Gli as a novel therapeutic target in malignant pleural mesothelioma

Our plain-English summary of Gli as a novel therapeutic target in malignant pleural mesothelioma, by H. Li, N. Lui, T. Cheng, et al (PloS One, 2013).

The study

• Authors: H. Li, N. Lui, T. Cheng, H.H. Tseng, D. Yue, E. Giroux-Leprieur, H.T. Do, Q. Sheng, J.Q. Jin, T.W. Luh, D.M. Jablons, B. He
• Journal: PloS One
• Published: 2013;8(3):e57346
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is a highly aggressive tumor with poor prognosis. Current treatment is rarely curative, thus novel meaningful therapies are urgently needed. Inhibition of Hedgehog (Hh) signaling at the cell membrane level in several cancers has shown anti-cancer activity in recent clinical studies. Evidence of Hh-independent Gli activation suggests Gli as a more potent therapeutic target. The current study is aimed to evaluate the potential of Gli as a therapeutic target to treat MPM. The expression profiles of Gli factors and other Hh signaling components were characterized in 46 MPM patient tissue samples by RT-PCR and immunohistochemistry. Cultured cell lines were employed to investigate the requirement of Gli activation in tumor cell growth by inhibiting Gli through siRNA or a novel small molecule Gli inhibitor (Gli-I). A xenograft model was used to evaluate Gli-I in vivo. In addition, a side by side comparison between Gli and Smoothened (Smo) inhibition was conducted in vitro using siRNA and small molecule inhibitors. Our study reported aberrant Gli1 and Gli2 activation in a large majority of tissues. Inhibition of Gli by siRNAs or Gli-I suppressed cell growth dramatically both in vitro and in vivo. Inhibition of Gli exhibited better cytotoxicity than that of Smo by siRNA and small molecule inhibitors vismodegib and cyclopamine. Combination of Gli-I and pemetrexed, as well as Gli-I and vismodegib demonstrated synergistic effects in suppression of MPM proliferation in vitro. In summary, Gli activation plays a critical role in MPM. Inhibition of Gli function holds strong potential to become a novel, clinically effective approach to treat MPM.

In plain English

This laboratory study asked whether Gli proteins could be a treatment target in malignant pleural mesothelioma. It did not study asbestos exposure. The authors analyzed tumors from 46 patients who had surgery (35 men, 11 women) and normal pleura from 7 patients. They also ran experiments on mesothelioma cell lines and in mice. Protein staining, done on tissue slides available for 27 tumors, found more than 90% positive for Gli1 and Gli2. Levels of gli2 RNA were on average 2.4 times as high in tumors as in normal pleura. Blocking Gli1 and Gli2 together reduced cancer cell growth, both with siRNA (molecules that temporarily switch off genes) and with the authors' experimental compound Gli-I. siRNA against either one alone did not significantly reduce growth. Gli-I worked at lower doses than vismodegib and cyclopamine, two drugs that act on a different protein, Smo. In mice with mesothelioma tumors, Gli-I reduced tumor growth by 51% after 14 days of treatment compared with control mice. Gli-I was tested only in cells and mice. The authors concluded that Gli-I has strong potential as a treatment.

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: analysis of patient tumor tissue, experiments on cultured mesothelioma cell lines, and an animal experiment (mouse xenograft)
• Who was studied: Tumor tissue came from 46 patients who had surgical resection for malignant pleural mesothelioma at UCSF (11 female, 35 male; average age 67.2 years, standard deviation 10.7). Of these tumors, 39 were epithelioid, 2 sarcomatous and 5 undetermined. Normal adjacent pleura came from 7 patients. Formalin-fixed, paraffin-embedded tissue (used to make slides) was available from 27 patients. The study also used human mesothelioma cell lines (NCI-H28, MS-1, REN, H2052, H2452, H290) and nude mice injected with MS-1 cells. No study dates are given.
• Exposure: No asbestos or other fiber exposure was studied. The experimental treatments were:
• the authors' Gli inhibitor (Gli-I);
• the Smo inhibitors vismodegib and cyclopamine;
• siRNAs that temporarily switch off genes (gli1 and gli2 together, or smo);
• Gli-I combined with vismodegib or with the chemotherapy drug pemetrexed.
  In mice, Gli-I was given at 50 mg/kg by injection for 14 days.
• Main results:
  • Protein staining used slides from the 27 patients with paraffin-embedded tissue. More than 90% of these tumor samples were positive for Gli1, Gli2 and Smo protein. Only 47% showed mild SHh expression.
  • Average gli2 RNA levels were 2.4 fold as high in the 46 tumor samples as in the 7 normal pleura samples (p less than 0.01). gli1 levels were statistically comparable.
  • No correlation was observed between shh and gli1 or gli2 expression in the tumor tissues.
  • Switching off both gli1 and gli2 together with siRNA significantly inhibited cell growth within 72 hours in all three cell lines tested (H28, REN, MS-1).
  • siRNA against gli1 alone or gli2 alone did not significantly inhibit cell growth. These data were not shown in the article.
  • Switching off gli1 and gli2 inhibited cell survival significantly better than switching off smo in two cell lines: MS1 (p less than 0.05) and REN (p less than 0.001). The effects were comparable in H28.
  • In five mesothelioma cell lines, the concentrations of Gli-I needed to halve cell growth (IC50) were much lower than those of vismodegib and cyclopamine. The Gli-I values ranged from 3.75 to 13.63, but the units are garbled in the text.
  • In mice with MS-1 tumors, Gli-I reduced tumor growth by 51% at the end of the 14-day treatment compared with control mice (p less than 0.05). Seven days after treatment stopped, the reduction was 63% (p less than 0.01).
  • In cell lines, Gli-I combined with vismodegib showed synergistic effects at lower dose and additive effects at higher dose. Gli-I combined with pemetrexed showed a synergistic effect.
• The authors' conclusion: The authors concluded that Gli proteins play a critical role in malignant pleural mesothelioma. They also concluded that their Gli inhibitor, Gli-I, has strong potential to become a clinically effective treatment.
• Limitations the authors state:
  • When explaining why their results differed from another study's, the authors pointed to two factors: their small number of patients, and the limited normal pleura samples used as the comparison baseline.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Prognosis, Immunohistochemistry, Pemetrexed (Alimta), Synergistic Effect.

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)
• Discussion — (2014)
• Targeting YAP in malignant pleural mesothelioma — W.Q. Zhang, Y.Y. Dai, et al. (2017)
• Antagonizing the Hedgehog Pathway with Vismodegib Impairs Malignant Pleural Mesothelioma Growth In Vivo by Affecting Stroma — M. Meerang, K. Bérard, et al. (2016)
• Anetumab ravtansine: a novel mesothelin-targeting antibody-drug conjugate cures tumors with heterogeneous target expression favored by bystander effect — S. Golfier, C. Kopitz, et al. (2014)
• An RNAi-based screen reveals PLK1, CDK1 and NDC80 as potential therapeutic targets in malignant pleural mesothelioma — A. Linton, Y.Y. Cheng, et al. (2014)

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