Long-Fiber Carbon Nanotubes Replicate Asbestos-Induced Mesothelioma with Disruption of the Tumor Suppressor Gene Cdkn2a (Ink4a/Arf)

Our plain-English summary of Long-Fiber Carbon Nanotubes Replicate Asbestos-Induced Mesothelioma with Disruption of the Tumor Suppressor Gene Cdkn2a (Ink4a/Arf), by T. Chernova, F.A. Murphy, S. Galavotti, et al (Current Biology, 2017).

The study

• Authors: T. Chernova, F.A. Murphy, S. Galavotti, X.M. Sun, I.R. Powley, S. Grosso, A. Schinwald, J. Zacarias-Cabeza, K.M. Dudek, D. Dinsdale, J. Le Quesne, J. Bennett, A. Nakas, P. Greaves, C.A. Poland, K. Donaldson, M. Bushell, A.E. Willis, M. MacFarlane
• Journal: Current Biology
• Published: 2017;27(21):3302-3314.e6
• Cited by: 85 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Mesothelioma is a fatal tumor of the pleura and is strongly associated with asbestos exposure. The molecular mechanisms underlying the long latency period of mesothelioma and driving carcinogenesis are unknown. Moreover, late diagnosis means that mesothelioma research is commonly focused on end-stage disease. Although disruption of the CDKN2A (INK4A/ARF) locus has been reported in end-stage disease, information is lacking on the status of this key tumor suppressor gene in pleural lesions preceding mesothelioma. Manufactured carbon nanotubes (CNTs) are similar to asbestos in terms of their fibrous shape and biopersistent properties and thus may pose an asbestos-like inhalation hazard. Here we show that instillation of either long CNTs or long asbestos fibers into the pleural cavity of mice induces mesothelioma that exhibits common key pro-oncogenic molecular events throughout the latency period of disease progression. Sustained activation of pro-oncogenic signaling pathways, increased proliferation, and oxidative DNA damage form a common molecular signature of long-CNT- and long-asbestos-fiber-induced pathology. We show that hypermethylation of p16/Ink4a and p19/Arf in CNT- and asbestos-induced inflammatory lesions precedes mesothelioma; this results in silencing of Cdkn2a (Ink4a/Arf) and loss of p16 and p19 protein, consistent with epigenetic alterations playing a gatekeeper role in cancer. In end-stage mesothelioma, silencing of p16/Ink4a is sustained and deletion of p19/Arf is detected, recapitulating human disease. This study addresses the long-standing question of which early molecular changes drive carcinogenesis during the long latency period of mesothelioma development and shows that CNT and asbestos pose a similar health hazard.

Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

In plain English

In this animal experiment, the authors injected long or short carbon nanotubes (CNTs) or amosite asbestos into the chest (pleural) cavity of female mice, studying short fibers to 12 weeks and long fibers up to 20 months. Long, but not short, fibers caused pleural inflammatory lesions. Long CNTs and long asbestos caused similar gene activity, sustained cancer-related signaling, more cell proliferation and rising oxidative DNA damage. Pleural mesothelioma developed in 1 of 4, 1 of 4, 1 of 5 and 1 of 12 mice at four long-nanotube doses, and in 3 of 32 asbestos-exposed mice. Both fiber types caused hypermethylation, which the authors linked to silencing, of the tumor suppressor gene Cdkn2a in lesions and tumors. In lesions of mice tumor-free at one year, most mesothelial cells lacked the gene's p16 and p19 proteins; tumors mixed stained and unstained areas. In p19-negative areas of one nanotube tumor, p19Arf gene copies were 60% below controls; another nanotube tumor also lost p19Arf. Tumor tissue from five patients showed similar signaling activation. The authors concluded that CNTs and asbestos pose a similar health hazard.

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: Animal experiment: intrapleural injection of carbon nanotubes or amosite asbestos in mice, with comparison to human mesothelioma tissue
• Who was studied: Eight-week-old female C57BL/6 mice. Short-fiber groups were studied only at 1 and 12 weeks (n = 4 per group). Long-fiber and control groups were studied at 6 months and 1 year (n = 4 per group). Prolonged exposure groups were followed up to 20 months: 4, 5 and 12 mice in the long-CNT groups, and 16 plus 16 in the asbestos groups. Tumor tissue from patients was also analyzed.
• Exposure: Long and short CNTs and long and short South African amosite asbestos, injected into the pleural cavity. CNT doses are printed as 5 mg/mouse (1 to 12 weeks), 2.5 mg (1 year), and 1, 0.5 and 0.2 mg (up to 20 months). Amosite comparator doses are printed as 25 mg (and 50 mg in prolonged studies). See text_problems on units.
• Main results:
  • Long, but not short, asbestos and CNTs caused inflammatory lesions along the pleura that progressed over time.
  • Gene expression samples from mice exposed to long amosite and long CNTs grouped together.
  • Cancer-related signaling pathways were activated, and stayed activated, in the pleurae of mice given long fibers but not short fibers.
  • Proliferating cells increased in lesions caused by both long amosite and long CNTs.
  • A marker of oxidative DNA damage (8-OHdG) progressively increased in mice exposed to long amosite or long CNTs, compared with vehicle controls (n = 4 per group).
  • Pleural mesothelioma in long-CNT-exposed mice: 1/4 at 2.5 mg for 1 year; 1/4 at 1 mg for 18 months; 1/5 at 0.5 mg; 1/12 at 0.2 mg for 20 months.
  • Three of 32 asbestos-exposed mice developed mesothelioma after 18 to 20 months.
  • In the long-CNT-induced tumor (#610), some areas stained positive and others negative for p16 and p19.
  • In microdissected p19-negative areas of that long-CNT-induced tumor, p19Arf gene copy number was reduced by 60% compared with controls.
  • A second long-CNT tumor (#461, 1 mg dose) showed loss of p16 and p19 protein, reduced Cdkn2a mRNA, and allelic loss of p19Arf.
  • In the long-amosite-induced mesothelioma, p16 and p19 protein loss appeared as a patchy staining pattern, and no reduction in p19Arf gene copy number was detected.
  • In lesions from long-CNT-exposed mice without tumors at 1 year, p16 and p19 proteins were absent in most mesothelial cells. Protein loss was also seen in advanced long-amosite lesions.
  • Hypermethylation of p16Ink4a and p19Arf was found in mesothelial cells of advanced lesions and in tumors caused by both long CNTs and long amosite, compared with vehicle controls.
  • Signaling pathway activation was examined in human mesothelioma tissue from five patients and compared with normal mesothelial cells.
• The authors' conclusion: The authors concluded that CNTs and asbestos pose a similar health hazard.
• Limitations the authors state:
  • The authors reported that, apart from histological analysis, data collection and analysis were not performed blind.

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, Tumor Suppressor Gene, CDKN2A, Pleura, Asbestos Exposure, Latency, Carcinogenesis, Pleural Cavity.

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• Asbestos-like pathogenicity of long carbon nanotubes alleviated by chemical functionalization — H. Ali-Boucetta, A. Nunes, et al. (2013)
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