Deep collective cancer invasion: Breaking radioresistance by anti-integrin therapy

The tumor microenvironment contributes to cancer invasion, growth and survival and thereby impacts tumor responses to therapy. We here show for orthotopic fibrosarcoma and melanoma xenografts deep invasive growth driven by proliferation concurrent with collective invasion of multicellular strands along the normoxic perivascular stroma. Invasion was fast (up to 200 µm per day), non-destructive and independent of β1 and β3 integrins. Despite normoxia, perivascular invasion strands were resistant to high-dose hypofractionated irradiation which otherwise was sufficient to induce regression of the tumor main mass. This invasion-associated radioresistance was sensitive to the simultaneous inhibition of β1 and β3 integrins by RNA interference or combined anti-β1/aV integrin antibody treatment caused byproliferation arrest, anoikis induction ablating both tumor lesion and invasion strands. Thus, collective invasion is an important invasion mode in solid tumors into a microenvironmentally privileged perivascular survival niche which conveys radioresistance by integrin-dependent signals. Consequently, combining anti-integrin therapy with hypofractionated irradiation may be amenable to clinical cancer treatment of locally destructive and otherwise radioresistant tumor lesions.

An experimental model to study isolated effects of thrombin in vivo

BACKGROUND

In addition to a recognized role in the coagulation cascade and haemostasis, thrombin is known to have multiple functions. We hypothesized that protracted intravenous infusion of thrombin at steady state will allow to study isolated thrombin effects in vivo.

METHODS

Thrombin (0.05-0.9U/kg/min) was continuously infused in Sprague Dawley rats over five hours (n=38). The study consisted of three parts: dose escalation (n=21), dose verification (n=5) and a parallel group study to investigate whether thrombin effects can be antagonised by concomitant infusion of lepirudin (n=12).

RESULTS

A thrombin dose of 0.9U/kg/min decreased platelet counts by 70% compared to the control group (median 230×10^9/L vs. 752×10^9/L; p=0.041). In accordance, infusion of 0.9U/kg/min of thrombin decreased fibrinogen level by 75% compared to the control group (56mg/dl vs. 220mg/dl; p=0.046). Cumulative thrombin doses of ≥0.1U/kg/min caused bleedings but not thromboembolic events. Thrombin at doses ≥0.15U/kg/min was lethal in four cases (30%). Platelet counts and fibrinogen levels after thrombin infusion correlated with bleeding events and mortality. Administration of thrombin at cumulative doses of 0.3-0.9U/kg/min was associated with a 3 to 6.5 -fold increase in IL-6 levels (139-306pg/ml vs. 47pg/ml, p<0.05). In contrast, thrombin infusion did not alter other markers of inflammation (IL-10, MCP-1 or TNF-alpha). In addition, lepirudin prevented thrombin- induced thrombocytopenia.

CONCLUSION

Protracted intravenous infusion of thrombin offers a new experimental model, where consumption of fibrinogen and platelets correlates with bleedings and mortality. Infusion of thrombin increased only IL-6 levels but not other cytokines.

A three-dimensional organotypic assay to measure target cell killing by cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTL) mediate antigen- and cell-cell contact dependent killing of target cells, such as cancer cells and virus-infected cells. In vivo, this process requires the active migration of CTL towards and away from target cells. We here describe an organotypic 3D collagen matrix assay to monitor CTL migration together with CTL-mediated killing of target cells. The assay supports both, time-lapse microscopy of killing dynamics as well as population analysis of killing after matrix digestion and flow cytometry. The assay was used to assess the detrimental effect of cyclosporine A (CsA) present during CTL activation, which caused an inhibition of CTL-target cell conjugation and strongly impaired CTL-mediated killing, particularly at low effector-target ratios. Thus, the organotypic assay is useful to monitor spatiotemporal control mechanisms of cytotoxic immune effector functions.

