The heparin binding 25 kDa fragment of thrombospondin-1 promotes angiogenesis and modulates gelatinase and TIMP-2 production in endothelial cells

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

PP2A Affects Angiogenesis via Its Interaction with a Novel Phosphorylation Site of TSP1

Alterations in angiogenic properties play a pivotal role in the manifestation and onset of various pathologies, including vascular diseases and cancer. Thrombospondin-1 (TSP1) protein is one of the master regulators of angiogenesis. This study unveils a novel aspect of TSP1 regulation through reversible phosphorylation. The silencing of the B55α regulatory subunit of protein phosphatase 2A (PP2A) in endothelial cells led to a significant decrease in TSP1 expression. Direct interaction between TSP1 and PP2A-B55α was confirmed via various methods. Truncated TSP1 constructs were employed to identify the phosphorylation site and the responsible kinase, ultimately pinpointing PKC as the enzyme phosphorylating TSP1 on Ser93. The biological effects of B55α-TSP1 interaction were also analyzed. B55α silencing not only counteracted the increase in TSP1 expression during wound closure but also prolonged wound closure time. Although B55α silenced cells initiated tube-like structures earlier than control cells, their spheroid formation was disrupted, leading to disintegration. Cells transfected with phosphomimic TSP1 S93D exhibited smaller spheroids and reduced effectiveness in tube formation, revealing insights into the effects of TSP1 phosphorylation on angiogenic properties. In this paper, we introduce a new regulatory mechanism of angiogenesis by reversible phosphorylation on TSP1 S93 by PKC and PP2A B55α.

Homeostatic Regulation of Pro-Angiogenic and Anti-Angiogenic Proteins via Hedgehog, Notch Grid, and Ephrin Signaling in Tibial Dyschondroplasia

Precise coupling of two fundamental mechanisms, chondrogenesis and osteogenesis via angiogenesis, plays a crucial role during rapid proliferation of growth plates, and alteration in their balance might lead to pathogenic conditions. Tibial dyschondroplasia (TD) is characterized by an avascular, non-mineralized, jade-white "cartilaginous wedge" with impaired endochondral ossification and chondrocyte proliferation at the proximal end of a tibial bone in rapidly growing poultry birds. Developing vascular structures are dynamic with cartilage growth and are regulated through homeostatic balance among pro and anti-angiogenic proteins and cytokines. Pro-angiogenic factors involves a wide spectrum of multifactorial mitogens, such as vascular endothelial growth factors (VEGF), platelet-derived growth factors (PDGF), basic fibroblast growth factor (bFGF), placental growth factors, transforming growth factor-β (TGF-β), and TNF-α. Considering their regulatory role via the sonic hedgehog, notch-gridlock, and ephrin-B2/EphB4 pathways and inhibition through anti-angiogenic proteins like angiostatin, endostatin, decoy receptors, vasoinhibin, thrombospondin, PEX, and troponin, their possible role in persisting inflammatory conditions like TD was studied in the current literature review. Balanced apoptosis and angiogenesis are vital for physiological bone growth. Any homeostatic imbalance among apoptotic, angiogenetic, pro-angiogenic, or anti-angiogenic proteins ultimately leads to pathological bone conditions like TD and osteoarthritis. The current review might substantiate solid grounds for developing innovative therapeutics for diseases governed by the disproportion of angiogenesis and anti-angiogenesis proteins.

Controlled extracellular proteolysis of thrombospondins

Limited proteolysis of thrombospondins is a powerful mechanism to ensure dynamic tuning of their activities in the extracellular space. Thrombospondins are multifunctional matricellular proteins composed of multiple domains, each with a specific pattern of interactions with cell receptors, matrix components and soluble factors (growth factors, cytokines and proteases), thus with different effects on cell behavior and responses to changes in the microenvironment. Therefore, the proteolytic degradation of thrombospondins has multiple functional consequences, reflecting the local release of active fragments and isolated domains, exposure or disruption of active sequences, altered protein location, and changes in the composition and function of TSP-based pericellular interaction networks. In this review current data from the literature and databases is employed to provide an overview of cleavage of mammalian thrombospondins by different proteases. The roles of the fragments generated in specific pathological settings, with particular focus on cancer and the tumor microenvironment, are discussed.

Serum levels of matrix metalloproteinase 2 and its inhibitor after tonic-clonic seizures

Damage to the blood-brain barrier (BBB) may result from on-going neuroinflammation, which can lead to leakage of blood components, such as leukocytes and serum proteins, into the brain, resulting in disturbed brain homeostasis. The aim of the project was to examine the involvement of modulatory proteins in the processes of BBB integration after epileptic seizures. We investigated serum changes in the levels of MMP-2 and MMP-7 and its inhibitors after seizures in epilepsy patients. Concentrations of these proteins were measured by ELISA in 50 patients at 1-3, 24, and 72 h after generalized tonic-clonic seizures and once in participants of the control group. The level of MMP-2 in serum was slightly higher after seizures (at 1-3 h time point), but the difference was not statistically significant. The levels of trombospondine (TSP) - 1 and - 2 were decreased at 1-3 h after seizures. The expression of TIMP-2 was increased 1 and 24 h after seizures. There were no significant changes in the level of α2-macroglobulin and MMP-7. Changes in the expression of both specific and non-specific inhibitors indicate the initiation of repair processes of the blood-brain barrier and improvement of its integrity. Since we performed serum analysis, further studies are necessary to investigate the correlation with the expression of the investigated markers in the brain. Perhaps this will allow for the identification of new biomarkers associated with epileptic seizures.

Endothelial Cell Behavior Is Determined by Receptor Clustering Induced by Thrombospondin-1

The thrombospondins (TSPs) are a family of multimeric extracellular matrix proteins that dynamically regulate cellular behavior and response to stimuli. In so doing, the TSPs directly and indirectly affect biological processes such as embryonic development, wound healing, immune response, angiogenesis, and cancer progression. Many of the direct effects of Thrombospondin 1 (TSP-1) result from the engagement of a wide range of cell surface receptors including syndecans, low density lipoprotein receptor-related protein 1 (LRP1), CD36, integrins, and CD47. Different or even opposing outcomes of TSP-1 actions in certain pathologic contexts may occur, depending on the structural/functional domain involved. To expedite response to external stimuli, these receptors, along with vascular endothelial growth factor receptor 2 (VEGFR2) and Src family kinases, are present in specific membrane microdomains, such as lipid rafts or tetraspanin-enriched microdomains. The molecular organization of these membrane microdomains and their constituents is modulated by TSP-1. In this review, we will describe how the presence of TSP-1 at the plasma membrane affects endothelial cell signal transduction and angiogenesis.

Studying Angiogenesis in the Rabbit Corneal Pocket Assay

The rabbit corneal micropocket assay uses the avascular cornea as a substrate to study angiogenesis in vivo. The continuous monitoring of neovascular growth in the same animal allows for the evaluation of drugs acting as suppressors or stimulators of angiogenesis. Through the use of standardized slow-release pellets, a predictable angiogenic response can be quantified over the course of 1-2 weeks. Uniform slow-release pellets are prepared by mixing purified angiogenic growth factors such as basic fibroblast growth factor (FGF) or vascular endothelial growth factor (VEGF) and a synthetic polymer to allow for their slow release. A micropocket is surgically created in the cornea thickness under anesthesia and in sterile conditions. The angiogenesis stimulus (growth factor but also tissue fragment or cell suspension) is placed into the pocket in order to induce vascular outgrowth from the limbal capillaries where vessels are preexisting. On the following days, the neovascular development and progression are measured and qualified using a slit lamp, as well as the concomitant vascular phenotype or inflammatory features. The results of the assay allow to assess the ability of potential therapeutic molecules to modulate angiogenesis in vivo, both when released locally or given by ocular formulations or through systemic treatment. In this chapter the experimental details of the avascular rabbit cornea assay, the technical challenges, advantages, and limitations are discussed.

