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Tumor-associated macrophages often correlate with tumor progression, and therapies targeting immune cells in tumors have emerged as promising treatments. To select effective therapies, we established an in vitro 3D multicellular spheroid model including cancer cells, fibroblasts, and monocytes. We analyzed monocyte infiltration and differentiation in spheroids generated from fibroblasts and either of the cancer cell lines MCF-7, HT-29, PANC-1, or MIA PaCa-2. Monocytes rapidly infiltrated spheroids and differentiated into mature macrophages with diverse phenotypes in a cancer cell line-dependent manner. MIA PaCa-2 spheroids polarized infiltrating monocytes to M2-like macrophages with high CD206 and CD14 expression, whereas monocytes polarized by MCF-7 spheroids displayed an M1-like phenotype. Monocytes in HT-29 and PANC-1 primarily obtained an M2-like phenotype but also showed upregulation of M1 markers. Analysis of the secretion of 43 soluble factors demonstrated that the cytokine profile between spheroid cultures differed considerably depending on the cancer cell line. Secretion of most of the cytokines increased upon the addition of monocytes resulting in a more inflammatory and pro-tumorigenic environment. These multicellular spheroids can be used to recapitulate the tumor microenvironment and the phenotype of tumor-associated macrophages in vitro and provide more realistic 3D cancer models allowing the in vitro screening of immunotherapeutic compounds.

Cancer cell spheroids are considered important preclinical tools to evaluate the efficacy of new drugs. In cancer cell spheroids, the cells assemble and grow in 3D structures with cell contact interactions that are partly impermeable, which leads to central hypoxia and necrosis. The cell spheroids thus possess several features identified in clinical tumors. Not only will the effect and behavior of therapeutic drugs in 3D cell spheroids be affected more similarly than in cells grown on culture plates, but molecular interactions and signaling pathways in cells are also more likely to mimic the in vivo situation. The monitoring of various biomarkers including lncRNAs in 3D cell spheroids is important to assess a potentially induced phenotype in the cells and the effects of drugs. Specifically, for lncRNAs, in situ localization can be done using locked nucleic acid (LNA) probe technology. Here we present a protocol for preparation of cell spheroids for use in LNA probe-based in situ hybridization to study lncRNA expression in paraffin embedded 3D cancer cell spheroids.