MMP13 mediates cell cycle progression in melanocytes and melanoma cells: in vitro studies of migration and proliferation

Background

Melanoma cells are usually characterized by a strong proliferative potential and efficient invasive migration. Among the multiple molecular changes that are recorded during progression of this disease, aberrant activation of receptor tyrosine kinases (RTK) is often observed. Activation of matrix metalloproteases goes along with RTK activation and usually enhances RTK-driven migration. The purpose of this study was to examine RTK-driven three-dimensional migration of melanocytes and the pro-tumorigenic role of matrix metalloproteases for melanocytes and melanoma cells.

Results

Using experimental melanocyte dedifferentiation as a model for early melanomagenesis we show that an activated EGF receptor variant potentiates migration through three-dimensional fibrillar collagen. EGFR stimulation also resulted in a strong induction of matrix metalloproteases in a MAPK-dependent manner. However, neither MAPK nor MMP activity were required for migration, as the cells migrated in an entirely amoeboid mode. Instead, MMPs fulfilled a function in cell cycle regulation, as their inhibition resulted in strong growth inhibition of melanocytes. The same effect was observed in the human melanoma cell line A375 after stimulation with FCS. Using sh- and siRNA techniques, we could show that MMP13 is the protease responsible for this effect. Along with decreased proliferation, knockdown of MMP13 strongly enhanced pigmentation of melanocytes.

Conclusions

Our data show for the first time that growth stimuli are mediated via MMP13 in melanocytes and melanoma, suggesting an autocrine MMP13-driven loop. Given that MMP13-specific inhibitors are already developed, these results support the evaluation of these inhibitors in the treatment of melanoma.

Influence of corneal collagen crosslinking with riboflavin and ultraviolet-a irradiation on excimer laser surgery

PURPOSE

Riboflavin/ultraviolet A (UVA) cross-linking (CXL) of corneal collagen is a novel method of stabilizing corneal mechanical properties and preventing progression of keratectasias. This study was conducted to investigate whether CXL influences ablation rate, flap thickness, and refractive results of excimer laser procedures ex vivo.

METHODS

Corneal epithelium was removed from enucleated porcine eyes, and CXL was performed with riboflavin 0.1% and UVA radiation (365 nm, 3 mW/cm(2)) for 30 minutes. Control eyes received epithelial abrasion only. Diffusion of riboflavin through the cornea was assessed by using infrared-excited, two-photon microscopy of riboflavin autofluorescence, combined with second-harmonic generation of fibrillar collagen. During phototherapeutic keratectomy, corneal thickness was measured by optical coherence pachymetry. During LASIK for myopia, the flap thickness of microkeratome cuts was measured and the induced refractive change assessed by Placido topography. Data were analyzed by Shapiro-Wilk test and Student's t-test.

RESULTS

Multiphoton imaging showed a rapid (30-minute) and even distribution of riboflavin throughout the corneal stroma. No difference in ablation rate was measured in treated and untreated corneas (P = 0.90). Mean flap thickness was increased by 44% in cross-linked corneas (P < 0.01). After LASIK for myopia of 4 to 25 D, the mean corneal refractive change was reduced in CXL-treated eyes by 20.1% (P < 0.05). This effect was less pronounced in thinner flaps.

CONCLUSIONS

CXL reduces the amount of refractive change after LASIK for myopia. Although the laser ablation rate is unaffected, CXL results in an increased flap thickness. This study suggests the need for adjustment of microkeratome and laser parameters for LASIK after CXL and indirectly endorses the theory of a direct stiffening effect of CXL.

Interstitial cell migration: integrin-dependent and alternative adhesion mechanisms

Adhesion and migration are integrated cell functions that build, maintain and remodel the multicellular organism. In migrating cells, integrins are the main transmembrane receptors that provide dynamic interactions between extracellular ligands and actin cytoskeleton and signalling machineries. In parallel to integrins, other adhesion systems mediate adhesion and cytoskeletal coupling to the extracellular matrix (ECM). These include multifunctional cell surface receptors (syndecans and CD44) and discoidin domain receptors, which together coordinate ligand binding with direct or indirect cytoskeletal coupling and intracellular signalling. We review the way that the different adhesion systems for ECM components impact cell migration in two- and three-dimensional migration models. We further discuss the hierarchy of these concurrent adhesion systems, their specific tasks in cell migration and their contribution to migration in three-dimensional multi-ligand tissue environments.