Remodeling of the interstitial extracellular matrix in white matter multiple sclerosis lesions: Implications for remyelination (failure)

The extracellular matrix (ECM) provides protection, rigidity, and structure toward cells. It consists, among others, of a wide variety of glycoproteins and proteoglycans, which act together to produce a complex and dynamic environment, most relevant in transmembrane events. In the brain, the ECM occupies a notable proportion of its volume and maintains the homeostasis of central nervous system (CNS). In addition, remodeling of the ECM, that is transient changes in ECM proteins regulated by matrix metalloproteinases (MMPs), is an important process that modulates cell behavior upon injury, thereby facilitating recovery. Failure of ECM remodeling plays an important role in the pathogenesis of multiple sclerosis (MS), a neurodegenerative demyelinating disease of the CNS with an inflammatory response against protective myelin sheaths that surround axons. Remyelination of denuded axons improves the neuropathological conditions of MS, but this regeneration process fails over time, leading to chronic disease progression. In this review, we uncover abnormal ECM remodeling in MS lesions by discussing ECM remodeling in experimental demyelination models, that is when remyelination is successful, and compare alterations in ECM components to the ECM composition and MMP expression in the parenchyma of demyelinated MS lesions, that is when remyelination fails. Inter- and intralesional differences in ECM remodeling in the distinct white matter MS lesions are discussed in terms of consequences for oligodendrocyte behavior and remyelination (failure). Hence, the review will aid to understand how abnormal ECM remodeling contributes to remyelination failure in MS lesions and assists in developing therapeutic strategies to promote remyelination.

Artemisinin inhibits angiogenesis by regulating p38 MAPK/CREB/TSP-1 signaling pathway in osteosarcoma

Osteosarcoma is the most common bone tumor and characterizes a high metastatic potential. In osteosarcoma, angiogenesis is reported to be closely associated with tumor metastasis. Understanding the underlying mechanisms and accordingly developing therapeutic strategies are urgently desired. Antimalarial agent, artemisinin, has been reported to inhibit tumor angiogenesis. However, we still knew little about the effects of artemisinin on angiogenesis and its potential molecular mechanisms in human osteosarcoma. In this study, we found that artemisinin could induce both the expression and secretion of thrombospondin-1 (TSP-1) in a dose-dependent way in osteosarcoma cells. In addition, TSP-1 could effectively restore the artemisinin-induced suppression of angiogenesis in human umbilical vein endothelial cells (HUVECs). More importantly, we further found that phosphorylation of cAMP response element-binding protein (CREB) bond specifically to the promoter of TSP-1 and promoted its transcriptional activation. Moreover, our results showed that artemisinin could induce the phosphorylation of CREB via the activation of p38 mitogen-activated protein kinase (MAPK) signaling pathway in osteosarcoma cells. In vivo, we also found that artemisinin could inhibit osteosarcoma proliferation and angiogenesis by regulating the p38 MAPK/CREB/TSP-1 signaling pathway. Taken together, our findings indicated that artemisinin could inhibit angiogenesis by regulating the p38 MAPK/CREB/TSP-1 signaling pathway in osteosarcoma.

Immunohistochemical investigation of prognostic biomarkers in resected colorectal liver metastases: a systematic review and meta-analysis

Background

Many studies have investigated the prognostic role of biomarkers in colorectal liver metastases (CRLM). However, no biomarker has been established in routine clinical practice. The aim of this study was to scrutinize the current literature for biomarkers evaluated by immunohistochemistry as prognostic markers in patients with resected CRLM.

Methods

A systematic review was performed according to the PRISMA guidelines. Articles were identified in the PubMed database with selected search terms and by cross-references search. The REMARK quality criteria were applied. Markers were included if they reported the prognostic impact of immunohistochemical markers in a multivariable setting in relation to overall survival (OS). A meta-analysis was conducted when more than one original article provided survival data of a marker.

Results

In total, 26 biomarkers were identified as independent significant markers for OS in resected CRLM. These biomarkers were found to be involved in multiple oncogenic signalling pathways that control cell growth, apoptosis, angiogenesis and evasion of immune detection. Among these biomarker candidates were Ki-67, EGFR, p53, hTERT, CD34, TSP-1, KISS1, Aurora kinase A and CDX2. CD34 and TSP-1 were reported as significantly associated with survival by more than one study and where therefore pooled in a meta-analysis.

Conclusion

A number of independent prognostic biomarkers for resected CRLM were identified. However, most markers were evaluated in a retrospective setting with small patient cohorts, without external validation. Large, prospective, multicentre studies with standardised methods are needed before biomarkers can translated into the clinic.

Neutrophil-Mediated Proteolysis of Thrombospondin-1 Promotes Platelet Adhesion and String Formation

Thrombospondin-1 (TSP-1) is primarily expressed by platelets and endothelial cells (ECs) and rapidly released upon their activation. It functions in haemostasis as a bridging molecule in platelet aggregation, by promoting platelet adhesion to collagen and by protecting von Willebrand factor strings from degradation. In blood of patients undergoing surgery and in co-cultures of neutrophils with platelets or ECs, we observed proteolysis of the 185 kDa full-length TSP-1 to a 160-kDa isoform. We hypothesized that TSP-1 processing may alter its haemostatic properties. Selective enzyme inhibitors in co-cultures revealed that neutrophil proteases elastase and cathepsin G mediate TSP-1 processing. The cut site of cathepsin G was mapped to TSP-1 amino acids R237/T238 by Edman sequencing. Formation of neutrophil extracellular traps protected TSP-1 from complete degradation and promoted controlled processing to the 160-kDa isoform. Haemostatic properties were tested by platelet aggregation, adhesion, coagulation and string formation under flow. Platelets from TSP-1 deficient mice did not differ from wild-type in platelet aggregation but showed severe impairment of platelet adhesion to collagen and string formation under flow. Reconstitution experiments revealed that the 160-kDa TSP-1 isoform was markedly more potent than the 185-kDa full-length molecule in restoring function. Thus, TSP-1 processing by neutrophil proteases yields a 160-kDa isoform which shows enhanced potency to promote platelet adhesion and string formation. This finding reveals a novel mechanism of neutrophil-mediated thrombus formation and provides first evidence for the impact of TSP-1 proteolysis on its haemostatic properties.

Targeting Difficult Protein-Protein Interactions with Plain and General Computational Approaches

Investigating protein-protein interactions (PPIs) holds great potential for therapeutic applications, since they mediate intricate cell signaling networks in physiological and disease states. However, their complex and multifaceted nature poses a major challenge for biochemistry and medicinal chemistry, thereby limiting the druggability of biological partners participating in PPIs. Molecular Dynamics (MD) provides a solid framework to study the reciprocal shaping of proteins’ interacting surfaces. Here, we review successful applications of MD-based methods developed in our group to predict interfacial areas involved in PPIs of pharmaceutical interest. We report two interesting examples of how structural, dynamic and energetic information can be combined into efficient strategies which, complemented by experiments, can lead to the design of new small molecules with promising activities against cancer and infections. Our advances in targeting key PPIs in angiogenic pathways and antigen-antibody recognition events will be discussed for their role in drug discovery and chemical biology.

N-Terminomics identifies HtrA1 cleavage of thrombospondin-1 with generation of a proangiogenic fragment in the polarized retinal pigment epithelial cell model of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the elderly population. Variants in the HTRA1-ARMS2 locus have been linked to increased AMD risk. In the present study we investigated the impact of elevated HtrA1 levels on the retina pigment epithelial (RPE) secretome using a polarized culture system. Upregulation of HtrA1 alters the abundance of key proteins involved in angiogenesis and extracellular matrix remodeling. Thrombospondin-1, an angiogenesis modulator, was identified as a substrate for HtrA1 using terminal amine isotope labeling of substrates in conjunction with HtrA1 specificity profiling. HtrA1 cleavage of thrombospondin-1 was further corroborated by in vitro cleavage assays and targeted proteomics together with small molecule inhibition of HtrA1. While thrombospondin-1 is anti-angiogenic, the proteolytically released N-terminal fragment promotes the formation of tube-like structure by endothelial cells. Taken together, our findings suggest a mechanism by which increased levels of HtrA1 may contribute to AMD pathogenesis. The proteomic data has been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier. For quantitative secretome analysis, project accession: PXD007691, username: reviewer45093@ebi.ac.uk, password: 1FUpS6Yq. For TAILS analysis, project accession: PXD007139, username: reviewer76731@ebi.ac.uk, password: sNbMp7xK.

