The Effect of Aquaporin 1-Inhibition on Vasculogenic Mimicry in Malignant Mesothelioma

Our plain-English summary of The Effect of Aquaporin 1-Inhibition on Vasculogenic Mimicry in Malignant Mesothelioma, by E. Pulford, J. McEvoy, A. Hocking, et al (International Journal of Molecular Sciences, 2017).

The study

• Authors: E. Pulford, J. McEvoy, A. Hocking, S. Prabhakaran, K. Griggs, S. Klebe
• Journal: International Journal of Molecular Sciences
• Published: 2017;18(11)
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an aggressive malignancy of the serosal membranes, with poor overall survival and quality of life. Limited targeted treatment strategies exist due to restricted knowledge of pathogenic pathways. Vasculogenic mimicry (VM) is a newly described phenomenon associated with increased aggressiveness in other malignancies, and has been characterized in MM. Normal mesothelium expresses aquaporin 1 (AQP1) and retained expression has been associated with improved survival in MM. AQP1 is expressed by normal vascular endothelium and is involved in mediating MM cell motility and proliferation. We investigated the role of AQP1 in VM, and its interaction with the pro-angiogenic factor vascular endothelial growth factor A (VEGFA), which is variably expressed in MM. Matrigel VM assays were performed using NCI-H226 and NCI-H28 MM cell lines and primary cells in hypoxia and normoxia. The synthetic blocker AqB050 and siRNA were used to inhibit AQP1, and bevacizumab was used to inhibit VEGF. Inhibition of AQP1 resulted in increased VEGFA secretion by MM cells and reduced VM in MM cell lines in hypoxia but not normoxia. No change in VM was seen in MM primary cells. Combined inhibition of AQP1 and VEGF had no effect on VM in normoxia. In a heterotopic xenograft mouse model, AqB050 treatment did not alter vessel formation. AQP1 may interact with VEGFA and play a role in VM, especially under hypoxic conditions, but the heterogeneity of MM cells may result in different dominant pathways between patients.

In plain English

This laboratory study used cells and mice, not people or asbestos exposure. The authors tested whether blocking aquaporin 1 (AQP1), a water-channel protein, affects vasculogenic mimicry (tumour cells forming vessel-like channels) in malignant mesothelioma. They used two mesothelioma cell lines (NCI-H226 and NCI-H28), cells grown from three patients' pleural effusions, and mice carrying NCI-H226 tumours (4 per group). AQP1 was blocked with a drug, AqB050, or with siRNA; VEGF was blocked with bevacizumab. At normal oxygen, AqB050 did not reduce vessel-like structures in either cell line or the patient cells (not tested at low oxygen). At low oxygen, it reduced them in both cell lines. In mice, mean vessel counts were similar: AqB050-treated 8.7 per field, DMSO-treated 8.6, untreated 9.6. Under normal oxygen, 40 µM AqB050 raised VEGFA in NCI-H28 cells after 24 hours; no significant change was found in NCI-H226 cells. Under normal oxygen, bevacizumab alone, or combined with AQP1 siRNA in NCI-H226 cells, did not change vessel-like structures. The authors concluded that AQP1 inhibition suppresses vasculogenic mimicry at low oxygen, while noting it may not be effective in living animals.

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: in vitro cell culture experiments (Matrigel vasculogenic mimicry assays) plus a mouse xenograft experiment
• Who was studied: Two malignant mesothelioma cell lines, NCI-H28 (high VEGFA) and NCI-H226 (low VEGFA). Also primary cells from three patients with epithelioid mesothelioma, isolated from pleural effusion samples (Adelaide, Australia). In addition, BALB/c nude mice injected with NCI-H226 cells: untreated, AqB050-treated and DMSO-treated groups, 4 mice each.
• Exposure: No asbestos exposure was studied. AQP1 was blocked with the drug AqB050 (20 µM and 40 µM) or with AQP1-specific siRNA (20 nM). VEGF was blocked with bevacizumab (10 µg/mL). Experiments were run in normal oxygen (21% O2) and low oxygen (0.1% O2).
• Main results:
  • Under normal oxygen, AqB050 did not inhibit vasculogenic mimicry in NCI-H226 or NCI-H28 cells compared with DMSO control.
  • Under low oxygen, 20 µM AqB050 reduced branch count (p = 0.015) and loop count (p = 0.015) in NCI-H226 cells.
  • Under low oxygen, NCI-H28 cells needed 40 µM AqB050 to significantly reduce branch count (p = 0.01) and loop count (p = 0.002).
  • AQP1 blockade did not inhibit vasculogenic mimicry in the three epithelioid primary (patient) cell samples tested under normal oxygen.
  • In the mouse xenograft model, mean microvessel counts did not differ between groups: AqB050-treated 8.7 plus or minus 4 counts per field, DMSO-treated 8.6 plus or minus 2.1, untreated 9.6 plus or minus 2.2.
  • In NCI-H28 cells under normal oxygen, 40 µM AqB050 significantly increased VEGFA protein after 24 hours (p = 0.002) and increased VEGFA mRNA 3.5 to 4.3 fold at 24 hours (p = 0.002).
  • In NCI-H226 cells, no significant difference was seen in VEGFA protein or mRNA levels with AqB050 treatment; the data were not shown.
  • In the normal-oxygen experiments, bevacizumab alone (10 µg/mL) did not alter vasculogenic mimicry in either cell line compared with control human IgG.
  • In NCI-H226 cells under normal oxygen, AQP1 siRNA and bevacizumab, alone or in combination, did not inhibit vasculogenic mimicry; the combination was not tested at low oxygen.
• The authors' conclusion: The authors concluded that inhibition of AQP1 suppresses vasculogenic mimicry under hypoxic (low-oxygen) conditions.
• Limitations the authors state:
  • Low-oxygen experiments could not be performed on the patient-derived primary cells because of departmental safety regulations.
  • The authors stated that testing primary cells from more patients would have helped interpret the results, but suitable primary cells are often limited.
  • There was a large standard deviation within the AqB050-treated mouse group.
  • The authors noted that, based on the mouse data, AQP1 blockade may not be effective for reducing vasculogenic mimicry in vivo, perhaps due to individual variation and tumour cell heterogeneity.

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, Overall Survival, Quality of Life, Mesothelium, Hypoxia, Bevacizumab.

Related studies

• Vasculogenic mimicry in malignant mesothelioma: an experimental and immunohistochemical analysis — E. Pulford, A. Hocking, et al. (2016)
• Blockade of aquaporin 1 inhibits proliferation, motility, and metastatic potential of mesothelioma in vitro but not in an in vivo model — S. Klebe, K. Griggs, et al. (2015)
• Usefulness of Aquaporin 1 as a Prognostic Marker in a Prospective Cohort of Malignant Mesotheliomas — J. Driml, E. Pulford, et al. (2016)
• Aquaporin 1 is an independent prognostic factor in pleural malignant mesothelioma — S.C. Kao, N. Armstrong, et al. (2012)
• Combination of onconase and dihydroartemisinin synergistically suppresses growth and angiogenesis of non-small-cell lung carcinoma and malignant mesothelioma — R. Shen, J. Li, et al. (2016)
• Aquaporins 1, 3 and 5 in Different Tumors, their Expression, Prognosis Value and Role as New Therapeutic Targets — M.S. Moosavi, Y. Elham (2020)

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