The polyphosphate/factor XII pathway in cancer-associated thrombosis: novel perspectives for safe anticoagulation in patients with malignancies

Pancreatic Cancer and Venous Thromboembolism

Pancreatic ductal adenocarcinoma (PDAC) accounts for more than 90% of all pancreatic cancers and is the most fatal of all cancers. The treatment response from combination chemotherapies is far from satisfactory and surgery remains the mainstay of curative strategies. These challenges warrant identifying effective treatments for combating this deadly cancer. PDAC tumor progression is associated with the robust activation of the coagulation system. Notably, cancer-associated thrombosis (CAT) is a significant risk factor in PDAC. CAT is a concept whereby cancer cells promote thromboembolism, primarily venous thromboembolism (VTE). Of all cancer types, PDAC is associated with the highest risk of developing VTE. Hypoxia in a PDAC tumor microenvironment also elevates thrombotic risk. Direct oral anticoagulants (DOACs) or low-molecular-weight heparin (LMWH) are used only as thromboprophylaxis in PDAC. However, a precision medicine approach is recommended to determine the precise dose and duration of thromboprophylaxis in clinical setting.

Using Machine Learning (ML) Models to Predict Risk of Venous Thromboembolism (VTE) Following Spine Surgery

STUDY DESIGN

A retrospective cohort study.

OBJECTIVES

Venous thromboembolism (VTE) is a potentially high-risk complication for patients undergoing spine surgery. Although guidelines for assessing VTE risk in this population have been established, development of new techniques that target different aspects of the medical history may prove to be of further utility. The goal of this study was to develop a predictive machine learning (ML) model to identify nontraditional risk factors for predicting VTE in spine surgery patients.

SUMMARY OF BACKGROUND DATA

A cohort of 63 patients was identified who had undergone spine surgery at a single center from 2015 to 2021. Thirty-one patients had a confirmed VTE, while 32 had no VTE. A total of 113 attributes were defined and collected via chart review. Attribute categories included demographics, medications, labs, past medical history, operative history, and VTE diagnosis.

METHODS

The Waikato Environment for Knowledge Analysis (WEKA) software was used in creating and evaluating the ML models. Six classifier models were tested with 10-fold cross-validation and statistically evaluated using t tests.

RESULTS

Comparing the predictive ML models to the control model (ZeroR), all predictive models were significantly better than the control model at predicting VTE risk, based on the 113 attributes ( P <0.001). The Random Forest model had the highest accuracy of 88.89% with a positive predictive value of 93.75%. The Simple Logistic algorithm had an accuracy of 84.13% and defined risk attributes to include calcium and phosphate laboratory values, history of cardiac comorbidity, history of previous VTE, anesthesia time, selective serotonin reuptake inhibitor use, antibiotic use, and antihistamine use. The J48 model had an accuracy of 80.95% and it defined hemoglobin laboratory values, anesthesia time, beta-blocker use, dopamine agonist use, history of cancer, and Medicare use as potential VTE risk factors.

CONCLUSION

Further development of these tools may provide high diagnostic value and may guide chemoprophylaxis treatment in this setting of high-risk patients.

Contact system and intrinsic pathway activation in patients with advanced pancreatic cancer: a prospective cohort study

BACKGROUND

Despite high risk of venous thromboembolism (VTE) in patients with pancreatic cancer, there are little data on contact system activation in these patients.

OBJECTIVES

To quantify contact system and intrinsic pathway activation and subsequent VTE risk in patients with pancreatic cancer.

METHODS

Patients with advanced pancreatic cancer were compared with controls. Blood was drawn at baseline and patients were followed for 6 months. Complexes of proteases with their natural inhibitors, C1-esterase inhibitor (C1-INH), antithrombin (AT), or alpha-1 antitrypsin (α1at), were measured for complexes containing kallikrein (PKa:C1-INH), factor (F)XIIa (FXIIa:C1-INH), and FXIa (FXIa:C1-INH, FXIa:AT, FXIa:α1at). The association of cancer with complex levels was assessed in a linear regression model, adjusted for age, sex, and body mass index. In a competing risk regression model, we assessed associations between complex levels and VTE.

