Tissue factor-positive tumor microvesicles activate platelets and enhance thrombosis in mice

Tissue factor expression, extracellular vesicles, and thrombosis after infection with the respiratory viruses influenza A virus and coronavirus

Tissue factor (TF) is induced in a variety of cell types during viral infection, which likely contributes to disseminated intravascular coagulation and thrombosis. TF-expressing cells also release TF-positive extracellular vesicles (EVs) into the circulation that can be measured using an EVTF activity assay. This review summarizes studies that analyze TF expression, TF-positive EVs, activation of coagulation, and thrombosis after infection with influenza A virus (IAV) and coronaviruses (CoVs), including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), SARS-CoV, and Middle East respiratory syndrome CoV (MERS-CoV). The current pandemic of coronavirus disease 2019 (COVID-19) is caused by infection with SARS-CoV-2. Infection of mice with IAV increased TF expression in lung epithelial cells as well as increased EVTF activity and activation of coagulation in the bronchoalveolar lavage fluid (BALF). Infection of mice with MERS-CoV, SARS-CoV, and SARS-CoV-2 also increased lung TF expression. Single-cell RNA sequencing analysis on the BALF from severe COVID-19 patients revealed increased TF mRNA expression in epithelial cells. TF expression was observed in peripheral blood mononuclear cells infected with SARS-CoV. TF was also expressed by peripheral blood mononuclear cells, monocytes in platelet-monocyte aggregates, and neutrophils isolated from COVID-19 patients. Elevated circulating EVTF activity was observed in severe IAV and COVID-19 patients. Importantly, EVTF activity was associated with mortality in severe IAV patients and with plasma D-dimer, severity, thrombosis, and mortality in COVID-19 patients. These studies strongly suggest that increased TF expression in patients infected with IAV and pathogenic CoVs contributes to thrombosis.

Roles of Microvesicles in Tumor Progression and Clinical Applications

Microvesicles are extracellular vesicles with diameter ranging from 100 to 1000 nm that are secreted by tumor cells or other cells in the tumor microenvironment. A growing number of studies demonstrate that tumor-derived microvesicles are involved in tumor initiation and progression, as well as drug resistance. In addition, tumor-derived microvesicles carry a variety of immunogenic molecules and inhibit tumor response to immunotherapy; therefore, they can be exploited for use in tumor vaccines. Moreover, because of their high stability, tumor-derived microvesicles extracted from body fluids can be used as biomarkers for cancer diagnosis or assessment of prognosis. Tumor-derived microvesicles can also be deployed to reverse drug resistance of tumor regenerative cells, or to deliver chemotherapeutic drugs and oncolytic adenovirus for the treatment of cancer patients. This review summarizes the general characteristics of tumor-derived microvesicles, focusing on their biological characteristics, their involvement in tumor progression, and their clinical applications.

Extracellular vesicles in pancreatic cancer progression and therapies

Pancreatic cancer (PC) is one of the leading causes of cancer-related death worldwide due to delayed diagnosis and limited treatments. More than 90% of all pancreatic cancers are pancreatic ductal adenocarcinoma (PDAC). Extensive communication between tumour cells and other cell types in the tumour microenvironment have been identified which regulate cancer hallmarks during pancreatic tumorigenesis via secretory factors and extracellular vesicles (EVs). The EV-capsuled factors not only facilitate tumour growth locally, but also enter circulation and reach distant organs to construct a pre-metastatic niche. In this review, we delineate the key factors in pancreatic ductal adenocarcinoma derived EVs that mediate different tumour processes. Also, we highlight the factors that are related to the crosstalk with cancer stem cells/cancer-initiating cells (CSC/CIC), the subpopulation of cancer cells that can efficiently metastasize and resist currently used chemotherapies. Lastly, we discuss the potential of EV-capsuled factors in early diagnosis and antitumour therapeutic strategies.

Extracellular Vesicles and Thrombosis: Update on the Clinical and Experimental Evidence

Extracellular vesicles (EVs) compose a heterogenous group of membrane-derived particles, including exosomes, microvesicles and apoptotic bodies, which are released into the extracellular environment in response to proinflammatory or proapoptotic stimuli. From earlier studies suggesting that EV shedding constitutes a cellular clearance mechanism, it has become evident that EV formation, secretion and uptake represent important mechanisms of intercellular communication and exchange of a wide variety of molecules, with relevance in both physiological and pathological situations. The putative role of EVs in hemostasis and thrombosis is supported by clinical and experimental studies unraveling how these cell-derived structures affect clot formation (and resolution). From those studies, it has become clear that the prothrombotic effects of EVs are not restricted to the exposure of tissue factor (TF) and phosphatidylserines (PS), but also involve multiplication of procoagulant surfaces, cross-linking of different cellular players at the site of injury and transfer of activation signals to other cell types. Here, we summarize the existing and novel clinical and experimental evidence on the role and function of EVs during arterial and venous thrombus formation and how they may be used as biomarkers as well as therapeutic vectors.

Tissue factor and its procoagulant activity on cancer-associated thromboembolism in pancreatic cancer

Pancreatic cancer frequently involves cancer-associated thromboembolism, which is strongly associated with poor prognosis. Tissue factor, a blood coagulation factor largely produced in cancer patients as a component of extracellular vesicles, plays a key role in the incidence of cancer-associated thromboembolism in patients with pancreatic cancer. However, no prospective studies have been published on the relationship between tissue factor and cancer-associated thromboembolism or patient clinical characteristics, including recent chemotherapy regimens. Thus, we aimed to address this in a Japanese cohort of 197 patients and 41 healthy volunteers. Plasma tissue factor levels were measured by ELISAs preevaluated by tissue factor specificity. Multivariable analysis was used to identify independent predictors of cancer-associated thromboembolism. We found that the cancer-associated thromboembolism rate in the patient cohort was 6.6% (4.6%, venous thromboembolism; 2.0%, arterial thromboembolism). Tissue factor levels of 100 pg/mL or higher at patient registration were predictive of cancer-associated thromboembolism, with positive and negative predictive values of 23.1% and 94.6%, respectively. Multivariable analysis showed that plasma tissue factor levels were an independent predictive factor for cancer-associated thromboembolism, with a risk ratio of 5.54 (95% confidence interval, 1.02-30.09). Unlike in healthy volunteers and patients without cancer-associated thromboembolism, tissue factor levels were highly correlated with extracellular vesicles' procoagulant activity in patients developing cancer-associated thromboembolism. Taken together, our data show that the tissue factor levels at patient registration were a predictive factor for cancer-associated thromboembolism in this cohort of patients with pancreatic cancer.

Tissue Factor and Extracellular Vesicles: Activation of Coagulation and Impact on Survival in Cancer

Simple Summary

The tissue factor (TF)-factor VIIa complex is the major physiological initiator of blood coagulation. Tumors express TF and release TF-positive extracellular vesicles (EVs) into the circulation, and this is associated with the activation of coagulation. Circulating levels of EVTF activity may be a useful biomarker to identify patients at risk for thrombosis. Tumor TF and TF-positive EVs are also associated with reduced survival.

Abstract

Tissue factor (TF) is a transmembrane glycoprotein that functions as a receptor for FVII/FVIIa and initiates the extrinsic coagulation pathway. Tumors and cancer cells express TF that can be released in the form of TF positive (TF+) extracellular vesicles (EVs). In this review, we summarize the studies of tumor TF and TF + EVs, and their association with activation of coagulation and survival in cancer patients. We also summarize the role of tumor-derived TF + EVs in venous thrombosis in mouse models. Levels of tumor TF and TF + EVs are associated with venous thromboembolism in pancreatic cancer patients. In addition, levels of EVTF activity are associated with disseminated intravascular coagulation in cancer patients. Furthermore, tumor-derived TF + EVs enhance venous thrombosis in mice. Tumor TF and TF + EVs are also associated with worse survival in cancer patients, particularly in pancreatic cancer patients. These studies indicate that EVTF activity could be used as a biomarker to identify pancreatic cancer patients at risk for venous thrombosis and cancer patients at risk for disseminated intravascular coagulation. EVTF activity may also be a useful prognostic biomarker in cancer patients.

