Growth and Dissemination of Lewis Lung Carcinoma in Plasminogen-Deficient Mice

Whole‑exome sequencing reveals Lewis lung carcinoma is a hypermutated Kras/Nras-mutant cancer with extensive regional mutation clusters in its genome

Lewis lung carcinoma (LLC), as a widely used preclinical cancer model, has still not been genetically and genomically characterized. Here, we performed a whole-exome sequencing analysis on the LLC cell line to elucidate its molecular characteristics and etiologies. Our data showed that LLC originated from a male mouse belonging to C57BL/6L (a transitional strain between C57BL/6J and C57BL/6N) and contains substantial somatic SNV and InDel mutations (> 20,000). Extensive regional mutation clusters are present in its genome, which were caused mainly by the mutational processes underlying the SBS1, SBS5, SBS15, SBS17a, and SBS21 signatures during frequent structural rearrangements. Thirty three deleterious mutations are present in 30 cancer genes including Kras, Nras, Trp53, Dcc, and Cacna1d. Cdkn2a and Cdkn2b are biallelically deleted from the genome. Five pathways (RTK/RAS, p53, cell cycle, TGFB, and Hippo) are oncogenically deregulated or affected. The major mutational processes in LLC include chromosomal instability, exposure to metabolic mutagens, spontaneous 5-methylcytosine deamination, defective DNA mismatch repair, and reactive oxygen species. Our data also suggest that LLC is a lung cancer similar to human lung adenocarcinoma. This study lays a molecular basis for the more targeted application of LLC in preclinical research.

Bone Metastasis of Breast Cancer: Molecular Mechanisms and Therapeutic Strategies

Bone metastasis is a common complication of many types of advanced cancer, including breast cancer. Bone metastasis may cause severe pain, fractures, and hypercalcemia, rendering clinical management challenging and substantially reducing the quality of life and overall survival (OS) time of breast cancer patients. Studies have revealed that bone metastasis is related to interactions between tumor cells and the bone microenvironment, and involves complex molecular biological mechanisms, including colonization, osteolytic destruction, and an immunosuppressive bone microenvironment. Agents inhibiting bone metastasis (such as bisphosphate and denosumab) alleviate bone destruction and improve the quality of life of breast cancer patients with bone metastasis. However, the prognosis of these patients remains poor, and the specific biological mechanism of bone metastasis is incompletely understood. Additional basic and clinical studies are urgently needed, to further explore the mechanism of bone metastasis and develop new therapeutic drugs. This review presents a summary of the molecular mechanisms and therapeutic strategies of bone metastasis of breast cancer, aiming to improve the quality of life and prognosis of breast cancer patients and provide a reference for future research directions.

The cell-line-derived subcutaneous tumor model in preclinical cancer research

Tumor-bearing experimental animals are essential for preclinical cancer drug development. A broad range of tumor models is available, with the simplest and most widely used involving a tumor of mouse or human origin growing beneath the skin of a mouse: the subcutaneous tumor model. Here, we outline the different types of in vivo tumor model, including some of their advantages and disadvantages and how they fit into the drug-development process. We then describe in more detail the subcutaneous tumor model and key steps needed to establish it in the laboratory, namely: choosing the mouse strain and tumor cells; cell culture, preparation and injection of tumor cells; determining tumor volume; mouse welfare; and an appropriate experimental end point. The protocol leads to subcutaneous tumor growth usually within 1-3 weeks of cell injection and is suitable for those with experience in tissue culture and mouse experimentation.

Vessel co-option in cancer

All solid tumours require a vascular supply in order to progress. Although the ability to induce angiogenesis (new blood vessel growth) has long been regarded as essential to this purpose, thus far, anti-angiogenic therapies have shown only modest efficacy in patients. Importantly, overshadowed by the literature on tumour angiogenesis is a long-standing, but continually emerging, body of research indicating that tumours can grow instead by hijacking pre-existing blood vessels of the surrounding nonmalignant tissue. This process, termed vessel co-option, is a frequently overlooked mechanism of tumour vascularization that can influence disease progression, metastasis and response to treatment. In this Review, we describe the evidence that tumours located at numerous anatomical sites can exploit vessel co-option. We also discuss the proposed molecular mechanisms involved and the multifaceted implications of vessel co-option for patient outcomes.

Dietary 2-deoxy-D-glucose impairs tumour growth and metastasis by inhibiting angiogenesis

Accumulating evidence suggests the antiangiogenic potential of the glycolytic inhibitor 2-deoxy-D-glucose (2-DG) among the anticancerous properties of this drug. In the present studies, we investigated the antiangiogenic effects of dietary 2-DG on tumour (Lewis lung carcinoma [LLC]) as well as ionising radiation-induced angiogenesis in mouse models. Dietary 2-DG reduced the serum vascular endothelial growth factor levels (∼40%) in LLC-bearing mice along with a significant inhibition of tumour growth and metastases. In vivo Matrigel plug assays showed significant decrease in vascularisation, Fluorescein isothiocyanate (FITC)-dextran fluorescence and factor VIII-positive cells in the plugs from 2-DG-fed mice, supporting the notion that dietary 2-DG significantly suppresses the tumour-associated and radiation-induced angiogenesis. 2-DG inhibited the glucose usage and lactate production as well as ATP levels of human umbilical vein endothelial cells (HUVECs) in a concentration-dependent manner, accompanied by growth inhibition and loss of viability in vitro. Furthermore, 2-DG inhibited the capillary-like tube formation in Matrigel as well as migration and transwell invasion by HUVECs, which are functional indicators of the process of angiogenesis. These results suggest that dietary 2-DG inhibits processes related to angiogenesis, which can impair the growth and metastasis of tumours.

Repurposing suramin for the treatment of breast cancer lung metastasis with glycol chitosan-based nanoparticles

Suramin (SM), a drug for African sleeping sickness and river blindness therapy, has been investigated in various clinical trials for cancer therapy. However, SM was eventually withdrawn from the market because of its narrow therapeutic window and the side effects associated with multiple targets. In this work, we developed a simple but effective system based on a nontoxic dose of SM combined with a chemotherapeutic agent for the treatment of metastatic triple-negative breast cancer (TNBC). SM and glycol chitosan (GCS) formed nanogels because of the electrostatic effect, whereas doxorubicin (DOX) was incorporated into the system through the hydrophilic and hydrophobic interactions between DOX and GCS as well as the ionic interactions between DOX and SM to yield GCS-SM/DOX nanoparticles (NPs). GCS-SM/DOX NPs have a size of approximately 186 nm and a spherical morphology. In vitro experiments showed that GCS-SM NPs could effectively inhibit cancer cell migration and invasion, as well as angiogenesis. Furthermore, in a TNBC lung metastasis animal model, GCS-SM/DOX NPs significantly reduced tumor burden and extended the lifespan of animals, while not inducing cardio and renal toxicities associated with the DOX and SM, respectively. As all the components used in this system are biocompatible and easy for large-scale fabrication, the GCS-SM/DOX system is highly translatable for the metastatic breast cancer treatment. STATEMENT OF SIGNIFICANCE: The doxorubicin-loaded glycol chitosan-suramin nanoparticle (GCS-SM/DOX) is novel in the following aspects: SM acts as not only a gelator for the first time in the preparation of the nanoparticle but also an active pharmaceutical agent in the dosage form. GCS-SM/DOX NP significantly reduced tumor burden and extended the lifespan of animals with triple-negative breast cancer lung metastasis. GCS-SM/DOX NPs attenuate cardio and renal toxicities associated with the DOX and SM. The GCS-SM/DOX system is highly translatable because of its simple, one-pot, and easy-to-scale-up preparation protocol.

