In vivo mechanisms by which tumors producing thrombospondin 1 bypass its inhibitory effects

New insights into the role of thrombospondin-1 in glioblastoma development

Glioblastoma (GB), the most malignant subtype of diffuse glioma, is highly aggressive, invasive and vascularized. Its median survival is still short even with maximum standard care. There is a need to identify potential new molecules and mechanisms, that are involved in the interactions of GB cells with the tumor microenvironment (TME), for therapeutic intervention. Thrombospondin-1 (TSP1) is a multi-faceted matricellular protein which plays a significant role in development, physiology and pathology including cancer. Recent studies have pinpoint an important role of TSP1 in GB development which will be summarized and discussed herein. We will discuss studies, mainly from preclinical research, which should lead to a deeper understanding of TSP1's role in GB development. We will also discuss some issues with regard to the use of this knowledge for the clinic.

Circ_0058063 regulates cell vitality and proliferation in oesophageal squamous-cell carcinomas

Oesophageal squamous-cell carcinoma (ESCC) is a malignant tumor of the digestive system with a poor prognosis. Recent studies have shown the promoting effect of hsa_circ_0058063 (circ_0058063) on ESCC, but the potential regulatory mechanisms of circ_0058063 in ESCC remain largely unclear. The levels of circ_0058063, microRNA-4319 (miR-4319) and mRNA of thrombospondin-1 (THBS1) were indicated by quantitative real-time polymerase chain reaction in ESCC tissues and cells. Meanwhile, the level of THBS1 was quantified by western blot analysis. In addition, the cell functions were examined by CCK8 assay, Edu assay, flow cytometry assay and transwell assay. Furthermore, the interplay between miR-4319 and circ_0058063 or THBS1 was detected by dual-luciferase reporter assay. Finally, an in vivo experiment was implemented to confirm the effect of circ_0058063. The level of circ_0058063 and THBS1 were increased, and the miR-4319 level was decreased in ESCC tissues in contrast to that in normal tissues and cells. For functional analysis, circ_0058063 deficiency inhibited cell vitality, cell proliferation, migration and invasion in ESCC cells, whereas promoted cell apoptosis. Moreover, miR-4319 was confirmed to repress the progression of ESCC cells by suppressing THBS1. In mechanism, circ_0058063 acted as a miR-4319 sponge to regulate the level of THBS1. Besides, circ_0058063 knockdown also attenuated tumour growth in vivo. Circ_0058063 facilitates the development of ESCC through increasing THBS1 expression by regulating miR-4319, which also offered an underlying targeted therapy for ESCC treatment.

LRRK2 Gly2019Ser Mutation Promotes ER Stress via Interacting with THBS1/TGF-β1 in Parkinson's Disease

The gene mutations of LRRK2, which encodes leucine-rich repeat kinase 2 (LRRK2), are associated with one of the most prevalent monogenic forms of Parkinson's disease (PD). However, the potential effectors of the Gly2019Ser (G2019S) mutation remain unknown. In this study, the authors investigate the effects of LRRK2 G2019S on endoplasmic reticulum (ER) stress in induced pluripotent stem cell (iPSC)-induced dopamine neurons and explore potential therapeutic targets in mice model. These findings demonstrate that LRRK2 G2019S significantly promotes ER stress in neurons and mice. Interestingly, inhibiting LRRK2 activity can ameliorate ER stress induced by the mutation. Moreover, LRRK2 mutation can induce ER stress by directly interacting with thrombospondin-1/transforming growth factor beta1 (THBS1/TGF-β1). Inhibition of LRRK2 kinase activity can effectively suppress ER stress and the expression of THBS1/TGF-β1. Knocking down THBS1 can rescue ER stress by interacting with TGF-β1 and behavior burden caused by the LRRK2 mutation, while suppression of TGF-β1 has a similar effect. Overall, it is demonstrated that the LRRK2 mutation promotes ER stress by directly interacting with THBS1/TGF-β1, leading to neural death in PD. These findings provide valuable insights into the pathogenesis of PD, highlighting potential diagnostic markers and therapeutic targets.

Counter Regulation of Tumor Angiogenesis by Vascular Endothelial Growth Factor and Thrombospondin-1

Considerable progress has been made in our understanding of the process of angiogenesis in the context of normal and tumor tissue over the last fifty years. Angiogenesis, like most physiological processes, is carefully controlled by dynamic and opposing effects of positive factors, such as vascular endothelial growth factor (VEGF), and negative factors, such as thrombospondin-1. In most cases, the progression of a small mass of cancerous cells to a life-threatening tumor depends upon the initiation of angiogenesis and involves the dysregulation of the angiogenic balance. Whereas our newfound appreciation for the role of angiogenesis in cancer has opened up new avenues for treatment, the success of these treatments, which have focused almost exclusively on antagonizing the VEGF pathway, has been limited to date. It is anticipated that this situation will improve as more therapeutics that target other pathways are developed, more strategies for combination therapies are advanced, more detailed stratification of patient populations occurs, and a better understanding of resistance to anti-angiogenic therapy is gained.

High Level of Staufen1 Expression Confers Longer Recurrence Free Survival to Non-Small Cell Lung Cancer Patients by Promoting THBS1 mRNA Degradation

Stau1 is a pluripotent RNA-binding protein that is responsible for the post-transcriptional regulation of a multitude of transcripts. Here, we observed that lung cancer patients with a high Stau1 expression have a longer recurrence free survival. Strikingly, Stau1 did not impair cell proliferation in vitro, but rather cell migration and cell adhesion. In vivo, Stau1 depletion favored tumor progression and metastases development. In addition, Stau1 depletion strongly impaired vessel maturation. Among a panel of candidate genes, we specifically identified the mRNA encoding the cell adhesion molecule Thrombospondin 1 (THBS1) as a new target for Staufen-mediated mRNA decay. Altogether, our results suggest that regulation of THBS1 expression by Stau1 may be a key process involved in lung cancer progression.

Platelet TSP-1 controls prostate cancer-induced osteoclast differentiation and bone marrow-derived cell mobilization through TGFβ-1

The development of distant metastasis is the leading cause of prostate cancer (CaP)-related death, with the skeleton being the primary site of metastasis. While the progression of primary tumors and the growth of bone metastatic tumors are well described, the mechanisms controlling pre-metastatic niche formation and homing of CaP to bone remain unclear. Through prior studies, we demonstrated that platelet secretion was required for ongoing tumor growth and pre-metastatic tumor-induced bone formation. Platelets stimulated bone marrow-derived cell (BMDC) mobilization to tumors supporting angiogenesis. We hypothesized that proteins released by the platelet α granules were responsible for inducing changes in the pre-metastatic bone niche. We found that the classically anti-angiogenic protein thrombospondin (TSP)-1 was significantly increased in the platelets of mice with RM1 murine CaP tumors. To determine the role of increased TSP-1, we implanted tumors in TSP-1 null animals and assessed changes in tumor growth and pre-metastatic niche. TSP-1 loss resulted in increased tumor size and enhanced angiogenesis by immunohistochemistry. Conversely, TSP-1 deletion reduced BMDC mobilization and enhanced osteoclast formation resulting in decreased tumor-induced bone formation as measured by microcomputed tomography. We hypothesized that changes in the pre-metastatic niche were due to the retention of TGF-β1 in the platelets of mice after TSP-1 deletion. To assess the importance of platelet-derived TGF-β1, we implanted RM1 CaP tumors in mice with platelet factor 4-driven deletion of TGF-β1 in platelets and megakaryocytes. Like TSP-1 deletion, loss of platelet TGF-β1 resulted in increased angiogenesis with a milder effect on tumor size and BMDC release. Within the bone microenvironment, platelet TGF-β1 deletion prevented tumor-induced bone formation due to increased osteoclastogenesis. Thus, we demonstrate that the TSP-1/TGF-β1 axis regulates pre-metastatic niche formation and tumor-induced bone turnover. Targeting the platelet release of TSP-1 or TGF-β1 represents a potential method to interfere with the process of CaP metastasis to bone.

