Vasculogenic mimicry: how convincing, how novel, and how significant?

Assessing tumor angiogenesis in histological samples

Tumor neovascularization acquires vessels through a number of processes, including angiogenesis, vasculogenesis, vascular remodelling, intussusception, and possibly vascular mimicry in certain tumors. The end result of the tumor vasculature has been quantified by counting the number of immunohistochemically identified microvessels in areas of maximal vascularity so-called hot spots. Other techniques have been developed, such as Chalkley counting and the use of image analysis systems that are robust and reproducible as well as more objective. Many of the molecular pathways that govern tumor neovascularization have been identified, and many reagents are now available to study these tissue sections. These include angiogenic growth factors and their receptors, cell adhesion molecules, proteases, and markers of activated, proliferating, cytokine-stimulated, or angiogenic vessels, such as CD105. It is also possible to differentiate quiescent from active vessels. Other reagents that can identify proteins involved in microenvironmental influences such as hypoxia have also been generated. Although the histological assessment of tumor vascularity is used mostly in the research context, it may also have clinical applications if appropriate methodology and trained observers perform the studies.

Breast tumour angiogenesis

The central importance of tumour neovascularization has been emphasized by clinical trials using antiangiogenic therapy in breast cancer. This review gives a background to breast tumour neovascularization in in situ and invasive breast cancer, outlines the mechanisms by which this is achieved and discusses the influence of the microenvironment, focusing on hypoxia. The regulation of angiogenesis and the antivascular agents that are used in an antiangiogenic dosing schedule, both novel and conventional, are also summarized.

Intra-tumor flow index can predict the malignant potential of breast tumor: dependent on age and volume

The aim of this study was to assess tumor vascularity through three dimensional (3D) power Doppler breast ultrasound (US) and propose a decision model for the classification of benign and malignant breast tumors. Patient recruitment for this study was performed consecutively during a 13-mo period (January 2003 to February 2004). A total of 102 benign and 93 malignant solid breast images were analyzed. Three-dimensional power Doppler US imaging was performed using a Voluson730 ultrasound system equipped with a relative stopping power index (RSP) 6 to 12 transducer. The Virtual Organ Computer-aided Analysis (VOCAL)-imaging program (version 2.1) was used to analyze the stored volume. Histogram indices of the vascularization index (VI), flow index (FI) and vascularization-flow index (VFI) for the intra-tumor and for shells with a thickness of 3 mm surrounding the breast lesion were calculated and showed that for both, malignancy had a higher VI, FI and VFI than benignancy, with statistical significance. Multivariate and stepwise logistic regression revealed the model (including patient age, volume and intra-tumor FI in 3D power Doppler vascularity) to be the best choice for malignant breast tumor characterization. The receiver operating characteristics (ROC) index for the performance of the model was 0.926. Histogram indices for the intra-tumor FI in the 3D power Doppler scan are a good choice of parameter for differentiating between malignant and benign tumors with respect to the power of sensitivity, no matter whether one index is suggested or the patients' age and volume are considered.

Endothelial stomatal and fenestral diaphragms in normal vessels and angiogenesis

Vascular endothelium lines the entire cardiovascular system where performs a series of vital functions including the control of microvascular permeability, coagulation inflammation, vascular tone as well as the formation of new vessels via vasculogenesis and angiogenesis in normal and disease states. Normal endothelium consists of heterogeneous populations of cells differentiated according to the vascular bed and segment of the vascular tree where they occur. One of the cardinal features is the expression of specific subcellular structures such as plas-malemmal vesicles or caveolae, transendothelial channels, vesiculo-vacuolar organelles, endothelial pockets and fenestrae, whose presence define several endothelial morphological types. A less explored observation is the differential expression of such structures in diverse settings of angiogenesis. This review will focus on the latest developments on the components, structure and function of these specific endothelial structures in normal endothelium as well as in diverse settings of angiogenesis.

Modeling the behavior of uveal melanoma in the liver

PURPOSE

To model the behavior of uveal melanoma in the liver.

METHODS

A 15-muL suspension of metastatic MUM2B or either primary OCM1 or M619 uveal melanoma cells was injected into the liver parenchyma of 105 CB17 SCID mice through a 1-cm abdominal incision. Animals were killed at 2, 4, 6, or 8 weeks after injection. Before euthanatization, 3% FITC-BSA buffer was injected into the retro-orbital plexus of one eye of three mice. Liver tissues were examined by light and fluorescence microscopy, and were stained with human anti-laminin. Vasculogenic mimicry patterns were reconstructed from serial laser scanning confocal microscopic stacks.

RESULTS

OCM1a cells formed microscopic nodules in the mouse liver within 2 weeks after injection and metastasized to the lung 6 weeks later. By contrast, M619 and MUM2B cells formed expansile nodules in the liver within 2 weeks and gave rise to pulmonary metastases within 4 weeks after injection. Vasculogenic mimicry patterns, composed of human laminin and identical with those in human primary and metastatic uveal melanomas, were detected in the animal model. The detection of human rather than mouse laminin in the vasculogenic mimicry patterns in this model demonstrates that these patterns were of tumor cell origin and were not co-opted from the mouse liver microenvironment.

CONCLUSIONS

There are currently no effective treatments for metastatic uveal melanoma. This direct-injection model focuses on critical interactions between the tumor cell and the liver. It provides for translationally relevant approaches to the development of new modalities to detect small tumor burdens in patients, to study the biology of clinical dormancy of metastatic disease in uveal melanoma, to design and test novel treatments to prevent the emergence of clinically manifest liver metastases after dormancy, and to treat established uveal melanoma metastases.

Comparing vasculogenic mimicry with endothelial cell-lined vessels: techniques for 3D reconstruction and quantitative analysis of tissue components from archival paraffin blocks

We previously described techniques to generate 3-dimensional reconstructions of the tumor microcirculation using immunofluorescence histochemistry and laser scanning confocal microscopy on serial sections from archival formalin-fixed, paraffin-embedded tissues. By aligning sequential z-stacks in an immersive visualization environment (ImmersaDesk), the need to insert fiduciary markers into tissue was eliminated. In this study, we developed methods to stitch overlapping confocal z-series together to extend the surface area of interest well beyond that captured by the confocal microscope objective and developed methods to quantify the distribution of markers of interest in 3 dimensions. These techniques were applied to the problem of comparing the surface area of nonendothelial cell-lined, laminin-rich looping vasculogenic mimicry (VM) patterns that are known to transmit fluid, with the surface area of endothelial cell-lined vessels in metastatic uveal melanoma to the liver in 3 dimensions. After labeling sections with antibodies to CD34 and laminin, the surface area of VM patterns to vessels was calculated by segmenting out structures that labeled with laminin but not with CD34 from those structures labeling with CD34, or CD34 and laminin. In metastatic uveal melanoma tissues featuring colocalization of high microvascular density [66.4 microvessels adjusted for 0.313 mm2 area (range 56.7 to 72.7)] and VM patterning, the surface area of VM patterns was 11.6-fold greater (range 10.8 to 14.1) than the surface provided by CD34-positive vessels. These methods may be extended to visualize and quantify molecular markers in 3 dimensions in a variety of pathologic entities from archival paraffin-embedded tissues.