RESULTS

One hundred nine patients with pancreatic cancer and 22 controls were included. The mean age was 66 years (SD, 8.4) in the cancer cohort and 52 years (SD, 10.1) in controls. In the cancer cohort, 18 (16.7%) patients developed VTE during follow-up. In the multivariable regression model, pancreatic cancer was associated with increased complexes of PKa:C1-INH (P < .001), FXIa:C1-INH (P < .001), and FXIa:AT (P < .001). High FXIa:α1at (subdistribution hazard ratio, 1.48 per log increase; 95% CI, 1.02-2.16) and FXIa:AT (subdistribution hazard ratio, 2.78 highest vs lower quartiles; 95% CI, 1.10-7.00) were associated with VTE.

CONCLUSION

Complexes of proteases with their natural inhibitors were elevated in patients with cancer. These data suggest that the contact system and intrinsic pathway activation are increased in patients with pancreatic cancer.

In-vivo functions and regulation of polyphosphate in the vascular system

PURPOSE OF REVIEW

Polyphosphate, an inorganic polymer consisting of linearly linked phosphate subunits, is ubiquitously found in living organisms. Functions and regulation of the polymer have been analyzed in plants, bacteria and yeast; however, the roles of polyphosphate in mammals are still emerging.

RECENT FINDINGS

In contrast to synthetic polyphosphate that has been extensively utilized in ex-vivo studies, natural polyphosphate is complexed with bivalent cations (mostly Ca 2+ ) and regardless of chain length, forms microparticles that are retained on the surface of procoagulant platelets, platelet-derived microparticles and cancer extracellular vesicles. On cell surfaces, these Ca 2+ /polyphosphate aggregates initiate the factor XII-driven contact system, triggering proinflammatory and procoagulant reactions through the kallikrein kinin system and intrinsic pathway of coagulation, respectively. Polyphosphate inhibitors interfere with thrombosis while sparing hemostasis, replicating the effect of factor XII neutralizing agents. Furthermore, polyphosphate binds to platelet factor 4, which has implications for autoimmune thrombotic diseases, such as heparin-induced thrombocytopenia (HIT) and vaccine-induced thrombotic thrombocytopenia (VITT), potentially contributing to their pathogenesis. The metabolism and organ-specific distribution of the polymer remain incompletely defined and is the topic of ongoing research.

SUMMARY

Polyphosphate acts as a procoagulant and proinflammatory mediator. Neutralizing polyphosphate provides well tolerated thromboprotection, mimicking the effects of factor XII deficiency.

Pathophysiology of Coagulation and Emerging Roles for Extracellular Vesicles in Coagulation Cascades and Disorders

The notion of blood coagulation dates back to the ancient Greek civilization. However, the emergence of innovative scientific discoveries that started in the seventeenth century formulated the fundamentals of blood coagulation. Our understanding of key coagulation processes continues to evolve, as novel homeostatic and pathophysiological aspects of hemostasis are revealed. Hemostasis is a dynamic physiological process, which stops bleeding at the site of injury while maintaining normal blood flow within the body. Intrinsic and extrinsic coagulation pathways culminate in the homeostatic cessation of blood loss, through the sequential activation of the coagulation factors. Recently, the cell-based theory, which combines these two pathways, along with newly discovered mechanisms, emerged to holistically describe intricate in vivo coagulation mechanisms. The complexity of these mechanisms becomes evident in coagulation diseases such as hemophilia, Von Willebrand disease, thrombophilia, and vitamin K deficiency, in which excessive bleeding, thrombosis, or unnecessary clotting, drive the development and progression of diseases. Accumulating evidence implicates cell-derived and platelet-derived extracellular vesicles (EVs), which comprise microvesicles (MVs), exosomes, and apoptotic bodies, in the modulation of the coagulation cascade in hemostasis and thrombosis. As these EVs are associated with intercellular communication, molecular recycling, and metastatic niche creation, emerging evidence explores EVs as valuable diagnostic and therapeutic approaches in thrombotic and prothrombotic diseases.

Inorganic Polyphosphate—Regulator of Cellular Metabolism in Homeostasis and Disease

Inorganic polyphosphate (polyP), a simple anionic polymer consisting of even hundreds of orthophosphate units, is a universal molecule present in both simple and complex organisms. PolyP controls homeostatic processes in animals, such as blood coagulation, tissue regeneration, and energy metabolism. Furthermore, this polymer is a potent regulator of inflammation and influences host immune response in bacterial and viral infections. Disturbed polyP systems have been related to several pathological conditions, including neurodegeneration, cardiovascular disorders, and cancer, but we lack a full understanding of polyP biogenesis and mechanistic insights into the pathways through which polyP may act. This review summarizes recent studies that describe the role of polyP in cell homeostasis and show how disturbances in polyP levels may lead to disease. Based on the collected findings, we highlight the possible usage of this polymer as a promising therapeutic tool in multiple pathologies.