Shear Stress Modulates the Expression of Thrombospondin-1 and CD36 in Endothelial Cells in vitro and during Shear Stress-Induced Angiogenesis in vivo

Binding of thrombospondin-1 (TSP-1) to the CD36 receptor inhibits angiogenesis and induces apoptosis in endothelial cells (EC). Conversely, matrix-bound TSP-1 supports vessel formation. In this study we analyzed the shear stress-dependent expression of TSP-1 and CD36 in endothelial cells in vitro and in vivo to reveal its putative role in the blood flow-induced remodelling of vascular networks. Shear stress was applied to EC using a cone-and-plate apparatus and gene expression was analyzed by RT-PCR, Northern and Western blot. Angiogenesis in skeletal muscles of prazosin-fed (50 mg/1 drinking water; 4 d) mice was assessed by measuring capillary-to-fiber (C/F) ratios. Protein expression in whole muscle homogenates (WMH) or BS-1 lectin-enriched EC fractions (ECF) was analyzed by Western blot. Shear stress down-regulated TSP-1 and CD36 expression in vitro in a force- and time-dependent manner sustained for at least 72 h and reversible by restoration of no-flow conditions. In vivo, shear stress-driven increase of C/F in prazosin-fed mice was associated with reduced expression of TSP-1 and CD36 in ECF, while TSP-1 expression in WMH was increased. Down-regulation of endothelial TSP-1/CD36 by shear stress suggests a mechanism for inhibition of apoptosis in perfused vessels and pruning in the absence of flow. The increase of extra-endothelial (e.g. matrix-bound) TSP-1 could support a splitting type of vessel growth.

Matricellular proteins in cancer: a focus on secreted Frizzled-related proteins

Tumours are complex entities, wherein cancer cells interact with myriad soluble, insoluble and cell associated factors. These microenvironmental mediators regulate tumour growth, progression and metastasis, and are produced by cancer cells and by stromal components such as fibroblast, adipocytes and immune cells. Through their ability to bind to extracellular matrix proteins, cell surface receptors and growth factors, matricellular proteins enable a dynamic reciprocity between cancer cells and their microenvironment. Hence, matricellular proteins play a critical role in tumour progression by regulating where and when cancer cells are exposed to key growth factors and regulatory proteins. Recent studies suggest that, in addition to altering Wingless (Wnt) signalling, certain members of the Secreted Frizzled Related Protein (sFRP) family are matricellular in nature. In this review, we outline the importance of matricellular proteins in cancer, and discuss how sFRPs may function to both inhibit and promote cancer progression in a context-dependent manner. By considering the matricellular functionality of sFRPs, we may better understand their apparently paradoxical roles in cancers.

Thrombospondin-1 is a multifaceted player in tumor progression

Thrombospondins are a family of extracellular matrix (ECM) proteins. Thrombospondin-1 (TSP1) was the first member to be identified and is a main player in tumor microenvironment. The diverse functions of TSP1 depend on the interactions between its structural domains and multiple cell surface molecules. TSP1 acts as an angiogenesis inhibitor by stimulating endothelial cell apoptosis, inhibiting endothelial cell migration and proliferation, and regulating vascular endothelial growth factor bioavailability and activity. In addition to angiogenesis modulation, TSP1 also affects tumor cell adhesion, invasion, migration, proliferation, apoptosis and tumor immunity. This review discusses the multifaceted and sometimes opposite effects of TSP1 on tumor progression depending on the molecular and cellular composition of the microenvironment. Clinical implications of TSP1-related compounds are also discussed.

High serum thrombospondin-1 concentration is associated with slower abdominal aortic aneurysm growth and deficiency of thrombospondin-1 promotes angiotensin II induced aortic aneurysm in mice

Abdominal aortic aneurysm (AAA) is a common age-related vascular disease characterized by progressive weakening and dilatation of the aortic wall. Thrombospondin-1 (TSP-1; gene Thbs1) is a member of the matricellular protein family important in the control of extracellular matrix (ECM) remodelling. In the present study, the association of serum TSP-1 concentration with AAA progression was assessed in 276 men that underwent repeated ultrasound for a median 5.5 years. AAA growth was negatively correlated with serum TSP-1 concentration (Spearman's rho -0.129, P=0.033). Men with TSP-1 in the highest quartile had a reduced likelihood of AAA growth greater than median during follow-up (OR: 0.40; 95% confidence interval (CI): 0.19-0.84, P=0.016, adjusted for other risk factors). Immunohistochemical staining for TSP-1 was reduced in AAA body tissues compared with the relatively normal AAA neck. To further assess the role of TSP-1 in AAA initiation and progression, combined TSP-1 and apolipoprotein deficient (Thbs1-/-ApoE-/-, n=20) and control mice (ApoE-/-, n=20) were infused subcutaneously with angiotensin II (AngII) for 28 days. Following AngII infusion, Thbs1-/- ApoE-/- mice had larger AAAs by ultrasound (P=0.024) and ex vivo morphometry measurement (P=0.006). The Thbs1-/-ApoE-/- mice also showed increased elastin filament degradation along with elevated systemic levels and aortic expression of matrix metalloproteinase (MMP)-9. Suprarenal aortic segments and vascular smooth muscle cells (VSMCs) isolated from Thbs1-/-ApoE-/- mice showed reduced collagen 3A1 gene expression. Furthermore, Thbs1-/-ApoE-/- mice had reduced aortic expression of low-density lipoprotein (LDL) receptor-related protein 1. Collectively, findings from the present study suggest that TSP-1 deficiency promotes maladaptive remodelling of the ECM leading to accelerated AAA progression.

Prostate Cancer-Associated Kallikrein-Related Peptidase 4 Activates Matrix Metalloproteinase-1 and Thrombospondin-1

Prostate cancer metastasis to bone is terminal; thus, novel therapies are required to prevent end-stage disease. Kallikrein-related peptidase 4 (KLK4) is a serine protease that is overproduced in localized prostate cancer and is abundant in prostate cancer bone metastases. In vitro, KLK4 induces tumor-promoting phenotypes; however, the underlying proteolytic mechanism is undefined. The protein topography and migration analysis platform (PROTOMAP) was used for high-depth identification of KLK4 substrates secreted by prostate cancer bone metastasis-derived PC-3 cells to delineate the mechanism of KLK4 action in advanced prostate cancer. Thirty-six putative novel substrates were determined from the PROTOMAP analysis. In addition, KLK4 cleaved the established substrate, urokinase-type plasminogen activator, thus validating the approach. KLK4 activated matrix metalloproteinase-1 (MMP1), a protease that promotes prostate tumor growth and metastasis. MMP1 was produced in the tumor compartment of prostate cancer bone metastases, highlighting its accessibility to KLK4 at this site. KLK4 further liberated an N-terminal product, with purported angiogenic activity, from thrombospondin-1 (TSP1) and cleaved TSP1 in an osteoblast-derived matrix. This is the most comprehensive analysis of the proteolytic action of KLK4 in an advanced prostate cancer model to date, highlighting KLK4 as a potential multifunctional regulator of prostate cancer progression.

