Angiostatin binds to tyrosine kinase substrate annexin II through the lysine-binding domain in endothelial cells

Anti-angiogenic activity of a novel angiostatin-like plasminogen fragment produced by a bacterial metalloproteinase

Tumor growth depends on angiogenesis, a process by which new blood vessel are formed from pre-existing normal blood vessels. Proteolytic fragments of plasminogen, containing varying numbers of plasminogen kringle domains, collectively known as angiostatin, are a naturally occurring inhibitor of angiogenesis and inhibit tumor growth. We have developed an "affinity-capture reactor" that enables a single-step method for the production/purification of an angiostatin-like plasminogen fragment from human plasma using an immobilized bacterial metalloproteinase. The resulting fragment, named BL-angiostatin, contains one or two glycosyl chains and the N-terminal PAN module, which are not present in canonical angiostatins tested for cancer treatment. BL-angiostatin inhibited angiogenesis in vitro at 20 nM and the growth of both allograft and human xenograft tumors as well as lung metastasis of primary tumors mice at 0.3-10 mg kg-1. Derivatives of BL angiostatin lacking the PAN module or the terminal sialic acids in the glycosyl chains showed reduced anti-angiogenic activity in vivo, suggesting a role for these functions in activity, possibly via conferring a pharmacokinetic advantage to BL angiostatin compared to recombinant angiostatin lacking both features. These results highlight the potential of BL-angiostatin for therapeutic applications.

Novel exosomal circEGFR facilitates triple negative breast cancer autophagy via promoting TFEB nuclear trafficking and modulating miR-224-5p/ATG13/ULK1 feedback loop

Triple-negative breast cancer (TNBC) cells are in a more hypoxic and starved state than non-TNBC cells, which makes TNBC cells always maintain high autophagy levels. Emerging evidence has demonstrated that circular RNAs (circRNAs) are involved in the progress of tumorigenesis. However, the regulation and functions of autophagy-induced circRNAs in TNBC remain unclear. In our study, autophagy-responsive circRNA candidates in TNBC cells under amino acid starved were identified by RNA sequencing. The results showed that circEGFR expression was significantly upregulated in autophagic cells. Knockdown of circEGFR inhibited autophagy in TNBC cells, and circEGFR derived from exosomes induced autophagy in recipient cells in the tumor microenvironment. In vitro and in vivo functional assays identified circEGFR as an oncogenic circRNA in TNBC. Clinically, circEGFR was significantly upregulated in TNBC and was positively associated with lymph node metastasis. CircEGFR in plasma-derived exosomes was upregulated in breast cancer patients compared with healthy people. Mechanistically, circEGFR facilitated the translocation of Annexin A2 (ANXA2) toward the plasma membrane in TNBC cells, which led to the release of Transcription Factor EB (a transcription factor of autophagy-related proteins, TFEB) from ANXA2-TFEB complex, causing nuclear translocation of TFEB, thereby promoting autophagy in TNBC cells. Meanwhile, circEGFR acted as ceRNA by directly binding to miR-224-5p and inhibited the expression of miR-224-5p, which weakened the suppressive role of miR-224-5p/ATG13/ULK1 axis on autophagy. Overall, our study demonstrates the key role of circEGFR in autophagy, malignant progression, and metastasis of TNBC. These indicate circEGFR is a potential diagnosis biomarker and therapeutic target for TNBC.

The Oxygen-Generating Calcium Peroxide-Modified Magnetic Nanoparticles Attenuate Hypoxia-Induced Chemoresistance in Triple-Negative Breast Cancer

Cancer response to chemotherapy is regulated not only by intrinsic sensitivity of cancer cells but also by tumor microenvironment. Tumor hypoxia, a condition of low oxygen level in solid tumors, is known to increase the resistance of cancer cells to chemotherapy. Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer. Due to lack of target in TNBC, chemotherapy is the only approved systemic treatment. We evaluated the effect of hypoxia on chemotherapy resistance in TNBC in a series of in vitro and in vivo experiments. Furthermore, we synthesized the calcium peroxide-modified magnetic nanoparticles (CaO₂-MNPs) with the function of oxygen generation to improve and enhance the therapeutic efficiency of doxorubicin treatment in the hypoxia microenvironment of TNBC. The results of gene set enrichment analysis (GSEA) software showed that the hypoxia and autophagy gene sets are significantly enriched in TNBC patients. We found that the chemical hypoxia stabilized the expression of hypoxia-inducible factor 1α (HIF-1α) protein and increased doxorubicin resistance in TNBC cells. Moreover, hypoxia inhibited the induction of apoptosis and autophagy by doxorubicin. In addition, CaO₂-MNPs promoted ubiquitination and protein degradation of HIF-1α. Furthermore, CaO₂-MNPs inhibited autophagy and induced apoptosis in TNBC cells. Our animal studies with an orthotopic mouse model showed that CaO₂-MNPs in combination with doxorubicin exhibited a stronger tumor-suppressive effect on TNBC, compared to the doxorubicin treatment alone. Our findings suggest that combined with CaO₂-MNPs and doxorubicin attenuates HIF-1α expression to improve the efficiency of chemotherapy in TNBC.

Important role of annexin A2 (ANXA2) in new blood vessel development in vivo and human triple negative breast cancer (TNBC) growth

Development of new blood vessels in the tumor microenvironment is an essential component of tumor progression during which newly formed blood vessels nourish tumor cells and play a critical role in rapid tumor growth, invasion and metastasis. Nevertheless, how tumor cells develop new blood vessels in the tumor microenvironment (TME) have been enigmatic. Previously, we have shown specific overexpression of ANX A2 in TNBC cells regulates plasmin generation and suspected a role in neoangiogenesis. In this report, we used Matrigel plug model of in vivo angiogenesis and confirmed its role in new blood vessel development. Next, we tested if blocking of ANX A2 in aggressive human breast TME can inhibit angiogenesis and tumor growth in vivo. We showed that aggressive human breast tumor cells growing in nude mice can induce intense neoangiogenesis in the tumor mass. Blocking of ANXA2 significantly inhibited neoangiogenesis and resulted in inhibition of tumor growth. Interestingly, we identified that blocking of ANXA2 significantly inhibited tyrosine phosphorylation (Tyr-P) of ANXA2 implying its involvement in tyrosine signaling pathway and suggesting it may regulate angiogenesis. Taken together, our experimental evidence suggests that ANX A2 could be a novel strategy for disruption of tyrosine signaling and inhibition of neoangiogenesis in breast tumor.

A novel RNA aptamer identifies plasma membrane ATP synthase beta subunit as an early marker and therapeutic target in aggressive cancer

PURPOSE

Primary breast and prostate cancers can be cured, but metastatic disease cannot. Identifying cell factors that predict metastatic potential could guide both prognosis and treatment.

METHODS

We used Cell-SELEX to screen an RNA aptamer library for differential binding to prostate cancer cell lines with high vs. low metastatic potential. Mass spectroscopy, immunoblot, and immunohistochemistry were used to identify and validate aptamer targets. Aptamer properties were tested in vitro, in xenograft models, and in clinical biopsies. Gene expression datasets were queried for target associations in cancer.

RESULTS

We identified a novel aptamer (Apt63) that binds to the beta subunit of F1Fo ATP synthase (ATP5B), present on the plasma membrane of certain normal and cancer cells. Apt63 bound to plasma membranes of multiple aggressive breast and prostate cell lines, but not to normal breast and prostate epithelial cells, and weakly or not at all to non-metastasizing cancer cells; binding led to rapid cell death. A single intravenous injection of Apt63 induced rapid, tumor cell-selective binding and cytotoxicity in MDA-MB-231 xenograft tumors, associated with endonuclease G nuclear translocation and DNA fragmentation. Apt63 was not toxic to non-transformed epithelial cells in vitro or adjacent normal tissue in vivo. In breast cancer tissue arrays, plasma membrane staining with Apt63 correlated with tumor stage (p < 0.0001, n = 416) and was independent of other cancer markers. Across multiple datasets, ATP5B expression was significantly increased relative to normal tissue, and negatively correlated with metastasis-free (p = 0.0063, 0.00039, respectively) and overall (p = 0.050, 0.0198) survival.

