Tumor plasticity allows vasculogenic mimicry, a novel form of angiogenic switch. A rose by any other name?

LIFU/MMP-2 dual-responsive release of repurposed drug disulfiram from nanodroplets for inhibiting vasculogenic mimicry and lung metastasis in triple-negative breast cancer

BACKGROUND

Vasculogenic mimicry (VM), when microvascular channels are formed by cancer cells independent of endothelial cells, often occurs in deep hypoxic areas of tumors and contributes to the aggressiveness and metastasis of triple-negative breast cancer (TNBC) cells. However, well-developed VM inhibitors exhibit inadequate efficacy due to their low drug utilization rate and limited deep penetration. Thus, a cost-effective VM inhibition strategy needs to be designed for TNBC treatment.

RESULTS

Herein, we designed a low-intensity focused ultrasound (LIFU) and matrix metalloproteinase-2 (MMP-2) dual-responsive nanoplatform termed PFP@PDM-PEG for the cost-effective and efficient utilization of the drug disulfiram (DSF) as a VM inhibitor. The PFP@PDM-PEG nanodroplets effectively penetrated tumors and exhibited substantial accumulation facilitated by PEG deshielding in a LIFU-mediated and MMP-2-sensitive manner. Furthermore, upon exposure to LIFU irradiation, DSF was released controllably under ultrasound imaging guidance. This secure and controllable dual-response DSF delivery platform reduced VM formation by inhibiting COL1/pro-MMP-2 activity, thereby significantly inhibiting tumor progression and metastasis.

CONCLUSIONS

Considering the safety of the raw materials, controlled treatment process, and reliable repurposing of DSF, this dual-responsive nanoplatform represents a novel and effective VM-based therapeutic strategy for TNBC in clinical settings.

Cancer stem cells: an insight into the development of metastatic tumors and therapy resistance

The term "cancer stem cells" (CSCs) refers to cancer cells that exhibit traits parallel to normal stem cells, namely the potential to give rise to every type of cell identified in a tumor microenvironment. It has been found that CSCs usually develops from other neoplastic cells or non-cancerous somatic cells by acquiring stemness and malignant characteristics through particular genetic modifications. A trivial number of CSCs, identified in solid and liquid cancer, can give rise to an entire tumor population with aggressive anticancer drug resistance, metastasis, and invasiveness. Besides, cancer stem cells manipulate their intrinsic and extrinsic features, regulate the metabolic pattern of the cell, adjust efflux-influx efficiency, modulate different signaling pathways, block apoptotic signals, and cause genetic and epigenetic alterations to retain their pluripotency and ability of self-renewal. Notably, to keep the cancer stem cells' ability to become malignant cells, mesenchymal stem cells, tumor-associated fibroblasts, immune cells, etc., interact with one another. Furthermore, CSCs are characterized by the expression of particular molecular markers that carry significant diagnostic and prognostic significance. Because of this, scientific research on CSCs is becoming increasingly imperative, intending to understand the traits and behavior of cancer stem cells and create more potent anticancer therapeutics to fight cancer at the CSC level. In this review, we aimed to elucidate the critical role of CSCs in the onset and spread of cancer and the characteristics of CSCs that promote severe resistance to targeted therapy.

Melanoma Tumour Vascularization and Tissue-Resident Endothelial Progenitor Cells

The aggressiveness of solid cancers, such as melanoma, relies on their metastatic potential. It has become evident that this key cause of mortality is largely conferred by the tumour-associated stromal cells, especially endothelial cells. In addition to their essential role in the formation of the tumour vasculature, endothelial cells significantly contribute to the establishment of the tumour microenvironment, thus enabling the dissemination of cancer cells. Melanoma tumour vascularization occurs through diverse biological processes. Vasculogenesis is the formation of de novo blood vessels from endothelial progenitor cells (EPCs), and recent research has shown the role of EPCs in melanoma tumour vascularization. A more detailed understanding of the complex role of EPCs and how they contribute to the abnormal vessel structures in tumours is of importance. Moreover, anti-angiogenic drugs have a limited effect on melanoma tumour vascularization, and the role of these drugs on EPCs remains to be clarified. Overall, targeting cancer vasculature remains a challenge, and the role of anti-angiogenic drugs and combination therapies in melanoma, a focus of this review, is an area of extensive exploration.

Non-coding RNAs and glioblastoma: Insight into their roles in metastasis

Glioma, also known as glioblastoma multiforme (GBM), is the most prevalent and most lethal primary brain tumor in adults. Gliomas are highly invasive tumors with the highest death rate among all primary brain malignancies. Metastasis occurs as the tumor cells spread from the site of origin to another site in the brain. Metastasis is a multifactorial process, which depends on alterations in metabolism, genetic mutations, and the cancer microenvironment. During recent years, the scientific study of non-coding RNAs (ncRNAs) has led to new insight into the molecular mechanisms involved in glioma. Many studies have reported that ncRNAs play major roles in many biological procedures connected with the development and progression of glioma. Long ncRNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) are all types of ncRNAs, which are commonly dysregulated in GBM. Dysregulation of ncRNAs can facilitate the invasion and metastasis of glioma. The present review highlights some ncRNAs that have been associated with metastasis in GBM. miRNAs, circRNAs, and lncRNAs are discussed in detail with respect to their relevant signaling pathways involved in metastasis.

Transmembrane Protein TMEM230, a Target of Glioblastoma Therapy

Glioblastomas (GBM) are the most aggressive tumors originating in the brain. Histopathologic features include circuitous, disorganized, and highly permeable blood vessels with intermittent blood flow. These features contribute to the inability to direct therapeutic agents to tumor cells. Known targets for anti-angiogenic therapies provide minimal or no effect in overall survival of 12–15 months following diagnosis. Identification of novel targets therefore remains an important goal for effective treatment of highly vascularized tumors such as GBM. We previously demonstrated in zebrafish that a balanced level of expression of the transmembrane protein TMEM230/C20ORF30 was required to maintain normal blood vessel structural integrity and promote proper vessel network formation. To investigate whether TMEM230 has a role in the pathogenesis of GBM, we analyzed its prognostic value in patient tumor gene expression datasets and performed cell functional analysis. TMEM230 was found necessary for growth of U87-MG cells, a model of human GBM. Downregulation of TMEM230 resulted in loss of U87 migration, substratum adhesion, and re-passaging capacity. Conditioned media from U87 expressing endogenous TMEM230 induced sprouting and tubule-like structure formation of HUVECs. Moreover, TMEM230 promoted vascular mimicry-like behavior of U87 cells. Gene expression analysis of 702 patients identified that TMEM230 expression levels distinguished high from low grade gliomas. Transcriptomic analysis of patients with gliomas revealed molecular pathways consistent with properties observed in U87 cell assays. Within low grade gliomas, elevated TMEM230 expression levels correlated with reduced overall survival independent from tumor subtype. Highest level of TMEM230 correlated with glioblastoma and ATP-dependent microtubule kinesin motor activity, providing a direction for future therapeutic intervention. Our studies support that TMEM230 has both glial tumor and endothelial cell intracellular and extracellular functions. Elevated levels of TMEM230 promote glial tumor cell migration, extracellular scaffold remodeling, and hypervascularization and abnormal formation of blood vessels. Downregulation of TMEM230 expression may inhibit both low grade glioma and glioblastoma tumor progression and promote normalization of abnormally formed blood vessels. TMEM230 therefore is both a promising anticancer and antiangiogenic therapeutic target for inhibiting GBM tumor cells and tumor-driven angiogenesis.

