Fitusiran reduces bleeding in Factor X-deficient mice.

Factor X (FX)-deficiency is a rare bleeding disorder manifesting a bleeding tendency caused by low FX activity levels. We aimed to explore the use of fitusiran (an investigational siRNA that silences antithrombin expression) to increase thrombin generation and the in vivo hemostatic potential under conditions of FX-deficiency. We therefore developed a novel model of inducible FX-deficiency, generating mice expressing <1% FX activity and antigen (f10low-mice). Compared to control f10WT-mice, f10low-mice had 6- and 4-fold prolonged clotting times in Prothrombin Time- and activated Partial Prothrombin Time-assays, respectively (p<0.001). Thrombin generation was severely reduced, irrespective whether tissue factor or factor XIa was used as initiator. In vivo analysis revealed near-absent thrombus formation in a laser-induced vessel injury-model. Furthermore, in two distinct bleeding models, f10low-mice displayed an increased bleeding tendency compared to f10WT-mice. In the tail-clip assay blood loss was increased from 12±16 microliter to 590±335 microliter (p<0.0001). In the saphenous vein puncture (SVP)-model, the number of clots generated was reduced from 19±5 clots/30 min for f10WT-mice to 2±2 clots/30 min (p<0.0001) for f10low-mice. In both models, bleeding was corrected upon infusion of purified FX. Treatment of f10low-mice with fitusiran (2x10 mg/kg at one-week interval) resulted in 17±6% residual antithrombin activity and increased thrombin generation (4-fold and 2-3-fold increase in endogenous thrombin potential and thrombin peak, respectively). In the SVP-model, the number of clots was increased to 8±6 clots/30 min (p=0.0029). Altogether, we demonstrate that reduction of antithrombin levels is associated with improved hemostatic activity under conditions of FX-deficiency.

A thrombus is formed by a gradient of platelet activation and procoagulant endothelium.

Background: The contribution of platelets in thrombosis within microcirculation has been extensively documented in the literature. We previously showed, in vivo, that platelet activation revealed by intracellular calcium mobilization was a crucial step in the growth of thrombi following laser-induced injury, a model of thromboinflammation. Objective: Our goal was to investigate the extent of platelet activation and the spatial distribution of platelets throughout a growing thrombus. Methods: We employed a multimodal, correlative microscopy approach and computational biology to study the state of platelets on a growing thrombus obtained after a laser injury. Results: We observed a reversible intracellular platelet calcium mobilization that correlates with the time a platelet resides during thrombus growth. Our bioinformatics analysis displayed the following 3 distinct platelet subpopulations resident within a thrombus: (1) resting, (2) partially activated, and (3) "fully" activated platelets. The spatial distribution of the platelet subpopulations in the thrombus creates a double gradient in both the transversal and longitudinal axis, with the maximal percentage of fully activated platelets close to the site of injury. However, these activated platelets did not express negative phospholipids. The injured endothelium was identified to play a vital role in activating the blood coagulation cascade in this model of thrombosis. Conclusion: Following a laser-induced injury, thrombi are formed by a gradient of activated platelets from the injury site to the periphery of the thrombus. These different activation states of platelets throughout the thrombi regulate the biomechanics of the thrombus. The injured endothelium, rather than platelets, was identified to play a key role in the activation of the blood coagulation cascade in this model of thromboinflammation.

An OMA1 redox site controls mitochondrial homeostasis, sarcoma growth, and immunogenicity.