CONCLUSION

Ecto-ATP5B binding by Apt63 may disrupt an essential survival mechanism in a subset of tumors with high metastatic potential, and defines a novel category of cancers with potential vulnerability to ATP5B-targeted therapy. Apt63 is a unique tool for elucidating the function of surface ATP synthase, and potentially for predicting and treating metastatic breast and prostate cancer.

Annexin A2 (ANX A2): An emerging biomarker and potential therapeutic target for aggressive cancers

ANX A2 is an important member of annexin family of proteins expressed on surface of endothelial cells (ECs), macrophages, mononuclear cells and various types of cancer cells. It exhibits high affinity binding for calcium (Ca⁺⁺ ) and phospholipids. ANX A2 plays an important role in many biological processes such as endocytosis, exocytosis, autophagy, cell-cell communications and biochemical activation of plasminogen. On the cell surface ANX A2 organizes the assembly of plasminogen (PLG) and tissue plasminogen activator (tPA) for efficient conversion of PLG to plasmin, a serine protease. Proteolytic activity of plasmin is required for activation of inactive pro-metalloproteases (pro-MMPs) and latent growth factors for their biological actions. These activation steps are critical for degradation of extracellular matrix (ECM) and basement proteins (BM) for cancer cell invasion and metastasis. Increased expression of ANX A2 protein/gene has been correlated with invasion and metastasis in a variety of human cancers. Moreover, clinical studies have positively correlated ANX A2 protein expression with aggressive cancers and with resistance to anticancer drugs, shorter disease-free survival (DFS), and worse overall survival (OS). The mechanism(s) by which ANX A2 regulates cancer invasion and metastasis are beginning to emerge. Investigators used various technologies to target ANX A2 in preclinical model of human cancers and demonstrated exciting results. In this review article, we analyzed existing literature concurrent with our own findings and provided a critical overview of ANX A2-dependent mechanism(s) of cancer invasion and metastasis.

Production of bioactive recombinant human Eb-peptide of pro-IGF-I and identification of binding components from the plasma membrane of human breast cancer cells (MDA-MB-231)

E-peptide of the pro-Insulin-like growth factor-I (pro-IGF-I) is produced from pre-pro-IGF-I by proteolytic cleavage in the post-translational processing. The human Eb-peptide (hEb-peptide), derived from the E domain of pro-IGF-IB isoform, is a bioactive molecule whose exact physiological role remains elusive. Accumulated evidence reported from our laboratory indicated that hEb-peptide possesses activity against multiple hallmark characteristics of solid tumor in different cancer cell types. In human breast carcinoma cells (MDA-MB-231), it was demonstrated that hEb-peptide can promote cell attachment to substratum, inhibit colony formation in a semisolid medium, reduce cancer cell invasion, and inhibit cancer-induced angiogenesis. Like the action of other peptide hormones, these cellular responses triggered by hEb may be initiated through binding to a receptor molecule residing on the surface of the cell. Our laboratory and the others have previously provided evidence demonstrating the existence of hEb-peptide specific binding components residing on the cell membrane. In this study, we report the isolation and identification of eight protein molecules bound reversibly with hEb-peptide from the membrane preparation of MDA-MB-231 cells. Some of the identified proteins are known to be present at cell surface and function as receptors while the others are not. The functions of these molecules reveal strong correlation with the demonstrated activities of hEb-peptide on MDA-MB-231cells, suggesting hEb-peptide activity on cancer cells might be mediated by these molecules.

Vascular-homing peptides for cancer therapy

In the past 30 years, a variety of phage libraries have been extensively utilized to identify and develop tumor homing peptides (THPs). THPs specifically bind to tumor cells or elements of the tumor microenvironment while no or low affinity to normal cells. In this regard, the efficacy of therapeutic agents in cancer therapy can be enhanced by targeting strategies based on coupling with THPs that recognize receptors expressed by tumor cells or tumor vasculature. Especially, vascular-homing peptides, targeting tumor vasculature, have their receptors expressed on or around the blood vessel including pro-angiogenic factors, metalloproteinase, integrins, fibrin-fibronectin complexes, etc. This review briefly summarizes recent studies on identification and therapeutic applications of vascular-homing peptides targeting common angiogenic markers or with unknown vascular targets in some certain types of cancers. These newly discovered vascular-homing peptides are promising candidates which could provide novel strategies for cancer therapy.

Long-term efficacy and downstream mechanism of anti-annexinA2 monoclonal antibody (anti-ANX A2 mAb) in a pre-clinical model of aggressive human breast cancer

There is considerable direct evidence that calcium binding protein ANX A2 is a potential target for treating aggressive breast cancer. The most compelling data are based on the finding of ANX A2 overexpression in aggressive triple negative human breast cancer (TNBC) cell lines and in human breast cancer tissues. Previously, we and others reported a unique role of ANX A2 in cancer invasion, including breast cancer. Moreover, we demonstrated that anti-ANX A2 mAb-mediated immunoneutralization of ANX A2 inhibited invasive human breast cancer growth in a xenograft model. We further evaluated the long-term effects of multiple treatments with anti-ANX A2 mAb and its mechanism of inhibition on human breast tumor growth. We now demonstrate that three treatments with anti-ANX A2 mAb led to significant inhibition of breast tumor growth in immunodeficient mice, and that the anti-tumor response was demonstrable from day 94. After treatment, we followed tumor growth for 172 days and demonstrated 67% inhibition of tumor growth without detectable adverse effects. Biochemical analysis demonstrated that anti-ANX A2 mAb treatment caused significant inhibition of conversion of tissue plasminogen activator (tPA) in the tumor microenvironment. This led to disruption of plasmin generation that consequently inhibited activation of MMP-9 and MMP-2. These results suggest that ANX A2 plays an important role in aggressive breast tumor growth by regulating proteolytic pathways in the tumor microenvironment. ANX A2 may represent a new target for the development of therapeutics for treatment of aggressive breast cancer.

Combination Low-Dose Tissue-Type Plasminogen Activator Plus Annexin A2 for Improving Thrombolytic Stroke Therapy

Risk of hemorrhagic transformation, incomplete reperfusion, neurotoxicity, and a short treatment time window comprises major challenges for tissue plasminogen activator (tPA) thrombolytic stroke therapy. Improving tPA therapy has become one of the highest priorities in the stroke field. This mini review article focuses on our recent efforts aimed at evaluating a novel combination approach of low-dose tPA plus recombinant annexin A2 (rA2, a tPA, and plasminogen co-receptor), which might enhance tPA thrombolytic efficacy, while reducing its associated complications related to intracerebral hemorrhagic transformation. Results of our experimental studies using a focal embolic stroke model in rats support the feasibility of the combination approach and suggest the potential for successful clinical translation.

Low dose tPA plus annexin A2 combination attenuates tPA delayed treatment-associated hemorrhage and improves recovery in rat embolic focal stroke

We previously have shown that tissue type plasminogen activator (tPA) in combination with its receptor annexin A2 (rA2) protein significantly improved tPA thrombolytic efficacy. In this study we aimed to examine the therapeutic effects of the combination when treated at delayed 4-hour window after stroke compared to standard conventional tPA alone in an embolic focal stroke rat model. We compared effects of intravenous tPA alone (10 mg/kg) versus a combination of low-dose tPA (5 mg/kg) plus 10 mg/kg rA2. Totally 152 rats were used. Our results showed that: (1) at 24 h after stroke, the combination slightly reduced brain infarction compared to saline (9.2% reduction), and tPA (7.4% reduction), although the reductions did not reach statistical significance; while the combination significantly reduced (22.2% reduction) the conventional tPA-elevated intracerebral hemorrhagic (ICH) transformation; (2) at 7 days after stroke, the combination significantly attenuated conventional tPA alone-elevated iron deposition at peri-lesion area (68.2% reduction); (3) at 28 days after stroke, the combination significantly improved performance of adhesive tape-removal test, which was accompanied by a significantly higher micro vessel density at peri- infarct areas compared to conventional tPA alone group.In conclusion, compared to conventional tPA alone, when treated at delayed 4-hour after stroke, the combination of low-dose tPA plus rA2 therapy provides a safer profile by lowering risk of ICH transformation and improves neurological function recovery after stroke.

