Putative cancer stem cells may be the key target to inhibit cancer cell repopulation between the intervals of chemoradiation in murine mesothelioma

Our plain-English summary of Putative cancer stem cells may be the key target to inhibit cancer cell repopulation between the intervals of chemoradiation in murine mesothelioma, by L. Wu, W. Blum, C.Q. Zhu, et al (BMC Cancer, 2018).

The study

• Authors: L. Wu, W. Blum, C.Q. Zhu, Z. Yun, L. Pecze, M. Kohno, M.L. Chan, Y. Zhao, E. Felley-Bosco, B. Schwaller, M. de Perrot
• Journal: BMC Cancer
• Published: 2018;18(1):471
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Cancer cell repopulation during chemotherapy or radiotherapy is a major factor limiting the efficacy of treatment. Cancer stem cells (CSC) may play critical roles during this process. We aim to demonstrate the role of mesothelioma stem cells (MSC) in treatment failure and eventually to design specific target therapies against MSC to improve the efficacy of treatment in malignant mesothelioma.

Methods: Murine mesothelioma AB12 and RN5 cells were used to compare tumorigenicity in mice. The expression of CSC-associated genes was evaluated by quantitative real-time PCR in both cell lines treated with chemo-radiation. Stemness properties of MSC-enriched RN5-EOS-Puro2 cells were characterized with flow cytometry and immunostaining. A MSC-specific gene profile was screened by microarray assay and confirmed thereafter. Gene Ontology analysis of the selected genes was performed by GOMiner.

Results: Tumor growth delay of murine mesothelioma AB12 cells was achieved after each cycle of cisplatin treatment, however, tumors grew back rapidly due to cancer cell repopulation between courses of chemotherapy. Strikingly, a 10-times lower number of irradiated cells in both cell lines led to a similar tumor incidence and growth rate as with untreated cells. The expression of CSC-associated genes such as CD24, CD133, CD90 and uPAR was dramatically up-regulated, while others did not change significantly after chemoradiation. Highly enriched MSC after selection with puromycin displayed an increasing GFP-positive population and showed typical properties of stemness. Comparatively, the proportion of MSC significantly increased after RN5-EOS parental cells were treated with either chemotherapy, γ-ray radiation, or a combination of the two, while MSC showed more resistance to the above treatments. A group of identified genes are most likely MSC-specific, and major pathways related to regulation of cell growth or apoptosis are involved. Upregulation of the gene transcripts Tnfsf18, Serpinb9b, Ly6a, and Nppb were confirmed.

Conclusion: Putative MSC possess the property of stemness showing more resistance to chemoradiation, suggesting that MSC may play critical roles in cancer cell repopulation. Further identification of selected genes may be used to design novel target therapies against MSC, so as to eliminate cancer cell repopulation in mesothelioma.

In plain English

This was a laboratory study using two mouse mesothelioma cell lines, AB12 and RN5, and mice. It did not study people or measure asbestos exposure, although the authors note that RN5 was established in their laboratory after a mouse was exposed to asbestos fibers. The authors asked whether putative mesothelioma stem cells help tumors regrow between treatments. In mice given weekly cisplatin, AB12 tumor growth was delayed after each cycle, but the tumors grew back rapidly between cycles. Cells that survived 15 Gy of gamma radiation produced tumors in mice at a rate similar to ten times as many untreated cells. Some genes previously linked to cancer stem cells rose after cisplatin or radiation. Cells enriched for putative stem cells formed spheres, stained for Oct4, and changed little after cisplatin or radiation. Treatment increased the share of these cells among unselected cells. Gene screening narrowed the candidates to 41 genes, and increases in four of them were confirmed. The authors concluded that these cells are more resistant to chemoradiation and said the genes' functions still need confirming.

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 experiment using mouse mesothelioma cell lines in culture and in mice (animal experiment), with gene-expression screening by microarray
• Who was studied: Mouse mesothelioma cell lines RN5 (from C57Bl/6 mice, established by the authors' team) and AB12 (from Balb/c mice), plus an RN5-derived line enriched for putative mesothelioma stem cells (RN5-EOS-Puro2). The cells were injected into 6 to 8 week-old female C57BL/6 and Balb/c mice, 5 mice per group, at University Health Network, Toronto. No study dates are given.
• Exposure: The cells were treated with cisplatin (chemotherapy) and with gamma-ray radiation (5, 10 or 15 Gy), alone or combined. Asbestos was not an exposure in these experiments. The authors state that the RN5 line was established after exposure to asbestos fibers in a mouse; no fiber type is named.
• Main results:
  • In Balb/c mice with AB12 tumors given cisplatin once weekly for up to 4 cycles (n = 5 mice), tumor growth was delayed after each cycle, but tumors grew back rapidly between cycles.
  • For both AB12 and RN5, 1 × 10^5 cells surviving 15 Gy gamma irradiation gave a tumor incidence in mice similar to 1 × 10^6 untreated cells. The same tenfold pattern was seen with 1 × 10^4 irradiated cells versus 1 × 10^5 untreated cells.
  • After cisplatin or radiation, the genes CD24, CD90, CD68 and CD117 were significantly upregulated in both cell lines. CD133, uPAR, CD34 and Bmi-1 tended to rise, mainly in AB12 cells, without reaching significance in RN5 cells.
  • After 2 to 3 weeks of puromycin selection, about 65 to 85% of RN5-EOS-Puro2 cells were GFP-positive (the putative stem cells). These cells formed spheres and stained positive for Oct4 in the nucleus.
  • The enriched putative stem cells changed little after cisplatin or radiation, which the authors took to suggest greater resistance. In unselected parental RN5-EOS cells, treatment increased the GFP-positive fraction, with cisplatin having the stronger effect.
  • Microarray comparison of untreated, cisplatin-treated, radiation-treated and stem-cell-enriched RN5 cells narrowed the shared candidate genes to 41.
  • Real-time PCR confirmed that Tnfsf18, Serpinb9b, Nppb and Ly6a (Sca-1) were significantly upregulated after treatment.
  • Gene Ontology analysis identified 7 pathways at a false discovery rate below 0.05. These related to cell development, differentiation and growth, and to reduced cell death and apoptosis. NGF and Spp1 were proposed as possible main drivers.
• The authors' conclusion: The authors concluded that the proportion of putative mesothelioma stem cells increases after chemoradiation and that these cells are more resistant to it in mouse mesothelioma. They suggested the cells may play critical roles in tumor regrowth, and that the identified genes might be used to design targeted therapies.
• Limitations the authors state:
  • The functions of the candidate stem-cell genes have not yet been confirmed.
  • Markers specific to mesothelioma stem cells have not yet been identified.

Topics

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

Medical terms in this study, explained in our Lexicon: STEM, Mesothelioma, Chemotherapy, Cisplatin, Apoptosis.

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