Expression of STAT3 and vasculogenic mimicry in gallbladder carcinoma promotes invasion and metastasis

Surgical treatment of gallbladder carcinoma remains challenging, while targeted therapy has been demonstrated to have potential. In the present study, the effect of signal transducer and activator of transcription 3 (STAT3) expression and vasculogenic mimicry (VM) on the occurrence and development of gallbladder carcinoma was evaluated. A total of 72 patients with gallbladder carcinoma and 10 patients with chronic cholecystitis were examined. Immunohistochemical staining was performed to determine the positive expression rates of STAT3. Periodic acid Schiff CD34 double staining was performed to detect VM in the gallbladder carcinoma group. STAT3 expression and VM in gallbladder carcinoma tissues was compared among patients with different clinical characteristics. In postoperative patients with gallbladder cancer, the relationship of the postoperative recurrence time with STAT3 expression and VM was assessed. STAT3 expression in gallbladder carcinoma tissue was significantly higher than that in cholecystitis tissue (P<0.05). STAT3 expression levels and VM were positively correlated in gallbladder carcinoma tissue. STAT3 protein expression in gallbladder carcinoma tissues differed significantly among patients with different degrees of differentiation and clinical stages (P<0.05). Among the 51 patients who completed the 3-year follow-up, the mean time to relapse was 17.353 and 35.647 months in those with high and low STAT3 expression, respectively, with significant differences (P<0.05). The VM structure was detected in 47 cases (92.15%) and not detected in four cases (7.84%), which exhibited no immediate recurrence after surgery, and the difference in the mean postoperative recurrence time was significant (22.38 vs. 36.00 months, respectively; P<0.05). In gallbladder carcinoma tissues, a lower degree of differentiation, higher malignancy degree and higher clinical stage were associated with higher expression of STAT3 and VM. Thus, STAT3 may promote VM formation in the process of tumor occurrence, development and metastasis. Therefore, STAT3 as a regulatory target, may inhibit the proliferation and invasion of tumor cells and block the development of VM, thereby representing a suitable target for antitumor angiogenesis therapy.

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.

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Plasticity and Potency of Mammary Stem Cell Subsets During Mammary Gland Development

It is now widely believed that mammary epithelial cell plasticity, an important physiological process during the stages of mammary gland development, is exploited by the malignant cells for their successful disease progression. Normal mammary epithelial cells are heterogeneous and organized in hierarchical fashion, in which the mammary stem cells (MaSC) lie at the apex with regenerative capacity as well as plasticity. Despite the fact that the majority of studies supported the existence of multipotent MaSCs giving rise to both basal and luminal lineages, others proposed lineage restricted unipotent MaSCs. Consistent with the notion, the latest research has suggested that although normal MaSC subsets mainly stay in a quiescent state, they differ in their reconstituting ability, spatial localization, and molecular and epigenetic signatures in response to physiological stimuli within the respective microenvironment during the stages of mammary gland development. In this review, we will focus on current research on the biology of normal mammary stem cells with an emphasis on properties of cellular plasticity, self-renewal and quiescence, as well as the role of the microenvironment in regulating these processes. This will include a discussion of normal breast stem cell heterogeneity, stem cell markers, and lineage tracing studies.

Functional invadopodia formed in glioblastoma stem cells are important regulators of tumor angiogenesis

Glioblastoma (GBM) represents the most common and lethal brain tumor. High vascularization, necrosis and invasiveness are hallmarks of GBM aggressiveness with recent data suggesting the important role of glioblastoma stem cells (GSCs) in these processes. It is now well established that cancer cells employ specialized structures termed invadosomes to potentiate invasion. However, the role of these structures in GBM dissemination remains poorly investigated. In this study, we showed that GBM-isolated GSCs form invadopodia-like protrusions endowed with degradative action. Interestingly, their formation depends on extracellular matrix (ECM) sensing via the CD44 receptor. We also found that GSCs invasive migration occurring during tubes assembly is promoted through invadopodia-mediated-ECM remodeling and LIM kinases signaling. Moreover, our study demonstrates that GSCs are highly adaptable cells that are able not only to restore damaged endothelial-derived tubes but also to generate in cooperation with normal endothelial cells (ECs) intact vascular channels. Taken together, our data provide new insights in GBM microvasculature and suggest that GSCs targeting in combination with anti-VEGF therapy may block tumor progression.

Differential regulation of the expression of aquaporins 3 and 9 by Auphen and dbcAMP in the SMMC-7721 hepatocellular carcinoma cell line

Aquaglycero-aquaporins (agAQPs) are the structural foundation of rapid water transport and they appear to participate in cancer proliferation and malignancy. AQP3 expression is increased and AQP9 expression is decreased in hepatocellular carcinoma (HCC) compared to normal liver, which suggests their possible use as targets for cancer treatment. AQP-based modifiers, such as Auphen and dibutyryladenosine 3', 5'-cyclic monophosphate (dbcAMP), might be used to treat several diseases and as chemical tools for assessing the functions of AQPs in biological systems. We investigated the effects of both Auphen on AQP3 and dbcAMP on AQP9 in SMMC-7721 cells. We used western blotting, real-time quantitative polymerase chain reaction (qPCR) and immunohistochemistry to evaluate changes in AQP3 and AQP9 expression in SMMC-7721 cells after culturing with Auphen and dbcAMP, respectively. We also determined the proliferation of SMMC-7721 cells. We found that compared to HL-7702 (L02) liver cells, Auphen increased AQP3 expression in tumor cells, whereas dbcAMP decreased expression of AQP9 in these cells. Also, high concentrations of Auphen and dbcAMP inhibited proliferation of SMMC-7721 cells in vitro. Auphen and dbcAMP may inhibit HCC development and could be considered targets for HCC diagnosis and therapy.

