Tumor endothelial marker 8 amplifies canonical Wnt signaling in blood vessels

TEM8 in Oncogenesis: Protein Biology, Pre-Clinical Agents, and Clinical Rationale

The TEM8 protein represents an emerging biomarker in many solid tumor histologies. Given the various roles it plays in oncogenesis, including but not limited to angiogenesis, epithelial-to-mesenchymal transition, and cell migration, TEM8 has recently served and will continue to serve as the target of novel oncologic therapies. We review herein the role of TEM8 in oncogenesis. We review its normal function, highlight the additional roles it plays in the tumor microenvironment, and synthesize pre-clinical and clinical data currently available. We underline the protein's prognostic and predictive abilities in various solid tumors by (1) highlighting its association with more aggressive disease biology and poor clinical outcomes and (2) assessing its associated clinical trial landscape. Finally, we offer future directions for clinical studies involving TEM8, including incorporating pre-clinical agents into clinical trials and combining previously tested oncologic therapies with currently available treatments, such as immunotherapy.

Evolving role of seneca valley virus and its biomarker TEM8/ANTXR1 in cancer therapeutics

Oncolytic viruses have made a significant inroad in cancer drug development. Numerous clinical trials are currently investigating oncolytic viruses both as single agents or in combination with various immunomodulators. Oncolytic viruses (OV) are an integral pillar of immuno-oncology and hold potential for not only delivering durable anti-tumor responses but also converting “cold” tumors to “hot” tumors. In this review we will discuss one such promising oncolytic virus called Seneca Valley Virus (SVV-001) and its therapeutic implications. SVV development has seen seismic evolution over the past decade and now boasts of being the only OV with a practically applicable biomarker for viral tropism. We discuss relevant preclinical and clinical data involving SVV and how bio-selecting for TEM8/ANTXR1, a negative tumor prognosticator can lead to first of its kind biomarker driven oncolytic viral cancer therapy.

TEM8 marks neovasculogenic tumor-initiating cells in triple-negative breast cancer

Enhanced neovasculogenesis, especially vasculogenic mimicry (VM), contributes to the development of triple-negative breast cancer (TNBC). Breast tumor-initiating cells (BTICs) are involved in forming VM; however, the specific VM-forming BTIC population and the regulatory mechanisms remain undefined. We find that tumor endothelial marker 8 (TEM8) is abundantly expressed in TNBC and serves as a marker for VM-forming BTICs. Mechanistically, TEM8 increases active RhoC level and induces ROCK1-mediated phosphorylation of SMAD5, in a cascade essential for promoting stemness and VM capacity of breast cancer cells. ASB10, an estrogen receptor ERα trans-activated E3 ligase, ubiquitylates TEM8 for degradation, and its deficiency in TNBC resulted in a high homeostatic level of TEM8. In this work, we identify TEM8 as a functional marker for VM-forming BTICs in TNBC, providing a target for the development of effective therapies against TNBC targeting both BTIC self-renewal and neovasculogenesis simultaneously.

Vasculogenic mimicry (VM) contributes to the development of triple-negative breast cancer. In this study, the authors show that TEM8 is expressed in VM-forming breast cancer stem cells and it promotes stemness and VM differentiation capacity through a RhoC/ROCK1/SMAD5 axis

Intussusceptive angiogenesis as a key therapeutic target for cancer therapy

Deregulation of angiogenesis is a key reason for tumor growth and progression. Several anti-angiogenic drugs in clinical practice attempt to normalize abnormal tumor vasculature. Unfortunately, these drugs are ineffective due to the development of resistance in patients after drug holidays. A sizable literature suggests that resistance to these anti-angiogenic drugs occurs due to various compensatory mechanisms of tumor angiogenesis. Therefore, we describe different compensatory mechanisms of tumor angiogenesis, and explain why intussusceptive angiogenesis (IA), is a crucial mechanism of compensatory angiogenesis in tumors which resist anti-VEGF (vascular endothelial growth factor) therapies. IA is often overlooked due to the scarcity of experimental models. Therefore, we examine data from existing experimental models and our novel ex-ovo model of angiogenesis in chick embryos, and explain the important genes and signaling pathways driving IA. Using bio-informatic analyses of major genes regulating conventional sprouting angiogenesis (SA) and intussusceptive angiogenesis, we provide fresh insights on the 'angiogenic switch' which regulates the transition from SA to IA. Finally, we examine the interplay between molecules regulating SA, IA, and molecules known to promote tumor progression. Based on these analyses, we conclude that intussusceptive angiogenesis (IA) is a promising therapeutic target for developing effective anti-cancer treatment regimes.

