Mitochondria-derived reactive oxygen species drive GANT61-induced mesothelioma cell apoptosis

Our plain-English summary of Mitochondria-derived reactive oxygen species drive GANT61-induced mesothelioma cell apoptosis, by C.B. Lim, C.M. Prêle, S. Baltic, et al (Oncotarget, 2015).

The study

• Authors: C.B. Lim, C.M. Prêle, S. Baltic, P.G. Arthur, J. Creaney, D.N. Watkins, P.J. Thompson, S.E. Mutsaers
• Journal: Oncotarget
• Published: 2015;6(3):1519-30
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Gli transcription factors of the Hedgehog (Hh) pathway have been reported to be drivers of malignant mesothelioma (MMe) cell survival. The Gli inhibitor GANT61 induces apoptosis in various cancer cell models, and has been associated directly with Gli inhibition. However various chemotherapeutics can induce cell death through generation of reactive oxygen species (ROS) but whether ROS mediates GANT61-induced apoptosis is unknown. In this study human MMe cells were treated with GANT61 and the mechanisms regulating cell death investigated. Exposure of MMe cells to GANT61 led to G1 phase arrest and apoptosis, which involved ROS but not its purported targets, GLI1 or GLI2. GANT61 triggered ROS generation and quenching of ROS protected MMe cells from GANT61-induced apoptosis. Furthermore, we demonstrated that mitochondria are important in mediating GANT61 effects: (1) ROS production and apoptosis were blocked by mitochondrial inhibitor rotenone; (2) GANT61 promoted superoxide formation in mitochondria; and (3) mitochondrial DNA-deficient LO68 cells failed to induce superoxide, and were more resistant to apoptosis induced by GANT61 than wild-type cells. Our data demonstrate for the first time that GANT61 induces apoptosis by promoting mitochondrial superoxide generation independent of Gli inhibition, and highlights the therapeutic potential of mitochondrial ROS-mediated anticancer drugs in MMe.

In plain English

This was a laboratory study of human malignant mesothelioma cells grown in dishes. It did not study asbestos exposure or patients. The authors treated mesothelioma cell lines with GANT61, an experimental drug meant to block Gli proteins, and studied how it killed the cells. GANT61 slowed the growth of all the mesothelioma cell lines tested. JU77 cells were the most sensitive (half of growth blocked at 4.02 micromolar) and NO36 the most resistant (31.8 micromolar). Most of the detailed experiments used LO68 cells. In these cells, GANT61 caused cell death (apoptosis) and raised levels of reactive oxygen species (ROS), and both rose with dose and time. The antioxidant NAC protected the cells. Reducing GLI1 and GLI2 expression with siRNA, singly or together, did not cause cell death, stop the cell cycle or raise ROS. Rotenone, which blocks complex I of the mitochondria, reduced the ROS and partly reduced the cell death caused by GANT61. LO68 cells lacking mitochondrial DNA showed negligible apoptosis after GANT61. The authors concluded this was the first report of GANT61 causing apoptosis through mitochondrial ROS.

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 (in vitro) cell-culture experiment
• Who was studied: Human malignant mesothelioma cell lines (MSTO-211H, NCI-H28, JU77, LO68, NO36, ONE58, STY51, GAY2911, OLD1612, VGE), with most experiments in LO68 cells; the colon cancer cell lines HCT116 and HT29 were also used
• Exposure: The drug GANT61, a Gli inhibitor, at 0.2 to 50 μM in growth tests and 10 to 30 μM in most other experiments; no asbestos exposure was studied
• Main results:
  • GANT61 inhibited growth of all mesothelioma cell lines; JU77 was the most sensitive (IC50 = 4.02 μM) and NO36 the most resistant (IC50 = 31.8 μM)
  • In LO68 cells, GANT61 increased apoptotic cell death in a dose- and time-dependent manner
  • GANT61 raised ROS levels in LO68 cells in a dose- and time-dependent manner
  • GANT61 also triggered ROS in HCT116 and HT29 colon cancer cells
  • Pretreatment with the antioxidant NAC protected LO68 cells from GANT61-induced apoptosis
  • siRNA knockdown of GLI1 and/or GLI2 mRNA in LO68 cells did not cause cell death (under 5% of knockdown cells in sub-G1 versus about 5% of control cells), did not cause G1 arrest and did not generate ROS
  • Rotenone, a mitochondrial complex I inhibitor, significantly blocked GANT61-induced ROS production and apoptosis in LO68 cells, although the authors described the blockade of apoptosis as partial
  • LO68 cells lacking mitochondrial DNA (LO68 ρ0 cells) showed negligible apoptosis after GANT61
  • With cisplatin, apoptosis did not differ statistically between LO68 and LO68 ρ0 cells (p greater than 0.05)
• The authors' conclusion: The authors concluded this was the first report of GANT61 causing apoptosis through mitochondrial ROS, and that their results offer an initial proof-of-concept that mitochondrial ROS-mediated anticancer mechanisms may be used for therapeutic benefit in mesothelioma
• Limitations the authors state:
  • The authors stated it was hard to determine which specific ROS species GANT61 generated in LO68 cells
  • Because rotenone only partly blocked GANT61-induced apoptosis, the authors said there could be other sites of ROS production

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: Reactive Oxygen Species (ROS), Mesothelioma, Apoptosis, Malignant Mesothelioma, Superoxide.

Related studies

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• Pemetrexed induces apoptosis in malignant mesothelioma and lung cancer cells through activation of reactive oxygen species and inhibition of sirtuin 1 — K.E. Hwang, Y.S. Kim, et al. (2015)
• Beyond foreign-body-induced carcinogenesis: impact of reactive oxygen species derived from inflammatory cells in tumorigenic conversion and tumor progression — F. Okada (2007)
• Inhibition of NADPH oxidase 4 induces apoptosis in malignant mesothelioma: Role of reactive oxygen species — M. Tanaka, Y. Miura, et al. (2015)
• The latent form of TGFbeta(1) is induced by TNFalpha through an ERK specific pathway and is activated by asbestos-derived reactive oxygen species in vitro and in vivo — D.E. Sullivan, M. Ferris, et al. (2008)
• Enhanced apoptosis by pemetrexed and simvastatin in malignant mesothelioma and lung cancer cells by reactive oxygen species-dependent mitochondrial dysfunction and Bim induction — K.E. Hwang, Y.S. Kim, et al. (2014)

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