Migratory activity of human glioma cell lines in vitro assessed by continuous single cell observation

Nuclear Rac1 controls nuclear architecture and cell migration of glioma cells

Rac1 (Ras-related C3 botulinum toxin substrate 1) protein has been found in the cell nucleus many years ago, however, its nuclear functions are still poorly characterized but some data suggest its nuclear accumulation in cancers. We investigated nuclear Rac1 in glioma cancer cells nuclei and compared its levels and activity to normal astrocytes, and also characterized the studied cells on various nuclear properties and cell migration patterns. Nuclear Rac1 indeed was found accumulated in glioma cells, but only a small percentage of the protein was in active, GTP-bound state in comparison to healthy control. Altering the nuclear activity of Rac1 influenced chromatin architecture and cell motility in GTP-dependent and independent manner. This suggests that the landscape of Rac1 nuclear interactions might be as complicated and wide as its well-known, non-nuclear signaling.

Long-term migratory velocity measurements of single glioma cells using microfluidics

Microfluidic platforms enabling single-cell measurements notably contribute to the identification and observation of rare cancer cells that are involved in tumor invasion. Most aggressive, invasive, and heterogeneous glioblastoma cells cause incurable primary brain tumors. Infiltrating gliomas of a brain tumor microenvironment have been intensively studied using conventional assays. Still, quantitative, simple, and precise tools are required for long-term, steady-state migratory-velocity measurements of single glioma cells. To measure long-term velocity changes and investigate the heterogeneity of glioma cells under different growth conditions, we developed a microfluidic platform. We cultured U87 glioma cells in the microfluidic device using either regular growth medium or conditional medium composed of 50% basal medium and 50% macrophage-depleted medium. We microscopically monitored the behavior of 40 glioma cells for 5 days. Using acquired images, we calculated cellular circularity and determined the migratory velocities of glioma cells from 60 h to 120 h. The mean migratory velocity values of the glioma cells were 1.513 μm h^-1 in the basal medium and 3.246 μm h^-1 in the conditional medium. The circularity values of the glioma cells decreased from 0.20-0.25 to 0.15-0.20 when cultured in the conditional medium. Here, we clearly showed that the glioma cells lost their circularity and increased their steady-state velocities; in other words, they adopted an invasive glioma phenotype in the presence of macrophage-depleted medium. Besides, the heterogeneity of the circularity and the velocity of glioma cells were enhanced in the conditional medium.

Cell – extracellular matrix interaction in glioma growth. In silico model

The study aims to investigate the role of viscoelastic interactions between cells and extracellular matrix (ECM) in avascular tumor growth. Computer simulations of glioma multicellular tumor spheroid (MTS) growth are being carried out for various conditions. The calculations are based on a continuous model, which simulates oxygen transport into MTS; transitions between three cell phenotypes, cell transport, conditioned by hydrostatic forces in cell–ECM composite system, cell motility and cell adhesion. Visco-elastic cell aggregation and elastic ECM scaffold represent two compressible constituents of the composite. Cell–ECM interactions form a Transition Layer on the spheroid surface, where mechanical characteristics of tumor undergo rapid transition. This layer facilitates tumor progression to a great extent. The study demonstrates strong effects of ECM stiffness, mechanical deformations of the matrix and cell–cell adhesion on tumor progression. The simulations show in particular that at certain, rather high degrees of matrix stiffness a formation of distant multicellular clusters takes place, while at further increase of ECM stiffness subtumors do not form. The model also illustrates to what extent mere mechanical properties of cell–ECM system may contribute into variations of glioma invasion scenarios.

Time-lapse phenotyping of invasive glioma cells ex vivo reveals subtype-specific movement patterns guided by tumor core signaling

The biology of glioblastoma invasion and its mechanisms are poorly understood. We demonstrate using time-lapse microscopy that grafting of glioblastoma (GBM) tumorspheres into rodent brain slices results in experimental ex vivo tumors with invasive properties that recapitulate the invasion observed after orthotopic transplantation into the rodent brain. The migratory movements and mitotic patterns were clearly modified by signals extrinsic to the invading cells. The cells migrated away from the tumorspheres, and removal of the spheres reduced the directed invasive movement. The cell cultures contained different populations of invasive cells that had distinct morphology and invasive behavior patterns. Grafts of the most invasive GBM culture contained 91±8% cells with an invasive phenotype, characterized by small soma with a distinct leading process. Conversely, the majority of cells in less invasive GBM grafts were phenotypically heterogeneous: only 6.3±4.1% of the cells had the invasive phenotype. Grafts of highly and moderately invasive cultures had different proportions of cells that advanced into the brain slice parenchyma during the observation period: 89.2±2.2% and 23.1±6.8%, respectively. In grafts with moderately invasive properties, most of the cells (76.8±6.8%) invading the surrounding brain tissue returned to the tumor bulk or stopped centrifugal migration. Our data suggest that the invasion of individual GBM tumors can be conditioned by the prevalence of a cell fraction with particular invasive morphology and by signaling between the tumor core and invasive cells. These findings can be important for the development of new therapeutic strategies that target the invasive GBM cells.

