A Heterotypic Tridimensional Model to Study the Interaction of Macrophages and Glioblastoma In Vitro.

Background: Glioblastoma multiforme (GBM) is the most frequent and aggressive primary brain tumor, and macrophages account for 30-40% of its composition. Most of these macrophages derive from bone marrow monocytes playing a crucial role in tumor progression. Unraveling the mechanisms of macrophages-GBM crosstalk in an appropriate model will contribute to the development of specific and more successful therapies. We investigated the interaction of U87MG human GBM cells with primary human CD14 monocytes or the THP-1 cell line with the aim of establishing a physiologically relevant heterotypic culture model.

Methods: primary monocytes and THP-1 cells were cultured in the presence of U87MG conditioned media or co-cultured together with previously formed GBM spheroids. Monocyte differentiation was determined by flow cytometry.

Results: primary monocytes differentiate to M2 macrophages when incubated with U87MG conditioned media in 2-dimensional culture, as determined by the increased percentage of CD14CD206 and CD64CD206 populations in CD11b cells. Moreover, the mitochondrial protein p32/gC1qR is expressed in monocytes exposed to U87MG conditioned media. When primary CD14 monocytes or THP-1 cells are added to previously formed GBM spheroids, both invade and establish within them. However, only primary monocytes differentiate and acquire a clear M2 phenotype characterized by the upregulation of CD206, CD163, and MERTK surface markers on the CD11bCD14 population and induce alterations in the sphericity of the cell cultures.

Conclusion: our results present a new physiologically relevant model to study GBM/macrophage interactions in a human setting and suggest that both soluble GBM factors, as well as cell-contact dependent signals, are strong inducers of anti-inflammatory macrophages within the tumor niche.