Overexpression of carcinoma and embryonic cytotrophoblast cell-specific Mig-7 induces invasion and vessel-like structure formation

Molecular requirements for carcinoma cell interactions with the microenvironment are critical for disease progression but are poorly understood. Integrin alpha v beta 5, which senses the extracellular matrix, is important for carcinoma cell dissemination in vivo. alpha v beta 5 signaling induces Mig-7, a novel human gene product that is apparently carcinoma-specific. We hypothesized that Mig-7 expression facilitates tumor cell dissemination by increasing invasion and vasculogenic mimicry. Results show that embryonic cytotrophoblasts up-regulated Mig-7 expression before they acquired an invasive phenotype capable of pseudovasculogenesis. Mig-7 protein primarily co-localized with vasculogenic mimicry markers factor VIII-associated antigen, vascular endothelial-cadherin, and laminin 5 gamma 2 chain domain III fragment in lymph node metastases. Overexpression of Mig-7 increased gamma 2 chain domain III fragments known to contain epidermal growth factor (EGF)-like repeats that can activate EGF receptor. Interestingly, EGF also induced Mig-7 expression. Carcinoma cell adhesion to laminins was significantly reduced by Mig-7 expression. Remarkably, in two-dimensional and three-dimensional Matrigel cultures, Mig-7 expression caused invasion and vessel-like structures. Melanoma cells, which were previously characterized to invade aggressively and to undergo vasculogenic mimicry, expressed Mig-7. Taken together, these data suggest that Mig-7 expression allows cells to sense their environment, to invade, and to form vessel-like structures through a novel relationship with laminin 5 gamma 2 chain domain III fragments.

Quantitative analysis of the microvasculature growing in the fibrin interface between a skin graft and the recipient site

Current tissue engineering techniques have failed to provide an established microvasculature in skin substitutes, a requisite for the maintenance of graft viability and rapid revascularization subsequent to graft transplantation in vivo. To improve outcomes for both conventional skin grafts and skin substitutes, the existing knowledge gap concerning the spatio-temporal mechanisms of skin graft revascularization must be abrogated. The current knowledge gap is due, at least in part, to a lack of appropriate diagnostic methods to quantify skin graft revascularization. To enhance the understanding of skin graft revascularization, we quantitatively evaluated revascularization of autologous skin grafts in a rat model by quantifying 2- and 3-dimensional vascular metrics in the fibrin interface 3, 7, and 10 days after transplantation. In this study, the fibrin interface appeared to be completely replaced with fibrovascular tissue by postoperative day 10. Although the mean vessel diameter was about 10 mum for the time points sampled, the mean vessel number, area, and volume fraction increased about 2.5-fold from postoperative day 3 to 7 and then decreased about 1.27-fold at postoperative day 10. There was no significant difference between 2- and 3-dimensional vascular metrics based on Bland-Altman analysis. In conclusion, these data establish a standard for metrics of vessels growing in the fibrin interface of a rat autologous skin graft and its donor site and suggests that once the blood supply has been restored to a viable transplant, the number, area, and volume fractions of vessels decrease to levels found at postoperative day 3.

Demonstrating circulation in vasculogenic mimicry patterns of uveal melanoma by confocal indocyanine green angiography

PURPOSE

Vasculogenic mimicry patterns, formed by highly invasive melanoma cells, connect to endothelial cell-lined blood vessels and contain fluid in vitroand in vivo. This study was designed to determine if fluid leaks into vasculogenic mimicry patterns without circulation, or if fluid circulates in and clears from these patterns.

METHODS

Indocyanine green (ICG) laser scanning confocal angiography (Heidelberg Retinal Angiograph (HRA); Heidelberg Engineering, Heidelberg, Germany) was performed on nine patients with posterior choroidal melanoma in an institutional setting. Blood was drawn before the ICG injection and from the contralateral arm of the ICG injection site and 1 min after the injection. Outcome measures include time to first filling of retinal vessels and vasculogenic mimicry patterns and the time at which no fluorescence could be detected by the HRA instrument. After fluorescence was no longer detected in vessels or patterns, the tubes containing the patient's blood was imaged by the Heidelberg HRA.

RESULTS

Looping vasculogenic mimicry patterns were detected focally in five patients within 30 s after injection and were detectable up to 12 min post-injection. Blood drawn before ICG injection did not autofluoresce but ICG-containing blood pooled in the tube continued to fluoresce at 1-month post-injection.

CONCLUSIONS

Vasculogenic mimicry patterns are not part of the endothelial cell-lined vascular system and fluid enters these patterns through leakage. The rapid infusion of ICG into these patterns after injection and the disappearance of fluorescence detectable by the Heidelberg HRA suggest that fluid circulates in these patterns and does not accumulate as a stagnant pool.

Vasculogenic mimicry: current status and future prospects

In 1999, Maniotis reported that blood vessels of highly aggressive uveal melanomas are formed by tumor cells instead of endothelial cells. He termed this novel concept in tumor vascularization vasculogenic mimicry (VM). Since then, VM has been seen in several malignant tumor types such as breast cancer, liver cancer, glioma, ovarian cancer, melanoma, prostate cancer, and bidirectional differentiated malignant tumors. Laser scanning confocal angiography, electron microscopy, and three-dimensional cell culture have confirmed the existence of VM. The molecular mechanisms that underlie VM are not fully clear, but metalloproteinases via their cleavage of laminin, VE-cadherin by promoting adherence of the VM channel wall to tumor cells, tumor cell dedifferentiation, and tumor microenvironment have been shown to play a role in VM. Zhang and co-workers have proposed a three-stage phenomenon among VM channels, mosaic blood vessels, and endothelium-dependent blood vessels, wherein all three patterns participate in tumor blood supply. Therapeutic strategies that target endothelial cells have no effect on tumor cells that engage in VM. VM-targeting strategies include suppressing tyrosine kinase activity and using a knockout EphA2 gene, downregulating VE-cadherin, using antibodies against human MMPs and the laminin 5gamma2 chain, and using anti-PI3K therapy. We review here the current status of research on VM; discuss molecular mechanisms of VM, factors affecting VM formation, and its clinical significance; and explore the development of novel tumor-targeted treatments that are based on the biochemical and molecular events that regulate VM.