Claudin-4 is required for vasculogenic mimicry formation in human breast cancer cells

Vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. Claudins are aberrantly expressed in aggressive breast cancer. However, the relationship between claudins and VM formation is not clear. We examined VM in two human breast cancer cell lines with different aggressive capabilities (MDA-MB-231 and MCF-7 cells) and one human umbilical vein endothelial cell line (HUVEC). Both HUVEC and MDA-MB-231 cells formed vascular channels in Matrigel cultures, while MCF-7 cells did not. Western blot analysis revealed a possible correlation between claudin-4 and -6 expression in breast cancer cell lines and tumor aggressiveness, with protein levels correlating with the ability to form vascular channels. Treatment of MDA-MB-231 and HUVEC cells with claudin-4 monoclonal antibodies completely inhibited the ability of cells to form vascular channels. Moreover, knockdown of claudin-4 by short hairpin RNA completely inhibited tubule formation in MDA-MB-231 cells. Overexpression of claudin-4 in MCF-7 cells induced formation of vascular channels. Immunocytochemistry revealed that membranous claudin-4 protein was significantly associated with vascular channel formation. Collectively, these results indicate that claudin-4 may play a critical role in VM in human breast cancer cells, opening new opportunities to improve aggressive breast cancer therapy.

Future options of anti-angiogenic cancer therapy

In human patients, drugs that block tumor vessel growth are widely used to treat a variety of cancer types. Many rigorous phase 3 clinical trials have demonstrated significant survival benefits; however, the addition of an anti-angiogenic component to conventional therapeutic modalities has generally produced modest survival benefits for cancer patients. Currently, it is unclear why these clinically available drugs targeting the same angiogenic pathways produce dissimilar effects in preclinical models and human patients. In this article, we discuss possible mechanisms of various anti-angiogenic drugs and the future development of optimized treatment regimens.

Endocan: a novel circulating proteoglycan

Endocan is a novel endothelium derived soluble dermatan sulfate proteoglycan. It has the property of binding to a wide range of bioactive molecules associated with cellular signaling and adhesion and thus regulating proliferation, differentiation, migration, and adhesion of different cell types in health and disease. An increase in tissue expression or serum level of endocan reflects endothelial activation and neovascularization which are prominent pathophysiological changes associated with inflammation and tumor progression. Consequently, endocan has been used as a blood-based and tissue-based biomarker for various cancers and inflammation and has shown promising results.

RANK-mediated signaling network and cancer metastasis

Cancer metastasis is highly inefficient and complex. Common features of metastatic cancer cells have been observed using cancer cell lines and genetically reconstituted mouse and human tumor xenograft models. These include cancer cell interaction with the tumor microenvironment and the ability of cancer cells to sense extracellular stimuli and adapt to adverse growth conditions. This review summarizes the coordinated response of cancer cells to soluble growth factors, such as RANKL, by a unique feed forward mechanism employing coordinated upregulation of RANKL and c-Met with downregulation of androgen receptor. The RANK-mediated signal network was found to drive epithelial to mesenchymal transition in prostate cancer cells, promote osteomimicry and the ability of prostate cancer cells to assume stem cell and neuroendocrine phenotypes, and confer the ability of prostate cancer cells to home to bone. Prostate cancer cells with activated RANK-mediated signal network were observed to recruit and even transform the non-tumorigenic prostate cancer cells to participate in bone and soft tissue colonization. The coordinated regulation of cancer cell invasion and metastasis by the feed forward mechanism involving RANKL, c-Met, transcription factors, and VEGF-neuropilin could offer new therapeutic opportunities to target prostate cancer bone and soft tissue metastases.

Merkel cell carcinoma expresses vasculogenic mimicry: demonstration in patients and experimental manipulation in xenografts

Merkel cell carcinoma (MCC) is a highly virulent cutaneous neoplasm that, like melanoma, is a frequent cause of patient morbidity and mortality. The cellular mechanisms responsible for the aggressive behavior of MCC remain unknown. Vasculogenic mimicry (VM) is a phenomenon associated with cancer virulence, including in melanoma, whereby anastomosing laminin networks form in association with tumor cells that express certain endothelial genes. To determine whether VM is a factor in MCC, we employed a relevant xenograft model using two independent human MCC lines. Experimentally induced tumors were remarkably similar histologically to patient MCC, and both contained laminin networks associated with vascular endothelial-cadherin (CD144) and vascular endothelial growth factor receptor 1, as well as Nodal expression typical of VM in melanoma. Moreover, two established chemotherapeutic agents utilized for human MCC, etoposide and carboplatin, induced necrosis in xenografts on systemic administration while enriching for laminin networks in apparently resistant viable tumor regions that persisted. These findings for the first time establish VM-like laminin networks as a biomarker in MCC, demonstrate the experimental utility of the MCC xenograft model, and suggest that VM-rich regions of MCC may be refractory to conventional chemotherapeutic agents.

[Effects of cetuximab combined with celecoxib on apoptosis and KDR and AQP1 expression in lung cancer]

BACKGROUND AND OBJECTIVE

Neoadjuvant chemotherapy is a new development in the treatment of lung cancer. In recent years, cetuximab and celecoxib have been commonly used in this procedure. This study aims to explore the effect of cetuximab combined with celecoxib on apoptosis and KDR and AQP1 expression in lung cancer A549 cells.

METHODS

The cells were cultured in RPMI-1640 and then divided into four groups: control group, 1 nmol/L cetuximab group, 25 µmol/L celecoxib group, and 1 nmol/L cetuximab+25 µmol/L celecoxib group. The treatment time was 48 h. The mRNA and protein expression levels of KDR and AQP1 were detected by RT-PCR and Western blot, respectively. The apoptosis, proliferation, and invasive ability of A549 cells before and after transfection were examined using flow cytometry, MTT, and transwell methods.

RESULTS

Cetuximab and celecoxib inhibited the growth of A549 cells in a dose-dependent manner. Their combination produced a greater growth inhibition than when either was used alone (P<0.01). Cetuximab and celecoxib both induced the apoptosis of A549 cells, and their combination produced a higher apoptosis rate (P<0.01). Cetuximab in combination with celecoxib also induced G1 phase arrest and downregulated the expression of KDR and AQP1 in A549 cells (P<0.05). As a result, the invasion ability of the A549 cells was significantly decreased.