Aggressive tumors often display mitochondrial dysfunction. Upon oxidative stress, mitochondria undergo fission through OMA1-mediated cleavage of the fusion effector OPA1. In yeast, a redox-sensing switch participates in OMA1 activation. 3D modeling of OMA1 comforted the notion that cysteine 403 might participate in a similar sensor in mammalian cells. Using prime editing, we developed a mouse sarcoma cell line in which OMA1 cysteine 403 was mutated in alanine. Mutant cells showed impaired mitochondrial responses to stress including ATP production, reduced fission, resistance to apoptosis, and enhanced mitochondrial DNA release. This mutation prevented tumor development in immunocompetent, but not nude or cDC1 dendritic cell-deficient, mice. These cells prime CD8+ lymphocytes that accumulate in mutant tumors, whereas their depletion delays tumor control. Thus, OMA1 inactivation increased the development of anti-tumor immunity. Patients with complex genomic soft tissue sarcoma showed variations in the level of OMA1 and OPA1 transcripts. High expression of OPA1 in primary tumors was associated with shorter metastasis-free survival after surgery, and low expression of OPA1, with anti-tumor immune signatures. Targeting OMA1 activity may enhance sarcoma immunogenicity.

Platelet and Cancer-Cell Interactions Modulate Cancer-Associated Thrombosis Risk in Different Cancer Types.

The first cause of death in cancer patients, after tumoral progression itself, is thrombo-embolic disease. This cancer-associated hypercoagulability state is known as Trousseau's syndrome, and the risk for developing thrombotic events differs according to cancer type and stage, as well as within patients. Massive platelet activation by tumor cells is the key mediator of thrombus formation in Trousseau's syndrome. In this literature review, we aimed to compare the interactions between cancer cells and platelets in three different cancer types, with low, medium and high thrombotic risk. We chose oral squamous cell carcinoma for the low-thrombotic-risk, colorectal adenocarcinoma for the medium-thrombotic-risk, and pancreatic carcinoma for the high-thrombotic-risk cancer type. We showcase that understanding these interactions is of the highest importance to find new biomarkers and therapeutic targets for cancer-associated thrombosis.

Neutrophils, Cancer and Thrombosis: The New Bermuda Triangle in Cancer Research.

Spontaneous venous thrombosis is often the first clinical sign of cancer, and it is linked to a worsened survival rate. Traditionally, tumor-cell induced platelet activation has been the main actor studied in cancer-associated-thrombosis. However, platelet involvement alone does not seem to be sufficient to explain this heightened pro-thrombotic state. Neutrophils are emerging as key players in both thrombus generation and cancer progression. Neutrophils can impact thrombosis through the release of pro-inflammatory cytokines and expression of molecules like P-selectin and Tissue Factor (TF) on their membrane and on neutrophil-derived microvesicles. Their role in cancer progression is evidenced by the fact that patients with high blood-neutrophil counts have a worsened prognosis. Tumors can attract neutrophils to the cancer site via pro-inflammatory cytokine secretions and induce a switch to pro-tumoral (or N2) neutrophils, which support metastatic spread and have an immunosuppressive role. They can also expel their nuclear contents to entrap pathogens forming Neutrophil Extracellular Traps (NETs) and can also capture coagulation factors, enhancing the thrombus formation. These NETs are also known to have pro-tumoral effects by supporting the metastatic process. Here, we strived to do a comprehensive literature review of the role of neutrophils as drivers of both cancer-associated thrombosis (CAT) and cancer progression.

Role of Neutrophils and NETs in Animal Models of Thrombosis.

Thrombosis is one of the major causes of mortality worldwide. Notably, it is not only implicated in cardiovascular diseases, such as myocardial infarction (MI), stroke, and pulmonary embolism (PE), but also in cancers. Understanding the cellular and molecular mechanisms involved in platelet thrombus formation is a major challenge for scientists today. For this purpose, new imaging technologies (such as confocal intravital microscopy, electron microscopy, holotomography, etc.) coupled with animal models of thrombosis (mouse, rat, rabbit, etc.) allow a better overview of this complex physiopathological process. Each of the cellular components is known to participate, including the subendothelial matrix, the endothelium, platelets, circulating cells, and, notably, neutrophils. Initially known as immune cells, neutrophils have been considered to be part of the landscape of thrombosis for more than a decade. They participate in this biological process through their expression of tissue factor (TF) and protein disulfide isomerase (PDI). Moreover, highly activated neutrophils are described as being able to release their DNA and thus form chromatin networks known as "neutrophil extracellular traps" (NETs). Initially, described as "dead sacrifices for a good cause" that prevent the dissemination of bacteria in the body, NETs have also been studied in several human pathologies, such as cardiovascular and respiratory diseases. Many articles suggest that they are involved in platelet thrombus formation and the activation of the coagulation cascade. This review presents the models of thrombosis in which neutrophils and NETs are involved and describes their mechanisms of action. We have even highlighted the medical diagnostic advances related to this research.

