Important functional role of the protein osteopontin in the progression of malignant pleural mesothelioma

Our plain-English summary of Important functional role of the protein osteopontin in the progression of malignant pleural mesothelioma, by E. Digifico, M. Erreni, L. Mannarino, et al (Frontiers in Immunology, 2023).

The study

• Authors: E. Digifico, M. Erreni, L. Mannarino, S. Marchini, A. Ummarino, C. Anfray, L. Bertola, C. Recordati, D. Pistillo, M. Roncalli, P. Bossi, P.A. Zucali, M. D'Incalci, C. Belgiovine, P. Allavena
• Journal: Frontiers in Immunology
• Published: 2023;14:1116430
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Malignant Pleural Mesothelioma (MPM) is an aggressive cancer of the mesothelial lining associated with exposure to airborne non-degradable asbestos fibers. Its poor response to currently available treatments prompted us to explore the biological mechanisms involved in its progression. MPM is characterized by chronic non-resolving inflammation; in this study we investigated which inflammatory mediators are mostly expressed in biological tumor samples from MPM patients, with a focus on inflammatory cytokines, chemokines and matrix components.

Methods: Expression and quantification of Osteopontin (OPN) was detected in tumor and plasma samples of MPM patients by mRNA, immunohistochemistry and ELISA. The functional role of OPN was investigated in mouse MPM cell lines in vivo using an orthotopic syngeneic mouse model.

Results: In patients with MPM, the protein OPN was significantly more expressed in tumors than in normal pleural tissues and predominantly produced by mesothelioma cells; plasma levels were elevated in patients and associated with poor prognosis. However, modulation of OPN levels was not significantly different in a series of 18 MPM patients receiving immunotherapy with durvalumab alone or with pembrolizumab in combination with chemotherapy, some of whom achieved a partial clinical response. Two established murine mesothelioma cell lines: AB1 and AB22 of sarcomatoid and epithelioid histology, respectively, spontaneously produced high levels of OPN. Silencing of the OPN gene (Spp1) dramatically inhibited tumor growth in vivo in an orthotopic model, indicating that OPN has an important promoting role in the proliferation of MPM cells. Treatment of mice with anti-CD44 mAb, blocking a major OPN receptor, significantly reduced tumor growth in vivo.

Conclusion: These results demonstrate that OPN is an endogenous growth factor for mesothelial cells and inhibition of its signaling may be helpful to restrain tumor progression in vivo. These findings have translational potential to improve the therapeutic response of human MPM.

Copyright © 2023 Digifico, Erreni, Mannarino, Marchini, Ummarino, Anfray, Bertola, Recordati, Pistillo, Roncalli, Bossi, Zucali, D’Incalci, Belgiovine and Allavena.

In plain English

This laboratory study examined the protein osteopontin (OPN) in malignant pleural mesothelioma (MPM). It used samples from patients at a hospital near Milan, Italy, and experiments in mice. Activity of the OPN gene was significantly higher in tumor samples than in nearby non-diseased tissue. Blood OPN levels were significantly higher in 99 MPM patients than in 101 healthy donors. Among 61 trabectedin trial patients, high OPN before treatment was significantly associated with worse overall survival. In 18 immunotherapy patients, OPN before treatment did not differ between those whose disease progressed, stayed stable or partly responded. The authors said the numbers were too small for conclusions about changes during treatment. In mice, mesothelioma cells originally made by injecting crocidolite asbestos into mice were placed in the chest. Reducing OPN production by silencing its gene (by 84% and 81% in two cell lines) reduced tumor growth. An antibody blocking CD44, an OPN receptor, reduced growth of AB22 tumors but not significantly of unmodified AB1 tumors. The authors concluded that OPN is an essential growth factor for mesothelioma cells. The article did not report patients' asbestos exposure.

