ER Stress Response and Induction of Apoptosis in Malignant Pleural Mesothelioma: The Achilles Heel Targeted by the Anticancer Ruthenium Drug BOLD-100

Our plain-English summary of ER Stress Response and Induction of Apoptosis in Malignant Pleural Mesothelioma: The Achilles Heel Targeted by the Anticancer Ruthenium Drug BOLD-100, by E. Ranzato, G. Bonsignore, S. Martinotti (Cancers, 2022).

The study

• Authors: E. Ranzato, G. Bonsignore, S. Martinotti
• Journal: Cancers
• Published: 2022;14(17)
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma is a rare cancer arising from the serosal surfaces of the body, mainly from the pleural layer. This cancer is strongly related to asbestos exposure and shows a very inauspicious prognosis, because there are scarce therapeutic options for this rare disease. Thus, there is an urgent need to develop novel therapeutic approaches to treat this form of cancer. To explore the biology of malignant pleural mesothelioma (MPM), we previously observed that MPM cell lines show high expression of the GRP78 protein, which is a chaperone protein and the master regulator of the unfolded protein response (UPR) that resides in the endoplasmic reticulum (ER). Based on our previous studies showing the importance of GRP78 in MPM, we observed that BOLD-100, a specific modulator of GRP78 and the UPR, shows cytotoxicity against MPM cells. Our studies demonstrated that BOLD-100 increases ROS production and Ca2+ release from the ER, leading to ER stress activation and, ultimately, to cell death. Our in vitro data strongly suggest that BOLD-100 inhibits the growth of MPM cell lines, proposing the application as a single agent, or in combination with other standard-of-care drugs, to treat MPM.

In plain English

This was a laboratory study of cells grown in dishes. It did not study people or asbestos exposure. The authors tested an experimental ruthenium-based drug, BOLD-100, on two human malignant pleural mesothelioma cell lines (REN and MM98) and on a non-cancerous human mesothelial cell line (Met5A). The drug was less toxic to the non-cancerous cells. The EC50 at 24 hours (the drug concentration that reduced cell viability by half) was 111 µM (95% confidence interval 81 to 152) for REN, 219 µM (176 to 273) for MM98 and 572 µM (460 to 712) for Met5A. In REN cells, BOLD-100 reduced colony formation by 50% compared with untreated cells. It also raised oxidative stress (reactive oxygen species), released calcium from the endoplasmic reticulum (a compartment inside the cell), and activated markers of programmed cell death (apoptosis), including caspases and calpain. The oxidative stress and calcium changes were not seen in Met5A cells. The authors concluded that further in vivo studies, in living organisms, are urgently needed to explore BOLD-100 alone or with other drugs against malignant pleural mesothelioma.

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: In vitro laboratory experiment on cultured human cell lines, studying how the drug BOLD-100 acts
• Who was studied: Human cell lines, not patients: REN (epithelial-subtype malignant pleural mesothelioma), MM98 (established from the pleural effusion of a sarcomatous malignant pleural mesothelioma), and Met5A (non-cancerous human mesothelial cell line). After the first toxicity tests, most experiments used REN cells, with Met5A as the reference control.
• Exposure: No asbestos exposure was studied. Cells were treated with the ruthenium drug BOLD-100 at increasing concentrations (0 to 1000 µM in the toxicity tests) for 24 or 48 hours. Most mechanism experiments used 100 µM.
• Main results:
  • EC50 values in µM (95% confidence intervals): REN 111 (81 to 152) at 24 h and 71 (50 to 102) at 48 h; MM98 219 (176 to 273) at 24 h and 90 (70 to 116) at 48 h; Met5A (non-cancerous) 572 (460 to 712) at 24 h and 399 (249 to 636) at 48 h.
  • In REN cells treated with 100 µM BOLD-100 for 48 h, colony formation was reduced by 50% compared with the control.
  • In REN cells, adding caffeine (which blocks a calcium-release channel) or NAC (which removes reactive oxygen species) gave 3 to 4 times higher EC50 values than BOLD-100 alone, meaning less toxicity.
  • In REN cells, BOLD-100 activated caspase 3/7 and increased caspase 8 activity. The caspase 8 increase was abolished by a caspase-8 inhibitor.
  • In REN cells, BOLD-100 alone doubled calpain activation compared with the control.
  • In REN cells, BOLD-100 destabilized mitochondrial membranes. The mitochondrial red-to-green fluorescence ratio was significantly lower than in untreated cells.
  • After 4 h of BOLD-100, reactive oxygen species rose with dose in REN cells, while no change was seen in Met5A cells.
  • Basal ERO1α protein was about 4-fold higher in REN than in Met5A cells. 100 µM BOLD-100 raised ERO1α in REN cells about 2-fold from baseline.
  • BOLD-100 changed cytosolic calcium only in REN cells, not in Met5A cells. Pretreatment with thapsigargin removed the calcium peak, which the authors took to show that the endoplasmic reticulum was the source.
  • In REN cells at 24 and 48 h, GRP78 protein decreased over time while CHOP and XBP1 increased.
  • GRP78 on the REN cell surface increased at 1 h, peaked at 3 h, then decreased.
• The authors' conclusion: The authors concluded that their observations call for further in vivo studies, which they described as urgently needed, of BOLD-100 alone or combined with other drugs against malignant pleural mesothelioma. They described the work as the first demonstration of how BOLD-100 kills mesothelioma cells.

Topics

Medical terms in this study, explained in our Lexicon: Apoptosis, Pleural Mesothelioma, Malignant Mesothelioma, Serosal Surface, Asbestos Exposure, Prognosis.

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