A peptide derived from the nonreceptor binding region of urokinase plasminogen activator (uPA) inhibits tumor progression and angiogenesis and induces tumor cell death in vivo

Urokinase-type plasminogen activator receptor (uPAR) as a therapeutic target in cancer

Urokinase-type plasminogen activator receptor (uPAR) is an attractive target for the treatment of cancer, because it is expressed at low levels in healthy tissues but at high levels in malignant tumours. uPAR is closely related to the invasion and metastasis of malignant tumours, plays important roles in the degradation of extracellular matrix (ECM), tumour angiogenesis, cell proliferation and apoptosis, and is associated with the multidrug resistance (MDR) of tumour cells, which has important guiding significance for the judgement of tumor malignancy and prognosis. Several uPAR-targeted antitumour therapeutic agents have been developed to suppress tumour growth, metastatic processes and drug resistance. Here, we review the recent advances in the development of uPAR-targeted antitumor therapeutic strategies, including nanoplatforms carrying therapeutic agents, photodynamic therapy (PDT)/photothermal therapy (PTT) platforms, oncolytic virotherapy, gene therapy technologies, monoclonal antibody therapy and tumour immunotherapy, to promote the translation of these therapeutic agents to clinical applications.

Therapeutic Strategies Targeting Urokinase and Its Receptor in Cancer

Several studies have ascertained that uPA and uPAR do participate in tumor progression and metastasis and are involved in cell adhesion, migration, invasion and survival, as well as angiogenesis. Increased levels of uPA and uPAR in tumor tissues, stroma and biological fluids correlate with adverse clinic-pathologic features and poor patient outcomes. After binding to uPAR, uPA activates plasminogen to plasmin, a broad-spectrum matrix- and fibrin-degrading enzyme able to facilitate tumor cell invasion and dissemination to distant sites. Moreover, uPAR activated by uPA regulates most cancer cell activities by interacting with a broad range of cell membrane receptors. These findings make uPA and uPAR not only promising diagnostic and prognostic markers but also attractive targets for developing anticancer therapies. In this review, we debate the uPA/uPAR structure-function relationship as well as give an update on the molecules that interfere with or inhibit uPA/uPAR functions. Additionally, the possible clinical development of these compounds is discussed.

Fibrinolytic System and Cancer: Diagnostic and Therapeutic Applications

Fibrinolysis is a crucial physiological process that helps to maintain a hemostatic balance by counteracting excessive thrombosis. The components of the fibrinolytic system are well established and are associated with a wide array of physiological and pathophysiological processes. The aberrant expression of several components, especially urokinase-type plasminogen activator (uPA), its cognate receptor uPAR, and plasminogen activator inhibitor-1 (PAI-1), has shown a direct correlation with increased tumor growth, invasiveness, and metastasis. As a result, targeting the fibrinolytic system has been of great interest in the field of cancer biology. Even though there is a plethora of encouraging preclinical evidence on the potential therapeutic benefits of targeting the key oncogenic components of the fibrinolytic system, none of them made it from “bench to bedside” due to a limited number of clinical trials on them. This review summarizes our existing understanding of the various diagnostic and therapeutic strategies targeting the fibrinolytic system during cancer.

Key Matrix Remodeling Enzymes: Functions and Targeting in Cancer

Tissue functionality and integrity demand continuous changes in distribution of major components in the extracellular matrices (ECMs) under normal conditions aiming tissue homeostasis. Major matrix degrading proteolytic enzymes are matrix metalloproteinases (MMPs), plasminogen activators, atypical proteases such as intracellular cathepsins and glycolytic enzymes including heparanase and hyaluronidases. Matrix proteases evoke epithelial-to-mesenchymal transition (EMT) and regulate ECM turnover under normal procedures as well as cancer cell phenotype, motility, invasion, autophagy, angiogenesis and exosome formation through vital signaling cascades. ECM remodeling is also achieved by glycolytic enzymes that are essential for cancer cell survival, proliferation and tumor progression. In this article, the types of major matrix remodeling enzymes, their effects in cancer initiation, propagation and progression as well as their pharmacological targeting and ongoing clinical trials are presented and critically discussed.

Design and Synthesis of Fragment Derivatives with a Unique Inhibition Mechanism of the uPAR·uPA Interaction

There is substantial interest in the development of small molecules that inhibit the tight and highly challenging protein-protein interaction between the glycophosphatidylinositol (GPI)-anchored cell surface receptor uPAR and the serine protease uPA. While preparing derivatives of a fragment-like compound that previously emerged from a computational screen, we identified compound 5 (IPR-3242), which inhibited binding of uPA to uPAR with submicromolar IC₅₀s. The high inhibition potency prompted us to carry out studies to rule out potential aggregation, lack of stability, reactivity, and nonspecific inhibition. We designed and prepared 16 derivatives to further explore the role of each substituent. Interestingly, the compounds only partially inhibited binding of a fluorescently labeled α-helical peptide that binds to uPAR at the uPAR·uPA interface. Collectively, the results suggest that the compounds bind to uPAR outside of the uPAR·uPA interface, trapping the receptor into a conformation that is not able to bind to uPA. Additional studies will have to be carried out to determine whether this unique inhibition mechanism can occur at the cell surface.

c-Src and EGFR Inhibition in Molecular Cancer Therapy: What Else Can We Improve?

The proto-oncogene c-Src is a non-receptor tyrosine kinase playing a key role in many cellular pathways, including cell survival, migration and proliferation. c-Src de-regulation has been observed in several cancer types, making it an appealing target for drug discovery efforts. Recent evidence emphasizes its crucial role not only in promoting oncogenic traits, but also in the acquisition and maintenance of cancer resistance to various chemotherapeutic or molecular target drugs. c-Src modulates epidermal growth factor receptor (EGFR) activation and amplifies its downstream oncogenic signals. In this review, we report several studies supporting c-Src kinase role in the intricate mechanisms of resistance to EGFR tyrosine kinase inhibitors (TKIs). We further highlighted pre- and clinical progresses of combined treatment strategies made in recent years. Several pre-clinical data have encouraged the use of c-Src inhibitors in combination with EGFR inhibitors. However, clinical trials provided controversial outcomes in some cancer types. Despite c-Src inhibitors showed good tolerability in cancer patients, no incontrovertible and consistent clinical responses were recorded, supporting the idea that a better selection of patients is needed to improve clinical outcome. Currently, the identification of biological markers predictive of therapy response and the accurate molecular screening of cancer patients aimed to gain most clinical benefits become decisive and mandatory.

Therapeutics targeting the fibrinolytic system

The function of the fibrinolytic system was first identified to dissolve fibrin to maintain vascular patency. Connections between the fibrinolytic system and many other physiological and pathological processes have been well established. Dysregulation of the fibrinolytic system is closely associated with multiple pathological conditions, including thrombosis, inflammation, cancer progression, and neuropathies. Thus, molecules in the fibrinolytic system are potent therapeutic and diagnostic targets. This review summarizes the currently used agents targeting this system and the development of novel therapeutic strategies in experimental studies. Future directions for the development of modulators of the fibrinolytic system are also discussed.

The fibrinolytic system was originally identified to dissolve blood clots, and is shown to have important roles in other pathological processes, including cancer progression, inflammation, and thrombosis. Molecules or therapeutics targeting fibrinolytic system have been successfully used in the clinical treatments of cancer and thrombotic diseases. The clinical studies and experimental models targeting fibrinolytic system are reviewed by Haili Lin at Sanming First Hosipital, Mingdong Huang at Fuzhou University in China, and Peng Xu at A*STAR in Singapore to demonstrate fibrinolytic system as novel therapeutic targets. As an example, the inhibition of fibrinolytic system protein can be used to suppress cancer prolifieration and metastasis. This review also discusses the potential therapeutic effects of inhibitiors of fibrinolytic system on inflammatory disorders.