Role of TSP-1 as prognostic marker in various cancers: a systematic review and meta-analysis

Background

Published studies present conflicting data regarding the impact of Thrombospondin-1 (TSP-1) expression on prognosis of various cancers. We performed this meta-analysis to illustrate the preliminary predictive value of TSP-1.

Methods

Twenty-four studies with a total of 2379 patients were included. A comprehensive literature search was performed by using PubMed, Cochrane Library, Web of Science, Embase, and hand searches were also conducted of relevant bibliographies. Pooled hazard ratios (HRs) with 95% confidence intervals (CIs) for patient survival and disease recurrence were initially identified to explore relationships between TSP-1 expression and patient prognosis.

Results

A total of 24 eligible studies were included in this meta-analysis. Our results showed that high level of TSP-1 was correlated significantly with poor overall survival (OS) (HR = 1.40, 95% CI: 1.17 ~ 1.68; P<0.001). However, high TSP-1 expression predicted no significant impact on progression-free survival (PFS)/ metastasis-free survival (MFS) (HR = 1.35, 95%CI: 0.87–2.10; P = 0.176) and disease-free survival (DFS)/ recurrence-free survival (RFS) (HR = 1.40, 95%CI: 0.77–2.53; P = 0.271). In addition, we performed subgroup analyses which showed that high TSP-1 expression predicted poor prognosis in breast cancer and gynecological cancer. Additionally, the relatively small number of studies on PFS/MFS and DFS/RFS is a limitation. The data extracted through Kaplan-Meier curves may not be accurate. Moreover, only English articles were included in this article, which may lead to deviations in the results.

Conclusions

Our findings indicated high TSP-1 expression may act as a promising biomarker of poor prognosis in cancers, especially in breast cancer and gynecological cancer.

Plasticity of patient-matched normal mammary epithelial cells is dependent on autologous adipose-derived stem cells

Due to the increasing clinical application of adipose-derived stem cells (ADSC), e.g. lipotransfer for breast reconstruction, this study aimed to gain novel insights regarding ADSC influence on breast tissue remodeling and determine patient-dependent factors affecting lipotransfer as well as begin to address its oncological risks. The ADSC secretome was analyzed from five normal breast reduction patients and contained elevated levels of growth factors, cytokines and proteins mediating invasion. ADSC/ADSC secretomes were tested for their influence on the function of primary mammary epithelial cells, and tumor epithelial cells using cell culture assays. ADSC/ADSC secretomes significantly stimulated proliferation, transmigration and 3D-invasion of primary normal and tumor epithelial cells. IL-6 significantly induced an EMT and invasion. The ADSC secretome significantly upregulated normal epithelial cell gene expression including MMPs and ECM receptors. Our study supports that ADSC and its secretome promote favorable conditions for normal breast tissue remodeling by changing the microenvironment. and may also be important regarding residual breast cancer cells following surgery.

Deciphering the complex role of thrombospondin-1 in glioblastoma development

We undertook a systematic study focused on the matricellular protein Thrombospondin-1 (THBS1) to uncover molecular mechanisms underlying the role of THBS1 in glioblastoma (GBM) development. THBS1 was found to be increased with glioma grades. Mechanistically, we show that the TGFβ canonical pathway transcriptionally regulates THBS1, through SMAD3 binding to the THBS1 gene promoter. THBS1 silencing inhibits tumour cell invasion and growth, alone and in combination with anti-angiogenic therapy. Specific inhibition of the THBS1/CD47 interaction using an antagonist peptide decreases cell invasion. This is confirmed by CD47 knock-down experiments. RNA sequencing of patient-derived xenograft tissue from laser capture micro-dissected peripheral and central tumour areas demonstrates that THBS1 is one of the gene with the highest connectivity at the tumour borders. All in all, these data show that TGFβ1 induces THBS1 expression via Smad3 which contributes to the invasive behaviour during GBM expansion. Furthermore, tumour cell-bound CD47 is implicated in this process.

Thrombospondin-1 (THSB1) is a component of the ECM with a role in regulating cancer development and tumour vasculature. Here, the authors show that TGF-beta-induced THBS1 expression contributes to the invasive behaviour of GBM cells and promotes resistance to antiangiogenic therapy partially through interaction with CD47.

Thrombospondins and remodeling of the tumor microenvironment

Vascular remodeling defines cancer growth and aggressiveness. Although cancer cells produce pro-angiogenic signals, the fate of angiogenesis critically depends on the cancer microenvironment. Composition of the extracellular matrix (ECM) and tumor inflammation determine whether a cancer will remain dormant, will be recognized by the immune system and eliminated, or whether the tumor will develop and lead to the spread and metastasis of cancer cells. Thrombospondins (TSPs), a family of ECM proteins that has long been associated with the regulation of angiogenesis and cancer, regulate multiple physiological processes that determine cancer growth and spreading, from angiogenesis to inflammation, metabolic changes, and properties of ECM. Here, we sought to review publications that describe various functions of TSPs that link these proteins to regulation of cancer growth by modulating multiple physiological and pathological events that prevent or support tumor development. In addition to its direct effects on angiogenesis, TSPs have important roles in regulation of inflammation, immunity, ECM properties and composition, and glucose and insulin metabolism. Furthermore, TSPs have distinct roles as regulators of remodeling in tissues and tumors, such that the pathways activated by a single TSP can interact and influence each other. The complex nature of TSP interactions and functions, including their different cell- and tissue-specific effects, may lead to confusing results and controversial conclusions when taken out of the context of interdisciplinary and holistic approaches. However, studies of TSP functions and roles in different systems of the organism offer an integrative view of tumor remodeling and a potential for finding therapeutic targets that would modulate multiple complementary processes associated with cancer growth.

Human expression patterns: qualitative and quantitative analysis of thrombospondin-1 under physiological and pathological conditions

Thrombospondin-1 (TSP-1), a matricellular protein and one of the first endogenous anti-angiogenic molecules identified, has long been considered a potent modulator of human diseases. While the therapeutic effect of TSP-1 to suppress cancer was investigated in both research and clinical settings, the mechanisms of how TSP-1 is regulated in cancer remain elusive, and the scientific answers to the question of whether TSP-1 expressions can be utilized as diagnostic or prognostic marker for patients with cancer are largely inconsistent. Moreover, TSP-1 plays crucial functions in angiogenesis, inflammation and tissue remodelling, which are essential biological processes in the progression of many cardiovascular diseases, and therefore, its dysregulated expressions in such conditions may have therapeutic significance. Herein, we critically analysed the literature pertaining to TSP-1 expression in circulating blood and pathological tissues in various types of cancer as well as cardiovascular and inflammation-related diseases in humans. We compare the secretion rates of TSP-1 by different cancer and non-cancer cells and discuss the potential connection between the expression changes of TSP-1 and vascular endothelial growth factor (VEGF) observed in patients with cancer. Moreover, the pattern and emerging significance of TSP-1 profiles in cardiovascular disease, such as peripheral arterial disease, diabetes and other related non-cancer disorders, are highlighted. The analysis of published TSP-1 data presented in this review may have implications for the future exploration of novel TSP-1-based treatment strategies for cancer and cardiovascular-related diseases.