Plasticity of cell migration: a multiscale tuning model

Cell migration underlies tissue formation, maintenance, and regeneration as well as pathological conditions such as cancer invasion. Structural and molecular determinants of both tissue environment and cell behavior define whether cells migrate individually (through amoeboid or mesenchymal modes) or collectively. Using a multiparameter tuning model, we describe how dimension, density, stiffness, and orientation of the extracellular matrix together with cell determinants—including cell–cell and cell–matrix adhesion, cytoskeletal polarity and stiffness, and pericellular proteolysis—interdependently control migration mode and efficiency. Motile cells integrate variable inputs to adjust interactions among themselves and with the matrix to dictate the migration mode. The tuning model provides a matrix of parameters that control cell movement as an adaptive and interconvertible process with relevance to different physiological and pathological contexts.

Proteolytic interstitial cell migration: a five-step process

Cell migration is a multi-step process that leads to the actin-driven translocation of cells on or through tissue substrate. Basic steps involved in cell migration have been defined for two-dimensional haptokinetic migration which, however, does not provide physical constraints imposed by three-dimensional interstitial tissues. We here describe the process of pericellular proteolysis that leads to extracellular matrix (ECM) degradation and realignment during cell movement and integrate it into established steps of cell migration. After actin-driven leading edge protrusion (step I) and anterior formation of integrin-mediated focal interactions to the substrate (step II), ECM breakdown is focalized towards physical ECM barriers several micrometer rearward of the leading edge (step III). Actomyosin-mediated cell contraction (step IV) then leads to rear-end retraction and forward sliding of cell body and nucleus so that a small tube-like matrix defect bordered by realigned ECM fibers becomes apparent (step V). Pericellular proteolysis is thus integral to the migration cycle and serves to widen ECM gaps and thereby lowers physical stress upon the cell body, which ultimately leads to aligned higher-oder ECM patterns.

Collagen-based cell migration models in vitro and in vivo

Fibrillar collagen is the most abundant extracellular matrix (ECM) constituent which maintains the structure of most interstitial tissues and organs, including skin, gut, and breast. Density and spatial alignments of the three-dimensional (3D) collagen architecture define mechanical tissue properties, i.e. stiffness and porosity, which guide or oppose cell migration and positioning in different contexts, such as morphogenesis, regeneration, immune response, and cancer progression. To reproduce interstitial cell movement in vitro with high in vivo fidelity, 3D collagen lattices are being reconstituted from extracted collagen monomers, resulting in the re-assembly of a fibrillar meshwork of defined porosity and stiffness. With a focus on tumor invasion studies, we here evaluate different in vitro collagen-based cell invasion models, employing either pepsinized or non-pepsinized collagen extracts, and compare their structure to connective tissue in vivo, including mouse dermis and mammary gland, chick chorioallantoic membrane (CAM), and human dermis. Using confocal reflection and two-photon-excited second harmonic generation (SHG) microscopy, we here show that, depending on the collagen source, in vitro models yield homogeneous fibrillar texture with a quite narrow range of pore size variation, whereas all in vivo scaffolds comprise a range from low- to high-density fibrillar networks and heterogeneous pore sizes within the same tissue. Future in-depth comparison of structure and physical properties between 3D ECM-based models in vitro and in vivo are mandatory to better understand the mechanisms and limits of interstitial cell movements in distinct tissue environments.