Thrombotic potential during pediatric acute lymphoblastic leukemia induction: Role of cell-free DNA

BACKGROUND

Thromboembolism affects up to 30% of children undergoing treatment for acute lymphoblastic leukemia (ALL). Increased thrombin generation has been reported in ALL, but the mechanisms remain elusive.

OBJECTIVE

We aimed to show that extracellular traps and cell-free DNA (cfDNA) promote thrombin generation in pediatric ALL.

METHODS

In a longitudinal single-center study, we recruited 17 consecutive pediatric ALL patients. Serial blood samples were collected at diagnosis and weekly during the 4-week induction phase of antileukemic chemotherapy. Healthy children (n = 14) and children with deep vein thrombosis (DVT; n = 7) or sepsis (n = 5) were recruited as negative and positive controls, respectively. In plasma, we measured endogenous thrombin generation potential (ETP) and components of extracellular traps, including cfDNA.

RESULTS

In patients with ALL, ETP was increased at baseline and remained significantly elevated throughout the induction therapy. Plasma levels of cfDNA were increased at baseline and during the first 3 weeks of induction therapy. The extent of enhancement of ETP and plasma cfDNA in patients with ALL was similar to that seen in patients with DVT or sepsis. Treatment of plasma with DNase 1 lowered ETP in patients with ALL at each time point but did not affect ETP in healthy controls.

CONCLUSION

We conclude that childhood ALL is associated with a prothrombotic milieu at the time of diagnosis that continues during induction chemotherapy, and cfDNA contributes to increased thrombogenic potential.

Coagulation signaling and cancer immunotherapy

The last decades have delineated many interactions of the hemostatic system with cancer cells that are pivotal for cancer-associated thrombosis, angiogenesis and metastasis. Expanding evidence shows that platelets, the tissue factor pathway, and proteolytic signaling involving protease-activated receptors (PARs) are also central players in innate and adaptive immunity. Recent studies in immune-competent mice have uncovered new immune-evasive roles of coagulation signaling networks in the development and growth of different preclinical tumor models. Tumor-type specific PAR1 signaling facilitates the escape from immune surveillance by cytotoxic T cells. In addition, tumor-associated macrophages produce factor X (FX) and cell autonomous FXa-PAR2 signaling emerges as a central mechanism for tumor-promoting macrophage polarization in the tumor microenvironment. Pharmacological targeting of this signaling pathway with tissue penetrating oral FXa inhibitor reprograms macrophage phenotypes, enhances tumor antigen presentation, and expands tumor-killing cytotoxic lymphocytes. Importantly, by specifically targeting innate immune cells, the oral FXa inhibitor rivaroxaban synergizes with checkpoint inhibitor therapy in enhancing antigen-specific antitumor immunity. In similar experiments, anticoagulation with heparin is inefficient to block extravascular coagulation signaling. Thus, antithrombotic therapy with oral FXa inhibitors may contribute to reversing tumor immune-evasive mechanisms and enhance the clinical outcome of targeted immuno-therapy regimens.

Factor VIIa induces extracellular vesicles from the endothelium: a potential mechanism for its hemostatic effect

Recombinant factor FVIIa (rFVIIa) is used as a hemostatic agent to treat bleeding disorders in hemophilia patients with inhibitors and other groups of patients. Our recent studies showed that FVIIa binds endothelial cell protein C receptor (EPCR) and induces protease-activated receptor 1 (PAR1)-mediated biased signaling. The importance of FVIIa-EPCR-PAR1-mediated signaling in hemostasis is unknown. In the present study, we show that FVIIa induces the release of extracellular vesicles (EVs) from endothelial cells both in vitro and in vivo. Silencing of EPCR or PAR1 in endothelial cells blocked the FVIIa-induced generation of EVs. Consistent with these data, FVIIa treatment enhanced the release of EVs from murine brain endothelial cells isolated from wild-type (WT), EPCR-overexpressing, and PAR1-R46Q-mutant mice, but not EPCR-deficient or PAR1-R41Q-mutant mice. In vivo studies revealed that administration of FVIIa to WT, EPCR-overexpressing, and PAR1-R46Q-mutant mice, but not EPCR-deficient or PAR1-R41Q-mutant mice, increased the number of circulating EVs. EVs released in response to FVIIa treatment exhibit enhanced procoagulant activity. Infusion of FVIIa-generated EVs and not control EVs to platelet-depleted mice increased thrombin generation at the site of injury and reduced blood loss. Administration of FVIIa-generated EVs or generation of EVs endogenously by administering FVIIa augmented the hemostatic effect of FVIIa. Overall, our data reveal that FVIIa treatment, through FVIIa-EPCR-PAR1 signaling, releases EVs from the endothelium into the circulation, and these EVs contribute to the hemostatic effect of FVIIa.

Large extracellular vesicles in the left atrial appendage in patients with atrial fibrillation-the missing link?

Atrial fibrillation (AF) is the most frequent arrhythmic disease in humans, which leads to thrombus formation in the left atrial appendage and stroke through peripheral embolization. Depending on their origin, large extracellular vesicles (lEVs) can exert pro-coagulant functions. In the present study, we investigated how different types of AF influence the levels of large EV subtypes in three distinct atrial localizations. Blood samples were collected from the right and left atrium and the left atrial appendage of 58 patients. 49% of the patients had permanent AF, 34% had non-permanent AF, and 17% had no history of AF. Flow cytometric analysis of the origin of the lEVs showed that the proportion of platelet-derived lEVs in the left atrial appendage was significantly higher in permanent AF patients compared to non-permanent AF. When we grouped patients according to their current heart rhythm, we also detected significantly higher levels of platelet-derived lEVs in the left atrial appendage (LAA) in patients with atrial fibrillation. In vitro studies revealed, that platelet activation with lipopolysaccharide (LPS) leads to higher levels of miR-222-3p and miR-223-3p in platelet-derived lEVs. Treatment with lEVs from LPS- or thrombin-activated platelets reduces the migration of endothelial cells in vitro. These results suggest that permanent atrial fibrillation is associated with increased levels of platelet-derived lEVs in the LAA, which are potentially involved in LAA thrombus formation.

Plasminogen activator inhibitor 1 and venous thrombosis in pancreatic cancer

Pancreatic cancer patients have a high risk of venous thromboembolism (VTE). Plasminogen activator inhibitor 1 (PAI-1) inhibits plasminogen activators and increases the risk of thrombosis. PAI-1 is expressed by pancreatic tumors and human pancreatic cell lines. However, to date, there are no studies analyzing the association of active PAI-1 and VTE in pancreatic cancer patients. We investigated the association of active PAI-1 in plasma and VTE in pancreatic cancer patients. In addition, we determined if the presence of human pancreatic tumors expressing PAI-1 impairs venous thrombus resolution in mice. Plasma levels of active PAI-1 in patients with pancreatic cancer and mice bearing human tumors were determined by enzyme-linked immunosorbent assay. We measured PAI-1 expression in 5 different human pancreatic cancer cell lines and found that PANC-1 cells expressed the highest level. PANC-1 tumors were grown in nude mice. Venous thrombosis was induced by complete ligation of the inferior vena cava (IVC). Levels of active PAI-1 were independently associated with increased risk of VTE in patients with pancreatic cancer (subdistribution hazard ratio per doubling of levels: 1.39 [95% confidence interval, 1.09-1.78], P = .007). Mice bearing PANC-1 tumors had increased levels of both active human and active mouse PAI-1 and decreased levels of plasmin activity. Importantly, mice bearing PANC-1 tumors exhibited impaired venous thrombus resolution 8 days after IVC stasis compared with nontumor controls. Our results suggest that PAI-1 contributes to VTE in pancreatic cancer.

Novel Pathophysiological Mechanisms of Thrombosis in Myeloproliferative Neoplasms

PURPOSE OF REVIEW

Thrombosis remains a leading cause of morbidity and mortality in BCR/ABL negative myeloproliferative neoplasms (MPN). Circulating blood cells are both increased in quantity and qualitatively abnormal in MPN, resulting in an increased thrombotic risk. Herein, we review recently elucidated mechanisms of MPN thrombosis and discuss implications of drugs currently under investigation for MPN.