Proteolysis is the most fundamental property of malignancy and its inhibition may be used therapeutically (Review)

The mortality rates of cancer patients decreased by ~1.5% per year between 2001 and 2015, although the decrease depends on patient sex, ethnic group and type of malignancy. Cancer remains a significant global health problem, requiring a search for novel treatments. The most common property of malignant tumors is their capacity to invade adjacent tissue and to metastasize, and this cancer aggressiveness is contingent on overexpression of proteolytic enzymes. The components of the plasminogen activation system (PAS) and the metal-loproteinase family [mainly matrix metalloproteinases (MMPs)] are overexpressed in malignant tumors, driving the local invasion, metastasis and angiogenesis. This is the case for numerous types of cancer, such as breast, colon, prostate and oral carcinoma, among others. Present chemotherapeutics agents typically attack all dividing cells; however, for future therapeutic agents to be clinically successful, they need to be highly selective for a specific protein(s) and act on the cancerous tissues without adverse systemic effects. Inhibition of proteolysis in cancerous tissue has the ability to attenuate tumor invasion, angiogenesis and migration. For that purpose, inhibiting both PAS and MMPs may be another approach, since the two groups of enzymes are overexpressed in cancer. In the present review, the roles and new findings on PAS and MMP families in cancer formation, growth and possible treatments are discussed.

Multifaceted Role of the Urokinase-Type Plasminogen Activator (uPA) and Its Receptor (uPAR): Diagnostic, Prognostic, and Therapeutic Applications

The plasminogen activator (PA) system is an extracellular proteolytic enzyme system associated with various physiological and pathophysiological processes. A large body of evidence support that among the various components of the PA system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) play a major role in tumor progression and metastasis. The binding of uPA with uPAR is instrumental for the activation of plasminogen to plasmin, which in turn initiates a series of proteolytic cascade to degrade the components of the extracellular matrix, and thereby, cause tumor cell migration from the primary site of origin to a distant secondary organ. The components of the PA system show altered expression patterns in several common malignancies, which have identified them as ideal diagnostic, prognostic, and therapeutic targets to reduce cancer-associated morbidity and mortality. This review summarizes the various components of the PA system and focuses on the role of uPA-uPAR in different biological processes especially in the context of malignancy. We also discuss the current state of knowledge of uPA-uPAR-targeted diagnostic and therapeutic strategies for various malignancies.

A novel peptide blocking cancer cell invasion by structure-based drug design

The receptor for the urokinase-type plasminogen activator (uPA), uPAR, facilitates tumor cell invasion and metastasis by focusing on several ligands, including uPA, integrins and vitronectin. With computational prediction algorithms and structure-based drug design, we identified peptides containing the Gly-Lys-Gly-Glu-Gly-Glu-Gly-Lys-Gly sequence (peptide H1), which strongly interacts with uPAR. The aim of the present study was to investigate the effect of allosteric inhibition at the uPAR interface using a novel synthetic peptide and its function on ovarian cancer cell invasion. The molecular and functional mechanisms of H1 were determined by complementary biochemical and biological methods in the promyeloid U937 cell line as well as ovarian cancer cell lines, including serous carcinoma SKOV3 and clear cell carcinoma TOV21G. The effects of H1 treatment on cancer cell invasion were evaluated in vitro. H1 inhibited cancer cell invasion, without affecting cell viability, accompanied by the suppression of extracellular signal-regulated kinase (ERK)-1 phosphorylation and then matrix metalloproteinase (MMP)-9 expression. H1 failed to block the interaction of uPA-uPAR protein-protein interaction in cells, but antagonized the uPA function. H1 failed to disrupt the uPA-uPAR complex, but abolished the invasion of ovarian cancer cells at least through suppression of the ERK-MMP-9 signaling pathway. Further studies are needed to confirm our observations and to describe the underlying molecular mechanism.

uPA-derived peptide, Å6 is involved in the suppression of lipopolysaccaride-promoted inflammatory osteoclastogenesis and the resultant bone loss

Introduction

Chronic inflammatory diseases such as rheumatoid arthritis and periodontitis frequently cause bone destruction. Inflammation‐induced bone loss results from the increase of bone‐resorbing osteoclasts. Recently, we demonstrated that urokinase type plasminogen activator (uPA) suppressed lipopolysaccaride (LPS)‐inflammatory osteoclastogenesis through the adenosine monophosphate‐activated protein kinase (AMPK) pathway, whereas its receptor (uPAR) promoted that through the Akt pathway.

Methods

We investigated the effects of uPA‐derived peptide (Å6) in the LPS‐induced inflammatory osteoclastogenesis and bone destruction.

Results

We found that Å6 attenuated inflammatory osteoclastogenesis and bone loss induced by LPS in mice. We also showed that Å6 attenuated the LPS‐promoted inflammatory osteoclastogenesis by inactivation of NF‐κB in RAW264.7 mouse monocyte/macrophage lineage cells. Furthermore, we showed that Å6 attenuated the Akt phosphorylation, and promoted the AMPK phosphorylation.

Conclusion

Å6 is involved in the suppression of LPS‐promoted inflammatory osteoclastgensis and bone destruction by regulating the AMPK and Akt pathways. These findings provide a basis for clinical strategies to improve the bone loss caused by inflammatory diseases.

Short peptides interfering with signaling pathways as new therapeutic tools for cancer treatment

Short peptides have many advantages, such as low molecular weight, selectivity for a specific target, organelles or cells with minimal toxicity. We describe properties of short peptides, which interfere with communication networks in tumor cells and within microenvironment of malignant gliomas, the most common brain tumors. We focus on ligand/receptor axes and intracellular signaling pathways critical for gliomagenesis that could be targeted with interfering peptides. We review structures and efficacy of organelle-specific and cell-penetrating peptides and describe diverse chemical modifications increasing proteolytic stability and protecting synthetic peptides against degradation. We report results of application of short peptides in glioma therapy clinical trials, their rises and falls. The most advanced examples of therapeutics such as short interfering peptides combined with cell-penetrating peptides that show good effectiveness in disease models are presented. It is foreseen that identification of peptides with better clinical properties may improve their success rates in clinical trials.

Size changeable nanosystems for precise drug controlled release and efficient overcoming of cancer multidrug resistance

Herein we demonstrate the rational design of a size changeable nanosystem for precise drug controlled release and efficient overcoming of cancer multidrug resistance in cancer cells by enhancing the cellular uptake and inhibiting the expression of ABC family proteins.

uPAR enhances malignant potential of triple-negative breast cancer by directly interacting with uPA and IGF1R

BACKGROUND

Due to lack of a targeted therapy for the triple-negative breast cancer (TNBC) patients, it is important to explore this aggressive breast cancer type in more detail and to establish novel therapeutic approaches. TNBC is defined negative for the protein expression of oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). One prominent feature of this cancer type is the frequent overexpression of major components of the urokinase-type plasminogen activator system (uPAS) including uPA, its receptor uPAR and the inhibitor PAI-1, which may be valuable as therapeutic targets.

METHODS

Direct interactions of uPAR with interactors were demonstrated by immunoprecipitations and proximity ligation assays. For stable knockdowns of target proteins, lentiviral vectors were used and the effects were analysed by immunoblottings and using in vitro cell viability, migration and invasion assays. Immunohistochemical and statistical analyses of biomarkers and clinical parameters were conducted in a TNBC cohort (n = 174).

RESULTS

Direct tumour-promoting interactions of uPAR with uPA and the insulin-like growth factor receptor 1 (IGF1R) were shown in TNBC cells and these interactions were significantly reduced (p = 0.001) when uPAR was downregulated. The combined knockdown of uPAR and uPA or IGF1R additively and significantly reduced cell viability, migration and invasion of the model cell lines. In TNBC tissue, the complexes formed by uPAR with uPA or with IGF1R significantly correlated with the histological grade (p = 0.0019) as well as with cathepsin B and D (p ≤ 0.0001) that are implicated in cell invasion and metastasis.

