Lung Micrometastases Display ECM Depletion and Softening While Macrometastases Are 30-Fold Stiffer and Enriched in Fibronectin

SIMPLE SUMMARY: This study examined the mechanical properties of the extracellular matrix (ECM) in lung metastases from two cancer models: lung carcinoma and melanoma. The ECM is the framework that holds tissues and organs together in the body. The researchers found that the ECM in the metastases was much denser and stiffer than healthy ECM. Fibronectin, a protein involved in cell adhesion, was overexpressed in both cancer models. Surprisingly, treatment with the anti-fibrotic drug nintedanib increased the stiffness of the tumor ECM and the amount of cell death (necrosis). The researchers suggest that targeting fibronectin and the mechanical properties of the tumor ECM could be a promising approach to cancer therapy and call for the development of new anti-fibrotic drugs to counteract abnormal ECM mechanics in metastases. ABSTRACT: Mechanical changes in tumors have long been linked to increased malignancy and therapy resistance and attributed to mechanical changes in the tumor extracellular matrix (ECM). However, to the best of our knowledge, there have been no mechanical studies on decellularized tumors. Here, we studied the biochemical and mechanical progression of the tumor ECM in two models of lung metastases: lung carcinoma (CAR) and melanoma (MEL). We decellularized the metastatic lung sections, measured the micromechanics of the tumor ECM, and stained the sections for ECM proteins, proliferation, and cell death markers. The same methodology was applied to MEL mice treated with the clinically approved anti-fibrotic drug nintedanib. When compared to healthy ECM (~0.40 kPa), CAR and MEL lung macrometastases produced a highly dense and stiff ECM (1.79 ± 1.32 kPa, CAR and 6.39 ± 3.37 kPa, MEL). Fibronectin was overexpressed from the early stages (~118%) to developed macrometastases (~260%) in both models. Surprisingly, nintedanib caused a 4-fold increase in ECM-occupied tumor area (5.1 ± 1.6% to 18.6 ± 8.9%) and a 2-fold in-crease in ECM stiffness (6.39 ± 3.37 kPa to 12.35 ± 5.74 kPa). This increase in stiffness strongly correlated with an increase in necrosis, which reveals a potential link between tumor hypoxia and ECM deposition and stiffness. Our findings highlight fibronectin and tumor ECM mechanics as attractive targets in cancer therapy and support the need to identify new anti-fibrotic drugs to abrogate aberrant ECM mechanics in metastases.