The P2Y12 Receptor Antagonist Selatogrel Dissolves Preformed Platelet Thrombi In Vivo.

Selatogrel, a potent and reversible antagonist of the P2Y12 receptor, inhibited FeCl3-induced thrombosis in rats. Here, we report the anti-thrombotic effect of selatogrel after subcutaneous applications in guinea pigs and mice. Selatogrel inhibited platelet function only 10 min after subcutaneous application in mice. In addition, in a modified Folts thrombosis model in guinea pigs, selatogrel prevented a decrease in blood-flow, indicative of the inhibition of ongoing thrombosis, approximately 10 min after subcutaneous injection. Selatogrel fully normalised blood flow; therefore, we speculate that it may not only prevent, but also dissolve, platelet thrombi. Thrombus dissolution was investigated using real-time intravital microscopy in mice. The infusion of selatogrel during ongoing platelet thrombus formation stopped growth and induced the dissolution of the preformed platelet thrombus. In addition, platelet-rich thrombi were given 30 min to consolidate in vivo. The infusion of selatogrel dissolved the preformed and consolidated platelet thrombi. Dissolution was limited to the disintegration of the occluding part of the platelet thrombi, leaving small mural platelet aggregates to seal the blood vessel. Therefore, our experiments uncovered a novel advantage of selatogrel: the dissolution of pre-formed thrombi without the disintegration of haemostatic seals, suggesting a bipartite benefit of the early application of selatogrel in patients with acute thrombosis.

P2RY12-Inhibitors Reduce Cancer-Associated Thrombosis and Tumor Growth in Pancreatic Cancers.

Platelet function can be modified by cancer cells to support tumor growth, causing alterations in the delicate hemostatic equilibrium. Cancer-cell and platelet interactions are one of the main pillars of Trousseau's syndrome: a paraneoplastic syndrome with recurring and migrating episodes of thrombophlebitis. Altogether, this leads to a four-fold risk of thrombotic events in cancer patients, which in turn, portend a poor prognosis. We previously demonstrated that anti-P2RY12 drugs inhibit cancer-associated-thrombosis and formation of tumor metastasis in pancreatic cancer models. Here, we aimed to (1) compare the effects of aspirin and clopidogrel on pancreatic cancer prevention, (2) characterize the effects of clopidogrel (platelet P2RY12 inhibitor) on cancer-associated thrombosis and cancer growth in vivo, (3) determine the effect of P2RY12 across different digestive-tract cancers in vitro, and (4) analyze the expression pattern of P2RY12 in two different cancer types affecting the digestive system. Clopidogrel treatment resulted in better survival rates with smaller primary tumors and less metastasis than aspirin treatment. Clopidogrel was also more effective than aspirin at dissolving spontaneous endogenous thrombi in our orthotopic advanced cancer mouse model. P2RY12 expression gives pancreatic adenocarcinomas proliferative advantages. In conclusion, we propose the hypothesis that clopidogrel should be further studied to target and prevent Trousseau's syndrome; as well as diminish cancer growth and spread. However, more studies are required to determine the implicated pathways and effects of these drugs on cancer development.

DNAse-dependent, NET-independent pathway of thrombus formation in vivo.

