Antagonizing the Hedgehog Pathway with Vismodegib Impairs Malignant Pleural Mesothelioma Growth In Vivo by Affecting Stroma

Our plain-English summary of Antagonizing the Hedgehog Pathway with Vismodegib Impairs Malignant Pleural Mesothelioma Growth In Vivo by Affecting Stroma, by M. Meerang, K. Bérard, E. Felley-Bosco, et al (Molecular Cancer Therapeutics, 2016).

The study

• Authors: M. Meerang, K. Bérard, E. Felley-Bosco, O. Lauk, B. Vrugt, A. Boss, D. Kenkel, A. Broggini-Tenzer, R.A. Stahel, S. Arni, W. Weder, I. Opitz
• Journal: Molecular Cancer Therapeutics
• Published: 2016;15(5):1095-105
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

An autocrine-driven upregulation of the Hedgehog (Hh) signaling pathway has been described in malignant pleural mesothelioma (MPM), in which the ligand, desert Hh (DHH), was produced from tumor cells. However, our investigation revealed that the Hh pathway is activated in both tumor and stroma of MPM tumor specimens and an orthotopic immunocompetent rat MPM model. This was demonstrated by positive immunohistochemical staining of Glioma-associated oncogene 1 (GLI1) and Patched1 (PTCH1) in both tumor and stromal fractions. DHH was predominantly expressed in the tumor fractions. To further investigate the role of the Hh pathway in MPM stroma, we antagonized Hh signaling in the rat model of MPM using a Hh antagonist, vismodegib, (100 mg/kg orally). Daily treatment with vismodegib efficiently downregulated Hh target genes Gli1, Hedgehog Interacting Protein (Hhip), and Ptch1, and caused a significant reduction of tumor volume and tumor growth delay. Immunohistochemical analyses revealed that vismodegib treatment primarily downregulated GLI1 and HHIP in the stromal compartment along with a reduced expression of previously described fibroblast Hh-responsive genes such as Fibronectin (Fn1) and Vegfa Primary cells isolated from the rat model cultured in 3% O2 continued to express Dhh but did not respond to vismodegib in vitro However, culture supernatant from these cells stimulated Gli1, Ptch1, and Fn1 expression in mouse embryonic fibroblasts, which was suppressed by vismodegib. Our study provides new evidence regarding the role of Hh signaling in MPM stroma in the maintenance of tumor growth, emphasizing Hh signaling as a treatment target for MPM. Mol Cancer Ther; 15(5); 1095-105. ©2016 AACR.

©2016 American Association for Cancer Research.

In plain English

This laboratory and animal study examined Hedgehog (Hh) signaling in malignant pleural mesothelioma (MPM). The authors stained human MPM tissue, including tissue arrays from 138 patients. They found the pathway marker GLI1 in both tumor cells and surrounding supporting tissue (stroma) in all samples. They then implanted a rat mesothelioma cell line under rats' chest lining. That cell line came from a rat exposed to asbestos in the abdomen. Six rats received vismodegib (100 mg/kg by mouth daily for 6 days); six received only the inactive liquid. Tumor volume on MRI was significantly lower in treated rats (3-fold difference, P = 0.03), as was volume measured at autopsy (P = 0.03). Growth tracked by bioluminescence did not differ statistically significantly. The drug mainly lowered pathway markers in the stroma and reduced tumor-cell division markers. No significant difference in measured cell death was detected. In lab dishes, vismodegib could not suppress pathway genes in the tumor cells themselves. The authors concluded that Hh signaling in MPM stroma has a role in maintaining tumor growth. They noted a short treatment and observation period.

