Mitochondrial-targeted nitroxides disrupt mitochondrial architecture and inhibit expression of peroxiredoxin 3 and FOXM1 in malignant mesothelioma cells

Our plain-English summary of Mitochondrial-targeted nitroxides disrupt mitochondrial architecture and inhibit expression of peroxiredoxin 3 and FOXM1 in malignant mesothelioma cells, by B. Cunniff, K. Benson, J. Stumpff, et al (Journal of Cellular Physiology, 2013).

The study

• Authors: B. Cunniff, K. Benson, J. Stumpff, K. Newick, P. Held, D. Taatjes, J. Joseph, B. Kalyanaraman, N.H. Heintz
• Journal: Journal of Cellular Physiology
• Published: 2013;228(4):835-45
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an intractable tumor of the peritoneal and pleural cavities primarily linked to exposure to asbestos. Recently, we described an interplay between mitochondrial-derived oxidants and expression of FOXM1, a redox-responsive transcription factor that has emerged as a promising therapeutic target in solid malignancies. Here we have investigated the effects of nitroxides targeted to mitochondria via triphenylphosphonium (TPP) moieties on mitochondrial oxidant production, expression of FOXM1 and peroxiredoxin 3 (PRX3), and cell viability in MM cells in culture. Both Mito-carboxy-proxyl (MCP) and Mito-TEMPOL (MT) caused dose-dependent increases in mitochondrial oxidant production that was accompanied by inhibition of expression of FOXM1 and PRX3 and loss of cell viability. At equivalent concentrations TPP, CP, and TEMPOL had no effect on these endpoints. Live cell ratiometric imaging with a redox-responsive green fluorescent protein targeted to mitochondria (mito-roGFP) showed that MCP and MT, but not CP, TEMPOL, or TPP, rapidly induced mitochondrial fragmentation and swelling, morphological transitions that were associated with diminished ATP levels and increased production of mitochondrial oxidants. Mdivi-1, an inhibitor of mitochondrial fission, did not rescue mitochondria from fragmentation by MCP. Immunofluorescence microscopy experiments indicate a fraction of FOXM1 coexists in the cytoplasm with mitochondrial PRX3. Our results indicate that MCP and MT inhibit FOXM1 expression and MM tumor cell viability via perturbations in redox homeostasis caused by marked disruption of mitochondrial architecture, and suggest that both compounds, either alone or in combination with thiostrepton or other agents, may provide credible therapeutic options for the management of MM.

Copyright © 2012 Wiley Periodicals, Inc.

In plain English

This laboratory study tested two experimental compounds, Mito-carboxy-proxyl (MCP) and Mito-TEMPOL (MT), on human malignant mesothelioma cells grown in culture. It did not study asbestos exposure or patients. The authors used two mesothelioma cell lines (HMESO1, called HM, and H2373) and compared them with LP9, an immortalized human mesothelial cell line. The mesothelioma cells made more mitochondrial oxidants than LP9 cells. MCP and MT raised oxidant levels in the mesothelioma cells as the dose increased, with significant increases at doses as low as 400 nM. At equivalent concentrations, the control compounds CP, TEMPOL and TPP had no effect on the endpoints measured, including oxidant production, mitochondrial structure and cell viability. MCP and MT broke the cells' mitochondria into fragments and vesicles, and MCP lowered ATP levels and mitochondrial membrane potential. MCP also reduced levels of the proteins FOXM1 and PRX3. MCP combined with the antibiotic thiostrepton had additive effects in reducing cell growth. The authors concluded that MCP and MT inhibit FOXM1 expression and mesothelioma cell viability by disrupting mitochondrial structure, and suggested they may provide therapeutic options. They noted that several mechanisms still need study.

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) experiments on human cell lines grown in culture
• Who was studied: Two human malignant mesothelioma cell lines: HMESO1 (HM, epithelioid in culture) and H2373 (fibrosarcomatoid). These were compared with LP9, an hTERT-immortalized human mesothelial cell line. SKOV3 ovarian cancer cells were also mentioned for one observation. No human subjects were studied.
• Exposure: No asbestos exposure was studied. Cells were treated with the mitochondria-targeted nitroxides MCP and MT. Controls were the untargeted parent compounds CP and TEMPOL and the targeting moiety TPP. Rotenone, mdivi-1 and thiostrepton were also used.
• Main results:
  • Mitochondrial oxidant levels were higher in the mesothelioma cell lines than in LP9 mesothelial cells at all phases of the cell cycle.
  • Rotenone increased FOXM1 expression in LP9 cells but decreased it in HM mesothelioma cells.
  • In mesothelioma cells, MCP and MT caused dose-dependent increases in the cellular oxidant signal (DHE fluorescence), significant at doses as low as 400 nM.
  • CP, TEMPOL and TPP did not change mitochondrial oxidant production in mesothelioma cells at any concentration tested.
  • At concentrations equivalent to those of MCP and MT, CP, TEMPOL and TPP had no effect on FOXM1 expression, mitochondrial architecture or cell viability.
  • In HM cells, MCP and MT markedly reduced mitochondrial form factor, a measure of mitochondrial length and branching.
  • Pre-treatment with mdivi-1, an inhibitor of mitochondrial fission, did not prevent the effect of MCP on mitochondrial architecture.
  • MCP led to moderate but significant decreases in ATP levels in mesothelioma cells after 6 hours.
  • MCP caused a marked loss of mitochondrial membrane potential. CP did not.
  • Under electron microscopy, mitochondria of MCP-treated HM cells appeared swollen, with loss of cristae.
  • In HM and H2373 cells, mdivi-1 caused a dose-dependent loss of FOXM1 protein after 12 hours.
  • MCP reduced FOXM1 and PRX3 protein levels in mesothelioma cells. CP and TPP had no effect at the same concentrations.
  • MCP did not affect levels of cytosolic PRX1.
  • Immunofluorescence microscopy showed that a significant fraction of FOXM1 coexisted with mitochondrial PRX3 in HM cells.
  • MCP combined with thiostrepton had additive effects in inhibiting cell growth in both HM and H2373 cells.
• The authors' conclusion: The authors concluded that MCP and MT inhibit FOXM1 expression and mesothelioma tumor cell viability through disturbed redox balance, caused by marked disruption of mitochondrial architecture. They suggested that both compounds, alone or combined with thiostrepton or other agents, may provide therapeutic options for mesothelioma.
• Limitations the authors state:
  • The authors did not investigate sulfiredoxin, so it is unclear whether hyper-oxidized PRX3 is repaired over time in mesothelioma cells.
  • A much better understanding of FOXM1 isoforms is needed before the mechanism of each agent can be worked out.
  • Studies of DRP1 in mesothelioma cells are still needed to determine whether enhanced mitochondrial fission is a characteristic of mesothelioma.
  • A possible increase in autophagosomes in MCP-treated cells was noted but requires further investigation.

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma.

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