Stem Cell Factor-Based Identification and Functional Properties of In Vitro-Selected Subpopulations of Malignant Mesothelioma Cells

Our plain-English summary of Stem Cell Factor-Based Identification and Functional Properties of In Vitro-Selected Subpopulations of Malignant Mesothelioma Cells, by W. Blum, L. Pecze, E. Felley-Bosco, et al (Stem Cell Reports, 2017).

The study

• Authors: W. Blum, L. Pecze, E. Felley-Bosco, L. Wu, M. de Perrot, B. Schwaller
• Journal: Stem Cell Reports
• Published: 2017;8(4):1005-1017
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an aggressive neoplasm characterized by a poor patient survival rate, because of rapid tumor recurrence following first-line therapy. Cancer stem cells (CSCs) are assumed to be responsible for initiating tumorigenesis and driving relapse after therapeutic interventions. CSC-enriched MM cell subpopulations were identified by an OCT4/SOX2 reporter approach and were characterized by (1) increased resistance to cisplatin, (2) increased sensitivity toward the FAK inhibitor VS-6063 in vitro, and (3) a higher tumor-initiating capacity in vivo in orthotopic xenograft and allograft mouse models. Overexpression of NF2 (neurofibromatosis 2, merlin), a tumor suppressor often mutated or lost in MM, did not affect proliferation and viability of CSC-enriched MM populations but robustly decreased the viability of reporter-negative cells. In contrast, downregulation of calretinin strongly decreased proliferation and viability of both populations. In summary, we have enriched and characterized a small MM cell subpopulation that bears the expected CSC characteristics.

Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

In plain English

This laboratory study used a lentiviral SOX2/OCT4-driven EGFP reporter to isolate cancer stem cell (CSC)-enriched subpopulations from malignant mesothelioma cell lines: human ZL55 (epithelioid), SPC111 and MSTO-211H (biphasic), and murine RN5 (sarcomatoid). Reporter-positive (EGFP(+)) cells made up 4.8% to 7.8% of the lines. The cisplatin IC50 was 0.92 µM for unselected ZL55-SO cells and 2.13 µM for puromycin-selected ZL55-SO-P2 cells. Among FACS-sorted cells, ZL55-SOhigh and ZL55-SOlow cells did not differ in 5-fluorouracil sensitivity, while ZL55-SOhigh cells were more susceptible to the FAK inhibitor VS-6063. ZL55-SO-P2 cells were also more resistant than ZL55-SO cells to acute cytotoxicity from crocidolite asbestos (5 µg/cm2 for 96 hr). In mice, sorted ZL55-SOhigh cells injected intraperitoneally produced greater tumour surface coverage (27.8%) than ZL55-SOlow cells (9.1%), and the tumour-initiating frequency of RN5-SOhigh cells was 17.4 times that of RN5-SOlow cells (p = 0.0063). Overexpressing the tumour suppressor NF2 blocked growth mainly in EGFP-negative cells, while calretinin (CALB2) knockdown affected both populations. The authors concluded they had enriched and characterised a small subpopulation bearing expected CSC characteristics.

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: in vitro experiments on human and mouse mesothelioma cell lines with a SOX2/OCT4 reporter, plus in vivo mouse xenograft and allograft (limiting dilution) experiments
• Who was studied: Human mesothelioma cell lines ZL55 (epithelioid), MSTO-211H and SPC111 (biphasic) and murine RN5 (sarcomatoid); NOD/SCID gamma mice and syngeneic C57Bl/6J mice injected intraperitoneally (four to five mice per group)
• Exposure: Lentiviral SOX2/OCT4-EGFP reporter selection, then treatment with cisplatin, 5-fluorouracil, the FAK inhibitor VS-6063, crocidolite asbestos (5 µg/cm2, 96 hr), NF2 overexpression and CALB2 (calretinin) shRNA knockdown
• Main results:
  • Cisplatin IC50 was 0.92 µM for unselected ZL55-SO cells and 2.13 µM for the puromycin-selected ZL55-SO-P2 cells (printed as mM because the micro symbol was lost)
  • Among FACS-sorted cells, no difference between ZL55-SOlow and ZL55-SOhigh cells in sensitivity to 5-fluorouracil
  • Sorted ZL55-SOhigh (reporter-positive) cells were more susceptible to the FAK inhibitor VS-6063 than ZL55-SOlow cells
  • ZL55-SO-P2 (reporter-positive, puromycin-selected) cells were more resistant than ZL55-SO cells to acute crocidolite cytotoxicity in the MTT assay
  • In NOD/SCID gamma mice, peritoneal surface covered by tumour nodules was 9.1% after ZL55-SOlow cells and 27.8% after ZL55-SOhigh cells
  • In C57Bl/6J mice, macroscopic tumours formed in 1 of 12 mice (8.3%) given RN5-SOlow cells versus 6 of 12 mice (50%) given RN5-SOhigh cells
  • Calculated tumour-initiating frequency was 17.4 times higher for RN5-SOhigh than RN5-SOlow cells (p = 0.0063)
  • NF2 (merlin) overexpression blocked proliferation only in the -SO populations made up mostly of reporter-negative cells, barely affecting reporter-positive cells
  • shRNA knockdown of calretinin (CALB2) reduced proliferation and viability of both reporter-positive and reporter-negative cells to a similar extent
  • Reporter-positive cells lost EGFP over time; in cultured tumour-derived RN5-SOhigh cells carrying NLS-mCherry, EGFP-negative cells rose from 0.4% to 22.2% over 57 days while mCherry-negative cells changed by only 0.8%
• The authors' conclusion: The authors concluded that they had enriched and characterised a small mesothelioma cell subpopulation with the expected cancer stem cell characteristics, and that calretinin remains a target for both CSC and non-CSC mesothelioma cells
• Limitations the authors state:
  • The authors noted the weaker NF2 effect in mouse cells may be because human, not mouse, NF2 was overexpressed
  • The authors attributed the smaller difference in resistance between puromycin-selected and unselected cells to the roughly 5% of reporter-positive cells already present in the parental population
  • The authors stated that no universal markers exist for unambiguously identifying cancer stem cells in mesothelioma or other cancers
  • Several observations (spheroid numbers, scratch-assay wound closure, MTT signal at 120 hr) are reported only as 'data not shown'

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: STEM, Mesothelioma, Neoplasm, First-line Therapy, Carcinogenesis, Cisplatin, Merlin, Calretinin.

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