Applications of High-Throughput Clonogenic Survival Assays in High-LET Particle Microbeams

Charged particle therapy is increasingly becoming a valuable tool in cancer treatment, mainly due to the favorable interaction of particle radiation with matter. Its application is still limited due, in part, to lack of data regarding the radiosensitivity of certain cell lines to this radiation type, especially to high-linear energy transfer (LET) particles. From the earliest days of radiation biology, the clonogenic survival assay has been used to provide radiation response data. This method produces reliable data but it is not optimized for high-throughput microbeam studies with high-LET radiation where high levels of cell killing lead to a very low probability of maintaining cells' clonogenic potential. A new method, therefore, is proposed in this paper, which could potentially allow these experiments to be conducted in a high-throughput fashion. Cells are seeded in special polypropylene dishes and bright-field illumination provides cell visualization. Digital images are obtained and cell detection is applied based on corner detection, generating individual cell targets as x-y points. These points in the dish are then irradiated individually by a micron field size high-LET microbeam. Post-irradiation, time-lapse imaging follows cells' response. All irradiated cells are tracked by linking trajectories in all time-frames, based on finding their nearest position. Cell divisions are detected based on cell appearance and individual cell temporary corner density. The number of divisions anticipated is low due to the high probability of cell killing from high-LET irradiation. Survival curves are produced based on cell's capacity to divide at least four to five times. The process is repeated for a range of doses of radiation. Validation shows the efficiency of the proposed cell detection and tracking method in finding cell divisions.

Dissecting the inter-substrate navigation of migrating glioblastoma cells with the stripe assay reveals a causative role of ROCK

A hallmark of gliomas is the growth and migration of cells over long distances within the brain and proliferation within selected niches, indicating that the migrating cells navigate between complex substrates. We demonstrate in the present study a differential preference for migration that depends on Rho-associated coil kinase (ROCK) signaling, using the alternating Bonhoeffer stripe assay. Membrane fractions from nonmyelinated and myelinated brain areas from female rats, purified myelin also from female rats, and commercial extracellular matrix were used as substrates, with each substrate being tested against the others. The human tumor cell lines exhibited a clear preference for extracellular matrix over all other substrates and for myelinated over nonmyelinated tissue. ROCK signaling was different when cells were cultured on either substrate. The ROCK inhibitor Y27632 significantly attenuated and neutralized the preference for extracellular matrix and myelin, indicating that ROCK controls the substrate selectivity. The findings of this study pave the way for navigation-targeted therapeutics.

Anti-tissue factor (TF9-10H10) treatment reduces tumor cell invasiveness in a novel migratory glioma model

In vitro and descriptive studies of human tissue samples revealed the pro-coagulant glycoprotein tissue factor (TF) as a potent player in glioma cell infiltration that is activated by hypoxia and has also been shown to be upregulated by mutations of TP53 or PTEN. Here we present the morphological and genetic characterization of a novel glioblastoma in vivo model and provide evidence that treatment with an antibody targeting TF leads to reduced glioma cell invasiveness. Therefore, we established a murine xenograft treatment model by transplanting the angiogenic and diffusely infiltrating human glioma cell line MZ-18 with endogenous TF expression into nude mice brains and treating these mice with an intracranial osmotic pump system continuously infusing a monoclonal antibody against TF (mAb TF9-10H10). The human MZ-18 cell line harbors two TP53 mutations resulting in a strong nuclear accumulation of p53, thereby facilitating the unambiguous identification of tumor cells in the xenograft model. Intracranial application of TF9-10H10 significantly reduced invasion of MZ-18 cells compared to mock-treated control animals. The extent of activated blood vessels was also reduced upon anti-TF treatment. Thus, targeting the TF pathway might be a promising treatment strategy for future glioblastoma therapies, by affecting both invading tumor cells and tumor vasculature.