SIS/aligned fibre scaffold designed to meet layered oesophageal tissue complexity and properties

With donor organs not readily available, the need for a tissue-engineered oesophagus remains high, particularly for congenital childhood conditions such as atresia. Previous attempts have not been successful, and challenges remain. Small intestine submucosa (SIS) is an acellular matrix material with good biological properties; however, as is common with these types of materials, they demonstrate poor mechanical properties. In this work, electrospinning was performed to mechanically reinforce tubular SIS with polylactic-co-glycolic acid (PLGA) nanofibres. It was hypothesised that if attachment could be achieved between the two materials, then this would (i) improve the SIS mechanical properties, (ii) facilitate smooth muscle cell alignment to support directional growth of muscle cells and (iii) allow for the delivery of bioactive molecules (VEGF in this instance). Through a relatively simple multistage process, adhesion between the layers was achieved without chemically altering the SIS. It was also found that altering mandrel rotation speed affected the alignment of the PLGA nanofibres. SIS-PLGA scaffolds performed mechanically better than SIS alone; yield stress improvement was 200% and 400% along the longitudinal and circumferential directions, respectively. Smooth muscle cells cultured on the aligned fibres showed resultant unidirectional alignment. In vivo the SIS-PLGA scaffolds demonstrated limited foreign body reaction judged by the type and proportion of immune cells present and lack of fibrous encapsulation. The scaffolds remained intact at 4 weeks in vivo, and good cellular infiltration was observed. The incorporation of VEGF within SIS-PLGA scaffolds increased the blood vessel density of the surrounding tissues, highlighting the possible stimulation of endothelialisation by angiogenic factor delivery. Overall, the designed SIS-PLGA-VEGF hybrid scaffolds might be used as a potential matrix platform for oesophageal tissue engineering. In addition to this, achieving improved attachment between layers of acellular matrix materials and electrospun fibre layers offers the potential utility in other applications. STATEMENT OF SIGNIFICANCE: Because of its multi-layered nature and complex structure, the oesophagus tissue poses several challenges for successful clinical grafting. Therefore, it is promising to utilise tissue engineering strategies to mimic and form structural compartments for its recovery. In this context, we investigated the use of tubular small intestine submucosa (SIS) reinforced with polylactic-co-glycolic acid (PLGA) nanofibres by using electrospinning and also, amongst other parameters, the integrity of the bilayered structure created. This was carried out to facilitate smooth muscle cell alignment, support directional growth of muscle cells and allow the delivery of bioactive molecules (VEGF in this study). We evaluated this approach by using in vitro and in vivo models to determine the efficacy of this new system.

The Anthrax Toxin Receptor 1 (ANTXR1) Is Enriched in Pancreatic Cancer Stem Cells Derived from Primary Tumor Cultures

Pancreatic ductal adenocarcinoma (PDAC) is currently the fourth leading cause of cancer-related mortality. Cancer stem cells (CSCs) have been shown to be the drivers of pancreatic tumor growth, metastasis, and chemoresistance, but our understanding of these cells is still limited by our inability to efficiently identify and isolate them. While a number of markers capable of identifying pancreatic CSCs (PaCSCs) have been discovered since 2007, there is no doubt that more markers are still needed. The anthrax toxin receptor 1 (ANTXR1) was identified as a functional biomarker of triple-negative breast CSCs, and PDAC patients stratified based on ANTXR1 expression levels showed increased mortality and enrichment of pathways known to be necessary for CSC biology, including TGF-β, NOTCH, Wnt/β-catenin, and IL-6/JAK/STAT3 signaling and epithelial to mesenchymal transition, suggesting that ANTXR1 may represent a putative PaCSC marker. In this study, we show that ANTXR1⁺ cells are not only detectable across a panel of 7 PDAC patient-derived xenograft primary cultures but ANTXR1 expression significantly increased in CSC-enriched 3D sphere cultures. Importantly, ANTXR1⁺ cells also coexpressed other known PaCSC markers such as CD44, CD133, and autofluorescence, and ANTXR1⁺ cells displayed enhanced CSC functional and molecular properties, including increased self-renewal and expression of pluripotency-associated genes, compared to ANTXR1⁻ cells. Thus, this study validates ANTXR1 as a new PaCSC marker and we propose its use in identifying CSCs in this tumor type and its exploitation in the development of CSC-targeted therapies for PDAC.