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 combining staining of human MPM tumor tissue, cell-culture experiments, and an animal experiment in rats with implanted mesothelioma tumors treated with vismodegib or vehicle
• Who was studied: Human MPM tumor specimens (8 diagnostic specimens plus tissue arrays from 138 patients collected 1999 to 2009); 12 male Fischer 344 rats implanted under the parietal pleura with the rat mesothelioma cell line IL45-luc. The parent line IL45 was originally produced in a rat exposed intraperitoneally to asbestos; fiber type not stated.
• Exposure: The exposure studied was the Hh pathway (SMO) antagonist drug vismodegib, 100 mg/kg given by mouth once daily for 6 days (6 treated rats), compared with vehicle solution only (6 control rats). Asbestos exposure itself was not studied.
• Main results:
  • In human MPM specimens, GLI1 was expressed in both tumor and stromal fractions in all samples assessed; DHH, PTCH1 and HHIP expression was higher in the tumor fraction.
  • In rats, tumor volume measured by MRI was significantly reduced in the vismodegib group compared with controls (3-fold difference, P = 0.03).
  • Macroscopic tumor volume measured at autopsy was also significantly reduced in the treated group (P = 0.03).
  • Tumor growth tracked by bioluminescence appeared reduced in treated rats, but the overall growth suppression was not statistically significant.
  • In rat tumors, mRNA levels of the Hh target genes Gli1, Hhip and Ptch1 were reduced after vismodegib compared with controls; Dhh, Gli2 and Gli3 showed no significant change.
  • On tissue staining, GLI1 and HHIP were significantly reduced in the stromal fraction of treated rats; GLI1 in tumor cells was only slightly reduced.
  • The proliferation (Ki-67) and mitosis (p-H3) indices of tumor cells were significantly reduced in treated rats. No significant difference in TUNEL-positive cells (a measure of cell death) was observed between groups; the percentage of dead cells was very low in both.
  • In cell culture, vismodegib could not suppress the Hh target genes Gli1 and Ptch1 in the rat mesothelioma cell lines. Growth was inhibited only at concentrations above 20 µmol/L; the text prints 'mmol/L', but the figure axis for this experiment is labeled µmol/L.
  • In treated rat tumors, Fn1 (fibronectin) mRNA was reduced and Vegf and Lif mRNA were significantly reduced compared with controls; collagen, CyclinD1 and Abcg2 were not changed.
  • Culture fluid from primary rat tumor cells strongly increased Gli1 and Ptch1 in mouse embryonic fibroblasts (NIH3T3), and vismodegib reduced this increase. Culture fluid from a primary human MPM culture also increased Gli1, Ptch1 and Fn1.
• The authors' conclusion: The authors concluded that their study provides new evidence that Hh signaling in MPM stroma has a role in maintaining tumor growth. They presumed that the drug's effects came primarily from acting on fibroblasts, and stated that this emphasizes Hh signaling as a treatment target for MPM.
• Limitations the authors state:
  • The treatment and observation period was short, mainly because the aggressiveness of the model affected the animals' well-being.
  • The growth-inhibiting effect of vismodegib seen in cell culture may have resulted from off-target effects.
  • The lack of statistical significance in the bioluminescence growth measurements may be partly due to the high standard deviation of the measurement.
  • The experiment using human MPM culture fluid could not be repeated because no material was available.
  • The rat and mouse cell lines were tested for Mycoplasma but were not authenticated by the authors.
  • The cell-culture conditions may not fully reproduce the tumor environment inside the body.

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, Immunohistochemistry, Fibroblast.

Related studies

• Targeting of the Hedgehog signal transduction pathway suppresses survival of malignant pleural mesothelioma cells in vitro — M. You, J. Varona-Santos, et al. (2014)
• Gli as a novel therapeutic target in malignant pleural mesothelioma — H. Li, N. Lui, et al. (2013)
• Inhibition of hedgehog signaling reduces the side population in human malignant mesothelioma cell lines — H.A. Kim, M.C. Kim, et al. (2015)
• Fibrous stroma: Driver and passenger in cancer development — V. Sharma, J. Letson, et al. (2022)
• Group I p21-activated kinases (PAKs) promote tumor cell proliferation and survival through the AKT1 and Raf-MAPK pathways — C.W. Menges, E. Sementino, et al. (2012)
• Adiponectin pathway attenuates malignant mesothelioma cell growth — K. Niu, M. Asada, et al. (2012)

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