CONCLUSIONS

Cetuximab in combination with celecoxib can synergistically inhibit the growth of A549 cells and downregulate the expression of KDR and AQP1 in A549 cells. The combination of cetuximab and celecoxib is a potential strategy for lung cancer therapy.

Brain tumor-targeted drug delivery strategies

Despite the application of aggressive surgery, radiotherapy and chemotherapy in clinics, brain tumors are still a difficult health challenge due to their fast development and poor prognosis. Brain tumor-targeted drug delivery systems, which increase drug accumulation in the tumor region and reduce toxicity in normal brain and peripheral tissue, are a promising new approach to brain tumor treatments. Since brain tumors exhibit many distinctive characteristics relative to tumors growing in peripheral tissues, potential targets based on continuously changing vascular characteristics and the microenvironment can be utilized to facilitate effective brain tumor-targeted drug delivery. In this review, we briefly describe the physiological characteristics of brain tumors, including blood–brain/brain tumor barriers, the tumor microenvironment, and tumor stem cells. We also review targeted delivery strategies and introduce a systematic targeted drug delivery strategy to overcome the challenges.

Transglutaminases: future perspectives

This is the third special issue focused on "Transglutaminases" that is now available on this journal and dedicated to one of the pioneers of these enzymes, John Edward Folk, who died December 2010 [see in this issue Beninati et al. 2012a]. The first edition, "Polyamines and Transglutaminases" was published in Amino Acids, vol 26, no. 4, 2004, with the contribution of two prestigious Guest Editors as Alberto Abbruzzese and Mauro Piacentini. This editorial initiative was followed by the second special issue published in occasion of the 50th years of the discovery of transglutaminase. Indeed, "Transglutaminase 2: 50th Anniversary of the Discovery" Amino Acids, vol 36, no. 4, 2009, was published with the valuable collaboration of Carlo Maria Bergamini and Mauro Piacentini (Beninati et al. 2009). To continue with this editorial tradition, on this occasion, an outstanding board of Guest Editors composed by Francesco Facchiano and Mauro Piacentini has also been invited to promote this initiative and recruit a selected panel of Authors, many of who participated in the first and second edition of the Gordon Conference on Transglutaminases: "Transglutaminases in Human Diseases Processes" chaired by Rickard L Eckert and Kapil Mehta on July 18-23, 2010, and by Kapil Mehta and Mauro Piacentini on July 15-20, 2012, held at Davidson College, NC, USA. In this Amino Acids special issue, the manuscripts were selected to reflect the progress and the future perspectives of transglutaminases.

FH535 inhibited migration and growth of breast cancer cells

There is substantial evidence indicating that the WNT signaling pathway is activated in various cancer cell types including breast cancer. Previous studies reported that FH535, a small molecule inhibitor of the WNT signaling pathway, decreased growth of cancer cells but not normal fibroblasts, suggesting this pathway plays a role in tumor progression and metastasis. In this study, we tested FH535 as a potential inhibitor for malignant phenotypes of breast cancer cells including migration, invasion, and growth. FH535 significantly inhibited growth, migration, and invasion of triple negative (TN) breast cancer cell lines (MDA-MB231 and HCC38) in vitro. We demonstrate that FH535 was a potent growth inhibitor for TN breast cancer cell lines (HCC38 and MDA-MB-231) but not for other, non-TN breast cancer cell lines (MCF-7, T47D or SK-Br3) when cultured in three dimensional (3D) type I collagen gels. Western blotting analyses suggest that treatment of MDA-MB-231 cells with FH535 markedly inhibited the expression of NEDD9 but not activations of FAK, Src, or downstream targets such as p38 and Erk1/2. We demonstrated that NEDD9 was specifically associated with CSPG4 but not with β1 integrin or CD44 in MDA-MB-231 cells. Analyses of gene expression profiles in breast cancer tissues suggest that CSPG4 expression is higher in Basal-type breast cancers, many of which are TN, than any other subtypes. These results suggest not only a mechanism for migration and invasion involving the canonical WNT-signaling pathways but also novel strategies for treating patients who develop TN breast cancer.

Tumor cell vasculogenic mimicry: from controversy to therapeutic promise

In 1999, The American Journal of Pathology published an article entitled "Vascular channel formation by human melanoma cells in vivo and in vitro: vasculogenic mimicry," by Maniotis and colleagues, which ignited a spirited debate for several years and earned distinction as a citation classic. Tumor cell vasculogenic mimicry (VM) refers to the plasticity of aggressive cancer cells forming de novo vascular networks, which thereby contribute to perfusion of rapidly growing tumors, transporting fluid from leaky vessels, and/or connecting with the constitutional endothelial-lined vasculature. The tumor cells capable of VM share a plastic, transendothelial phenotype, which may be induced by hypoxia. Since VM was introduced as a novel paradigm for melanoma tumor perfusion, many studies have contributed new findings illuminating the underlying molecular pathways supporting VM in a variety of tumors, including carcinomas, sarcomas, glioblastomas, astrocytomas, and melanomas. Facilitating the functional plasticity of tumor cell VM are key proteins associated with vascular, stem cell, and hypoxia-related signaling pathways, each deserving serious consideration as potential therapeutic targets and diagnostic indicators of the aggressive, metastatic phenotype.

Hypoxia-induced vasculogenic mimicry formation via VE-cadherin regulation by Bcl-2

Vasculogenic mimicry (VM) refers to the unique ability of highly aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. Hypoxia plays a pivotal role in the formation of VM. Hypoxia-induced Bcl-2 overexpression is observed in many types of tumors including melanoma, in which it is associated with tumorigenicity and angiogenesis. VE-cadherin, the major endothelial adhesion molecule controlling cellular junctions and blood vessel formation, is also overexpressed in melanoma. Despite these connections, whether hypoxia induces VM formation via VE-cadherin regulation by Bcl-2 is not confirmed. We used human melanoma cells to upregulate or knockdown the expression of Bcl-2 to investigate the possible molecular mechanism of VM formation under hypoxia. Bcl-2 overexpression increased VE-cadherin expression and VM formation under normoxia, whereas Bcl-2 siRNA significantly decreased VE-cadherin expression and VM formation under hypoxia. We then demonstrated that Bcl-2 regulated VE-cadherin transcription activity by Western blot, three-dimensional cultures, reporter gene assay, and clinical analysis. Therefore, Bcl-2-dependent VE-cadherin overexpression may be an important mechanism by which hypoxia induces VM.

