Effects of Intracellular Force Localization on Cancer Cell Invasion: Revealing Mechanical Trade-offs through...

Metastasis, leading to 90% of cancer-related deaths, is driven by invasive forces exerted by cancer cells on their microenvironment. While actin is central to force generation and motility, the effects of intracellular force-localization during invasion remain largely unexplored. We previously demonstrated, in a clinically relevant assay, invasive cancer cells indenting soft, elastic gels to cell-scale depths, and developed corresponding experimentally validated finite element models. Here, we applied those models to investigate how the force-application location, above (top) or below (bottom) the nucleus, affects invasion efficiency. Under low force-levels (≤100 nN), top-applied forces produce 35-42% deeper indentations than bottom-applied forces, with modest increases in intracellular stress, indicating potentially increased invasiveness. However, with top-applied forces, ∼10% less stress is transmitted to the gel, suggesting less effective microenvironmental mechanical interaction. In contrast, under higher forces (≥150 nN), bottom-applied forces become more effective, transmitting >15% more stress to the gel, with indentation depths becoming comparable between top- and bottom-applied configurations, and significantly (>250%) less nuclear stress generated, thereby supporting invasion. These trends are particularly evident when the cytoplasm is softer than the nucleus, as is typical of (invasive cancer) cells. Thus, top-applied forces may support shallow invasion into soft environments, whereas bottom-applied forces mimicking actin-rich, stiff, leading-edge protrusions, optimize deep, forceful invasion with reduced cell-integrity risk. We demonstrate that intracellular force-localization critically influences the mechanical trade-offs between invasion efficiency and cellular stability, potentially offering targets for antimetastatic strategies.