PPARγ Contributes to Immunity Induced by Cancer Cell Vaccines That Secrete GM-CSF

Peroxisome proliferator activated receptor-γ (PPARγ) is a lipid-activated nuclear receptor that promotes immune tolerance through effects on macrophages, dendritic cells (DCs), and regulatory T cells (Tregs). Granulocyte-macrophage colony stimulating factor (GM-CSF) induces PPARγ expression in multiple myeloid cell types. GM-CSF contributes to both immune tolerance and protection, but the role of PPARγ in these pathways is poorly understood. Here, we reveal an unexpected stimulatory role for PPARγ in the generation of antitumor immunity with irradiated, GM-CSF-secreting tumor-cell vaccines (GVAX). Mice harboring a deletion of pparg in lysozyme M (LysM)-expressing myeloid cells (KO) showed a decreased ratio of CD8⁺ T effectors to Tregs and impaired tumor rejection with GVAX. Diminished tumor protection was associated with altered DC responses and increased production of the Treg attracting chemokines CCL17 and CLL22. Correspondingly, the systemic administration of PPARγ agonists to vaccinated mice elevated the CD8⁺ T effector to Treg ratio through effects on myeloid cells and intensified the antitumor activity of GVAX combined with cytotoxic T lymphocyte-associated antigen-4 antibody blockade. PPARγ agonists similarly attenuated Treg induction and decreased CCL17 and CCL22 levels in cultures of human peripheral blood mononuclear cells with GM-CSF-secreting tumor cells. Together, these results highlight a key role for myeloid cell PPARγ in GM-CSF-stimulated antitumor immunity and suggest that PPARγ agonists might be useful in cancer immunotherapy. Cancer Immunol Res; 6(6); 723-32. ©2018 AACR.

Is Circulating D-Dimer Level a Better Prognostic Indicator than Cea in Resectable Colorectal Cancer? Our Experience on 199 Cases

Purpose

To evaluate the clinical impact of D-dimer (DD) as a tumor marker in patients with colorectal cancer (CRC). The prognostic value of preoperative DD measurement was assessed in relation to carcinoembryonic antigen (CEA) levels.

Methods

DD and CEA levels were measured preoperatively in 199 patients who underwent resection for CRC and the results were analyzed statistically.

Results

The preoperative mean (±SD) levels of DD and CEA were 347.5 (±940.1) ng/mL and 106.4 (±1099.2) ng/mL. The DD level was significantly correlated with the nature of surgery (emergency vs. elective; p=0.002), presence of residual tumor (R1–2 vs R0; p=0.037), and tumor diameter (p<0.001). Conversely, DD was not correlated with tumor grade, pT, pN and M stages, and stage according to the Dukes classification. The 5-year survival rates were 80% and 64% for patients with negative and positive DD values, respectively (p=0.156). CEA was significantly related to all major prognostic factors (resection category, pT, pN and M stages as well as Dukes stage). A significantly worse prognosis was observed for patients with positive CEA levels. Multivariate analysis confirmed CEA as an independent prognostic factor (p=0.005), whilst DD was not (p=0.796).

Conclusions

The possible clinical usefulness of preoperative assessment of DD suggested by previous studies has not been confirmed by our data. CEA was confirmed to be the most reliable and valid indicator of prognosis.

The prognostic value of D-dimer levels in metastatic osteosarcoma patients treated with second-line chemotherapy

We performed a retrospective analysis of 32 metastatic osteosarcoma cases to examine the prognostic value of the plasma D-dimer level. We assessed the D-dimer level before second-line chemotherapy (D1) and the D-dimer level after two cycles of second-line chemotherapy (D2). The change in D-dimer level (ΔD) was defined as D2 minus D1. The overall survival (OS) of patients with a high D1 was significantly shorter than those with a low D1 (median OS, 4.7 vs. 16.2 months, P=0.001). Similar results were observed for the D2 (median OS, 4.7 vs. 8.6 months, P=0.033). Multivariable analysis demonstrated that a high D1 (hazard ratio, 3.375; 95% confidence interval, 1.133-10.053; P=0.029) was an unfavorable independent prognostic factor. The mean D2 of 11 patients with stable disease decreased by 0.69 mg/mL compared to the D1 (P = 0.016). The mean D2 increased by 1.47 mg/mL compared to the D1 in 21 patients with progressive disease (P = 0.004). The data suggest that D-dimer may serve as a prognostic biomarker for metastatic osteosarcoma patients treated with second-line chemotherapy.

Targeting of embryonic annexin A2 expressed on ovarian and breast cancer by the novel monoclonal antibody 2448

Monoclonal antibodies (mAbs) play an increasingly important role in cancer therapy. To address the wide heterogeneity of the disease, the identification of novel antigen targets and the development of mAbs against them are needed. Our lab previously generated a panel of mAbs against human embryonic stem cells (hESC) using a whole cell immunization approach in mice. These mAbs can potentially target oncofetal antigens and be repurposed for antibody or antibody drug conjugate (ADC) therapy. From this panel, the novel IgG1 2448 was found to bind surface antigens on hESC and multiple cancer cell lines. Here, we show 2448 targets a unique glycan epitope on annexin A2 (ANXA2) and can potentially monitor the Epithelial-Mesenchymal Transition (EMT) in ovarian and breast cancer. To evaluate 2448 as a potential drug, 2448 was engineered and expressed as a chimeric IgG1. Chimeric 2448 (ch2448) demonstrated efficient and specific killing when conjugated to cytotoxic payloads as an ADC. In addition, ch2448 elicited potent antibody-dependent cell-mediated cytotoxicity (ADCC) activity in vitro and in vivo. Further engineering of ch2448 to remove fucose in the Fc domain enhanced ADCC. Overall, these findings indicate that embryonic ANXA2 is an attractive target and suggest that ch2448 is a promising candidate for further therapeutic development.