Intracellular annexin A2 regulates NF-κB signaling by binding to the p50 subunit: implications for gemcitabine resistance in pancreatic cancer

Annexin A2 (ANXA2) expression is highly upregulated in many types of cancer. Although cell surface localization of ANXA2 has been reported to have a critical role in the progression and metastasis of a variety of tumors, including pancreatic cancer, the biological role of intracellular ANXA2 is not fully understood. Herein the role of intracellular ANXA2 was investigated in a pancreatic cancer cell line. We first determined whether ANXA2 is involved in NF-κB signaling pathways. ANXA2 bound to the p50 subunit of NF-κB in a calcium-independent manner, and the ANXA2–p50 complex translocated into the nucleus. Furthermore, ANXA2 increased the transcriptional activity of NF-κB in both the resting and activated states and upregulated the transcription of several target genes downstream of NF-κB, including that encoding interleukin (IL)-6, which contributes to anti-apoptotic signaling. In Mia-Paca2 cells, we determined the effects of wild-type ANXA2 and an ANXA2 mutant, Y23A, which suppresses the cell surface localization, on upregulation of NF-κB transcriptional activity and secretion of IL-6. Both wild-type and Y23A ANXA2 induced anti-apoptotic effects in response to treatment with tumor necrosis factor-α or gemcitabine. Based on these results, we suggest that ANXA2 mediates resistance to gemcitabine by directly increasing the activity of NF-κB. Collectively, these data may provide additional information about the biological role of ANXA2 in pancreatic cancer and suggest that ANXA2 is a potential biomarker for the drug resistance phenotype and a candidate therapeutic target for the treatment of pancreatic cancer.

Inhibition of triple-negative and Herceptin-resistant breast cancer cell proliferation and migration by Annexin A2 antibodies

Background:

Annexin A2 (AnxA2), a calcium-dependent phospholipid binding protein, is abundantly present at the surface of triple-negative and Herceptin-resistant breast cancer cells. Interactions between cell-surface AnxA2 and tyrosine kinase receptors have an important role in the tumour microenvironment and act together to enhance tumour growth. The mechanism supporting this role is still unknown.

Methods:

The membrane function of AnxA2 was blocked by incubating cells with anti-AnxA2 antibodies. Western blotting, immunoprecipitation, immunofluorescence, 1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), flow cytometry, Clonogenic, and wound-healing assays were performed in this study.

Results:

We demonstrate that AnxA2 interacts with epidermal growth factor receptor (EGFR) at the cell surface and has an important role in cancer cell proliferation and migration by modulating EGFR functions. Blocking AnxA2 function at the cell surface by anti-AnxA2 antibody suppressed the EGF-induced EGFR tyrosine phosphorylation and internalisation by blocking its homodimerisation. Furthermore, addition of AnxA2 antibody significantly inhibited the EGFR-dependent PI3K-AKT and Raf-MEK-ERK downstream pathways under both EGF-induced and basal growth conditions, resulting in lower cell proliferation and migration.

Conclusions:

These findings suggest that cell-surface AnxA2 has an important regulatory role in EGFR-mediated oncogenic processes by keeping EGFR signalling events in an activated state. Therefore, AnxA2 could potentially be used as a therapeutic target in triple-negative and Herceptin-resistant breast cancers.

Effects of tissue plasminogen activator and annexin A2 combination therapy on long-term neurological outcomes of rat focal embolic stroke

BACKGROUND AND PURPOSE

Tissue-type plasminogen activator (tPA) in combination with recombinant annexin A2 (rA2) is known to reduce acute brain damage after focal ischemia. Here, we ask whether tPA-plus-rA2 combination therapy can lead to sustained long-term neurological improvements as well.

METHODS

We compared the effects of intravenous high-dose tPA alone (10 mg/kg) versus a combination of low-dose tPA (5 mg/kg) plus 10 mg/kg rA2 in a model of focal embolic cerebral ischemia in rats. All rats were treated at 3 hours after embolization. Brain tissue and neurological outcomes were assessed at 1 month. Surrogate biomarkers for endogenous neurovascular remodeling in peri-infarct area were analyzed by immunohistochemistry.

RESULTS

Compared with high-dose tPA alone, low-dose tPA-plus-rA2 significantly decreased infarction and improved neurological function at 1-month poststroke. In peri-infarct areas, tPA-plus-rA2 combination therapy also significantly augmented microvessel density, vascular endothelial growth factor, and synaptophysin expression.

CONCLUSIONS

Compared with conventional high-dose tPA alone, combination low-dose tPA plus rA2 therapy may provide a safe and effective way to improve long-term neurological outcomes after stroke.

Annexin A2 heterotetramer: structure and function

Annexin A2 is a pleiotropic calcium- and anionic phospholipid-binding protein that exists as a monomer and as a heterotetrameric complex with the plasminogen receptor protein, S100A10. Annexin A2 has been proposed to play a key role in many processes including exocytosis, endocytosis, membrane organization, ion channel conductance, and also to link F-actin cytoskeleton to the plasma membrane. Despite an impressive list of potential binding partners and regulatory activities, it was somewhat unexpected that the annexin A2-null mouse should show a relatively benign phenotype. Studies with the annexin A2-null mouse have suggested important functions for annexin A2 and the heterotetramer in fibrinolysis, in the regulation of the LDL receptor and in cellular redox regulation. However, the demonstration that depletion of annexin A2 causes the depletion of several other proteins including S100A10, fascin and affects the expression of at least sixty-one genes has confounded the reports of its function. In this review we will discuss the annexin A2 structure and function and its proposed physiological and pathological roles.

Antibody-directed neutralization of annexin II (ANX II) inhibits neoangiogenesis and human breast tumor growth in a xenograft model

Activation of the fibrinolytic pathway has long been associated with human breast cancer. Plasmin is the major end product of the fibrinolytic pathway and is critical for normal physiological functions. The mechanism by which plasmin is generated in breast cancer is not yet fully described. We previously identified annexin II (ANX II), a fibrinolytic receptor, in human breast tumor tissue samples and observed a strong positive correlation with advanced stage cancer (Sharma et al., 2006a). We further demonstrated that tissue plasminogen activator (tPA) binds to ANX II in invasive breast cancer MDA-MB231cells, which leads to plasmin generation (Sharma et al., 2010). We hypothesize that ANX II-dependent plasmin generation in breast tumor is necessary to trigger the switch to neoangiogenesis, thereby stimulating a more aggressive cancer phenotype. Our immunohistochemical studies of human breast tumor tissues provide compelling evidence of a strong positive correlation between ANX II expression and neoangiogenesis, and suggest that ANX II is a potential target to slow or inhibit breast tumor growth by inhibiting neoangiogenesis. We now report that administration of anti-ANX II antibody potently inhibits the growth of human breast tumor in a xenograft model. Inhibition of tumor growth is at least partly due to attenuation of neoangiogenic activity within the tumor. In vitro studies demonstrate that anti-ANX II antibody inhibits angiogenesis on three dimensional matrigel cultures by eliciting endothelial cell (EC) death likely due to apoptosis. Taken together, these data suggest that selective disruption of the fibrinolytic activity of ANX II may provide a novel strategy for specific inhibition of neoangiogenesis in human breast cancer.

The role of annexin A2 in tumorigenesis and cancer progression

Annexin A2 is a calcium-dependent, phospholipid-binding protein found on various cell types. It is up-regulated in various tumor types and plays multiple roles in regulating cellular functions, including angiogenesis, proliferation, apoptosis, cell migration, invasion and adhesion. Annexin A2 binds with plasminogen and tissue plasminogen activator on the cell surface, which leads to the conversion of plasminogen to plasmin. Plasmin is a serine protease which plays a key role in the activation of metalloproteinases and degradation of extracellular matrix components essential for metastatic progression. We have recently found that both annexin A2 and plasmin are increased in conditioned media of co cultured ovarian cancer and peritoneal cells. Our studies suggest that annexin A2 is part of a tumor-host signal pathway between ovarian cancer and peritoneal cells which promotes ovarian cancer metastasis. Accumulating evidence suggest that interactions between annexin A2 and its binding proteins play an important role in the tumor microenvironment and act together to enhance cancer metastasis. This article reviews the current knowledge on the biological role of annexin A2 and its binding proteins in solid malignancies including ovarian cancer.