Microenvironmental regulation of tumour angiogenesis

Tumours display considerable variation in the patterning and properties of angiogenic blood vessels, as well as in their responses to anti-angiogenic therapy. Angiogenic programming of neoplastic tissue is a multidimensional process regulated by cancer cells in concert with a variety of tumour-associated stromal cells and their bioactive products, which encompass cytokines and growth factors, the extracellular matrix and secreted microvesicles. In this Review, we discuss the extrinsic regulation of angiogenesis by the tumour microenvironment, highlighting potential vulnerabilities that could be targeted to improve the applicability and reach of anti-angiogenic cancer therapies.

Matricellular TSP-1 as a target of interest for impeding melanoma spreading: towards a therapeutic use for TAX2 peptide

Thrombospondin-1 (TSP-1) is a matricellular glycoprotein known for being highly expressed within a tumor microenvironment, where it promotes an aggressive phenotype particularly by interacting with the CD47 cell-surface receptor. While it originates from the stromal compartment in many malignancies, melanoma is an exception as invasive and metastatic melanoma cells overexpress TSP-1. We recently demonstrated that a new molecular agent that selectively prevents TSP-1 binding to CD47, called TAX2, exhibits anti-cancer properties when administered systemically by decreasing viable tumor tissue within subcutaneous B16 melanoma allografts. At the same time, emerging evidence was published suggesting a contribution of TSP-1 in melanoma metastatic dissemination and resistance to treatment. Through a comprehensive systems biology approach based on multiple genomics and proteomics databases analyses, we first identified a TSP-1-centered interaction network that is overexpressed in metastatic melanoma. Then, we investigated the effects of disrupting TSP-1:CD47 interaction in A375 human malignant melanoma xenografts. In this model, TAX2 systemic administrations induce tumor necrosis by decreasing intra-tumoral blood flow, while concomitantly making tumors less infiltrative. Besides, TAX2 treatment also drastically inhibits B16F10 murine melanoma cells metastatic dissemination and growth in a syngeneic experimental model of lung metastasis, as demonstrated by histopathological analyses as well as longitudinal and quantitative µCT follow-up of metastatic progression. Altogether, the results obtained by combining bioinformatics and preclinical studies strongly suggest that targeting TSP-1/CD47 axis may represent a valuable therapeutic alternative for hampering melanoma spreading.

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.

Surface profiles of live colorectal cancer cells and tumor infiltrating lymphocytes from surgical samples correspond to prognostic categories

Extensive surface profiles of colorectal cancer (CRC) cells and tumor infiltrating lymphocytes (TIL) have been obtained from 45 surgical resection samples. Live cells were captured on an antibody microarray and stained with fluorescently-labeled antibodies. Minimal panels of 11 CRC antigens (CD13, CD24, CD26, CD49d, CD138, CD166, CA-125, CA19-9, EGFR, Galectin-4 and HLA-DR) and 11 T-cell antigens (CD10, CD11b, CD11c, CD25, CD31, CD95, CD151, CD181, Galectin-4, CA19-9, TSP-1) provide signatures for relapse and survival. Hierarchical clustering of profiles from CRC cells and TIL identified groups of patients for survival, systemic relapse and death. The groups from CRC and TIL profiles for systemic relapse showed 79.2% concordance, enabling prediction of relapse after surgery. The results demonstrate communication between CRC cells and TIL.

Ossifying fibroma tumor stem cells are maintained by epigenetic regulation of a TSP1/TGF-β/SMAD3 autocrine loop

Abnormal stem cell function makes a known contribution to many malignant tumors, but the role of stem cells in benign tumors is not well understood. Here, we show that ossifying fibroma (OF) contains a stem cell population that resembles mesenchymal stem cells (OFMSCs) and is capable of generating OF-like tumor xenografts. Mechanistically, OFMSCs show enhanced TGF-β signaling that induces aberrant proliferation and deficient osteogenesis via Notch and BMP signaling pathways, respectively. The elevated TGF-β activity is tightly regulated by JHDM1D-mediated epigenetic regulation of thrombospondin-1 (TSP1), forming a JHDM1D/TSP1/TGF-β/SMAD3 autocrine loop. Inhibition of TGF-β signaling in OFMSCs can rescue their abnormal osteogenic differentiation and elevated proliferation rate. Furthermore, chronic activation of TGF-β can convert normal MSCs into OF-like MSCs via establishment of this JHDM1D/TSP1/TGF-β/SMAD3 autocrine loop. These results reveal that epigenetic regulation of TGF-β signaling in MSCs governs the benign tumor phenotype in OF and highlight TGF-β signaling as a candidate therapeutic target.

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.

Comparative analysis of each prescription of Jiedu Huayu Jianpi Fang for multiple gene demethylation and expression in mucosal dysplasia in rats

AIM: To evaluate the contribution of each prescription of Jiedu Huayu Jianpi Fang to the therapeutic effects on gastric mucosal dysplasia from the perspective of induced gene expression.

METHODS: We divided gastric mucosal dysplasia rats into a model control (MG) group, a Western medicine (retinoic acid) treatment (PCG) group, a combined prescription (Jiedu Huayu Jianpi) treatment (A) group, and Jiedu (B), Huayu (C), Yiqi (D), Yangying (E) and Liqi (F) single prescription treatment groups. Normal rats were used as controls (CG). Methylation specific PCR technique was used to detect the methylation status of p16, PETN, Thbs1, E-Cadherin, and Runx3 genes in gastric mucosal cells of rats. Real-time PCR and immunohistochemistry were used to detect the mRNA and protein expression of each genes.

RESULTS: All of the Jiedu Huayu Jianpi treatment groups showed a certain degree of demethylation of p16, PETN, Thbs1, E-Cadherin, and Runx3 gene. Compared with group CG, the mRNA expression of p16 (P < 0.01), PETN, E-Cadherin and Thbs1 in group A, Thbs1 in group B, p16, PETN and Thbs1 in group C, Thbs1 in group E, p16 and Thbs1 in group F increased significantly (P < 0.05 for all); and the protein expression of p16, PTEN, E-cad, RUNX3, and THBS1 in group A, p16 in group B, p16 and THBS1 in group C, p16, PTEN, E-cad and THBS1 in group D, p16, E-cad, RUNX3 and THBS1 in group E, p16, PTEN, E-cad, RUNX3 and THBS1 in group F increased significantly (P < 0.05 for all). The effect of Jiedu Huayu Jianpi Fang on gastric mucosal dysplasia was the most prominent, followed by Liqi, Yangyin, Huayu, Yiqi and Jiedu single prescriptions.

