The Collagen Receptor uPARAP in Malignant Mesothelioma: A Potential Diagnostic Marker and Therapeutic Target

Our plain-English summary of The Collagen Receptor uPARAP in Malignant Mesothelioma: A Potential Diagnostic Marker and Therapeutic Target, by P. Çakılkaya, R.R. Sørensen, H.J. Jürgensen, et al (International Journal of Molecular Sciences, 2021).

The study

• Authors: P. Çakılkaya, R.R. Sørensen, H.J. Jürgensen, O. Krigslund, H. Gårdsvoll, C.F. Nielsen, E. Santoni-Rugiu, N. Behrendt, L.H. Engelholm
• Journal: International Journal of Molecular Sciences
• Published: 2021;22(21)
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is a highly aggressive cancer with limited therapeutic options. We have previously shown that the endocytic collagen receptor, uPARAP, is upregulated in certain cancers and can be therapeutically targeted. Public RNA expression data display uPARAP overexpression in MM. Thus, to evaluate its potential use in diagnostics and therapy, we quantified uPARAP expression by immunohistochemical H-score in formalin-fixed paraffin-embedded bioptic/surgical human tissue samples and tissue microarrays. We detected pronounced upregulation of uPARAP in the three main MM subtypes compared to non-malignant reactive mesothelial proliferations, with higher expression in sarcomatoid and biphasic than in epithelioid MM. The upregulation appeared to be independent of patients' asbestos exposure and unaffected after chemotherapy. Using immunoblotting, we demonstrated high expression of uPARAP in MM cell lines and no expression in a non-malignant mesothelial cell line. Moreover, we showed the specific internalization of an anti-uPARAP monoclonal antibody by the MM cell lines using flow cytometry-based assays and confocal microscopy. Finally, we demonstrated the sensitivity of these cells towards sub-nanomolar concentrations of an antibody-drug conjugate formed with the uPARAP-directed antibody and a potent cytotoxin that led to efficient, uPARAP-specific eradication of the MM cells. Further studies on patient cohorts and functional preclinical models will fully reveal whether uPARAP could be exploited in diagnostics and therapeutic targeting of MM.

In plain English

This laboratory study from Copenhagen, Denmark, examined a protein called uPARAP in malignant mesothelioma. The authors stained 53 tissue specimens from 28 mesothelioma patients and 12 control patients with reactive mesothelial proliferation, a non-cancerous condition. The mesothelioma specimens were collected in 2017–2020. They also stained commercial tissue microarrays with 130 evaluable cases. uPARAP was markedly higher in mesothelioma than in non-cancerous tissue. In the microarrays, sarcomatoid and biphasic tumors showed significantly higher levels than epithelioid ones. Expression did not differ significantly between asbestos-exposed and non-exposed patients (p = 0.8819 in resections, p = 0.9745 in biopsies). In 12 patients with matched samples, levels before and after chemotherapy did not differ significantly (p = 0.3149). Three mesothelioma cell lines expressed uPARAP strongly and took up an antibody against it. Linked to a toxin, the antibody reduced the cells' viability. The concentration that halved viability (EC50) ranged from 0.014 µg/mL (95% confidence interval 0.011–0.016) to 0.26 µg/mL (95% confidence interval 0.174–0.339). The authors concluded that uPARAP is a promising focus for further study as a diagnostic marker and treatment target. They noted that small sample numbers limited some comparisons.

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: retrospective immunohistochemistry (protein staining) on archived human tissue and commercial tissue microarrays, plus experiments on cultured cell lines
• Who was studied: 53 archived tissue specimens from 28 malignant mesothelioma patients (7 epithelioid, 11 biphasic, 10 sarcomatoid) and 12 control patients with reactive mesothelial proliferation, Rigshospitalet, Copenhagen, Denmark. The mesothelioma specimens date from 2017–2020; the article gives no period for the control specimens. The study also used commercial tissue microarrays with 130 evaluable cases (73 epithelioid, 27 biphasic and 17 sarcomatoid mesothelioma, plus 13 reactive mesothelial proliferation), three mesothelioma cell lines and one non-malignant mesothelial cell line.
• Exposure: Patients' asbestos exposure (exposed vs not exposed) came from their clinical history. No fiber types, products, jobs or doses are given. Some patients had received 3 cycles of neoadjuvant cisplatin-pemetrexed chemotherapy before surgery.
• Main results:
  • uPARAP was markedly higher in mesothelioma specimens than in non-malignant reactive mesothelial proliferation. The increase was statistically significant for biphasic and sarcomatoid mesothelioma in both biopsies and resections, and for epithelioid mesothelioma in resections.
  • In biopsies from epithelioid mesothelioma, uPARAP was roughly 100-fold higher by the numbers, but this did not reach statistical significance.
  • In the tissue microarrays, expression was significantly higher in sarcomatoid and biphasic than in epithelioid mesothelioma. In the patient tissue sections, no significant difference between subtypes was observed.
  • There was no significant difference in uPARAP expression between asbestos-exposed and non-exposed patients: p = 0.8819 for resection samples and p = 0.9745 for biopsy samples.
  • In the 12 mesothelioma cases with paired samples, uPARAP did not differ significantly between biopsies taken before chemotherapy and resections taken after chemotherapy (p = 0.3149).
  • In the tissue microarrays, pleural mesothelioma showed significantly higher expression than peritoneal mesothelioma (p = 0.0227). There was no significant difference between pleural and pericardial mesothelioma (p = 0.8418) or between peritoneal and pericardial mesothelioma (p = 0.4305).
  • All three mesothelioma cell lines (ONE58, JL-1, H-Meso-1) were strongly uPARAP-positive. The non-malignant mesothelial cell line MeT-5A showed very low expression.
  • For the ONE58 mesothelioma cell line, the uPARAP-directed antibody-drug conjugate had the lowest EC50 (the concentration needed to cut cell viability by 50%) among the mesothelioma lines: 0.014 µg/mL (95% CI 0.011–0.016).
  • For the H-Meso-1 mesothelioma cell line, the uPARAP-directed conjugate had the highest EC50 among the mesothelioma lines: 0.26 µg/mL (95% CI 0.174–0.339). The JL-1 line fell in between.
  • A control conjugate built with an irrelevant antibody needed 10- to 100-fold higher concentrations to reduce cell viability by the same amount.
• The authors' conclusion: The authors concluded that uPARAP is a promising focus for further studies in mesothelioma, both as a possible diagnostic marker and as a potential treatment target. They stated that the drug conjugate they used was a proof-of-concept tool, not a proposed drug candidate.
• Limitations the authors state:
  • The relatively low number of samples hampered comparison between mesothelioma subtypes in the patient tissue sections.
  • The commercial tissue microarrays were incompatible with the staining method used for the patient sections, so a modified, automated method was used.
  • The difference between pleural and peritoneal mesothelioma needs further studies to validate it.
  • The drug conjugate was tested only on cultured cells. Optimized conjugates would need to be studied in mouse models.

Topics

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

Medical terms in this study, explained in our Lexicon: Collagen, Malignant Mesothelioma, Sarcomatoid, Biphasic Mesothelioma, Epithelioid, Asbestos Exposure, Chemotherapy, Mesothelial Cells.

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