Development and characterization of an in vitro model of colorectal adenocarcinoma with MDR phenotype

The major cause of failure in cancer chemotherapy is the development of multidrug resistance (MDR), and the characterization of biological factors involved in this response to therapy is particularly needed. A doxorubicin-resistant HCT-8/R clone was selected from sensitive parental cells and characterized analyzing several parameters (cell cycle phase distribution, apoptotic activity, expression, distribution and functionality of the P-gp efflux pump, the response to other chemotherapy agents, its ultrastructural features, invasiveness, and transcriptomic profile). HCT-8/R cells showed a peculiar S phase distribution, characterized by a single pulse of proliferation, resistance to drug-mediated apoptosis, increased expression and functionality of P-gp and overexpression of stem cell markers (CD44 and aldehyde dehydrogenase 1A2). At the ultrastructural level, HCT-8/R presented a greater cell volume and several intracytoplasmic vesicles respect to HCT-8. Moreover, the resistant clone was characterized by cross resistance to other cytotoxic drugs and a greater capacity for migration and invasion, compared to parental cells. Our data reinforce the concept that the MDR phenotype in HCT-8/R cells is multifactorial and involves multiple mechanisms, representing an interesting tool to understand the biological basis of MDR and to test strategies that overcome resistance to chemotherapy.

The Rabbit Corneal Pocket Assay

The rabbit corneal micropocket angiogenesis assay uses the avascular cornea as a substrate canvas to study angiogenesis in vivo. Through the use of standardized slow-release pellets, a predictable angiogenic response is generated over the course of 1-2 weeks and then quantified. Uniform slow-release pellets are prepared by mixing purified angiogenic growth factors such as basic fibroblast growth factor or vascular endothelial growth factor and a synthetic polymer to allow slow release. A micropocket is surgically created in the rabbit cornea under anesthesia and a pellet implanted. On the days later, the angiogenic response is measured and qualified using a slit lamp, as well as the concomitant vascular phenotype or inflammatory features. The results of the assay are used to assess the ability of potential therapeutic molecules to modulate angiogenesis in vivo, both when released locally or given by ocular formulations or through systemic treatment. In this chapter, the experimental details of the rabbit cornea assay and technical implementations to the original protocol are described.

Expression of thrombospondin-1 by tumor cells in patient-derived ovarian carcinoma xenografts

PURPOSE

Thrombospondin-1 (TSP-1), a major regulator of cell interaction with the environment, is often deregulated in cancers, including ovarian carcinoma. Both the tumor and the host cells can release TSP-1 in the tumor microenvironment. The relative contribution of the two sources in determining TSP-1 levels in ovarian cancer remains to be elucidated. This study was designed to investigate the expression of tumor TSP-1 in a panel of 29 patient-derived ovarian adenocarcinoma xenografts (PDX), using analytical tools specific for human (tumor-derived) rather than murine (host-derived) TSP-1.

METHODOLOGY

Human-specific microarray and ELISA were used to measure tumor TSP-1 expression and plasma levels.

RESULTS

Tumor-derived TSP-1 was heterogeneously expressed in PDX. Expression was higher in the corresponding original patient's tumor, where stroma-derived TSP-1 is also analyzed, indicating that both the tumor and the host contribute to TSP-1 production. TSP-1 was differentially expressed according to tumor grade, but not affected by p53 expression or mutational status. Findings were confirmed in an external gene expression dataset (101 patients). In a functional enrichment analysis, TSP-1 correlated with genes related to angiogenesis, cell motility, communication and shape. Plasma TSP-1, detectable in 10/11 PDX, was not associated to its expression in the tumor. The possible association of plasma TSP-1 with p53 mutations and response to chemotherapy warrants further investigation.

CONCLUSIONS

Ovarian carcinoma PDX are a useful tool to investigate the relative contribution of stroma and tumor cells in the production of tumor associated factors, in relation to the tumor behavior, molecular properties and response to therapy.

The corneal pocket assay

The cornea in most species is physiologically avascular, and thus this assay allows the measurement of newly formed vessels. The continuous monitoring of neovascular growth in the same animal allows the evaluation of drugs acting as suppressors or stimulators of angiogenesis. Under anesthesia a micropocket is produced in the cornea thickness and the angiogenesis stimulus (tumor tissue, cell suspension, growth factor) is placed into the pocket in order to induce vascular outgrowth from the limbal capillaries. Neovascular development and progression can be modified by the presence of locally released or applied inhibitory factors or by systemic treatments. In this chapter the experimental details of the avascular cornea assay, the technical challenges, and advantages and disadvantages in different species are discussed. Protocols for local drug treatment and tissue sampling for histology and pharmacokinetic profile are reported.

ADAMTS13 and its variants promote angiogenesis via upregulation of VEGF and VEGFR2

Severe plasma ADAMTS13 deficiency results in the clinical disorder thrombotic thrombocytopenic purpura. However, other potential pathophysiological roles of ADAMTS13 in endothelial cell biology remain unexplored. The goals of this study were to understand the angiogenic pathways ADAMTS13 activates and to identify the important structural components of ADAMTS13 that stimulate angiogenesis. Incubation of human umbilical vein endothelial cells (HUVEC) with 150 ng/mL (1 nM) of recombinant human ADAMTS13 induced VEGF expression by 53 % and increased VEGF mRNA by over sixfold, both within 10 min; the measured VEGF levels steadily decreased over 2 h, as shown by Western blot and ELISA. Phosphorylation of VEGFR2 was significantly enhanced in HUVEC after incubation with ADAMTS13 (1 nM). Structure-function analysis showed that an ADAMTS13 variant containing thrombospondin type 1 (TSP1) 2-8 repeats (TSP1 2-8), TSP1 2-8 plus CUB domains (TSP1 2-8 plus CUB), or TSP1 5-8 repeats plus CUB domains (TSP1 5-8 plus CUB) increased HUVEC proliferation by 41-54 % as compared to the EBM-2 controls. Chemotaxis assays further demonstrated that the TSP1 domains of ADAMTS13 increased HUVEC migration by 2.65-fold. Incubation of HUVEC with both ADAMTS13 variants containing TSP1 repeats and anti-VEGF IgG abrogated the enhanced effect of ADAMTS13 on proliferation, migration, and VEGFR2 phosphorylation. In conclusion, ADAMTS13-induced endothelial cell angiogenesis occurs via the upregulation of VEGF and phosphorylation of VEGFR2. This angiogenic activity depends on the C-terminal TSP1 repeats of ADAMTS13.

Intermittent whole-body vibration attenuates a reduction in the number of the capillaries in unloaded rat skeletal muscle

Background

Whole-body vibration has been suggested for the prevention of muscle mass loss and muscle wasting as an attractive measure for disuse atrophy. This study examined the effects of daily intermittent whole-body vibration and weight bearing during hindlimb suspension on capillary number and muscle atrophy in rat skeletal muscles.

Methods

Sixty male Wistar rats were randomly divided into four groups: control (CONT), hindlimb suspension (HS), HS + weight bearing (WB), and HS + whole-body vibration (VIB) (n = 15 each). Hindlimb suspension was applied for 2 weeks in HS, HS + WB, and HS + VIB groups. During suspension, rats in HS + VIB group were placed daily on a vibrating whole-body vibration platform for 20 min. In HS + WB group, suspension was interrupted for 20 min/day, allowing weight bearing. Untreated rats were used as controls.

Results

Soleus muscle wet weights and muscle fiber cross-sectional areas (CSA) significantly decreased in HS, HS + WB, and HS + VIB groups compared with CONT group. Both muscle weights and CSA were significantly greater in HS + WB and HS + VIB groups compared with HS group. Capillary numbers (represented by capillary-to-muscle fiber ratio) were significantly smaller in all hindlimb suspension-treated groups compared with CONT group. However, a reduction in capillary number by unloading hindlimbs was partially prevented by whole-body vibration. These findings were supported by examining mRNA for angiogenic-related factors. Expression levels of a pro-angiogenic factor, vascular endothelial growth factor-A mRNA, were significantly lower in all hindlimb suspension-treated groups compared with CONT group. There were no differences among hindlimb suspension-treated groups. Expression levels of an anti-angiogenic factor, CD36 (receptor for thrombospondin-1) mRNA, were significantly higher in all hindlimb suspension-treated groups compared with CONT group. Among the hindlimb suspension-treated groups, expression of CD36 mRNA in HS + VIB group tended to be suppressed (less than half the HS group).