Antiangiogenic kringles derived from human plasminogen and apolipoprotein(a) inhibit fibrinolysis through a mechanism that requires a functional lysine-binding site

Many proteins in the fibrinolysis pathway contain antiangiogenic kringle domains. Owing to the high degree of homology between kringle domains, there has been a safety concern that antiangiogenic kringles could interact with common kringle proteins during fibrinolysis leading to adverse effects in vivo. To address this issue, we investigated the effects of several antiangiogenic kringle proteins including angiostatin, apolipoprotein(a) kringles IV(9)-IV(10)-V (LK68), apolipoprotein(a) kringle V (rhLK8) and a derivative of rhLK8 mutated to produce a functional lysine-binding site (Lys-rhLK8) on the entire fibrinolytic process in vitro and analyzed the role of lysine binding. Angiostatin, LK68 and Lys-rhLK8 increased clot lysis time in a dose-dependent manner, inhibited tissue-type plasminogen activator-mediated plasminogen activation on a thrombin-modified fibrinogen (TMF) surface, showed binding to TMF and significantly decreased the amount of plasminogen bound to TMF. The inhibition of fibrinolysis by these proteins appears to be dependent on their functional lysine-binding sites. However, rhLK8 had no effect on these processes owing to an inability to bind lysine. Collectively, these results indicate that antiangiogenic kringles without lysine binding sites might be safer with respect to physiological fibrinolysis than lysine-binding antiangiogenic kringles. However, the clinical significance of these findings will require further validation in vivo.

Hypoxia increases Annexin A2 expression in osteoblastic cells via VEGF and ERK

Vascular endothelial growth factor (VEGF)-stimulated angiogenesis is critical for endochondral ossification that occurs during bone development and bone repair. Under these circumstances, VEGF production appears to be driven by low oxygen tension, under the control of the hypoxia-inducible factor-α family of transcription factors (HIF-α). Annexin 2 (AnxA2) a calcium-dependent phospholipid binding protein has been implicated in VEGF-mediated retinal neovascularization and is upregulated by VEGF in choroid retinal endothelial cells. AnxA2 is also expressed in cells of the osteoblast lineage and chondrocytes and may play a role in matrix mineralization. In this paper, we examined the effects of hypoxia (1% O(2)) and VEGF on the expression of AnxA2 in osteoblastic MC3T3-E1 cells. Hypoxia, desferrioxamine (hypoxia mimetic), and recombinant VEGF all increased AnxA2 mRNA and protein levels in osteoblastic cells. The hypoxia-induced increase in AnxA2 was inhibited by a blocking antibody to VEGF-R1; however, VEGF(120), a VEGF-R1 agonist, demonstrated no influence upon Anxa2 expression. This suggests that VEGF induction of Annexin A2 is not mediated via VEGF-R1 agonism alone but by VEGF-R1 and Neuropilin-1 or Neuropilin-2 heterodimers. In addition, we demonstrated that VEGF-stimulated changes in AnxA2 expression via a pathway involving Src and MEK kinase. These data demonstrate that AnxA2 expression in osteoblasts is under the control of VEGF, which may have implications for both angiogenesis and bone mineralization under low oxygen conditions.

Agents that bind annexin A2 suppress ocular neovascularization

TM601 is a synthetic polypeptide with sequence derived from the venom of the scorpion Leiurus quinquestriatus that has anti-neoplastic activity. It has recently been demonstrated to bind annexin A2 on cultured tumor and vascular endothelial cells and to suppress blood vessel growth on chick chorioallantoic membrane. In this study, we investigated the effects of TM601 in models of ocular neovascularization (NV). When administered by intraocular injection, intravenous injections, or periocular injections, TM601 significantly suppressed the development of choroidal NV at rupture sites in Bruch's membrane. Treatment of established choroidal NV with TM601 caused apoptosis of endothelial cells and regression of the NV. TM601 suppressed ischemia-induced and vascular endothelial growth factor-induced retinal NV and reduced excess vascular permeability induced by vascular endothelial growth factor. Immunostaining with an antibody directed against TM601 showed that after intraocular or periocular injection, TM601 selectively bound to choroidal or retinal NV and co-localized with annexin A2, which is undetectable in normal retinal and choroidal vessels, but is upregulated in endothelial cells participating in choroidal or retinal NV. Intraocular injection of plasminogen or tissue plasminogen activator, which like TM601 bind to annexin A2, also suppressed retinal NV. This study supports the hypothesis that annexin A2 is an important target for treatment of neovascular diseases and suggests that TM601, through its interaction with annexin A2, causes suppression and regression of ocular NV and reduces vascular leakage and thus may provide a new treatment for blinding diseases such as neovascular age-related macular degeneration and diabetic retinopathy.

Breast cancer cell surface annexin II induces cell migration and neoangiogenesis via tPA dependent plasmin generation

Annexin II, an abundant phospholipids binding cell surface protein, binds tPA and functions as a regulator of fibrinolysis. Annexin II also mediates angiogenesis and enhances tumor growth and metastasis. However, the mechanism supporting this role is not known. Using human breast cancer model we show that invasive human breast cancer cells (MDA-MB231) synthesize annexin II and tissue plasminogen activator (tPA). In vitro both annexin II and tPA interacts which in turn convert zymogen plasminogen to reactive enzyme plasmin. Cell surface produced plasmin inhibited the migration of MDA-MB231 cells. Silencing of annexin II gene in MDA-MB231 cells abolished tPA binding therefore inhibited tPA dependent plasmin generation. These annexin II suppressed MDA-MB231 cells showed reduced motility. Immunohistochemical analysis of prediagnosed clinical specimens showed abundant secretion of tPA and expression of annexin II on the surface of invasive human breast cancer cells which correlates with neovascularization of the tumor. Taken together, these data indicate that annexin II may regulate localized plasmin generation in breast cancer. This may be an early event switching breast cancer from the prevascular phase to the vascular phase and thus contributing to aggressive cancer with the possibility of metastasis. The data provide a mechanism explaining the role of annexin II in breast cancer progression and suggest that annexin II may be an attractive target for therapeutic strategies aimed to inhibit angiogenesis and breast cancer.

Angiostatin regulates the expression of antiangiogenic and proapoptotic pathways via targeted inhibition of mitochondrial proteins

Angiostatin, a proteolytic fragment of plasminogen, is a potent endogenous antiangiogenic agent. The molecular mechanisms governing angiostatin's antiangiogenic and antitumor effects are not well understood. Here, we report the identification of mitochondrial compartment as the ultimate target of angiostatin. After internalization of angiostatin into the cell, at least 2 proteins within the mitochondria bind this molecule: malate dehydrogenase, a member of Krebs cycle, and adenosine triphosphate synthase. In vitro and in vivo studies revealed differential regulation of key prosurvival and angiogenesis-related proteins in angiostatin-treated tumors and tumor-endothelium. Angiostatin induced apoptosis via down-regulation of mitochondrial BCL-2. Angiostatin treatment led to down-regulation of c-Myc and elevated levels of another key antiangiogenic protein, thrombospondin-1, reinforcing its antitumor and antiangiogenic effects. Further evidence is provided for reduced recruitment and infiltration of bone marrow-derived macrophages in angiostatin-treated tumors. The observed effects of angiostatin were restricted to the tumor site and were not observed in other major organs of the mice, indicating unique tumor specific bioavailability. Together, our data suggest mitochondria as a novel target for antiangiogenic therapy and provide mechanistic insights to the antiangiogenic and antitumor effects of angiostatin.