Tumor-Associated Macrophages Derived from Circulating Inflammatory Monocytes Degrade Collagen through Cellular Uptake

Physiologic turnover of interstitial collagen is mediated by a sequential pathway in which collagen is fragmented by pericellular collagenases, endocytosed by collagen receptors, and routed to lysosomes for degradation by cathepsins. Here, we use intravital microscopy to investigate if malignant tumors, which are characterized by high rates of extracellular matrix turnover, utilize a similar collagen degradation pathway. Tumors of epithelial, mesenchymal, or neural crest origin all display vigorous endocytic collagen degradation. The cells engaged in this process are identified as tumor-associated macrophage (TAM)-like cells that degrade collagen in a mannose receptor-dependent manner. Accordingly, mannose-receptor-deficient mice display increased intratumoral collagen. Whole-transcriptome profiling uncovers a distinct extracellular matrix-catabolic signature of these collagen-degrading TAMs. Lineage-ablation studies reveal that collagen-degrading TAMs originate from circulating CCR2+ monocytes. This study identifies a function of TAMs in altering the tumor microenvironment through endocytic collagen turnover and establishes macrophages as centrally engaged in tumor-associated collagen degradation.

Harnessing innate lung anti-cancer effector functions with a novel bacterial-derived immunotherapy

Acute infection is known to induce strong anti-tumor immune responses, but clinical translation has been hindered by the lack of an effective strategy to safely and consistently provoke a therapeutic response. These limitations are overcome with a novel treatment approach involving repeated subcutaneous delivery of a Klebsiella-derived investigational immunotherapeutic, QBKPN. In preclinical models of lung cancer, QBKPN administration consistently showed anti-cancer efficacy, which was dependent on Klebsiella pre-exposure, but was independent of adaptive immunity. Rather, QBKPN induced anti-tumor innate immunity that required NK cells and NKG2D engagement. QBKPN increased NK cells and macrophages in the lungs, altered macrophage polarization, and augmented the production of cytotoxic molecules. An exploratory trial in patients with non-small cell lung cancer demonstrated QBKPN was well tolerated, safe, and induced peripheral immune changes suggestive of macrophage polarization and reduction of PD-1 and PD-L1 expression on leukocytes. These data demonstrate preclinical efficacy, and clinical safety and tolerability, for this cancer immunotherapy strategy that exploits innate anti-tumor immune mechanisms.

Clinical significance of coagulation factors in operable colorectal cancer

Abnormal hemostasis in cancer patients has prev iously been studied. The primary objective of the present study was to evaluate the association between preoperative hemostasis markers and clinicopathological parameters, and to identify a hemostasis marker affecting survival in patients following curative resection for colorectal cancer. A total of 170 patients who underwent curative surgery for colorectal carcinoma were evaluated. Preoperative coagulation tests included platelet, prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, D-dimer and fibrinogen degradation product (FDP). The clinicopathological variables, including age, gender, tumor location (rectum/colon), tumor size (≥5 cm vs. <5 cm), depth of tumor invasion, lymph node metastasis, stage, lymphovascular invasion, margin involvement and histological differentiation were analyzed. The median age of analyzed patients was 63 years (range, 28-84). The male to female ratio was 62:38. Increased levels of plasma fibrinogen, PT and platelet count (PLT) were associated with larger tumor size (P<0.001, P=0.015 and P=0.002, respectively). Increased plasma fibrinogen levels were significantly associated with depth of tumor invasion and stage (P=0.014 and P=0.048, respectively). Increased plasma D-dimer and FDP levels were significantly associated with tumor node metastasis stage (P=0.031 and P=0.002, respectively). Prolonged PT level (≥11.7 sec), hyper-fibrinogenemia (≥327 mg/dl), high D-dimer level (≥1.3 µg/ml) and increased FDP level (≥2.7 µg/ml) were the prognostic factors associated with shorter survival. Preoperative plasma fibrinogen level was significantly associated with tumor size and depth of tumor invasion. Preoperative plasma prolonged PT level, hyperfibrinogenemia, high D-dimer level and increased FDP level may function as hemostasis markers that predict overall survival in operable patients with colorectal cancer.

From plasminogen to plasmin: role of plasminogen receptors in human cancer

Cell surface-associated proteolysis mediated by plasmin (PLA) is an essential feature of wound healing, angiogenesis and cell invasion, processes that are dysregulated in cancer development, progression and systemic spread. The generation of PLA, initiated by the binding of its precursor plasminogen (PLG) to the cell surface, is regulated by an array of activators, inhibitors and receptors. In this review, we will highlight the importance of the best-characterized components of the PLG/PLA cascade in the pathogenesis of cancer focusing on the role of the cell surface-PLG receptors (PLG-R). PLG-R overexpression has been associated with poor prognosis of cancer patients and resistance to chemotherapy. We will also discuss recent findings on the molecular mechanisms regulating cell surface expression and distribution of PLG-R.

Annexin A2: the importance of being redox sensitive

Hydrogen peroxide (H₂O₂) is an important second messenger in cellular signal transduction. H₂O₂-dependent signalling regulates many cellular processes, such as proliferation, differentiation, migration and apoptosis. Nevertheless, H₂O₂ is an oxidant and a major contributor to DNA damage, protein oxidation and lipid peroxidation, which can ultimately result in cell death and/or tumourigenesis. For this reason, cells have developed complex antioxidant systems to scavenge ROS. Recently, our laboratory identified the protein, annexin A2, as a novel cellular redox regulatory protein. Annexin A2 possesses a reactive cysteine residue (Cys-8) that is readily oxidized by H₂O₂ and subsequently reduced by the thioredoxin system, thereby enabling annexin A2 to participate in multiple redox cycles. Thus, a single molecule of annexin A2 can inactivate several molecules of H₂O₂. In this report, we will review the studies detailing the reactivity of annexin A2 thiols and the importance of these reactive cysteine(s) in regulating annexin A2 structure and function. We will also focus on the recent reports that establish novel functions for annexin A2, namely as a protein reductase and as a cellular redox regulatory protein. We will further discuss the importance of annexin A2 redox regulatory function in disease, with a particular focus on tumour progression.

Cell surface remodeling by plasmin: a new function for an old enzyme

Plasmin, one of the most potent and reactive serine proteases, is involved in various physiological processes, including embryo development, thrombolysis, wound healing and cancer progression. The proteolytic activity of plasmin is tightly regulated through activation of its precursor, plasminogen, only at specific times and in defined locales as well as through inhibition of active plasmin by its abundant natural inhibitors. By exploiting the plasminogen activating system and overexpressing distinct components of the plasminogen activation cascade, such as pro-uPA, uPAR and plasminogen receptors, malignant cells can enhance the generation of plasmin which in turn, modifies the tumor microenvironment to sustain cancer progression. While plasmin-mediated degradation and modification of extracellular matrix proteins, release of growth factors and cytokines from the stroma as well as activation of several matrix metalloproteinase zymogens, all have been a focus of cancer research studies for decades, the ability of plasmin to cleave transmembrane molecules and thereby to generate functionally important cleaved products which induce outside-in signal transduction, has just begun to receive sufficient attention. Herein, we highlight this relatively understudied, but important function of the plasmin enzyme as it is generated de novo at the interface between cross-talking cancer and host cells.