Molecular imaging of angiogenesis

Angiogenesis (the growth of new blood vessels) is a complex multistep process that involves multiple cell types, numerous growth factors, and complex regulatory checks and balances. Tight control of vascular remodeling evolved to ensure stability of the vasculature while maintaining the body's ability to rapidly mount an angiogenic response requiring a high degree of plasticity. Angiogenesis is critical not only for physiological development, but also for the progression of pathologies, and is thus a target for therapeutic intervention. The importance of the process coupled with the ease of access for delivery of contrast agents makes the vasculature at large, and angiogenesis in particular, a favorable target of functional and molecular imaging. Recent developments in molecular imaging tools have expanded our views to encompass many components of the process. Functional imaging of blood volume, vessel permeability, and vasoreactivity is complemented by novel contrast agents that reveal specific targets on endothelial cells. Methods have been developed to label vascular cells so as to track their recruitment to sites of angiogenesis, and new "smart" contrast agents have been designed to reveal the activity of enzymatic reactions in altering the extracellular matrix (ECM) during angiogenesis.

Cooperative Activity of Cytotoxic Chemotherapy with Antiangiogenic Thrombospondin-I Peptides, ABT-526 in Pet Dogs with Relapsed Lymphoma

PURPOSE

Thrombospondin-I (TSP-I) is a natural antiangiogenic protein that enhances apoptosis of activated endothelial cells. A modified nonapeptide from TSP-I, ABT-526, has been found to be active in mouse cancer models and in dogs with naturally occurring cancers. To further assist in the development of ABT-526, we report herein on its evaluation in combination with cytotoxic chemotherapy in pet dogs with relapsed non-Hodgkin's lymphoma (NHL).

EXPERIMENTAL DESIGN

Ninety-four pet dogs with naturally occurring first-relapse NHL were entered into a prospective randomized placebo controlled double-blinded trial of ABT-526 plus CeeNu (Bristol-Myers Squibb, New York, NY) versus CeeNu alone. Endpoints included response rate, duration of response, time to progression, and incidence of toxicoses.

RESULTS

No significant ABT-526-specific toxicities were seen. CeeNu-associated toxicities, including neutropenia, thrombocytopenia, gastroenteritis, and elevated alanine transaminase, were similar. No significant difference in objective response rate was seen (ABT-526 + CeeNu versus placebo + CeeNu, 23/49 versus 23/37; P > 0.25). Cooperative activity between ABT-526 and CeeNu chemotherapy was evident based on a significant increase in the median response duration of dogs receiving ABT-526 plus CeeNu compared with placebo plus CeeNu (35 versus 15 days; P < 0.05). The time to progression for responding cases was also significantly greater in dogs receiving ABT-526 plus CeeNu compared with placebo plus CeeNu (41 versus 21 days; P < 0.05).

CONCLUSIONS

Results of this preclinical trial suggest that the activity of ABT-526 is sustained when combined with cytotoxic chemotherapy; furthermore, the activity seems to be associated with the maintenance of CeeNu-induced treatment responses. Further studies of TSP-I peptide antiangiogenic therapy in pet dogs and humans with NHL are warranted.

Functional implication of BMP4 expression on angiogenesis in malignant melanoma

Analyses of malignant melanomas revealed a strong expression of bone morphogenic proteins (BMPs) and their autocrine effect in promoting cell invasion and migration. Here, we report a paracrine effect of BMPs on the vascular network. Both BMP2 and BMP4 induced tube formation as well as the migratory efficiency of microvascular endothelial cells. Melanoma cells with reduced BMP activity attracted less endothelial cells in invasion assays than control cells. Furthermore, reduction of BMPs in melanoma cells had a strong effect on vasculogenic mimicry. Tube formation on matrigel was analysed for melanoma cells as well as in co-cultures of endothelial and melanoma cells. Melanoma cells with reduced BMP activity were not capable of forming cord-like structures by themselves and additionally inhibited tube formation of the endothelial cells. Genes involved in angiogenesis turned out to be strongly downregulated in these cell clones. Tumors derived from cells with impaired BMP activity showed reduced tumor growth or large necrotic areas owing to lack of angiogenesis in in vivo analyses.

The structure of the vascular network of tumors

Tumor blood vessels display many structural and functional abnormalities. Their unusual leakiness, potential for rapid growth and remodeling, and expression of distinctive surface molecules mediate the dissemination of tumor cells in the bloodstream and maintain the tumor microenvironment. Like normal blood vessels, they consist of endothelial cells, mural cells and their enveloping basement membrane. Common features, irrespective of their origin, size and growth pattern, are absent hierarchy, formation of large-caliber sinusoidal vessels and markedly heterogeneous density. This review will focus on the factors influencing this heterogeneity.

Involvement of HIF-1 in invasion of Mum2B uveal melanoma cells

The propensity of uveal melanoma cells for invasion and metastasis is critical factor for the clinical outcome of this form of cancer, and the essential biology of its aggressiveness is not completely understood. In the present study we investigated the involvement of hypoxia-inducible factor 1 (HIF-1) in uveal melanoma migration, invasion and adhesion, the hallmarks of aggressive behavior of cancer cells. We demonstrate that exposure to hypoxia increased migration, invasion and adhesion of uveal melanoma cells in in vitro assays. The "silencing" of HIF-1alpha, the oxygen-regulated subunit of HIF-1, using RNA interference technology resulted in a marked decrease of the uveal melanoma cell migration, invasion and adhesion. GeneChip microarray analysis revealed that a number of genes which regulate cancer invasion and metabolism such as CXCR4, angiopoietin-related protein, pyruvate dehydrogenase kinase 1 (PDK1) are also activated by hypoxia in a HIF-1-dependent manner in Mum2B uveal melanoma cells. We further demonstrate that serum deprivation resulted in HIF-1 and CXCR4 activation, suggesting specific metabolic regulation of HIF-1 in these cells. Microarray analysis of serum-deprived cells identified among the upregulated genes a number of cancer invasion-related genes, some of them being known HIF-1-regulated targets. Taken together, these results suggest that the involvement of HIF-1 in uveal melanoma tumorigenesis is significant and complex, and that metabolic regulation of HIF-1 activation in Mum2B uveal melanoma cells has its specificities.

Analysis of neovasculature in uveal melanoma by targeting the TGFbeta-binding receptor endoglin: is there prognostic relevance of proliferating endothelium?