Vasculogenic mimicry is a marker of poor prognosis in prostate cancer

We investigated the role of vasculogenic mimicry (VM) in the progression of prostate cancer (PCa). Ninety-six patients who had undergone prostatectomy for treatment of PCa and for whom a complete record of clinical and follow-up data were available were reviewed. VM and matrix metalloproteinase-2 (MMP-2) were detected by immunohistochemical staining in frozen tissue sections. Relationship between VM and clinicopathological variables was analyzed statistically. Multivariate analyses were performed to assess the prognostic significance of VM. Results showed that out of the 96 PCa cases studied here, VM was detectable in 24 (25%) and was positively correlated with preoperative prostate-specific antigen (PSA) level, Gleason score, pathological stage, lymph node metastasis, seminal vesicle invasion, distant metastasis and PSA doubling time (PSADT). Univariate analysis showed that VM, PSA level, Gleason score, distant metastasis and PSADT were correlated with overall survival (OS), while VM, Gleason score, distant metastasis, local recurrence and PSADT were correlated with disease-free survival (DFS). Multivariable analysis indicated that the presence of VM, higher Gleason score and distant metastasis were the adverse predictors of OS and DFS. A higher widespread staining for MMP-2 was correlated with the VM-positive subgroup. In conclusion, VM mainly exists in the high risk PCa patients and is an independent marker of poor prognosis.

miR-409-3p inhibits HT1080 cell proliferation, vascularization and metastasis by targeting angiogenin

Although the expression of angiogenin (ANG), an angiogenic and tumorigenic factor, is elevated in various types of cancers, its regulation mechanism remains unclear. In the present study, in silico search predicted that miR-409-3p targeted to the 3' untranslated region (3'UTR) of the ANG mRNA. Overexpression of miR-409-3p in fibrosarcoma HT1080 cells resulted in decreased steady-state level of ANG transcript and ANG production which were achieved through direct binding of this miRNA to the ANG 3'UTR. The suppressions of miR-409-3p to rRNA transcription, cell proliferation and vasculogenic mimicry could be partially restored by overexpression of ANG with a mutated binding site of miR-409-3p within the ANG 3'UTR. Ectopic expression of miR-409-3p in transplanted HT1080 cells led to the retardation of tumor growth, vascularization and lung metastasis in mouse tumor xenografts. In these xenografts tissues, the expression of miR-409-3p displayed an inverse correlation with ANG, which was also detected in human fibrosarcoma samples. In addition, the suppression effects of miR-409-3p on cell proliferation and angiogenesis in vitro were also found in human umbilical vein endothelial cells. Taken together, these data demonstrate that miR-409-3p inhibits tumor growth, vascularization and metastasis through down-regulating ANG expression.

Molecular pathways: vasculogenic mimicry in tumor cells: diagnostic and therapeutic implications

Tumor cell vasculogenic mimicry (VM) describes the functional plasticity of aggressive cancer cells forming de novo vascular networks, thereby providing a perfusion pathway for rapidly growing tumors, transporting fluid from leaky vessels, and/or connecting with endothelial-lined vasculature. The underlying induction of VM seems to be related to hypoxia, which may also promote the plastic, transendothelial phenotype of tumor cells capable of VM. Since its introduction in 1999 as a novel paradigm for melanoma tumor perfusion, many studies have contributed new insights into the underlying molecular pathways supporting VM in a variety of tumors, including melanoma, glioblastoma, carcinomas, and sarcomas. In particular, critical VM-modulating genes are associated with vascular (VE-cadherin, EphA2, VEGF receptor 1), embryonic and/or stem cell (Nodal, Notch4), and hypoxia-related (hypoxia-inducible factor, Twist1) signaling pathways. Each of these pathways warrants serious scrutiny as potential therapeutic, vascular targets, and diagnostic indicators of plasticity, drug resistance, and the aggressive metastatic phenotype.

The role of TG2 in ECV304-related vasculogenic mimicry

Tumour vasculogenesis can occur by a process referred to as vasculogenic mimicry, whereby the vascular structures are derived from the tumour itself. These tumours are highly aggressive and do not respond well to anti-angiogenic therapy. Here, we use the well characterised ECV304 cell line, now known as the bladder cancer epithelial cell line T24/83 which shows both epithelial and endothelial characteristics, as a model of in vitro vasculogenic mimicry. Using optimised ratios of co-cultures of ECV304 and C378 human fibroblasts, tubular structures were identifiable after 8 days. The tubular structures showed high levels of TG2 antigen and TG in situ activity. Tubular structures and in situ activity could be blocked either by site-directed irreversible inhibitors of TG2 or by silencing the ECV304 TG2 by antisense transfection. In situ activity for TG2 showed co-localisation with both fibronectin and collagen IV. Deposition of these proteins into the extracellular matrix could be reduced by inclusion of non-cell penetrating TG inhibitors when analysed by Western blotting suggesting that the contribution of TG2 to tube formation is extracellular. Incubation of ECV304 cells with these same irreversible inhibitors reduced cell migration which paralleled a loss in focal adhesion assembly, actin cytoskeleton formation and fibronectin deposition. TG2 appears essential for ECV304 tube formation, thus representing a potential novel therapeutic target in the inhibition of vasculogenic mimicry.

Cancer stem cells in tumor heterogeneity

Cancer cells within a given tumor were long regarded as a largely homogeneous group of cells originating from a common progenitor cell. However, it is increasingly appreciated that there is a considerable heterogeneity within tumors also on the tumor cell level. This heterogeneity extends to virtually all measurable properties of cancer cells, ranging from differentiation state, proliferation rate, migratory and invasive capacity to size, and therapeutic response. Such heterogeneity likely represents a major therapeutic hurdle, but the mechanisms underlying its emergence remain poorly understood and a controversial topic. The cancer stem cell model of tumor progression has gained increasing support during the past several years. In this review, I will discuss some major implications of the cancer stem cell hypothesis on the origins of tumor heterogeneity, focusing both on heterogeneity within the tumor cells proper and on potential transdifferentiation of cancer stem cells into stromal and endothelial lineages, as well as on heterogeneity of the therapeutic response. Evidence for and against a direct and causal role of cancer stem cells in the emergence of tumor heterogeneity will be weighed and alternative explanations for apparently contradictory observations discussed. Finally, I will discuss the potential origins of cancer stem cells and the various implications of origin to the contribution to tumor heterogeneity, and outline some future directions.

