Abstract 2348: Expression of CECR1 by activated M2-type macrophages in glioma

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Abstract Objectives Glial neoplasms harbor macrophages which are mainly of the M2 type and secrete Th2 cytokines. These M2 macrophages are not only involved in immune suppression but also serve functions in angiogenesis. Recent studies have shown that the adenosine deaminase CECR1 is involved in the maintenance of vascular homeostasis and M2-macrophage differentiation. Here we aim to identify the expressional levels of CECR1 in M1 and M2 macrophage populations in gliomas and investigate the role of these cells in glioma development. Methods To identify the relation between CECR1 expression and the macrophage subtypes, tissue samples of human glioma and normal brain controls were used for Real Time PCR and immunostaining. For in vitro functional studies, we generated M1 and M2-like macrophages by differentiating CD14+ monocytes isolated from human peripheral blood in GM-CSF and M-CSF medium. With and without stimulation of GBM conditioned medium, CECR1 level was measured by RT-PCR and western blot. CECR1 protein was added to the macrophage culture medium and the expression level of the M1 marker CD80 and the M2 marker CD163 were measured by flow cytometry and confocal microscopy. Results The macrophages were predominantly present in perivascular spaces, but also in the tumor tissue and neuropil of the normal brain. At the mRNA level the expression of CECR1 was positively correlated with the M2 markers CD204 and IL-10. Immunohistochemical investigation revealed that CECR1 is localized in microglia and macrophages in low-grade gliomas and control brain and it overlaps and co-localizes with the M2-markers CD204 and CD163, but not the M1-marker CD80. In vitro experiments showed that CECR1 expression is higher in the M-CSF-induced M2-macrophages than in their GM-CSF-induced M1 counterparts. Under the stimulation of GBM conditioned medium, increased CECR1 is detected in both M1 and M2-like macrophages. In addition, exogenous CECR1 greatly affects both M-CSF and GM-CSF induced macrophages’ response by up-regulating CD163 in M1-like macrophages and increasing CD163 positive cells in M2-like macrophages. As a result, CECR1 skews macrophage differentiation towards the M2 phenotype. Conclusion This study is the first to show that the M2-macrophage, not the M1-macrophage in glioma, is the main source of CECR1. In addition, CECR1 is shown to be a potent regulator of M2-macrophages. High levels of CECR1 is able to skew GM-CSF driven M1 macrophage differentiation towards an M2 macrophage phenotype. We propose that CECR1 expression by macrophages promotes M2-macrophage differentiation under the influence of an adenosine-rich glioma microenvironment to support tumor growth and tumor angiogenesis. The findings may well direct the search for new anti-angiogenic target molecules for the treatment of glioma. Citation Format: Changbin Zhu, Marcel M. van der Weiden, Adrea Scchetti, Thierry P.P. van den Bosch, Ihsan Chrifi, Maarten M. Brandt, Dana A.M. Mustafa, Caroline Cheng, Johan M. Kros. Expression of CECR1 by activated M2-type macrophages in glioma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2348. doi:10.1158/1538-7445.AM2015-2348