Live-Cell Mesothelioma Biobank to Explore Mechanisms of Tumor Progression

Our plain-English summary of Live-Cell Mesothelioma Biobank to Explore Mechanisms of Tumor Progression, by K. Oehl, J. Kresoja-Rakic, I. Opitz, et al (Frontiers in Oncology, 2018).

The study

• Authors: K. Oehl, J. Kresoja-Rakic, I. Opitz, B. Vrugt, W. Weder, R. Stahel, P. Wild, E. Felley-Bosco
• Journal: Frontiers in Oncology
• Published: 2018;8:40
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Experimental models closely representing in vivo conditions allow investigating mechanisms of resistance. Our aims were to establish a live-cell biobank of malignant pleural mesothelioma (MPM) samples and to obtain proof of principle that primary culture chemoresistant models, mimicking tumor progression observed in patients, can be obtained in vitro, providing a useful tool to investigate underlying mechanisms. Primary mesothelioma cultures were established from 235 samples between 2007 and 2014. Of two MPM patients, primary cultures obtained at different time points: at initial diagnosis, after neoadjuvant treatment at surgery and/or after tumor recurrence, were deeply investigated. Cells and corresponding tumor tissue were characterized by mesothelial protein and gene expression analysis. In addition, primary cultures from chemo naive patients were exposed to increasing doses of cisplatin/pemetrexed during three months and compared with non-treated cells in a cytotoxicity assay, and by selected profiling of senescence markers. In vitro chemoresistance in the primary mesothelioma cell cultures was associated with increased Thy1 (CD90) expression. Thy1 expression in MPM samples was significantly associated with poor overall survival in the TCGA MPM cohort. Our results illustrate that the establishment of a large live-cell MPM biobank contributes to a better understanding of therapy resistance observed in vivo, which eventually may lead to a more logical approach for developing new treatment strategies.

In plain English

This was a laboratory study at University Hospital Zürich. Between 2007 and 2014, the authors processed 235 surgical samples from patients treated for malignant pleural mesothelioma; when enough tumor tissue was available, part was used to grow live tumor cells. Usable cultures were obtained from 159 of the 235 samples (68%). The article does not report the patients' asbestos exposure. As a proof of principle, the authors studied cells from two patients in detail. One patient's tumor showed few genetic changes. The other's showed widespread loss of heterozygosity, meaning one of two differing gene versions was lost, in regions including the NF2, BAP1 and TP53 tumor suppressor genes. Cells were then exposed to gradually increasing low doses of the chemotherapy drugs cisplatin and pemetrexed. A drug-resistant culture developed from patient P236 but not from patient P95, whose untreated cells were already more resistant. In the resistant culture, markers of cell aging (senescence), autophagy and DNA damage rose, and the surface protein Thy1 increased 10-fold. The authors described higher Thy1 as consistent with worse overall survival in the TCGA dataset. They concluded that Thy1-positive cells became enriched as resistance developed.

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: establishment of a live-cell biobank of primary mesothelioma cultures, with an in-depth proof-of-principle analysis of cultures from two patients and an in vitro chemoresistance experiment
• Who was studied: 235 surgical tumor samples from patients treated for malignant pleural mesothelioma at the Departments of Medical Oncology and Thoracic Surgery, University Hospital Zürich, 2007 to 2014. Two patients were studied in detail: P95, a 69-year-old man with epithelioid MPM, and P236, a 50-year-old woman with papillary epithelioid tumor morphology.
• Exposure: No asbestos exposure data are reported. The exposure studied was laboratory treatment of chemotherapy-naive primary cultures with cisplatin and pemetrexed, starting at 3 nM cisplatin and 1 nM pemetrexed. Treatment ran in cycles of 4 days on and 3 days of recovery, with the dose doubled until cisplatin reached 48 nM and pemetrexed 16 nM.
• Main results:
  • Primary cultures were established when large representative tumor tissue was available. Successful cultures were achieved from 68% of the initial samples (159 of 235).
  • Patient P95's tumor showed widespread loss of heterozygosity (LOH) including the NF2, BAP1 and TP53 tumor suppressor genes. Patient P236's tumor showed few genetic alterations.
  • For patient P236, gene expression differences seen in the tumor were weakly but significantly correlated with those seen in the primary cultures (R2 = 0.2641).
  • A chemoresistant culture was generated from patient P236's cells but not from patient P95's cells.
  • Patient P95's cells had higher baseline chemoresistance: IC50 of 2.5 µM, compared with 1.5 µM in patient P236's culture.
  • Doubling time did not differ between treated and untreated cultures in either patient.
  • In patient P236's resistant culture, the autophagy markers increased: LC3B-II by 53% and p62 by 41%.
  • In patient P236's resistant culture, H2AX phosphorylation (a DNA-damage marker) increased more than sevenfold.
  • By flow cytometry, Thy1 surface protein expression increased 10-fold in the cisplatin/pemetrexed-exposed cells at the third time point.
  • The authors described higher Thy1 with tumor progression as consistent with the finding that high Thy1 expression went with worst overall survival in the TCGA dataset. These data are shown only in a supplementary figure; no figures are given in the text.
• The authors' conclusion: The authors concluded that their data indicate an enrichment of Thy1-positive cells during chemoresistance development and a possible role for the long non-coding RNA RP11-334E6.12. They also concluded that chemotherapy can induce resistance through senescence, while the cancer's genetic background is likely responsible for senescence and resistance through genomic instability.
• Limitations the authors state:
  • The authors state that whether Thy1 expression contributes to chemoresistance remains to be investigated in future studies.
  • The authors' idea that the RNA molecule RP11-334E6.12 regulates THY1 was speculative and not tested in this study.
  • The original primers detected both THY1 and the lncRNA RP11-334E6.12, so the authors redesigned them.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleural Mesothelioma, Cisplatin, Pemetrexed (Alimta), Overall Survival.

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