Conclusions

Our results suggest that weight bearing with or without vibration is effective for disuse-derived disturbance by preventing muscle atrophy, and whole-body vibration exercise has an additional benefit of maintaining microcirculation of skeletal muscle.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-315) contains supplementary material, which is available to authorized users.

Monoclonal antibodies to murine thrombospondin-1 and thrombospondin-2 reveal differential expression patterns in cancer and low antigen expression in normal tissues

There is a considerable interest for the discovery and characterization of tumor-associated antigens, which may facilitate antibody-based pharmacodelivery strategies. Thrombospondin-1 and thrombospondin-2 are homologous secreted proteins, which have previously been reported to be overexpressed during remodeling typical for wound healing and tumor progression and to possibly play a functional role in cell proliferation, migration and apoptosis. To our knowledge, a complete immunohistochemical characterization of thrombospondins levels in normal rodent tissues has not been reported so far. Using antibody phage technology, we have generated and characterized monoclonal antibodies specific to murine thrombospondin-1 and thrombospondin-2, two antigens which share 62% aminoacid identity. An immunofluorescence analysis revealed that both antigens are virtually undetectable in normal mouse tissues, except for a weak staining of heart tissue by antibodies specific to thrombospondin-1. The analysis also showed that thrombospondin-1 was strongly expressed in 5/7 human tumors xenografted in nude mice, while it was only barely detectable in 3/8 murine tumors grafted in immunocompetent mice. By contrast, a high-affinity antibody to thrombospondin-2 revealed a much lower level of expression of this antigen in cancer specimens. Our analysis resolves ambiguities related to conflicting reports on thrombosponding expression in health and disease. Based on our findings, thrombospondin-1 (and not thrombospondin-2) may be considered as a target for antibody-based pharmacodelivery strategies, in consideration of its low expression in normal tissues and its upregulation in cancer.

Current understanding of the thrombospondin-1 interactome

The multifaceted action of thrombospondin-1 (TSP-1) depends on its ability to physically interact with different ligands, including structural components of the extracellular matrix, other matricellular proteins, cell receptors, growth factors, cytokines and proteases. Through this network, TSP-1 regulates the ligand activity, availability and structure, ultimately tuning the cell response to environmental stimuli in a context-dependent manner, contributing to physiological and pathological processes. Complete mapping of the TSP-1 interactome is needed to understand its diverse functions and to lay the basis for the rational design of TSP-1-based therapeutic approaches. So far, large-scale approaches to identify TSP-1 ligands have been rarely used, but many interactions have been identified in small-scale studies in defined biological systems. This review, based on information from protein interaction databases and the literature, illustrates current knowledge of the TSP-1 interactome map.

TP53 Status is Associated with Thrombospondin1 Expression In vitro

Objectives: To elucidate the association between thrombospondin1 (THBS1) expression and TP53 status and THBS1 promoter methylation in epithelial ovarian cancer (EOC).

Methods: Epithelial ovarian cancer cell lines with known TP53 status were analyzed for THBS1 gene expression using Affymetrix U133 microarrays and promoter methylation by pyrosequencing. THBS1 mRNA expression was obtained pre- and post-exposure to radiation and hypoxia treatment in A2780 parent wild-type (wt) and mutant (m)TP53 cells. THBS1 expression was compared to tumor growth properties.

Results:THBS1 gene expression was higher in cells containing a wtTP53 gene or null TP53 mutation (p = 0.005) and low or absent p53 protein expression (p = 0.008) compared to those harboring a missense TP53 gene mutation and exhibiting high p53 protein expression. Following exposure to radiation, there was a 3.4-fold increase in THBS1 mRNA levels in the mTP53 versus wtTP53 A2780 cells. After exposure to hypoxia, THBS1 mRNA levels increased approximately fourfold in both wtTP53 and mTP53 A2780 cells. Promoter methylation levels were low (median = 8.6%; range = 3.5–88.8%). There was a non-significant inverse correlation between THBS1 methylation and transcript levels. There was no association between THBS1 expression and population doubling time, invasive capacity, or anchorage-independent growth.

Conclusion:THBS1 expression may be regulated via the TP53 pathway, and induced by hypoxic tumor microenvironment conditions. Overall low levels of THBS1 promoter methylation imply that methylation is not the primary driver of THBS1 expression in EOC.

A motif within the N-terminal domain of TSP-1 specifically promotes the proangiogenic activity of endothelial colony-forming cells

Thrombospondin-1 (TSP-1) gives rise to fragments that have both pro- and anti-angiogenic effects in vitro and in vivo. The TSP-HepI peptide (2.3 kDa), located in the N-terminal domain of TSP-1, has proangiogenic effects on endothelial cells. We have previously shown that TSP-1 itself exhibits a dual effect on endothelial colony-forming cells (ECFC) by enhancing their adhesion through its TSP-HepI fragment while reducing their proliferation and differentiation into vascular tubes (tubulogenesis) in vitro. This effect is likely mediated through CD47 binding to the TSP-1 C-terminal domain. Here we investigated the effect of TSP-HepI peptide on the angiogenic properties of ECFC in vitro and in vivo. TSP-HepI peptide potentiated FGF-2-induced neovascularisation by enhancing ECFC chemotaxis and tubulogenesis in a Matrigel plug assay. ECFC exposure to 20 μg/mL of TSP-HepI peptide for 18 h enhanced cell migration (p < 0.001 versus VEGF exposure), upregulated alpha 6-integrin expression, and enhanced their cell adhesion to activated endothelium under physiological shear stress conditions at levels comparable to those of SDF-1α. The adhesion enhancement appeared to be mediated by the heparan sulfate proteoglycan (HSPG) syndecan-4, as ECFC adhesion was significantly reduced by a syndecan-4-neutralising antibody. ECFC migration and tubulogenesis were stimulated neither by a TSP-HepI peptide with a modified heparin-binding site (S/TSP-HepI) nor when the glycosaminoglycans (GAGs) moieties were removed from the ECFC surface by enzymatic treatment. Ex vivo TSP-HepI priming could potentially serve to enhance the effectiveness of therapeutic neovascularisation with ECFC.

ADAMTS13 promotes angiogenesis and modulates VEGF-induced angiogenesis

Plasma ADAMTS13 deficiency results in the clinical disorder thrombotic thrombocytopenic purpura. However, other potential pathophysiological roles of ADAMTS13 in endothelial cell biology remain unexplored. To assess the possible role of ADAMTS13 and its interactions with VEGF-mediated angiogenesis, the effects of ADAMTS13 on human umbilical vein endothelial cell (HUVEC) were studied in Matrigel tube formation, proliferation, cell migration, and scratch wound assays. Treatment of endothelial cells with exogenous recombinant full-length ADAMTS13 alone promoted angiogenesis in a dose-dependent manner. HUVEC incubated with 200 ng/mL ADAMTS13 (1.4 nM) resulted in a 65% increase in cell tube formation when compared to the EBM-2 control. HUVEC treated with 30 ng/mL ADAMTS13 (204.1 pM) resulted in an 83% increase in proliferation in a visual counting assay, whereas HUVEC treated with 10 ng/mL ADAMTS13 (68.0 pM) yielded a 295% increase in EC migration in a Boyden chamber assay. In contrast, ADAMTS13 inhibited VEGF-induced angiogenesis in a dose-dependent manner, with 200ng/mL inhibiting tube formation by 35%. HUVEC co-incubated with ADAMTS13 and an antibody to the ADAMTS13 thrombospondin domains 5-7 reversed the inhibition of tube formation. HUVEC treated with 30 ng/mL ADAMTS13 and 6.2 ng/mL (323.0 pM) VEGF proliferated 40% slower than the VEGF control after 24 h of incubation as measured by visual counting assay. Treatment of HUVEC with 6.2 ng/mL VEGF and 10 ng/mL ADAMTS13 inhibited cell migration by 48%, compared to the VEGF control. Substitution of ADAMTS13 with truncated ADAMTS13 (deletion of C-terminal TSP1 domain) did not significantly increase angiogenesis or suppress VEGF-induced angiogenesis, suggesting that the TSP1 domain is involved in ADAMTS13 angiogenic activities. Co-immunoprecipitation experiments provided further evidence that ADAMTS13 binds to VEGF via its TSP1 domain.