RECENT FINDINGS

Recent studies highlight that in JAK2^V617F granulocytes and platelets, thrombo-inflammatory genes are upregulated. Furthermore, in JAK2^V617F granulocytes, protein expression of integrin CD11b, tissue factor, and leukocyte alkaline phosphatase are all increased. Overall, myeloid cells, namely neutrophils, may contribute in several ways, such as through increased adhesion via β1 integrin binding to VCAM1, increased infiltration, and enhanced inducibility to extrude neutrophil extracellular traps. Non-myeloid inflammatory cells may also contribute via secretion of cytokines. With regard to red blood cells, number, rigidity, adhesion, and generation of microvesicles may lead to increased vascular resistance as well as increased cell-cell interactions that promote rolling and adhesion. Platelets may also contribute in a similar fashion. Lastly, the vasculature is also increasingly appreciated, as several studies have demonstrated increased endothelial expression of pro-coagulant and pro-adhesive proteins, such as von Willebrand factor or P-selectin in JAK2^V617F endothelial cells. With the advent of molecular diagnostics, MPN therapeutics are advancing beyond cytoreduction. Our increased understanding of pro-inflammatory and thrombotic pathophysiology in MPN provides a rational basis for evaluation of in-development MPN therapeutics to reduce thrombosis.

Phosphatidylserine-exposing tumor-derived microparticles exacerbate coagulation and cancer cell transendothelial migration in triple-negative breast cancer

Background: Neoadjuvant chemotherapy is relevant to the formation of thromboembolism and secondary neoplasms in triple-negative breast cancer (TNBC). Chemotherapy-induced breast cancer cell-derived microparticles (BCMPs) may have important thrombogenic and pro-metastatic effects on platelets and endothelium, which may be related to the expression and distribution of phosphatidylserine (PS). However, investigating these interactions is challenging due to technical limitations. Methods: A study was conducted in 20 healthy individuals and 18 patients who had been recently diagnosed with TNBC and were undergoing neoadjuvant chemotherapy with doxorubicin and cyclophosphamide. BCMPs were isolated from patient blood samples and doxorubicin-treated breast cancer cell lines. Their structure and morphology were studied by electron microscopy and antigen levels were measured by fluorescence-activated cell sorting. In an inhibition assay, isolated BCMPs were pretreated with lactadherin or tissue factor antibodies. Platelets isolated from healthy subjects were treated with BCMPs and coagulation time, fibrin formation, and expression of intrinsic/extrinsic factor Xase (FXa) and thrombin were evaluated. The effects of BCMPs on endothelial thrombogenicity and integrity were assessed by confocal microscopy, electron microscopy, measurement of intrinsic/extrinsic FXa, prothrombinase assay, and transwell permeability assay. Results: Neoadjuvant chemotherapy significantly increased the expression of PS+ BCMPs in patient plasma. Its expression was associated with a rapid increase in procoagulant activity. Treatment with lactadherin, a PS-binding scavenging molecule, markedly reduced the adhesion of BCMPs and abolished their procoagulant activity, but this was not observed with tissue factor antibody treatment. Intravenous injection of BCMPs in mice induced a significant hypercoagulable state, reducing the extent of plasma fibrinogen and promoting the appearance of new thrombus. Cancer cells incubated with doxorubicin released large numbers of PS+ BCMPs, which stimulated and transformed endothelial cells into a procoagulant phenotype and increased the aggregation and activation of platelets. Moreover, cancer cells exploited this BCMP-induced endothelial leakiness and showed promoted metastasis. Pretreatment with lactadherin increased uptake of both PS+ BCMPs and cancer cells by endothelial cells and limited the transendothelial migration of cancer cells. Conclusion: Lactadherin, a biosensor that we developed, was used to study the extracellular vesicle distribution of PS, which revealed a novel PS+ BCMPs administrative axis that initiated a local coagulation cascade and facilitated metastatic colonization of circulating cancer cells.

Spontaneous arterial thrombosis in a patient with advanced ovarian clear cell cancer: a case report and literature review

Patients with ovarian cancer are often in a hypercoagulable state and have a high risk of venous thrombosis, including deep vein thrombosis and pulmonary embolism. However, arterial thrombosis is relatively rare in ovarian cancer. We report a case a 46-year-old woman with ovarian clear cell carcinoma who developed arterial and venous thrombosis in the lower extremities as the first manifestation. Her arterial thrombosis-related ischemic symptoms were not responsive to anticoagulant treatment of low-molecular-weight heparin, but improved after neoadjuvant chemotherapy and surgery. Therefore, we hypothesize that the optimal therapy for arterial thrombosis in ovarian cancer is treatment for the underlying disease (i.e., ovarian cancer). A thorough investigation is required to determine the relationships between arterial thrombosis and ovarian cancer and antithrombotic treatments for ovarian cancer related-arterial thrombosis.

Progress on the Mechanism for Aspirin's Anti-tumor Effects

Since its discovery more than 100 years ago, aspirin has been widely used for its antipyretic, analgesic, anti-inflammatory, and anti-rheumatic activities. In addition to these applications, it is increasingly becoming clear that the drug also has great potential in the field of cancer. Here, we briefly review the current insights on aspirin's anti-tumor effects. These are multiple and vary from inhibiting the major cellular mTOR pathways, acting as a calorie-restricted mimetic by inhibition of energy production, suppressing platelet aggregation and granule release, inhibiting the immune escape of tumor cells, to decreasing inflammatory responses. We consider these five mechanisms of action the most significant for aspirin's anti-tumor effects, whereby the anti-tumor effect may ultimately stem from its inhibition of energy metabolism, platelet function, and inflammatory response. As such, aspirin can play an important role to reduce the occurrence, proliferation, and metastasis of various types of tumors. However, most of the collected data are still based on epidemiological investigations. More direct and effective evidence is needed, and the side effects of aspirin intake need to be solved before this drug can be widely applied in cancer treatment.

Deciphering the Role of the Coagulation Cascade and Autophagy in Cancer-Related Thrombosis and Metastasis

Thrombotic complications are the second leading cause of death among oncology patients worldwide. Enhanced thrombogenesis has multiple origins and may result from a deregulation of megakaryocyte platelet production in the bone marrow, the synthesis of coagulation factors in the liver, and coagulation factor signaling upon cancer and the tumor microenvironment (TME). While a hypercoagulable state has been attributed to factors such as thrombocytosis, enhanced platelet aggregation and Tissue Factor (TF) expression on cancer cells, further reports have suggested that coagulation factors can enhance metastasis through increased endothelial-cancer cell adhesion and enhanced endothelial cell activation. Autophagy is highly associated with cancer survival as a double-edged sword, as can both inhibit and promote cancer progression. In this review, we shall dissect the crosstalk between the coagulation cascade and autophagic pathway and its possible role in metastasis and cancer-associated thrombosis formation. The signaling of the coagulation cascade through the autophagic pathway within the hematopoietic stem cells, the endothelial cell and the cancer cell are discussed. Relevant to the coagulation cascade, we also examine the role of autophagy-related pathways in cancer treatment. In this review, we aim to bring to light possible new areas of cancer investigation and elucidate strategies for future therapeutic intervention.

Venous Thromboembolism Prophylaxis with Low-Molecular-Weight Heparin in Primary Central Nervous System Lymphoma

BACKGROUND

Venous thromboembolism (VTE) is a frequent, potentially lethal complication in individuals with cancer. Patients with brain tumors are at particularly high risk for VTE. Primary central nervous system lymphoma (PCNSL) is a rare subtype of diffuse large B cell lymphoma, involving the craniospinal axis. The incidence of VTE in patients with PCNSL was reported as very high, occurring mostly in the early period of therapy.

OBJECTIVES

We aimed to evaluate the efficacy and safety of prophylactic low-molecular-weight heparin (LMWH) throughout the treatment of PCNSL.

PATIENTS

All patients >18 years of age diagnosed and treated for PCNSL at our institution in 2005-2017 were included.