Collective behavior of brain tumor cells: the role of hypoxia

We consider emergent collective behavior of a multicellular biological system. Specifically, we investigate the role of hypoxia (lack of oxygen) in migration of brain tumor cells. We performed two series of cell migration experiments. In the first set of experiments, cell migration away from a tumor spheroid was investigated. The second set of experiments was performed in a typical wound-healing geometry: Cells were placed on a substrate, a scratch was made, and cell migration into the gap was investigated. Experiments show a surprising result: Cells under normal and hypoxic conditions have migrated the same distance in the "spheroid" experiment, while in the "scratch" experiment cells under normal conditions migrated much faster than under hypoxic conditions. To explain this paradox, we formulate a discrete stochastic model for cell dynamics. The theoretical model explains our experimental observations and suggests that hypoxia decreases both the motility of cells and the strength of cell-cell adhesion. The theoretical predictions were further verified in independent experiments.

SNAI2/Slug promotes growth and invasion in human gliomas

Background

Numerous factors that contribute to malignant glioma invasion have been identified, but the upstream genes coordinating this process are poorly known.

Methods

To identify genes controlling glioma invasion, we used genome-wide mRNA expression profiles of primary human glioblastomas to develop an expression-based rank ordering of 30 transcription factors that have previously been implicated in the regulation of invasion and metastasis in cancer.

Results

Using this approach, we identified the oncogenic transcriptional repressor, SNAI2/Slug, among the upper tenth percentile of invasion-related transcription factors overexpressed in glioblastomas. SNAI2 mRNA expression correlated with histologic grade and invasive phenotype in primary human glioma specimens, and was induced by EGF receptor activation in human glioblastoma cells. Overexpression of SNAI2/Slug increased glioblastoma cell proliferation and invasion in vitro and promoted angiogenesis and glioblastoma growth in vivo. Importantly, knockdown of endogenous SNAI2/Slug in glioblastoma cells decreased invasion and increased survival in a mouse intracranial human glioblastoma transplantation model.

Conclusion

This genome-scale approach has thus identified SNAI2/Slug as a regulator of growth and invasion in human gliomas.

ROCKs are expressed in brain tumors and are required for glioma-cell migration on myelinated axons

The interactions between migrating glioma cells and myelinated fiber tracts are poorly understood. We identified that C6 glioma cells can migrate along myelinated chicken retinal axons in a novel coculture, thereby expressing small GTPases of the Rho family and serine/threonine Rho-associated kinases (ROCKs). We found that the ROCK1 isoform is also highly expressed in native human high-grade gliomas. Glioma cells migrated faster in vitro along myelinated axons than on laminin-1, with the former but not the latter being specifically and reversibly blocked by the ROCK inhibitor Y27632. These data suggest that the mechanisms underlying the migration of glioma cells on myelinated axons differ from those underlying the migration on extracellular matrix molecules such as laminin-1.

In vitro assessment of motility and proliferation of human osteogenic cells on different isolated extracellular matrix components compared with enamel matrix derivative by continuous single-cell observation

OBJECTIVES

The composition of the extracellular matrix (ECM) plays a substantial role in bone remodelling, fracture healing and osseointegration of dental implants by regulating proliferation, migration and finally differentiation of osteogenic cell populations. Emdogain, a composition of an enamel matrix derivative (EMD), has been introduced as a potential candidate to promote tissue regeneration. We investigated whether EMD could serve as a potential promoter of cell proliferation and motility as a dynamic cell response and compared the results with the ubiquitous single ECM components type I collagen and laminin.

MATERIAL AND METHODS

In the investigation presented, we used a continuous observation method for the analysis of migratory and proliferative patterns of individual cells. We analyzed the response of four osteoblastic cell lines to specific extracellular ligands (type I collagen, laminin and EMD) over a period of 24 h compared with untreated glass surface and bovine serum albumin (BSA) as control groups.

RESULTS

Type I collagen and laminin promoted cell motility significantly compared with the control groups and, in part, compared with EMD as well. The analysis of all 451 investigated cells revealed the following mean values for cell motiliy: untreated glass (n=99): 5.46+/-2.74 microm/h, BSA (n=89): 6.35+/-2.43 microm/h, type I collagen (n=108): 8.77+/-3.42 microm/h, laminin (n=74): 9.89+/-5.10 microm/h and EMD (n=81): 7.92+/-3.35 microm/h. Proliferation rates on the different surfaces were heterogenous for all investigated cell lines and varied from 0% to 50% within 24 h without a correlation to cell motility.

CONCLUSION

In our study, EMD promotes cell motility better than the control groups. The two investigated single ECM components type I collagen and laminin promoted cell motility superior to EMD. This supports the hypothesis that EMD promotes a less mobile but more differentiated osteogenic phenotype.

