Open Access

The tumor architecture of high-grade gliomas is shaped by tumor cell necrosis, invasive growth, and the leakage of a fibrin-rich edema from poorly organized tumor blood vessels. In this study, we demonstrate a marked upregulation of clot formation in the interstitial spaces of tumor tissues from patients with glioblastoma (GBM) whereas a tumor-free brain is essentially devoid of fibrin. The accumulation of fibrin in tumor interstitial spaces is functionally relevant as we demonstrate increased infiltration and growth of primary GBM cells after embedding in a 3-dimensional matrix made of fibrin ex vivo. Additionally, we detected accelerated tumor growth after implanting GBM cells together with clotted plasma in brains of immunodeficient mice whereas GBM development in clotting-deficient hemophilia mice was delayed. GBM growth correlated with the outgrowth of invadopodia and their adhesive interactions with the 3-dimensional clot matrix, which was mediated by integrins β1 and β3 and their common downstream target focal adhesion kinase (FAK). Knocking down FAK with CRISPR Cas9 caused an upregulation of p21/p27 cell-cycle inhibitors, strong growth inhibition in cultured GBM cells, and sustained antitumorigenic effects in orthotopic GBM xenografts in vivo. These results go hand in hand with genomic data from The Cancer Genome Atlas that indicate increased clotting activity and reduced patient survival in glioma subgroups with high integrin β1 and β3 expression. We therefore conclude that clotting in glioma interstitial spaces provides tumor cells with a potent proliferative stimulus that can be reversed by targeting the adhesive machinery of GBM cells via inhibition of FAK.