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

An Overview of Angiogenesis in Bladder Cancer

PURPOSE OF THE REVIEW

Angiogenesis plays a key role in bladder cancer (BC) pathogenesis. In the last two decades, an increasing number of publications depicting a multitude of novel angiogenic molecules and pathways have emerged. The growing complexity necessitates an evaluation of the breadth of current knowledge to highlight key findings and guide future research.

RECENT FINDINGS

Angiogenesis is a dynamic biologic process that is inherently difficult to assess. Clinical assessment of angiogenesis in BCs is advancing with the integration of image analysis systems and dynamic contrast-enhanced and magnetic resonance imaging (DCE-MRI). Tumour-associated macrophages (TAMs) significantly influence the angiogenic process, and further research is needed to assess their potential as therapeutic targets. A rapidly growing list of non-coding RNAs affect angiogenesis in BCs, partly through modulation of vascular endothelial growth factor (VEGF) activity. Vascular mimicry (VM) has been repeatedly associated with increased tumour aggressiveness in BCs. Standardised assays are needed for appropriate identification and quantification of VM channels. This article demonstrates the dynamic and complex nature of the angiogenic process and asserts the need for further studies to deepen our understanding.

Fact or Fiction, It Is Time for a Verdict on Vasculogenic Mimicry?

The term vasculogenic mimicry (VM) refers to the capacity of certain cancer cells to form fluid-conducting structures within a tumor in an endothelial cell (EC)-free manner. Ever since its first report by Maniotis in 1999, the existence of VM has been an extremely contentious issue. The overwhelming consensus of the literature suggests that VM is frequently observed in highly aggressive tumors and correlates to lower patient survival. While the presence of VM in vivo in animal and patient tumors are claimed upon the strong positive staining for glycoproteins (Periodic Acid Schiff, PAS), it is by no means universally accepted. More controversial still is the existence of an in vitro model of VM that principally divides the scientific community. Original reports demonstrated that channels or tubes occur in cancer cell monolayers in vitro when cultured in matrigel and that these structures may support fluid movement. However, several years later many papers emerged stating that connections formed between cancer cells grown on matrigel represented VM. We speculate that this became accepted by the cancer research community and now the vast majority of the scientific literature reports both presence and mechanisms of VM based on intercellular connections, not the presence of fluid conducting tubes. In this opinion paper, we call upon evidence from an exhaustive review of the literature and original data to argue that the majority of in vitro studies presented as VM do not correspond to this phenomenon. Furthermore, we raise doubts on the validity of concluding the presence of VM in patient samples and animal models based solely on the presence of PAS+ staining. We outline the requirement for new biomarkers of VM and present criteria by which VM should be defined in vitro and in vivo.

Tumor cells forming sinusoids connected to vasculature are involved in hemorrhage of pineal choriocarcinoma

Intratumor hemorrhage is a poor prognostic factor in pineal choriocarcinoma (PCCC). The aim of this study was to understand the relationship of tumor cells to the blood vessels to gain insights into the formation of intratumor hemorrhage in PCCC. The clinical data indicated that total tumor removal by surgical procedures followed immediately by radiotherapy and chemotherapy improved the prognosis in PCCC. The PCCC tissues removed from the patients were examined by histology and immunohistochemistry. Hematoxylin and eosin staining showed that the tumor stroma mainly consists of hemorrhagic tissues with tumor cells scattered inside. The pattern of distribution suggests that the tumor cells were possibly flushed and compressed by the bleeding. The tumor cells tended to form sinusoids that lacked CD34, but laminin expression provided evidence of vasculogenic mimicry. Interestingly, CD34-positive blood vessels were found connected to these sinusoids, suggesting that blood may flow from the tumor vasculature to the sinusoids. This may subsequently cause the enlargement of the sinusoids, blood clotting, the widening of the blood lakes, and eventually extensive hemorrhagic necrosis. Our study identified the key features of the PCCC vasculature. The findings add to the previous understanding of the formation of vascular channels, blood lakes, and extensive hemorrhagic necrosis. The intimate connections between the tumor-formed sinusoids and the blood vessels might be a major cause of severe hemorrhage in PCCC. The new information may be useful for the development of treatment strategies for managing PCCC.