Nitric oxide regulates intussusceptive-like angiogenesis in wound repair in chicken embryo and transgenic zebrafish models

Angiogenesis is the formation of new blood vessels that occurs by two distinct processes following sprouting angiogenesis (SA) and intussusceptive angiogenesis (IA). Nitric oxide (NO) is known for its pro-angiogenic functions. However, no clear mechanisms are delineated on its role in promoting angiogenesis in reparative wound healing. We propose that NO regulates SA to IA transition and vice versa in wound milieu. We have used three models which include a new chick embryo extra-vasculature (CEV) burn wound model, adult Tie2-GFP transgenic Zebrafish caudal fin regeneration model and Zebrafish skin wound model to study the mechanisms underlying behind the role of NO in wound healing. Wounds created in CEV were treated with NO donor (Spermine NONOate (SPNO)), NOS inhibitor (L-nitro-l-arginine-methyl ester (l-NAME)), NaNO₂, NaNO₃, and beetroot juice, a nitrite-rich juice respectively and the pattern of wound healing was assessed. Morphological and histological techniques tracked the wound healing at the cellular level, and the molecular changes were investigated by using real-time RT-PCR gene expression analysis. The result concludes that NO donor promotes wound healing by activating SA at an early phase of healing while NOS inhibitor induces wound healing via IA. At the later phase of wound healing NO donor followed IA while NOS inhibitor failed to promote wound repair. The current work underpinned a differential regulation of NO on angiogenesis in wound milieu and this study would provide new insights in designing therapeutics for promoting wound repair.

Tumor endothelial marker 8 promotes cancer progression and metastasis

Every year more than 8 million people suffer from cancer-related deaths worldwide [1]. Metastasis, the spread of cancer to distant sites, accounts for 90% of these deaths. A promising target for blocking tumor progression, without causing severe side effects [2], is Tumor Endothelial Marker 8 (TEM8), an integrin-like cell surface protein expressed predominantly in the tumor endothelium and in cancer cells [3, 4]. Here, we have investigated the role of TEM8 in cancer progression, angiogenesis and metastasis in invasive breast cancer, and validated the main findings and important results in colorectal cancer. We show that the loss of TEM8 in cancer cells results in inhibition of cancer progression, reduction in tumor angiogenesis and reduced metastatic burden in breast cancer mouse models. Furthermore, we show that TEM8 regulates cancer progression by affecting the expression levels of cell cycle-related genes. Taken together, our findings may have broad clinical and therapeutic potential for breast and colorectal primary tumor and metastasis treatment by targeting TEM8.

Nitric oxide signaling regulates tumor-induced intussusceptive-like angiogenesis

Existing animal models for screening tumor angiogenic process have various setbacks that necessitate further investigations. In this study, we developed an ex-ovo egg yolk angiogenesis model to screen the angiogenic potency of tumor cells (HeLa and SiHa cell lines). The egg yolk angiogenesis assay was applied to study the nitric oxide (NO) influence on switching from sprouting angiogenesis (SA) to intussusceptive angiogenesis (IA) under tumor microenvironment. Morphological analysis and SA-like or IA-like markers expression were determined during the development of chicken chorioallantoic membrane (CAM) from day 5 to 13. Expression of Notch1, Notch2, EphrinB2, and Tie2 were considered as SA-like while TEM8, CALD1, CXCR4 and HOMX1 were followed as IA-like markers. The HeLa and SiHa cell lines embedded CAM showed an increase in micro and macro blood vessels and vascular size, junction and length which are the pivotal morphological parameters of angiogenesis. Further, the study revealed that HeLa is more aggressive than SiHa in inducing tumor angiogenesis. To determine the NO signaling implication in tumor milieu, NO donor (Spermine NONOate (SPNO)), NOS inhibitor (L-nitro-L-arginine-methyl ester (L-NAME) and VEGF inhibitor (Avastin) were administrated to chick embryo vascular bed with and without HeLa cells. The results demonstrated that HeLa cells promote IA through NO signaling, VEGF and eNOS and it was documented by angiogenic morphological parameters and SA-like or IA-like markers expression. Therefore, our study claims that ex-ovo egg yolk angiogenesis model could be used to study tumor angiogenesis and NO plays a key role in switching of IA under tumor microenvironment.

