Effects of Photon Radiation on DNA Damage, Cell Proliferation, Cell Survival, and Apoptosis of Murine and Human Mesothelioma Cell Lines

Our plain-English summary of Effects of Photon Radiation on DNA Damage, Cell Proliferation, Cell Survival, and Apoptosis of Murine and Human Mesothelioma Cell Lines, by S. Keam, K.M. MacKinnon, R.A. D'Alonzo, et al (Advances in Radiation Oncology, 2022).

The study

• Authors: S. Keam, K.M. MacKinnon, R.A. D'Alonzo, S. Gill, M.A. Ebert, A.K. Nowak, A.M. Cook
• Journal: Advances in Radiation Oncology
• Published: 2022;7(6):101013
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: To characterize the cellular responses of murine and human mesothelioma cell lines to different doses of photon radiation with a long-term aim of optimizing a clinically relevant in vivo model in which to study the interaction of radiation therapy and immunotherapy combinations.

Methods And Materials: Two murine mesothelioma cell lines (AB1 and AE17) and 3 human cell lines (BYE, MC, and JU) were used in the study. Cells were treated with increasing doses of photon radiation. DNA damage, DNA repair, cell proliferation, and apoptosis at different time points after irradiation were quantified by flow cytometry, and cell survival probability was examined using clonogenic survival assay.

Results: DNA damage increased with escalating dose in all cell lines. Evident G2/M arrest and reduced cell proliferation were observed after irradiation with 8 Gy. DNA repair was uniformly less efficient at higher compared with lower radiation-fraction doses. The apoptosis dose response varied between cell lines, with greater apoptosis observed at 16 Gy with human BYE and murine AB1 cell lines but less for other studied cell lines, regardless of dose and time. The α/β ratio from the cell survival fraction of human mesothelioma cell lines was smaller than from murine ones, suggesting human cell lines in our study were more sensitive to a change of dose per fraction than were murine mesothelioma cell lines. However, in all studied cell lines, colony formation was completely inhibited at 8 Gy.

Conclusions: A threshold dose of 8 Gy appeared to be appropriate for hypofractionated radiation therapy. However, the radiation therapy doses between 4 and 8 Gy remain to be systematically analyzed. These observations provide an accurate picture of the in vitro response of mesothelioma cell lines to photon irradiation and characterize the heterogeneity between human and murine cell lines. This information may guide in vivo experiments and the strengths and limitations of extrapolation from murine experimentation to potential human translation.

© 2022 The Authors.

In plain English

This laboratory study tested how mesothelioma cells respond to photon (gamma) radiation. It did not study people or asbestos exposure. It used two mouse lines (AB1, AE17) and three human lines (BYE, MC, JU) from patient pleural effusions. The AB1 line received 1 to 32 Gy, and the other lines received 2, 8 and 16 Gy in most tests. They measured DNA damage, DNA repair, cell division, cell death and colony formation. DNA damage rose with dose and peaked at about 8 Gy in four lines. Cell division fell from 24 hours after 8 Gy in mouse and human lines, and no line tested formed colonies at 8 Gy. Alpha/beta ratios were 1.76 (BYE) and 0.97 (JU) in human lines and 3.34 (AB1) and 4.79 (AE17) in mouse lines. The authors read this as the human lines being more sensitive to changes in dose per fraction. Apoptosis varied between lines. The authors concluded that about 8 Gy may be an optimal dose for future mouse studies. They noted that only epithelioid human lines were tested and that living tumors may respond differently.

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 mouse and human mesothelioma cell lines
• Who was studied: Two murine (mouse) mesothelioma cell lines (AB1, AE17) and three human mesothelioma cell lines (JU, MC, BYE). The human lines were generated from patient pleural effusions and sourced from the National Centre for Asbestos Related Diseases Biobank, Perth, Australia.
• Exposure: Photon radiation from a cesium-137 Gammacell irradiator. AB1 received 1 to 32 Gy and the other lines 2, 8 and 16 Gy for most measures. The colony assay used 1 to 8 Gy. No asbestos exposure was studied.
• Main results:
  • DNA damage (gamma-H2AX) increased with radiation dose, reaching a maximum at about 8 Gy in the AB1, AE17, BYE and JU lines. In the MC line it did not differ between 0 and 2 Gy but rose significantly at 8 Gy.
  • Higher doses arrested the cell cycle at the G2/M phase in the mouse lines, temporarily at 8 Gy. No G2/M arrest was seen in the human lines.
  • DNA repair was less efficient at higher doses (8 Gy and above) than at lower doses. Overall DNA repair did not differ significantly between the mouse and human lines.
  • Cell division was not changed by 1, 2 or 4 Gy, and no decrease was seen at 1 or 6 hours at any dose. Cell division decreased 24 hours after 8 Gy in both mouse and human lines.
  • Alpha/beta ratios for the mouse lines were 3.34 (AB1) and 4.79 (AE17).
  • Alpha/beta ratios for the human lines were 1.76 (BYE) and 0.97 (JU). The MC line did not form colonies and was not used in this experiment.
  • Colony formation was completely inhibited at 8 Gy in all cell lines tested in the colony assay.
  • In the BYE and AB1 lines, about 10% of cells underwent apoptosis 24 hours after 16 Gy. In BYE this rose to 20% after a further 24 hours.
  • In the AE17, JU and MC lines, apoptosis reached only 4% to 5% of cells even 72 hours after 16 Gy.
• The authors' conclusion: The authors concluded that a dose of about 8 Gy may be an optimal hypofractionated dose to damage cells in the lines they studied. They also concluded that the mouse cell lines are broadly analogous to the human lines, although the human lines varied in their response.
• Limitations the authors state:
  • Only epithelioid human mesothelioma cell lines were studied, so the findings may not apply to nonepithelioid mesothelioma, which is typically more resistant to radiation.
  • DNA damage seen in cells in the lab may not be seen in living tumors, where surrounding tissue and low oxygen may affect the response. Only single cell suspensions were irradiated.
  • Only AB1 received the full dose range, so the exact dose at which G2/M arrest begins could not be pinpointed. The gaps between time points were also wide.
  • The latest time point was 72 hours, so more apoptosis might have been seen in some lines with longer observation.
  • Delivering radiation in multiple fractions was technically difficult in the lab. It is therefore unclear whether the findings would hold in living animals or in the clinic, where fractionated radiation is normally used.

Topics

Medical terms in this study, explained in our Lexicon: Apoptosis, Mesothelioma, Immunotherapy.

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