotic pathways. RNA-Seq experiments demonstrated that TTFields induced a transcriptional response already detectable at early time points (8 h). The number of differentially expressed genes was higher in CD473 than in CD60 cells, involving several pathways, such as those pertinent to cell cycle checkpoints, DNA repair, and histone modifications. Our data provide further support to the notion that the antitumor effects of TTFields are not simply related to a non-specific reaction to a physical stimulus, but are dependent on the biological background of the cells and the particular sensitivity to TTFields observed in epithelioid MPM cells is associated with a higher transcriptional activity than that observed in sarcomatoid models.

© 2022. The Author(s).

In plain English

This laboratory study tested Tumor Treating Fields (TTFields), alternating electric fields used as a cancer treatment, on six cell lines. The cell lines were grown from chest-cavity fluid of patients with malignant pleural mesothelioma in Alessandria, Italy: two epithelioid, two biphasic and two sarcomatoid. The study did not examine asbestos exposure. Cells were treated at 150 kHz and 1.12 V/cm. After 72 hours, growth was reduced in all lines, and the epithelioid cells were the most sensitive. The authors then compared the most sensitive line (epithelioid CD473) with the least sensitive (sarcomatoid CD60). In CD473, cells stalled before dividing and some became polyploid (cells with extra DNA). Cell death appeared from 24 hours, and growth did not restart during the 72 hours observed after treatment stopped. CD60 cells were mainly slowed, with cell death from 48 hours, and they regrew, though more slowly than untreated cells. Gene activity changed more in CD473 (1951 genes at its peak, 24 hours) than in CD60 (374 at 48 hours). The authors concluded that the response depends on the cells' genetic background. They said further laboratory and animal experiments are needed.

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: Laboratory (in vitro) experiment on patient-derived mesothelioma cell lines, with genomic and RNA-Seq analyses
• Who was studied: Six malignant pleural mesothelioma cell lines (epithelioid CD473 and CD484, biphasic CD487 and CD491, sarcomatoid CD60 and CD432), isolated from pleural effusions and/or thoracic lavage of untreated patients, with the collaboration of a hospital in Alessandria, Italy. The cell lines' gene activity was compared with 69 patient biopsies. No dates are given for when the cell lines were collected.
• Exposure: Tumor Treating Fields at 150 kHz, mainly at 1.12 V/cm, with 0.76 V/cm and 1.41 V/cm also tested. Asbestos exposure was not studied.
• Main results:
  • At 72 hours, cell growth was inhibited in all six cell lines, and the epithelioid cells were the most sensitive
  • In epithelioid CD473 cells, some cells were blocked in the G2M phase; after 48 hours some restarted DNA replication without dividing, producing polyploid cells
  • In sarcomatoid CD60 cells, growth inhibition was not linked to a major cell cycle disturbance, suggesting a general delay
  • Apoptosis (cell death) appeared at 24 hours in the epithelioid cells and only from 48 hours in the sarcomatoid cells
  • After 72 hours of treatment at 1.12 V/cm followed by an additional 72 hours in normal growth conditions, the epithelioid cells did not restart growth, while the sarcomatoid cells did, more slowly than the controls
  • Biphasic CD487 cells showed about 10% apoptotic cells after 24 hours of treatment
  • The number of differentially expressed genes was highest at 24 hours in CD473 (1951) and at 48 hours in CD60 (374)
  • TTFields increased NOTUM protein levels in both CD473 and CD60 cells
• The authors' conclusion: The authors concluded that the effects of TTFields differ between mesothelioma subtypes, and that the response is not just a reaction to a physical stimulus but also depends on the cells' genetic background
• Limitations the authors state:
  • The authors stated that further laboratory and animal experiments are needed to confirm their speculations
  • The authors stated that the idea that CD473's genetic variants explain its sensitivity needs confirmation in isogenic cell lines
  • Genetic variant calling used only one reference sample, blood from a mesothelioma patient, which the authors noted could cause false positive results

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), Mesothelioma, Pleural Mesothelioma, Pleural Effusion, Epithelioid, Biphasic Mesothelioma, Sarcomatoid, Apoptosis.

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