A biallelic ANTXR1 variant expands the anthrax toxin receptor associated phenotype to tooth agenesis

Tooth development is regulated by multiple genetic pathways, which ultimately drive the complex interactions between the oral epithelium and mesenchyme. Disruptions at any time point during this process may lead to failure of tooth development, also known as tooth agenesis (TA). TA is a common craniofacial abnormality in humans and represents the failure to develop one or more permanent teeth. Many genes and potentially subtle variants in these genes contribute to the TA phenotype. We report the clinical and genetic impact of a rare homozygous ANTXR1 variant (c.1312C>T), identified by whole exome sequencing (WES), in a consanguineous Turkish family with TA. Mutations in ANTXR1 have been associated with GAPO (growth retardation, alopecia, pseudoanodontia, and optic atrophy) syndrome and infantile hemangioma, however no clinical characteristics associated with these conditions were observed in our study family. We detected the expression of Antxr1 in oral and dental tissues of developing mouse embryos, further supporting a role for this gene in tooth development. Our findings implicate ANTXR1 as a candidate gene for isolated TA, suggest the involvement of specific hypomorphic alleles, and expand the previously known ANTXR1-associated phenotypes.

MicroRNA-493 suppresses hepatocellular carcinoma tumorigenesis through down-regulation of anthrax toxin receptor 1 (ANTXR1) and R-Spondin 2 (RSPO2)

Hepatocellular carcinoma (HCC) is known as a highly prevalent cancer with a poor prognosis and short survival time, despite intensive research and clinical efforts. Increasing numbers of studies have reported that microRNAs are involved in the malignant behavior of hepatocellular carcinoma cells via directly targeting multiple oncogenes or tumor suppressors. Here, we report that the expression of microRNA-493 (miR-493) is decreased in HCC cell lines and in tumor tissues. Overexpression of miR-493 in HCC cells dramatically inhibited cell proliferation and colony-formation in vitro and inhibited tumor formation of HCC cell xenografts in vivo. miR-493 also suppressed cell migration and invasion in HCC cell lines. Novel targets ANTXR1 and RSPO2 were confirmed to be suppressed by miR-493 directly, and overexpression of ANTXR1 and RSPO2 could restore tumorigenesis in miR-493 treated HCC cell. Moreover, Wnt/β-catenin signaling pathway, which was reported to be activated by ANTXR1 and RSPO2, was also inhibited by miR-493 overexpression and might be involved in anti-tumor function of miR-493. These findings suggest that miR-493 acts as a negative regulator in hepatocellular carcinoma progression and may be a potential therapeutic target for HCC.

A candidate transacting modulator of fetal hemoglobin gene expression in the Arab-Indian haplotype of sickle cell anemia

Fetal hemoglobin (HbF) levels are higher in the Arab-Indian (AI) β-globin gene haplotype of sickle cell anemia compared with African-origin haplotypes. To study genetic elements that effect HbF expression in the AI haplotype we completed whole genome sequencing in 14 Saudi AI haplotype sickle hemoglobin homozygotes-seven selected for low HbF (8.2% ± 1.3%) and seven selected for high HbF (23.5% ± 2.6%). An intronic single nucleotide polymorphism (SNP) in ANTXR1, an anthrax toxin receptor (chromosome 2p13), was associated with HbF. These results were replicated in two independent Saudi AI haplotype cohorts of 120 and 139 patients, but not in 76 Saudi Benin haplotype, 894 African origin haplotype and 44 AI haplotype patients of Indian origin, suggesting that this association is effective only in the Saudi AI haplotype background. ANTXR1 variants explained 10% of the HbF variability compared with 8% for BCL11A. These two genes had independent, additive effects on HbF and together explained about 15% of HbF variability in Saudi AI sickle cell anemia patients. ANTXR1 was expressed at mRNA and protein levels in erythroid progenitors derived from induced pluripotent stem cells (iPSCs) and CD34⁺ cells. As CD34⁺ cells matured and their HbF decreased ANTXR1 expression increased; as iPSCs differentiated and their HbF increased, ANTXR1 expression decreased. Along with elements in cis to the HbF genes, ANTXR1 contributes to the variation in HbF in Saudi AI haplotype sickle cell anemia and is the first gene in trans to HBB that is associated with HbF only in carriers of the Saudi AI haplotype. Am. J. Hematol. 91:1118-1122, 2016. © 2016 Wiley Periodicals, Inc.