Spontaneous metastasis in congenic mice with transgenic breast cancer is unaffected by plasminogen gene ablation

Plasminogen (Plg) plays a central role in tissue remodeling during ontogeny, development, and in pathological tissue remodeling following physical injury, inflammation and cancer. Plg/plasmin is, however, not critical for these processes, as they all occur to a varying extent in its absence, suggesting that there is a functional redundancy with other proteases. To explore this functional overlap in the transgenic MMTV-PyMT breast cancer metastasis model, we have combined Plg deficiency and a pharmacological metalloprotease inhibitor, which is known to reduce metastasis in this model, and has been shown to synergistically inhibit other tissue remodeling events in Plg-deficient mice. While metalloprotease inhibition dramatically reduced metastasis, we found no effect of Plg deficiency on metastasis, either independently or in combination with metalloprotease inhibition. We further show that Plg gene deficiency is of no significant consequence in this metastasis model, when analyzed in two different congenic strains: the FVB strain, and a F1 hybrid of the FVB and C57BL/6J strains. We suggest that the extensive backcrossing performed prior to our studies has eliminated the confounding effect of a known polymorphic metastasis modifier gene region located adjacent to the Plg gene.

Plasmin-driven fibrinolysis facilitates skin tumor growth in a gender-dependent manner

Rearrangement of the skin during wound healing depends on plasmin and plasminogen, which serve to degrade fibrin depositions in the provisional matrix and thereby facilitate keratinocyte migration. In the current study, we investigated whether plasmin and plasminogen likewise played a role during the development of skin cancer. To test this, we set up a chemically induced skin tumor model in a cohort of mice and found that skin tumor growth in Plg(-/-) male mice was reduced by 52% compared with wild-type controls. Histological analyses suggested that the growth-restricting effect of plasminogen deficiency was due to thrombosis and lost patency of the tumor vasculature, resulting in tumor necrosis. The connection between plasmin-dependent fibrinolysis, vascular patency, and tumor growth was further substantiated as the effect of plasminogen deficiency on tumor growth could be reverted by superimposing heterozygous fibrinogen deficiency on Plg(-/-) mice. Tumors derived from these Fib(-/+);Plg(-/-) mice displayed a significantly decreased level of tumor thrombosis compared with Plg(-/-) mice. In summary, these data indicate that plasmin-driven fibrinolysis facilitates tumor growth by maintaining patency of the tumor vasculature.

Annexin A2 is a novel cellular redox regulatory protein involved in tumorigenesis

Annexins are a structurally related family of calcium and phospholipid-binding proteins that are involved in the regulation of a wide range of molecular and cellular processes. Annexin A2 is unique among the annexins in that it possesses redox sensitive cysteine(s). The ubiquitous and abundant expression of ANXA2 in cells and its reactivity with hydrogen peroxide led us to hypothesize that this protein could play a role in cellular redox regulation. Here we show that ANXA2 protein levels are induced by hydrogen peroxide. Furthermore, depletion of ANXA2 resulted in the elevation of cellular reactive oxygen species (ROS) upon oxidative stress, increased activation of the ROS-induced pro-apoptotic kinases, JNK, p38 and Akt and elevated sensitivity to ROS-mediated cellular damage/death. ANXA2-null mice showed significantly elevated protein oxidation in the liver and lung tissues compared to WT mice. ANXA2 depleted cancer cells showed enhanced cellular protein oxidationconcomitant with decreased tumor growth compared to control cancer cells andboth the oxidation of cellular proteins and tumor growth deficit werereversed by the antioxidant N-acetyl cysteine, indicating that ANXA2 plays akey role in the regulation of cellular redox during tumorigenesis. Ex-vivo human cancer studies showed that up-regulation of the reduced form of ANXA2 is associated with protection of the tumor proteins from oxidation. In summary, our results indicate that ANXA2 plays an important role incellular redox regulation by protecting cells from oxidative stress, aneffect that is particularly important during tumorigenesis.

New functions of the fibrinolytic system in bone marrow cell-derived angiogenesis

Angiogenesis is a process by which new blood vessels form from preexisting vasculature. This process includes differentiation of angioblasts into endothelial cells with the help of secreted angiogenic factors released from cells such as bone marrow (BM)-derived cells. The fibrinolytic factor plasmin, which is a serine protease, has been shown to promote endothelial cell migration either directly, by degrading matrix proteins such as fibrin, or indirectly, by converting matrix-bound angiogenic growth factors into a soluble form. Plasmin can also activate other pericellular proteases such as matrix metalloproteinases (MMPs). Recent studies indicate that plasmin can additionally alter cellular adhesion and migration. We showed that factors of the fibrinolytic pathway can recruit BM-derived hematopoietic cells into ischemic/hypoxic tissues by altering the activation status of MMPs. These BM-derived cells can function as accessory cells that promote angiogenesis by releasing angiogenic signals. This review will discuss recent data regarding the role of the fibrinolytic system in controlling myeloid cell-driven angiogenesis. We propose that plasmin/plasminogen may be a potential target not only for development of effective angiogenic therapeutic strategies for the treatment of cancer, but also for development of strategies to promote ischemic tissue regeneration.

Efficient targeting of head and neck squamous cell carcinoma by systemic administration of a dual uPA and MMP-activated engineered anthrax toxin

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Although considerable progress has been made in elucidating the etiology of the disease, the prognosis for individuals diagnosed with HNSCC remains poor, underscoring the need for development of additional treatment modalities. HNSCC is characterized by the upregulation of a large number of proteolytic enzymes, including urokinase plasminogen activator (uPA) and an assortment of matrix metalloproteinases (MMPs) that may be expressed by tumor cells, by tumor-supporting stromal cells or by both. Here we explored the use of an intercomplementing anthrax toxin that requires combined cell surface uPA and MMP activities for cellular intoxication and specifically targets the ERK/MAPK pathway for the treatment of HNSCC. We found that this toxin displayed strong systemic anti-tumor activity towards a variety of xenografted human HNSCC cell lines by inducing apoptotic and necrotic tumor cell death, and by impairing tumor cell proliferation and angiogenesis. Interestingly, the human HNSCC cell lines were insensitive to the intercomplementing toxin when cultured ex vivo, suggesting that either the toxin targets the tumor-supporting stromal cell compartment or that the tumor cell requirement for ERK/MAPK signaling differs in vivo and ex vivo. This intercomplementing toxin warrants further investigation as an anti-HNSCC agent.