BACKGROUND

Endoglin/CD105 is a transmembrane regulatory receptor for transforming growth factor-beta (TGF-beta) that is predominantly expressed on proliferating endothelial cells (ECs) in culture and on angiogenic blood vessels in vivo. Endoglin has been associated with angiogenesis and prognosis in several malignancies. Although microvascular structure has been characterized by a variety of different other endothelial markers so far, there is no consensus on the prognostic value of microvessel quantification in uveal melanoma due to differences in tissue pretreatment, variability in the reactivity of endothelial cell markers, blood vessel counting methods, and vasculogenic mimicry by melanoma cells expressing endothelial cell markers. The aim of this study was to investigate the expression pattern of endoglin and to evaluate whether proliferative activity of ECs determines the clinical prognosis of uveal melanoma.

METHODS

Paraffin sections from 35 clinicopathologically well-characterized cases of primary uveal melanomas were stained for Ki-67, von Willebrand factor (vWF) and endoglin. In 16 cases, metastatic disease led to death. The mean follow-up of the nonmetastasized cases was 10.6 (9-13) years. The immunohistological specimens were evaluated by three independent observers who were masked to the follow-up of patients. Statistical analyzes included Kaplan-Meier survival curves and the fitting of log-rank and Wilcoxon test models.

RESULTS

Immunohistochemistry with vWF confirmed that all examined specimens were vascularized. Expression of Ki-67 could be found in 26 (74%) of the samples. Moderate to high expression of endoglin was found in 13 cases (37%). Kaplan-Meier analysis showed a significant association (p<0.001) between an enhanced endoglin expression and death due to metastatic uveal melanoma.

CONCLUSIONS

The study demonstrates for the first time that the expression of endoglin can be used as a specific marker for angiogenesis in uveal melanomas. Thus, differentiation between the quiescent and proliferating ECs enables the location and characterization of hot spots of angiogenesis in melanomas. The data suggest not only a prognostic relevance in individual patients but promise applications in assessing the efficacy of antiangiogenic agents.

Aneuploidy, stem cells and cancer

Telomeres which protect the individual chromosomes from disintegration, end-to-end fusion and maintain the genomic integrity during the somatic cell divisions play an important role in cellular aging. Aging and cancer development are linked with each other because cancer is considered a group of complex genetic diseases that develop in old cells and, in both, telomere attrition is involved. Numeric chromosome imbalance also known as aneuploidy is the hallmark of most solid tumors, whether spontaneous or induced by carcinogens. We provide evidence in support of the hypothesis that telomere attrition is the earliest genetic alteration responsible for the induction of aneuploidy. Dysfunctional telomeres are highly recombinogenic leading to the formation of dicentric chromosomes. During cell divisions, such complex chromosome alterations undergo breakage fusion bridge cycles and may lead to loss of heterozygosity (LOH) and gene amplification. Furthermore, we have provided evidence in support of the hypothesis that all types of cancer originate in the organ- or tissue-specific stem cells present in a particular organ. Cancer cells and stem cells share many characteristics, such as, self-renewal, migration, and differentiation. Metaphases with abnormal genetic constitution present in the lymphocytes of cancer patients and in some of their asymptomatic family members may have been derived from the organ-specific stem cells. In addition, evidence and discussion has been presented for the existence of cancer-specific stem cells. Successful treatment of cancer, therefore, should be directed towards these cancer stem cells.

Increased laser Doppler flow in skin tumors corresponds to elevated vessel density and reactive hyperemia

BACKGROUND/PURPOSE

Tumor angiogenesis plays a key role in tumor growth and formation of metastasis. Quantitative analysis of tumor blood flow is a prerequisite for developing novel treatment strategies such as antiangiogenic and antivascular treatment options. Laser Doppler flow in malignant melanomas has been shown to be increased compared with normal skin and melanocytic nevi. This study investigated whether this phenomenon is originated by elevated blood vessel density or by reactive hyperemia.

METHODS

Laser Doppler flow was studied in 35 melanocytic nevi, 22 malignant melanomas and three basal cell carcinomas. After excision digital imaging analysis was performed in microtome sections (factor VIII-associated antigen and CD 31 labelled). The ratio of vessel area in histological sections from tumor tissue and in non-lesional skin was calculated and related to Doppler flow values.

RESULTS

Malignant melanomas demonstrated an enlargement of vessel cross-sectional area by factor 3.7+/-1.9 and of Doppler flow by factor 10.56+/-10.7, and melanocytic nevi accomplished increase of vessel cross-sectional area by factor 1.7+/-0.9 and of Doppler flow by factor 2.7+/-3.5.

CONCLUSION

The laser Doppler flow is influenced by the number and the velocity of erythrocytes in the tissue. The greater increase of laser Doppler flow than of vessel density in histological sections demonstrates that the flow signal in skin tumors is caused by neovascularization as well as by functional hyperemia. Laser Doppler perfusion imaging is a useful method for non-invasive, repeated and quantitative assessment of tumor vascular network and effects of antiangiogenic treatment directed vs. tumor vasculature in vivo, but it cannot distinguish between increased vessel density and reactive hyperemia.

Angiogenesis and cerebral neoplasia

Angiogenesis is a fundamental process in reproduction and wound healing. It is a tightly regulated process causing neovascularization. However, if angiogenesis becomes unregulated, it may be responsible for several disease processes such as brain tumour growth and metastasis. An understanding of the factors implicated in angiogenesis and its inhibition is essential if they are to be exploited as possible clinical treatments for brain tumours. Unfortunately, there are multiple factors known to be involved in the regulation of angiogenesis, and hence, the clinical application of any single agent may not be effective. This article summarizes the processes of blood vessel formation in the brain, examines the angiogenic factors that are important in the nervous system and discusses their role in brain tumour development and possible treatment.

Molecular mechanisms of tumor vascularization

Tumor angiogenesis is a fast growing sub-domain of angiogenesis research and tumor biology. Basic mechanisms have been unraveled and many key players identified. For many years, tumor vascularization was explained solely by the ingrowth of new vessels into the tumor from preexisting one's. However, in recent years, additional mechanisms have been recognized. These include angioblasts recruitment, cooption, vasculogenic mimicry and mosaic vessels. These different mechanisms may exist concomitantly in the same tumor or may be selectively involved in a specific tumor type or host environment. In this article, we will review, in depth, these different mechanisms and also discuss some aspects of anti-angiogenic tumor therapy.

