Restoring expression of miR-16: a novel approach to therapy for malignant pleural mesothelioma

Our plain-English summary of Restoring expression of miR-16: a novel approach to therapy for malignant pleural mesothelioma, by G. Reid, M.E. Pel, M.B. Kirschner, et al (Annals of Oncology, 2013).

The study

• Authors: G. Reid, M.E. Pel, M.B. Kirschner, Y.Y. Cheng, N. Mugridge, J. Weiss, M. Williams, C. Wright, J.J. Edelman, M.P. Vallely, B.C. McCaughan, S. Klebe, H. Brahmbhatt, J.A. MacDiarmid, N. van Zandwijk
• Journal: Annals of Oncology
• Published: 2013;24(12):3128-35
• Cited by: 207 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Malignant pleural mesothelioma (MPM) is recalcitrant to treatment and new approaches to therapy are needed. Reduced expression of miR-15/16 in a range of cancer types has suggested a tumour suppressor function for these microRNAs, and re-expression has been shown to inhibit tumour cell proliferation. The miR-15/16 status in MPM is largely unknown.

Materials And Methods: MicroRNA expression was analysed by TaqMan-based RT-qPCR in MPM tumour specimens and cell lines. MicroRNA expression was restored in vitro using microRNA mimics, and effects on proliferation, drug sensitivity and target gene expression were assessed. Xenograft-bearing mice were treated with miR-16 mimic packaged in minicells targeted with epidermal growth factor receptor (EGFR)-specific antibodies.

Results: Expression of the miR-15 family was consistently downregulated in MPM tumour specimens and cell lines. A decrease of 4- to 22-fold was found when tumour specimens were compared with normal pleura. When MPM cell lines were compared with the normal mesothelial cell line MeT-5A, the downregulation of miR-15/16 was 2- to 10-fold. Using synthetic mimics to restore miR-15/16 expression led to growth inhibition in MPM cell lines but not in MeT-5A cells. Growth inhibition caused by miR-16 correlated with downregulation of target genes including Bcl-2 and CCND1, and miR-16 re-expression sensitised MPM cells to pemetrexed and gemcitabine. In xenograft-bearing nude mice, intravenous administration of miR-16 mimics packaged in minicells led to consistent and dose-dependent inhibition of MPM tumour growth.

Conclusions: The miR-15/16 family is downregulated and has tumour suppressor function in MPM. Restoring miR-16 expression represents a novel therapeutic approach for MPM.

In plain English

This was a laboratory study of malignant pleural mesothelioma (MPM). It did not measure asbestos exposure. The authors measured a family of small gene-regulating molecules called microRNAs (miR-15/16) in 60 tumour samples from patients who had an extrapleural pneumonectomy and in 23 normal pleural tissue samples from patients having cardiac or aortic surgery in Sydney. miR-16 was 22-fold lower in tumours than in normal tissue. miR-15a, miR-15b and miR-195 were 4-, 10- and 11-fold lower. In six MPM cell lines, levels were two- to fivefold lower than in a normal mesothelial cell line, MeT-5A. Adding synthetic miR-16 slowed the growth of MPM cells but not MeT-5A cells. It also made MPM cells more sensitive to the drugs gemcitabine and pemetrexed, but not cisplatin. In mice carrying transplanted human MPM tumours, miR-16 given into a vein inside antibody-coated bacterial minicells inhibited tumour growth, and higher doses had a greater effect. The authors concluded that miR-16 replacement represents a novel approach to therapy for MPM. These were laboratory and animal experiments, not tests in patients.

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: microRNA measurement in archived human tumour and normal tissue, cell-line experiments, and an animal (mouse xenograft) experiment. Not a study of patients' treatment or of asbestos exposure.
• Who was studied: 60 formalin-fixed tumour samples from MPM patients who underwent extrapleural pneumonectomy, and 23 normal pleural tissue samples from patients undergoing cardiac or aortic surgery at Royal Prince Alfred Hospital, Sydney. Also the normal mesothelial cell line MeT-5A, up to six MPM cell lines, and nude mice carrying tumours grown from the MPM cell line MSTO-211H. Collection dates were not given.
• Exposure: No asbestos exposure was studied. The experimental treatment was synthetic miR-16 (also miR-15a and miR-15b) mimics added to cells. In mice, miR-16 mimic was packaged in bacterially derived minicells targeted with an EGFR-specific antibody and given intravenously.
• Main results:
  • In the 60 tumour samples compared with the 23 normal pleural samples, miR-16 expression was 22-fold lower in tumours. miR-15a and miR-15b were lower by 4- and 10-fold, and miR-195 was 11-fold lower.
  • Across six MPM cell lines compared with the normal mesothelial cell line MeT-5A, RT-qPCR showed a two- to fivefold decrease for each miR-15 family microRNA.
  • Synthetic mimics of miR-16, miR-15a or miR-15b inhibited growth of MPM cell lines but not normal MeT-5A cells. miR-16 was the most effective.
  • After miR-16 mimic was added, protein levels of its known targets Bcl-2 and CCND1 fell. In MSTO-211H cells it caused cells to accumulate at an early, resting stage of the cell-division cycle (G0/G1) and caused cell death (apoptosis).
  • In MPM cells (MSTO-211H, MM05), 5 nM miR-16 increased sensitivity to gemcitabine threefold and to pemetrexed sevenfold. It did not change MeT-5A cells' sensitivity to either drug.
  • Restoring miR-16 did not change MPM cells' sensitivity to cisplatin.
  • In mice with MSTO-211H tumours, 1 × 10^9 minicells containing miR-16 mimic (about 0.3 µg) given once, twice or four times per week for 3 weeks gave significant, dose-dependent inhibition of tumour growth compared with controls. Raising the dose to 2 × 10^9 minicells four times per week gave greater inhibition.
  • In tumours from mice given the higher dose, lymphocyte infiltration was grade 3 or 4 (grades 1 to 2 in control mice) and there were half as many dividing cells (mitoses). The authors observed no other non-specific effects.
• The authors' conclusion: The authors concluded that the miR-15/16 family is consistently reduced in MPM, and that miR-16 replacement represents a novel approach to therapy for MPM patients.

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: Pleural Mesothelioma, EGFR, Pleura, Mesothelial Cells, MeT-5A Cells, Pemetrexed (Alimta), Gemcitabine.

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