Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy

Our plain-English summary of Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy, by E. Varin, C. Denoyelle, E. Brotin, et al (Carcinogenesis, 2010).

The study

• Authors: E. Varin, C. Denoyelle, E. Brotin, M. Meryet-Figuière, F. Giffard, E. Abeilard, D. Goux, P. Gauduchon, P. Icard, L. Poulain
• Journal: Carcinogenesis
• Published: 2010;31(6):984-93
• Cited by: 57 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive tumor with poor prognosis and limited response to platinum-based chemotherapy. Several lines of evidence support a role for the anti-apoptotic protein Bcl-x(L) in MPM chemoresistance. Since it has been recently suggested that Mcl-1 cooperates with Bcl-x(L) for protection against cell death, we investigated the response of mesothelioma cell lines to the downregulation of Bcl-x(L) (alone or in combination with cisplatin) and the potential interest of its concomitant inhibition with that of Mcl-1. Using RNA interference, we showed that Bcl-x(L) depletion sensitized two highly chemoresistant mesothelioma cell lines to cisplatin and that under this treatment, one cell line, MSTO-211H, displayed an apoptotic type of cell death, whereas the other, NCI-H28, evidenced mainly necrotic-type cell death. Otherwise, the inhibition of Mcl-1 by cisplatin may contribute to this induction of cell death observed after Bcl-x(L) downregulation. Strikingly, we observed that the simultaneous inhibition of Bcl-x(L) and Mcl-1 using small interfering RNA (siRNA) induced a massive cell death in the absence of chemotherapy and was sufficient to avoid escape to treatment in MSTO-211H cells. In NCI-H28, the addition of a low cisplatin concentration allowed to impede the long-term recovery observed after treatment by the siRNA combination. Together, these findings provide a strong molecular basis for the clinical evaluation of therapies targeting both Bcl-x(L) and Mcl-1, alone or in combination with conventional chemotherapy, for the treatment of MPM.

In plain English

This laboratory study used human malignant mesothelioma cell lines; no patients or asbestos exposure were studied. All four lines resumed growth after treatment with the chemotherapy drug cisplatin. The authors used small interfering RNA to reduce Bcl-xL and Mcl-1, two proteins that help cells resist death. Lowering Bcl-xL made MSTO-211H and NCI-H28 cells more sensitive to cisplatin. When Bcl-xL-reduced cells were given 20 micrograms per millilitre of cisplatin, only 11.8% of MSTO-211H and 22.6% of NCI-H28 cells remained viable 24 hours later, compared with control cells. Over the following weeks this combination led to complete annihilation of both cell populations. Cell death looked mainly like apoptosis in MSTO-211H and like necrosis in NCI-H28. Cisplatin on its own lowered Mcl-1. Reducing both proteins together, without chemotherapy, cut viable cells to between 2.2% and 38.3% of the control level across the four lines. This was measured at 48 hours (MSTO-211H) or 72 hours (the others). In NCI-H28, the surviving cells regrew unless a low cisplatin dose was added. The authors concluded that Mcl-1 cooperates with Bcl-xL to protect mesothelioma cells and that both proteins could be potential therapeutic targets.

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) experiments on human mesothelioma cell lines, using RNA interference and cisplatin
• Who was studied: Four human malignant mesothelioma cell lines: MSTO-211H, NCI-H28 and NCI-H2052 from the American Type Culture Collection, and IST-Mes3, a gift from Alessandria, Italy. Most detailed work used MSTO-211H and NCI-H28.
• Exposure: Cisplatin (5 or 20 micrograms per ml for 2 h), given 48 h after transfection with siRNA against Bcl-xL (siXL1) and/or Mcl-1 (siMCL1) at 10 nM, or with a control siRNA. Asbestos exposure was not studied.
• Main results:
  • With cisplatin alone, both MSTO-211H and NCI-H28 cells escaped treatment and recovered normal proliferation after more than 3 weeks.
  • In cells first transfected with siXL1 and then given 20 micrograms per ml cisplatin, 11.8% of MSTO-211H cells and 22.6% of NCI-H28 cells remained viable compared with control cells, 24 h after exposure.
  • In MSTO-211H, 40.9% of cells were in the sub-G1 (apoptotic) fraction after siXL1 plus 20 micrograms per ml cisplatin. This compared with 15.1% with cisplatin alone and 13.2% with control siRNA plus cisplatin.
  • Under siXL1 plus 20 micrograms per ml cisplatin, most NCI-H28 cells showed features of necrotic cell death, whereas MSTO-211H showed apoptotic features.
  • In both cell lines, siXL1 combined with 20 micrograms per ml cisplatin led to complete annihilation of the cell population over long-term follow-up.
  • Cisplatin lowered Mcl-1 protein in both cell lines, earlier in MSTO-211H (24 h) than in NCI-H28 (96 h).
  • Combined siXL1 and siMCL1 without chemotherapy reduced viable cells to 2.2% of the control condition in MSTO-211H, measured at 48 h.
  • Combined siXL1 and siMCL1 without chemotherapy reduced viable cells to 24.4% of control in NCI-H28, 25.7% in NCI-H2052 and 38.3% in IST-Mes3, measured at 72 h.
  • Viability after the double siRNA treatment was expressed as a percentage of viable cells relative to the control condition.
  • Cells were cultured 48 h (MSTO-211H) or 72 h (IST-Mes3, NCI-H28, NCI-H2052) after the double siRNA transfection.
  • In NCI-H28, cells surviving siXL1 plus siMCL1 alone recolonized the flask after 2 weeks.
  • In NCI-H28, adding 5 micrograms per ml cisplatin to siXL1 plus siMCL1 produced nearly complete annihilation of the cells, with no escape even after 3 weeks.
  • In the normal mesothelial Met-5A cell line, the combination did not cause such strong cytotoxicity (data in a supplementary figure).
• The authors' conclusion: The authors concluded that Mcl-1 cooperates with Bcl-xL to protect mesothelioma cells against oncogenic stress and chemotherapy. They concluded that lowering both proteins together is sufficient to induce massive cell death, and that the two proteins could constitute potential therapeutic targets.
• Limitations the authors state:
  • Transfection efficiency may explain why some cells survived. The reduction of both proteins could vary from cell to cell, leaving some cells with enough residual protein to avoid death.
  • The mechanism by which cisplatin inactivates Mcl-1 was not fully defined and needs further investigation.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chemotherapy, Pleural Mesothelioma, Prognosis, Cisplatin.

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