Annexin A2 regulates the levels of plasmin, S100A10 and Fascin in L5178Y cells

Annexin A2 (ANXA2) was reported as the receptor, activator, expression enhancer, or cooperator for plasmin, S100A10, and others. To delineate the effect of ANXA2 on the proteins that are probably associated with tumor development and metastasis by a credible experimental method, we generated an ANXA2 gene knockout tumor cell line, ANXA2(-/-) L5178Y, and compared the expression levels of plasmin, S100A10 and fascin in the generated cell line with in wild type of L5178Y at mRNA and protein levels. The results showed that the mRNA level of plasminogen (PLG) was not substantially changed in cultured ANXA2(-/-) cells, but the protein level of plasmin was significantly lower in the cultured ANXA2(-/-) cells than in cultured ANXA2(+/+) cells. For S100A10 and fascin, their mRNA and protein levels were significantly lower in the cultured ANXA2(-/-) cells than in cultured ANXA2(+/+) cells. Results indicate that ANXA2 introduces the generation or expression of plasmin, S100A10, and fascin in tumor cells. ANXA2 affects PLG/plasmin level by a way post transcription and may be an inducer or enhancer to fascin expression at transcription level. By the regulations, ANXA2 enhances the development, invasion, and metastasis of tumor. The detailed mechanism for the regulations above remains to be further investigated, but our results show the potential of ANXA2 as a new target molecule for the strategies of tumor biotherapy or tumor gene therapy.

Factor Xa binding to annexin 2 mediates signal transduction via protease-activated receptor 1

The serine protease zymogen factor X is converted to its catalytically active form factor Xa by the binary complex of factor VIIa bound to its cell surface receptor tissue factor (TF) or by the intrinsic Xase complex, which consists of active factors VIII (VIIIa), IX (IXa), factor X, and Ca2+. Factor Xa has procoagulant activity by conversion of prothrombin to thrombin and also induces signal transduction, either alone or in the ternary TF:VIIa:factor Xa coagulation initiation complex. Factor Xa cleaves and activates protease activated receptor (PAR)1 or -2, but factor Xa signaling efficiency varies among cell types. We show here that annexin 2 acts as a receptor for factor Xa on the surface of human umbilical vein endothelial cells and that annexin 2 facilitates factor Xa activation of PAR-1 but does not enhance coagulant function of factor Xa. Overexpression of TF abolishes annexin 2 dependence on factor Xa signaling and diminishes binding to cell surface annexin 2, whereas selectively abolishing TF promotes the annexin 2/factor Xa interaction. We propose that annexin 2 serves to regulate factor Xa signaling specifically in the absence of cell surface TF and may thus play physiological or pathological roles when factor Xa is generated in a TF-depleted environment.

Complications from vascular disrupting agents and angiogenesis inhibitors: aberrant control of hemostasis and thrombosis

PURPOSE OF REVIEW

To discuss thrombotic and hemorrhagic complications from angiogenesis inhibitors and vascular disrupting agents, pathogenesis, and recommendations for prophylaxis and management of those complications.

RECENT FINDINGS

Venous thromboembolism has been a significant complication of the angiogenesis inhibitors thalidomide and lenalidomide. Prophylaxis with aspirin, low-molecular-weight heparin, or warfarin has been shown to decrease rates of venous thromboembolism in patients treated with these agents. Life-threatening hemorrhage and arterial thromboembolism have been observed in patients using treatments that inhibit the vascular endothelial growth factor signaling pathway. Patients should be screened for arterial thromboembolism and hemorrhage risk prior to using vascular endothelial growth factor signal inhibitors. It is not known how angiogenesis inhibitors and vascular disrupting agents upset normal hemostasis. It is likely that disruption of the function and/or integrity of vascular endothelium leads to an increased risk for thrombosis and/or hemorrhage.

SUMMARY

New angiogenesis inhibitors and vascular disrupting agents have been developed that have significant activity against neoplasms. Potentially life-threatening side effects of hemorrhage and thrombosis have been observed with many of these new agents. As new treatments that disrupt angiogenesis or existing tumor vasculature are developed, attention should be given to these toxicities in clinical practice and clinical trials.

Annexinopathies

Annexins comprise a conserved family of proteins characterised by their ability to bind and order charged phospholipids in membranes, often in response to elevated intracellular calcium. The family members (there are at least 12 in humans) have become specialised over evolutionary time and are involved in a diverse range of cellular functions both inside the cell and extracellularly Although a mutation in an annexin has never been categorically proven to be the cause of a disease state, they have been implicated in pathologies as diverse as autoimmunity, infection, heart disease, diabetes and cancer. 'Annexinopathies' were first described by Jacob H. Rand to describe the pathological sequelae in two disease states, the overexpression of annexin 2 in a patients with a haemorrhagic form of acute promyelocytic leukaemia, and the under-expression of annexin 5 on placental trophoblasts in the antiphospholipid syndrome. In this chapter we will outline some of the more recent observations in regard to these conditions, and describe the involvement of annexins in some other major causes of human morbidity.

Plasmin-cleaved beta-2-glycoprotein 1 is an inhibitor of angiogenesis

beta-2-Glycoprotein 1, an abundant plasma glycoprotein, binds anionic cell surfaces and functions as a regulator of thrombosis. Here, we show that cleavage of the kringle domain at Lys317/Thr318 switches its function to a regulator of angiogenesis. In vitro, the cleaved protein specifically inhibited the proliferation and migration of endothelial cells. The protein was without effect on preformed endothelial cell tubes. In vivo, the cleaved protein inhibited neovascularization into subcutaneously implanted Matrigel and Gelfoam sponge implants and the growth of orthotopically injected tumors. Collectively, these data indicate that plasmin-cleaved beta-2-glycoprotein 1 is a potent antiangiogenic and antitumor molecule of potential therapeutic significance.

Expression of annexin A2 in GABAergic interneurons in the normal rat brain

Expression of the Ca(2+)-dependent phospholipids binding protein annexin A2 (ANX2) in the brain is thought to be largely associated with brain pathological conditions such as tumor, inflammation, and neurodegeneration. The recent findings that ANX2 heterotetramer is involved in learning and neuronal activities necessitates a systematic investigation of the physiological expression of ANX2 in the brain. With combination of in situ hybridization and immunohistochemistry, ANX2 mRNA and protein were specifically detected in a group of GABAergic interneurons throughout the brain. Although ANX2 was absent from the interior of pyramidal neurons, it was found on the membrane and seemly the extracellular space of those neurons, where they closely co-localized with glutamate decarboxylase terminals. In cultured developing neurons, ANX2 was present at high concentrations in the growth cones co-distributing with several growth-associated proteins such as growth associated protein 43 (GAP43), turned on after division/Ulip/CRMP (TUC-4), tubulin, and tissue-plasminogen activator. It then became predominantly distributed on the membrane and mostly in axonal branches as neurons grew and extended synaptic networks. ANX2 was also secreted from cultured neurons, in a membrane-bound form that was Ca(2+)-dependent, which was significantly increased by neuronal depolarization. These results may have implications in the function and regulatory mechanism of ANX2 in the normal brain.

Plasminogen and angiostatin interact with heat shock proteins

Previous studies from this laboratory have demonstrated that plasminogen and angiostatin bind to endothelial cell (EC) surface-associated actin via their kringles in a specific manner. Heat shock proteins (hsps) like hsp 27 are constitutively expressed by vascular ECs and regulate actin polymerization, cell growth, and migration. Since many hsps have also been found to be highly abundant on cell surfaces and there is evidence that bacterial surface hsps may interact with human plasminogen, the purpose of this study was to determine whether human plasminogen and angiostatin would interact with human hsps. ELISAs were developed in our laboratory to assess these interactions. It was observed that plasminogen bound to hsps 27, 60, and 70. In all cases, binding was inhibited (85-90%) by excess (50 mM) lysine indicating kringle involvement. Angiostatin predominantly bound to hsp 27 and to hsp 70 in a concentration- and kringle-dependent manner. As observed previously for actin, there was concentration-dependent inhibition of angiostatin's interaction with hsp 27 by plasminogen. In addition, 30-fold molar excess actin inhibited (up to 50%), the interaction of plasminogen with all hsps. However, 30-fold molar excess actin could only inhibit the interaction of angiostatin with hsp 27 by 15-20%. Collectively, these data indicate that (i) while plasminogen interacts specifically with hsp 27, 60, and 70, angiostatin interacts predominantly with hsp 27 and to some extent with hsp 70; (ii) plasminogen only partially displaces angiostatin's binding to hsp 27 and (iii) actin only partially displaces plasminogen/angiostatin binding to hsps. It is conceivable therefore that surface-associated hsps could mediate the binding of these ligands to cells like ECs.