A mathematical model of glioblastoma tumor spheroid invasion in a three-dimensional in vitro experiment

Glioblastoma, the most malignant form of brain cancer, is responsible for 23% of primary brain tumors and has extremely poor outcome. Confounding the clinical management of glioblastomas is the extreme local invasiveness of these cancer cells. The mechanisms that govern invasion are poorly understood. To gain insight into glioblastoma invasion, we conducted experiments on the patterns of growth and dispersion of U87 glioblastoma tumor spheroids in a three-dimensional collagen gel. We studied two different cell lines, one with a mutation to the EGFR (U87DeltaEGFR) that is associated with increased malignancy, and one with an endogenous (wild-type) receptor (U87WT). We developed a continuum mathematical model of the dispersion behaviors with the aim of identifying and characterizing discrete cellular mechanisms underlying invasive cell motility. The mathematical model quantitatively reproduces the experimental data, and indicates that the U87WT invasive cells have a stronger directional motility bias away from the spheroid center as well as a faster rate of cell shedding compared to the U87DeltaEGFR cells. The model suggests that differences in tumor cell dispersion may be due to differences in the chemical factors produced by cells, differences in how the two cell lines remodel the gel, or different cell-cell adhesion characteristics.

Correlating velocity patterns with spatial dynamics in glioma cell migration

Highly malignant neuroepithelial tumors are known for their extensive tissue invasion. Investigating the relationship between their spatial behavior and temporal patterns by employing detrended fluctuation analysis (DFA), we report here that faster glioma cell motility is accompanied by both greater predictability of the cells' migration velocity and concomitantly, more directionality in the cells' migration paths. Implications of this finding for both experimental and clinical cancer research are discussed.

Dynamic analysis of glioma cells: looking into "movement phenotypes"

One of the major obstacles to the successful treatment of diffuse gliomas is their highly infiltrative property. It is one of the important therapeutic strategies to inhibit infiltration of glioma cells and make it possible to locally control a lesion. To achieve this, we first need to observe and describe detailed movement profiles of glioma cells in the brain tissue at the cellular level. Then we further need to determine extra and intracellular molecules that play a key role in glioma cell invasion. Live cell imaging is a powerful technique to investigate the basic movement pattern of glioma cells as well as the effects of therapeutic interventions on their migration. In this review, we describe a technical aspect of live cell imaging with special regard to time-lapse video imaging and discuss the relevance of the methods to glioma studies.

Cancer Cell Invasion of Brain Tissue: Guided by a Prepattern?

The malignant brain tumourGlioblastoma multiforme(GBM) displays a highly invasive behaviour. Spreading of the malignant cells appears to be guided by the white matter fibre tracts within the brain. In order to understand the global growth process we introduce a lattice-gas cellular automaton model which describes the local interaction between individual malignant cells and their neighbourhood. We consider interactions between cells (brain cells and tumour cells) and between malignant cells and the fibre tracts in the brain, which are considered as a prepattern. The prepattern implies persistent individual cell motion along the fibre structure. Simulations with the model show that only the inclusion of the prepattern results in invading tumour and growing tumour islets in front of the expanding tumour bulk (i.e. the growth pattern observed in clinical practice). Our results imply that the infiltrative growth of GBMs is, in part, determined by the physical structure of the surrounding brain rather than by intrinsic properties of the tumour cells.

Testing the "Go or Grow" hypothesis in human medulloblastoma cell lines in two and three dimensions

OBJECTIVE

The "Go or Grow" hypothesis proposes that cell division and cell migration are temporally exclusive events and that tumor cells defer cell division to migrate. The purpose of this study was to assess the Go or Grow hypothesis using medulloblastoma cell lines in directional migration and invasion assays in monolayer and three-dimensional cultures.

METHODS

Time-lapse videomicroscopy was used to continually monitor the directional migration, invasion, and mitosis of individual cells. The mitotic activity observed by time-lapse videomicroscopy was compared with staining for the proliferating cell nuclear antigen Ki-67.

RESULTS

A positive correlation exists between the migratory/invasive and mitotic activities of the four medulloblastoma cell lines studied. Within individual cell lines, however, migration and invasion distances are not influenced by the number of cell divisions. Time-lapse videomicroscopy and Ki-67 staining revealed similar trends in mitotic activity between migrating and nonmigrating cells within cell lines. Analysis of cell velocities before, after, and between cell divisions revealed an increase in cell velocity after cell divisions.

CONCLUSION

In the models studied, four medulloblastoma cell lines do not defer cell proliferation for migration across an uncoated surface or invasion of a Type I collagen matrix, contrary to the Go or Grow hypothesis. Migrating and invading cells continue to proliferate and migrate/invade a cell line-dependent distance irrespective of the number of divisions that take place. These findings emphasize the need to evaluate the effect of future therapies on both biological events and, if possible, to identify intracellular signaling proteins that negatively regulate medulloblastoma migration/invasion and proliferation.