Metalloproteinases and their inhibitors in tumor angiogenesis

Angiogenesis is the process by which new blood vessels are formed from preexisting vasculature. It is an essential feature of the female reproductive cycle, embryonic development and wound repair. Angiogenesis has also been identified as a causal or contributing factor in several pathologies, including cancer, where it is a rate-limiting step during tumor progression. Matrix metalloproteinases (MMPs) are a family of soluble and membrane-anchored proteolytic enzymes that can degrade components of the extracellular matrix (ECM) as well as a growing number of modulators of cell function. Several of the MMPs, in particular the gelatinases and membrane-type 1 MMP (MT1-MMP), have been linked to angiogenesis. Potential roles for these proteases during the angiogenic process include degradation of the basement membrane and perivascular ECM components, unmasking of cryptic biologically relevant sites in ECM components, modulation of angiogenic factors and production of endogenous angiogenic inhibitors. This review brings together what is currently known about the functions of the MMPs and the closely related ADAM (a disintegrin and metalloproteinase domain) and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) families in angiogenesis and considers how this information might be useful in manipulation of the angiogenic process, with a view to constraining tumor progression.

Distinguishing fibrovascular septa from vasculogenic mimicry patterns

CONTEXT

Molecular analyses indicate that periodic acid-Schiff (PAS)-positive (laminin-rich) patterns in melanomas are generated by invasive tumor cells by vasculogenic mimicry. Some observers, however, consider these patterns to be fibrovascular septa, generated by a stromal host response.

OBJECTIVE

To delineate differences between vasculogenic mimicry patterns and fibrovascular septa in primary uveal melanomas.

DESIGN

Frequency distributions, associations with outcome, and thicknesses of trichrome-positive and PAS-positive looping patterns were determined in 234 primary uveal melanomas. Sequential sections of 13 additional primary uveal melanomas that contained PAS-positive/trichrome-negative looping patterns were stained for type I and type IV collagens, laminin, and fibronectin. Real-time quantitative polymerase chain reaction was performed on RNA from cultured uveal melanoma cells for the expression of COL1A1, COL4A2, and fibronectin.

RESULTS

Trichrome-positive loops were encountered less frequently than PAS-positive loops (10% vs 56%, respectively). Death from metastatic melanoma was strongly associated with PAS-positive (P < .001) but not with trichrome-positive (P = .57) loops. Trichrome-positive loops were significantly thicker than PAS-positive loops (P < .001). The PAS-positive patterns stained positive for laminin, type I and type IV collagens, and fibronectin. Type I collagen was detected within melanoma cells and focally within some PAS-positive patterns. Real-time quantitative polymerase chain reaction revealed 3-fold, 25-fold, and 97-fold increases, respectively, in expression of COL4A2, fibronectin, and COL1A1 by invasive pattern-forming primary melanoma cells compared with poorly invasive non-pattern-forming cells.

CONCLUSIONS

Fibrovascular septa are rare and prognostically insignificant in uveal melanomas, whereas vasculogenic mimicry patterns are associated with increased mortality. Type I collagen, seen focally in some vasculogenic mimicry patterns, may be synthesized by tumor cells, independent of a host stromal response.

Vascular disrupting agents: a new class of drug in cancer therapy

AIMS

To provide a comprehensive overview of the current state of development of a novel class of anti-cancer drugs, the vascular disrupting agents (VDAs), previously known as vascular targeting agents (VTAs).

MATERIALS AND METHODS

A comprehensive review, analysis and commentary of the published medical literature on VDAs was performed.

RESULTS

Tumour vascular targeting therapy exploits known differences between normal and tumour blood vessels. VDAs target the preexisting vessels of tumours (cf anti-angiogenics), and cause vascular shutdown leading to tumour cell death and rapid haemorrhagic necrosis within hours. It is becoming clear that VDAs have overlapping activity with anti-angiogenic drugs, which prevent the formation of new blood vessels. There are two types of VDA. First, biological or ligand-directed VDAs use antibodies, peptides or growth factors to target toxins or pro-coagulants to the tumour endothelium. In contrast, small molecule VDAs work either as tubulin-binding agents or through induction of local cytokine production. VDAs can kill tumour cells resistant to conventional chemotherapy and radiotherapy, and work best on cells in the poorly perfused hypoxic core of tumours, leaving a viable rim of well-perfused tumour tissue at the periphery, which rapidly regrows. Consequently, responses of tumours to VDAs given as single agents have been poor; however, combination therapy with cytotoxic chemotherapy, external-beam radiotherapy, and radioimmunotherapy, which target the peripheral tumour cells, has produced some excellent responses in animal tumours. VDAs are generally well tolerated with different side-effect profiles to current oncological therapies. Dynamic magnetic resonance imaging is most frequently used to obtain a pharmacodynamic end point to determine whether the VDA is acting on its intended target.

CONCLUSIONS

VDAs are a promising new class of drug, which offer the attractive possibility of inducing responses in all tumour types with combination therapy.

Monocytes and macrophages form branched cell columns in matrigel: implications for a role in neovascularization

Linear arrays of cells, or cell columns, have been observed in the extracellular matrix prior to neovascularization, but their nature and significance remains elusive. Based on the emerging evidence implicating a role for monocytes and macrophages (MC/MPH) in vasculogenesis, we hypothesized that MC/MPH also can form linear or branched columns, facilitating the co-migration and the spatial arrangement of other cell types. To test this hypothesis, we studied the distribution of MC/MPH effected by chemotactic migration in novel in vitro and in vivo models of development. We induced transversal and lateral migration of THP-1 monocytoid cells in Matrigel in vitro. The effect of this process on co-localization of other micro-objects was assessed using erythrocytes and micron-sized plastic beads. In vivo, we analyzed MC/MPH infiltration in subcutaneously implanted Matrigel plugs containing angiogenic factors and across a microporous filter comprising the wall of a chamber filled with Matrigel, also placed subcutaneously in mice. In vitro, we found that migrating THP-1 cells induced the lasting degradation of Matrigel and produced cell columns, a process amplified by monocyte chemoattractant protein-1 (MCP-1). We also report the co-localization of erythrocytes with THP-1 cells in cell columns. Endothelium-free tunnels containing MC/MPH, neutrophils, or erythrocytes were also observed in the Matrigel-filled chambers. In free subcutaneous Matrigel plugs, we found MC/MPH-based columns harboring isolated Tie-2+ cells (a marker of endothelial progenitor phenotype), as well as fibroblasts, dendritic cells, and adypocytes. Many of these cell columns displayed conspicuous branching. Our data demonstrate formation of branched MC/MPH cell columns in vitro and in vivo, a previously unrecognized pattern of penetration of extracellular matrices by inflammatory cells. Thus, monocytes and macrophages influence the distribution of neovessels as well as their branching points. These cells are the "architects of development," assisting organogenesis, tumorigenesis, and wound healing by patterning the tissular space.