Breast carcinomatous tumoral emboli can result from encircling lymphovasculogenesis rather than lymphovascular invasion

The canonical view of the origin of tumor lymphovascular emboli is that they usually originate from lymphovascular invasion as part of a multistep metastatic process. Recent experimental evidence has suggested that metastasis can occur earlier than previously thought and we found evidence that tumor emboli formation can result from the short-circuiting step of encircling lymphovasculogenesis. Experimentally, we used a xenograft of human inflammatory breast cancer (MARY-X), a model that exhibited florid tumor emboli, to generate tumoral spheroids in vitro. In observational studies, we chose human breast carcinoma cases where there appeared to be a possible transition of in situ carcinoma to lymphovascular emboli without intervening stromal invasion. These cases were studied by morphometry as well as IHC with tumor proliferation (Ki-67) and adhesion (E-cadherin) markers, myoepithelial (p63), as well as endothelial (podoplanin [D2-40], CD31, VEGFR-3, Prox-1) markers. Unlabelled spheroids coinjected with either GFP or RFP-human myoepithelial cells or murine embryonal fibroblasts (MEFs) gave rise to tumors which exhibited GFP/RFP immunoreactivity within the cells lining the emboli-containing lymphovascular channels. In vitro studies demonstrated that the tumoral spheroids induced endothelial differentiation of cocultured myoepithelial cells and MEFs, measured by real time PCR and immunofluorescence. In humans, the in situ clusters exhibited similar proliferation, E-cadherin immunoreactivity and size as the tumor emboli (p =.5), suggesting the possibility that the latter originated from the former. The in situclusters exhibited a loss (50%-100%) of p63 myoepithelial immunoreactivity but not E-cadherin epithelial immunoreactivity. The tumor emboli were mainly present within lymphatic channels whose dual p63/CD31, p63/D2-40 and p63/VEGFR-3 and overall weak patterns of D2-40/CD31/VEGFR-3 immunoreactivities suggested that they represented immature and newly created vasculature derived from originally myoepithelial-lined ducts. Collectively both experimental as well as observational studies suggested the possibility that these breast cancer emboli resulted from encircling lymphovasculogenesis rather than conventional lymphovascular invasion.

Overexpression of microtubule-associated protein-1 light chain 3 is associated with melanoma metastasis and vasculogenic mimicry

Vasculogenic mimicry (VM) is an alternative type of blood supplement and is responsible for aggressive tumor biology and increased tumor-related mortality. Tumor cells obtain oxygen and nutriment through VM channels in the early, rapid-growth stage when blood vessels are insufficient. VM channels are characterized by tubular structures with tumor cells. Autophagy is a catabolic process, by which the cell digests damaged components or organelles of its own cytoplasm in response to nutrient deprivation, hypoxia, and the presence of non-functional protein aggregates. In fact, autophagy plays an important role in normal cell growth, development, and homeostasis. However, it is still controversial whether autophagy is also involved in cell death or cell survival in malignancy. In the present study, we therefore investigated the expression levels of two autophagy-related proteins, microtubule-associated protein-1 light chain 3 (LC3) and beclin-1, with respect to melanoma metastasis and vasculogenic mimicry. Melanoma is characterized by rapid growth, high-metastasis rate, and unpredictable behavior. A total of 70 human melanoma tissues were analyzed, showing that VM was present in 31 melanoma specimens (44.3%). Melanoma cells displayed high levels of autophagy when VM was present. Real-time quantitative PCR and immunohistochemical analyses showed that the expression levels of beclin-1 and LC3 mRNAs and proteins were both higher in the VM-positive melanoma than those in the VM-negative melanoma (p<0.05). Moreover, the expression of LC3, rather than beclin-1, was strongly associated with metastasis and poor clinical prognosis of human melanoma. Therefore, the enhanced autophagic activity may be related to VM and metastasis of melanoma.

Vitamin D binding protein-macrophage activating factor inhibits HCC in SCID mice

BACKGROUND

A high incidence of recurrence after treatment is the most serious problem in hepatocellular carcinoma (HCC). Therefore, a new strategy for the treatment of the disease is needed. The aim of the present study was to investigate whether vitamin D binding protein-macrophage activating factor (DBP-maf) is able to inhibit the growth of HCC.

METHODS

The effects of DBP-maf on endothelial cells and macrophage were evaluated by WST-1 assay and phagocytosis assay, respectively. Human HCC cells (HepG2) were implanted into the dorsum of severe combined immunodeficiency (SCID) mice. These mice were divided into control and DBP-maf treatment groups (n = 10/group). The mice in the treatment group received 40 ng/kg/d of DBP-maf for 21 d.

RESULTS

DBP-maf showed anti-proliferative activity against endothelial cells and also activated phagocytosis by macrophages. DBP-maf inhibited the growth of HCC cells (treatment group: 126 ± 18mm(3), untreated group: 1691.5 ± 546.9mm(3), P = 0.0077). Histologic examinations of the tumors revealed the microvessel density was reduced and more macrophage infiltration was demonstrated in the tumor of mice in the treatment group.

CONCLUSION

DBP-maf has at least two novel functions, namely, an anti-angiogenic activity and tumor killing activity through the activation of macrophages. DBP-maf may therefore represent a new strategy for the treatment of HCC.

Breast carcinomatous tumoral emboli can result from encircling lymphovasculogenesis rather than lymphovascular invasion

The canonical view of the origin of tumor lymphovascular emboli is that they usually originate from lymphovascular invasion as part of a multistep metastatic process. Recent experimental evidence has suggested that metastasis can occur earlier than previously thought and we found evidence that tumor emboli formation can result from the short-circuiting step of encircling lymphovasculogenesis. Experimentally, we used a xenograft of human inflammatory breast cancer (MARY-X), a model that exhibited florid tumor emboli, to generate tumoral spheroids in vitro. In observational studies, we chose human breast carcinoma cases where there appeared to be a possible transition of in situ carcinoma to lymphovascular emboli without intervening stromal invasion. These cases were studied by morphometry as well as IHC with tumor proliferation (Ki-67) and adhesion (E-cadherin) markers, myoepithelial (p63), as well as endothelial (podoplanin [D2-40], CD31, VEGFR-3, Prox-1) markers. Unlabelled spheroids coinjected with either GFP or RFP-human myoepithelial cells or murine embryonal fibroblasts (MEFs) gave rise to tumors which exhibited GFP/RFP immunoreactivity within the cells lining the emboli-containing lymphovascular channels. In vitro studies demonstrated that the tumoral spheroids induced endothelial differentiation of cocultured myoepithelial cells and MEFs, measured by real time PCR and immunofluorescence. In humans, the in situ clusters exhibited similar proliferation, E-cadherin immunoreactivity and size as the tumor emboli (p =.5), suggesting the possibility that the latter originated from the former. The in situclusters exhibited a loss (50%-100%) of p63 myoepithelial immunoreactivity but not E-cadherin epithelial immunoreactivity. The tumor emboli were mainly present within lymphatic channels whose dual p63/CD31, p63/D2-40 and p63/VEGFR-3 and overall weak patterns of D2-40/CD31/VEGFR-3 immunoreactivities suggested that they represented immature and newly created vasculature derived from originally myoepithelial-lined ducts. Collectively both experimental as well as observational studies suggested the possibility that these breast cancer emboli resulted from encircling lymphovasculogenesis rather than conventional lymphovascular invasion.