Fell-Muir Lecture: Regulatory mechanisms of skeletal and connective tissue development and homeostasis - lessons from studies of human disorders

Studies of proliferative hemangiomas have led to the discovery that interactions of endothelial cells with extracellular matrix and/or Vascular Endothelial Growth Factor (VEGF)-A stimulate the expression of VEGFR1, the VEGF decoy receptor, and suppress VEGF-dependent VEGFR2 signalling by a mechanism that requires the matrix-binding receptor Anthrax Toxin Receptor (ANTXR)1, VEGFR2, β1 integrin and the Nuclear Factor of Activated T cells (NFAT). In hemangioma endothelial cells, all these components are present, but are functionally compromised, so that the levels of VEGFR1 are extremely low and VEGFR2 signalling is constitutively active. Consequently, the levels of Hypoxia Inducible Factor (HIF)-1α and its transcriptional targets, VEGF-A and C-X-C motif chemokine 12 (CxCl12), are elevated and a positive VEGF-A feedback loop is established. Overexpression of ANTXR1, carrying a heterozygous Ala-to-Thr mutation, induces hemangioma-like signalling in control endothelial cells; VEGF signalling is normalized when wild-type ANTXR1 is overexpressed in hemangioma cells. These findings suggest that ANTXR1 functions as a negative regulator of VEGF-A signalling. Studies of a mouse model of the Growth Retardation, Alopecia, Pseudo-anodontia and Optic Atrophy (GAPO) syndrome, caused by the loss-of-function mutations in ANTXR1, as well as knock-in mice carrying the Ala-to-Thr ANTXR1 mutation, confirm that ANTXR1 functions as a suppressor of VEGF-A signalling. Cutaneous endothelial cells isolated from ANTXR1-deficient mice exhibit low levels of VEGFR1, elevated levels of VEGF-A, HIF-1α and CxCl12 and activated VEGFR2 signalling as in hemangioma. Increased numbers of myeloid cells in the skin of ANTXR1-deficient mice are associated with reduced vascularity and increased skin fibrosis, suggesting a mechanism for hemangioma involution and replacement by fibrotic scars. Through controlling VEGF-A signalling and extracellular matrix synthesis, ANTXR1 is emerging as a key regulator of skeletal and connective tissue development and homeostasis.

In ovo administration of human recombinant leptin shows dose dependent angiogenic effect on chicken chorioallantoic membrane

Background

Leptin, the cytokine produced by white adipose tissue is known to regulate food energy homeostasis through its hypothalamic receptor. In vitro studies have demonstrated that leptin plays a major role in angiogenesis through binding to the receptor Ob-R present on ECs by stimulating and initiating new capillary like structures from ECs. Various in vivo studies indicate that leptin has diverse effect on angiogenesis. A few reports have showed that leptin exerts pro angiogenic effects while some suggested that it has antiangiogenic potential. It is theoretically highly important to understand the effect of leptin on angiogenesis to use as a therapeutic molecule in various angiogenesis related pathological conditions. Chicken chorio allantoic membrane (CAM) on 9th day of incubation was incubated with 1, 3 and 5 μg concentration of HRL for 72 h using gelatin sponge. Images where taken after every 24 h of incubation and analysed with Angioguant software. The treated area was observed under microscope and histological evaluation was performed for the same. Tissue thickness was calculated morphometrically from haematoxylin and eosin stained cross sections. Reverse transcriptase PCR and immunohistochemistry were also performed to study the gene and protein level expression of angiogenic molecules.

Results

HRL has the ability to induce new vessel formation at the treated area and growth of the newly formed vessels and cellular morphological changes occur in a dose dependent manner. Increase in the tissue thickness at the treated area is suggestive of initiation of new capillary like structures. Elevated mRNA and protein level expression of VEGF165 and MMP2 along with the activation of ECs as demonstrated by the presence of CD34 expression supports the neovascularization potential of HRL.