Induction of the fibrinolytic system by cartilage extract mediates its antiangiogenic effect in mouse glioma

Both the antiangiogenic and antitumoral activity of shark cartilage extracts (SCE) have been demonstrated in animal models and clinical trials. Studies reported that SCE induces the expression of tissue plasminogen activator gene (PLAT) in endothelial cells and increases the activity of the protein (t-PA) in vitro. The aim of this study was to demonstrate the crucial role of t-PA induction in the antiangiogenic and antitumor activity of SCE in experimental glioma. This study showed antiangiogenic and antitumoral effects of SCE in three mice glioma models (C6, HGD and GL26). Histological examination suggested perivascular proteolysis and edema as well as important intratumoral necrosis, which artefactually increased the tumor volume at high doses. Thus, the antiangiogenic effect of SCE correlated with the presence of t-PA and angiostatin in degenerating vessels. Functional in vivo experiments were conducted to modulate the plasminogen pathway. No antiangiogenic effect was observed on tumors overexpressing the plasminogen activator inhibitor-1 (PAI-1). Moreover, therapeutical effects were neutralized in mice that were cotreated with ε-aminocaproic acid (EACA, 120 mg/kg p.o.), an inhibitor that blocks the high-affinity lysine binding sites of both plasminogen and plasmin. In contrast, cotreatment with N-acetylcysteine (NAC, 7,5mg/kg i.p.), a sulfhydril donor that reduces plasmin into angiostatin or other antiangiogenic fragments, increased the benefit of SCE on mice survival. In subcutaneous models, NAC prevented the increase in tumor volume caused by high doses of cartilage extract. In conclusion, this study indicates that induction of t-PA by shark cartilage extract plays an essential role in its antiangiogenic activity, but that control of excessive proteolysis by a plasmin reductor could prevent edema and uncover the full benefit of shark cartilage extract in the treatment of intracranial tumors.

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.

Navigating ECM barriers at the invasive front: the cancer cell-stroma interface

A seminal event in cancer progression is the ability of the neoplastic cell to mobilize the necessary machinery to breach surrounding extracellular matrix barriers while orchestrating a host stromal response that ultimately supports tissue-invasive and metastatic processes. With over 500 proteolytic enzymes identified in the human genome, interconnecting webs of protease-dependent and protease-independent processes have been postulated to drive the cancer cell invasion program via schemes of daunting complexity. Increasingly, however, a body of evidence has begun to emerge that supports a unifying model wherein a small group of membrane-tethered enzymes, termed the membrane-type matrix metalloproteinases (MT-MMPs), plays a dominant role in regulating cancer cell, as well as stromal cell, traffic through the extracellular matrix barriers assembled by host tissues in vivo. Understanding the mechanisms that underlie the regulation and function of these metalloenzymes as host cell populations traverse the dynamic extracellular matrix assembled during neoplastic states should provide new and testable theories regarding cancer invasion and metastasis.

Plasminogen deficiency

Plasminogen (plg) deficiency has been classified as (i) hypoplasminogenemia or 'true' type I plg deficiency, and (ii) dysplasminogenemia, also called type II plg deficiency. Both forms, severe hypoplasminogenemia and dysplasminogenemia, are not causally linked to venous thrombosis. Dysplasminogenemia does not lead to a specific clinical manifestation and probably represents only a polymorphic variation in the general population, mainly in Asian countries. Severe hypoplasminogenemia is associated with compromised extracellular fibrin clearance during wound healing, leading to pseudomembraneous (ligneous) lesions on affected mucous membranes (eye, middle ear, mouth, pharynx, duodenum, upper and lower respiratory tract and female genital tract). Ligneous conjunctivitis is by far the most common clinical manifestation. More than 12% of patients with severe hypoplasminogenemia exhibit congenital occlusive hydrocephalus. In milder cases of ligneous conjunctivitis, topical application of plg-containing eye drops, fresh frozen plasma, heparin, corticosteroids or certain immunosuppressive agents (such as azathioprine) may be more or less effective. Oral treatment with sex hormones was successful in two female patients with ligneous conjunctivitis. In severe cases with possibly life-threatening multi-organ involvement, true therapeutic options are not available at present. The plg-knockout mouse is a useful tool to study the many different properties of plg in a variety of settings, such as wound healing, tissue repair and tissue remodeling, virulence and invasiveness of certain bacteria in the human host, tumor growth and dissemination, as well as arteriosclerosis.

A guide to murine fibrinolytic factor structure, function, assays, and genetic alterations

The components and functions of the murine fibrinolytic system are quite similar to those of humans. Because of these similarities and the adaptability of mice to genetic manipulation, murine fibrinolysis has been studied extensively. These studies have yielded important information regarding the function of the several components of fibrinolysis. This review presents information on the structure, function and assay of mouse fibrinolytic parameters and it discusses the results of the extensive studies of genetically modified mice. It is intended to be a convenient reference resource for investigators of fibrinolysis.

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.

Plasminogen inhibits TNFalpha-induced apoptosis in monocytes

Monocytes are major mediators of inflammation, and apoptosis provides a mechanism for regulating the inflammatory response by eliminating activated macrophages. Furthermore, as a consequence of apoptosis, plasminogen binding is markedly increased on monocytoid cells. Therefore, we investigated the ability of plasminogen to modulate monocyte apoptosis. Apoptosis of monocytoid cells (human monocytes and U937 cells) was induced with either TNFalpha or cycloheximide. When apoptosis was induced in the presence of increasing concentrations of plasminogen, apoptosis was inhibited in a dose-dependent manner with full inhibition achieved at 2 microM plasminogen. Plasminogen treatment also markedly reduced internucleosomal DNA fragmentation and reduced levels of active caspase 3, caspase 8, and caspase 9 induced by TNFalpha or by cycloheximide. We examined the requirement for plasmin proteolytic activity in the cytoprotective function of plasminogen. A plasminogen active site mutant, [D(646)E]-Plg, failed to recapitulate the cytoprotective effect of wild-type plasminogen. Furthermore, antibodies against PAR1 blocked the antiapoptotic effect of plasminogen. Our results suggest that plasminogen inhibits monocyte apoptosis. The cytoprotective effect of plasminogen requires plasmin proteolytic activity and requires PAR1. Because apoptosis of monocytes plays a key role in inflammation and atherosclerosis, these results provide insight into a novel role of plasminogen in these processes.

Aspects of extracellular matrix remodeling in development and disease

The extracellular matrix is the major constituent of organic matter in both plants and animals, where it provides the interface between individual cells. In most tissues, with some notable exceptions such as bone marrow, the volume of extracellular matrix equals or exceeds the volume of intracellular space and organelles, making matrix an abundant constituent through which cells exert their functions and receive cues. The matrix may therefore be considered the basic structural entity that supports the function of an organ, and in connective tissues the matrix is the organ itself to which function is tied throughout the life of its resident cells. In this review, a select number of proteinases involved in some of the more conspicuous matrix remodeling events of the mammalian organism are explored. Evidence from both animal models and human diseases is discussed in relation to normal physiological processes, including instances in which aberrant matrix remodeling leads to disease states.

Proteases and glioma angiogenesis

Angiogenesis, the process by which new branches sprout from existing vessels, requires the degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissues. Serine, metallo, and cysteine proteinases are 3 types of a family of enzymes that proteolytically degrade various components of extracellular matrix. These proteases release various growth factors and also increase adhesive molecules and signaling pathway molecules upon their activation, which plays a significant role in angiogenesis. Downregulation of these molecules by antisense/siRNA or synthetic inhibitors decreases the levels of these molecules, inhibits the release of growth factors, and decreases the levels of various signaling pathway molecules, thereby leading to the inhibition of angiogenesis. Furthermore, MMPs degrade specific substrates and release angiogenic inhibitors which inhibit angiogenesis. Downregulation of 2 molecules, such as uPA and uPAR, uPAR and MMP-9, or Cathepsin B and MMP-9, are more effective to inhibit angiogenesis rather than downregulation of single molecules. However, careful testing of these combinations are most important because multiple effects of these combinations play a significant role in angiogenesis.