The contribution of NETs (neutrophil extracellular traps) to thrombus formation has been intensively documented in both arterial and venous thrombosis in mice. We previously demonstrated that adenosine triphosphate (ATP)-activated neutrophils play a key role in initiating the tissue factor-dependent activation of the coagulation cascade, leading to thrombus formation following laser-induced injury. Here, we investigated the contribution of NETs to thrombus formation in a laser-induced injury model. In vivo, treatment of mice with DNase-I significantly inhibited the accumulation of polymorphonuclear neutrophils at the site of injury, neutrophil elastase secretion, and platelet thrombus formation within seconds following injury. Surprisingly, electron microscopy of the thrombus revealed that neutrophils present at the site of laser-induced injury did not form NETs. In vitro, ATP, the main neutrophil agonist present at the site of laser-induced injury, induced the overexpression of PAD4 and CitH3 but not NETosis. However, compared to no treatment, the addition of DNase-I was sufficient to cleave ATP and adenosine diphosphate (ADP) in adenosine. Human and mouse platelet aggregation by ADP and neutrophil activation by ATP were also significantly reduced in the presence of DNase-I. We conclude that following laser-induced injury, neutrophils but not NETs are involved in thrombus formation. Treatment with DNase-I induces the hydrolysis of ATP and ADP, leading to the generation of adenosine and the inhibition of thrombus formation in vivo.

Oral Squamous Cell Carcinoma Is Associated with a Low Thrombosis Risk Due to Storage Pool Deficiency in Platelets.

Venous thrombo-embolism (VTE) disease is the second most common cause of mortality in cancer patients, and evaluation and prevention of thrombosis risk is essential. VTE-associated risk varies according to the type of tumor disease. Oral cancer is the most frequent type of head and neck cancer, and it represents approximately 2.1% of all cancers worldwide. Most tumors are squamous cell carcinomas and are mainly due to tobacco and alcohol abuse. VTE risk associated with oral squamous cell carcinoma (OSCC) is low. However, many studies have shown that OSCC has the following biological features of cancers associated with a high thrombosis risk: modified thrombosis and fibrinolysis mechanisms; strong expression of procoagulant proteins; secretion of procoagulant microparticles; and production of procoagulant cytokines. Using an original mouse model of tongue squamous cell carcinoma, our study aimed to clarify this paradoxical situation. First, we showed that OSCC tumors have a pro-aggregatory phenotype and a high local thrombosis risk. Second, we found that tongue tumor mice do not have an elevated systemic thrombosis risk (the risk of an "at distance" thrombosis event such as lower extremity deep venous thrombosis or pulmonary embolism) and even show a reduction in risk. Third, we demonstrated that tongue tumor mice show a reduction in platelet reactivity, which explains the low systemic thrombosis risk. Finally, we found that tongue tumor mice present granule pool deficiency, thereby explaining the reduction in platelet reactivity and systemic thrombosis risk.

Selatogrel, a reversible P2Y12 receptor antagonist, has reduced off-target interference with haemostatic factors in a mouse thrombosis model.

INTRODUCTION: Selatogrel is a reversible antagonist of the P2Y12 receptor. In rat thrombosis/haemostasis models, selatogrel was associated with lower blood loss than clopidogrel or ticagrelor at equivalent anti-thrombotic effect. MATERIAL AND METHODS: We sought to elucidate the mechanism underlying the observed differences in blood loss, using real-time intravital microscopy in mouse. RESULTS: Selatogrel, ticagrelor and clopidogrel dose-dependently inhibited laser-induced platelet thrombus formation. At maximal antithrombotic effect, only small mural platelets aggregates, corresponding to hemostatic seals, were present. The phenotype of these hemostatic seals was dependent on the type of P2Y12 receptor antagonist. In the presence of clopidogrel and ticagrelor, detachment of platelets from the hemostatic seals was increased, indicative of reduced stability. In contrast, in the presence of selatogrel, platelet detachment was not increased. Moreover, equivalent antithrombotic dosing regimens of ticagrelor and clopidogrel reduced laser-induced calcium mobilization in the endothelium, restricted neutrophil adhesion and subsequent fibrin formation and thus reduced fibrin-mediated stabilization of the hemostatic seals. The effects of ticagrelor were also observed in P2Y12 receptor deficient mice, indicating that the effects are off-target and independent of the P2Y12 receptor. In contrast, selatogrel did not interfere with these elements of haemostasis in wild-type or in P2Y12 receptor deficient mice. CONCLUSION: In the presence of selatogrel the stability of hemostatic seals was unperturbed, translating to an improved blood loss profile. Our data suggest that the mechanism underlying the differences in blood loss profiles of P2Y12 receptor antagonists is by off-target interference with endothelial activation, neutrophil function and thus, fibrin-mediated stabilization of haemostatic seals.

