HMGB1 targeting by ethyl pyruvate suppresses malignant phenotype of human mesothelioma

Our plain-English summary of HMGB1 targeting by ethyl pyruvate suppresses malignant phenotype of human mesothelioma, by L. Pellegrini, J. Xue, D. Larson, et al (Oncotarget, 2017).

The study

• Authors: L. Pellegrini, J. Xue, D. Larson, S. Pastorino, S. Jube, K.H. Forest, Z.S. Saad-Jube, A. Napolitano, I. Pagano, V.S. Negi, M.E. Bianchi, P. Morris, H.I. Pass, G. Gaudino, M. Carbone, H. Yang
• Journal: Oncotarget
• Published: 2017;8(14):22649-22661
• Cited by: 47 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Human malignant mesothelioma (MM) is an aggressive cancer linked to asbestos and erionite exposure. We previously reported that High-Mobility Group Box-1 protein (HMGB1), a prototypic damage-associated molecular pattern, drives MM development and sustains MM progression. Moreover, we demonstrated that targeting HMGB1 inhibited MM cell growth and motility in vitro, reduced tumor growth in vivo, and prolonged survival of MM-bearing mice. Ethyl pyruvate (EP), the ethyl ester of pyruvic acid, has been shown to be an effective HMGB1 inhibitor in inflammation-related diseases and several cancers. Here, we studied the effect of EP on the malignant phenotype of MM cells in tissue culture and on tumor growth in vivo using an orthotopic MM xenograft model. We found that EP impairs HMGB1 secretion by MM cells leading to reduced RAGE expression and NF-κB activation. As a consequence, EP impaired cell motility, cell proliferation, and anchorage-independent growth of MM cells. Moreover, EP reduced HMGB1 serum levels in mice and inhibited the growth of MM xenografts.Our results indicate that EP effectively hampers the malignant phenotype of MM, offering a novel potential therapeutic approach to patients afflicted with this dismal disease.

In plain English

This was a laboratory study, not a study of people. The authors tested whether ethyl pyruvate (EP), a compound previously reported to inhibit the protein HMGB1, affected human malignant mesothelioma cells in culture and tumors in mice. In two mesothelioma cell lines, REN and HP3, EP lowered the amount of HMGB1 the cells released. It also reduced RAGE, an HMGB1 receptor, and NF-κB activity. Cell viability fell after 24 hours only at a high dose (40 mM); at 10 mM, cell counts fell only after 5 days. EP slowed cell movement and reduced colony growth in soft agar. Migration of PPM-MILL, a cell line that does not depend on HMGB1, was unaffected. Twenty mice were injected in the abdomen with REN cells. The ten given EP had smaller tumors and lower blood HMGB1 than the ten controls. Survival did not differ significantly; the authors noted the experiment was not sized to detect this. EP also reduced foci formation in crocidolite-exposed human mesothelial cells grown with macrophages, and lowered blood HMGB1 in crocidolite-injected mice. The authors concluded that EP may be a reasonable treatment candidate.

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: cell-culture experiments on human mesothelioma cell lines and mouse experiments (an orthotopic human mesothelioma xenograft model, plus a short crocidolite injection experiment)
• Who was studied: Two HMGB1-secreting human malignant mesothelioma cell lines (REN and HP3), plus a non-HMGB1-dependent line (PPM-MILL); primary human mesothelial cells co-cultured with macrophages; 20 female immunodeficient (NOD.CB17-SCID) mice injected intraperitoneally with REN cells (10 per group); BALB/c female mice in groups of 5 for the asbestos experiment
• Exposure: Ethyl pyruvate (EP) at various concentrations in culture (for example 1, 2.5, 5, 10 and 40 mM). In xenograft mice: 2 mg (100 mg/kg/day) EP per injection, three times a week for 8 weeks. Crocidolite asbestos was used to induce transformation in cell co-cultures (5 µg/cm2) and was injected intraperitoneally into mice (1 mg).
• Main results:
  • In REN and HP3 cells, EP (5 mM, 48 h) reduced HMGB1 released into the culture medium compared with vehicle-treated cells, and HMGB1 accumulated in the cell nucleus
  • EP reduced RAGE mRNA levels in both cell lines
  • EP inhibited NF-κB p65 movement into the nucleus in both REN and HP3 cells
  • Viability of both cell lines fell after 24 h only at 40 mM EP; 10 mM EP reduced cell count only after 5 days
  • EP delayed wound closure and migration of REN and HP3 cells compared with controls
  • Migration of PPM-MILL, a mesothelioma cell line not dependent on HMGB1, was not affected by EP
  • EP reduced colony growth in soft agar (anchorage-independent growth) in both REN and HP3 cells; in HP3, 1 mM was enough
  • In xenograft mice, the EP-treated group had lower serum HMGB1 than untreated animals two months after tumor cell injection
  • Tumors in the EP-treated mice were significantly smaller (t(145) = 5.3, p less than 0.0001)
  • There was no statistically significant survival difference between groups; the authors reported a trend toward improved survival in EP-treated mice
  • No systemic toxicity, measured as body weight change, was seen with EP in the mice
  • In co-cultures of human mesothelial cells and macrophages exposed to crocidolite, EP reduced the number of foci (transformed cell clusters)
  • In mice injected with crocidolite, EP reduced serum HMGB1 levels
• The authors' conclusion: The authors concluded that EP may represent a reasonable therapeutic candidate for malignant mesothelioma treatment, acting by inhibiting the HMGB1-RAGE signaling axis. They also suggested that EP, by targeting HMGB1, can inhibit asbestos-mediated carcinogenesis.
• Limitations the authors state:
  • The mouse experiment was not powered to detect a difference in survival
  • The study could not tell how much of the lower HMGB1 in treated mice came directly from EP and how much came from the mice having smaller tumors
  • EP was not directly compared with other HMGB1 inhibitors

Topics

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

Medical terms in this study, explained in our Lexicon: High Mobility Group Box 1 (HMGB1), Mesothelioma, Malignant Mesothelioma, erionite, Inflammation.

Related studies

• Continuous exposure to chrysotile asbestos can cause transformation of human mesothelial cells via HMGB1 and TNF-α signaling — F. Qi, G. Okimoto, et al. (2013)
• Asbestos induces mesothelial cell transformation via HMGB1-driven autophagy — J. Xue, S. Patergnani, et al. (2020)
• Cancer cell secretion of the DAMP protein HMGB1 supports progression in malignant mesothelioma — S. Jube, Z.S. Rivera, et al. (2012)
• HMGB1 and Its Hyperacetylated Isoform are Sensitive and Specific Serum Biomarkers to Detect Asbestos Exposure and to Identify Mesothelioma Patients — A. Napolitano, D.J. Antoine, et al. (2016)
• BAP1 forms a trimer with HMGB1 and HDAC1 that modulates gene × environment interaction with asbestos — F. Novelli, A. Bononi, et al. (2021)
• HMGB1 released by mesothelial cells drives the development of asbestos-induced mesothelioma — J.S. Suarez, F. Novelli, et al. (2023)

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