CONCLUSION: The effect of Jiedu Huayu Jianpi Fang on gastric mucosal dysplasia is much better than those of each single prescription. Gastric mucosal dysplasia should be treated mainly by means of Liqi and Yangyin.

Synergistic anticancer activity of valproate combined with nicotinamide enhances anti-proliferation response and apoptosis in MIAPaca2 cells

Histone deacetylase is strongly associated with epigenetic regulation and carcinogenesis, and its inhibitors can induce cell cycle arrest and apoptosis of the cancer cells. In this study we aimed to examine the antiproliferative effects a combination of the valproate with nicotinamide in MIAPaca2 cell line. We revealed that valproate acted in a synergistic/additive with nicotinamide to inhibit the proliferation and induction of apoptosis in MIAPaca2 cancer cell line. MIAPaca2 was treated with various concentrations of valproate. The MTT assay and colony formation in soft agar indicated that valproate at 0.5 mM, when used alone weakly, suppressed proliferation of cells (37 ± 3.02%) whereas the combination treatment of valproate + nicotinamide significantly suppressed cell proliferation (58 ± 3.5%). The effect of nicotinamide at 25 mM on cell proliferation and cell colonization induced 50% apoptosis of MIAPaca2 cells. To identify the anti-proliferation and apoptotic effects of valproate and nicotinamide we performed flow cytometric and microscopic analyses. The results indicated significant apoptosis induction and nuclear morphological alterations greater than when valproate was used alone. Furthermore, western blot analyses was performed to study the role of acetyl-histone H3 levels, and quantitative RNA expression analyses were performed on expression of thrombospondin (TSP) and maspin genes in MIAPaca2. We found that the combination treatment of valproate + nicotinamide enhanced the expression of maspin and TSP genes and the biological response of the cell line was correlated with the increase of histone H3 acetylation after nicotinamide and valproate application. Together our findings indicate that valproate which act as inhibitor of cell proliferation and inducer of apoptosis in human cancer MIAPaca2 cells when used in combination with nicotinamide makes it a potentially good candidate for new anticancer drug development.

Matrikine and matricellular regulators of EGF receptor signaling on cancer cell migration and invasion

Cancer invasion is a complex process requiring, among other events, extensive remodeling of the extracellular matrix including deposition of pro-migratory and pro-proliferative moieties. In recent years, it has been described that while invading through matrices cancer cells can change shape and adapt their migration strategies depending on the microenvironmental context. Although intracellular signaling pathways governing the mesenchymal to amoeboid migration shift and vice versa have been mostly elucidated, the extracellular signals promoting these shifts are largely unknown. In this review, we summarize findings that point to matrikines that bind specifically to the EGF receptor as matricellular molecules that enable cancer cell migrational plasticity and promote invasion.

The role of the tumor microenvironment in regulating angiogenesis

The tumor-associated stroma has been shown to play a significant role in cancer formation. Paracrine signaling interactions between epithelial tumor cells and stromal cells are a key component in the transformation and proliferation of tumors in several organs. Whereas the intracellular signaling pathways regulating the expression of several pro- and antiangiogenic proteins have been well characterized in human cancer cells, the intercellular signaling that takes place between tumor cells and the surrounding tumor-associated stroma has not been as extensively studied with regard to the regulation of angiogenesis. In this chapter we define the key players in the regulation of angiogenesis and examine how their expression is regulated in the tumor-associated stroma. The resulting analysis is often seemingly paradoxical, underscoring the complexity of intercellular signaling within tumors and the need to better understand the environmental context underlying these signaling mechanisms.

Extracellular matrix proteins modulate antimigratory and apoptotic effects of Doxorubicin

Anticancer drug resistance is a multifactorial process that includes acquired and de novo drug resistances. Acquired resistance develops during treatment, while de novo resistance is the primary way for tumor cells to escape chemotherapy. Tumor microenvironment has been recently shown to be one of the important factors contributing to de novo resistance and called environment-mediated drug resistance (EMDR). Two forms of EMDR have been described: soluble factor-mediated drug resistance (SFM-DR) and cell adhesion-mediated drug resistance (CAM-DR). Anthracyclines, among the most potent chemotherapeutic agents, are widely used in clinics against hematopoietic and solid tumors. Their main mechanism of action relies on the inhibition of topoisomerase I and/or II and the induction of apoptosis. Beyond this well-known antitumor activity, it has been recently demonstrated that anthracyclines may display potent anti-invasive effects when used at subtoxic concentrations. In this paper, we will describe two particular modes of EMDR by which microenvironment may influence tumor-cell response to one of these anthracyclines, doxorubicin. The first one considers the influence of type I collagen on the antimigratory effect of doxorubicin (CAM-DR). The second considers the protection of tumor cells by thrombospondin-I against doxorubicin-induced apoptosis (SFM-DR).

Proteolytically Derived Endogenous Angioinhibitors Originating from the Extracellular Matrix

Angiogenesis, a neovascularization process induced from the existing parent blood vessels, is a prerequisite for many physiological and pathological conditions. Under physiological conditions it is regulated by a balance between endogenous angioinhibitors and angioactivators, and an imbalance between them would lead to pathological conditions such as cancer, age-related macular degeneration (AMD), diabetic retinopathy, cardiovascular diseases, etc. Several proteolytically generated endogenous molecules have been identified which exhibit angioinhibition and/or antitumor activities. These angioinhibitors interact with endothelial and tumor cells by binding to distinct integrins and initiate many of their intracellular signaling mechanisms regulating the cell survival and or apoptotic pathways. The present review will focus on the extracellular matrix derived angioinhibitors, and their mechanisms of actions that point to the clinical significance and therapeutic implications.

New agents targeting angiogenesis in glioblastoma

Glioblastoma is the most common malignant glioma in adults, and despite recent advances in standard treatment, the prognosis still remains dismal, with a median survival of 15 months. The incorporation of bevacizumab in the standard treatment of relapsed glioblastoma has been a significant step towards combining targeted agents with chemotherapy, and there is an increasing number of new antiangiogenic agents in various stages of development, that are being tested both in relapsed and newly diagnosed disease, alone or in combination with standard treatment. The relatively favorable toxicity profile for most of them presents an advantage, but several concerns arise regarding their actual efficacy on the clinical level and the most efficient schedule of administration for each of them, as their molecular targets and patterns of action may vary significantly. This may lead to future modifications of the current rational of administering these agents concomitantly with initial chemotherapy or maintenance treatment.

Thrombospondin-1 triggers cell migration and development of advanced prostate tumors

The antitumor effects of pharmacologic inhibitors of angiogenesis are hampered in patients by the rapid development of tumor resistance, notably through increased invasiveness and accelerated metastasis. Here, we reevaluated the role of the endogenous antiangiogenic thrombospondin 1 (TSP1) in prostate carcinomas in which angiogenesis is an active process. In xenografted tumors, we observed that TSP1 altogether inhibited angiogenesis and fostered tumor development. Our results show that TSP1 is a potent stimulator of prostate tumor cell migration. This effect required CD36, which also mediates TSP1 antiangiogenic activity, and was mimicked by an antiangiogenic TSP1-derived peptide. As suspected for pharmacologic inhibitors of angiogenesis, the TSP1 capacities to increase hypoxia and to trigger cell migration are thus inherently linked. Importantly, although antiangiogenic TSP1 increases hypoxia in vivo, our data show that, in turn, hypoxia induced TSP1, thus generating a vicious circle in prostate tumors. In radical prostatectomy specimens, we found TSP1 expression significantly associated with invasive tumors and with tumors which eventually recurred. TSP1 may thus help select patients at risk of prostate-specific antigen relapse. Together, the data suggest that intratumor disruption of the hypoxic cycle through TSP1 silencing will limit tumor invasion.