CONCLUSIONS

Our outcomes show that not only overexpressed biomarkers promote tumourigenesis, but rather their interactions further potentiate tumour progression. This study emphasises the potential of combined approaches targeting uPAR and its interactors with regard to an improved therapy of TNBC.

A novel uPAg-KPI fusion protein inhibits the growth and invasion of human ovarian cancer cells in vitro

Urokinase-type plasminogen activator (uPA) acts by breaking down the basement membrane and is involved in cell proliferation, migration and invasion. These actions are mediated by binding to the uPA receptor (uPAR) via its growth factor domain (GFD). The present study evaluated the effects of uPAg-KPI, a fusion protein of uPA-GFD and a kunitz protease inhibitor (KPI) domain that is present in the amyloid β-protein precursor. Using SKOV-3 cells, an ovarian cancer cell line, we examined cell viability, migration, invasion and also protein expression. Furthermore, we examined wound healing, and migration and invasion using a Transwell assay. Our data showed that uPAg-KPI treatment reduced the viability of ovarian cancer SKOV-3 cells in both a concentration and time-dependent manner by arresting tumor cells at G1/G0 phase of the cell cycle. The IC₅₀ of uPAg-KPI was 0.5 µg/µl after 48 h treatment. At this concentration, uPAg-KPI also inhibited tumor cell colony formation, wound closure, as well as cell migration and invasion capacity. At the protein level, western blot analysis demonstrated that uPAg-KPI exerted no significant effect on the expression of total extracellular signal-regulated kinase (ERK)1/ERK2 and AKT, whereas it suppressed levels of phosphorylated ERK1/ERK2 and AKT. Thus, we suggest that this novel uPAg-KPI fusion protein reduced cell viability, colony formation, wound healing and the invasive ability of human ovarian cancer SKOV-3 cells in vitro by regulating ERK and AKT signaling. Further studies using other cell lines will confirm these findings.

Modulation of CD44 Activity by A6-Peptide

Hyaluronan (HA) is a non-sulfated glycosaminoglycan distributed throughout the extracellular matrix that plays a major role in cell adhesion, migration, and proliferation. CD44, a multifunctional cell surface glycoprotein, is a receptor for HA. In addition, CD44 is known to interact with other receptors and ligands, and to mediate a number of cellular functions as well as disease progression. Studies have shown that binding of HA to CD44 in cancer cells activates survival pathways resulting in cancer cell survival. This effect can be blocked by anti-CD44 monoclonal antibodies. A6 is a capped, eight l-amino acid peptide (Ac-KPSSPPEE-NH2) derived from the biologically active connecting peptide domain of the serine protease, human urokinase plasminogen activator (uPA). A6 neither binds to the uPA receptor (uPAR) nor interferes with uPA/uPAR binding. A6 binds to CD44 resulting in the inhibition of migration, invasion, and metastasis of tumor cells, and the modulation of CD44-mediated cell signaling. A6 has been shown to have no dose-limiting toxicity in animal studies. A6 has demonstrated efficacy and an excellent safety profile in Phase 1a, 1b, and 2 clinical trials. In animal models, A6 has also exhibited promising results for the treatment of diabetic retinopathy and wet age-related macular degeneration through the reduction of retinal vascular permeability and inhibition of choroidal neovascularization, respectively. Recently, A6 has been shown to be directly cytotoxic for B-lymphocytes obtained from patients with chronic lymphocytic leukemia expressing the kinase, ZAP-70. This review will discuss the activity of A6, A6 modulation of HA and CD44, and a novel strategy for therapeutic intervention in disease.

Small-molecule inhibition of the uPAR·uPA interaction: synthesis, biochemical, cellular, in vivo pharmacokinetics and efficacy studies in breast cancer metastasis

The uPAR·uPA protein-protein interaction (PPI) is involved in signaling and proteolytic events that promote tumor invasion and metastasis. A previous study had identified 4 (IPR-803) from computational screening of a commercial chemical library and shown that the compound inhibited uPAR·uPA PPI in competition biochemical assays and invasion cellular studies. Here, we synthesize 4 to evaluate in vivo pharmacokinetic (PK) and efficacy studies in a murine breast cancer metastasis model. First, we show, using fluorescence polarization and saturation transfer difference (STD) NMR, that 4 binds directly to uPAR with sub-micromolar affinity of 0.2 μM. We show that 4 blocks invasion of breast MDA-MB-231, and inhibits matrix metalloproteinase (MMP) breakdown of the extracellular matrix (ECM). Derivatives of 4 also inhibited MMP activity and blocked invasion in a concentration-dependent manner. Compound 4 also impaired MDA-MB-231 cell adhesion and migration. Extensive in vivo PK studies in NOD-SCID mice revealed a half-life of nearly 5h and peak concentration of 5 μM. Similar levels of the inhibitor were detected in tumor tissue up to 10h. Female NSG mice inoculated with highly malignant TMD-MDA-MB-231 in their mammary fat pads showed that 4 impaired metastasis to the lungs with only four of the treated mice showing severe or marked metastasis compared to ten for the untreated mice. Compound 4 is a promising template for the development of compounds with enhanced PK parameters and greater efficacy.

A phase II study of a urokinase-derived peptide (A6) in the treatment of persistent or recurrent epithelial ovarian, fallopian tube, or primary peritoneal carcinoma: a Gynecologic Oncology Group study

PURPOSE

This multi-institutional phase II trial assessed the activity and tolerability of the anti-metastatic A6 peptide that binds CD44 in patients with persistent or recurrent epithelial ovarian, fallopian tube, or primary peritoneal carcinoma (EOC/FTC/PPC).

PATIENTS AND METHODS

Women with persistent or recurrent EOC/FTC/PPC were eligible for participation if they had measurable disease defined by RECIST criteria, good performance status, and good overall organ function. Patients must have received one prior platinum-based chemotherapeutic regimen and were allowed to have received one additional cytotoxic regimen for the management of recurrent or persistent disease. Women received a 150 mg twice daily subcutaneous dose of A6 and continued on treatment until disease progression or unacceptable toxicity. Primary measures of clinical efficacy were objective tumor response and progression-free survival (PFS) at 6 months. The association of CD44 in archival tissue specimens with clinical outcome was investigated.

RESULTS

Thirty-one eligible patients were evaluated. No responses were observed. Two patients (6.5%) were progression free for at least 6 months. The median PFS was 2.0 months, and median overall survival has not yet been reached. One patient died of hemorrhage which was possibly study related. There were no grade 4 toxicities. The most common grade 3 toxicities were constitutional (2/31; 6.5%). Archival specimens were available for 27 patients, and 5 (18.5%) were CD44 positive by immunohistochemistry. CD44 expression was not associated with the 6-month PFS (p=0.342).

CONCLUSION

A6 was well tolerated but had minimal activity in patients with persistent or recurrent EOC/FTC/PPC.

Knockdown of VEGF receptor-1 (VEGFR-1) impairs macrophage infiltration, angiogenesis and growth of clear cell renal cell carcinoma (CRCC)

Angiogenesis is essential for tumor growth and metastasis. VEGF has been shown to be a central player in this process. The biological activity of VEGF is mainly mediated by two tyrosine kinase receptors, VEGFR-1 and VEGFR-2. While increasing evidence suggests that VEGF/VEGFR-1 signaling is crucial for tumor angiogenesis, its molecular mechanism is not well understood. Here we show that VEGFR-1 knockdown dramatically inhibits tumor growth. This inhibition is associated with significant decrease of tumor VEGF levels and tumor angiogenesis as well as an increased tumor necrosis. Moreover, we demonstrate that VEGF in CRCC tumors is mainly produced by tumor stromal cells instead of the tumor cells themselves. It has been shown that macrophages constitute a significant part of tumor stromal cells and produce a large amount of VEGF. We therefore examined the macrophage infiltration in the xenograft tumors. Remarkably, VEGFR-1 knockdown attenuates the tumor macrophages infiltration. To understand the mechanism, we investigated the impact of VEGFR-1 knockdown on the expression of monocyte chemoattractant protein-1 (MCP-1), one of the main chemoattractants for macrophages. Significantly, VEGFR-1 knockdown inhibits MCP-1 expression of CRCC cells. Taken together, these data indicate that VEGF/VEGFR-1 signaling plays an essential role in initiating tumor angiogenesis by regulating MCP-1 expression, which in turn, attracts macrophages infiltration and VEGF production. Thus, these studies suggest that blockade of VEGFR-1 function may provide a tumor-specific, VEGF-based therapeutic strategy for treatment of CRCC.