Peptide Bbeta(15-42) preserves endothelial barrier function in shock

Loss of vascular barrier function causes leak of fluid and proteins into tissues, extensive leak leads to shock and death. Barriers are largely formed by endothelial cell-cell contacts built up by VE-cadherin and are under the control of RhoGTPases. Here we show that a natural plasmin digest product of fibrin, peptide Bß15-42 (also called FX06), significantly reduces vascular leak and mortality in animal models for Dengue shock syndrome. The ability of Bß15-42 to preserve endothelial barriers is confirmed in rats i.v.-injected with LPS. In endothelial cells, Bß15-42 prevents thrombin-induced stress fiber formation, myosin light chain phosphorylation and RhoA activation. The molecular key for the protective effect of Bß15-42 is the src kinase Fyn, which associates with VE-cadherin-containing junctions. Following exposure to Bß15-42 Fyn dissociates from VE-cadherin and associates with p190RhoGAP, a known antagonists of RhoA activation. The role of Fyn in transducing effects of Bß15-42 is confirmed in Fyn^−/− mice, where the peptide is unable to reduce LPS-induced lung edema, whereas in wild type littermates the peptide significantly reduces leak. Our results demonstrate a novel function for Bß15-42. Formerly mainly considered as a degradation product occurring after fibrin inactivation, it has now to be considered as a signaling molecule. It stabilizes endothelial barriers and thus could be an attractive adjuvant in the treatment of shock.

Dynamic imaging of cancer growth and invasion: a modified skin-fold chamber model

The metastatic invasion of cancer cells from the primary lesion into the adjacent stroma is a key step in cancer progression, and is associated with poor outcome. The principles of cancer invasion have been experimentally addressed in various in vitro models; however, key steps and mechanisms in vivo remain unclear. Here, we establish a modified skin-fold chamber model for orthotopic implantation, growth and invasion of human HT-1080 fibrosarcoma cells, dynamically reconstructed by epifluorescence and multiphoton microscopy. This strategy allows repeated imaging of tumor growth, tumor-induced angiogenesis and invasion, as either individual cells, or collective strands and cell masses that move along collagen-rich extracellular matrix and coopt host tissue including striated muscle strands and lymph vessels. This modified window model will be suited to address mechanisms of cancer invasion and metastasis, and related experimental therapy.

Tube travel: the role of proteases in individual and collective cancer cell invasion

Recent advances in high-resolution multimodal microscopy reveal how MT1-matrix metalloproteinase (MMP)/MMP-14 and other cell surface proteases degrade and remodel the extracellular matrix (ECM) to drive the dissemination of cancer cells into normal adjacent tissue. By cleaving collagen fibers and repatterning them into parallel bundles, individual cells reorient the ECM to permit movement in tube-like microtracks. Cells along the edge of these tubes can excavate ECM outward, generating macrotracks through which collective mass movement of cancer cells can occur. These findings develop our understanding of invasive processes in cancer and how to attack them by interfering with MMP-14 activity.

CCL11 and GM-CSF differentially use the Rho GTPase pathway to regulate motility of human eosinophils in a three-dimensional microenvironment

Asthma is a common disease that causes considerable morbidity. Increased numbers of airway eosinophils are a hallmark of asthma. Mechanisms controlling the entry of eosinophils into asthmatic lung have been intensively investigated, but factors regulating migration within the tissue microenvironment are less well understood. We modeled this by studying chemoattractant and growth factor-mediated human eosinophil migration within a three-dimensional collagen matrix. Stimulation with GM-CSF induced dose-dependent, random migration with a maximum of 77 +/- 4.7% of cells migrating. In contrast, CCL11 and C5a caused a more modest although significant degree of migration (19 +/- 1.8% and 20 +/- 2.6%, respectively). Migration to GM-CSF was partially dependent on Ca(2+) and alpha(M)beta(2) integrins. The Rho family of small GTPases regulates intracellular signaling of cell migration. GM-CSF-induced migration was only partially dependent on Rho kinase/Rho-associated kinase (ROCK) and was independent of RhoA activation. In contrast, CCL11-induced migration was fully dependent on both RhoA and ROCK. Activation of RhoA was therefore neither necessary nor sufficient to cause eosinophil migration in a three-dimensional collagen environment. This study suggests that eosinophil growth factors are likely to be required for eosinophil migration within the bronchial mucosa, and this involves signal transduction pathways distinct from those used by G protein-associated chemoattractants.