Polyphosphate expression by cancer cell extracellular vesicles mediates binding of factor XII and contact activation

Cleaved HK is observed in many patients with cancer, suggesting activation of the contact system.

EVs from cancer cell lines or patients with cancer express polyphosphate, bind and activate FXII, and are prothrombotic.

Extracellular vesicles (EV) have been implicated in diverse biological processes, including intracellular communication, transport of nucleic acids, and regulation of vascular function. Levels of EVs are elevated in cancer, and studies suggest that EV may stimulate thrombosis in patients with cancer through expression of tissue factor. However, limited data also implicate EV in the activation of the contact pathway of coagulation through activation of factor XII (FXII) to FXIIa. To better define the ability of EV to initiate contact activation, we compared the ability of EV derived from different cancer cell lines to activate FXII. EV from all cell lines activated FXII, with those derived from pancreatic and lung cancer cell lines demonstrating the most potent activity. Concordant with the activation of FXII, EV induced the cleavage of high molecular weight kininogen (HK) to cleaved kininogen. We also observed that EVs from patients with cancer stimulated FXII activation and HK cleavage. To define the mechanisms of FXII activation by EV, EV were treated with calf intestinal alkaline phosphatase or Escherichia coli exopolyphosphatase to degrade polyphosphate; this treatment blocked binding of FXII to EVs and the ability of EV to mediate FXII activation. In vivo, EV induced pulmonary thrombosis in wild-type mice, with protection conferred by a deficiency in FXII, HK, or prekallikrein. Moreover, pretreatment of EVs with calf intestinal alkaline phosphatase inhibited their prothrombotic effect. These results indicate that polyphosphate mediates the binding of contact factors to EV and that EV-associated polyphosphate may contribute to the prothrombotic effects of EV in cancer.

Polyanions in Coagulation and Thrombosis: Focus on Polyphosphate and Neutrophils Extracellular Traps

Neutrophil extracellular traps (NETs) and polyphosphates (polyP) have been recognized as procoagulant polyanions. This review summarizes the activities and regulation of the two procoagulant mediators and compares their functions. NETs are composed of DNA which like polyP is built of phosphate units linked by high-energy phosphoanhydride bonds. Both NETs and polyP form insoluble particulate surfaces composed of a DNA/histone meshwork or Ca²⁺-rich nanoparticles, respectively. These polyanionic molecules modulate coagulation involving an array of mechanisms and trigger thrombosis via activation of the factor XII-driven procoagulant and proinflammatory contact pathway. Here, we outline the current knowledge on NETs and polyP with respect to their procoagulant and prothrombotic nature, strategies for interference of their activities in circulation, as well as the crosstalk between these two molecules. A better understanding of the underlying, cellular mechanisms will shed light on the therapeutic potential of targeting NETs and polyP in coagulation and thrombosis.

Influence of factor XII deficiency on activated partial thromboplastin time (aPTT) in critically ill patients

FXII deficiency results in spontaneous prolongation of activated partial thromboplastin time (aPTT), which is widely used to monitor thromboprophylaxis. Misinterpretation of spontaneously prolonged aPTT may result in omission of thromboembolic treatment or even unnecessary transfusion of blood products. This retrospective analysis was performed to calculate a threshold level of FXII resulting in aPTT prolongation. 79 critically ill patients with spontaneous prolongation of aPTT were included. A correlation analysis and a ROC curve for aPTT prolongation predicted by FXII level were created to find the FXII threshold level. Prolongation of aPTT was associated with disease severity. A significant inverse proportionality between FXII and aPTT was seen. A ROC curve for aPTT prolongation, predicted by FXII level (AUC 0.85; CI 0.76–0.93), revealed a FXII threshold level of 42.5%. Of our patients 50.6% experienced a FXII deficiency, in 80.0% of whom we found aPTT to be prolonged without a significantly higher bleeding rate. The FXII deficiency was more common in patients with higher SAPS3 scores, septic shock, transfusion of red blood cells and platelet concentrates as well as in patients receiving renal replacement therapy. Patients with a FXII deficiency and prolonged aPTT less often received anticoagulatory therapy although they were more severely ill. The rate of thromboembolic events was higher in these patients although the difference was not statistically significant. Of all patients with spontaneous aPTT prolongation 50.6% had a FXII level of 42.5% or less. Those patients received insufficient thromboembolic prophylaxis.