Cancer therapy trials employing level-of-evidence-1 disease forecast cancer biomarkers uPA and its inhibitor PAI-1

Clinical research on cancer biomarkers is essential in understanding recent discoveries in cancer biology and heterogeneity of the cancer disease. However, there are only a few examples of clinically useful studies that have identified cancer biomarkers with clinical benefit. Urokinase-type plasminogen activator (uPA) and its inhibitor plasminogen activator inhibitor type 1 (PAI-1) are two of the few tumor tissue-associated cancer biomarkers that have been evaluated successfully and extensively in many preclinical and clinical studies for their clinical utility. Most of the studies have been conducted in early breast cancer to demonstrate the prognostic and predictive value for this malignancy. As a result of these investigations, uPA and PAI-1 have reached the highest level of clinical evidence, level of evidence 1. This article sheds light on the current status of major clinical Phase II and III breast cancer therapy trials (Chemo-N0, NNBC-3 and Plan B), and introduces ongoing clinical trials targeting uPA in advanced cancers of the breast and pancreas, employing synthetic small-size drugs to counteract uPA activity (WX-UK1, Mesupron(®)). The therapeutic effect of a uPA-derived small-size synthetic peptide (Å6) is tested in advanced ovarian cancer patients.

SR16388: a steroidal antiangiogenic agent with potent inhibitory effect on tumor growth in vivo

Angiogenesis is one of the major processes controlling growth and metastasis of tumors. Angiogenesis inhibitors have been targeted for the treatment of various cancers for more than 2 decades. We have developed a novel class of steroidal compounds aimed at blocking the angiogenic process in cancerous tissues. Our lead compound, SR16388, is a potent antiangiogenic agent with binding affinity to estrogen receptor-α (ER-α) and -β (ER-β) at the nanomolar range. This compound inhibited the proliferation of human microvascular endothelial cells (HMVEC) and various types of human cancer cells in vitro. SR16388 inhibited embryonic angiogenesis as measured in the chick chorioallantoic membrane (CAM) assay. The blood vessel density in the CAM was greatly reduced after the embryos were treated with 3 μg/CAM of SR16388 for 24 h. SR16388 at a dose of 2 μM prevented tube formation in Matrigel after HMVEC cells were treated for 8 h. In a modified Boyden chamber assay, SR16388 inhibited the migration of HMVECs by 80% at 500 nM. Using a novel in vivo Fibrin Z-chamber model, we demonstrated that SR16388 at a single daily oral dose of 3 mg/kg for 12 days significantly inhibited the granulation tissue (GT) thickness and the microvessel density of the GT as compared to control. More importantly, SR16388 down-regulated the pro-angiogenic transcription factors, hypoxia inducible factor 1α (HIF-1α) and signal transducer and activator of transcription 3 (STAT3) in non-small cell lung cancer (NSCLC) cells. Together, these effects of SR16388 can lead to the reduction of vascularization and tumor growth in vivo.

Modulators of the urokinase-type plasminogen activation system for cancer

IMPORTANCE OF THE FIELD

The serine protease urokinase-type plasminogen activator (uPA) and its receptor uPAR as well as two specific inhibitors, the plasminogen activator inhibitor type-1 (PAI-1) and type-2 (PAI-2), are involved in the control of extracellular matrix turnover and tumor growth. Data accumulating over the past 20 years have made increasingly clear that the uPA system has a multifunctional role in neoplastic evolution, affecting cancer cell proliferation, tumor angiogenesis, adhesion and migration.

AREAS COVERED IN THIS REVIEW

Several therapeutic strategies inhibiting the uPA system have been or are currently being developed for suppression of tumor growth. This review examines the role of the uPA system in tumor progression and assesses the various therapeutic strategies developed to selectively exploit this system.

WHAT WILL THE READER GAIN

We focus on the therapeutic developments of the last 15 years. In addition to antibodies and recombinant uPA- or uPAR-derived proteins, various antagonistic peptides as well as small molecules have been designed and synthesized that inhibit the uPA system, leading to reduced tumor progression.

TAKE HOME MESSAGE

The multifunctional potential of the uPA system in cancer has rendered this system an attractive novel target for anticancer therapy. A few novel tumor biology-based therapeutic strategies reported here, opening new ways for patient-optimized and individualized cancer therapy. It may be the right time to evaluate the hypothesis that the uPA system plays a pivotal role in cancer progression and that targeting this system will lead to clinical benefit in cancer patients.

Immunohistochemical analysis of urokinase plasminogen activator and its prognostic value in canine mammary tumours

Urokinase plasminogen activator (uPA) has been associated with aggressive behaviour and poor prognosis in human breast cancer, but there is no information on its expression in canine mammary tumours (CMT). uPA immunohistochemical expression was studied in 119 CMT (24 benign, 95 malignant) to investigate its relationship with clinical and histopathological parameters. Dogs with malignant mammary tumours (MMT) underwent a 2-year follow-up evaluation. MMT expressed significantly more uPA than benign tumours. In MMT, high uPA stromal expression was significantly associated with larger tumour size, high Ki-67 expression, invasive growth, high histological grade, regional lymph node metastases, development of distant metastases, and lower overall survival (OS) and disease-free survival (DFS). On the basis of these results, uPA could be considered a useful prognostic factor in dogs with MMT.

Inhibition of urokinase activity reduces primary tumor growth and metastasis formation in a murine lung carcinoma model

RATIONALE

Lung cancer is the most common malignancy in humans. Urokinase (uPA) plays a crucial role in carcinogenesis by facilitating tumor cell invasion and metastasis.

OBJECTIVES

We investigated the effect of the highly specific urokinase inhibitor CJ-463 (benzylsulfonyl-D-Ser-Ser-4-amidinobenzylamide) on tumor growth, metastasis formation, and tumor vascularization in the murine Lewis lung carcinoma (LLC) and a human small lung cancer model.

METHODS

A quantity of 3 x 10(6) LLC cells were subcutaneously injected into the right flank of C57Bl6/N mice, uPA knock out, and uPA receptor knockout mice. Seven days later mice were randomized to receive intraperitoneally either saline (control group), CJ-463 (10 and 100 mg/kg, twice a day), or its ineffective stereoisomer (10 mg/kg, twice a day). Tumor volume was measured every second day and metastasis formation was monitored by volumetric-computed tomography. Twelve days after onset of treatment mice were killed and tumors were prepared for histologic examination.

MEASUREMENTS AND MAIN RESULTS

Treatment with CJ-463 resulted in a significant inhibition of primary tumor growth, with the highest efficacy seen in the 100 mg/kg group. In addition, histological analysis of the lung revealed a significant reduction in lung micrometastasis in the 100 mg/kg group. Similarly, a reduced seeding of tumor cells into the lung after intravenous injection of LLC cells was observed in inhibitor-treated mice. In these mice, treatment with CJ-463 appeared not to significantly alter the relative extent of tumor vascularization. In vitro, proliferation of LLC cells remained unchanged upon inhibitor treatment. CJ-463 was found to similarly reduce tumor growth in uPA receptor knockout mice, but was ineffective in uPA knockout mice.

CONCLUSIONS

Our results suggest that synthetic low-molecular-weight uPA-inhibitors offer as novel agents for treatment of lung cancer.