RESULTS

There were 44 patients; mean age at diagnosis was 61.5 years. Three patients (6.8%) had a personal history of thrombosis, 11 (25%) had a history of diabetes or smoking, and 32 (72%) had an Eastern Cooperative Oncology Group performance status of 0-1 at diagnosis. During treatment with LMWH, no VTE events were recorded; 2 (4.5%) patients experienced a minor bleeding event and 1 (2.3%) a major bleeding event.

CONCLUSIONS

Among our 44 patients with PCNSL treated with prophylactic LMWH, no VTE events were recorded, and only 1 (asymptomatic) intracranial bleed was recorded. Within the limitations of a retrospective nonrandomized study, our findings suggest that VTE prophylaxis may be beneficial for individuals with PCNSL.

Engineering of biomaterials for tumor modeling

Development of biomaterials mimicking tumor and its microenvironment has recently emerged for the use of drug discovery, precision medicine, and cancer biology. These biomimetic models have developed by reconstituting tumor and stroma cells within the 3D extracellular matrix. The models are recently extended to recapitulate the in vivo tumor microenvironment, including biological, chemical, and mechanical conditions tailored for specific cancer type and its microenvironment. In spite of the recent emergence of various innovative engineered tumor models, many of these models are still early stage to be adapted for cancer research. In this article, we review the current status of biomaterials engineering for tumor models considering three main aspects - cellular engineering, matrix engineering, and engineering for microenvironmental conditions. Considering cancer-specific variability in these aspects, our discussion is focused on pancreatic cancer, specifically pancreatic ductal adenocarcinoma (PDAC). In addition, we further discussed the current challenges and future opportunities to create reliable and relevant tumor models.

Hemostatic changes by thrombopoietin-receptor agonists in immune thrombocytopenia patients

Thrombopoietin receptor agonist (TPO-RA) treatment increases the thrombosis rate in immune thrombocytopenia (ITP). We hypothesize that TPO-RAs influence platelet function, global and secondary hemostasis and/or fibrinolysis. A systematic review was performed. If possible, data were compared between responders (relevant increase in platelet count), and non-responders. Twelve observational studies with 305 patients were included (responders (127/150 (85%))). There were indications that TPO-RA treatment enhanced platelet function, with respect to platelet-monocyte aggregates, soluble P-selectin, GPVI expression, and adhesion under flow. Studies addressing global and secondary hemostasis and fibrinolysis were scarce. Overall, no changes were found during TPO-RA treatment, apart from an accelerated clot formation and conflicting data on levels of plasminogen activator inhibitor (PAI)-1. The parameters that increased have previously been associated with thrombosis in other patient groups, and might contribute to the increased rate of thrombosis observed in TPO-RA-treated ITP patients.

Mechanisms and biomarkers of cancer-associated thrombosis

Cancer-associated thrombosis is a leading cause of non-cancer death in cancer patients and is comprised of both arterial and venous thromboembolism (VTE). There are multiple risk factors for developing VTE, including cancer type, stage, treatment, and other medical comorbidities, which suggests that the etiology of thrombosis is multifactorial. While cancer-associated thrombosis can be treated with anticoagulation, benefits of therapy must be balanced with the increased bleeding risks seen in patients with cancer. Although risk models exist for primary and recurrent VTE, additional predictors are needed to improve model performance and discrimination of high-risk patients. This review will outline the diverse mechanisms driving thrombosis in cancer patients, as well as provide an overview of biomarkers studied in thrombosis risk and important considerations when selecting candidate biomarkers.

Circulating blood extracellular vesicles as a tool to assess endothelial injury and chemotherapy toxicity in adjuvant cancer patients

Extracellular vesicles (EVs) are subcellular membrane blebs that include exosomes and microparticles, which represent a potential source for cancer biomarker discovery. We assess EVs characteristics as a tool to evaluate the endothelial and anti-tumor treatment injury during adjuvant chemotherapy in breast (BC) and colon cancer (CC) patients. Blood samples were taken from 29 BC and 25 CC patients before and after chemotherapy, as well as from healthy control donors (HC). Circulating blood EVs were isolated and characterized by size/concentration, membrane antigens for cell origin, thrombogenicity, and protein content. We observed higher EVs concentration and particle size in CC patients after chemotherapy compared with HC. Higher levels of endothelial EVs (CD144-positive) and vascular endothelial growth factor receptor 1 (VEGFR1), apparently as an indication of endothelial dysfunction, were found in all cancer patients, regardless of a given treatment, compared to HC. Levels of EVs labeled CD62E, CD34+41-, the lymphocyte markers CD11+ and CD-14+, Annexin-V, and the coagulation proteins TF and TFPI, however, sometimes demonstrate significant differences between patients, although HC did not show significant differences between patients pre- and post-chemotherapy. Most importantly, increasing levels of EVs encapsulated Angiostatin were found in patients with CC, while chemotherapy treatment leads to its notable rise in circulating blood EVs. Our results demonstrate the potential of EVs encapsulated Angiostatin as a tool to evaluate endothelial damage during adjuvant chemotherapy in BC and CC patients.

Platelet-derived extracellular vesicles regulate cell cycle progression and cell migration in breast cancer cells

Platelets have been extensively implicated in the progression of cancer and platelet-derived extracellular vesicles (PEVs) are gaining growing attention as potential mediators of the platelet-cancer interplay. PEVs are shed from platelet membrane in response to extracellular stimuli and carry important biological signals for intercellular communication. In this study we demonstrate that PEVs specifically bind to different breast cancer cells and elicit cell-specific functional responses. PEVs were massively internalized by the metastatic cell lines MDA-MB-231 and SKBR3 and the ductal carcinoma cell line BT474, but not by the MCF-7 cell line. In SKBR3 cells, PEVs decreased mitochondrial dehydrogenase activities and altered cell cycle progression without affecting cell viability. Conversely, PEVs potently stimulated migration and invasion of MDA-MB-231, without affecting the distribution in the different phases of the cell cycle. In all the analyzed breast cancer cells, PEVs triggered a sustained increase of intracellular Ca²⁺, but only in MDA-MB-231 cells, this was associated to the stimulation of selected signaling proteins implicated in migration, including p38MAPK and myosin light chain. Importantly, inhibition of myosin light chain phosphorylation by a Rho kinase inhibitor prevented PEVs-stimulated migration of MDA-MB-231 cells. Our results demonstrate that PEVs are versatile regulators of cancer cell behavior and elicit a variety of different responses depending on the specific breast cancer cell subtype.

The procoagulant activity of tissue factor expressed on fibroblasts is increased by tissue factor-negative extracellular vesicles

Tissue factor (TF) is critical for the activation of blood coagulation. TF function is regulated by the amount of externalised phosphatidylserine (PS) and phosphatidylethanolamine (PE) on the surface of the cell in which it is expressed. We investigated the role PS and PE in fibroblast TF function. Fibroblasts expressed 6-9 x 104 TF molecules/cell but had low specific activity for FXa generation. We confirmed that this was associated with minimal externalized PS and PE and characterised for the first time the molecular species of PS/PE demonstrating that these differed from those found in platelets. Mechanical damage of fibroblasts, used to simulate vascular injury, increased externalized PS/PE and led to a 7-fold increase in FXa generation that was inhibited by annexin V and an anti-TF antibody. Platelet-derived extracellular vesicles (EVs), that did not express TF, supported minimal FVIIa-dependent FXa generation but substantially increased fibroblast TF activity. This enhancement in fibroblast TF activity could also be achieved using synthetic liposomes comprising 10% PS without TF. In conclusion, despite high levels of surface TF expression, healthy fibroblasts express low levels of external-facing PS and PE limiting their ability to generate FXa. Addition of platelet-derived TF-negative EVs or artificial liposomes enhanced fibroblast TF activity in a PS dependent manner. These findings contribute information about the mechanisms that control TF function in the fibroblast membrane.

