Characterisation of mesothelioma-initiating cells and their susceptibility to anti-cancer agents

Our plain-English summary of Characterisation of mesothelioma-initiating cells and their susceptibility to anti-cancer agents, by E.A. Pasdar, M. Smits, M. Stapelberg, et al (PloS One, 2015).

The study

• Authors: E.A. Pasdar, M. Smits, M. Stapelberg, M. Bajzikova, M. Stantic, J. Goodwin, B. Yan, J. Stursa, J. Kovarova, K. Sachaphibulkij, A. Bezawork-Geleta, M. Sobol, A. Filimonenko, M. Tomasetti, R. Zobalova, P. Hozak, L.F. Dong, J. Neuzil
• Journal: PloS One
• Published: 2015;10(5):e0119549
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an aggressive type of tumour causing high mortality. One reason for this paradigm may be the existence of a subpopulation of tumour-initiating cells (TICs) that endow MM with drug resistance and recurrence. The objective of this study was to identify and characterise a TIC subpopulation in MM cells, using spheroid cultures, mesospheres, as a model of MM TICs. Mesospheres, typified by the stemness markers CD24, ABCG2 and OCT4, initiated tumours in immunodeficient mice more efficiently than adherent cells. CD24 knock-down cells lost the sphere-forming capacity and featured lower tumorigenicity. Upon serial transplantation, mesospheres were gradually more efficiently tumrigenic with increased level of stem cell markers. We also show that mesospheres feature mitochondrial and metabolic properties similar to those of normal and cancer stem cells. Finally, we show that mesothelioma-initiating cells are highly susceptible to mitochondrially targeted vitamin E succinate. This study documents that mesospheres can be used as a plausible model of mesothelioma-initiating cells and that they can be utilised in the search for efficient agents against MM.

In plain English

This was a laboratory study of human and mouse malignant mesothelioma cell lines combined with grafting into immunodeficient mice. Ist-Mes-2 (epithelioid), Meso-2 (sarcomatoid), MM-BI (biphasic) and murine AE17 cells were grown in serum-free medium, where they formed spherical clusters (mesospheres) of 30-100 micrometres after 3-5 days. By limiting dilution, the number of cells needed to form one sphere was 1.81 plus or minus 0.24 for Ist-Mes-2, 4.54 plus or minus 0.39 for MM-BI and 7.53 plus or minus 0.89 for Meso-2. Spheres showed 1.5 to 4-fold higher CD24, OCT4 and ABCG2 mRNA than adherent cells; in the mouse experiment, which used Ist-Mes-2 cells only, sphere-derived cells formed tumours in Balb-c/nude mice more efficiently than adherent cells, especially at lower cell numbers. On serial transplantation the lag to tumour appearance fell from 52 days (G1) to 5 days (G4). CD24 knock-down cells lost sphere formation and grew tumours more slowly in NOD/SCID mice. In cultured Ist-Mes-2 cells the IC50 for MitoVES was 25.83 plus or minus 1.47 micromolar for adherent and 6.924 plus or minus 0.5 micromolar for sphere cells. The authors concluded mesospheres are a plausible model of mesothelioma-initiating cells; asbestos was mentioned only as background.

