Inhibition of the Histone Methyltransferase EZH2 Enhances Protumor Monocyte Recruitment in Human Mesothelioma Spheroids

Our plain-English summary of Inhibition of the Histone Methyltransferase EZH2 Enhances Protumor Monocyte Recruitment in Human Mesothelioma Spheroids, by S. Mola, G. Pinton, M. Erreni, et al (International Journal of Molecular Sciences, 2021).

The study

• Authors: S. Mola, G. Pinton, M. Erreni, M. Corazzari, M. De Andrea, A.A. Grolla, V. Martini, L. Moro, C. Porta
• Journal: International Journal of Molecular Sciences
• Published: 2021;22(9)
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is a highly aggressive cancer with a long latency period and dismal prognosis. Recently, tazemetostat (EPZ-6438), an inhibitor of the histone methyltransferase EZH2, has entered clinical trials due to the antiproliferative effects reported on MPM cells. However, the direct and indirect effects of epigenetic reprogramming on the tumor microenvironment are hitherto unexplored. To investigate the impact of tumor-associated macrophages (TAMs) on MPM cell responsiveness to tazemetostat, we developed a three-dimensional MPM spheroid model that recapitulates in vitro, both monocytes' recruitment in tumors and their functional differentiation toward a TAM-like phenotype (Mo-TAMs). Along with an increased expression of genes for monocyte chemoattractants, inhibitory immune checkpoints, immunosuppressive and M2-like molecules, Mo-TAMs promote tumor cell proliferation and spreading. Prolonged treatment of MPM spheroids with tazemetostat enhances both the recruitment of Mo-TAMs and the expression of their protumor phenotype. Therefore, Mo-TAMs profoundly suppress the antiproliferative effects due to EZH2 inhibition in MPM cells. Overall, our findings indicate that TAMs are a driving force for MPM growth, progression, and resistance to tazemetostat; therefore, strategies of TAM depletion might be evaluated to improve the therapeutic efficacy of pharmacological inhibition of EZH2.

In plain English

This was a laboratory study using a three-dimensional cell culture model, not a study of patients. The authors grew the human biphasic mesothelioma cell line MSTO-211H as multicellular spheroids and added monocytes freshly isolated from the blood (buffy coats) of healthy donors; the epithelioid BR-95 line was used only in separate monolayer experiments with monocyte-conditioned medium. Spheroids were treated with the EZH2 inhibitor EPZ-6438 (tazemetostat, 10 micromolar) or vehicle. EPZ-6438 reduced spheroid volume and raised the cell-cycle inhibitor p21. Monocytes migrated into the spheroids and differentiated: control monocytes were mainly CD14+CD16- (86.9 plus or minus 3.5 percent), whereas after 48 hours of coculture 21.1 plus or minus 1.1 percent were CD14+CD16 intermediate and 54 plus or minus 1.8 percent CD14+CD16+. These spheroid-derived macrophage-like cells (Mo-TAMs) expressed M2-like and immunosuppressive genes and increased spheroid growth. EPZ-6438 raised tumour-cell expression of monocyte-attracting molecules and monocyte infiltration, and strengthened the Mo-TAM protumour gene profile; Mo-TAMs in turn cancelled the drug's antiproliferative effect and reverted p21 induction.

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 study using a three-dimensional multicellular spheroid model of human mesothelioma cells cocultured with primary human monocytes
• Who was studied: Human mesothelioma cell lines (biphasic MSTO-211H used for spheroids; epithelioid BR-95 used only in monolayer conditioned-medium experiments) and monocytes isolated from buffy coats of healthy donors; no patients studied
• Exposure: The EZH2 inhibitor EPZ-6438 (tazemetostat), 10 micromolar, for 24 to 96 hours, with or without coculture with monocytes; polarizing stimuli LPS, IFN-gamma, IL-4, IL-10
• Main results:
  • EPZ-6438 treatment of tumour spheroids alone reduced spheroid volume and increased the cell cycle inhibitor p21
  • After 48 hours of coculture most monocytes had differentiated toward macrophages, compared with monocytes cultured alone
  • Spheroid-infiltrating monocytes (Mo-TAMs) acquired an M2-skewed phenotype
  • Coculture with monocytes increased spheroid volume compared with spheroids alone
  • EPZ-6438 treatment of spheroids increased transcripts for monocyte-recruiting molecules and increased monocyte infiltration
  • EPZ-6438 did not change monocyte chemokine/growth factor receptor expression
  • Mo-TAMs from EPZ-6438-treated spheroids upregulated many protumour genes compared with Mo-TAMs from vehicle-treated spheroids
  • In coculture with monocytes, the antiproliferative effect of EPZ-6438 on spheroids was lost; spheroid volume roughly doubled and p21 induction was reverted
  • Monocytes increased tumour cell spreading from spheroids and MMP9 expression in tumour cells
  • Medium from M1-polarized monocytes killed MSTO-211H and BR-95 monolayers, but in the spheroid model M1 and M0 monocytes acted similarly in promoting spreading
• The authors' conclusion: The authors concluded that TAMs drive mesothelioma growth, progression and resistance to tazemetostat, and that strategies of TAM depletion might be evaluated to improve the efficacy of EZH2 inhibition
• Limitations the authors state:
  • The epithelial-mesenchymal transition findings were limited to the biphasic model; the authors said work with epithelioid spheroids is needed
  • Whether the increased macrophage infiltration seen in vitro would occur in patients, alongside T cell recruitment, and what it would mean clinically, was not answered by this study

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleural Mesothelioma, Latency, Prognosis, Clinical Trial, Tumor Microenvironment, Macrophage.

Related studies

• Tazemetostat: First Approval — S.M. Hoy (2020)
• 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)
• 2-Deoxy-glucose Enhances the Effect of Cisplatin and Pemetrexed in Reducing Malignant Pleural Mesothelioma Cell Proliferation But Not Spheroid Growth — I. Gerogianni, E. Pitaraki, et al. (2019)
• Inhibition of EZH2 methyltransferase decreases immunoediting of mesothelioma cells by autologous macrophages through a PD-1-dependent mechanism — M. Hamaidia, H. Gazon, et al. (2019)
• The Bcl-2 repertoire of mesothelioma spheroids underlies acquired apoptotic multicellular resistance — D. Barbone, J.A. Ryan, et al. (2011)
• Pleural Effusions from Patients with Mesothelioma Induce Recruitment of Monocytes and Their Differentiation into M2 Macrophages — A.L. Chéné, S. d'Almeida, et al. (2016)

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