Merlin/NF2 regulates angiogenesis in schwannomas through a Rac1/semaphorin 3F-dependent mechanism

Neurofibromatosis type 2 (NF2) is an autosomal-dominant multiple neoplasia syndrome that results from mutations in the NF2 tumor suppressor gene. Patients with NF2 develop hallmark schwannomas that require surgery or radiation, both of which have significant adverse effects. Recent studies have indicated that the tumor microenvironment-in particular, tumor blood vessels-of schwannomas may be an important therapeutic target. Furthermore, although much has been done to understand how merlin, the NF2 gene product, functions as a tumor suppressor gene in schwannoma cells, the functional role of merlin in the tumor microenvironment and the mechanism(s) by which merlin regulates angiogenesis to support schwannoma growth is largely unexplored. Here we report that the expression of semaphorin 3F (SEMA3F) was specifically downregulated in schwannoma cells lacking merlin/NF2. When we reintroduced SEMA3F in schwannoma cells, we observed normalized tumor blood vessels, reduced tumor burden, and extended survival in nude mice bearing merlin-deficient brain tumors. Next, using chemical inhibitors and gene knockdown with RNA interference, we found that merlin regulated expression of SEMA3F through Rho GTPase family member Rac1. This study shows that, in addition to the tumor-suppressing activity of merlin, it also functions to maintain physiological angiogenesis in the nervous system by regulating antiangiogenic factors such as SEMA3F. Restoring the relative balance of proangiogenic and antiangiogenic factors, such as increases in SEMA3F, in schwannoma microenvironment may represent a novel strategy to alleviate the clinical symptoms of NF2-related schwannomas.

The recombinant lectin-like domain of thrombomodulin inhibits angiogenesis through interaction with Lewis Y antigen

Lewis Y Ag (LeY) is a cell-surface tetrasaccharide that participates in angiogenesis. Recently, we demonstrated that LeY is a specific ligand of the recombinant lectin-like domain of thrombomodulin (TM). However, the biologic function of interaction between LeY and TM in endothelial cells has never been investigated. Therefore, the role of LeY in tube formation and the role of the recombinant lectin-like domain of TM-TM domain 1 (rTMD1)-in antiangiogenesis were investigated. The recombinant TM ectodomain exhibited lower angiogenic activity than did the recombinant TM domains 2 and 3. rTMD1 interacted with soluble LeY and membrane-bound LeY and inhibited soluble LeY-mediated chemotaxis of endothelial cells. LeY was highly expressed on membrane ruffles and protrusions during tube formation on Matrigel. Blockade of LeY with rTMD1 or Ab against LeY inhibited endothelial tube formation in vitro. Epidermal growth factor (EGF) receptor in HUVECs was LeY modified. rTMD1 inhibited EGF receptor signaling, chemotaxis, and tube formation in vitro, and EGF-mediated angiogenesis and tumor angiogenesis in vivo. We concluded that LeY is involved in vascular endothelial tube formation and rTMD1 inhibits angiogenesis via interaction with LeY. Administration of rTMD1 or recombinant adeno-associated virus vector carrying TMD1 could be a promising antiangiogenesis strategy.

Targeting tumor angiogenesis with TSP-1-based compounds: rational design of antiangiogenic mimetics of endogenous inhibitors

Inhibitors of angiogenesis are an important addition to conventional chemotherapy. Among different "druggable" angiogenic factors, fibroblast growth factor-2 (FGF-2) is an attractive target for novel therapies because of its intricated involvement in tumor neovascularization, tumor cell proliferation and migration, and the acquisition of resistance to antiangiogenic therapies. FGF-2 bioavailability and activity is affected by several natural ligands, including the endogenous inhibitor of angiogenesis thrombospondin-1 (TSP-1). We hypothesized that the FGF-2-binding sequence of TSP-1 might serve as a template for the development of non-peptide inhibitors of angiogenesis. Computational biology and nuclear magnetic resonance spectroscopy approaches, major investigative tools in the characterizations of protein-protein interaction (PPI), were used to map the residues at the TSP-1/FGF-2 interface. The translation of this three-dimensional information into a pharmacophore model allowed screening a small molecule databases, identifying three FGF-2-binding, antiangiogenic small molecules, mimetic of TSP-1. Pharmacophore-based approaches are thus feasible tools to exploit naturally occurring PPI, by generating a set of lead compounds mimetic of endogenous proteins, as a starting point for the development of novel therapeutic agents.

Targeting tumor angiogenesis with TSP-1-based compounds: rational design of antiangiogenic mimetics of endogenous inhibitors

Inhibitors of angiogenesis are an important addition to conventional chemotherapy. Among different "druggable" angiogenic factors, fibroblast growth factor-2 (FGF-2) is an attractive target for novel therapies because of its intricated involvement in tumor neovascularization, tumor cell proliferation and migration, and the acquisition of resistance to antiangiogenic therapies. FGF-2 bioavailability and activity is affected by several natural ligands, including the endogenous inhibitor of angiogenesis thrombospondin-1 (TSP-1). We hypothesized that the FGF-2-binding sequence of TSP-1 might serve as a template for the development of non-peptide inhibitors of angiogenesis. Computational biology and nuclear magnetic resonance spectroscopy approaches, major investigative tools in the characterizations of protein-protein interaction (PPI), were used to map the residues at the TSP-1/FGF-2 interface. The translation of this three-dimensional information into a pharmacophore model allowed screening a small molecule databases, identifying three FGF-2-binding, antiangiogenic small molecules, mimetic of TSP-1. Pharmacophore-based approaches are thus feasible tools to exploit naturally occurring PPI, by generating a set of lead compounds mimetic of endogenous proteins, as a starting point for the development of novel therapeutic agents.

Predictive and prognostic angiogenic markers in a gynecologic oncology group phase II trial of bevacizumab in recurrent and persistent ovarian or peritoneal cancer

OBJECTIVE

Potential predictive/prognostic angiogenic markers were prospectively examined in a phase II trial of bevacizumab in epithelial ovarian cancer (EOC)/primary peritoneal cancer (PPC).

METHODS

Recurrent/persistent EOC/PPC patients were treated with bevacizumab (15 mg/kg IV q21days) until disease progression. Validated-immunohistochemistry (IHC) assays were performed on pre-cycle 1/4 tumor biopsies for CD31-microvessel density (MVD), VEGF-histoscore (HS), p53-HS, and TSP1 image analysis score (IA). Pre-cycle 1/4 serum and plasma VEGF were quantified using a validated-ELISA.

RESULTS

CD31-MVD and serum VEGF, evaluated pre-cycle 1 in 41/61 and 51/61 eligible patients, respectively, did not appear to be correlated. High CD31-MVD, categorized at the median, appeared to be associated with tumor response, a 13-month shorter median survival, and an increased risk of death (unadjusted hazard ratio [HR] = 2.2, 95% confidence interval [CI] = 1.067-4.467). In addition, each standard deviation (SD) increase in CD31-MVD appeared to be associated with worse survival in unadjusted and adjusted analyses. IHC and plasma biomarkers did not change with bevacizumab treatment except for serum VEGF, which appeared to decrease during bevacizumab treatment. This decrease was not associated with response. High pre-cycle 1 serum VEGF, categorized at the median, was associated with 22-month shorter median survival and an increased risk of death (unadjusted HR = 2.7, 95% CI = 1.369-5.191). Categorized p53 appeared to be associated with unadjusted survival and each SD increase in TSP1-IA appeared to be associated with a decreased risk of progression in unadjusted and adjusted analyses.