Vasculogenic mimicry

The term vasculogenic mimicry describes the formation of fluid-conducting channels by highly invasive and genetically dysregulated tumor cells. Two distinctive types of vasculogenic mimicry have been described. Vasculogenic mimicry of the tubular type may be confused morphologically with endothelial cell-lined blood vessels. Vasculogenic mimicry of the patterned matrix type in no way resembles blood vessels morphologically or topologically. Matrix proteins such as laminin, heparan sulfate proteoglycan, and collagens IV and VI have been identified in these patterns. The patterned matrix anastomoses with blood vessels, and systemically injected tracers co-localize to these patterns. Vasculogenic mimicry of the patterned matrix type has been identified in uveal, cutaneous and mucous membrane melanomas, inflammatory and ductal breast carcinoma, ovarian and prostatic carcinoma, and soft tissue sarcomas, including synovial sarcoma rhabdomyosarcoma, osteosarcoma, and pheochromocytoma. Because the microcirculation of many tumors may be heterogeneous -- including incorporated or co-opted vessels, angiogenic vessels, mosaic vessels, and vasculogenic mimicry of the tubular and patterned matrix types -- therapeutic regimens that target angiogenesis alone may be ineffective against highly invasive tumors that contain patterned matrices. Vasculogenic mimicry provides an opportunity to investigate the interrelationships between the genetically dysregulated invasive tumor cell, the microenvironment, and the malignant switch.

Histological quantitation of tumour angiogenesis

Tumours establish their blood supply via a number of processes in addition to angiogenesis. These include vasculogenesis, vascular remodelling, intussusception and possibly vascular mimicry in certain tumours. The mainstay of the assessment of tumour vascularity has been counting the number of immunohistochemically identified microvessels in vascular hot spots. Nevertheless, several other techniques are available, including Chalkley counting, vascular grade and the use of image analysis systems. Angiogenic activity can furthermore be assessed in histological samples by measuring the molecules involved in the establishment of the tumour vasculature, including angiogenic growth factors and their receptors, cell adhesion molecules, proteases and markers of activated, proliferating, cytokine stimulated or angiogenic vessels, such as CD105. Measuring the maturity of vessels may give an indication of the proportion of the tumour vasculature that is functional. Other reagents that can identify hypoxia-activated pathways are also being developed. The histological assessment of tumour vascularity is mainly used in the research setting but may also have applications in the clinic if appropriate methodology and trained observers perform the studies. Gene arrays may be able to provide an angiogenesis profile. Continued study into the processes involved in generating a tumour blood supply is likely to identify new markers that may be more accurate measures.

Injury and progressive loss of peritubular capillaries in the development of chronic allograft nephropathy

BACKGROUND

Chronic allograft nephropathy (CAN) remains the most important cause of late renal graft loss. However, the mechanism for graft dysfunction and the process of the development of CAN are not well understood. This study examined the role of microvascular injury in the development of CAN.

METHODS

We studied renal biopsies obtained from grafts with CAN (N= 79) and pretransplant control kidneys (N= 20). Microvascular injury was examined morphologically, and was correlated with interstitial fibrosis, glomerular sclerosis, graft function, and the severity of CAN. The humoral and cellular immunity involved in CAN were examined by C4d, CD3, and TIA-1 staining.

RESULTS

In all the cases of CAN, microvascular injury was evident with or without CD3-positive T cells, TIA-1-positive cytotoxic cells, and/or C4d+ complement deposition. Irrespective of chronic rejection (N= 14), C4d+ chronic humoral rejection (N= 6), or other CAN, the development process of CAN was characterized by injury and progressive loss of identifiable peritubular capillaries (PTCs) accompanied with the development of interstitial fibrosis. Injured PTCs were characterized morphologically by the process of angioregression with the presence of apoptotic cells, lamination of the basement membrane, and loss of PTCs. The low number of PTCs correlated significantly with the severity of CAN (r=-0.74, P < 0.001), the development of interstitial fibrosis (r=-0.75, P < 0.001), graft dysfunction (r=-0.69, P < 0.001), and also correlated weakly with proteinuria (r=-0.45, P < 0.05). In the glomeruli, capillary loss significantly correlated with the degree of glomerular sclerosis (r=-0.66, P < 0.001) and proteinuria (r=-0.65, P < 0.001), but did not correlate with the severity of CAN (r=-0.24, P > 0.05) or graft dysfunction (r=-0.32, P > 0.05).

CONCLUSION

CAN was characterized by progressive injury to the renal microvasculature and the development of renal scarring. In particular, injury, angioregression and progressive loss of the PTC network strongly contributed to the development of interstitial fibrosis and graft dysfunction in CAN, and might play a crucial role in the development of CAN.

Angiogenesis as an immunopharmacologic target in inflammation and cancer

Many pathological processes including wound healing, chronic inflammation and cancer require angiogenesis, i.e., the formation of new vasculature in the lesions. Accumulating evidence indicates that angiogenesis is crucial for both chronic inflammation and the growth of malignant tumors with the participation of diverse cytokines, chemokines and growth factors. It is nevertheless believed that differences exist in angiogenesis between cancer and chronic inflammatory diseases. The aim of this review is to outline the characteristics of angiogenesis in chronic inflammation and cancer. A better understanding of the angiogenic processes may facilitate the design of more effective therapies for chronic inflammation and cancer.

Molecular targeting of angiogenesis

The majority of pharmacological approaches for the treatment of solid tumors suffer from poor selectivity, thus limiting dose escalation (i.e., the doses of drug which are required to kill tumor cells cause unacceptable toxicities to normal tissues). The situation is made more dramatic by the fact that the majority of anticancer drugs accumulate preferentially in normal tissues rather than in neoplastic sites, due to the irregular vasculature and to the high interstitial pressure of solid tumors. One avenue towards the development of more efficacious and better tolerated anti-cancer drugs relies on the targeted delivery of therapeutic agents to the tumor environment, thus sparing normal tissues. Molecular markers which are selectively expressed in the stroma and in neo-vascular sites of aggressive solid tumors appear to be particularly suited for ligand-based tumor targeting strategies. Tumor blood vessels are accessible to agents coming from the bloodstream, and their occlusion may result in an avalanche of tumor cell death. Furthermore, endothelial cells and stromal cells are genetically more stable than tumor cells and can produce abundant markers, which are ideally suited for tumor targeting strategies. This review focuses on recent advances in the development of ligands for the selective targeting of tumor blood vessels and new blood vessels in other angiogenesis-related diseases.