Role of Urokinase Inhibitors in Choroidal Neovascularization

Cell migration is a critical step in the angiogenesis cascade that involves proteolysis of the basement membrane and extracellular matrix around existing blood vessels. The urokinase plasminogen activator (uPA) system has been involved in cellular invasion, angiogenesis and tumor growth. Similar expression of urokinase and its receptor (uPAR) is seen in both retinal and choroidal neovascularization. Significant inhibition of choroidal neovascularization (CNV) has been observed when cell surface associated uPA-uPAR activity is prevented with a specific inhibitor of this proteinase system. As the current treatments of CNV are not optimal, the urokinase-uPAR system appears to be an attractive target for alternative pharamacological therapy for CNV.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Selective inhibition of matrix metalloproteinase-14 blocks tumor growth, invasion, and angiogenesis

Inhibition of specific matrix metalloproteinases (MMP) is an attractive noncytotoxic approach to cancer therapy. MMP-14, a membrane-bound zinc endopeptidase, has been proposed to play a central role in tumor growth, invasion, and neovascularization. Besides cleaving matrix proteins, MMP-14 activates proMMP-2 leading to an amplification of pericellular proteolytic activity. To examine the contribution of MMP-14 to tumor growth and angiogenesis, we used DX-2400, a highly selective fully human MMP-14 inhibitory antibody discovered using phage display technology. DX-2400 blocked proMMP-2 processing on tumor and endothelial cells, inhibited angiogenesis, and slowed tumor progression and formation of metastatic lesions. The combination of potency, selectivity, and robust in vivo activity shows the potential of a selective MMP-14 inhibitor for the treatment of solid tumors.

A phase 2, randomized, double-blind, placebo-controlled trial of clinical activity and safety of subcutaneous A6 in women with asymptomatic CA125 progression after first-line chemotherapy of epithelial ovarian cancer

OBJECTIVES

A6 is a novel peptide that interferes with single-chain urokinase plasminogen activator activity and has shown anti-angiogenic, anti-migratory, and anti-invasive properties. We evaluated clinical efficacy and safety of subcutaneously administered A6 in women with epithelial ovarian cancer.

METHODS

Women with epithelial ovarian, fallopian tube, or primary peritoneal cancer in clinical remission after first-line chemotherapy with 2 consecutive increases of CA125 values above normal but with no disease on physical examination or imaging studies were randomly assigned to receive daily subcutaneous injections of placebo, low-dose A6 (150 mg), or high-dose A6 (300 mg) until disease progression or end of study participation. Primary endpoints were time to clinical progression of disease and safety of A6. Secondary endpoints were changes in serum CA125 and biomarkers of the urokinase system.

RESULTS

Data are available for 24 women (placebo, n=12; low-dose, n=8; high-dose n=4). A6 therapy was associated with a statistically significant delay in time to clinical progression (log-rank p-value 0.01) with a median of 100 days (95% CI: 64,168) for women who received A6 compared with 49 days (95% CI: 29,67) for women who received placebo. The treatments appeared to be well tolerated. Treatment was not associated with CA125 response (p=0.44). On-treatment values for plasma urokinase plasminogen activator receptor were statistically significantly lower in the A6 groups compared with placebo (p=0.02).

CONCLUSIONS

A6 therapy increases time to clinical disease progression and appears to be well tolerated in this patient population.

PEGylated DX-1000: pharmacokinetics and antineoplastic activity of a specific plasmin inhibitor

Novel inhibitors of the urokinase-mediated plasminogen (plg) activation system are potentially of great clinical benefit as anticancer treatments. Using phage display, we identified DX-1000 a tissue factor pathway inhibitor-derived Kunitz domain protein which is a specific high-affinity inhibitor of plasmin (pln) (K(i) = 99 pM). When tested in vitro, DX-1000 blocks plasmin-mediated pro-matrix metalloproteinase-9 (proMMP-9) activation on cells and dose-dependently inhibits tube formation, while not significantly affecting hemostasis and coagulation. However, this low-molecular weight protein inhibitor ( approximately 7 kDa) exhibits rapid plasma clearance in mice and rabbits, limiting its potential clinical use in chronic diseases. After site-specific PEGylation, DX-1000 retains its activity and exhibits a decreased plasma clearance. This PEGylated derivative is effective in vitro, as well as potent in inhibiting tumor growth of green fluorescent protein (GFP)-labeled MDA-MB-231 cells. 4PEG-DX-1000 treatment causes a significant reduction of urokinase-type plasminogen activator (uPA) and plasminogen expressions, a reduction of tumor proliferation, and vascularization. 4PEG-DX-1000 treatment significantly decreases the level of active mitogen-activated protein kinase (MAPK) in the primary tumors and reduces metastasis incidence. Together, our results demonstrate the potential value of plasmin inhibitors as therapeutic agents for blocking breast cancer growth and metastasis.

RNAi-mediated downregulation of urokinase plasminogen activator receptor and matrix metalloprotease-9 in human breast cancer cells results in decreased tumor invasion, angiogenesis and growth

The serine protease urokinase-type plasminogen activator (uPA) plays a significant role in tumor cell invasion and metastasis when bound to its specific receptor, uPAR (also known as CD87). In addition to the uPA-uPAR system, matrix metalloproteinases (MMPs) are involved in tumor cell invasion and metastasis. In this study, we achieved specific inhibition of uPAR and MMP-9 using RNAi technology. We introduced small interfering RNA to downregulate the expression of uPAR and MMP-9 (pUM) in breast cancer cell lines (MDA MB 231 and ZR 75 1). In vitro angiogenesis studies indicated a decrease in the angiogenic potential of the treated cells; in particular, a remarkable decrease was observed in the cells treated with bicistronic construct (pUM) in comparision to the controls. Additionally, bicistronic construct inhibited the formation of capillary-like structures in in vivo models of angiogenesis. Similarly, the invasive potential and migration decreased dramatically when treated with the bicistronic construct as shown by matrigel invasion and migration assays. These results suggest a synergistic effect from the simultaneous downregulation of uPAR and MMP-9. We also assessed the levels of phosphorylated forms of MAPK, ERK and AKT signaling pathway molecules and found reduction in the levels of these molecules in cells treated with the bicistronic construct as compared to the control cells. Furthermore, targeting both uPAR and MMP-9 totally regressed orthotopic breast tumors in nude mice. In conclusion, our results provide evidence that the simultaneous downregulation of uPAR and MMP-9 using RNAi technology may provide an effective tool for breast cancer therapy.

Deciphering the molecular basis of breast cancer metastasis with mouse models

Breast cancer begins as a localized disease, but has the potential to spread to distant sites within the body. This process--known as metastasis--is the leading cause of death from breast cancer. Whether the ability of cancer cells to metastasize is an intrinsic or acquired feature is currently a topic of considerable debate. Nevertheless, the key cellular events required for metastasis are generally accepted. These include invasion of the surrounding stromal tissue, intravasation, evasion of programmed cell death, arrest within the vasculature at a distant site, extravasation, and establishment and growth within a new microenvironment. The development of mouse models that faithfully mimic critical aspects of human neoplasia has been instrumental in framing our current understanding of multistage carcinogenesis. This review examines the advantages and limitations of existing murine models for mammary carcinogenesis for probing the molecular mechanisms that contribute to metastasis, as well as non-invasive tumor imaging approaches to facilitate these investigations.

A Src/Abl Kinase Inhibitor, SKI-606, Blocks Breast Cancer Invasion, Growth, and MetastasisIn vitroandIn vivo

The central role of Src in the development of several malignancies, including breast cancer, and the accumulating evidence of its interaction with receptor tyrosine kinases, integrins, and steroid receptors have identified it as an attractive therapeutic target. In the current study, we have evaluated the effect of a Src/Abl kinase inhibitor, SKI-606, on breast cancer growth, migration, invasion, and metastasis. Treatment of human breast cancer cells MDA-MB-231 with SKI-606 caused a marked inhibition of cell proliferation, invasion, and migration by inhibiting mitogen-activated protein kinase and Akt phosphorylation. For in vivo studies, MDA-MB-231 cells transfected with the plasmid encoding green fluorescent protein (GFP; MDA-MB-231-GFP) were inoculated into the mammary fat pads of female BALB/c nu/nu mice. Once tumor volume reached 30 to 50 mm(3), animals were randomized and treated with vehicle alone or 150 mg/kg SKI-606 by daily oral gavage. Experimental animals receiving SKI-606 developed tumors of significantly smaller volume (45-54%) compared with control animals receiving vehicle alone. Analysis of lungs, liver, and spleen of these animals showed a significant decrease in GFP-positive tumor metastasis in animals receiving SKI-606 at a dose that was well tolerated. Western blot analysis and immunohistochemical analysis of primary tumors showed that these effects were due to the ability of SKI-606 to block tumor cell proliferation, angiogenesis, growth factor expression, and inhibition of Src-mediated signaling pathways in vivo. Together, the results from these studies provide compelling evidence for the role of Src inhibitors as therapeutic agents for blocking breast cancer growth and metastasis.