CONCLUSIONS

Despite the limitations in sample size and exploratory nature of the study, angiogenic markers in tumor and serum may provide prognostic value in recurrent/persistent EOC/PPC, and are being prospectively evaluated in the GOG phase III trial of carboplatin, paclitaxel and bevacizumab/placebo in previously untreated EOC/PPC.

Predictive and prognostic angiogenic markers in a gynecologic oncology group phase II trial of bevacizumab in recurrent and persistent ovarian or peritoneal cancer

OBJECTIVE

Potential predictive/prognostic angiogenic markers were prospectively examined in a phase II trial of bevacizumab in epithelial ovarian cancer (EOC)/primary peritoneal cancer (PPC).

METHODS

Recurrent/persistent EOC/PPC patients were treated with bevacizumab (15 mg/kg IV q21days) until disease progression. Validated-immunohistochemistry (IHC) assays were performed on pre-cycle 1/4 tumor biopsies for CD31-microvessel density (MVD), VEGF-histoscore (HS), p53-HS, and TSP1 image analysis score (IA). Pre-cycle 1/4 serum and plasma VEGF were quantified using a validated-ELISA.

RESULTS

CD31-MVD and serum VEGF, evaluated pre-cycle 1 in 41/61 and 51/61 eligible patients, respectively, did not appear to be correlated. High CD31-MVD, categorized at the median, appeared to be associated with tumor response, a 13-month shorter median survival, and an increased risk of death (unadjusted hazard ratio [HR] = 2.2, 95% confidence interval [CI] = 1.067-4.467). In addition, each standard deviation (SD) increase in CD31-MVD appeared to be associated with worse survival in unadjusted and adjusted analyses. IHC and plasma biomarkers did not change with bevacizumab treatment except for serum VEGF, which appeared to decrease during bevacizumab treatment. This decrease was not associated with response. High pre-cycle 1 serum VEGF, categorized at the median, was associated with 22-month shorter median survival and an increased risk of death (unadjusted HR = 2.7, 95% CI = 1.369-5.191). Categorized p53 appeared to be associated with unadjusted survival and each SD increase in TSP1-IA appeared to be associated with a decreased risk of progression in unadjusted and adjusted analyses.

CONCLUSIONS

Despite the limitations in sample size and exploratory nature of the study, angiogenic markers in tumor and serum may provide prognostic value in recurrent/persistent EOC/PPC, and are being prospectively evaluated in the GOG phase III trial of carboplatin, paclitaxel and bevacizumab/placebo in previously untreated EOC/PPC.

Predictive and prognostic angiogenic markers in a gynecologic oncology group phase II trial of bevacizumab in recurrent and persistent ovarian or peritoneal cancer

OBJECTIVE

Potential predictive/prognostic angiogenic markers were prospectively examined in a phase II trial of bevacizumab in epithelial ovarian cancer (EOC)/primary peritoneal cancer (PPC).

METHODS

Recurrent/persistent EOC/PPC patients were treated with bevacizumab (15 mg/kg IV q21days) until disease progression. Validated-immunohistochemistry (IHC) assays were performed on pre-cycle 1/4 tumor biopsies for CD31-microvessel density (MVD), VEGF-histoscore (HS), p53-HS, and TSP1 image analysis score (IA). Pre-cycle 1/4 serum and plasma VEGF were quantified using a validated-ELISA.

RESULTS

CD31-MVD and serum VEGF, evaluated pre-cycle 1 in 41/61 and 51/61 eligible patients, respectively, did not appear to be correlated. High CD31-MVD, categorized at the median, appeared to be associated with tumor response, a 13-month shorter median survival, and an increased risk of death (unadjusted hazard ratio [HR] = 2.2, 95% confidence interval [CI] = 1.067-4.467). In addition, each standard deviation (SD) increase in CD31-MVD appeared to be associated with worse survival in unadjusted and adjusted analyses. IHC and plasma biomarkers did not change with bevacizumab treatment except for serum VEGF, which appeared to decrease during bevacizumab treatment. This decrease was not associated with response. High pre-cycle 1 serum VEGF, categorized at the median, was associated with 22-month shorter median survival and an increased risk of death (unadjusted HR = 2.7, 95% CI = 1.369-5.191). Categorized p53 appeared to be associated with unadjusted survival and each SD increase in TSP1-IA appeared to be associated with a decreased risk of progression in unadjusted and adjusted analyses.

CONCLUSIONS

Despite the limitations in sample size and exploratory nature of the study, angiogenic markers in tumor and serum may provide prognostic value in recurrent/persistent EOC/PPC, and are being prospectively evaluated in the GOG phase III trial of carboplatin, paclitaxel and bevacizumab/placebo in previously untreated EOC/PPC.

Mapping pro- and antiangiogenic factors on the surface of prostasomes of normal and malignant cell origin

BACKGROUND

Angiogenesis is the formation of new blood vessels by capillary sprouting from pre-existing vessels. Tumor growth is angiogenesis-dependent and the formation of new blood vessels is associated with the increased expression of angiogenic factors. Prostasomes are secretory granules produced, stored and released by the glandular epithelial cells of the prostate. We investigated the expression of selected angiogenic and anti-angiogenic factors on the surface of prostasomes of different origins as well as the direct effect of prostasomes on angiogenesis.

METHODS

VEGF, endothelin-1, endostatin, and thrombospondin-1 were determined on prostasomes from seminal fluid and human prostate cancer cell lines (DU145,PC-3,LNCaP) using different immunochemical techniques. Human dermal microvascular endothelial cells were incubated with seminal and DU145 cell-prostasomes and with radioactive thymidine. The effect of prostasomes on angiogenesis was judged by measuring the uptake of labeled thymidine. The presence of any deleterious effects of prostasomes on the endothelial cells was investigated using thymidine assay and confocal laser microscopy.

RESULTS

VEGF and endothelin-1 were determined on malignant cell-prostasomes (no difference between cell lines) but not determined on seminal prostasomes. The same applies for the expression of endostatin but with much higher expression on malignant cell-prostasomes with obvious differences between them. Seminal and DU145 cell-prostasomes were found to have anti-angiogenic effect which was more expressed by DU145 cell-prostasomes. No deleterious effect of prostasomes on endothelial function was detected using either thymidine assay or microscopy.

CONCLUSIONS

Prostasomes contain pro- and anti-angiogenic factors that function to counteract each other unless the impact from one side exceeds the other to bring about dysequilibrium.

Potential relevance of bell-shaped and u-shaped dose-responses for the therapeutic targeting of angiogenesis in cancer

Tumor angiogenesis, the growth of new blood vessels into tumors, facilitates tumor growth and thus represents an attractive therapeutic target. Numerous experimental angiogenesis inhibitors have been characterised and subsequently trialled in patients. Some of these agents have failed to show any substantial activity in patients. In contrast, others have been more successful, but even these provide only a few months extra patient survival. Recent work has focused on understanding the effects of anti-angiogenic agents on tumor biology and has revealed a number of new findings that may help to explain the limited efficacy of angiogenesis inhibitors. Herein, I review the evidence that hormetic dose-responses (i.e. bell-shaped and U-shaped dose-response curves) are often observed with anti-angiogenic agents. Agents reported to exhibit these types of dose-response include: 5-fluorouracil, ATN-161, bortezomib, cisplatin, endostatin, enterostatin, integrin inhibitors, interferon-α, plasminogen activator-1 (PAI-1), rapamycin, rosiglitazone, statins, thrombospondin-1, TGF-α1 and TGF-α3. Hormesis may also be relevant for drugs that target the vascular endothelial growth factor (VEGF) signalling pathway and for metronomic chemotherapy. Here I argue that hormetic dose-responses present a challenge for the clinical translation of several anti-angiogenic agents and discuss how these problems might be circumvented.