Mesenchymal/stromal gene expression signature relates to basal-like breast cancers, identifies bone metastasis and predicts resistance to therapies

BACKGROUND

Mounting clinical and experimental evidence suggests that the shift of carcinomas towards a mesenchymal phenotype is a common paradigm for both resistance to therapy and tumor recurrence. However, the mesenchymalization of carcinomas has not yet entered clinical practice as a crucial diagnostic paradigm.

METHODOLOGY/PRINCIPAL FINDINGS

By integrating in silico and in vitro studies with our epithelial and mesenchymal tumor models, we compare herein crucial molecular pathways of previously described carcinoma-derived mesenchymal tumor cells (A17) with that of both carcinomas and other mesenchymal phenotypes, such as mesenchymal stem cells (MSCs), breast stroma, and various types of sarcomas. We identified three mesenchymal/stromal-signatures which A17 cells shares with MSCs and breast stroma. By using a recently developed computational approach with publicly available microarray data, we show that these signatures: 1) significantly relates to basal-like breast cancer subtypes; 2) significantly relates to bone metastasis; 3) are up-regulated after hormonal treatment; 4) predict resistance to neoadjuvant therapies.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that mesenchymalization is an intrinsic property of the most aggressive tumors and it relates to therapy resistance as well as bone metastasis.

c-Ski overexpression promotes tumor growth and angiogenesis through inhibition of transforming growth factor-beta signaling in diffuse-type gastric carcinoma

c-Ski, originally identified as a proto-oncogene product, is an important negative regulator of transforming growth factor (TGF)-beta family signaling through interaction with Smad2, Smad3, and Smad4. High expression of c-Ski has been found in some cancers, including gastric cancer. We previously showed that disruption of TGF-beta signaling by dominant-negative TGF-beta type II receptor in a diffuse-type gastric carcinoma model accelerated tumor growth through induction of tumor angiogenesis by decreased expression of the anti-angiogenic factor thrombospondin (TSP)-1. Here, we examined the function of c-Ski in human diffuse-type gastric carcinoma OCUM-2MLN cells. Overexpression of c-Ski inhibited TGF-beta signaling in OCUM-2MLN cells. Interestingly, c-Ski overexpression resulted in extensive acceleration of the growth of subcutaneous xenografts in BALB/c nu/nu female mice (6 weeks of age). Similar to tumors expressing dominant-negative TGF-beta type II receptor, histochemical studies revealed less fibrosis and increased angiogenesis in xenografted tumors expressing c-Ski compared to control tumors. Induction of TSP-1 mRNA by TGF-beta was attenuated by c-Ski in vitro, and expression of TSP-1 mRNA was decreased in tumors expressing c-Ski in vivo. These findings suggest that c-Ski overexpression promotes the growth of diffuse-type gastric carcinoma through induction of angiogenesis.

Regulation of tumor dormancy as a function of tumor-mediated paracrine regulation of stromal Tsp-1 and VEGF expression

Tumor dormancy is a critical yet poorly understood phenomenon affecting both the diagnosis and treatment of human cancers. This is due in large part to the lack of model systems available to study dormant tumor cells and the length of time needed to adequately examine the models that do exist. It has been demonstrated in several types of human cancer that tumor dormancy is a function of an impairment in angiogenesis. The intracellular signaling pathways regulating the expression of several pro- and anti-angiogenic proteins have been well characterized in human cancer cells. The intercellular signaling that takes place between tumor cells and the surrounding tumor-associated stroma has not been as extensively studied with regard to the regulation of angiogenesis, and as a result dormancy. In this review we define the key players in the regulation of angiogenesis and examine how their expression is regulated in the tumor-associated stroma. The resulting analysis is often seemingly paradoxical, underscoring the complexity of intercellular signaling within tumors and the need to better understand the environmental context underlying these signaling mechanisms.

New molecular targets in angiogenic vessels of glioblastoma tumours

Antiangiogenesis approaches have the potential to be particularly effective in the treatment of glioblastoma tumours. These tumours exhibit extremely high levels of neovascularisation, which may contribute to their extremely aggressive behaviour, not only by providing oxygenation and nutrition, but also by establishing a leaky vasculature that lacks a blood-brain barrier. This leaky vasculature enables migration of tumour cells, as well as the build up of fluid, which exacerbates tissue damage due to increased intracranial pressure. Here, we discuss the considerable progress that has been made in the identification of the pro- and antiangiogenic factors produced by glioblastoma tumours and the effects of these molecules in animal models of the disease. The safety and efficacy of some of these approaches have now been demonstrated in clinical trials. However, the ability of tumours to overcome these therapies and to re-establish angiogenesis requires further clinical research regarding potential multimodality therapies, as well as basic research into the regulation of angiogenesis by as yet unidentified factors. Optimisation of noninvasive procedures for monitoring of angiogenesis would greatly facilitate such research.

Thrombospondins in cancer

The thrombospondins (TSPs) are a family of five proteins that are involved in the tissue remodeling that is associated with embryonic development, wound healing, synaptogenesis, and neoplasia. These proteins mediate the interaction of normal and neoplastic cells with the extracellular matrix and surrounding tissue. In the tumor microenvironment, TSP-1 has been shown to suppress tumor growth by inhibiting angiogenesis and by activating transforming growth factor beta. TSP-1 inhibits angiogenesis through direct effects on endothelial cell migration and survival, and through effects on vascular endothelial cell growth factor bioavailability. In addition, TSP-1 may affect tumor cell function through interaction with cell surface receptors and regulation of extracellular proteases. Whereas the role of TSP-1 in the tumor microenvironment is the best characterized, the other TSPs may have similar functions. (Part of a Multi-author Review).

Thrombospondin-based antiangiogenic therapy

Thrombospondins (TSPs) are a family of extracellular matrix proteins that regulate tissue genesis and remodeling. TSP-1 plays a pivotal role in the regulation of both physiological and pathological angiogenesis. The inhibitory effects of TSP-1 on angiogenesis have been established in numerous experimental models. Among other TSP members, TSP-2 has equivalent domain structure as TSP-1 and shares most functions of TSP-1. The mechanisms by which TSP-1 and -2 inhibit angiogenesis can be broadly characterized as direct effects on vascular endothelial cells and indirect effects on the various angiogenic regulators. The fact that TSP-1 and -2 are potent endogenous angiogenic inhibitors has prompted studies to explore their therapeutic applications, and detailed understanding of the mechanisms of action of TSP-1 and -2 has facilitated the design of therapeutic strategies to optimize these activities. The therapeutic effects can be achieved by up-regulation of endogenous TSPs, or by the delivery of recombinant proteins or synthetic peptides that contain sequences from the angiogenic domain of TSP-1. In this article, we review the progress in thrombospondin-based antiangiogenic therapy and discuss the perspectives on the significant challenges that remain.