Eph receptors and ephrin ligands: important players in angiogenesis and tumor angiogenesis

Eph receptors and their ephrin ligands were identified in the late 1980's. Subsequently, they were linked to different physiological and pathophysiological processes like embryonic development, angiogenesis, and tumorigenesis. In this regard, recent work focused on the distribution and effects of Eph receptors and ephrins on tumor cells and tumor microenvironment. The purpose of this review is to outline the role of these molecules in physiological angiogenesis and pathophysiological tumor angiogenesis. Furthermore, novel therapeutical approaches are discussed as Eph receptors and ephrins represent attractive targets for antiangiogenic therapy.

Expression and functional significance of Twist1 in hepatocellular carcinoma: its role in vasculogenic mimicry

The up-regulation and nuclear relocation of epithelial-mesenchymal transition (EMT) regulator Twist1 have been implicated in the tumor invasion and metastasis of human hepatocellular carcinoma (HCC). The term vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. However, the relationship between Twist1 and VM formation is not clear. In this study, we explored HCC as a VM and EMT model in order to investigate the role of Twist1 in VM formation. We first examined the expression of Twist1 in human HCC samples and cell lines and found that Twist1 was frequently overexpressed in the nuclear relocation occurring in VM-positive HCCs (13/18 [72%]). Twist1 nuclear expression was likewise significantly associated with VM formation. Clinicopathological analysis revealed that both VM and Twist1 nuclear expressions present shorter survival durations than those without expression. We consistently demonstrated that an overexpression of Twist1 significantly enhanced cell motility, invasiveness, and VM formation in an HepG2 cell. Conversely, a knockdown of Twist1 by the short hairpin RNA approach remarkably reduced Bel7402 cell migration, invasion, and VM formation. Using chromatin immunoprecipitation, we also showed that Twist1 binds to the vascular endothelial (VE)-cadherin promoter and enhances its activity in a transactivation assay.

CONCLUSION

The results of this study indicate that Twist1 induces HCC cell plasticity in VM cells more through the suppression of E-cadherin expression and the induction of VE-cadherin up-regulation than through the VM pattern in vivo and in a three-dimensional in vitro system. Our findings also demonstrate a novel cogitation in cancer stem-like cell differentiation and that related molecular pathways may be used as novel therapeutic targets for the inhibition of HCC angiogenesis and metastasis.

Senescence-induced alterations of laminin chain expression modulate tumorigenicity of prostate cancer cells

Prostate cancer is an age-associated epithelial cancer, and as such, it contributes significantly to the mortality of the elderly. Senescence is one possible mechanism by which the body defends itself against various epithelial cancers. Senescent cells alter the microenvironment, in part, through changes to the extracellular matrix. Laminins (LMs) are extracellular proteins important to both the structure and function of the microenvironment. Overexpression of the senescence-associated gene mac25 in human prostate cancer cells resulted in increased mRNA levels of the LM alpha4 and beta2 chains compared to empty vector control cells. The purpose of this study was to examine the effects of these senescence-induced LM chains on tumorigenicity of prostate cancer cells. We created stable M12 human prostate cancer lines overexpressing either the LM alpha4 or beta2 chain or both chains. Increased expression of either the LM alpha4 or beta2 chain resulted in increased in vitro migration and in vivo tumorigenicity of those cells, whereas high expression of both chains led to decreased in vitro proliferation and in vivo tumorigenicity compared to M12 control cells. This study demonstrates that senescent prostate epithelial cells can alter the microenvironment and that these changes modulate progression of prostate cancer.

Tissue-type plasminogen activator has antiangiogenic properties without effect on tumor growth in a rat C6 glioma model

Tissue-type plasminogen activator (tPA) plays a major role in the fibrinolytic system. According to several reports, tPA may also have antiangiogenic properties, especially in combination with a free sulfhydryl donor (FSD). In the rat C6 glioma model, in vitro and in vivo tPA synthesis by glioma cells is enhanced by differentiation therapy. To address the antiangiogenic potential of tPA in this model, tPA was overexpressed in glioma tumors by ex vivo transduction of C6 cells with a lentiviral vector encoding tPA. The transduced cells were subcutaneously implanted into nude mice. Gene transfer allowed for efficient synthesis of tPA by the C6 tumors. Although the treatment of tPA+ tumor-bearing animals with the FSD captopril generated angiostatin in situ and reduced endothelial vascularization of the tumors, it had no effect on tumor growth. Alternative mechanisms could account for this lack of effect and consequently have important implications for vascular the treatment of glioblastoma.

Therapeutic Targets of Multiple Angiogenic Factors for the Treatment of Cancer and Metastasis

Like any growing healthy tissues, tumors build up their blood vessels by three mechanisms: angiogenesis, vasculogenesis, and intersucception. Vascular endothelial growth factor-A (VEGF-A) is one of the key factors responsible for stimulation and maintenance of the disorganized, leaky, and torturous tumor vasculature. In addition to VEGF-A, tumors produce multiple other factors to stimulate blood vessel growth. These include members in the platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), VEGF-C, insulin-like growth factor (IGF), angiopoietin (Ang), and hepatocyte growth factor (HGF) families. Recent studies show that these angiogenic factors can also promote lymphangiogenesis and potentially lymphatic metastasis. Understanding the roles of individual and combined angiogenic factors in promoting tumor angiogenesis is crucial for defining therapeutic targets and antiangiogenic drug development for the treatment of cancer.

Hypoxia influences vasculogenic mimicry channel formation and tumor invasion-related protein expression in melanoma

BACKGROUND

Hypoxia can enhance tumor cell invasion and metastasis. The cause and the molecular mechanism are still not clear.

METHODS

In our study, mouse melanoma B16 cells were inoculated into mouse ischemic limbs and non-ischemic controls and the engrafted melanomas were subsequently observed. Vasculogenic mimicry channels in melanoma tumors of the two groups were counted and the expression of HIF-1alpha, MMP-2, MMP-9 and VEGF was assessed by immunohistochemical staining. Formalin-fixed, paraffin-embedded tissues were used for immunohistochemical staining.

