Glioblastoma (GBM), the most aggressive and most common form of primary brain tumor, has a median survival of 12–15 months. Surgical excision, radiation and chemotherapy are rarely curative since tumor cells broadly disperse within the brain. Preventing dispersal could be of therapeutic benefit. Previous studies have reported that increased cell-cell cohesion can markedly reduce invasion by discouraging cell detachment from the tumor mass. We have previously reported that α5β1 integrin-fibronectin interaction is a powerful mediator of indirect cell-cell cohesion and that the process of fibronectin matrix assembly (FNMA) is crucial to establishing strong bonds between cells in 3D tumor-like spheroids. Here, we explore a potential role for FNMA in preventing dispersal of GBM cells from a tumor-like mass. Using a series of GBM-derived cell lines we developed an in vitro assay to measure the dispersal velocity of aggregates on a solid substrate. Despite their similar pathologic grade, aggregates from these lines spread at markedly different rates. Spreading velocity is inversely proportional to capacity for FNMA and restoring FNMA in GBM cells markedly reduces spreading velocity by keeping cells more connected. Blocking FNMA using the 70 KDa fibronectin fragment in FNMA-restored cells rescues spreading velocity, establishing a functional role for FNMA in mediating dispersal. Collectively, the data support a functional causation between restoration of FNMA and decreased dispersal velocity. This is a first demonstration that FNMA can play a suppressive role in GBM dispersal.

Glioblastoma multiforme (GBM), the most aggressive and most common form of primary brain tumor, has a median survival of 12-15 months. Surgical excision, radiation and chemotherapy are rarely curative since tumor cells broadly disperse within the brain. Preventing local invasion could be of therapeutic benefit. Previous studies have reported that increased cell-cell cohesion can markedly reduce invasion in several cancer models. We have previously reported that α5β1 integrin-fibronectin interaction is a powerful mediator of indirect cell-cell cohesion and that the process of fibronectin matrix assembly (FNMA) is crucial to establishing strong bonds between cells in 3D tumor-like spheroids. Using a series of glioblastoma-derived immortalized cell lines we assessed FNMA by immunohistochemistry. We then measured the rate of dispersal of tumor cells from a spheroid mass, expressible as dispersal velocity. Next, we restored FNMA in GBM cells using agents previously demonstrated to up-regulate FNMA by targeting the MAPK pathway and measured their effects on dispersal velocity. We show by immunohistochemistry that more invasive U-87MG cells are deficient in FNMA as compared to their less invasive counterparts. Measurement of dispersal velocity showed that aggregates of U-87MG cells had higher dispersal velocities (21.4 ± 2.0 μ/h) than those of less invasive LN-229 (4.9 ± 0.6 μ/h), and U-118MG (4.1 ± 0.6 μ/h) (ANOVA, P<0.0001). In the absence of soluble FN, aggregates of U-87MG cells dispersed more quickly (unpaired t-test, p=0.0004) on a FN-coated substrate (5.56 ± 0.38 μ/h) than on uncoated tissue culture plastic (3.83 ± 0.11 μ/h). We also showed that for aggregates between 55 and 85μ in diameter dispersal velocity was independent of aggregate size (r2=0.0136). Treatment with Dexamethasone (Dex), MEK inhibitor (MEKi), or Geldanamycin (GA) restores FNMA. Interestingly, these agents regulated FNMA distinctively in different cell lines; Dex optimally up-regulating FNMA in U-87MG cells, whereas GA optimally restoring FNMA in cells of U-118MG. MEKi only marginally restored FNMA in both lines. Irrespective of the agent used, restored FNMA resulted in an overall decrease in tumor dispersal velocity; aggregates of U-87MG cells dispersing more slowly when treated with Dex or GA (7.5 ± 1.5 μ/h and 8.8 ± 0.6 μ/h, respectively) than those treated with MEKi (17.3 ± 0.5 μ/h), or with carrier controls. In contrast, the dispersal velocity of aggregates of U-118MG cells, treated with DMSO or with GA, exhibited an 11-fold decrease from 18.2 ± 0.6 μ/h to 1.6 ± 0.2 μ/h. Dex and MEKi treatment produced only a 4-fold or 3-fold decrease, respectively. Collectively, there appears to be a correlation between restoration of FNMA and decreased dispersal velocity. This is a first demonstration that GBM dispersal velocity can be significantly decreased by restoring FNMA using agents that target the MAPK pathway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 512.