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: Original laboratory research: analysis of tumor tissue and blood samples from mesothelioma patients, combined with cell culture and animal (mouse) experiments
• Who was studied: Patients with pathologically confirmed malignant mesothelioma at IRCCS Humanitas (Rozzano, Milano, Italy). The groups were 15 tumor samples for gene testing, 99 patients compared with 101 healthy donors for blood OPN, 61 patients from the ATREUS trabectedin trial, 28 tumor tissues for staining, and 18 patients on immunotherapy. The animal experiments used BALB/c mice. Dates of sample collection were not given.
• Exposure: The study did not measure asbestos exposure. It studied the protein osteopontin and blocking it (silencing the OPN gene, or an anti-CD44 antibody). The mouse mesothelioma cell lines AB1 and AB22 had originally been generated in mice by injecting crocidolite asbestos fibers into the abdomen.
• Main results:
  • In 15 MPM samples, OPN gene (Spp1) mRNA levels were significantly higher in tumor tissue than in un-diseased tissue.
  • Blood plasma OPN levels were significantly higher in MPM patients (n=99) than in healthy donors (n=101).
  • In 61 patients in the ATREUS study receiving trabectedin, high plasma OPN at baseline was significantly associated with worse overall survival.
  • In 28 surgical MPM tissues, OPN staining was located in the cytoplasm of tumor cells in 75% of cases.
  • In 18 MPM patients on immunotherapy, baseline OPN levels did not differ between patients with progressive disease, stable disease or partial response.
  • Among these immunotherapy patients, 5 of 12 with progressive or stable disease had increased OPN levels after 4-6 months, while none of the responding patients had increased levels.
  • In culture, mouse AB1 cells secreted up to 1900 ng/ml of OPN and AB22 cells produced 220 ng/ml.
  • Silencing of the OPN gene reached 84% in AB1 cells and 81% in AB22 cells. Silencing was not complete in the AB1 cell line.
  • In culture, silencing OPN had no effect on growth of AB1 cells, while OPN-silenced AB22 cells formed 47% fewer colonies than control AB22 cells.
  • In mice, OPN silencing almost completely abolished growth of AB1 tumors at day 14. The OPN-silenced AB1 cells started growing again by day 33 in 2 of 5 mice.
  • With AB22 cells, mice given control cells had to be sacrificed at day 17, while the endpoint for mice given OPN-silenced cells was days 45-56.
  • An anti-CD44 antibody reduced growth of AB22 tumors in mice (10 mice per group, p = 0.0024) compared with an irrelevant antibody.
  • The anti-CD44 antibody did not significantly reduce growth of unmodified AB1 tumors. It did significantly reduce growth of OPN-silenced AB1 tumors.
  • An aptamer drug designed to block OPN (OPN-R3) did not affect growth of AB22 tumors in mice.
• The authors' conclusion: The authors concluded that their hypothesis was confirmed: OPN is an essential endogenous growth factor for mesothelioma cells. They suggested that therapies based on inhibiting OPN could have an impact for MPM patients.
• Limitations the authors state:
  • The small number of immunotherapy patients did not allow conclusions about changes in OPN levels during treatment.
  • Silencing of the OPN gene was not complete in the AB1 cell line, which produces very high levels of OPN.

Topics

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

Medical terms in this study, explained in our Lexicon: Osteopontin, Pleural Mesothelioma, Inflammation, Cytokine, Immunohistochemistry, Mesothelioma, Prognosis, Immunotherapy.

Related studies

• Osteopontin modulates inflammation, mucin production, and gene expression signatures after inhalation of asbestos in a murine model of fibrosis — T. Sabo-Attwood, M.E. Ramos-Nino, et al. (2011)
• Comparison of osteopontin, megakaryocyte potentiating factor, and mesothelin proteins as markers in the serum of patients with malignant mesothelioma — J. Creaney, D. Yeoman, et al. (2008)
• Effectiveness of mesothelin family proteins and osteopontin for malignant mesothelioma — I. Pantazopoulos, P. Boura, et al. (2013)
• Soluble mesothelin related peptides (SMRP) and osteopontin as protein biomarkers for malignant mesothelioma: analytical validation of ELISA based assays and characterization at mRNA and protein levels — A.J. Rai, R.M. Flores, et al. (2010)
• Utility of osteopontin and serum mesothelin in malignant pleural mesothelioma diagnosis and prognosis assessment — B.D. Grigoriu, A. Scherpereel, et al. (2007)
• Soluble mesothelin, megakaryocyte potentiating factor, and osteopontin as markers of patient response and outcome in mesothelioma — K. Hollevoet, K. Nackaerts, et al. (2011)

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