Cancer animal models in thrombosis research.

The cancer-thrombosis relationship has been established for decades, in both cancer biology and in the clinical signs and symptoms seen in cancer patients (thrombosis in cancer patients has been associated with a worse prognosis and survival). As the link between the pathologies becomes clearer, so does the need to develop models that enable researchers to study them simultaneously in vivo. Mouse models have often been used, and they have helped determine molecular pathways between cancer spread and thrombosis in humans. This review is a summary of the current literature that describes the use of cancer mouse models in thrombosis research. We included cancer models that are not yet used in thrombosis research, but that can positively impact this area of research in the near future. We describe the most commonly used techniques to generate thrombosis as well as the mouse strains and cancer cell types that are commonly used along with inoculation techniques. We endeavoured to create a compendium of the different mouse models that are beneficial for cancer-thrombosis research, as understanding these mechanisms is crucial for creating better and more effective treatments for thrombosis in cancer patients.

Assessment of Thrombotic and Bleeding Tendency in Two Mouse Models of Chronic Kidney Disease: Adenine-Diet and 5/6th Nephrectomy.

The coexistence of bleeding and thrombosis in patients with chronic kidney disease (CKD) is frequent and poorly understood. Mouse models are essential to understand complications of CKD and to develop new therapeutic approaches improving the health of patients. We evaluated the hemostasis in two models of renal insufficiency: adenine-diet and 5/6th nephrectomy (5/6Nx). Compared with 5/6Nx mice, mice fed with 0.25% adenine had more severe renal insufficiency and so higher levels of prothrombotic uremic toxins like indoxyl sulfate. More severe renal inflammation and fibrosis were observed in the adenine group, as demonstrated by histological and reverse transcription quantitative polymerase chain reaction experiments. Liver fibrinogen γ chain expression and level of plasma fibrinogen were increased only in adenine mice. In both CKD mouse models, tissue factor (TF) expression was increased in kidney and aorta extracts. Immunochemistry analysis of kidney sections showed that TF is localized in the vascular walls. Thrombin-antithrombin complexes were significantly increased in plasma from both adenine and 5/6Nx mice. Tail bleeding time increased significantly only in adenine mice, whereas platelet count was not significant altered. Finally, results obtained by intravital microscopy after laser-induced endothelial injury showed impaired platelet function in adenine mice and an increase in fibrin generation in 5/6Nx mice. To summarize, adenine diet causes a more severe renal insufficiency compared with 5/6Nx. The TF upregulation and the hypercoagulable state were observed in both CKD models. Bleeding tendency was observed only in the adenine model of CKD that recapitulates the whole spectrum of hemostasis abnormalities observed in advanced human CKD.

The Interaction of Platelets with Colorectal Cancer Cells Inhibits Tumor Growth but Promotes Metastasis.