Synergy between a plasminogen cascade and MMP-9 in autoimmune disease

Extracellular proteolysis by the plasminogen/plasmin (Plg/plasmin) system and MMPs is required for tissue injury in autoimmune and inflammatory diseases. We demonstrate that a Plg cascade synergizes with MMP-9/gelatinase B in vivo during dermal-epidermal separation in an experimental model of bullous pemphigoid (BP), an autoimmune disease. BP was induced in mice by antibodies to the hemidesmosomal antigen BP180. Mice deficient in MMP-9 were resistant to experimental BP, while mice deficient in Plg and both tissue Plg activator (tPA) and urokinase Plg activator (uPA) showed delayed and less intense blister formation induced by antibodies to BP180. Plg-deficient mice reconstituted locally with Plg or the active form of MMP-9 (actMMP-9), but not the proenzyme form of MMP-9 (proMMP-9), developed BP. In contrast, proMMP-9 or actMMP-9, but not Plg, reconstituted susceptibility of MMP-9-deficient mice to the skin disease. In addition, MMP-3-deficient mice injected with pathogenic IgG developed the same degree of BP and expressed levels of actMMP-9 in the skin similar to those of WT controls. Thus, the Plg/plasmin system is epistatic to MMP-9 activation and subsequent dermal-epidermal separation in BP.

Gene expression profile identifies a rare epithelioid variant case of pleomorphic liposarcoma carrying FUS-CHOP transcript

AIMS

To describe a tumour with morphological and immunophenotypic characteristics of epithelioid variant of pleomorphic liposarcoma. Pleomorphic liposarcoma is a very rare variant of liposarcoma defined morphologically by the presence of pleomorphic lipoblasts showing peculiar epithelial-like features that can be confused with primary or metastatic carcinoma.

METHODS AND RESULTS

Molecular analysis demonstrated for the first time the presence of FUS-CHOP transcript in this liposarcoma variant. Microarray analysis revealed a gene expression profile related to a more aggressive tumour type when compared with other myxoid/round cell liposarcomas.

CONCLUSIONS

The present data show that the epithelioid variant of pleomorphic liposarcoma represents a further variant of myxoid liposarcoma sharing the FUS-CHOP fusion transcript but carrying a distinct expression profile, in keeping with its aggressive clinical course.

Laser capture microdissection (LCM) for analysis of gene expression in specific tissues during embryonic epithelial-mesenchymal transformation

The analysis of gene expression in developing organs is a valuable tool for the assessment of genetic fingerprints during the various stages of tissue differentiation and epithelial-mesenchymal transformation (EMT). However, the variety of differentiating cells and the close association of epithelial and mesenchymal cells makes it difficult to extract protein and mRNA from specific cells and tissue and, thus, to assign expressed genes to specific cell populations. We report here the analysis of LEF1 mRNA in epithelial and mesenchymal cells isolated by LCM from different stages of EMT during development of the mouse palate and describe our techniques in detail. By applying a laser capture microdissection (LCM) technique and real-time polymerase chain reaction, we were able to determine mRNA levels that accurately reflect changes in gene expression in specific cells. The sensitivity of the technique is remarkable. Indeed, the mRNAs can be detected for many proteins too low in abundance to stain with antibodies. These techniques will enable embryologists to collect homogeneous groups of cells from heterogeneous populations in developing organs, which otherwise would not be available for gene analysis.

Molecular regulation of the VEGF family – inducers of angiogenesis and lymphangiogenesis

The vascular endothelial growth factor (VEGF) family of secreted glycoproteins are critical inducers of angiogenesis (growth of blood vessels) and lymphangiogenesis (growth of lymphatic vessels). These proteins are attractive therapeutic targets for blocking growth of blood vessels and lymphatics in tumors and thereby inhibiting the growth and spread of cancer -- in fact, the first VEGF inhibitor has recently entered the clinic for treatment of cancer. In addition, the VEGFs are being considered for stimulation of angiogenesis in the context of ischemic disease and lymphangiogenesis for treatment of lymphedema. These therapeutic possibilities have focused great interest on the molecular regulation of VEGF family members. Much has been learned in the past five years about the mechanisms controlling the action of the VEGFs, including the importance of hypoxia, proteolysis, transcription factors and RNA splicing. An understanding of these mechanisms offers broader opportunities to manipulate expression and activity of the VEGFs for treatment of disease.

Circulating D-dimer levels are better predictors of overall survival and disease progression than carcinoembryonic antigen levels in patients with metastatic colorectal carcinoma

BACKGROUND

Fibrin formation is required for tumor angiogenesis, metastasis, and invasion. D-dimer, a fibrin degradation product, is produced when crosslinked fibrin is degraded by plasmin. The current study prospectively examined D-dimer levels in patients with metastatic colorectal carcinoma treated in a Phase II randomized trial comparing bevacizumab (Avastin, Genentech, South San Francisco, CA) plus 5-fluorouracil/leucovorin (5-FU/LV) with 5-FU/LV alone.

METHODS

At least one circulating D-dimer level was evaluable in 98 of the 104 previously untreated patients with metastatic colorectal carcinoma in the current trial. Plasma D-dimer levels were determined using a quantitative immunoassay kit at enrollment, before each treatment, and at the time of trial completion or disease progression.

RESULTS

At trial enrollment, 86 of 104 patients (88%) had elevated D-dimer levels (> 20 ng/mL), and 86 of 102 patients (84%) had elevated carcinoembryonic antigen (CEA) levels (> 3 ng/mL). Baseline D-dimer levels were correlated with the following baseline characteristics: CEA (Pearson coefficient, 0.31; P = 0.002), albumin levels (Pearson coefficient, -0.32; P = 0.002), tumor burden (Pearson coefficient, 0.30; P = 0.003), and number of metastatic sites (Pearson coefficient, 0.21; P = 0.04). At the time of progression, plasma D-dimer levels reached a maximum postbaseline value in 51 of 61 patients (84%), whereas the CEA level was at its maximum postbaseline value in 39 of 55 patients (71%). Baseline D-dimer levels were a strong predictor of overall survival on univariate analysis (P = 0.008) and multivariate analysis (P = 0.03). Overall, treatment with bevacizumab (5 mg/kg) and baseline D-dimer levels were the only predictors of overall survival (P < 0.05).

CONCLUSIONS

The current study indicates that fibrin remodeling is an important prognostic feature in metastatic colorectal carcinoma. D-dimer levels should be incorporated into prognostic models, and D-dimer may represent a useful biomarker for patients treated with antiangiogenic agents.

