This study examined how mechanical rigidity of the metastatic niche (e.g., bone) affects cancer cell stiffness, metastatic seeding, and antitumor immunosurveillance — using immunodeficient vs. immunocompetent mouse models and patient metastatic samples.
Stiffer microenvironments induced cancer cell stiffening, which mechanically sensitized cancer cells to cytotoxic lymphocyte killing; in immunocompetent hosts, stiffer cancer cells were selectively eliminated and bone metastasis was suppressed. Osteopontin (Spp1) expression defined a cancer cell subset that expanded in bone, and Spp1 deletion reduced cancer cell stiffening, bone colonization, and immune vulnerability.
Causal mechanisms linking Spp1/osteopontin to cell stiffening are not fully delineated; patient data are associative (stiffness correlated with rigidity and inversely with immune infiltration, but causality is not proven); findings are centered on bone metastasis, limiting generalizability to other metastatic niches.
Osteopontin (Spp1) may be a targetable mediator of bone-specific immune evasion via mechanosensing — clinicians should watch for therapeutic strategies aimed at disrupting environmentally driven cancer cell stiffening in bone metastasis. Environmental mechanical properties of metastatic sites should be considered when evaluating immune checkpoint efficacy in bone-metastatic disease.