Differential expression of angiogenesis-related genes in human gastric cancers with and those without high-frequency microsatellite instability

Gastric cancers with and those without high-frequency microsatellite instability (MSI-H) represent distinctive pathways of carcinogenesis. The aim of this study was to clarify if expression of p53 related genes involved in angiogenesis is differentially regulated between these cancers. We systematically analyzed the expression of vascular endothelial growth factor A (VEGFA), fibroblast growth factor 2 (FGF2), thrombospondin 1 (THBS1), and brain-specific angiogenesis inhibitor 1 (BAI1), and we correlated the results with microvessel count (MVC), MSI status, p53 mutations, and prostaglandin-endoperoxide synthase 2 (PTGS2) expression in gastric cancers. Expression of VEGFA in carcinoma cells was immunohistochemically seen in 46% of 200 cases. VEGFA positivity was significantly associated with higher MVC, vascular invasion, lymph node and distant metastasis, and advanced tumor stage. FGF2 positivity was significantly associated with poor differentiation, depth of invasion, and higher MVC. VEGFA and FGF2 positivities and MVC were lower in MSI-H cancers than in MSI-L or MSS cancers. VEGFA expression was associated with both p53 mutations and PTGS2 expression. Methylation of the THBS1 gene was detected in 6 of 11 cancer cell lines and in 44% of 200 cases. THBS1 methylation was significantly associated with distal location, vascular invasion, distant metastasis, MSI-H, wild-type p53, and higher MVC. The prognosis was worst in patients with cancers that were VEGFA-positive and THBS1 methylation-positive. Gastric cancers with MSI-H were characterized by lower MVC, low frequency of VEGFA, FGF2, and PTGS2 overexpression, and high frequency of THBS1 methylation. Our results suggest that gastric cancers with and those without MSI-H represent distinctive pathways of carcinogenesis, including aberrant expression of factors regulating angiogenesis. The difference may be associated with less aggressive phenotype of these cancers with MSI-H and affect future molecular targeted therapeutics.

Antibody array profiling reveals serum TSP-1 as a marker to distinguish benign from malignant prostatic disease

BACKGROUND

Blood protein markers that provide more accurate or earlier diagnosis of prostate cancer should have a positive impact on prostate cancer treatment and management.

METHODS

Serum samples from control subjects and patients with benign or malignant prostatic disease were analyzed on antibody arrays targeting multiple candidate prostate cancer markers and detected with two-color, rolling-circle amplification (TC-RCA). The measurements of certain antibodies were validated using immunoblots, immunoprecipitation/mass spectrometry, and sandwich immunoassays.

RESULTS

Several potential disease-associated protein alterations were uncovered. The most significant was thrombospondin-1, which was strongly elevated in patients with benign prostatic disease and repressed in patients with prostate cancer. Thrombospondin-1 levels did not correlate with prostate-specific antigen (PSA) levels and differentiated benign from malignant disease with 79% sensitivity and 81% specificity.

CONCLUSIONS

The measurement of thrombospondin-1 could be used to assist the decision to obtain a biopsy in men with suspected prostate cancer, which could lead to a reduction in the number of unnecessary prostatic biopsies.

Syndecan-4 contributes to endothelial tubulogenesis through interactions with two motifs inside the pro-angiogenic N-terminal domain of thrombospondin-1

Thrombospondin-1 (TSP-1) is an extracellular matrix protein that modulates focal adhesion in mammalian cells and exhibits dual roles in angiogenesis. In a previous work, we showed that a recombinant 18 kDa protein encompassing the N-terminal residues 1-174 of human TSP-1 (TSP18) induced tubulogenesis of human umbilical vein endothelial cells and protected them from apoptosis. Our results indicated that these effects were possibly mediated by syndecan-4 proteoglycan, since binding of TSP18 to endothelial extracts was inhibited by anti-syndecan-4 antibody. Syndecan-4 is a heparan-sulfate proteoglycan that regulates cell-matrix interactions and is the only member of its family present in focal adhesions. In this report, we demonstrate that a monoclonal antibody against syndecan-4 blocks TSP18-induced tubulogenesis. Furthermore, through 2D adhesion and 3D angiogenic assays, we demonstrate that two sequences, TSP Hep I and II, retain the major pro-angiogenic activity of TSP18. These TSP-1 motifs also compete with the fibronectin Hep II domain for binding to syndecan-4 on endothelial cell surface, indicating that they may exert their effects by interfering with the recognition of fibronectin by syndecan-4. Additionally, TSP18 and its derived peptides activate the PKC-dependent Akt-PKB signaling pathway. Blockage of PKC activation prevented HUVEC spreading when seeded on TSP18 fragment, and on TSP Hep I and TSP Hep II peptides, but not on gelatin-coated substrates. Our results identify syndecan-4 as a novel receptor for the N-terminus of TSP-1 and suggest that TSP-1 N-terminal pro-angiogenic activity is linked to its capacity of interfering with syndecan-4 functions in the course of cell adhesion.

The C-terminal CD47/IAP-binding domain of thrombospondin-1 prevents camptothecin- and doxorubicin-induced apoptosis in human thyroid carcinoma cells

Camptothecin and doxorubicin belong to a family of anticancer drugs that exert cytotoxic effects by triggering apoptosis in various cell types. However there have only been few investigations showing that matricellular proteins like thrombospondin-1 (TSP-1) could be involved in the underlying mechanism of this cytotoxicity. In this report, using Hoechst reagent staining, reactive oxygen species production and caspase-3 activity measurement, we determined that both camptothecin and doxorubicin induced apoptosis in human thyroid carcinoma cells (FTC-133). On the one hand, we demonstrated that camptothecin and doxorubicin inhibited TSP-1 expression mainly occurring at the transcriptional level. On the other hand, drug-induced apoptosis determined by western blot analysis for PARP cleavage and caspase-3 activity measurement, was significantly decreased in presence of exogenous TSP-1. In order to identify the sequence responsible for this effect, we used the CD47/IAP-binding peptide 4N1 (RFYVVMWK), derived from the C-terminal domain of TSP-1, and known to play a role in apoptosis. Thus, in presence of 4N1, camptothecin and doxorubicin-induced pro-apoptotic activity was considerably inhibited. These findings suggest that induction of apoptosis by camptothecin or doxorubicin in FTC-133 cells is greatly dependent by a down-regulation of TSP-1 expression and shed new light on a possible role for TSP-1 in drug resistance.

Expression of ADAMTS-8, a secreted protease with antiangiogenic properties, is downregulated in brain tumours

Angiogenesis and extracellular matrix degradation are key events in tumour progression, and factors regulating stromal-epithelial interactions and matrix composition are potential targets for the development of novel anti-invasive/antiangiogenic therapies. Here, we examine the expression of ADAMTS-8, a secreted protease with antiangiogenic properties, in brain tissues. Using quantitative RT-polymerase chain reaction (PCR), high, equivalent expression of ADAMTS-8 was found in normal whole brain, cerebral cortex, frontal lobe, cerebellum and meninges. ADAMTS-8 expression in 34 brain tumours (including 22 high-grade gliomas) and four glioma cell lines indicated at least two-fold reduction in mRNA compared to normal whole brain in all neoplastic tissues, and no detectable expression in 14 out of 34 (41%) tumours or four out of four (100%) cell lines. In contrast, differential expression of TSP1 and VEGF was seen in nine out of 15 (60%) and seven out of 13 (54%) tumours, with no relationship in the expression of these genes. Immunohistochemistry and Western analysis indicated downregulation of ADAMTS-8 protein in >77% tumours. Methylation-specific PCR analysis of ADAMTS-8 indicated promoter hypermethylation in one out of 24 brain tumours (a metastasis) and three out of four glioma cell lines suggesting an alternative mechanism of downregulation. These data suggest a role for ADAMTS-8 in brain tumorigenesis, warranting further investigation into its role in regulation of tumour angiogenesis and local invasion.