A non-RGD-based integrin binding peptide (ATN-161) blocks breast cancer growth and metastasis in vivo

PURPOSE

Integrins are expressed by numerous tumor types including breast cancer, in which they play a crucial role in tumor growth and metastasis. In this study, we evaluated the ability of ATN-161 (Ac-PHSCN-NH2), a 5-mer capped peptide derived from the synergy region of fibronectin that binds to alpha5beta1 and alphavbeta3 in vitro, to block breast cancer growth and metastasis.

EXPERIMENTAL DESIGN

MDA-MB-231 human breast cancer cells were inoculated s.c. in the right flank, or cells transfected with green fluorescent protein (MDA-MB-231-GFP) were inoculated into the left ventricle of female BALB/c nu/nu mice, resulting in the development of skeletal metastasis. Animals were treated with vehicle alone or by i.v. infusion with ATN-161 (0.05-1 mg/kg thrice a week) for 10 weeks. Tumor volume was determined at weekly intervals and tumor metastasis was evaluated by X-ray, microcomputed tomography, and histology. Tumors were harvested for histologic evaluation.

RESULT

Treatment with ATN-161 caused a significant dose-dependent decrease in tumor volume and either completely blocked or caused a marked decrease in the incidence and number of skeletal as well as soft tissue metastases. This was confirmed histologically as well as radiographically using X-ray and microcomputed tomography. Treatment with ATN-161 resulted in a significant decrease in the expression of phosphorylated mitogen-activated protein kinase, microvessel density, and cell proliferation in tumors grown in vivo.

CONCLUSION

These studies show that ATN-161 can block breast cancer growth and metastasis, and provides a rationale for the clinical development of ATN-161 for the treatment of breast cancer.

Antiprotease therapy in cancer: hot or not?

The activity of a set of peptidases (proteases) involved in cancer progression is collectively known as the cancer 'degradome'. Invasion and metastasis were initially considered as late events in cancer development and the processes in which proteases were involved. However, recent studies indicate that invasion and metastasis are not late events, but can occur during early stages as well. Moreover, other processes occurring in various stages of cancer progression are also protease-dependent, such as (upregulation of) cell proliferation, (downregulation of) apoptosis, involvement of white blood cells, angiogenesis and induction of multi-drug resistance. Proteolytic activity in tumours is regulated in a complex manner, as both genetically unstable cancer cells and stable stromal cells, such as fibroblasts, endothelial cells and inflammatory cells, are involved. In vitro studies and studies using animal models have clearly shown protease dependency of many processes in carcinogenesis. However, clinical trials using protease inhibitors have thus far been unsuccessful except for a few applications of matrix metalloprotease (MMP) inhibitors when used in combination with cytostatic anticancer agents and/or in the early stages of cancer. Antithrombotics, such as low-molecular-weight heparin and warfarin, were also successful in clinical trials, probably by interfering with proteases of the coagulation cascade. The two-way association between cancer and thrombosis has long been recognised in the clinic. The poor outcome of other clinical trials of protease inhibitors is probably due to the late stages of cancer of the patient populations included, and the limited understanding of the complex regulation and effects of the activity of the various proteases in tumours depending on, among others, tumour type and stage, interactions between the cancer cells, other cells and the extracellular matrix in tumours. Therefore, a better fundamental understanding of the proteolytic complexity in tumours is essential before clinical trials can be rationally designed. At present, antithrombotics, the urokinase-type plasminogen activator system, the membrane-bound membrane-type 1-MMP, cathepsin L and the proteasome seem the most promising candidates as targets for anticancer strategies in early stages of cancer in combination with cytotoxic drugs. Moreover, metronomic therapy is an attractive approach using low doses of inhibitors for prolonged periods of time without interruption to specifically target endothelial cells that are involved in angiogenesis.

Targeting of urokinase plasminogen activator receptor in human pancreatic carcinoma cells inhibits c-Met- and insulin-like growth factor-I receptor-mediated migration and invasion and orthotopic tumor growth in mice

Pancreatic carcinomas express high levels of urokinase-type plasminogen activator (uPA) and its receptor (uPAR), both of which mediate cell migration and invasion. We investigated the hypotheses that (a) insulin-like growth factor-I (IGF-I)- and hepatocyte growth factor (HGF)-mediated migration and invasion of human pancreatic carcinoma cells require uPA and uPAR function and (b) inhibition of uPAR inhibits tumor growth, retroperitoneal invasion, and hepatic metastasis of human pancreatic carcinomas in mice. Using transwell assays, we investigated the effect of IGF-I and HGF on L3.6pl migration and invasion. We measured the induction of uPA and uPAR following treatment of cells with IGF-I and HGF using immunoprecipitation and Western blot analysis. The importance of uPA and uPAR on L3.6pl cell migration and invasion was studied by inhibiting their activities with amiloride and antibodies before cytokine treatment. In an orthotopic mouse model of human pancreatic carcinoma, we evaluated the effect of anti-uPAR monoclonal antibodies with and without gemcitabine on primary tumor growth, retroperitoneal invasion, and hepatic metastasis. IGF-I and HGF mediated cell migration and invasion in L3.6pl cells. In addition, IGF-I and HGF induced uPA and uPAR expression in L3.6pl cells. In vitro, blockade of uPA and uPAR activity inhibited IGF-I- and HGF-mediated cell migration and invasion. Treatment of mice with anti-uPAR monoclonal antibody significantly decreased pancreatic tumor growth and hepatic metastasis and completely inhibited retroperitoneal invasion. Our study shows the importance of the uPA/uPAR system in pancreatic carcinoma cell migration and invasion. These findings suggest that uPAR is a potential target for therapy in patients with pancreatic cancer.

A6, a urokinase plasminogen activator (uPA)-derived peptide in patients with advanced gynecologic cancer: a phase I trial

OBJECTIVES

The aim of this study was to define the toxicity, maximum feasible dose (MFD), and pharmacokinetics (PK) of A6, a peptide derived from human urokinase plasminogen activator (uPA), in patients with advanced gynecologic cancers, and to explore anti-tumor activity and the effects of A6 on biomarkers of the urokinase system.

METHODS

A6 was administered subcutaneously daily, and doses were escalated in cohorts of three to six subjects. Serial blood specimens were obtained for pharmacokinetics and levels of urokinase plasminogen activator (uPA), uPA receptor (uPAR), and plasminogen activator inhibitor-1 (PAI-1).

RESULTS

Sixteen patients were enrolled and eligible for evaluation. No serious drug-related adverse events or dose-limiting toxicity occurred. A6-related toxicities were limited to grades 1 and 2 adverse effects including local injection site reactions. Five patients had stable tumor measurements for at least 4 cycles, one of whom stayed on study for 12 months. One patient had a confirmed cancer antigen (CA)-125 response (decrease in CA-125 of >50%) with stable disease on CT scan after 14 cycles and continues on study. Time to peak plasma level of A6 was 1-2 h. C(max) is proportional to dose. The half-life of A6 was approximately 2 h. Baseline biomarker levels did not predict response and trends over time did not correlate with outcome.