Conclusion

Angiogenic potential of HRL depends on the concentration and time of incubation and is involved in the activation of ECs along with the major interaction of VEGF 165 and MMP2. It is also observed that 3 μg of HRL exhibits maximum angiogenic potential at 72 h of incubation. Thus our data suggest that dose dependent angiogenic potential HRL could provide a novel role in angiogenic dependent therapeutics such as ischemia and wound healing conditions.

Chicken chorioallantoic membrane as a reliable model to evaluate osteosarcoma-an experimental approach using SaOS2 cell line

BACKGROUND

Osteosarcoma is the most common primary tumor that affects usually children. Due to its cellular complex and osteoid formation it is very difficult to understand the mechanism behind the progressiveness of osteosarcoma. Various animal models are available to study the issue but they are time consuming and costly. We aimed to understand the progressiveness and invasiveness of osteosarcoma induced by SaOS2 cells using chicken chorioallantoic membrane. CAM is a well-established model which allows in vivo studies of tumor induced angiogenesis and the testing of anti angiogenic molecules. However only a few reports showed the tumor forming ability of SaOS2 cells on CAM.

METHOD

Angiogenic ability of SaOS2 cells on CAM was validated by various methods. Angiogenic ability was scored by direct visualization and scanning microscopic analysis. The sprouting ability and growth of the vessel was measured by Angioquant software under different cellular volume. The invasiveness was analyzed by histological staining. Involvement of angiogenic factors at differential stage of progressiveness was confirmed by the molecular and protein level expression analysis.

RESULT

SaOS2 cells induces sprouting angiogenesis on CAM and shows its aggressiveness by rupturing the ectodermal layer of the CAM. Growth and development of osteosarcoma depends mainly on the activation of VEGF165, MMP2 and MMP9. CAM able to reproduce angiogenic response against the stimulation of SaOS2 cells exactly as in other animal models without inflammatory reactions.

CONCLUSION

CAM is an excellent alternative in vivo model for studying the aggressiveness and tumor progression of osteosarcoma using various angiogenic techniques in an easily, faster and affordable way. We further provided insight about the involvement of various angiogenic growth factors on the development of osteosarcoma which will enable to find the suitable therapeutic molecule for the treatment of osteosarcoma. CAM model could provide a wide space using modern techniques like micro array or in situ hybridization to have a better understanding about the progression and invasiveness of osteosarcoma cells to develop suitable therapeutic molecules.

Regulatory mechanisms of anthrax toxin receptor 1-dependent vascular and connective tissue homeostasis

It is well known that angiogenesis is linked to fibrotic processes in fibroproliferative diseases, but insights into pathophysiological processes are limited, due to lack of understanding of molecular mechanisms controlling endothelial and fibroblastic homeostasis. We demonstrate here that the matrix receptor anthrax toxin receptor 1 (ANTXR1), also known as tumor endothelial marker 8 (TEM8), is an essential component of these mechanisms. Loss of TEM8 function in mice causes reduced synthesis of endothelial basement membrane components and hyperproliferative and leaky blood vessels in skin. In addition, endothelial cell alterations in mutants are almost identical to those of endothelial cells in infantile hemangioma lesions, including activated VEGF receptor signaling in endothelial cells, increased expression of the downstream targets VEGF and CXCL12, and increased numbers of macrophages and mast cells. In contrast, loss of TEM8 in fibroblasts leads to increased rates of synthesis of fiber-forming collagens, resulting in progressive fibrosis in skin and other organs. Compromised interactions between TEM8-deficient endothelial and fibroblastic cells cause dramatic reduction in the activity of the matrix-degrading enzyme MMP2. In addition to insights into mechanisms of connective tissue homeostasis, our data provide molecular explanations for vascular and connective tissue abnormalities in GAPO syndrome, caused by loss-of-function mutations in ANTXR1. Furthermore, the loss of MMP2 activity suggests that fibrotic skin abnormalities in GAPO syndrome are, in part, the consequence of pathophysiological mechanisms underlying syndromes (NAO, Torg and Winchester) with multicentric skin nodulosis and osteolysis caused by homozygous loss-of-function mutations in MMP2.