Extraction of RNA from archival tissues and measurement of thrombospondin-1 mRNA in normal, dysplastic, and malignant oral tissues

Thrombospondin-1 (TSP-1) is an extracellular matrix glycoprotein implicated in the regulation of angiogenesis and tumour development. Our objectives were to ascertain the quantity and quality of RNA extracted from archival, formalin-fixed, paraffin embedded, oral tissues and their application in measuring the concentrations of TSP-1 mRNA in these tissues. We compared three techniques of isolation of RNA as well as related experimental variables. TSP-1 mRNA was measured in specimens of normal, dysplastic, and malignant oral tissues by real-time reverse transcriptase polymerase chain reaction (RT-PCR). RNA suitable for analysis by real-time RT-PCR was obtained by the three techniques tested, although the yield varied depending on the protocol used (range 0.2-3.6 microg/mm(3)). The mean (S.D.) concentrations of TSP-1 mRNA relative to 18S were 21.1 (7.2) in normal oral tissues (n=9), 11.0 (8.2) in dysplastic tissue (n=8) and 7.3 (5.3) in carcinomatous tissue (n=17). The difference between normal and carcinomatous specimens was significant (p=0.01). This reduction in expression of TSP-1 mRNA from normal to dysplasia to carcinoma may favour the angiogenic drive that accompanies the development of oral tumours.

Regulation of tumor angiogenesis by thrombospondin-1

Angiogenesis plays a critical role in the growth and metastasis of tumors. Thrombospondin-1 (TSP-1) is a potent angiogenesis inhibitor, and down-regulation of TSP-1 has been suggested to alter tumor growth by modulating angiogenesis in a variety of tumor types. Expression of TSP-1 is up-regulated by the tumor suppressor gene, p53, and down-regulated by oncogenes such as Myc and Ras. TSP-1 inhibits angiogenesis by inhibiting endothelial cell migration and proliferation and by inducing apoptosis. In addition, activation of transforming growth factor beta (TGF-beta) by TSP-1 plays a crucial role in the regulation of tumor progression. An understanding of the molecular basis of TSP-1-mediated inhibition of angiogenesis and tumor progression will aid in the development of novel therapeutics for the treatment of cancer.

Type I collagen is a molecular target for inhibition of angiogenesis by endogenous thrombospondin-1

Three-dimensional explant cultures of muscle tissue were used to characterize secreted proteins regulated by endogenous levels of the angiogenesis modulator thrombospondin (TSP)-1. Explants from TSP1 null mice exhibit enhanced neovascularization associated with increased endothelial outgrowth but decreased outgrowth of perivascular smooth muscle cells . The absence of endogenous TSP1 did not diminish activation of latent transforming growth factor-beta and moderately decreased matrix metalloproteinase levels. However, significant changes in other secreted proteins were observed. Endogenous TSP1 decreased mRNA levels for collagens Ialpha1, Ialpha2, and IIIalpha1 and laminin alpha4 and increased collagen IValpha1 mRNA expression. Endogenous TSP1 also decreased the level of type I collagen protein produced by the vascular outgrowths. Collagens Ialpha1, Ialpha2, and IIIalpha1 are known tumor endothelial markers, suggesting that TSP1 coordinately regulates a set of extracellular matrix genes that reverse the angiogenic switch. Suppression of collagen Ialpha1 or Ialpha2 mRNAs using antisense morpholinos inhibited outgrowth in TSP1 null explants and proliferation of TSP1 null endothelial cells, indicating that type I collagen synthesis is limiting for this neovascularization response.

Antiangiogenic treatment with the three thrombospondin-1 type 1 repeats recombinant protein in an orthotopic human pancreatic cancer model

PURPOSE

This study investigates the antiangiogenesis and antitumor efficacy of a recombinant protein composed of the three type 1 repeats (3TSR) of thrombospondin-1 in an orthotopic human pancreatic cancer model and provides useful preclinical data for pancreatic cancer treatment.

EXPERIMENTAL DESIGN

Human pancreatic cancer cells (AsPC-1) were injected into the pancreas of severe combined immunodeficient mice. The animals were treated with 3TSR (3 mg per kg per day) or PBS for 3 weeks. Subsequently, the effects of 3TSR on tumor growth, microvessel density, cancer cell proliferation, apoptosis, and endothelial cell apoptosis were analyzed. The in vitro effects of 3TSR on human pancreatic cancer cells were also studied.

RESULTS

3TSR treatment significantly reduced angiogenesis and tumor growth of orthotopic pancreatic cancer. 3TSR-treated mice had a 69% reduction in tumor volume (316.6 +/- 79.3 versus 1,012.2 +/- 364.5 mm(3); P = 0.0001), and a significant increase in tumor necrotic area. After 3TSR treatment, both the vessel number and average microvessel size were significantly decreased, and microvessel density was decreased from 8.0% to 3.7% (P < 0.0001). The apoptotic rate of tumoral endothelial cells in 3TSR-treated tumors increased to 14.7% comparing to 4.2% in control tumors (P < 0.0001). 3TSR showed no direct effects on pancreatic cancer cell proliferation or apoptosis either in vivo or in vitro.

CONCLUSION

3TSR, a domain of a natural occurring angiogenesis inhibitor, showed potent therapeutic effect in pancreatic cancer by inhibiting tumor angiogenesis and may prove to be a promising agent for clinical pancreatic cancer treatment.

Short interfering RNAs as a tool for cancer gene therapy

There are mainly two types of short RNAs that target complementary messengers in animals: small interfering RNAs and micro-RNAs. Both are produced by the cleavage of double-stranded RNA precursors by Dicer, a member of the Rnase III family of double-stranded specific endonucleases, and both guide the RNA-induced silencing complex to cleave specifically RNAs sharing sequence identity with them. In designing a particular RNA interference (RNAi), it is important to identify the sense/antisense combination that provides the most potent suppression of the target mRNA, and several rules have been established to give >90% gene expression inhibition. RNAi technology can be directed against cancer using a variety of strategies. These include the inhibition of overexpressed oncogenes, blocking cell division by interfering with cyclin E and related genes or promoting apoptosis by suppressing antiapoptotic genes. RNAi against multidrug resistance genes or chemoresistance targets may also provide useful cancer treatments. Studies investigating these approaches in preclinical models are also reviewed.