Platelets promote metastasis, however, their role in tumor growth remains controversial. Here, we investigated the effect of platelet interactions with colorectal tumor cells. Platelets extravasated into the tumor microenvironment and interacted with tumor cells in a cadherin-6-dependent manner. The interaction induced platelet spreading, release of their granule content, and the generation of three types of microparticles (iMP) that expressed platelet markers, tumor markers, or both. The presence of iMPs was confirmed in colorectal cancer tissue specimens. Platelets significantly reduced tumor growth and increased intratumoral macrophages. This was mediated by iMP recruitment of macrophages via the chemoattractants RANTES, MIF, CCL2, and CXCL12 and activation of their tumor cell killing capacity through IFNγ and IL4, which led to cell-cycle arrest of tumor cells in a p21-dependent manner. In contrast, in the bloodstream, iMPs activated endothelial cells and platelets and induced epithelial-to-mesenchymal transition of tumor cells, promoting metastasis. Altogether, these results indicate that depending on the environment, local or bloodstream, the consequences of the interactions between platelets and a tumor may promote or prevent cancer progression. SIGNIFICANCE: Tumor cell interaction with platelets produces chimeric extracellular vesicles that suppress primary tumor growth by activating tumor-eliminating macrophages, while promoting metastasis through EMT and endothelial activation.

Platelets, Thrombo-Inflammation, and Cancer: Collaborating With the Enemy.

Platelets are small anucleate cells present in the blood stream, their typical role in primary hemostasis has been well-described. However, new evidence suggests that they have critically important roles in cancer progression and inflammation. Cancer cells can activate platelets, thus using them as physical shields from blood shear forces and natural killer (NK) cells. The activated platelets may also regulate hematopoietic and immune cell migration toward the tumor site; therefore, contributing to the cancer-associated inflammation. The activation of platelets by cancer cells may also contribute to metastasis and cancer progression by stimulating deep venous thrombosis and neutrophil extracellular trap formations (NETs) that "hide" cancer cells. We strived to review the current literature to dissect the role of platelets in cancer-associated thrombosis and tumor microenvironment inflammation.

Increased levels of the megakaryocyte and platelet expressed cysteine proteases stefin A and cystatin A prevent thrombosis.

Increased platelet activity occurs in type 2 diabetes mellitus (T2DM) and such platelet dysregulation likely originates from altered megakaryopoiesis. We initiated identification of dysregulated pathways in megakaryocytes in the setting of T2DM. We evaluated through transcriptomic analysis, differential gene expressions in megakaryocytes from leptin receptor-deficient mice (db/db), exhibiting features of human T2DM, and control mice (db/+). Functional gene analysis revealed an upregulation of transcripts related to calcium signaling, coagulation cascade and platelet receptors in diabetic mouse megakaryocytes. We also evidenced an upregulation (7- to 9.7-fold) of genes encoding stefin A (StfA), the human ortholog of Cystatin A (CSTA), inhibitor of cathepsin B, H and L. StfA/CSTA was present in megakaryocytes and platelets and its expression increased during obesity and diabetes in rats and humans. StfA/CSTA was primarily localized at platelet membranes and granules and was released upon agonist stimulation and clot formation through a metalloprotease-dependent mechanism. StfA/CSTA did not affect platelet aggregation, but reduced platelet accumulation on immobilized collagen from flowing whole blood (1200 s-1). In-vivo, upon laser-induced vascular injury, platelet recruitment and thrombus formation were markedly reduced in StfA1-overexpressing mice without affecting bleeding time. The presence of CA-074Me, a cathepsin B specific inhibitor significantly reduced thrombus formation in-vitro and in-vivo in human and mouse, respectively. Our study identifies StfA/CSTA as a key contributor of platelet-dependent thrombus formation in both rodents and humans.

Thrombosis Risk Associated with Head and Neck Cancer: A Review.