Ocular neovascularization: Implication of endogenous angiogenic inhibitors and potential therapy

Ocular neovascularization (NV) is the primary cause of blindness in a wide range of ocular diseases, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). The exact mechanism underlying the pathogenesis of ocular NV is not yet well understood, and as a consequence, there is no satisfactory therapy for ocular NV. In the last 10 years, a number of studies provided increasing evidence demonstrating that the imbalance between angiogenic stimulating factors and angiogenic inhibitors is a major contributor to the angiogenesis induced by various insults, such as hypoxia or ischemia, inflammation and tumor. The angiogenic inhibitors alone or in combination with other existing therapies are, therefore, believed to be promising in the treatment of ocular NV in the near future. This article reviews recent progress in studies on the mechanisms and treatment of ocular NV, focusing on the implication and therapeutic potential of endogenous angiogenic inhibitors in ocular NV.

Antibody-directed targeting of angiostatin's receptor annexin II inhibits Lewis Lung Carcinoma tumor growth via blocking of plasminogen activation: Possible biochemical mechanism of angiostatin's action

Angiostatin, the N-terminal four kringles (K1-4) of parent molecule plasminogen, is reported to block Lewis Lung Carcinoma (LLC) tumor growth and metastasis. However, angiostatin's mechanism of action is unclear. We earlier reported that angiostatin binds to cell surface annexin II through the lysine-binding domain (kringles 1-4) [Tuszynski, G.P., Sharma, M., Rothman, V.L., Sharma, M.C., 2002. Angiostatin binds to tyrosine kinase substrate annexin II through the lysine-binding domain in endothelial cells. Microvasc. Res. 64:448-462.]). We now show that annexin II on the cell surface of LLC cells regulates conversion of plasminogen to plasmin. Activation of plasminogen to plasmin is time-dependent, with the linear activation lasting up to 120 min. Monoclonal antibodies to annexin II reduced plasminogen activation by 92.6%, suggesting a specific role of annexin II in plasmin generation. Angiostatin also reduced plasmin generation by 81.6%, suggesting that angiostatin may be competing with plasminogen through lysine-binding domain. epsilon-Aminocaproic acid, a lysine analogue, effectively blocked plasminogen activation indicating that, indeed, the lysine-binding site of the kringles domain is required for activation. These data suggest that annexin II may be a receptor target for angiostatin's action. Therefore, we tested the effect of high affinity monoclonal antibody to annexin II in mouse model of LLC. A single dose of antibody treatment inhibited LLC tumor growth almost 70% with concomitant inhibition of circulating plasmin generation and its proteolytic activity. Taken together, it is possible that inhibition of LLC tumor growth and metastasis reported by angiostatin therapy may be due to blocking of annexin-II-dependent plasmin generation. Plasmin is known to influence angiogenic, invasive and metastatic capability of tumors.

Angiogenesis-associated protein annexin II in breast cancer: selective expression in invasive breast cancer and contribution to tumor invasion and progression

Many advanced human tumors including breast cancer overproduce plasmin that is known to promote angiogenesis and metastasis. The mechanism of this effect is poorly understood. Here we report that annexin II, an endothelial co-receptor for tPA (tissue-type plasminogen activator) and plasminogen, was undetectable in normal and hyperplastic ductal epithelial cells and ductal complexes. By contrast, it was consistently expressed in invasive breast cancer and ductal carcinoma in situ (DCIS) indicating its involvement in breast cancer. Using the well established invasive/metastatic MDA-MB231 cell line and the noninvasive/nonmetastatic MCF-7 human breast cancer cell line, we investigated the mechanism by which annexin II regulates breast cancer progression and metastasis. Western and Northern blot analyses demonstrate selective expression of annexin II in MDA-MB231 cells but not in poorly invasive MCF-7 cells suggesting its participation in invasive breast cancer. Since annexin II is a receptor for plasminogen, we tested whether MDA-MB231 cells are capable of producing plasmin in vitro. MDA-MB231 cell membranes induced plasmin generation in a time-dependent manner while those from MCF-7 cells failed to convert plasminogen to plasmin. The generated plasmin is capable of degrading ECM consequently facilitating cell invasion and migration, biological functions required for angiogenesis and metastasis. Plasmin generation and its dependent invasion and migration can be blocked by a monoclonal antibody to annexin II or angiostatin, potent inhibitors of angiogenesis, breast cancer, and metastasis. Our findings indicate that annexin II-dependent localized plasmin generation by human breast cancer cells could contribute to angiogenesis and metastasis. These results suggest that annexin II may be an attractive target for new anti-angiogenic and anti-breast cancer therapies.

Angiostatin and plasminogen share binding to endothelial cell surface actin

Previous studies from this laboratory have demonstrated that plasminogen binds to endothelial cell surface-associated actin via its kringles in a dose-dependent and specific manner. The purpose of this study was to determine whether angiostatin, a proteolytic fragment of plasminogen, shares binding properties with plasminogen. Our results indicated that like plasminogen, angiostatin bound to actin in a time-, concentration-, and kringle-dependent manner. Furthermore, this binding was significantly inhibited by excess plasminogen, suggesting that both proteins shared binding motifs on the actin molecule. Fluorescence studies demonstrated that angiostatin bound to intact endothelial cells through its kringles, and this binding was also inhibited by plasminogen but not by unrelated proteins. Ligand blot analyses on endothelial cell lysates indicated that angiostatin interacted with a 42 kDa protein, which was identified as actin. Furthermore, an anti-actin antibody inhibited binding of angiostatin to endothelial cells by approximately 25%. These results suggest that angiostatin and plasminogen share binding to endothelial cell surface actin and, therefore, that angiostatin has the potential to inhibit plasmin-dependent processes such as cell migration-movement.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Angiostatin's molecular mechanism: aspects of specificity and regulation elucidated

Tumor growth requires the development of new vessels that sprout from pre-existing normal vessels in a process known as "angiogenesis" [Folkman (1971) N Engl J Med 285:1182-1186]. These new vessels arise from local capillaries, arteries, and veins in response to the release of soluble growth factors from the tumor mass, enabling these tumors to grow beyond the diffusion-limited size of approximately 2 mm diameter. Angiostatin, a naturally occurring inhibitor of angiogenesis, was discovered based on its ability to block tumor growth in vivo by inhibiting the formation of new tumor blood vessels [O'Reilly et al. (1994a) Cold Spring Harb Symp Quant Biol 59:471-482]. Angiostatin is a proteolytically derived internal fragment of plasminogen and may contain various members of the five plasminogen "kringle" domains, depending on the exact sites of proteolysis. Different forms of angiostatin have measurably different activities, suggesting that much remains to be elucidated about angiostatin biology. A number of groups have sought to identify the native cell surface binding site(s) for angiostatin, resulting in at least five different binding sites proposed for angiostatin on the surface of endothelial cells (EC). This review will consider the data supporting all of the various reported angiostatin binding sites and will focus particular attention on the angiostatin binding protein identified by our group: F(1)F(O) ATP synthase. There have been several developments in the quest to elucidate the mechanism of action of angiostatin and the regulation of its receptor. The purpose of this review is to describe the highlights of research on the mechanism of action of angiostatin, its' interaction with ATP synthase on the EC surface, modulators of its activity, and issues that should be explored in future research related to angiostatin and other anti-angiogenic agents.