Endogenous inhibitors of angiogenesis in malignant gliomas: nature's antiangiogenic therapy

Angiogenesis is necessary for tumor growth beyond a volume of approximately 2 mm(3). This observation, along with the accessibility of tumor vessels to therapeutic targeting, has resulted in a research focus on inhibitors of angiogenesis. A number of endogenous inhibitors of angiogenesis are found in the body. Some of these are synthesized by specific cells in different organs, and others are created by extracellular proteolytic cleavage of plasma-derived or extracellular matrix-localized proteins. In this review, we focus on angiostatin, endostatin, PEX, pigment epithelial-derived factor, and thrombospondin (TSP)-1 and -2, either because these molecules are expressed in malignant glioma biopsies or because animal studies in malignant glioma models have suggested that their therapeutic administration could be efficacious. We review the known mechanisms of action, potential receptors, expression in glioma biopsy samples, and studies testing their potential therapeutic efficacy in animal models of malignant glioma. Two conclusions can be made regarding the mechanisms of action of these inhibitors: (1) Several of these inhibitors appear to mediate their antiangiogenic effect through multiple protein-protein interactions that inhibit the function of proangiogenic molecules rather than through a specific receptor-mediated signaling event, and (2) TSP-1 and TSP-2 appear to mediate their antiangiogenic effect, at least in part, through a specific receptor, CD36, which initiates the antiangiogenic signal. Although not proven in gliomas, evidence suggests that expression of specific endogenous inhibitors of angiogenesis in certain organs may be part of a host antitumor response. The studies reviewed here suggest that new antiangiogenic therapies for malignant gliomas offer exciting promise as nontoxic, growth-inhibitory agents.

Careful decoy receptor titering is required to inhibit tumor angiogenesis while avoiding adversely altering VEGF bioavailability

To inhibit tumor-induced angiogenesis, the VEGF signaling pathway was targeted using AAV vectors encoding a VEGF decoy receptor, a truncated, soluble form of the murine VEGF receptor-2 (tsFlk-1). This approach initially had significant anti-neuroblastoma efficacy in murine xenograft models of local and metastatic disease, but when higher circulating levels of tsFlk-1 were established, tumor growth was more aggressive than even in control mice. Part of the mechanism for this apparent tumor resistance was increased human VEGF expression by the tumor cells. However, further investigation revealed that although a greater amount of VEGF could be bound by higher levels of tsFlk-1, more VEGF also existed in an unbound state and was, therefore, available to support angiogenesis. This novel, tumor-independent mechanism for resistance to antiangiogenic strategies suggests that careful titering of angiogenesis inhibitors may be required to achieve maximal antitumor efficacy and avoid therapy resistance mediated, in part, by ligand bioavailability. This has important implications for therapeutic strategies that use decoy receptors and other agents, such as antibodies, to bind angiogenic factors, in an attempt to inhibit tumor neovascularization.

Human breast tumors override the antiangiogenic effect of stromal thrombospondin-1in vivo

The antiangiogenic extracellular matrix protein thrombospondin-1 (TSP-1) inhibits tumor growth and metastasis in animals. However, the clinical relevance of such findings are equivocal as increased stromal TSP-1 expression has been associated with either good or poor prognosis. In an effort to obtain a more integrated understanding of the role of TSP-1 in breast cancer, we first used a breast tumorigenesis model in which tumor-associated stromal fibroblasts were engineered to produce high levels of TSP-1. We demonstrate here that stromal TSP-1 delayed human MDA-MB-231/B02 breast tumor growth. However, this delay in MDA-MB-231/B02 tumor growth upon exposure to TSP-1 was associated with an increased vascular endothelial growth factor (VEGF) expression in tumor cells themselves, leading to a tumor growth rate comparable to that of tumors whose fibroblasts did not overproduce TSP-1. Clinical evidence also suggested that primary breast carcinomas have adapted to escape the effects of stromal TSP-1. TSP-1 was found to be expressed in the stroma of human breast carcinomas where, although its level correlated with decreased vascularization, it was unexpectedly associated with a reduction of relapse-free survival. In metastatic axillary lymph nodes, tumor cells expressed high levels of VEGF and TSP-1 expression were no longer associated with a decreased vascularization. Overall, these results suggest that a resistance may develop early in human breast cancers as a result of high in situ exposure to stromal TSP-1, leading to disease progression.

Androgens Repress the Expression of the Angiogenesis Inhibitor Thrombospondin-1 in Normal and Neoplastic Prostate

In order to understand why the angiogenesis inhibitor thrombospondin-1 (TSP1) is often, although not always, associated with prostatic tumors, we have investigated its relationship with the testosterone and the vasculature on which both normal and tumorigenic prostatic epithelia depend. In vivo, androgen withdrawal led to increased TSP1 production and decreased vascularization in the normal rat prostate which was reversed by androgen replacement. Androgen repression of TSP1 production occurred at the transcriptional level and was dependent on the presence of the first intron of the TSP1 gene. In an experimental model of prostate tumorigenesis, TSP1, when delivered by admixed stromal fibroblasts, markedly delayed LNCaP tumor growth and limited tumor vascularization. However, prolonged exposure to TSP1 resulted in the growth of tumors secreting high levels of vascular endothelial growth factor in the bloodstream of tumor-bearing animals and tumor growth was no longer sensitive to TSP1 inhibitory effects. Clinical evidence also suggested that prostate carcinomas are able to adapt to escape the antiangiogenic effects of TSP1. In human androgen–dependent localized prostate carcinomas, TSP1 expression was inversely correlated with blood vessel density. Androgen deprivation in patients with hormone-responsive tumors led to increased TSP1 expression and vascular regression. In contrast, despite a sustained expression in the tumor bed, TSP1 was no longer associated with decreased vascularization in hormone-refractory prostate tumors. Overall, these results suggest that the high in situ TSP1 exposure triggered by androgen deprivation in patients with prostate cancer could lead to early tumor resistance. Such patients could benefit from a combination of androgen deprivation and antiangiogenic therapy in order to minimize the induction of such tumor escape.

Tumor progression: the effects of thrombospondin-1 and -2

The thrombospondins (TSPs) are a family of proteins that regulate tissue genesis and remodeling. In many tumors, down-regulation of TSPs accompanies activation of oncogenes or inactivation of tumor suppresser genes and appears to be a prerequisite for the aquisition of a pro-angiogenic phenotype. The normal suppression of angiogenesis by TSP-1 and -2 involves multiple mechanisms including direct interaction with vascular endothelial cell growth factor (VEGF), inhibition of matrix metalloproteinase 9 (MMP9) activation, inhibition of endothelial cell migration and induction of endothelial cell apoptosis. The importance of down-regulation of TSPs for tumor progression is further established by the fact that several different approaches that are designed to increase the levels of TSP-1 or -2 in tumor tissue inhibit tumor growth. These approaches include cell-based gene therapy, low dose chemotherapeutics and systemic delivery of recombinant proteins or synthetic peptides that include type 1 repeat (TSR) sequences. Initial studies indicate that these reagents, in combination with established approaches for the treatment of cancer, will offer more efficacious therapies.

Vasohibin: the feedback on a new inhibitor of angiogenesis

Angiogenesis is regulated in large part by the balance of various proangiogenic stimulators, such as VEGF, and a diverse group of endogenous inhibitors of angiogenesis, most of which are extrinsic to endothelial cells. With respect to the latter, until recently, none have appeared to be induced as a consequence of a specific, self-regulating, feedback inhibition response. A new inhibitor, called vasohibin, has been uncovered. Vasohibin is selectively induced in endothelial cells by proangiogenic stimulatory growth factors such as VEGF; it appears to operate as an intrinsic and highly specific feedback inhibitor of activated endothelial cells engaged in the process of angiogenesis.