Zoledronic acid impairs myeloid differentiation to tumour-associated macrophages in mesothelioma

Our plain-English summary of Zoledronic acid impairs myeloid differentiation to tumour-associated macrophages in mesothelioma, by J.D. Veltman, M.E. Lambers, M. van Nimwegen, et al (British Journal of Cancer, 2010).

The study

• Authors: J.D. Veltman, M.E. Lambers, M. van Nimwegen, R.W. Hendriks, H.C. Hoogsteden, J.P. Hegmans, J.G. Aerts
• Journal: British Journal of Cancer
• Published: 2010;103(5):629-41
• Cited by: 84 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Suppressive immune cells present in tumour microenvironments are known to augment tumour growth and hamper efficacy of antitumour therapies. The amino-bisphosphonate Zoledronic acid (ZA) is considered as an antitumour agent, as recent studies showed that ZA prolongs disease-free survival in cancer patients. The exact mechanism is a topic of debate; it has been suggested that ZA targets tumour-associated macrophages (TAMs).

Methods: We investigate the role of ZA on the myeloid differentiation to TAMs in murine mesothelioma in vivo and in vitro. Mice were intraperitoneally inoculated with a lethal dose of mesothelioma tumour cells and treated with ZA to determine the effects on myeloid differentiation and survival.

Results: We show that ZA impaired myeloid differentiation. Inhibition of myeloid differentiation led to a reduction in TAMs, but the number of immature myeloid cells with myeloid-derived suppressor cell (MDSC) characteristics was increased. In addition, ZA affects the phenotype of macrophages leading to reduced level of TAM-associated cytokines in the tumour microenvironment. No improvement of survival was observed.

Conclusion: We conclude that ZA leads to a reduction in macrophages and impairs polarisation towards an M2 phenotype, but this was associated with an increase in the number of immature myeloid cells, which might diminish the effects of ZA on survival.

In plain English

This was a laboratory study in mice and cell cultures. It tested whether zoledronic acid (ZA), a bone drug, affects tumour-associated macrophages in mesothelioma. It did not study asbestos exposure. Female CBA-j mice were injected in the abdomen with AC29 mesothelioma tumour cells. Some received daily ZA injections under the skin; others received salt solution (PBS). In bone marrow cultures, ZA slowed, dose-dependently, the maturation of immature myeloid cells into macrophages. It also blocked a shift toward the M2 macrophage type. ZA did not significantly prolong survival; of 10 mice per group, five were killed at day 25 and the rest followed until profoundly ill. At day 25, ZA-treated mice had fewer macrophages in the spleen. They also had more MO-MDSC, a type of immature suppressor cell, in the spleen and abdominal fluid, and altered levels of immune signalling proteins. The authors concluded that ZA inhibited myeloid differentiation and shifted the balance of macrophage types toward M1. They attributed the lack of survival benefit to the persisting immature suppressor cells. They noted the doses were higher than clinically advised.

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: Animal experiment (mouse mesothelioma model) combined with laboratory cell-culture (in vitro) experiments
• Who was studied: Female CBA-j mice, 6 to 8 weeks old, were injected into the abdomen (peritoneal cavity) with the AC29 mouse mesothelioma cell line. For the treatment experiment, mice were divided into two groups of 10. In each group, five mice were killed at day 25 and the others were followed until they were profoundly ill. Survival experiments were repeated three times. Bone marrow cells from untreated mice were used for the cultures. The work was done at Erasmus MC, Rotterdam, the Netherlands.
• Exposure: The drug zoledronic acid (Zometa), given as daily injections under the skin starting at day 5 after tumour injection, compared with PBS injections as a control. In the cultures, ZA was added at three concentrations. In a separate experiment, macrophages were depleted with liposome-encapsulated clodronate. No asbestos or fiber exposure was studied.
• Main results:
  • Macrophage depletion with clodronate: all 5 control mice had profound tumour growth at day 12. Three of the five clodronate-treated mice had no visible tumour.
  • In bone marrow cultures, ZA inhibited the differentiation of myeloid cells into macrophages in a dose-dependent way. By day 6 this gave significant differences in the numbers of macrophages and immature cells.
  • In cultures with tumour supernatant, macrophages shifted toward the M2 type (marked by CD206). ZA prevented this shift in vitro.
  • In tumour-bearing mice, ZA did not significantly prolong survival compared with PBS. The text gives P = 0.2183 and the Figure 4 legend gives P = 0.3675. Groups were allocated 10 mice each, but five per group were killed at day 25, so the number followed for survival is not clearly stated. No significant differences were reported in effusion fluid volume.
  • At day 25 (n = 6 per group in the figure legend), ZA-treated mice had a significantly lower proportion of macrophages in the spleen than PBS-treated mice (P = 0.0091).
  • In the spleen, there was only a trend toward a shift from M2 to M1 macrophages; the reduction in M2 macrophages was not statistically significant (P = 0.18). In the peritoneal effusion fluid, the M1 to M2 ratio differed significantly between groups (P = 0.011).
  • ZA-treated mice had significantly more MO-MDSC (a type of immature myeloid suppressor cell) in the spleen (P = 0.0312) and in the peritoneal effusion fluid (P = 0.034). The other MDSC subtypes did not differ significantly.
  • In the effusion fluid of ZA-treated mice, IL-6, IL-12 and IL-1b were significantly higher (P = 0.049, 0.042 and 0.005). VEGF and CCL-2 (MCP-1) were significantly lower (P = 0.05 and 0.039).
• The authors' conclusion: The authors concluded that daily ZA in tumour-bearing mice inhibited myeloid differentiation and shifted the balance from the M2 macrophage phenotype toward the M1 phenotype. However, immature myeloid cells, especially MO-MDSC, remained high. The authors attributed the lack of survival improvement to the immunosuppressive effect of these cells.
• Limitations the authors state:
  • The ZA doses used were higher than clinically advised. The authors state that further studies are needed on the safety and efficacy of higher doses.
  • Most other ZA studies used highly metastatic tumours, in which metastasis may be the cause of death. In this model it was not, so ZA's effects on metastasis may not have mattered here.

Topics

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

Medical terms in this study, explained in our Lexicon: Macrophage, Mesothelioma, Disease-Free Survival, Cytokine.

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• Zoledronic acid induces apoptosis and S-phase arrest in mesothelioma through inhibiting Rab family proteins and topoisomerase II actions — S. Okamoto, Y. Jiang, et al. (2014)
• Zoledronic acid overcomes chemoresistance and immunosuppression of malignant mesothelioma — I.C. Salaroglio, I. Campia, et al. (2015)
• Combination of a third generation bisphosphonate and replication-competent adenoviruses augments the cytotoxicity on mesothelioma — Y. Jiang, B. Zhong, et al. (2016)
• Effect of IL-18 on expansion of gammadelta T cells stimulated by zoledronate and IL-2 — W. Li, S. Kubo, et al. (2010)

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