Tumor growth and metastasis are not affected in thrombin-activatable fibrinolysis inhibitor-deficient mice

Many studies have indicated that the plasminogen activation system may have a prominent role in cancer. Activation of the zymogen plasminogen into the serine protease plasmin by plasminogen activator is mediated by carboxyterminal basic amino acids in fibrin, including lysines and arginines. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating carboxypeptidase B-type proenzyme that, after activation, removes carboxyterminal lysine or arginine residues in fibrin, resulting in decreased plasminogen activation and attenuated fibrinolysis. To determine directly whether TAFI is involved in primary tumor growth and metastasis formation, we examined the effects of TAFI deficiency on subcutaneous growth and experimentally or spontaneously induced pulmonary metastasis formation of different tumor cell types in mice. In all tumor models TAFI deficiency did not affect the formation and growth of primary and metastasized tumors.

Plasmin‐activated doxorubicin prodrugs containing a spacer reduce tumor growth and angiogenesis without systemic toxicity

To generate doxorubicin (Dox) specifically at the tumor site, the chemotherapeutic agent was incorporated into a prodrug by linkage to a peptide specifically recognized by plasmin, which is overproduced in many cancers. ST-9905, which contains an elongated self-elimination spacer, is activated more rapidly in vitro by plasmin than is ST-9802. Prodrug activation in vitro depended on the level of urokinase produced by tumor cells and was inhibited by aprotinin, a plasmin inhibitor. Comparison of equimolar concentrations of ST-9905, ST-9802, and Dox in EF43.fgf-4 and MCF7 models revealed that both prodrugs, in sharp contrast to Dox, displayed antiproliferative and antiangiogenic activities without discernible toxicity. Although MCF7 cells are poor urokinase producers in vitro, prodrug efficacy in this model may be explained by production of plasmin by tumor-infiltrating host cells. Mice treated with equitoxic concentrations (maximum tolerated doses) of prodrugs showed 100% survival and negligible body weight loss, in contrast to results after Dox treatment. ST-9905 was substantially more effective than ST-9802 and induced similar tumor growth inhibition as Dox but without apparent toxicity. This finding may be explained by the elongated spacer, which facilitates enzymatic prodrug activation. These data validate both the use of elongated spacers in vivo and the concept of targeting anticancer prodrugs to tumor-associated plasmin.

Plasminogen supports tumor growth through a fibrinogen-dependent mechanism linked to vascular patency

The growth of Lewis lung carcinoma (LLC) was sustained in plasminogen-deficient mice when transplanted into the dorsal skin but was dramatically suppressed in another anatomic location, the footpad. This unanticipated negative effect of plasminogen deficiency on footpad tumor growth was entirely relieved by superimposing a deficit in fibrinogen. This finding was not simply an unusual feature of LLC tumors--T241 fibrosarcoma growth in the footpad was also restricted by plasminogen deficiency in a fibrinogen-dependent manner. The probable mechanistic basis for suppression of tumor growth was revealed through transmission electron microscopy studies of tumor tissues. Occlusive microvascular thrombi were commonplace within footpad tumors from plasminogen-deficient mice, whereas no such lesions were observed within either dorsal skin tumors from plasminogen-deficient mice or footpad tumors from mice that also lacked fibrinogen. The data infer that tumor growth in the footpad of plasminogen-deficient mice is compromised as a function of the formation and persistence of vaso-occlusive thrombi that limit tumor blood supply. These studies indicate that plasminogen and fibrinogen can serve as critical determinants of tumor growth, but their relative importance is dependent on the tumor microenvironment. Furthermore, these studies suggest that one target of plasmin(ogen) relevant to tumor progression in vivo is intravascular fibrin.

Stromal cell involvement in cancer

Solid tumors co-opt the body's endogenous extracellular proteolytic machinery for their invasion and metastasis. This is supported by a large number of independent observations ranging from histochemical and prognostic studies of cancer patient material to animal experiments. There are several extracellular proteolytic systems that are relevant in the context of cancer, but the plasminogen activation (PA) system and the matrix metalloproteases (MMPs) remain the most thoroughly investigated. Localization studies by immunohistochemistry and in situ mRNA hybridization in tumors of common human cancers have repeatedly identified members of the PA and MMP systems in stromal cells. The cancer cells, of epithelial origin, contribute PA and MMP components in some cases, but their contribution fades in comparison with the overwhelming expression of proteolytic components by fibroblasts, macrophages, endothelial cells, and other stromal cells. Ideal animal models of human cancers should recapitulate this fundamental proteolytic aspect of tumor biology. However, in the transplantable tumor models where PA or MMP components have been studied at the cellular level in vivo, this is most often not the case. Transgenic cancer models may provide a closer parallel to the human situation, in that PA and MMP components are synthesized by the tumor stroma. The pivotal role of stromal cells has been confirmed experimentally in mouse models in which the expression pattern of proteolytic components is strongly reminiscent of human tumors. In these models it is possible to reconstitute the wild-type tumor characteristics of proteolytically deficient tumor-bearing mice by transplantation with wild-type fibroblasts or hemapoietic cells. These studies collectively show that cancer-associated proteolysis is a collaborative effort of malignant cancer cells and various stromal cells--a collaboration in which stromal cells contribute the majority of the active proteolytic components that are necessary for the invasive behavior of the tumors. This cellular division of labor positions the stromal cells as prime targets for future research and possibly therapy. Vascular endothelial cells are already the focus of intense therapeutically relevant research, but tumor-associated fibroblasts, macrophages, neutrophils, lymphendothelial cells, etc. provide additional largely unexplored territory in the ongoing search for efficient countermeasures against invasive cancer.

Plasmin activates the lymphangiogenic growth factors VEGF-C and VEGF-D

Vascular endothelial growth factor (VEGF) C and VEGF-D stimulate lymphangiogenesis and angiogenesis in tissues and tumors by activating the endothelial cell surface receptor tyrosine kinases VEGF receptor (VEGFR) 2 and VEGFR-3. These growth factors are secreted as full-length inactive forms consisting of NH2- and COOH-terminal propeptides and a central VEGF homology domain (VHD) containing receptor binding sites. Proteolytic cleavage removes the propeptides to generate mature forms, consisting of dimers of the VEGF homology domain, that bind receptors with much greater affinity than the full-length forms. Therefore, proteolytic processing activates VEGF-C and VEGF-D, although the proteases involved were unknown. Here, we report that the serine protease plasmin cleaved both propeptides from the VEGF homology domain of human VEGF-D and thereby generated a mature form exhibiting greatly enhanced binding and cross-linking of VEGFR-2 and VEGFR-3 in comparison to full-length material. Plasmin also activated VEGF-C. As lymphangiogenic growth factors promote the metastatic spread of cancer via the lymphatics, the proteolytic activation of these molecules represents a potential target for antimetastatic agents. Identification of an enzyme that activates the lymphangiogenic growth factors will facilitate development of inhibitors of metastasis.