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 study: mesothelioma cell lines cultured as spheres, with gene/protein, mitochondrial and drug-sensitivity assays, plus xenograft experiments in immunodeficient mice
• Who was studied: Three human malignant mesothelioma cell lines (Ist-Mes-2 epithelioid, Meso-2 sarcomatoid, MM-BI biphasic) and the murine AE17 line, plus Balb-c/nude and NOD/SCID mice used for grafting (4-5 animals per group)
• Exposure: Not an asbestos exposure study; cells were exposed to serum-free sphere culture conditions, CD24 shRNA knock-down, and anti-cancer agents doxorubicin, 5-fluorouracil, tamoxifen, alpha-tocopheryl succinate and mitochondrially targeted vitamin E succinate (MitoVES)
• Main results:
  • Number of cells needed to form one sphere: 1.81 plus or minus 0.24 (Ist-Mes-2), 4.54 plus or minus 0.39 (MM-BI), 7.53 plus or minus 0.89 (Meso-2)
  • Spheres of all lines expressed 1.5 to 4-fold more CD24, OCT4 and ABCG2 mRNA than the corresponding adherent cells
  • In the xenograft comparison, which used Ist-Mes-2 cells only, sphere-derived cells formed tumours in Balb-c/nude mice more efficiently than adherent cells, particularly at lower grafted cell numbers (10^4, 10^5, 10^6 cells per mouse)
  • Sphere-derived cells were more efficient in tumour formation than adherent cells, in particular at the lower cell numbers
  • In serial transplantation of Ist-Mes-2 sphere cells, the lag time to tumour initiation shortened across generations: 52 days (G1), 15 days (G2), 7 days (G3), 5 days (G4)
  • CD24 knock-down (clone 2, about 80% decrease) abolished sphere formation and slowed tumour progression in NOD/SCID mice; the knock-down tumours also lacked CD47, EpCAM and Oct3/4
  • IC50 values in cultured parental and CD24- adherent and sphere Ist-Mes-2 cells (mean plus or minus S.D.): MitoVES 25.83 plus or minus 1.47 micromolar in adherent cells, 6.924 plus or minus 0.5 micromolar in sphere cells, 7.709 plus or minus 3.6 micromolar in CD24- cells; alpha-TOS 40.8 plus or minus 0.28, 108.3 plus or minus 5.50 and 42.33 plus or minus 0.28 micromolar respectively; doxorubicin 14.79 plus or minus 1.23 (adherent) and 20.74 plus or minus 3.45 micromolar (sphere)
  • IC50 values were higher for sphere than adherent cells for doxorubicin and alpha-TOS, unchanged for 5FU and tamoxifen, and about 4-5-fold lower for MitoVES in sphere cells
  • Sphere cells from later tumour generations respired more than G0 spheres and differed in mitochondrial mass, superoxide, glucose uptake and mitochondrial potential, with lower ATP and lactate
• The authors' conclusion: The authors concluded that mesothelioma cell lines contain a large tumour-initiating cell subset modelled by mesospheres, that mesospheres form tumours more efficiently and become progressively more aggressive on serial grafting, that stemness depends on CD24, and that mesospheres are susceptible to MitoVES
• Limitations the authors state:
  • The authors stated they could not explain the causal link between CD24 and the other stemness markers
  • The authors stated further work is needed to establish the mechanism by which CD24 acts as a stem cell marker in mesothelioma
  • The authors noted that cell cycle data for CD24- and sphere cells were not shown, and some imaging and blot results came from only one tumour or two experiments

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: Mesothelioma, STEM.

Related studies

• Indoleamine-2,3-dioxygenase elevated in tumor-initiating cells is suppressed by mitocans — M. Stapelberg, R. Zobalova, et al. (2014)
• Mitochondrial targeting of α-tocopheryl succinate enhances its anti-mesothelioma efficacy — J. Kovarova, M. Bajzikova, et al. (2014)
• Characterization of cancer stem cell properties of CD24 and CD26-positive human malignant mesothelioma cells — H. Yamazaki, M. Naito, et al. (2012)
• Differential regulation of the sphere formation and maintenance of cancer-initiating cells of malignant mesothelioma via CD44 and ALK4 signaling pathways — Y. Ohno, S. Shingyoku, et al. (2018)
• The inhibition of FGF receptor 1 activity mediates sorafenib antiproliferative effects in human malignant pleural mesothelioma tumor-initiating cells — A. Pattarozzi, E. Carra, et al. (2017)
• Pyruvate Treatment Restores the Effectiveness of Chemotherapeutic Agents in Human Colon Adenocarcinoma and Pleural Mesothelioma Cells — E. Mungo, L. Bergandi, et al. (2018)

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