Cancer cell-derived tissue factor-positive extracellular vesicles: biomarkers of thrombosis and survival

PURPOSE OF REVIEW

Tissue factor (TF) is released from cancer cells and tumors in the form of extracellular vesicles (EVs). This review summarizes our current knowledge of the mechanisms of release of TF-positive EVs (TF+EVs) from cancer cells and the effect of these TF+EVs on cultured endothelial cells. In addition, we will summarize the contribution of TF+EVs to thrombosis in mice, and the association between plasma EVTF activity and venous thrombosis as well as survival of cancer patients.

RECENT FINDINGS

The release of TF+EVs from cancer cells is regulated by multiple factors, including hypoxia, epithelial-mesenchymal transition, and various intracellular signaling pathways. Cancer cell-derived, TF+EVs confer procoagulant activity to endothelial cells and induce the expression of adhesion proteins and IL-8. In addition, they contribute to thrombosis by directly activating the coagulation system and by generating thrombin that activates platelets in mouse models. Finally, there is an association between EVTF activity and venous thrombosis in pancreatic cancer patients as well as mortality in cancer patients.

SUMMARY

Cancer cell-derived TF+EVs bind to and activate endothelial cells. In addition, they serve as biomarkers of survival of cancer patients and venous thrombosis in pancreatic cancer patients.

Sickle Cell Disease: A Paradigm for Venous Thrombosis Pathophysiology

Venous thromboembolism (VTE) is an important cause of vascular morbidity and mortality. Many risk factors have been identified for venous thrombosis that lead to alterations in blood flow, activate the vascular endothelium, and increase the propensity for blood coagulation. However, the precise molecular and cellular mechanisms that cause blood clots in the venous vasculature have not been fully elucidated. Patients with sickle cell disease (SCD) demonstrate all the risk factors for venous stasis, activated endothelium, and blood hypercoagulability, making them particularly vulnerable to VTE. In this review, we will discuss how mouse models have elucidated the complex vascular pathobiology of SCD. We review the dysregulated pathways of inflammation and coagulation in SCD and how the resultant hypercoagulable state can potentiate thrombosis through down-regulation of vascular anticoagulants. Studies of VTE pathogenesis using SCD mouse models may provide insight into the intersection between the cellular and molecular processes involving inflammation and coagulation and help to identify novel mechanistic pathways.

Intratumoral platelet aggregate formation in a murine preclinical glioma model depends on podoplanin expression on tumor cells

Binding of the sialomucin-like transmembrane glycoprotein podoplanin (PDPN) to the platelet receptor C-type lectin-like receptor 2 induces platelet activation and aggregation. In human high-grade gliomas, PDPN is highly expressed both in tumor cells and in tumor-associated astrocytes. In glioma patients, high expression of PDPN is associated with worse prognosis and has been shown to correlate with intratumoral platelet aggregation and an increased risk of venous thromboembolism (VTE). To functionally assess the role of PDPN in platelet aggregation in vivo, we established a syngeneic orthotopic murine glioma model in C57/Bl6 mice, based on transplantation of p53- and Pten-deficient neural stem cells. This model is characterized by the presence of intratumoral platelet aggregates and by the upregulation of PDPN both in glioma cells and in astrocytes, reflecting the characteristics of human gliomas. Deletion of PDPN either in tumor cells or in astrocytes resulted in glioma formation with similar penetrance and grade compared with control mice. Importantly, only the lack of PDPN in tumor cells, but not in astrocytes, caused a significant reduction in intratumoral platelet aggregates, whereas in vitro, both cell types have similar platelet aggregation-inducing capacities. Our results demonstrate a causative link between PDPN and platelet aggregation in gliomas and pinpoint the tumor cells as the major players in PDPN-induced platelet aggregation. Our data indicate that blocking PDPN specifically on tumor cells could represent a novel strategy to prevent platelet aggregation and thereby reduce the risk of VTE in glioma patients.

Clinical Significance of Factor XIII Activity and Monocyte-Derived Microparticles in Cancer Patients

Background

The aim was to evaluate factor XIII activity (FXIIIa) and monocyte-derived microparticles (MDMPs) in cancer patients.

Methods

In total, 138 cancer patients (31 malignant lymphomas, 39 multiple myelomas, and 68 lung cancers) were analyzed. We measured various biomarkers including FXIIIa and MDMPs.

Results

The values of endothelial activation markers, monocyte chemoattractant peptide (MCP)-1, soluble (s)CD14, and MDMPs were higher in cancer patients than in non-cancerous controls. MCP-1, sCD14, and MDMPs were significantly correlated with FXIIIa in multivariate analysis in cancer patients. In addition, MCP-1, sCD14, and MDMP levels were significantly increased in the high FXIIIa group of patients. Finally, the survival rate of the high FXIIIa group was significantly poor in the Kaplan–Meier analysis.

Conclusion

These results suggest that abnormal levels of FXIIIa and MDMPs may offer promise as poor prognostic factors in cancer patients.

Urothelial Carcinoma of the Bladder Induces Endothelial Cell Activation and Hypercoagulation

Cancer-related venous thromboembolisms (VTE) are associated with metastasis and reduced survival in patients with urothelial cancer of the bladder. Although previous reports suggest the contribution of tissue factor and podoplanin, the mechanistic linkage between VTE and bladder cancer cell-derived molecules is unknown. Therefore, we compared distinct procoagulant pathways in four different cell lines. In vitro findings were further confirmed by microfluidic experiments mimicking the pathophysiology of tumor blood vessels and in tissue samples of patients with bladder cancer by transcriptome analysis and immunohistology. In vitro and microfluidic experiments identified bladder cancer-derived VEGF-A as highly procoagulant because it promoted the release of von Willebrand factor (VWF) from endothelial cells and thus platelet aggregation. In tissue sections from patients with bladder cancer, we found that VWF-mediated blood vessel occlusions were associated with a poor outcome. Transcriptome data further indicate that elevated expression levels of enzymes modulating VEGF-A availability were significantly connected to a decreased survival in patients with bladder cancer. In comparison with previously postulated molecular players, we identified tumor cell-derived VEGF-A and endothelial VWF as procoagulant mediators in bladder cancer. Therapeutic strategies that prevent the VEGF-A-mediated release of VWF may reduce tumor-associated hypercoagulation and metastasis in patients with bladder cancer. IMPLICATIONS: We identified the VEGF-A-mediated release of VWF from endothelial cells to be associated with bladder cancer progression.

Clinical-grade cryopreserved doxorubicin-loaded platelets: role of cancer cells and platelet extracellular vesicles activation loop

BACKGROUND

Human platelets (PLT) and PLT-extracellular vesicles (PEV) released upon thrombin activation express receptors that interact with tumour cells and, thus, can serve as a delivery platform of anti-cancer agents. Drug-loaded nanoparticles coated with PLT membranes were demonstrated to have improved targeting efficiency to tumours, but remain impractical for clinical translation. PLT and PEV targeted drug delivery vehicles should facilitate clinical developments if clinical-grade procedures can be developed.

METHODS

PLT from therapeutic-grade PLT concentrate (PC; N > 50) were loaded with doxorubicin (DOX) and stored at - 80 °C (DOX-loaded PLT) with 6% dimethyl sulfoxide (cryopreserved DOX-loaded PLT). Surface markers and function of cryopreserved DOX-loaded PLT was confirmed by Western blot and thromboelastography, respectively. The morphology of fresh and cryopreserved naïve and DOX-loaded PLT was observed by scanning electron microscopy. The content of tissue factor-expressing cancer-derived extracellular vesicles (TF-EV) present in conditioned medium (CM) of breast cancer cells cultures was measured. The drug release by fresh and cryopreserved DOX-loaded PLT triggered by various pH and CM was determined by high performance liquid chromatography. The thrombin activated PEV was analyzed by nanoparticle tracking analysis. The cellular uptake of DOX from PLT was observed by deconvolution microscopy. The cytotoxicities of DOX-loaded PLT, cryopreserved DOX-loaded PLT, DOX and liposomal DOX on breast, lung and colon cancer cells were analyzed by CCK-8 assay.