Microvascular loops and networks in uveal melanoma

Microvascular patterns--three-dimensional architectural arrangements of microvessels and extravascular matrix in uveal melanoma--were discovered when investigators were looking for histopathological features of sufficient size to be imaged clinically. Evidence that these patterns may be formed by tumour cells and that they may be able to conduct plasma and blood as well as discovery of similar elements in other cancers make them of general importance. Of nine different patterns described, closed microvascular loops and networks have been studied most extensively. When cell type, microvascular density and nucleolar size are controlled for, these two patterns independently predict time to metastasis. In addition to visualization in tumour specimens stained with periodic acid-Schiff reagent, they can often be visualized clinically on confocal indocyanine green angiography. The presence of networks is clinically associated with probability of growth of small uveal melanocytic tumours and with the rate of regression of uveal melanoma after brachytherapy. Networks are also associated with development of exudative retinal detachment from uveal melanoma. Histopathological studies show that loops and networks are less common in tumours enucleated after irradiation and that they are frequently repeated in metastases of uveal melanoma. Avenues for immediate future research include detailed elucidation of the histogenesis of microvascular patterns and determination of these patterns in metastatic melanoma to identify new histopathological characteristics for prognostication when clinical metastases have developed.

Vasculogenic mimicry has no prognostic significance in pT3 and pT4 cutaneous melanoma

The concept of vasculogenic mimicry has been introduced to define periodic acid-Schiff (PAS)-positive channels and loops lined by tumor cells, instead of endothelium, able to contribute to microcirculation in uveal melanomas. Previous studies have shown that the PAS-positive patterns are associated with a poor prognosis in uveal melanoma. The aim of the current study was to investigate whether vasculogenic mimicry has a prognostic impact in pT3 and pT4 cutaneous melanoma. Fifteen patients with pT3 and pT4 cutaneous melanoma who did not experience progression after 10 years of follow-up and 30 matched controls who underwent progression were selected. Tumor sections were stained with PAS reaction, omitting the nuclear counterstaining. For immunohistochemistry, sections were stained with CD31, CD105 (endoglin), and laminin. Differences in the distribution of the PAS-positive patterns and a series of clinicopathological variables were evaluated by the Pearson chi(2) and Mann-Whitney U tests. We observed PAS-positive linear sheets, arcs, elliptical loops, and networks encircling roundish to oval aggregates of melanoma cells. The overall distribution of the PAS-positive patterns did not match with the blood microvessels' architecture as detected by immunohistochemical analysis. No statistically significant differences in the distribution of PAS-positive patterns were found between cases and controls. The presence of a parallel pattern correlated significantly with thickness (P = 0.04), whereas an inverse correlation was found with vessel area (P = 0.05). In conclusion, our results suggest that there is a mismatch between vasculogenic mimicry and tumor angiogenesis and do not support any prognostic role of vasculogenic mimicry in thick cutaneous melanoma.

Prognostic Significance of Periodic Acid-Schiff-Positive Patterns in Primary Breast Cancer and its Lymph Node Metastases

Invasive ductal carcinoma is by far the largest histological subtype of breast cancer, but clinical behavior can differ greatly. Reliable morphological markers are, therefore, of invaluable help to distinguish between patients with good and poor prognosis. Histological patterns stained with periodic acid-Schiff (PAS) were previously shown to be of prognostic significance in cutaneous and uveal melanoma. In this study, we examined the presence of different PAS-positive (PAS+) structures in 54 women with infiltrating ductal adenocarcinoma of the breast and at least one axillary lymph node metastasis but no distant metastases who were followed for at least 11 years. We found that the complexity of the thin PAS+ patterns in lymph node metastases is associated with a shorter period of disease free survival (DFS) as well as of total survival (Kaplan-Meier curves). Furthermore, the presence of PAS+ networks - the most complex thin PAS+ pattern - in lymph node metastases is one of the two independent factors associated with the occurrence of a distant metastasis (multivariate Cox model). Moreover, the presence of PAS+ networks in positive lymph nodes is the feature most strongly associated with DFS. In conclusion, the presence of PAS+ networks in lymph node metastases is a new, reliable and convenient indicator for prognosis of breast cancer patients.

Generation of non-permissive basement membranes by anti-laminin antibody fragments produced by matrix-embedded gene-modified cells

Tumor-induced blood vessel formation is a key process for the growth and spread of solid tumors, traditionally attributed to activated host endothelial cells (angiogenesis). Recently, highly aggressive cancer cells have been shown to form vascular channels in the absence of endothelial cells (vasculogenic mimicry). In this work, we have focused on the common dependence of both processes in their interactions with the surrounding extracellular matrix. We had previously described a human recombinant anti-laminin antibody that blocked the capillary morphogenesis of human endothelial cells. Here, we demonstrate that the purified antibody is capable of inhibiting channel formation by human cancer cells, suggesting a common morphogenic pathway in both processes. Moreover, matrix-embedded cells producing antibody fragments may render the surrounding matrix non-permissive for aggressive tumor cells. These results open the way for the development of new therapeutic strategies for cancer.

New non-angiogenesis dependent pathways for tumour growth

The current wisdom is that tumours are endowed with an angiogenic capability and that their growth, invasion and metastasis are angiogenesis-dependent. This article summarises the literature concerning recent histomorphological studies that indicate that some tumours may be vascularised without significant angiogenesis, probably by using existing vessels, a process later described as vascular co-option, or even by forming vascular channels on their own through a non-endothelial cell process called "vascular mimicry". Moreover, the possibility that bone marrow-derived stem cells may also be a source of endothelial precursor cells recruited for tumour-induced neovascularisation, is reviewed. In fact, it has been assumed that the additional endothelial cells required to construct new tumour vessels come from the division and proliferation of local endothelial cells and that endothelial cells incorporated into sites of neovascularisation, including tumour-induced new blood vessels, may be derived from these precursor cells. Finally, lymphoangiogenesis as a mechanism of de novo formation of lymphatics, favouring the metastatic dissemination of tumour cells, is summarised. Potential therapeutic applications are also discussed.

Spectral parameter imaging for detection of prognostically significant histologic features in uveal melanoma

Specific extracellular matrix patterns in uveal melanoma are associated with metastatic risk. The laminin-rich composition and dimensions (on the order of a wavelength or less) of these structures suggest that acoustic backscatter might be affected by their presence. In this study, 10-MHz radiofrequency (RF) ultrasound (US) data were acquired before surgical removal of 117 eyes with uveal malignant melanoma. Histologic sections were evaluated for the presence of matrix patterns and acoustic backscatter was characterized using calibrated spectrum analysis. Statistical correlations between acoustic and histologic patterns were determined and linear discriminant analysis (LDA) and radial basis networks (RBN) were used to develop classification models for histologically based risk groups. Statistically significant correlations were found between acoustic parameters and the presence of histologic matrix-rich patterns. Retrospective classification accuracies of 74.4% and 78.6% were obtained with LDA and RBN, respectively. Leave-one-out analyses indicated estimated predictive accuracies of 71.8% and 75.0% for LDA and RBN, respectively.