Thrombospondin-1 as a Paradigm for the Development of Antiangiogenic Agents Endowed with Multiple Mechanisms of Action

Uncontrolled neovascularization occurs in several angiogenesis-dependent diseases, including cancer. Neovascularization is tightly controlled by the balance between angiogenic growth factors and antiangiogenic agents. The various natural angiogenesis inhibitors identified so far affect neovascularization by different mechanisms of action. Thrombospondin-1 (TSP-1) is a matricellular modular glycoprotein that acts as a powerful endogenous inhibitor of angiogenesis. It acts both indirectly, by sequestering angiogenic growth factors and effectors in the extracellular environment, and directly, by inducing an antiangiogenic program in endothelial cells following engagement of specific receptors including CD36, CD47, integrins and proteoglycans (all involved in angiogenesis ). In view of its central, multifaceted role in angiogenesis, TSP-1 has served as a source of antiangiogenic tools, including TSP-1 fragments, synthetic peptides and peptidomimetics, gene therapy strategies, and agents that up-regulate TSP-1 expression. This review discusses TSP-1-based inhibitors of angiogenesis, their mechanisms of action and therapeutic potential, drawing our experience with angiogenic growth factor-interacting TSP-1 peptides, and the possibility of exploiting them to design novel antiangiogenic agents.

Biological activities and molecular interactions of the C-terminal residue of thrombospondin-4, an epitome of acidic amphipathic peptides

C21, the C-terminal residue of thrombospondin-4 (TSP-4), was identified as a peptide growth factor during an investigation concerning erythropoietin-dependent, erythroid stimulating factors of endothelial origin. It is active in cultures of several human hematopoietic stem cells, skin fibroblasts and kidney epithelial cells and stimulates red cell formation in anemic mice. A method of affinity chromatography in the presence of high concentrations of Triton X-100, previously developed for identifying proteins associated with the TSP-1 receptor CD47, was utilized for the detection of C21 binding molecules and their detergent-resistant, associated partners. These experiments helped to delineate two different mechanisms of C21 action, which are compatible with its cell proliferating activity. As a cell matrix peptide, C21 binds to the osteopontin receptor CD44 and could act as an osteopontin antagonist, preventing the inhibition of primitive hematopoietic stem cell proliferation. TSP-1, another matrix protein, binds to C21 and could indirectly act as an antagonist, by shunting C21-CD44 interactions. The second mechanism is a direct effect of C21 on cell proliferation. The extremely rapid internalization and nuclear localization of the peptide could be explained by CD44-mediated internalization, followed by a microtubule-mediated transport towards the nucleus, or, eventually, direct membrane insertion. These alternative hypotheses are supported by previously observed membrane insertion of similar synthetic and viral acidic amphipathic peptides, the presence of microtubule-associated protein 1B (MAP1B) and dynactin in the triton-soluble complexes associated with C21 and the presence in such complexes of dual compartment proteins for nuclei and plasma membranes, such as MAP1B, AHNAK and CD44.

Thrombospondins in the heart: potential functions in cardiac remodeling

Cardiac remodeling after myocardial injury involves inflammation, angiogenesis, left ventricular hypertrophy and matrix remodeling. Thrombospondins (TSPs) belong to the group of matricellular proteins, which are non-structural extracellular matrix proteins that modulate cell-matrix interactions and cell function in injured tissues or tumors. They interact with different matrix and membrane-bound proteins due to their diverse functional domains. That the expression of TSPs strongly increases during cardiac stress or injury indicates an important role for them during cardiac remodeling. Recently, the protective properties of TSP expression against heart failure have been acknowledged. The current review will focus on the biological role of TSPs in the ischemic and hypertensive heart, and will describe the functional consequences of TSP polymorphisms in cardiac disease.

Thrombospondins function as regulators of angiogenesis

Thrombospondins (TSPs) -1 and -2 were among the first protein inhibitors of angiogenesis to be identified, a property that was subsequently attributed to the interactions of sequences in their type I repeats with endothelial cell-surface receptors. The interactions of TSPs-1 and -2 with cell-surface receptors, proteases, growth factors, and other bioactive molecules, coupled with the absence of direct structural functions that can be attributed to these matrix proteins, qualify them for inclusion in the category of ‘matricellular proteins’. The phenotypes of TSP-1, TSP-2, and double TSP-1/2-null mice confirm the roles that these proteins play in the regulation of angiogenesis, and provide clues to some of the other important functions of these multi-domain proteins. One of these functions is the ability of TSP-1 to activate the latent TGFβ1 complex, a property that is not shared by TSP-2. A major pathway by which TSP1 or TSP2 inhibits angiogenesis involves an interaction with CD 36 on endothelial cells, which leads to apoptosis of both the liganded and adjacent cells. However a homeostatic mechanism, which inhibits endothelial cell proliferation, and may be physiologically preferable under some circumstances, has also been elucidated, and involves interaction with the very low density lipoprotein receptor (VLDLR). The interaction of TSP1with its receptor, CD47, further inhibits angiogenesis by antagonizing nitric oxide signaling in endothelial and vascular smooth muscle cells. Paradoxically, there is also evidence that TSP-1 can function to promote angiogenesis. This apparent contradiction can be explained by the presence of sequences in different domains of the protein that interact with different receptors on endothelial cells. The anti-angiogenic function of TSPs has spurred interest in their use as anti-tumor agents. Currently, peptide mimetics, based on sequences in the type I repeats of TSPs that have been shown to have anti-angiogenic properties, are undergoing clinical testing.

Estrogen regulation of thrombospondin-1 in human breast cancer cells

Expression of thrombospondin-1 (TSP-1), a large extracellular matrix protein, has been associated with modulation of angiogenesis and tumor growth. Both pro and antiangiogenic properties of TSP-1 have been described, and the role of TSP-1 expression in the growth and progression of human breast cancer is not clear. Because estrogens cause progression of many breast cancers, and estradiol (E2) downregulates a TSP-1 receptor, we examined whether TSP-1 is regulated by estrogen and involved in tumor progression. E2 induced TSP-1 expression in T47-D and MCF-7 breast cancer cells in vitro within 3 to 6 hr; the induction was blocked by the anti-estrogen ICI 182,780, indicating that estrogen receptors (ER) are necessary for this effect. Furthermore, E2 caused the production of TSP-1 protein from tumor cells in an ER-alpha-dependent manner. The E2-mediated TSP-1 RNA induction was dose-dependent and blocked by actinomycin D, indicating that the response to E2 was at least partly transcriptional. Transfection studies with deletion constructs of the TSP-1 promoter identified an estrogen-responsive region in the human TSP-1 promoter, located between -2,200 and -1,792 bp upstream of the transcription start site. An antibody against TSP-1 restricted the proliferation of E2-dependent MCF-7 cells in vitro and in vivo. A panel of breast cancer cells proliferated in the presence of low concentrations of exogenous TSP-1, whereas higher concentrations inhibited proliferation. A real-time PCR analysis showed that E2 also induced TSP-1 mRNA in the normal mammary glands of immature ovariectomized mice in an ER-dependent manner. In summary, we report the novel observation that TSP-1 production is directly controlled by estrogens in ER-positive breast cancer cells, and the released protein has pro-growth regulatory functions. Consequently, we propose that TSP-1 could be a therapeutic target for anti-tumor therapy in early-stage tumors. (c) 2009 UICC.

Regulation of nitric oxide signalling by thrombospondin 1: implications for anti-angiogenic therapies

In addition to long-term regulation of angiogenesis, angiogenic growth factor signalling through nitric oxide (NO) acutely controls blood flow and haemostasis. Inhibition of this pathway may account for the hypertensive and pro-thrombotic side effects of the vascular endothelial growth factor antagonists that are currently used for cancer treatment. The first identified endogenous angiogenesis inhibitor, thrombospondin 1, also controls tissue perfusion, haemostasis and radiosensitivity by antagonizing NO signalling. We examine the role of these and other emerging activities of thrombospondin 1 in cancer. Clarifying how endogenous and therapeutic angiogenesis inhibitors regulate vascular NO signalling could facilitate development of more selective inhibitors.