CONCLUSIONS

A6 given daily continuously is well tolerated at all dose levels, without any dose-limiting toxicity. Based on the preliminary activity of A6, a phase II trial is underway in ovarian cancer.

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.

Intraocular properties of urokinase-derived antiangiogenic A6 peptide in rabbits

To investigate the intraocular properties of an antiangiogenic peptide, A6, a total of 70 New Zealand rabbit eyes were used. For the toxicity study, 0.05 mL of 0.459 M or 0.148 M A6 was injected intravitreally; right eyes received A6, and left eyes received a vehicle. Serial intraocular pressure measurement, slit lamp, and indirect ophthalmoscopy were performed. The rabbit eyes were evaluated by fluorescein angiography, electroretinography, and histology after the scheduled sacrifice. The pharmacokinetics of an intravitreal A6 (0.05 mL of 0.488 M) and a subtenon A6 (0.5 mL of 0.305 M) injection was studied. There was no toxicity observed following the 0.148 M A6 intravitreal injections. In 2 eyes with a 0.459 M A6 intravitreal injection, focal retinal pigmentary change was observed at the injection site, which was contacted by the hyperosmolar drug bolus. Choroidal A6, following the intravitreal injection, remained therapeutic (>or=10 microM) for 72 hours. The vitreous half-life was 19.4 hours. Choroidal concentrations following the subtenon injection were minimal. The low choroidal concentrations observed may relate to the polar nature of A6. More hydrophobic analogs of A6 are likely to cross the retina more efficiently. However, in diseased eyes, in the area of choroidal neovascularization (CNV), the fluid-filled, damaged, edematous retina may permit the drug to enter the choroid in higher concentrations.

Adenovirus-Mediated Expression of Antisense Urokinase Plasminogen Activator Receptor and Antisense Cathepsin B Inhibits Tumor Growth, Invasion, and Angiogenesis in Gliomas

We have shown previously that urokinase plasminogen activator receptor (uPAR) and cathepsin B are overexpressed during glioma progression, particularly at the leading edge of the tumor. In the present study, we simultaneously down-regulated uPAR and cathepsin B in SNB19 glioma cell monolayer or SNB19 spheroids using an adenoviral vector carrying antisense uPAR and antisense cathepsin B and a combination of these genes as determined by Western blot analysis. The Ad-uPAR-Cath B-infected cells revealed a marked reduction in tumor growth and invasiveness as compared with the parental and vector controls. In vitro and in vivo angiogenic assays demonstrated inhibition of capillary-like structure formation and microvessel formation after Ad-uPAR-Cath B infection of SNB19 cells when compared with Ad-cytomegalovirus (CMV)-infected or mock-infected controls. Furthermore, using a near infrared fluorescence probe, in vivo imaging for cathepsin B indicated low/undetectable levels of fluorescence after injection of the Ad-uPAR-Cath B construct into pre-established s.c. tumors as compared with Ad-CMV-treated and untreated tumors. The effect with bicistronic construct (Ad-uPAR-Cath B) was much higher than with single (Ad-uPAR/Ad-Cath B) constructs. These results indicate that the down-regulation of cathepsin B and uPAR plays a significant role in inhibiting tumor growth, invasion, and angiogenesis. Hence, the targeting of these two proteases may be a potential therapy for brain tumors and other cancers.

Demethylation of Urokinase Promoter as a Prognostic Marker in Patients with Breast Carcinoma

PURPOSE

Urokinase (uPA) is expressed in a number of highly invasive malignancies including breast cancer. Because production of uPA is associated with breast cancer progression and can serve as a useful prognostic marker, the purpose of this study was to examine the role of uPA promoter methylation as an indicator of uPA production in breast cancer patients.

EXPERIMENTAL DESIGN

We examined the methylation status of the uPA promoter and the levels of uPA expression in normal human breast epithelial cells and several human breast cancer cells by bisulfite sequencing analysis and reverse transcription-PCR. We also analyzed the methylation status of the uPA promoter in surgical biopsy samples from patients with breast cancer of different grades, as determined by the Elston-Ellis histological grading system.

RESULTS

Expression of uPA mRNA was only detected in the highly invasive estrogen receptor-negative breast cancer cell lines, where the promoter was completely demethylated. In normal and low invasive breast cancer cells, the uPA promoter was methylated, resulting in lack of uPA mRNA expression. Analysis of biopsy samples showed that demethylation of the uPA promoter is associated with malignant transformation. Reverse transcription-PCR analysis revealed that this demethylation of the uPA promoter is directly associated with induction of uPA mRNA expression, which is well known to be associated with poor prognosis in breast cancer patients.

CONCLUSIONS

This study indicated that uPA expression in breast cancer patients is under epigenetic control via methylation of its promoter. Determination of uPA promoter methylation can therefore serve as an early reliable indicator of uPA production in breast cancer patients.

Inhibition of choroidal neovascularization in rats by the urokinase-derived peptide A6

PURPOSE

To evaluate the inhibitory effects of a urokinase-derived octapeptide A6 on laser-induced choroidal neovascularization (CNV).

METHODS

In the first arm of the study, subcutaneous injection of A6 (200 mg/kg per day) into the right eyes in 20 rats and phosphate-buffered saline in 20 control rats was started 1 day before laser injury. Angiography was performed at week 2. To evaluate the dose response, a second arm of the study was performed in the left eyes. Half of the treatment group was treated with 400 mg/kg per day, and the remaining half continued to receive 200 mg/kg per day beginning on week 4. Laser injury was made at week 5 and angiography was performed at week 7. Angiographic evaluation, histopathologic evaluation including maximum CNV thickness and factor-VIII-stained endothelium counting were performed in the second arm of the study. Choroidal concentrations of A6 were measured.

RESULTS

In the first arm of the study, angiography showed a 40.8% reduction in CNV in the 200-mg/kg per day treatment group, compared with the control (P = 0.0008). In the second arm of the study, angiographic reduction in CNV was 37.9% in the 200-mg/kg per day group (P = 0.0314) and 70.0% in the 400-mg/kg per day group (P = 0.0124), compared with the control. CNV was significantly less in the 400-mg/kg per day group than in the 200-mg/kg per day group (P = 0.0393). Both CNV thickness and number of endothelial cells were reduced in a dose-dependent manner and significantly less than in the control (P < 0.05). Mean choroidal concentration of A6 2 hours after injection was 0.72 micro M in the 200-mg/kg per day (100 mg/kg every 12 hours) and 1.75 micro M in the 400-mg/kg per day (200 mg/kg every 12 hours) treatment groups. Levels at 11 hours after injections were undetectable.

CONCLUSIONS

A6 demonstrated antiangiogenic properties in a rat model of CNV and may be useful in the treatment of CNV.

Retinal and choroidal angiogenesis: pathophysiology and strategies for inhibition

Retinal angiogenesis and choroidal angiogenesis are major causes of vision loss, and the pathogenesis of this angiogenesis process is still uncertain. However, several key steps of the angiogenic cascade have been elucidated. In retinal angiogenesis, hypoxia is the initial stimulus that causes up regulation of growth factors, integrins and proteinases, which result in endothelial cell proliferation and migration that are critical steps in this process. Once the endothelial tube is formed from the existing blood vessels, maturation starts with recruitment of mural cell precursors and formation of the basement membrane. Normally, there is a tight balance between angiogenic factors and endogenous angiogenesis inhibitors that help to keep the angiogenic process under control. Although the steps of choroidal angiogenesis seem to be similar to those of retinal angiogenesis, there are some major differences between these two processes. Several anti-angiogenic approaches are being developed in animal models to prevent ocular angiogenesis by blocking the key steps of the angiogenic cascade. Based on these pre-clinical studies, several anti-angiogenic clinical trials are ongoing in patients with diabetic retinopathy and age-related macular degeneration. This review discusses the pathogenesis of retinal and choroidal angiogenesis, and alternative pharmacological approaches to inhibit angiogenesis in ocular diseases.

