Metformin Induces Apoptosis and Inhibits Notch1 in Malignant Pleural Mesothelioma Cells

Our plain-English summary of Metformin Induces Apoptosis and Inhibits Notch1 in Malignant Pleural Mesothelioma Cells, by M. Rossini, F. Martini, E. Torreggiani, et al (Frontiers in Cell and Developmental Biology, 2020).

The study

• Authors: M. Rossini, F. Martini, E. Torreggiani, F. Fortini, G. Aquila, F.V.D. Sega, S. Patergnani, P. Pinton, P. Maniscalco, G. Cavallesco, P. Rizzo, M. Tognon
• Journal: Frontiers in Cell and Developmental Biology
• Published: 2020;8:534499
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive asbestos-related cancer arising from the mesothelial cells lining the pleural cavity. MPM is characterized by a silent clinical progression and a highly resistance to conventional chemo/radio-therapies. MPM patients die in a few months/years from diagnosis. Notch signaling is a well-conserved cell communication system, which regulates many biological processes. In humans, the dysregulation of Notch pathway potentially contributes to cancer onset/progression, including MPM. Metformin is the first-line drug used to treat type 2 diabetes mellitus. Metformin is proven to be an effective antitumor drug in preclinical models of different types of cancer. To date, clinical efficacy is being studied in many clinical trials. In this study, the anti-proliferative effect of metformin on MPM cells and the putative involvement of Notch1 as a mediator of metformin activities, were investigated. MPM cells showed high levels of Notch1 activation compared to normal pleural mesothelial cells. Furthermore, metformin treatment hampered MPM cell proliferation and enhanced the apoptotic process, accompanied by decreased Notch1 activation.

Copyright © 2021 Rossini, Martini, Torreggiani, Fortini, Aquila, Vieceli Dalla Sega, Patergnani, Pinton, Maniscalco, Cavallesco, Rizzo and Tognon.

In plain English

This was a laboratory study testing the diabetes drug metformin on cells grown in dishes. The authors used two human malignant pleural mesothelioma cell lines, MMP89 (sarcomatoid type) and IST-Mes2 (epithelioid type). They compared them with normal pleural mesothelial cells from non-cancer patients with pneumothorax. No patients or animals were treated, and asbestos was not studied. After 48 hours at 50 mM metformin, viability fell to 37.3% of untreated levels in MMP89 cells and 36.1% in IST-Mes2 cells. No statistically significant drop in viability was found in normal cells, although at 50 mM for 48 hours the result was borderline (P = 0.0512). At 25 mM for 24 hours, metformin increased apoptosis (programmed cell death) in both cancer cell lines, with no statistically significant increase in normal cells. Both cancer cell lines had more activated Notch1, a signaling protein, than normal cells, and metformin lowered it. Adding the Notch blocker DAPT strengthened metformin's effect. The authors concluded that metformin inhibits Notch1 and arrests growth of mesothelioma cells. They said further studies, including in vivo studies, 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) cell culture experiment, published as a brief research report
• Who was studied: Two human malignant pleural mesothelioma cell lines (MMP89, sarcomatoid; IST-Mes2, epithelioid) from a cell bank in Genoa, Italy, and primary normal pleural mesothelial (HM) cells from biopsies of non-oncologic pneumothorax patients at the University/Hospital of Ferrara. The number of patients who supplied biopsies is not stated.
• Exposure: Cells were treated with metformin (1, 5, 10, 25 and 50 mM; 25 and 50 mM reported in detail) and with the Notch inhibitor DAPT (1 to 50 µM), alone or combined (25 mM metformin with 10 µM DAPT). Asbestos exposure was not part of the experiments.
• Main results:
  • MMP89 cells: viability (percent of untreated control, mean ± SEM) was 79.7% (±9.3) at 24 h and 71.1% (±15.9) at 48 h with 25 mM metformin. With 50 mM it was 37.4% (±12.3) at 24 h and 37.3% (±6.9) at 48 h.
  • IST-Mes2 cells: viability was 67.6% (±26.6) at 24 h and 61.9% (±10.5) at 48 h with 25 mM metformin. With 50 mM it was 50.3% (±29.1) at 24 h and 36.1% (±13.3) at 48 h.
  • Normal human mesothelial (HM) cells: the authors described metformin as not cytotoxic. The figure legend reports that at 48 h the 50 mM versus untreated comparison in HM cells had P = 0.0512, just above the 0.05 significance cutoff.
  • With 25 mM metformin for 24 h, Annexin V-positive (apoptotic) cells increased significantly in both MPM cell lines, with no significant increase in HM cells. Necrotic cells increased in MMP89 only.
  • Both MPM cell lines had higher levels of activated Notch1 (N1ICD) than HM cells. Treatment with 25 mM metformin lowered N1ICD and Notch1 TM levels in both MPM cell lines.
  • Pre-treatment with 10 µM DAPT increased metformin's reduction of viability. In MMP89 cells the difference from metformin alone was significant at 72 h. In IST-Mes2 cells it was significant at each time point.
• The authors' conclusion: The authors concluded that metformin inhibits Notch1 and arrests growth of MPM cells. They suggested the results could lead to a therapy combining metformin with gamma-secretase inhibitors.
• Limitations the authors state:
  • The reasons the two cell lines responded differently remain to be investigated.
  • DAPT can affect pathways other than gamma-secretase, so more studies are needed on how metformin inhibits Notch1.
  • Whether metformin causes caspase-dependent cell death has not yet been demonstrated. Further experiments are planned.
  • In vivo studies will be required.

Topics

Medical terms in this study, explained in our Lexicon: Apoptosis, Pleural Mesothelioma, Mesothelial Cells, Pleural Cavity, Clinical Trial.

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