Phenotype of ribonuclease 1 deficiency in mice

Biological roles for extracellular RNA (eRNA) have become apparent. For example, eRNA can induce contact activation in blood via activation of the plasma proteases factor XII (FXII) and factor XI (FXI). We sought to reveal the biological role of the secretory enzyme ribonuclease 1 (RNase 1) in an organismal context by generating and analyzing RNase 1 knockout (Rnase1^-/-) mice. We found that these mice are viable, healthy, and fertile, though larger than Rnase1^+/+ mice. Rnase1^-/- plasma contains more RNA than does the plasma of Rnase1^+/+ mice. Moreover, the plasma of Rnase1^-/- mice clots more rapidly than does wild-type plasma. This phenotype appeared to be due to increased levels of the active form of FXII (FXIIa) in the plasma of Rnase1^-/- mice compared to Rnase1^+/+ mice, and is consistent with the known effects of eRNA on FXII activation. The apparent activity of FXI in the plasma of Rnase1^-/- mice was 1000-fold higher when measured in an assay triggered by a low concentration of tissue factor than in assays based on recalcification, consistent with eRNA enhancing FXI activation by thrombin. These findings suggest that one of the physiological functions of RNase 1 is to degrade eRNA in blood plasma. Loss of this function facilitates FXII and FXI activation, which could have effects on inflammation and blood coagulation. We anticipate that Rnase1^-/- mice will be a useful tool for evaluating other hypotheses about the functions of RNase 1 and of eRNA in vivo.

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.

A hypercoagulable state leading to venous limb gangrene associated with occult lung adenocarcinoma

We report a case of lung adenocarcinoma-associated hypercoagulability leading to venous limb gangrene, managed successfully with argatroban and then dabigatran. Use of idarucizumab permitted diagnostic investigations, leading to targeted antineoplastic therapy with crizotinib, surgical resection with curative intent, and continued survival over 2 years after the index event.

Polyphosphate as a Target for Interference With Inflammation and Thrombosis

Activated platelets and mast cells expose the inorganic polymer, polyphosphate (polyP) on their surfaces. PolyP initiates procoagulant and proinflammatory reactions and the polymer has been recognized as a therapeutic target for interference with blood coagulation and vascular hyperpermeability. PolyP content and chain length depend on the specific cell type and energy status, which may affect cellular functions. PolyP metabolism has mainly been studied in bacteria and yeast, but its roles in eukaryotic cells and mammalian systems have remained enigmatic. In this review, we will present an overview of polyP functions, focusing on intra- and extracellular roles of the polymer and discuss open questions that emerge from the current knowledge on polyP regulation.

Net Clinical Benefit of Non-vitamin K Antagonist Oral Anticoagulants for Venous Thromboembolism Prophylaxis in Patients With Cancer: A Systematic Review and Trade-Off Analysis From 9 Randomized Controlled Trials