Inhibition of pathological corneal neovascularization by a small peptide derived from human apolipoprotein (a) Kringle V

PURPOSE

The aim of this study was to evaluate the antiangiogenic activity of AU6, a novel 6-amino acid peptide derived from Kringle V of human apolipoprotein (a).

METHODS

RF/6A rhesus macaque choroid endothelial cells were used for in vitro studies. MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt] assays and modified Boyden chamber and Matrigel assays were used to evaluate the inhibitory effect of AU6 on vascular endothelial growth factor (VEGF)-stimulated endothelial cell functions, including cell proliferation, migration, and tube formation. The chick chorioallantoic membrane model, micropocket corneal neovascularization (CNV) model, and alkali burn CNV model were evaluated in vivo. Bevacizumab (Avastin), the VEGF-neutralizing antibody, and a scrambled peptide (AU6s) were used as positive and negative controls, respectively.

RESULTS

AU6 inhibited VEGF-induced RF/6A cell migration, proliferation, and tube formation. It also reduced pathological neovascularization in the chorioallantoic membrane model and in the 2 CNV models, that is, the mouse corneal micropocket model and the rat cornea alkali burn model.

CONCLUSIONS

AU6 effectively inhibited pathogenic CNV. This novel peptide shows potential as a new treatment for ocular neovascularization.

ANTXR1, a stem cell-enriched functional biomarker, connects collagen signaling to cancer stem-like cells and metastasis in breast cancer

Cancer stem-like cells are thought to contribute to tumor recurrence. The anthrax toxin receptor 1 (ANTXR1) has been identified as a functional biomarker of normal stem cells and breast cancer stem-like cells. Primary stem cell-enriched basal cells (CD49f(+)/EpCAM(-)/Lin(-)) expressed higher levels of ANTXR1 compared with mature luminal cells. CD49f(+)/EpCAM(-), CD44(+)/EpCAM(-), CD44(+)/CD24(-), or ALDEFLUOR-positive subpopulations of breast cancer cells were enriched for ANTXR1 expression. CD44(+)/CD24(-)/ANTXR1(+) cells displayed enhanced self-renewal as measured by mammosphere assay compared with CD44(+)/CD24(-)/ANTXR1(-) cells. Activation of ANTXR1 by its natural ligand C5A, a fragment of collagen VI α3, increased stem cell self-renewal in mammosphere assays and Wnt signaling including the expression of the Wnt receptor-lipoprotein receptor-related protein 6 (LRP6), phosphorylation of GSK3α/β, and elevated expression of Wnt target genes. RNAi-mediated silencing of ANTXR1 enhanced the expression of luminal-enriched genes but diminished Wnt signaling including reduced LRP6 and ZEB1 expression, self-renewal, invasion, tumorigenicity, and metastasis. ANTXR1 silencing also reduced the expression of HSPA1A, which is overexpressed in metastatic breast cancer stem cells. Analysis of public databases revealed ANTXR1 amplification in medullary breast carcinoma and overexpression in estrogen receptor-negative breast cancers with the worst outcome. Furthermore, ANTXR1 is among the 10% most overexpressed genes in breast cancer and is coexpressed with collagen VI. Thus, ANTXR1:C5A interactions bridge a network of collagen cleavage and remodeling in the tumor microenvironment, linking it to a stemness signaling network that drives metastatic progression.

Mutations in ANTXR1 cause GAPO syndrome

The genetic cause of GAPO syndrome, a condition characterized by growth retardation, alopecia, pseudoanodontia, and progressive visual impairment, has not previously been identified. We studied four ethnically unrelated affected individuals and identified homozygous nonsense mutations (c.262C>T [p.Arg88*] and c.505C>T [p.Arg169*]) or splicing mutations (c.1435-12A>G [p.Gly479Phefs*119]) in ANTXR1, which encodes anthrax toxin receptor 1. The nonsense mutations predictably trigger nonsense-mediated mRNA decay, resulting in the loss of ANTXR1. The transcript with the splicing mutation theoretically encodes a truncated ANTXR1 containing a neopeptide composed of 118 unique amino acids in its C terminus. GAPO syndrome's major phenotypic features, which include dental abnormalities and the accumulation of extracellular matrix, recapitulate those found in Antxr1-mutant mice and point toward an underlying defect in extracellular-matrix regulation. Thus, we propose that mutations affecting ANTXR1 function are responsible for this disease's characteristic generalized defect in extracellular-matrix homeostasis.