Inhibition of the tumor-associated urokinase-type plasminogen activation system: effects of high-level synthesis of soluble urokinase receptor in ovarian and breast cancer cells in vitro and in vivo

Tumor cell invasion and metastasis depend on the coordinated and temporal expression of proteolytic enzymes to degrade the surrounding extracellular matrix and of adhesion molecules to remodel cell-cell and/or cell-matrix attachments. The tumor cell-associated urokinase-type plasminogen activator system, consisting of the serine protease uPA, its substrate plasminogen, its membrane-bound receptor uPAR, as well as its inhibitors PAI-1 and PAI-2, plays an important role in these pericellular processes. Especially, association of the proteolytic activity of uPA with the cell surface via interaction with uPAR significantly increases the invasive capacity of tumor cells. Consequently, various approaches have been pursued to interfere with the expression or activity of uPA and/or uPAR, including antisense strategies and the development of active-site inhibitors of uPA or inhibitors of uPA/uPAR interaction. In this review, we focus on the results obtained in vitro and in vivo with tumor cells producing high levels of a recombinant soluble form of uPAR, which efficiently inhibits uPA binding to cell surface-associated uPAR and, by this, acts as a scavenger for uPA.

Peptides with anticancer use or potential

This review is an attempt to illustrate the diversity of peptides reported for a potential or an established use in cancer therapy. With 612 references, this work aims at covering the patents and publications up to year 2000 with many inroads in years 2001-2002. The peptides are classed according to four categories of effective (or plausible) biological mechanisms of action: receptor-interacting compounds; inhibitors of protein-protein interaction; enzymes inhibitors; nucleic acid-interacting compounds. The fifth group is made of the peptides for which no mechanism of action has been found yet. Incidentally this work provides an overview of many of the modern targets of anticancer research.

Methylation status of uPA promoter as a molecular mechanism regulating prostate cancer invasion and growth in vitro and in vivo

Urokinase plasminogen activator (uPA) promotes tumor invasion and metastasis in several malignancies including prostate cancer, one of the most commonly detected male cancers that result in a high incidence of mortality. In the present study we have examined the differential regulation of uPA gene expression in different stages of prostate cancer by DNA methylation. We determined levels of uPA expression in normal prostate epithelial cells (PrEC) and in hormone-responsive (LNCaP) and -insensitive (PC-3) prostate cancer cell lines. We found that uPA is expressed only in the highly invasive PC-3 cells where the uPA promoter is unmethylated. The lack of uPA expression in PrEC and LNCaP cells, where uPA promoter is highly methylated, is due to suppression of uPA gene transcription by DNA methylation. Treatment of LNCaP cells with 5'-azacytidine, a potent demethylating agent, resulted in induction of uPA mRNA expression, uPA activity, and higher invasive capacity in vitro. Additionally, a marked increase in tumor volume was observed after inoculation of these cells into the flank of male BALB/c (nu/nu) mice. Collectively these studies have demonstrated that DNA methylation is the underlying molecular mechanism responsible for uPA gene silencing in normal and early stages of prostate cancer, which has a direct effect on tumor cell invasion and growth in vitro and in vivo.

Caveolin-1 knockout mice show an impaired angiogenic response to exogenous stimuli

Recent studies have shown that caveolin-1 (Cav-1) plays an important role as a regulator of angiogenesis in vitro. Here, we use Cav-1 knockout (KO) mice as a model system to examine the in vivo relevance of these findings. A primary mediator of angiogenesis is basic fibroblast growth factor (bFGF). Thus, we studied bFGF-induced angiogenesis in Cav-1 KO mice using a reconstituted basement membrane system, ie, Matrigel plugs, supplemented with bFGF. In Cav-1 KO mice, implanted Matrigel plugs showed a dramatic reduction in both vessel infiltration and density, as compared with identical plugs implanted in wild-type control mice. We also examined the necessity of Cav-1 to support the angiogenic response of an exogenous tumor by subcutaneously injecting Cav-1 KO mice with the melanoma cell line, B16-F10. We show that tumor weight, volume, and vessel density are all reduced in Cav-1 KO mice, consistent with diminished angiogenesis. Ultrastructural analysis of newly formed capillaries within the exogenous tumors reveals a lack of endothelial caveolae and incomplete capillary formation in Cav-1 KO mice. These results provide novel evidence that Cav-1 and caveolae play an important positive role in the process of pathological angiogenesis in vivo.

The protease inhibitor bikunin, a novel anti-metastatic agent

Bikunin is a Kunitz-type protease inhibitor predominantly found in human amniotic fluid. In cancers, administration of bikunin may block tumor cell invasion by a direct inhibition of tumor cell-associated plasmin activity as well as by inhibiting urokinase-type plasminogen activator (uPA) expression at the gene and protein levels, possibly through suppression of CD44 dimerization and/or the MAP kinase signaling cascade. Treatment of cancer patients with bikunin may be beneficial in the adjuvant setting to delay the onset of metastasis development and/or in combination with cytotoxic agents to improve treatment efficacy in patients with advanced ovarian cancer.

A urokinase-derived peptide (A6) increases survival of mice bearing orthotopically grown prostate cancer and reduces lymph node metastasis

The high rate of prostate cancer mortality invariably reflects the inability to control the spread of the disease. The urokinase-type plasminogen activator and its receptor (u-PAR) contribute to prostate cancer metastases by promoting extracellular matrix degradation and growth factor activation. The current study was undertaken to determine the efficacy of a urokinase-derived peptide (A6) in reducing the lymph node metastases of prostate cancer using a model in which prostatic tumors established in nude mice from orthotopically implanted PC-3 LN4 prostate cancer cells disseminate to the lymph nodes. As a first step in evaluating the in vivo effectiveness of A6, we determined its effect on in vitro invasiveness. In vitro, A6 reduced the invasiveness of PC-3 LN4 cells through a Matrigel-coated filter without affecting growth rate. A first in vivo survival experiment showed that all A6-treated mice were alive after 57 days, and half of them tumor-free, whereas all control mice receiving vehicle had died. In a second experiment with a larger tumor inoculum and a longer delay until treatment, whereas 71% of control mice and 83% of mice treated with a scrambled peptide developed lymph node metastases, only 22 to 25% of A6-treated mice had positive lymph nodes. Further, lymph node volume, reflective of tumor burden at the secondary site, was diminished 70% in A6-treated mice. In conclusion, we provide definitive evidence that a peptide spanning the connecting region of urokinase suppresses metastases and, as a single modality, prolongs the life span of prostate tumor-bearing mice.

Increase of Anti-Metastatic Efficacy by Selectivity- But Not Affinity-Optimization of Synthetic Serine Protease Inhibitors

Although tumors frequently show elevated protease activities, the concept of anti-proteolytic cancer therapy has lost momentum after failure of clinical trials with broad-spectrum matrix metalloproteinase inhibitors. Thus we need to adapt our design strategies for protease inhibitors. Here, we employed a series of seven structurally fine-modulated and pharmacokinetically closely related synthetic 4-amidinobenzylamine-based inhibitors with distinct selectivity for prototypical serine proteases in a murine T cell lymphoma liver metastasis model. This in vivo screening revealed efficacy of urokinase inhibitors but no correlation between urokinase selectivity or affinity and anti-metastatic effect. In contrast, factor Xa-selective inhibitors were more potent, demonstrating factor Xa or a factor Xa-like serine protease likely to be more determinant in this model. Factor Xa selectivity, but not affinity, significantly improved anti-metastatic efficacy. For example, factor Xa inhibitors CJ-504 and CJ-510 exert similar affinity for factor Xa (K(i)=14 nM versus 8.8 nM) but CJ-504 was 70-fold more selective for factor Xa. This correlated with higher anti-metastatic efficacy (58.8% with CJ-504; 28.2% with CJ-510). Our results show that among the protease inhibitors employed that have affinities in the nanomolar range, the strategy of selectivity-optimization is superior to further improvement of affinity to significantly enhance anti-metastatic efficacy. This appreciation may be important for the future rational design of new anti-proteolytic agents for cancer therapy.