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Background: The human bone marrow can become a target of disseminated tumor cells in a relevant proportion of breast cancer patients. However, the underlying pathophysiology is incompletely understood. This study aims to identify and characterize potential mechanisms modulating the bone marrow hematopoietic microenvironment by invading breast cancer cells (BCC) as a basis for experimental evaluation.
Methods: Static cell-cell communication networks, representing the integrated signaling among breast carcinoma cell lines (MCF-7 or MDA-MB-231), bone marrow-derived mesenchymal stromal cells (MSC) and hematopoietic stem and progenitor cells (HSPC), were constructed in-silico by combining differentially overexpressed genes of the involved cell populations with known ligand-receptor interactions. Using the networks as guidance, pathophysiological relevance of the analyzed populations to breast cancer-initiated hematologic abnormalities was appraised by systematic literature mining. In-vitro co-culture modeling was performed to evaluate the paracrine effects of BCC on MSC-HSPC signaling and to validate main implications of the exposed signaling network.
Results: Breast cancer cells exhibited intensive bidirectional intercellular signaling with MSC and to a lesser extent with HSPC. BCC-derived signals were reported to recruit MSC to sites of breast cancer, activate tumor associated fibroblasts (TAF) and modify MSC differentiation. Hematopoietic microenvironment-derived signals were predominantly associated with BCC attraction and metastatic progression. Potential ligands that protect from metastases were exclusively HSPCderived. In-vitro co-culture modeling revealed that BCC mediated loss of the niche-derived hematopoiesis-supporting factor SDF-1 and the emergence of FGF-2 in the MSC-HSPC interaction.
Conclusion: We propose a modulation of MSC by BCC, inter alia via the FGF-2/FGFR1 pathway, resulting in activation of TAF, generation of a vascularized tumor stroma, breast cancer progression and consequential impairment of hematopoiesis by reduction of SDF-1 levels. Those indirect changes in the HSC niche upon BCC invasion might increase the vulnerability for bone metastasis in breast cancer patients.