Vasculogenic mimicry of HT1080 tumour cells in vivo: critical role of HIF-1α-neuropilin-1 axis

HT1080 - a human fibrosarcoma-derived cell line – forms aggressive angiogenic tumours in immuno-compromised mice. In spite of its extensive use as a model of tumour angiogenesis, the molecular event(s) initiating the angiogenic program in these cells are not known. Since hypoxia stimulates tumour angiogenesis, we examined the hypoxia-induced events evoked in these cells. In contrast to cells grown under normoxic conditions, hypoxia-primed (1% O₂) HT1080 cells formed robust tubules on growth factor-reduced matrigel and formed significantly larger tumours in xenograft models in a chetomin-sensitive manner, indicating the role of HIF-1α-mediated transcription in these processes. Immuno-histochemical analyses of tumours formed by GFP-expressing HT1080 cells clearly showed that the tumour cells themselves expressed various angiogenic markers including Neuropilin-1 (NRP-1) and formed functional vessels containing red blood cells, thereby unambiguously demonstrating the vasculogenic mimicry of HT1080 cells in vivo. Experiments performed with the HT1080 cells stably transfected with plasmid constructs expressing shNRP-1 or full-length NRP-1 clearly established that the HIF1α-mediated up-regulation of NRP-1 played a deterministic role in the process. Hypoxia-exposure resulted in an up-regulation of c-Myc and OCT3/4 and a down-regulation of KLF4 mRNAs, suggesting their involvement in the tumour formation and angiogenesis. However, silencing of NRP-1 alone, though not affecting proliferation in culture, was sufficient to abrogate the tumour formation completely; clearly establishing that the hypoxia-mediated HIF-1α-dependent up-regulation of NRP-1 is a critical molecular event involved in the vasculogenic mimicry and tumor formation by HT1080 cells in vivo.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

Fibronectin as target for tumor therapy

During cancer progression, the extracellular matrix (ECM) of the tissue in which the tumor grows is extensively remodeled, both by degradation of preexisting ECM molecules and by the neosynthesis of ECM components, which in many cases are not present in the ECM of normal tissues. Fibronectin (FN), a class of high-molecular-weight adhesive glycoproteins, plays a prominent role in mediating ECM function, because of its high abundance and its interaction with cellular components. Furthermore, the generation of tumor-associated FN isoforms allows the development of specific ligands (e.g., antibodies), which can be used for the selective delivery of therapeutic agents to the tumor environment. In view of these considerations, it is not surprising that FN is being used as a target for biomolecular intervention, both for the development of inhibitory molecules that block the interaction of FN with integrins and other receptors on the cell surface, and for the development of ligand-based targeted imaging and therapeutic strategies. In this review, we briefly present the essential properties of FN, and we then focus on the therapeutic strategies that are currently in preclinical or clinical development and feature FN as a target, or that are based on FN fragments so as to promote tumor-growth inhibition.

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.

Enhanced antiangiogenic therapy with antibody-collagen XVIII NC1 domain fusion proteins engineered to exploit matrix remodeling events

Antiangiogenic therapy is nowadays one of the most active fields in cancer research. The first strategies, aimed at inhibiting tumor vascularization, included upregulation of endogenous inhibitors and blocking of the signals delivered by angiogenic factors. But interaction between endothelial cells and their surrounding extracellular matrix also plays a critical role in the modulation of the angiogenic process. This study introduces a new concept to enhance the efficacy of antibody-based antiangiogenic cancer therapy strategies, taking advantage of a key molecular event occurring in the tumor context: the proteolysis of collagen XVIII, which releases the endogenous angiogenesis inhibitor endostatin. By fusing the collagen XVIII NC1 domain to an antiangiogenic single-chain antibody, a multispecific agent was generated, which was efficiently processed by tumor-associated proteinases to produce monomeric endostatin and fully functional trimeric antibody fragments. It was demonstrated that the combined production in the tumor area of complementary antiangiogenic agents from a single molecular entity secreted by gene-modified cells resulted in enhanced antitumor effects. These results indicate that tailoring recombinant antibodies with extracellular matrix-derived scaffolds is an effective approach to convert tumor progression associated processes into molecular clues for improving antibody-based therapies.

Antibody-based antiangiogenic cancer therapy

Monoclonal antibodies are beginning to fulfil their potential as therapeutics in different pathological conditions, with a special focus on cancer. At the same time, antiangiogenic therapy has evolved into one of the most active fields in cancer research. The logical combination of both strategies has produced a growing number of antibodies aimed to interfere with tumour angiogenesis at different steps of the angiogenic process. This development has taken advantage of recombinant technologies that have revolutionised the selection and production of monoclonal antibodies, and gene therapy approaches that achieve sustained and effective concentrations of therapeutic antibodies in vivo. Here, the current knowledge about these antibody-based antiangiogenic strategies is summarised and the authors propose a novel therapeutic approach based on the blocking of crucial binding sites present in the extracellular matrix.

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.

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.