Proteomic analysis of vascular endothelial growth factor-induced endothelial cell differentiation reveals a role for chloride intracellular channel 4 (CLIC4) in tubular morphogenesis

Formation of new vessels from pre-existing capillaries demands extensive reprogramming of endothelial cells through transcriptional and post-transcriptional events. We show that 120 protein spots in a two-dimensional isoelectric focusing/electrophoretic analysis were affected during vascular endothelial growth factor-A-induced endothelial cell tubular morphogenesis in vitro, as a result of changes in charge or expression level of the corresponding proteins. For about 22% of the spots, the protein products could be identified, of which several previously have been implicated in cytoskeletal reorganization and angiogenesis. One such protein was heat shock protein 27, a chaperone involved in beta-actin rearrangement that was identified as regulated in degree of serine phosphorylation. We also identified regulation of chloride intracellular channel 4 (CLIC4), the expression of which decreased during tubular morphogenesis. CLIC4 was expressed at high levels in resting vessels, whereas expression was modulated during pathological angiogenesis such as in tumor vessels. The subcellular localization of CLIC4 in endothelial cells was dependent on whether cells were engaged in proliferation or tube formation. Antisense- and small interfering RNA-mediated suppression of CLIC4 expression led to arrest in tubular morphogenesis. Our data implicate CLIC4 in formation of a vessel lumen.

The human prothrombin kringle-2 derived peptide, NSA9, is internalized into bovine capillary endothelial cells through endocytosis and energy-dependent pathways

Human prothrombin kringle-2 and its partial peptide, NSA9 (NSAVQLVEN), have been reported to have potent anti-angiogenic activities. Here, the internalization mechanism of NSA9 into bovine capillary endothelial (BCE) cells was examined using lactate dehydrogenase (LDH) release assay, fluorescence microscopy, and flow cytometry. LDH release assay results suggested that the integrity of the BCE cell membrane was unaffected by NSA9. Fluorescence microscopy indicated that internalized NSA9 was localized in the cytoplasm around the nucleus, and showed a punctuated fluorescence pattern, which is indicative of endocytic vesicles. Also, the cellular internalization of NSA9 is significantly inhibited by depletion of the cellular ATP pool, endocytosis inhibitors such as chloroquine and nocodazole, and incubation at low temperature (4 degrees C). In addition, the anti-proliferative activity of NSA9 against BCE cells was diminished in the presence of endocytosis or metabolic inhibitors. In conclusion, these results strongly suggest that NSA9 might exert its anti-proliferative activity through internalization into BCE cells by endocytosis and energy-dependent pathways.

Mechanisms and significance of bifunctional NK4 in cancer treatment

Based on the background that hepatocyte growth factor (HGF) and c-Met/HGF receptor tyrosine kinase play a definite role in tumor invasion and metastasis, NK4, four-kringles containing intramolecular fragment of HGF, was isolated as a competitive antagonist for the HGF-c-Met system. Independent of its HGF-antagonist action, NK4 inhibited angiogenesis induced by vascular endothelial cell growth factor and basic fibroblast growth factor, as well as HGF, indicating that NK4 is a bifunctional molecule that acts as an HGF-antagonist and angiogenesis inhibitor. Interestingly, kringle domains in distinct types of proteins, e.g., plasminogen, prothrombin, plasminogen activators, apolipoprotein(a), and HGF, share angioinhibitory actions. In experimental models of distinct types of cancers, NK4 protein administration or NK4 gene therapy inhibited tumor invasion, metastasis, and angiogenesis-dependent tumor growth. Cancer treatment with NK4 may prove to suppress malignant tumors to be 'static' in both tumor growth and spreading, as based on biological characteristics of malignant tumors.

Antineovascular therapy, a novel antiangiogenic approach

Angiogenesis is a crucial event in tumour growth, since the growth of tumour cells depends on the supply of essentials such as oxygen and nutrients. Therefore, suppression of angiogenesis is expected to show potent therapeutic effects on various cancers. Additionally, this 'antiangiogenic therapy' is thought not only to eradicate primary tumour cells, but also suppress tumour metastases through disruption of haematogenous metastatic pathways. Tumour dormancy therapy does not aim to disrupt newly formed angiogenic vessels but aims to inhibit further formation of neovessels through inhibiting certain processes of angiogenesis. This raises a question of whether or not these antiangiogenic agents bring complete cure of tumours as complete cut-off of oxygen and nutrients is not expected by the treatment with these agents. This paper will review a novel antiangiogenic therapy, antineovascular therapy (ANET). ANET is categorised in antiangiogenic therapy but is different from tumour dormancy therapy using conventional angiogenic inhibitors: ANET aims to disrupt neovessels rather than to inhibit neovessel formation. ANET is based on the fact that angiogenic endothelial cells are growing cells and would be effectively damaged by cytotoxic agents when the agents are effectively delivered to the neovessels. The complete eradication of angiogenic endothelial cells may cause complete cut-off of essential supplies to the tumour cells and lead to indirect but strong cytotoxicity instead of cytostasis caused by the inhibition of angiogenesis. For the purpose of ANET, an angiogenic vasculature-targeting probe has been developed, by which cytotoxic anticancer agents are actively delivered to the angiogenic endothelial cells by using drug delivery system (DDS) technology. Another way to damage newly formed vessels by cytotoxic agents is achieved by metronomic-dosing chemotherapy. This chemotherapy shifts the target of chemotherapeutic agents from tumour cells to angiogenic endothelial cells by selective dosing schedule. Similarly, the shift of target from tumour cells to angiogenic endothelial cells enhanced therapeutic efficacy of cancer photo-dynamic therapy (PDT): in this antiangiogenic PDT, photosensitizers are delivered more to neovessel endothelial cells than to tumour cells. These therapeutic strategies would be clinically applied in the future.

Annexins and disease

The annexins are a family of closely related calcium- and membrane-binding proteins expressed in most eukaryotic cell types. Despite their structural and biochemical similarities annexins have diverse functions, in cellular activities that include vesicle trafficking, cell division, apoptosis, calcium signalling, and growth regulation. To date there is no evidence to suggest that any individual member of the annexin family is a disease-causing gene, i.e., a gene that through loss, mutation, translocation or amplification leads to a known human disease. However, there is good evidence that in certain clinical conditions, changes in annexin expression levels or localisation may contribute to the pathological consequences and sequelae of disease. In this way, annexins are indirectly linked to some of the most serious human disease classes including cardiovascular disease and cancer. In this review we consider the roles played by annexins in disease and examine the molecular basis for anomalous annexin behaviour that may contribute to disease pathophysiology.

Angiostatin-induced inhibition of endothelial cell proliferation/apoptosis is associated with the down-regulation of cell cycle regulatory protein cdk5

Endothelial cells (ECs) are quiescent in normal blood vessels, but undergo rapid bursts of proliferation after vascular injury, hypoxia or induced by powerful angiogenic cytokines like fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). Deregulated proliferation of ECs facilitates angiogenic processes and promotes tumor growth. In dividing cells, cell cycle-associated protein kinases, which are referred as cyclin-dependent kinases (cdks), regulate proliferation, differentiation, senescence, and apoptosis. Cyclin-dependent kinase-5 (cdk5) is expressed in neuronal cells and plays an important role in neurite outgrowth, of neuronal migration and neurogenesis, its functions in non-neuronal cells are unclear. Here, we show for the first time that the cdk5 is expressed at high levels in proliferating bovine aortic endothelial (BAE) cells, by contrast insignificant low levels of cdk5 expression in quiescent BAE cells. In addition, bFGF up-regulates cdk5 expression in a dose-dependent fashion. Interestingly, temporal expression data suggests that cdk5 expression is very low between 24-48 h, but high level of cdk5 expression was detected during 60-72 h. This later time corresponds to the time of completion of one cell cycle (doubling of cell population) of BAE cell culture. Angiostatin (AS), a powerful inhibitor of angiogenesis inhibits ECs proliferation in dose-dependent manner with concomitant down-regulation of cdk5 expression. The role of cdk5 in ECs, proliferation and apoptosis was confirmed by selective inhibition of cdk5 expression by the purine derivative roscovitine, which inhibits bFGF-stimulated BAE cells proliferation and induces apoptosis in dose-specific manner. By contrast, the roscovitine analog olomoucine, which is a specific inhibitor of cdk4, but not of cdk5 failed to affect ECs proliferation and apoptosis. These data suggest for the first time that neuron specific protein cdk5 may have significant role in the regulation of ECs proliferation, apoptosis, and angiogenesis and extends beyond its role in neurogenesis.