RESULTS

In the early stage of engrafted melanoma growth, the size of melanomas in ischemic limbs increased slower than in the controls. However, later there was no obvious difference in their size. Melanoma tumors in the ischemic group had more vasculogenic mimicry channels than those in the controls (P=0.039). Similarly, the expression of HIF-1alpha, MMP-2, MMP-9 and VEGF was higher in the ischemic group than in the non-ischemic controls (P=0.024, 0.047, 0.007 and 0.025, respectively). There was a positive association in melanoma cells of the ischemic group between expression of HIF-1alpha and VEGF, and also between MMP-9 and MMP-2. In the ischemic group, there was statistical significance for the correlation between HIF-1alpha and VEGF expression (r=0.456, P=0.038). Furthermore, MMP-2 expression was positively correlated with MMP-9 and VEGF expression (r=0.589 and 0.502, P=0.008 and 0.024, respectively).

CONCLUSIONS

Melanoma cells in a hypoxic microenvironment increased HIF-1alpha expression and induced the formation of vasculogenic mimicry channels to acquire an adequate blood supply. On the other hand, the expression of MMP-2 and MMP-9 in tumor tissue increased to enhance the invasiveness. HIF-1alpha, MMP-2 and MMP-9 may be associated with the failure of stop-flow perfusion in some patients with melanoma.

Heterogeneity of Tie2 expression in tumor microcirculation: influence of cancer type, implantation site, and response to therapy

To evaluate the expression of the Tie2/Tek tyrosine kinase receptor in tumor blood vessels, we examined Tie2lacZ(+)/RAG1(-) mice. There was considerable heterogeneity (Tie2-negative, Tie2-positive, or Tie2-composite blood vessels) in subcutaneous xenografts of human colorectal carcinoma (HCT116; 97.5% Tie2-positive vessels) versus human melanoma (WM115; 75.9% Tie2-positive vessels). Similar patterns of Tie2 expression occurred in abdominal metastases derived from the same cell lines. Immunostaining for endothelial markers and Tie2 revealed that endogenous protein levels corresponded with transgene activity. Endothelial cells were confirmed to be of mouse origin through triple immunofluorescence staining with mouse antiserum to human nuclei, isolectin GS-IB(4), and anti-Tie2. Similar Tie2 heterogeneity was observed in clinical specimens from a variety of human cancers, including malignant melanoma and colorectal carcinoma. We also examined the effect of Tek-Delta Fc anti-angiogenic therapy on tumor growth and Tie2 expression patterns in HCT116 and WM115 subcutaneous xenografts. Tek-Delta induced extensive tumor regression in HCT116 tumors and concomitant reductions in Tie2-expressing blood vessels. However, no significant responses were seen in Tek-Delta-treated WM115 tumors. Thus, vascular heterogeneity of Tie2 expression is cancer-type specific, suggesting that the tumor microenvironment and/or direct cancer cell interactions influence Tie2 endothelial expression.

Three-dimensional co-culture models to study prostate cancer growth, progression, and metastasis to bone

Cancer-stromal interaction results in the co-evolution of both the cancer cells and the surrounding host stromal cells. As a consequence of this interaction, cancer cells acquire increased malignant potential and stromal cells become more inductive. In this review we suggest that cancer-stromal interaction can best be investigated by three-dimensional (3D) co-culture models with the results validated by clinical specimens. We showed that 3D culture promoted bone formation in vitro, and explored for the first time, with the help of the astronauts of the Space Shuttle Columbia, the co-culture of human prostate cancer and bone cells to further understand the interactions between these cells. Continued exploration of cancer growth under 3D conditions will rapidly lead to new discoveries and ultimately to improvements in the treatment of men with hormonal refractory prostate 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.

Functional role of matrix metalloproteinases in ovarian tumor cell plasticity

OBJECTIVE

We previously demonstrated that aggressive ovarian cancer cells are able to display in vitro vasculogenic mimicry, which is reflected by their ability to form vasculogenic-like networks in 3-dimensional cultures and to express vascular cell-associated markers. The goal of this study was to examine the functional role of specific matrix metalloproteinases in the formation of vasculogenic-like networks and extracellular matrix remodeling in vitro. We also investigated the clinical relevance of matrix metalloproteinase-2 and -9 and membrane type 1-matrix metalloproteinase in human ovarian cancers with evidence of tumor cell-lined vasculature.

STUDY DESIGN

Ovarian cancer cells (A2780-PAR, SKOV3, and EG) were seeded onto separate 3-dimensional cultures that contained either Matrigel or type I collagen, in the absence of endothelial cells or fibroblasts. These cultures were treated with either chemically modified tetracycline-3 (general matrix metalloproteinase inhibitor), recombinant tissue inhibitor of metalloproteinase-1 or -2, or function-blocking antibodies to matrix metalloproteinase-2 or -9 or membrane type 1-matrix metalloproteinase. In addition, 78 invasive epithelial ovarian cancers were evaluated for expression of matrix metalloproteinase-2 and -9 and membrane type 1-matrix metalloproteinase and correlated with various clinical parameters.

RESULTS

The aggressive ovarian cancer cells (SKOV3 and EG) were able to form in vitro vasculogenic-like networks and contract 3-dimensional collagen I gels, whereas the poorly aggressive A2780-PAR cell line did not. Chemically modified tetracycline-3 completely blocked the network formation. Blocking antibodies to matrix metalloproteinase-2 and membrane type 1-matrix metalloproteinase inhibited the formation of the vasculogenic-like networks and collagen gel contraction, but the antibody to matrix metalloproteinase-9 had no effect on network formation and minimal effect on gel contraction. Treatment of 3-dimensional cultures with tissue inhibitor of metalloproteinase-2 retarded the network formation and only small, partially developed structures were noted that did not form network connections. Tissue inhibitor of metalloproteinase-1 had no appreciable effect on the extent or efficiency of network formation. Human invasive ovarian cancers with evidence of tumor cell-lined vasculature were significantly more likely to have strong epithelial and stromal matrix metalloproteinase-2 and -9 and membrane type 1-matrix metalloproteinase expression (all probability values were <.05).

CONCLUSION

Matrix metalloproteinase-2 and membrane type 1-matrix metalloproteinase appear to play a key role in the development of vasculogenic-like networks and matrix remodeling by aggressive ovarian cancer cells. Human ovarian cancers with matrix metalloproteinase overexpression are more likely to have tumor cell-lined vasculature. These results may offer new insights for consideration in ovarian cancer treatment strategies.

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.