Combination of EZH2 and ATM inhibition in BAP1-deficient mesothelioma

Our plain-English summary of Combination of EZH2 and ATM inhibition in BAP1-deficient mesothelioma, by N. Landman, D. Hulsman, J. Badhai, et al (British Journal of Cancer, 2024).

The study

• Authors: N. Landman, D. Hulsman, J. Badhai, J. Kopparam, J. Puppe, G.K. Pandey, M. van Lohuizen
• Journal: British Journal of Cancer
• Published: 2024;130(11):1855-1865
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: More than half of mesothelioma tumours show alterations in the tumour suppressor gene BAP1. BAP1-deficient mesothelioma is shown to be sensitive to EZH2 inhibition in preclinical settings but only showed modest efficacy in clinical trial. Adding a second inhibitor could potentially elevate EZH2i treatment efficacy while preventing acquired resistance at the same time.

Methods: A focused drug synergy screen consisting of 20 drugs was performed by combining EZH2 inhibition with a panel of anti-cancer compounds in mesothelioma cell lines. The compounds used are under preclinical investigation or already used in the clinic. The synergistic potential of the combinations was assessed by using the Bliss model. To validate our findings, in vivo xenograft experiments were performed.

Results: Combining EZH2i with ATMi was found to have synergistic potential against BAP1-deficient mesothelioma in our drug screen, which was validated in clonogenicity assays. Tumour growth inhibition potential was significantly increased in BAP1-deficient xenografts. In addition, we observe lower ATM levels upon depletion of BAP1 and hypothesise that this might be mediated by E2F1.

Conclusions: We demonstrated the efficacy of the combination of ATM and EZH2 inhibition against BAP1-deficient mesothelioma in preclinical models, indicating the potential of this combination as a novel treatment modality using BAP1 as a biomarker.

© 2024. The Author(s).

In plain English

This was a laboratory study, in cells and mice, of possible drug treatment for mesothelioma whose tumour cells lack a working BAP1 gene. It did not study asbestos exposure. The authors tested the EZH2 inhibitor GSK126 together with each of 20 anti-cancer compounds in mouse mesothelioma cell lines and in 8 human mesothelioma cell lines (4 BAP1 mutant, 4 BAP1 wild-type). The ATM inhibitor AZD1390 gave high synergy scores with GSK126 in Bap1-deficient mouse cells, and in human cells almost only in BAP1-deficient lines. In colony-growth tests, the combination worked well in all four BAP1-negative human lines, where single drugs had no or limited effect. In mice carrying human BAP1-deficient tumours, 5 to 7 mice per group treated for 28 days, the combination significantly slowed tumour growth. In tumours with BAP1 restored, no statistically significant differences were seen. Lowering BAP1 in cells also lowered ATM levels. The authors concluded that combining EZH2 and ATM inhibition was highly synergistic in preclinical models of BAP1-deficient 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: Preclinical laboratory study: a drug combination (synergy) screen in mouse and human mesothelioma cell lines, follow-up cell experiments, and xenograft experiments in mice
• Who was studied: Mouse mesothelioma cell lines derived from the authors' mouse models, with and without Bap1. Also 8 human malignant mesothelioma cell lines (4 BAP1 mutant, 4 BAP1 wild-type), and a human NCI-H226 cell line with and without re-expressed BAP1. These cells were grown as tumours under the skin of NOD-Scid IL2Rγnull mice, 5 to 7 mice per treatment group, at the Netherlands Cancer Institute.
• Exposure: No asbestos exposure was studied. The exposures were drugs: the EZH2 inhibitor GSK126 combined with each of 20 anti-cancer compounds, chiefly the ATM inhibitor AZD1390. In mice, AZD1390 was given at 15 mg/kg and GSK126 at 30 mg/kg, each once daily into the abdomen, for 28 days.
• Main results:
  • In the screen, the ATM inhibitor AZD1390 combined with GSK126 showed high synergy scores in Bap1-deficient mouse cell lines, and in human cell lines almost exclusively in BAP1-deficient cells.
  • ATM inhibition alone showed no clear difference in sensitivity between BAP1-deficient and BAP1-proficient human cell lines.
  • In colony-formation assays, the combination showed high efficacy in all four BAP1-negative human lines, while single compounds had no or limited effect. Single or combined treatment had no or little effect on BAP1-proficient lines.
  • Apoptosis (cell death) increased significantly with the combination in BAP1-deficient cell lines but not in BAP1-proficient cell lines.
  • In NCI-H226 cells, the synergy score of the combination was lower in the variant with BAP1 re-expressed. The figure shows a mean of 43.55 for NCI-H226 and 9.86 for NCI-H226 + BAP1 WT.
  • In mice, the combination, unlike single drugs, resulted in significant growth inhibition of BAP1-deficient NCI-H226 xenografts. Tumour weight in this group was lower than with single drugs. In BAP1-proficient xenografts no statistically significant differences were observed.
  • Acute depletion of BAP1 in cells lowered ATM protein and mRNA levels. Lower ATM levels were not consistently seen in BAP1-deficient tumour cell lines.
  • After BAP1 knock-down, RT-qPCR showed significant upregulation of E2F1 only. The authors suggested BAP1 might regulate ATM indirectly via E2F1.
• The authors' conclusion: The authors concluded that simultaneous inhibition of EZH2 and ATM is a highly synergistic regimen against preclinical models of BAP1-deficient mesothelioma. They said this warrants investigating its clinical possibilities.
• Limitations the authors state:
  • The authors noted inconsistencies in synergy scores between mouse and human cell lines. Some combinations synergistic in mouse cells were not necessarily synergistic in human cells.
  • The authors stated that the lack of ATM differences between BAP1-proficient and BAP1-deficient cell lines, possibly due to a compensatory mechanism in culture, needs 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: BAP1, Mesothelioma, Clinical Trial, Biomarker.

Related studies

• Combined Inhibition of EZH2 and FGFR is Synergistic in BAP1-deficient Malignant Mesothelioma — J. Badhai, N. Landman, et al. (2024)
• Diagnostic utility of BAP1 and EZH2 expression in malignant mesothelioma — A. Shinozaki-Ushiku, T. Ushiku, et al. (2017)
• Diagnostic Utility of BAP1, EZH2 and Survivin in Differentiating Pleural Epithelioid Mesothelioma and Reactive Mesothelial Hyperplasia: Immunohistochemical Study — S.A. Hakim, H.H. Abou Gabal (2021)
• Highly expressed EZH2 in combination with BAP1 and MTAP loss, as detected by immunohistochemistry, is useful for differentiating malignant pleural mesothelioma from reactive mesothelial hyperplasia — M. Yoshimura, Y. Kinoshita, et al. (2019)
• Loss of BAP1 function leads to EZH2-dependent transformation — L.M. LaFave, W. Béguelin, et al. (2015)
• EZH2 Inhibition in Mesothelioma Cells Increases the Release of Extracellular Vesicles That Skew Neutrophils Toward a Protumor Phenotype — G. Pinton, E. Bari, et al. (2025)

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