RESULTS

15~36 × 106 molecules of DOX could be loaded in each PLT within 3 to 9 days after collection. The characterization and bioreactivity of cryopreserved DOX-loaded PLT were preserved, as evidenced by (a) microscopic observations, (b) preservation of important PLT membrane markers CD41, CD61, protease activated receptor-1, (c) functional activity, (d) reactivity to TF-EV, and (e) efficient generation of PEV upon thrombin activation. The transfer of DOX from cryopreserved PLT to cancer cells was achieved within 90 min, and stimulated by TF-EV and low pH. The cryopreserved DOX-loaded PLT formulation was 7~23-times more toxic to three cancer cells than liposomal DOX.

CONCLUSIONS

Cryopreserved DOX-loaded PLT can be prepared under clinically compliant conditions preserving the membrane functionality for anti-cancer therapy. These findings open perspectives for translational applications of PLT-based drug delivery systems.

Neutrophils and neutrophil extracellular traps enhance venous thrombosis in mice bearing human pancreatic tumors

Pancreatic cancer is associated with a high incidence of venous thromboembolism. Neutrophils have been shown to contribute to thrombosis in part by releasing neutrophil extracellular traps (NET). A recent study showed that increased plasma levels of the NET biomarker, citrullinated histone H3 (H3Cit), are associated with venous thromboembolism in patients with pancreatic and lung cancer but not in those with other types of cancer, including breast cancer. In this study, we examined the contribution of neutrophils and NET to venous thrombosis in nude mice bearing human pancreatic tumors. We found that tumor-bearing mice had increased circulating neutrophil counts and levels of granulocyte-colony stimulating factor, neutrophil elastase, H3Cit and cell-free DNA compared with controls. In addition, thrombi from tumor-bearing mice contained increased levels of the neutrophil marker Ly6G, as well as higher levels of H3Cit and cell-free DNA. Thrombi from tumor-bearing mice also had denser fibrin with thinner fibers consistent with increased thrombin generation. Importantly, either neutrophil depletion or administration of DNase I reduced the thrombus size in tumor-bearing but not in control mice. Our results, together with clinical data, suggest that neutrophils and NET contribute to venous thrombosis in patients with pancreatic cancer.

Update from the laboratory: mechanistic studies of pathways of cancer-associated venous thrombosis using mouse models

Cancer patients have an increased risk of venous thromboembolism (VTE). The rate of VTE varies with cancer type, with pancreatic cancer having one of the highest rates, suggesting that there are cancer type-specific mechanisms of VTE. Risk assessment scores, such as the Khorana score, have been developed to identify ambulatory cancer patients at high risk of VTE. However, the Khorana score performed poorly in discriminating pancreatic cancer patients at risk of VTE. Currently, thromboprophylaxis is not recommended for cancer outpatients. Recent clinical trials showed that factor Xa (FXa) inhibitors reduced VTE in high-risk cancer patients but also increased major bleeding. Understanding the mechanisms of cancer-associated thrombosis should lead to the development of safer antithrombotic drugs. Mouse models can be used to study the role of different prothrombotic pathways in cancer-associated thrombosis. Human and mouse studies support the notion that 2 prothrombotic pathways contribute to VTE in pancreatic cancer patients: tumor-derived, tissue factor-positive (TF+) extracellular vesicles (EVs), and neutrophils and neutrophil extracellular traps (NETs). In pancreatic cancer patients, elevated levels of plasma EVTF activity and citrullinated histone H3 (H3Cit), a NET biomarker, are independently associated with VTE. We observed increased levels of circulating tumor-derived TF+ EVs, neutrophils, cell-free DNA, and H3Cit in nude mice bearing human pancreatic tumors. Importantly, inhibition of tumor-derived human TF, depletion of neutrophils, or administration of DNAse I to degrade cell-free DNA (including NETs) reduced venous thrombosis in tumor-bearing mice. These studies demonstrate that tumor-derived TF+ EVs, neutrophils, and cell-free DNA contribute to venous thrombosis in a mouse model of pancreatic cancer.

Rivaroxaban does not affect growth of human pancreatic tumors in mice

BACKGROUND

Some clinical studies have shown that low-molecular-weight heparins (LMWHs) prolong the survival of cancer patients. In addition, various anticoagulants have been shown to reduce growth of tumors in mice. However, there are no studies on the effect of the factor Xa inhibitor rivaroxaban on growth of human pancreatic tumors in nude mice.

OBJECTIVES

To test the hypothesis that the factor Xa inhibitor rivaroxaban reduces the growth of tissue factor (TF)-positive pancreatic tumors but not TF-negative pancreatic tumors in mice.

METHODS

The TF-positive human pancreatic cancer cell line BxPc-3 and the TF-negative human pancreatic cancer cell line MIA PaCa-2 were injected subcutaneously into nude mice and tumors grown to a mean volume of ~100 mm3 . Mice were then divided into two groups. One group was fed chow containing rivaroxaban (0.5 g/kg chow) whereas the other group was fed chow without rivaroxaban.

RESULTS

Rivaroxaban significantly prolonged prothrombin time in tumor-bearing mice. Rivaroxaban did not affect cell proliferation or growth of either BxPc-3 or MIA PaCa-2 tumors grown subcutaneously in nude mice.

CONCLUSION

Our results indicate that inhibition of factor Xa with rivaroxaban does not affect the growth of two human pancreatic tumors in nude mice.

The relationship between pancreatic cancer and hypercoagulability: a comprehensive review on epidemiological and biological issues

It has long been recognised that pancreatic cancer induces a hypercoagulable state that may lead to clinically apparent thrombosis. Although the relationship between pancreatic cancer and hypercoagulability is well described, the underlying pathological mechanism(s) and the interplay between these pathways remain a matter of intensive study. This review summarises existing data on epidemiology and pathogenesis of thrombotic complications in pancreatic cancer with a particular emphasis on novel pathophysiological pathways. Pancreatic cancer is characterised by high tumoural expression of tissue factor, activation of leukocytes with the release of neutrophil extracellular traps, the dissemination of tumour-derived microvesicles that promote hypercoagulability and increased platelet activation. Furthermore, other coagulation pathways probably contribute to these processes, such as those that involve heparanase, podoplanin and hypofibrinolysis. In the era in which heparin and its derivatives—the currently recommended therapy for cancer-associated thrombosis—might be superseded by direct oral anticoagulants, novel data from mouse models of cancer-associated thrombosis suggest the possibility of future personalised therapeutic approaches. In this dynamic era for cancer-associated thrombosis, the discovery of novel prothrombotic and proinflammatory mechanisms will potentially uncover pharmacological targets to prevent and treat thrombosis without adversely affecting haemostasis.

Increasing the sensitivity of the human microvesicle tissue factor activity assay

INTRODUCTION

The TF-FVIIa complex is the primary activator of coagulation. Elevated levels of microvesicle (MV) bearing tissue factor (TF)-dependent procoagulant activity are detectable in patients with an increased risk of thrombosis. Several methods have been described to measure MV TF activity but they are hampered by limited sensitivity and specificity. The aim of this work was to increase the sensitivity of the MV TF activity assay (called Chapel Hill assay).

MATERIAL AND METHODS

Improvements of the MV TF activity assay included i/ speed and time of centrifugation, ii/ use of a more potent inhibitory anti-TF antibody iii/ use of FVII and a fluorogenic substrate to increase specificity.

RESULTS

The specificity of the MV TF activity assay was demonstrated by the absence of activity on MV derived from a knock-out-TF cell line using an anti-human TF monoclonal antibody called SBTF-1, which shows a higher TF inhibitory effect than the anti-human TF monoclonal antibody called HTF-1. Experiments using blood from healthy individuals, stimulated or not by LPS, or plasma spiked with 3 different levels of MV, demonstrated that the new assay was more sensitive and this allowed detection of MV TF activity in platelet free plasma (PFP) samples from healthy individuals. However, the assay was limited by an inter-assay variability, mainly due to the centrifugation step.

CONCLUSIONS

We have improved the sensitivity of the MV TF activity assay without losing specificity. This new assay could be used to evaluate levels of TF-positive MV as a potential biomarker of thrombotic risk in patients.

