Paracrine Signals from the Tumor Microenvironment Modulate Stem Cell Collagen Interaction and Remodeling, Indicating Early Functional Changes

The tumor microenvironment (TME) is shaped by dynamic interactions between malignant cells and stromal components, with mesenchymal stem cells (MSCs) contributing to extracellular matrix (ECM) remodeling. Here, we examined how secretomes from two hematological cancer cell lines, RPMI-8226 (multiple myeloma) and HG-3 (B-cell leukemia), influence early functional responses of human adipose-derived MSCs (AD-MSCs) and their interaction with and reorganization of collagen. Cancer-conditioned media accelerated MSC proliferation (~2-fold faster doubling time) and increased SA-β-galactosidase activity (~3–4-fold above control). Upon adhesion to collagen, treated MSCs displayed distinct morphologies and reduced cell spreading (~2100 μm2 vs. ~2500 μm2 in controls), accompanied by altered collagen organization. To quantify collagen remodeling, we introduced the collagen removal index (CRI), expressing reorganized collagen area relative to cell spreading area. CRI revealed higher remodeling efficiency in HG-3-treated MSCs than in RPMI-8226-treated and control cells, indicating enhanced collagen-interacting capacity. Secretome exposure also modulated cytokine secretion, with increased bFGF under both conditions and IL-6 upregulation specifically following HG-3 exposure. After secretome withdrawal, most functional alterations, including senescence-associated changes, motility, and elevated bFGF, persisted. Notably, IL-6 upregulation and increased CRI emerged in RPMI-8226-exposed MSCs after withdrawal, suggesting a delayed response. Together, these findings reveal early, partially persistent functional shifts in MSC behavior and collagen remodeling that may represent an early stromal response with potential relevance to tumor progression.