Plasminogen directs the pleiotropic effects of uPA in liver injury and repair

The urokinase-type plasminogen activator (uPA) plays a central role in liver repair. Nevertheless, the hepatic overexpression of uPA results in panlobular injury and neonatal mortality. Here, we define the molecular mechanisms of liver injury and explore whether uPA can regulate liver repair independently of plasminogen. To address the hypothesis that the liver injury in transgenic mice results from the intracellular activation of plasminogen by transgene-derived uPA (uPAT), we generated mice that overexpress uPAT and lack functional plasminogen (uPAT-Plg(-)). In these mice, loss of plasminogen abolished the hepatocyte-specific injury and prevented the formation of regenerative nodules displayed by uPAT littermates. Despite the increased expression of hepatic uPA, livers of uPAT-Plg(-) mice were unable to clear necrotic cells and restore normal lobular organization after an acute injury. Notably, high levels of circulating uPA in uPAT-Plg(-) mice did not prevent the long-term extrahepatic abnormalities previously associated with plasminogen deficiency. These data demonstrate that plasminogen directs the hepatocyte injury induced by uPAT and mediates the reparative properties of uPA in the liver.

Potent antitumor activity of a urokinase-activated engineered anthrax toxin

The acquisition of cell-surface urokinase plasminogen activator activity is a hallmark of malignancy. We generated an engineered anthrax toxin that is activated by cell-surface urokinase in vivo and displays limited toxicity to normal tissue but broad and potent tumoricidal activity. Native anthrax toxin protective antigen, when administered with a chimeric anthrax toxin lethal factor, Pseudomonas exotoxin fusion protein, was extremely toxic to mice, causing rapid and fatal organ damage. Replacing the furin activation sequence in anthrax toxin protective antigen with an artificial peptide sequence efficiently activated by urokinase greatly attenuated toxicity to mice. In addition, the mutation conferred cell-surface urokinase-dependent toxin activation in vivo, as determined by using a panel of plasminogen, plasminogen activator, plasminogen activator receptor, and plasminogen activator inhibitor-deficient mice. Surprisingly, toxin activation critically depended on both urokinase plasminogen activator receptor and plasminogen in vivo, showing that both proteins are essential cofactors for the generation of cell-surface urokinase. The engineered toxin displayed potent tumor cell cytotoxicity to a spectrum of transplanted tumors of diverse origin and could eradicate established solid tumors. This tumoricidal activity depended strictly on tumor cell-surface plasminogen activation. The data show that a simple change of protease activation specificity converts anthrax toxin from a highly lethal to a potent tumoricidal agent.

Rac1-MKK3-p38-MAPKAPK2 pathway promotes urokinase plasminogen activator mRNA stability in invasive breast cancer cells

We reported previously that down-regulating or functionally blocking alphav integrins inhibits endogenous p38 mitogen-activated protein kinase (MAPK) activity and urokinase plasminogen activator (uPA) expression in invasive MDA-MB-231 breast cancer cells whereas engaging alphav integrins with vitronectin activates p38 MAPK and up-regulates uPA expression (Chen, J., Baskerville, C., Han, Q., Pan, Z., and Huang, S. (2001) J. Biol. Chem. 276, 47901-47905). Currently, it is not clear what upstream and downstream signaling molecules of p38 MAPK mediate alphav integrin-mediated uPA up-regulation. In the present study, we found that alphav integrin ligation activated small GTPase Rac1 preferentially, and dominant negative Rac1 inhibited alphav integrin-mediated p38 MAPK activation. Using constitutively active MAPK kinases, we found that both constitutively active MKK3 and MKK6 mutants were able to activate p38 MAPK and up-regulate uPA expression, but only dominant negative MKK3 blocked alphav integrin-mediated p38 MAPK activation and uPA up-regulation. These results suggest that MKK3, rather than MKK6, mediates alphav integrin-induced p38 MAPK activation. Among the potential downstream effectors of p38 MAPK, we found that only MAPK-activated protein kinase 2 affects alphav integrin-mediated uPA up-regulation significantly. Finally, using beta-globin reporter gene constructs containing uPA mRNA 3'-untranslated region (UTR) and adenosine/uridine-rich elements-deleted 3'-UTR, we demonstrated that p38 MAPK/MAPK-activated protein kinase 2 signaling pathway regulated uPA mRNA stability through a mechanism involving the adenosine/uridine-rich elements sequence in 3'-UTR of uPA mRNA.

Matrix metalloproteinases (MMPs) regulate fibrin-invasive activity via MT1-MMP-dependent and -independent processes

Cross-linked fibrin is deposited in tissues surrounding wounds, inflammatory sites, or tumors and serves not only as a supporting substratum for trafficking cells, but also as a structural barrier to invasion. While the plasminogen activator-plasminogen axis provides cells with a powerful fibrinolytic system, plasminogen-deleted animals use alternate proteolytic processes that allow fibrin invasion to proceed normally. Using fibroblasts recovered from wild-type or gene-deleted mice, invasion of three-dimensional fibrin gels proceeded in a matrix metalloproteinase (MMP)-dependent fashion. Consistent with earlier studies supporting a singular role for the membrane-anchored MMP, MT1-MMP, in fibrin-invasive events, fibroblasts from MT1-MMP-null mice displayed an early defect in invasion. However, MT1-MMP-deleted fibroblasts circumvented this early deficiency and exhibited compensatory fibrin-invasive activity. The MT1-MMP-independent process was sensitive to MMP inhibitors that target membrane-anchored MMPs, and further studies identified MT2-MMP and MT3-MMP, but not MT4-MMP, as alternate pro-invasive factors. Given the widespread distribution of MT1-, 2-, and 3-MMP in normal and neoplastic cells, these data identify a subset of membrane-anchored MMPs that operate in an autonomous fashion to drive fibrin-invasive activity.

Regulation of extravascular coagulation and fibrinolysis by heparin-dependent mast cell chymase

We recently characterized a heparin-deficient mouse strain generated by targeting the gene for N-deacetylase/N-sulfotransferase-2 (NDST-2). The NDST-2-/- mice show severe defects in their organization of mast cell (MC) secretory granules, with an almost total absence of the various heparin-binding MC proteases. In the present report we have studied the consequences of heparin/MC protease deficiency for extravascular coagulation and fibrinolysis. Addition of prothrombin to peritoneal cells-a mixture of macrophages, lymphocytes, and MCs-resulted in formation of thrombin but the accumulation of thrombin occurred faster in the NDST-2-/-cells than in normal controls. Further, the generated thrombin was subsequently inactivated in the NDST-2+/+ cell cultures but not in the NDST-2-/- cells. Plasminogen was activated to plasmin at an apparently higher rate in peritoneal cells from NDST-2 null mice than in the normal controls. Similar to thrombin, the generated plasmin was inactivated by NDST-2+/+ but not by the NDST-2-/- cells. Subsequent experiments with normal cells showed that cell surface-associated MC chymase, in a strongly heparin-dependent manner, was responsible for both the thrombin-inactivating- and plasmin-inactivating activities. These results show that MC chymase-heparin complexes have the potential to regulate extravascular coagulation processes, as well as the plasminogen activator/plasmin system.