Pleural mesothelioma side populations have a precursor phenotype

Our plain-English summary of Pleural mesothelioma side populations have a precursor phenotype, by C. Frei, I. Opitz, A. Soltermann, et al (Carcinogenesis, 2011).

The study

• Authors: C. Frei, I. Opitz, A. Soltermann, B. Fischer, U. Moura, H. Rehrauer, W. Weder, R. Stahel, E. Felley-Bosco
• Journal: Carcinogenesis
• Published: 2011;32(9):1324-32
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

DyeCycleViolet was used to set up the side population (SP) functional assay aimed at identifying subpopulations of malignant pleural mesothelioma (MPM) tumor cells with chemoresistance phenotype associated with ABCG2 transporter activity. Self-renewal, chemoresistance and tumorigenicity were tested for SP and non-side population (NSP) cells. Tumors were characterized by mesothelin, calretinin, N-cadherin, D2-40 and Wilms tumor 1 (WT1) immunohistochemistry. Surface expression of mesenchymal stem cell markers CD90, CD73 and CD105 was investigated in SP and NSP cells. We identified SP cells with self-renewal properties and increased chemoresistance in MPM cell lines and tumor-derived primary cell cultures. Compared with the non-SP fraction (NSP), the SP fraction led to the development of tumors including cells with mesothelium precursor phenotype characterized by mesenchymal morphology, being WT1 negative but cytoplasmic D2-40 positive and having a tendency of increased tumorigenicity. The same phenotypic shift was observed in patients with relapsing tumors after chemotherapy. Furthermore, the SP cells were enriched in CD105(-)(/low) expressing cells, which were small sized and had increased tumorigenicity compared with CD105(high) cells. Taken together, our results support the hypothesis that MPM CD105(-)(/low), chemoresistant small sized SP cells may constitute the cellular pool out of which recurrence develops. Further characterization of mechanisms of chemoresistance and self-renewal should lead to targets specific for this subpopulation in MPM patients.

In plain English

This laboratory study, not a study of asbestos-exposed people, looked for a small subgroup of cells, the "side population", in malignant pleural mesothelioma cell lines and in cultures grown from patients' tumors. A side population was found in every line and culture tested, including normal mesothelial cells. In the ZL55 line it averaged 2.1% of cells and regenerated itself. Cells sorted directly from the ZL55 line showed no difference in tumor formation. Among cells sorted from tumors grown in mice, side population implants formed tumors in 8 of 14 cases versus 4 of 14 for the others, a tendency with P = 0.12. Side population tumors shifted toward spindle-shaped cells with less WT1 staining, as did a relapsed tumor from one patient. The authors reported similar tumor evolution in two other patients. Cells from a side population tumor were more resistant to mitoxantrone and high-dose cisplatin. Side population cells were enriched for low or absent CD105. ZL55 cells sorted for low or absent CD105 formed tumors five times larger than ZL55 cells with high CD105. The authors concluded that their results support the hypothesis that these chemoresistant cells may be where recurrence develops.

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 of human mesothelioma cell lines and primary cell cultures, including tumor implants (xenografts) in immunodeficient NOD/SCID mice
• Who was studied: Malignant pleural mesothelioma cell lines ZL55, ZL34 and H28; primary mesothelioma cultures SDM96, SDM100 and SDM138; the xenograft-derived culture SDM103T2; the primary mesothelial cell culture SDM104; and tumor tissue from patient SDM103, including the relapsed tumor SDM141. The study was done in Zurich, Switzerland.
• Exposure: Asbestos exposure was not studied. Cells were tested with the chemotherapy drugs mitoxantrone and cisplatin, and with verapamil, a drug that blocks the cell pumps that push drugs out of cells.
• Main results:
  • In the ZL55 mesothelioma cell line, the side population averaged 2.1 plus or minus 1.9% of cells across 31 replicates.
  • Sorted ZL55 side population cells regenerated a side population (2.25%, in 2 experiments). Sorted non-side population cells gave only non-side population cells.
  • A side population was also present in the primary culture of normal mesothelial cells (SDM104).
  • For cells sorted directly from the ZL55 cell line, no difference in tumor formation was seen between side population and non-side population cells.
  • Among cells sorted from tumors grown as xenografts in mice, the side population formed tumors in 8 of 14 cases and the non-side population in 4 of 14 cases. The authors called this a tendency (P = 0.12, two-tailed chi-square test).
  • Tumors grown from side population cells shifted from fully epithelioid to mixed or more spindle-shaped morphology.
  • Tumors grown from side population cells had significantly fewer cells with positive nuclear WT1 staining (p less than 0.01).
  • The relapsed tumor SDM141 from patient SDM103 showed loss of WT1, more cytoplasmic podoplanin staining and a shift toward sarcomatoid morphology, compared with the original epithelioid tumor.
  • The authors reported similar tumor evolution in two other patients.
  • Cells derived from a ZL55 side population tumor (ZL55 SPT) were more resistant to mitoxantrone than cells from a non-side population tumor. This difference disappeared when verapamil was added.
  • ZL55 SPT cells were also significantly more resistant to a high concentration of cisplatin (p less than 0.001).
  • In SDM103T2 cells, the side population was enriched in cells with low or absent CD105, by 4.9 plus or minus 2.8-fold (p less than 0.05, 4 experiments).
  • In mice, ZL55 cells sorted by CD105 level alone gave different tumor sizes. Cells with low or absent CD105 produced tumors five times larger than cells with high CD105 (p less than 0.02, 4 experiments).
• The authors' conclusion: The authors put forward the hypothesis that side population cells with low or absent CD105 include the mesothelioma cells responsible for tumor recurrence in patients.
• Limitations the authors state:
  • Too few side population cells with low or absent CD105 were obtained to study cells selected for both features together.
  • It is not known whether CD105 itself plays a role in tumor formation. The authors stated that functional studies are needed.
  • Differences in mesothelin and N-cadherin seen in culture were not seen in the mouse tumors. The authors said this could have many reasons, including growth in a living animal.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Mesothelin, Calretinin, Podoplanin (D2-40), Wilms Tumor 1 (WT-1), Immunohistochemistry, STEM, Mesothelium.

Related studies

• Characterization of side population cells in human malignant mesothelioma cell lines — K. Kai, S. D'Costa, et al. (2010)
• A liquid biopsy for detecting circulating mesothelial precursor cells: A new biomarker for diagnosis and prognosis in mesothelioma — B.T.V. Duong, L. Wu, et al. (2020)
• Podoplanin overexpression in human mesothelioma cell lines enhances the tumorigenic phenotype — E. Yamaki, T. Yajima, et al. (2013)
• Inhibition of phosphoinositide-3 kinase pathway down regulates ABCG2 function and sensitizes malignant pleural mesothelioma to chemotherapy — B. Fischer, C. Frei, et al. (2012)
• Inhibition of hedgehog signaling reduces the side population in human malignant mesothelioma cell lines — H.A. Kim, M.C. Kim, et al. (2015)
• How asbestos drives the tissue towards tumors: YAP activation, macrophage and mesothelial precursor recruitment, RNA editing, and somatic mutations — H. Rehrauer, L. Wu, et al. (2018)

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