Identification of small molecules that inhibit the interaction of TEM8 with anthrax protective antigen using a FRET assay

Tumor marker endothelial 8 (TEM8) is a receptor for the protective antigen (PA) component of anthrax toxin. TEM8 is upregulated on endothelial cells lining the blood vessels within tumors, compared with normal blood vessels. A number of studies have demonstrated a pivotal role for TEM8 in developmental and tumor angiogenesis. We have also shown that targeting the anthrax receptors with a mutated form of PA inhibits angiogenesis and tumor formation in vivo. Here we describe the development and testing of a high-throughput fluorescence resonance energy transfer assay to identify molecules that strongly inhibit the interaction of PA and TEM8. The assay we describe is sensitive and robust, with a Z' value of 0.8. A preliminary screen of 2310 known bioactive library compounds identified ebselen and thimerosal as inhibitors of the TEM8-PA interaction. These molecules each contain a cysteine-reactive transition metal, and complementary studies indicate that their inhibition of interaction is due to modification of a cysteine residue in the TEM8 extracellular domain. This is the first demonstration of a high-throughput screening assay that identifies inhibitors of TEM8, with potential application for antianthrax and antiangiogenic diseases.

Novel approaches to the treatment of systemic anthrax

Anthrax continues to generate concern as an agent of bioterrorism and as a natural cause of sporadic disease outbreaks. Despite the use of appropriate antimicrobial agents and advanced supportive care, the mortality associated with the systemic disease remains high. This is primarily due to the pathogenic exotoxins produced by Bacillus anthracis as well as other virulence factors of the organism. For this reason, new therapeutic strategies that target events in the pathogenesis of anthrax and may potentially augment antimicrobials are being investigated. These include anti-toxin approaches, such as passive immune-based therapies; non-antimicrobial drugs with activity against anthrax toxin components; and agents that inhibit binding, processing, or assembly of toxins. Adjunct therapies that target spore germination or downstream events in anthrax intoxication are also under investigation. In combination, these modalities may enhance the management of systemic anthrax.

The dark sides of capillary morphogenesis gene 2

Capillary morphogenesis gene 2 (CMG2) is a type I membrane protein involved in the homeostasis of the extracellular matrix. While it shares interesting similarities with integrins, its exact molecular role is unknown. The interest and knowledge about CMG2 largely stems from the fact that it is involved in two diseases, one infectious and one genetic. CMG2 is the main receptor of the anthrax toxin, and knocking out this gene in mice renders them insensitive to infection with Bacillus anthracis spores. On the other hand, mutations in CMG2 lead to a rare but severe autosomal recessive disorder in humans called Hyaline Fibromatosis Syndrome (HFS). We will here review what is known about the structure of CMG2 and its ability to mediate anthrax toxin entry into cell. We will then describe the limited knowledge available concerning the physiological role of CMG2. Finally, we will describe HFS and the consequences of HFS-associated mutations in CMG2 at the molecular and cellular level.

Novel common integration sites targeted by mouse mammary tumor virus insertion in mammary tumors have oncogenic activity

Non-acute transforming retroviruses like mouse mammary tumor virus (MMTV) cause cancer, at least in part, through integration near cellular genes involved in growth control, thereby de-regulating their expression. It is well-established that MMTV commonly integrates near and activates expression of members of the Wnt and Fgf pathways in mammary tumors. However, there are a significant number of tumors for which the proviral integration sites have not been identified. Here, we used high through-put screening to identify common integration sites (CISs) in MMTV-induced tumors from C3H/HeN and BALB/c mice. As expected, members of both the Wnt and Fgf families were identified in this screen. In addition, a number of novel CISs were found, including Tcf7l2, Antxr1/Tem8, and Arhgap18. We show here that expression of these three putative oncogenes in normal murine mammary gland cells altered their growth kinetics and caused their morphological transformation when grown in three dimensional cultures. Additionally, expression of Tcf7l2 and Antxr1/Tem8 sensitized cells to exogenous WNT ligand. As Tcf7l2, Antxr1/Tem8, and Arhgap18 have been associated with human breast and other cancers, these data demonstrate that MMTV-induced insertional mutation remains an important means for identifying genes involved in breast cancer.