Novel Aspects of Extracellular Vesicles as Mediators of Cancer-Associated Thrombosis

The establishment of prothrombotic states during cancer progression is well reported but the precise mechanisms underlying this process remain elusive. A number of studies have implicated the presence of the clotting initiator protein, tissue factor (TF), in circulating tumor-derived extracellular vesicles (EVs) with thrombotic manifestations in certain cancer types. Tumor cells, as well as tumor-derived EVs, may activate and promote platelet aggregation by TF-dependent and independent pathways. Cancer cells and their secreted EVs may also facilitate the formation of neutrophil extracellular traps (NETs), which may contribute to thrombus development. Alternatively, the presence of polyphosphate (polyP) in tumor-derived EVs may promote thrombosis through a TF-independent route. We conclude that the contribution of EVs to cancer coagulopathy is quite complex, in which one or more mechanisms may take place in a certain cancer type. In this context, strategies that could attenuate the crosstalk between the proposed pro-hemostatic routes could potentially reduce cancer-associated thrombosis.

Tumor-Specific Silencing of Tissue Factor Suppresses Metastasis and Prevents Cancer-Associated Hypercoagulability

Within tumors, the coagulation-inducing protein tissue factor (TF), a major initiator of blood coagulation, has been shown to play a critical role in the hematogenous metastasis of tumors, due to its effects on tumor hypercoagulability and on the mediation of interactions between platelets and tumor cells. Targeting tumor-associated TF has therefore great therapeutic potential for antimetastasis therapy and preventing thrombotic complication in cancer patients. Herein, we reported a novel peptide-based nanoparticle that targets delivery and release of small interfering RNA (siRNA) into the tumor site to silence the expression of tumor-associated TF. We showed that suppression of TF expression in tumor cells blocks platelet adhesion surrounding tumor cells in vitro. The downregulation of TF expression in intravenously administered tumor cells (i.e., simulated circulating tumor cells [CTCs]) prevented platelet adhesion around CTCs and decreased CTCs survival in the lung. In a breast cancer mouse model, siRNA-containing nanoparticles efficiently attenuated TF expression in the tumor microenvironment and remarkably reduced the amount of lung metastases in both an experimental lung metastasis model and tumor-bearing mice. What's more, this strategy reversed the hypercoagulable state of the tumor bearing mice by decreasing the generation of thrombin-antithrombin complexes (TAT) and activated platelets, both of which are downstream products of TF. Our study describes a promising approach to combat metastasis and prevent cancer-associated thrombosis, which advances TF as a therapeutic target toward clinic applications.

Targeting Tyrosine Phosphatases by 3-Bromopyruvate Overcomes Hyperactivation of Platelets from Gastrointestinal Cancer Patients

Venous thromboembolism (VTE) is one of the most common causes of cancer related mortality. It has been speculated that hypercoagulation in cancer patients is triggered by direct or indirect contact of platelets with tumor cells, however the underlying molecular mechanisms involved are currently unknown. Unraveling these mechanisms may provide potential avenues for preventing platelet-tumor cell aggregation. Here, we investigated the role of protein tyrosine phosphatases in the functionality of platelets in both healthy individuals and patients with gastrointestinal cancer, and determined their use as a target to inhibit platelet hyperactivity. This is the first study to demonstrate that platelet agonists selectively activate low molecular weight protein tyrosine phosphatase (LMWPTP) and PTP1B, resulting in activation of Src, a tyrosine kinase known to contribute to several platelet functions. Furthermore, we demonstrate that these phosphatases are a target for 3-bromopyruvate (3-BP), a lactic acid analog currently investigated for its use in the treatment of various metabolic tumors. Our data indicate that 3-BP reduces Src activity, platelet aggregation, expression of platelet activation makers and platelet-tumor cell interaction. Thus, in addition to its anti-carcinogenic effects, 3-BP may also be effective in preventing platelet-tumor cell aggregationin cancer patients and therefore may reduce cancer mortality by limiting VTE in patients.

Biology and Role of Extracellular Vesicles (EVs) in the Pathogenesis of Thrombosis

Extracellular vesicles (EVs) are well-established mediators of cell-to-cell communication. EVs can be released by every cell type and they can be classified into three major groups according to their biogenesis, dimension, density, and predominant protein markers: exosomes, microvesicles, and apoptotic bodies. During their formation, EVs associate with specific cargo from their parental cell that can include RNAs, free fatty acids, surface receptors, and proteins. The biological function of EVs is to maintain cellular and tissue homeostasis by transferring critical biological cargos to distal or neighboring recipient cells. On the other hand, their role in intercellular communication may also contribute to the pathogenesis of several diseases, including thrombosis. More recently, their physiological and biochemical properties have suggested their use as a therapeutic tool in tissue regeneration as well as a novel option for drug delivery. In this review, we will summarize the impact of EVs released from blood and vascular cells in arterial and venous thrombosis, describing the mechanisms by which EVs affect thrombosis and their potential clinical applications.

Tissue Factor and Cancer: Regulation, Tumor Growth, and Metastasis

There is a strong relationship between tissue factor (TF) and cancer. Many cancer cells express high levels of both full-length TF and alternatively spliced (as) TF. TF expression in cancer is associated with poor prognosis. In this review, the authors summarize the regulation of TF expression in cancer cells and the roles of TF and asTF in tumor growth and metastasis. A variety of different signaling pathways, transcription factors and micro ribonucleic acids regulate TF gene expression in cancer cells. The TF/factor VIIa complex enhances tumor growth by activating protease-activated receptor 2 signaling and by increasing the expression of angiogenic factors, such as vascular endothelial growth factor. AsTF increases tumor growth by enhancing integrin β1 signaling. TF and asTF also contribute to metastasis via multiple thrombin-dependent and independent mechanisms that include protecting tumor cells from natural killer cells. Finally, a novel anticancer therapy is using tumor TF as a target to deliver cytotoxic drugs to the tumor. TF may be useful in diagnosis, prognosis, and treatment of cancer.

Ectonucleotidase tri(di)phosphohydrolase-1 (ENTPD-1) disrupts inflammasome/interleukin 1β-driven venous thrombosis

Deep vein thrombosis (DVT), caused by alterations in venous homeostasis is the third most common cause of cardiovascular mortality; however, key molecular determinants in venous thrombosis have not been fully elucidated. Several lines of evidence indicate that DVT occurs at the intersection of dysregulated inflammation and coagulation. The enzyme ectonucleoside tri(di)phosphohydrolase (ENTPD1, also known as CD39) is a vascular ecto-apyrase on the surface of leukocytes and the endothelium that inhibits intravascular inflammation and thrombosis by hydrolysis of phosphodiester bonds from nucleotides released by activated cells. Here, we evaluated the contribution of CD39 to venous thrombosis in a restricted-flow model of murine inferior vena cava stenosis. CD39-deficiency conferred a >2-fold increase in venous thrombogenesis, characterized by increased leukocyte engagement, neutrophil extracellular trap formation, fibrin, and local activation of tissue factor in the thrombotic milieu. This was orchestrated by increased phosphorylation of the p65 subunit of NFκB, activation of the NLRP3 inflammasome, and interleukin-1β (IL-1β) release in CD39-deficient mice. Substantiating these findings, an IL-1β-neutralizing antibody attenuated the thrombosis risk in CD39-deficient mice. These data demonstrate that IL-1β is a key accelerant of venous thrombo-inflammation, which can be suppressed by CD39. CD39 inhibits in vivo crosstalk between inflammation and coagulation pathways, and is a critical vascular checkpoint in venous thrombosis.