Tissular insemination of progenitor endothelial cells: the problem, and a suggested solution

The contribution of circulating precursor endothelial cells (CPEC) to adult angiogenesis is now well established. However, the mechanism of their tissular engrafting remains poorly understood. The classical paradigm of "sprouting" cannot accommodate the main features of the CPEC-based angiogenic process. Additionally, vasculogenesis based on the differentiation of angioblasts, as defined in the embryonic stages, is not applicable to adult neo-vascularization either. In search for a solution to this dilemma, I suggest that the ability of monocytes/macrophages to produce tunnels, as effect of their protease-dependent migration in the extracellular matrices, is instrumental for the tissular insemination of CPEC. Here I present in vivo and in vitro experimental evidence for the existence of tunnels, and for their colonization by monocytes/macrophages and by other cells, including CPEC. As a paradigm of CPEC behavior, the tunneling model (in an extended sense) may also explain the propagation of the endothelium with arteriolar phenotype within the pre-existent downstream capillary network. Thus, the sprouting mechanism might be a valid explanation for the formation of new capillaries and venules, whereas CPEC would contribute mostly, if not exclusively, to the extension of arteriolar branches of microvasculature. Adult angiogenesis occurs therefore as a multifunctional process based on intercellular cooperation, in which there are involved endothelial cells (EC) or their precursors, as well as other cell types. In specific circumstances, the lumen (i.e. the tunnel) may occur before the "definitive" microvessel. Therefore the very notion of microvessel may need to be extended, to include the tunnels.

Tumorigenesis and the angiogenic switch

It has become evident that we cannot understand tumour growth without considering components of the stromal microenvironment, such as the vasculature. At the same time, the tumour phenotype determines the nature of the tumour vasculature. Much research is now devoted to determining the impact of angiogenesis on tumour development and progression, and the reciprocal influences of tumour products on the microvasculature. A more detailed understanding of the complex parameters that govern the interactions between the tumour and vascular compartments will help to improve anti-angiogenic strategies-- not only for cancer treatment, but also for preventing recurrence.

The extracellular matrix: a new turn-of-the-screw for anti-angiogenic strategies

Anti-angiogenic therapy is currently one of most active fields in cancer research. The initial strategies, which were aimed at inhibiting tumor vascularization, included upregulation of endogenous inhibitors and blocking of the signals delivered by angiogenic factors. However, interactions between endothelial cells and their surrounding extracellular matrix also play a crucial role in modulation of the angiogenic process. Compounds that target either the integrins implicated in these interactions or the proteases responsible for matrix remodeling have been shown to halt tumor growth in murine models and are now in clinical trials. However, little attention has been paid to integrin ligands, the extracellular matrix components that support endothelial cell survival, movement and reorganization. Here, we summarize the current knowledge about these angiogenesis inhibitors and propose a novel therapeutic approach based on the blocking of crucial binding sites present in the extracellular matrix.

Vasculogenic mimicry and tumour-cell plasticity: lessons from melanoma

The gene-expression profile of aggressive cutaneous and uveal melanoma cells resembles that of an undifferentiated, embryonic-like cell. The plasticity of certain types of cancer cell could explain their ability to mimic the activities of endothelial cells and to participate in processes such as neovascularization and the formation of a fluid-conducting, matrix-rich meshwork. This ability has been termed 'vasculogenic mimicry'. How does vasculogenic mimicry contribute to tumour progression, and can it be targeted by therapeutic agents?

Stromal cell-derived factor-1 effects on ex vivo expanded endothelial progenitor cell recruitment for ischemic neovascularization

BACKGROUND

Stromal cell-derived factor-1 (SDF-1) is a chemokine considered to play an important role in the trafficking of hematopoietic stem cells. Given the close relationship between hematopoietic stem cells and endothelial progenitor cells (EPCs), we investigated the effect of SDF-1 on EPC-mediated vasculogenesis.

METHODS AND RESULTS

Flow cytometric analysis demonstrated expression of CXCR4, the receptor of SDF-1, by 66+/-3% of EPCs after 7 days in culture. In vitro modified Boyden chamber assay showed a dose-dependent EPC migration toward SDF-1 (control versus 10 ng/mL SDF-1 versus 100 ng/mL SDF-1, 24+/-2 versus 71+/-3 versus 140+/-6 cells/mm2; P<0.0001). SDF-1 attenuated EPC apoptosis (control versus SDF-1, 27+/-1 versus 7+/-1%; P<0.0001). To investigate the effect of SDF-1 in vivo, we locally injected SDF-1 into athymic ischemic hindlimb muscle of nude mice combined with human EPC transplantation to determine whether SDF-1 augmented EPC-induced vasculogenesis. Fluorescence microscopic examination disclosed increased local accumulation of fluorescence-labeled EPCs in ischemic muscle in the SDF-1 treatment group (control versus SDF-1=241+/-25 versus 445+/-24 cells/mm2, P<0.0001). At day 28 after treatment, ischemic tissue perfusion was improved in the SDF-1 group and capillary density was also increased. (control versus SDF-1, 355+/-26 versus 551+/-30 cells/mm2; P<0.0001).

CONCLUSION

These findings indicate that locally delivered SDF-1 augments vasculogenesis and subsequently contributes to ischemic neovascularization in vivo by augmenting EPC recruitment in ischemic tissues.

Pathophysiological implications of stroma pattern formation in uveal melanoma

Clinical outcome of cancer patients is mainly determined by the rate of metastasis and, also by primary tumor growth. Formation of extracellular matrix and interactions of neoplastic and non-neoplastic (host) cells in solid tumors have been shown to be essential for these processes. One result of such interactions is the outgrowth of new blood vessels from existing ones, angiogenesis, to provide the tumor tissue with oxygen and nutrients. It is assumed that the neovascular bed also facilitates the escape of metastatic cells from the primary lesions. In addition, recent reports suggested the existence of blood-conducting channels lined by melanoma cells (so-called "vascular channels") accompanied by depositions of extracellular matrix patterns in cutaneous and uveal melanoma. Since the presence of these matrix structures has been negatively associated with prognosis, we hypothesize that they play a role in melanoma outgrowth or metastasis. In this review, we will discuss the morphological and functional properties of the extracellular matrix patterns in that may underlie these clinical phenomena.