Macrophage–Fibroblast Crosstalk Governs Tumor Mechanics, as Revealed by Spatiotemporal Force Mapping in 3D Spheroids

Understanding how stromal and immune cells regulate tumor mechanics is essential for deciphering cancer progression and therapy resistance. This study presents a microparticle-based traction force microscopy strategy for in situ quantification of compressive forces within 3D tumor spheroids. Multicellular spheroids composed of tumor cells (T), fibroblasts (F), and macrophages (M) were generated to mimic the tumor microenvironment and to understand the contribution of fibroblast-macrophage crosstalk in tumor mechanobiology. Tri-culture spheroids exhibited the highest proliferative capacity compared to mono- and bi-cultured tumor spheroids. Gene expression profiling indicated strong fibroblast activation, extracellular matrix remodeling, and M2-like macrophage polarization, highlighting a pro-tumoral phenotype. Incorporation of deformable hydrogel microparticles allowed direct mapping of local compressive and indirect quantification of anisotropic stresses. This mapping revealed fibroblasts are the principal source of force generation with the spheroids. Notably, macrophages amplified bulk and anisotropic stresses over two-fold through paracrine activation of fibroblasts. Spatial mapping showed pressure gradients from the core to the periphery, while temporal analyses demonstrated a progressive increase in mechanical stresses with spheroid growth. Together, these findings reveal a surprising governing of intratumoral mechanics by macrophage-fibroblast interactions and demonstrate the potential of microparticle-based 3D force mapping within complex tumor environments.