Venous thromboembolism (VTE) is a common complication for cancer patients. VTE-associated risk varies according to the type of tumor disease. Head and neck cancer is a common cancer worldwide, and most tumors are squamous cell carcinomas due to tobacco and alcohol abuse. The risk of VTE associated with head and neck (H&N) cancer is considered empirically low, but despite the high incidence of H&N cancer, few data are available on this cancer; thus, it is difficult to state the risk of VTE. Our review aims to clarify this situation and tries to assess the real VTE risk associated with H&N cancer. We report that most clinical studies have concluded that there is a very low thrombosis risk associated with H&N cancer. Even with the biases that often exist, this clinical review seems to confirm that the risk of VTE was empirically hypothesized. Furthermore, we highlight that H&N cancer has all the biological features of a cancer associated with a high thrombosis risk, including a strong expression of procoagulant proteins, modified thrombosis/fibrinolysis mechanisms, and secretions of procoagulant microparticles and procoagulant cytokines. Thus, this is a paradoxical situation, and some undiscovered mechanisms that could explain this clinical biological ambivalence might exist.

Neutrophil extracellular traps are associated with the pathogenesis of diffuse alveolar hemorrhage in murine lupus.

Diffuse alveolar hemorrhage (DAH) is a life-threatening complication of systemic lupus erythematosus (SLE) and systemic vasculitis. Although initially described to have antibacterial properties, increasing evidence suggests that neutrophil extracellular traps (NETs) have a detrimental role in both autoimmune diseases and acute lung injury. We investigated whether NETs could be detected in a murine model of pristane-induced lupus DAH and contribute to lung injury. Such NETs might constitute a therapeutic target. NETs were characterized by immunofluorescence staining of DNA, neutrophil elastase and citrullinated histones. Evaluation of lung injury was performed by haematoxylin-eosin staining and a quantification program. Clinical status of the mice was assessed by measurement of arterial oxygen saturation and survival curves after recombinant human deoxyribonuclease-1 (Rh-DNase-1) inhalations or polymorphonuclear neutrophil (PMN) depletion. Pristane was found to promote NETs formation in vitro and in vivo. Treatment of mice with Rh-DNase-1 inhalations cleared NETs and reduced lung injury. Clinical status improved significantly, with increased arterial oxygenation and survival. Following PMN depletion, NETs were absent with a subsequent reduction of lung injury and improved arterial oxygenation. These results support a pathogenic role of PMNs and NETs in lung injury during pristane-induced DAH. Targeting NETs with Rh-DNase-1 inhalations could constitute an interesting adjuvant therapy in human DAH.

Impacts of Cancer on Platelet Production, Activation and Education and Mechanisms of Cancer-Associated Thrombosis.

Platelets are small anucleate cells that are traditionally described as the major effectors of hemostasis and thrombosis. However, increasing evidence indicates that platelets play several roles in the progression of malignancies and in cancer-associated thrombosis. A notable cross-communication exists between platelets and cancer cells. On one hand, cancer can "educate" platelets, influencing their RNA profiles, the numbers of circulating platelets and their activation states. On the other hand, tumor-educated platelets contain a plethora of active biomolecules, including platelet-specific and circulating ingested biomolecules, that are released upon platelet activation and participate in the progression of malignancy. The numerous mechanisms by which the primary tumor induces the production, activation and aggregation of platelets (also known as tumor cell induced platelet aggregation, or TCIPA) are directly related to the pro-thrombotic state of cancer patients. Moreover, the activation of platelets is critical for tumor growth and successful metastatic outbreak. The development or use of existing drugs targeting the activation of platelets, adhesive proteins responsible for cancer cell-platelet interactions and platelet agonists should be used to reduce cancer-associated thrombosis and tumor progression.

Effects of platelets on cancer progression.

Platelets are small (2-4 µm), anucleate, hematopoietic cells released by bone marrow megakaryocytes in the bloodstream. For a long time, platelets were described as the major effectors of hemostasis and thrombosis. In 1865, Armand Trousseau demonstrated a close relation between thrombosis and cancer. Subsequently, much clinical and experimental evidence supports the idea that platelets play several roles in the progression of malignancies and in cancer-associated thrombosis. In this review, we will discuss the roles of tumor-educated platelets (TEPs) in the progression of cancer from primary tumors to secondary metastatic outbreaks.