Matrix metalloproteinases and matrikines in angiogenesis

Neoangiogenesis, the formation of new blood capillaries from pre-existing vessels, plays an important role in a number of physiological and pathological processes, particularly in tumor growth and metastasis. Extracellular proteolysis by matrix metalloproteinases or other neutral proteinases is an absolute requirement for initiating tumor invasion and angiogenesis. Cryptic segments or pre-existing domains within larger proteins, most of them belonging to the extracellular matrix, can be exposed by conformational changes and/or generated by partial enzymatic hydrolysis. They can positively or negatively regulate important functions of endothelial cells including adhesion, migration, proliferation, cell survival and cell-cell interactions. Such regulations by cryptic segments and proteolytic fragments led to the concept of matricryptins and matrikines, respectively. Matrix metalloproteinases and matrikines in conjunction with other pro- or anti-angiogenic factors might act in concert at any step of the angiogenesis process. A number of matrikines have been identified as potent anti-angiogenic factors, which could provide a new alternative to anti-proteolytic strategies for the development of anti-angiogenic therapeutic molecules aimed at inhibiting tumor growth and metastasis. Some of them are currently being investigated in clinical trials.

Cancer Anti-angiogenic Therapy

Tumor angiogenesis affords new targets for cancer therapy, since inhibition of angiogenesis suppresses tumor growth by cutting out the supply of oxygen and nutrients. Anti-angiogenic therapy is thought to be free of the severe side effects that are usually seen with cytotoxic anticancer drugs. Furthermore, anti-angiogenic therapy is thought not only to eradicate primary tumor tissues, but also to suppress tumor metastases. However, it is uncertain whether this therapy causes tumor regression because it inhibits only angiogenic events. Recently, a novel anti-angiogenic therapy called anti-neovascular therapy (ANET) has become notable. This therapy inflicts indirect lethal damage on tumor cells by damaging newly formed blood vessels using anti-cancer drugs targeting the angiogenic vasculature, since cytotoxic anti-cancer drugs cause damage to proliferating neovascular endothelial cells as well as tumor cells. Moreover, neovascular endothelial cells would not be expected to acquire drug-resistance. Traditional chemotherapy, which directly targets tumor cells, has potential problems such as low specificity and severe side effects. On the contrary, in ANET, severe side effects may be suppressed, since traditional anti-cancer agents are delivered to the neovessels by DDS technology. Besides the usage of DDS technology, anti-neovascular scheduling of chemotherapy, or metronomic-dosing chemotherapy, has also been attempted in which anti-cancer drugs are administered on a schedule to damage neovessels. In this review, we describe traditional anti-angiogenic therapy and ANET. We also discuss anti-angiogenic cancer photodynamic therapy (PDT), since PDT is clinically applied to treat age-related macular degeneration (AMD), in which uncontrolled angiogenesis occurs.

Expression of biomarkers modulating prostate cancer angiogenesis: differential expression of annexin II in prostate carcinomas from India and USA

BACKGROUND

Prostate cancer (PCa) incidences vary with genetic, geographical and ethnic dietary background of patients while angiogenesis is modulated through exquisite interplay of tumor-stromal interactions of biological macromolecules. We hypothesized that comprehensive analysis of four biomarkers modulating angiogenesis in PCa progression in two diverse populations might explain the variance in the incidence rates.

RESULTS

Immunohistochemical analysis of 42 PCa biopsies reveals that though Anx-II expression is lost in both the Indian and American population with Gleason scores (GS) ranging between 6 and 10, up to 25 % of cells in the entire high grade (GS > 8) PD PCa samples from US show intense focal membrane staining for Anx-II unlike similarly graded specimens from India. Consistent with this observation, the prostate cancer cell lines PC-3, DU-145 and MDA PCa 2A, but not LNCaP-R, LNCAP-UR or MDA PCa 2B cell lines, express Anx-II. Transcriptional reactivation of Anx-II gene with Aza-dC could not entirely account for loss of Anx-II protein in primary PCa. Cyclooxygenase-2 (COX-2) was moderately expressed in most of high grade PIN and some MD PCa and surrounding stroma. COX-2 was not expressed in PD PCa (GS approximately 7-10), while adjacent smooth muscles cells stained weakly positive. Decorin expression was observed only in high grade PIN but not in any of the prostate cancers, atrophy or BPH while stromal areas of BPH stained intensively for DCN and decreased with advancing stages of PCa. Versican expression was weak in most of the MD PCa, moderate in all of BPH, moderately focal in PD PC, weak and focal in PIN, atrophy and adjacent stroma.

CONCLUSIONS

Expression of pro- and anti-angiogenic modulators changes with stage of PCa but correlates with angiogenic status. Focal membrane staining of Anx-II reappears in high grade PCa specimens only from US indicating differential expression of Anx-II. COX-2 stained stronger in American specimens compared to Indian specimens. The sequential expression of DCN and VCN in progressive stages was similar in specimens from India and USA indicating no population-based differences. The mechanistic and regulatory role of Anx-II in PCa progression warrants further investigation.

Loss of responsiveness to chemotactic factors by deletion of the C-terminal protein interaction site of angiomotin

We have recently identified a novel protein, named angiomotin, by its ability to bind the angiogenesis inhibitor angiostatin in the yeast two-hybrid system. Angiomotin belongs to a family with two other members, AmotL-1 and -2 characterized by coiled-coil and C-terminal PDZ binding domains. Here we show that the putative PDZ binding motif of angiomotin serves as a protein recognition site and that deletion of three amino acids in this site results in inhibition of chemotaxis. Furthermore, endothelial cells expressing mutant angiomotin failed to migrate and form tubes in an in vitro tube formation assay. To study the effect of angiomotin on embryonic angiogenesis, we generated transgenic mice expressing wild-type angiomotin and the C-terminal deletion mutant driven by the endothelial cell-specific receptor tyrosine kinase (TIE) promoter. Expression of mutant angiomotin in endothelial cells inhibited migration into the neuroectoderm and intersomitic regions resulting in death at embryonic day 9.5. In contrast, mice expressing wild-type angiomotin developed normally and were fertile. These results suggest that the putative PDZ binding motif of angiomotin plays a critical role in regulating the responsiveness of endothelial cells to chemotactic cues.

Inhibition of angiogenesis and angiogenesis-dependent tumor growth by the cryptic kringle fragments of human apolipoprotein(a)

Apolipoprotein(a) (apo(a)) contains tandemly repeated kringle domains that are closely related to plasminogen kringle 4, followed by a single kringle 5-like domain and an inactive protease-like domain. Recently, the anti-angiogenic activities of apo(a) have been demonstrated both in vitro and in vivo. However, its effects on tumor angiogenesis and the underlying mechanisms involved have not been fully elucidated. To evaluate the anti-angiogenic and anti-tumor activities of the apo(a) kringle domains and to elucidate their mechanism of action, we expressed the last three kringle domains of apo(a), KIV-9, KIV-10, and KV, in Escherichia coli. The resultant recombinant protein, termed rhLK68, exhibited a dose-dependent inhibition of basic fibroblast growth factor-stimulated human umbilical vein endothelial cell proliferation and migration in vitro and inhibited the neovascularization in chick chorioallantoic membranes in vivo. The ability of rhLK68 to abrogate the activation of extracellular signal-regulated kinases appears to be responsible for rhLK68-mediated anti-angiogenesis. Furthermore, systemic administration of rhLK68 suppressed human lung (A549) and colon (HCT-15) tumor growth in nude mice. Immunohistochemical examination and in situ hybridization analysis of the tumors showed a significant decrease in the number of blood vessels and the reduced expression of vascular endothelial growth factor, basic fibroblast growth factor, and angiogenin, indicating that suppression of angiogenesis may have played a significant role in the inhibition of tumor growth. Collectively, these results suggest that a truncated apo(a), rhLK68, is a potent anti-angiogenic and anti-tumor molecule.