Red blood cells modulate structure and dynamics of venous clot formation in sickle cell disease

Sickle cell disease (SCD) is associated with chronic activation of coagulation and an increased risk of venous thromboembolism. Erythrocyte sickling, the primary pathologic event in SCD, results in dramatic morphological changes in red blood cells (RBCs) because of polymerization of the abnormal hemoglobin. We used a mouse model of SCD and blood samples from sickle patients to determine if these changes affect the structure, properties, and dynamics of sickle clot formation. Sickling of RBCs and a significant increase in fibrin deposition were observed in venous thrombi formed in sickle mice. During ex vivo clot contraction, the number of RBCs extruded from sickle whole blood clots was significantly reduced compared with the number released from sickle cell trait and nonsickle clots in both mice and humans. Entrapment of sickled RBCs was largely factor XIIIa-independent and entirely mediated by the platelet-free cellular fraction of sickle blood. Inhibition of phosphatidylserine, but not administration of antisickling compounds, increased the number of RBCs released from sickle clots. Interestingly, whole blood, but not plasma clots from SCD patients, was more resistant to fibrinolysis, indicating that the cellular fraction of blood mediates resistance to tissue plasminogen activator. Sickle trait whole blood clots demonstrated an intermediate phenotype in response to tissue plasminogen activator. RBC exchange in SCD patients had a long-lasting effect on normalizing whole blood clot contraction. Furthermore, RBC exchange transiently reversed resistance of whole blood sickle clots to fibrinolysis, in part by decreasing platelet-derived PAI-1. These properties of sickle clots may explain the increased risk of venous thromboembolism observed in SCD.

Hemostasis based on a novel 'two-path unifying theory' and classification of hemostatic disorders

: Hemostasis is the most important protective mechanism for human survival following harmful vascular damage caused by internal disease or external injury. Physiological mechanism of hemostasis is partially understood. Hemostasis can be initiated by either intravascular injury or external bodily injury involving two different levels of damage [i.e., limited to the endothelium or combined with extravascular tissue (EVT)]. In intravascular injury, traumatic damage limited to local endothelium typically is of no consequence, but disease-induced endothelial damage associated with systemic endothelial injury seen in sepsis and other critical illnesses could cause generalized 'endotheliopathy'. It triggers no bleeding but promotes serious endothelial molecular response. If intravascular local trauma extends beyond the endothelium and into EVT, it causes intravascular 'bleeding' and initiate 'clotting' via normal hemostasis. In external bodily injury, local traumatic damage always extends to the endothelium and EVT, and triggers 'bleeding' and 'clotting'. Systemic endotheliopathy activates only unusually large von Willebrand factor multimers (ULVWF) path and mediates 'microthrombogenesis', producing 'microthrombi' strings. This partial activation of hemostasis with ULVWF path leads to vascular microthrombotic disease. But localized traumatic injury extending to the endothelium and EVT activates both ULVWF and tissue factor paths. Combined activation of ULVWF and tissue factor paths provides normal hemostasis in external bodily injury, but causes 'macrothrombus' formation in intravascular injury. This 'two-path unifying theory' concept succinctly elucidates simplified nature of hemostasis in intravascular and external bodily injuries. It also clarifies different pathogenesis of every hemorrhagic disease and thrombotic disorder related to internal vascular disease and external vascular injury.

Thrombin Generation and Cancer: Contributors and Consequences

The high occurrence of cancer-associated thrombosis is associated with elevated thrombin generation. Tumour cells increase the potential for thrombin generation both directly, through the expression and release of procoagulant factors, and indirectly, through signals that activate other cell types (including platelets, leukocytes and erythrocytes). Furthermore, cancer treatments can worsen these effects. Coagulation factors, including tissue factor, and inhibitors of coagulation are altered and extracellular vesicles (EVs), which can promote and support thrombin generation, are released by tumour and other cells. Some phosphatidylserine-expressing platelet subsets and platelet-derived EVs provide the surface required for the assembly of coagulation factors essential for thrombin generation in vivo. This review will explore the causes of increased thrombin production in cancer, and the availability and utility of tests and biomarkers. Increased thrombin production not only increases blood coagulation, but also promotes tumour growth and metastasis and as a consequence, thrombin and its contributors present opportunities for treatment of cancer-associated thrombosis and cancer itself.

Biomarkers of Cancer-Associated Thromboembolism

Venous thromboembolism is known to be associated with an increase in morbidity and mortality in patients with malignancy. Predictive laboratory biomarkers of venous thromboembolism (VTE) have long been sought after to improve outcomes and help guide clinical decision making. Previously studied biomarkers include C reactive protein (CRP), tissue factor expressing microparticles (TF MP), D-dimer, soluble P-selectin (sP-selectin), plasminogen activator inhibitor 1 (PAI-1), factor VIII, platelet count, and leukocyte counts. This chapter will focus on these possible biomarkers for cancer-associated thrombosis (CAT) with particular emphasis on the pathophysiology behind thrombosis formation as well as data from clinical studies in patients with malignancy. The incorporation of the above biomarkers into risk assessment tools to predict CAT will also be reviewed, as will risk factors for recurrent VTE in patients with malignancy. Further studies are ongoing to develop readily available biomarkers that can be incorporated into future risk assessment models with the goal of reducing morbidity and mortality due to cancer-associated thrombosis.

Cancer-Associated Thrombosis in Cirrhotic Patients with Hepatocellular Carcinoma

It is common knowledge that cancer patients are more prone to develop venous thromboembolic complications (VTE). It is therefore not surprising that patients with hepatocellular carcinoma (HCC) present with a significant risk of VTE, with the portal vein being the most frequent site (PVT). However, patients with HCC are peculiar as both cancer and liver cirrhosis are conditions that can perturb the hemostatic balance towards a prothrombotic state. Because HCC-related hypercoagulability is not clarified at all, the aim of the present review is to summarize the currently available knowledge on epidemiology and pathogenesis of non-malignant thrombotic complications in patients with liver cirrhosis and HCC. They are at increased risk to develop both PVT and non-splanchnic VTE, indicating that both local and systemic factors can foster the development of site-specific thrombosis. Recent studies have suggested multiple and often interrelated mechanisms through which HCC can tip the hemostatic balance of liver cirrhosis towards hypercoagulability. Described mechanisms include increased fibrinogen concentration/polymerization, thrombocytosis, and release of tissue factor-expressing extracellular vesicles. Currently, there are no specific guidelines on the use of thromboprophylaxis in this unique population. There is the urgent need of prospective studies assessing which patients have the highest prothrombotic profile and would therefore benefit from early thromboprophylaxis.

Cancer-Associated Thrombosis: An Overview of Mechanisms, Risk Factors, and Treatment

Cancer-associated thrombosis is a major cause of mortality in cancer patients, the most common type being venous thromboembolism (VTE). Several risk factors for developing VTE also coexist with cancer patients, such as chemotherapy and immobilisation, contributing to the increased risk cancer patients have of developing VTE compared with non-cancer patients. Cancer cells are capable of activating the coagulation cascade and other prothrombotic properties of host cells, and many anticancer treatments themselves are being described as additional mechanisms for promoting VTE. This review will give an overview of the main thrombotic complications in cancer patients and outline the risk factors for cancer patients developing cancer-associated thrombosis, focusing on VTE as it is the most common complication observed in cancer patients. The multiple mechanisms involved in cancer-associated thrombosis, including the role of anticancer drugs, and a brief outline of the current treatment for cancer-associated thrombosis will also be discussed.

Cancer-associated thrombosis: The search for the holy grail continues

Cancer patients have an increased risk of developing venous thromboembolism (VTE), a condition that is associated with increased morbidity and mortality. Although risk assessment tools have been developed, it is still very challenging to predict which cancer patients will suffer from VTE. The scope of this review is to summarize and discuss studies focusing on the link between genetic alterations and risk of cancer-associated thrombosis (CAT). Thus far, classical risk factors that contribute to VTE have been tried as risk factors of CAT, with low success. In support, hypercoagulant plasma profiles in patients with CAT differ from those with only VTE, indicating other risk factors that contribute to VTE in cancer. As germline mutations do not significantly contribute to elevated risk of VTE, somatic mutations in tumors may significantly associate with and contribute to CAT. As it is very time-consuming to investigate each and every mutation, an unbiased approach is warranted. In this light we discuss our own recent unbiased proof-of-principle study using RNA sequencing in isolated colorectal cancer cells. Our work has uncovered candidate genes that associate with VTE in colorectal cancer, and these gene profiles associated with VTE more significantly than classical parameters such as platelet counts, D-dimer, and P-selectin levels. Genes associated with VTE could be linked to pathways being involved in coagulation, inflammation and methionine degradation. We conclude that tumor cell-specific gene expression profiles and/or mutational status has superior potential as predictors of VTE in cancer patients.