Venous thromboembolism (VTE) is highly prevalent in patients with cancer. Non-vitamin K antagonist oral anticoagulants (NOACs), directly targeting the enzymatic activity of thrombin or factor Xa, have been shown to be as effective as and safer than traditional anticoagulation for VTE prophylaxis in no-cancer patients. However, related studies that focused on the anticoagulation in cancer patients are lacked, and almost no net clinical benefit (NCB) analyses that quantified both VTE events and bleeding events have been addressed in this fragile population. Therefore, we aim to investigate this issue using a systematic review and NCB analysis. A comprehensive search of Medline, Embase, and Cochrane Library were performed for randomized controlled trials (RCTs) that reported the VTE events and major bleeding of NOACs and traditional anticoagulants in patients with or without cancer. Odds ratios (ORs) and 95% confidence intervals (CIs) of VTE and bleeding events were calculated using a random-effects model. The primacy outcome of narrow NCB was calculated by pooling ORs of VTE and major bleeding, with a weighting of 1.0. Similarly, the broad NCB was calculated by pooling ORs of VTE and clinically relevant bleeding. Heterogeneity was assessed through I² test and Q statistic, and subgroup analyses were performed on the basis of different patients (VTE patients or acutely ill patients), comparators (vitamin-K antagonists or low-molecular-weight heparin), and follow-up duration (≤6 months or >6 months). Overall, 9 RCTs including 41,454 patients were enrolled, of which 2,902 (7%) were cancer patients, and 38,552 (93%) were no-cancer patients; 20,712 (50%) were administrated with NOACs and 20,742 (50%) were administrated with traditional anticoagulants. The use of NOACs had a superior NCB than traditional anticoagulation in both cancer patients (OR: 0.68, 95%CI: 0.50-0.85 for narrow NCB; OR: 0.76, 95%CI: 0.61–0.91 for broad NCB) and no-cancer patients (OR: 0.75, 95%CI: 0.54-0.96 for narrow NCB; OR: 0.85, 95%CI: 0.67–1.04 for broad NCB), with the estimates mainly from VTE patients receiving long-term warfarin treatment. In conclusion, NOACs may represent a better NCB property compared to traditional anticoagulants in cancer patients who need long-term anticoagulation treatment.

Ability of Polyphosphate and Nucleic Acids to Trigger Blood Clotting: Some Observations and Caveats

Polyphosphate plays several roles in coagulation and inflammation, while extracellular DNA and RNA are implicated in thrombosis and as disease biomarkers. We sought to compare the procoagulant activities of polyphosphate versus DNA or RNA isolated from mammalian cells. In a recent study, we found that much of the procoagulant activity of DNA isolated from mammalian cells using Qiagen kits resisted digestion with nuclease or polyphosphatase, and even resisted boiling in acid. These kits employ spin columns packed with silica, which is highly procoagulant. Indeed, much of the apparent procoagulant activity of cellular DNA isolated with such kits was attributable to silica particles shed by the spin columns. Therefore, silica-based methods for isolating nucleic acids or polyphosphate from mammalian cells are not suitable for studying their procoagulant activities. We now report that polyphosphate readily co-purified with DNA and RNA using several popular isolation methods, including phenol/chloroform extraction. Thus, cell-derived nucleic acids are also subject to contamination with traces of cellular polyphosphate, which can be eliminated by alkaline phosphatase digestion. We further report that long-chain polyphosphate was orders of magnitude more potent than cell-derived DNA (purified via phenol/chloroform extraction) or RNA at triggering clotting. Additional experiments using RNA homopolymers found that polyG and polyI have procoagulant activity similar to polyphosphate, while polyA and polyC are not procoagulant. Thus, the procoagulant activity of RNA is rather highly dependent on base composition.

Mast cells co-expressing CD68 and inorganic polyphosphate are linked with colorectal cancer

Inflammation is a hallmark of colorectal cancer (CRC). Neutrophils are well-known mediators in tumor biology but their role in solid tumors, including CRC, was redefined by neutrophil extracellular traps (NETs). Given that it was recently demonstrated that platelet-derived polyP primes neutrophils to release NETs, we examined surgical specimens from CRC to investigate the presence of polyP, as a possible NET inducer. Biopsies with adenomas, hyperplastic polyps, inflammatory bowel disease and healthy colon tissues were used as controls. In all cases, the presence of polyP was apparent, with the main source of polyP being the mast cells. In all CRC and all adenomas with high-grade dysplasia, a substantial number of mast cells, more than 50%, co-expressed intracellularly polyP with CD68 surface antigen (CD68+), but this was not the case in the other examined disorders. PolyP-expressing mast cells were detected in close proximity with tumor cells and neutrophils, suggesting polyP expression by CD68+ mast cells among the stimuli which prime neutrophils to release NETs, in CRC. Moreover, the detection of CD68+ polyP-expressing mast cells could represent a potential prognostic marker in colorectal adenomas and/or carcinomas.

Association of impaired renal function with venous thrombosis: A genetic risk score approach

OBJECTIVE

The association between impaired kidney function and venous thrombosis has been previously reported but supportive data are still sparse. We here wish to strengthen this association by investigating, by use of a genetic risk score approach, whether single nucleotide polymorphisms (SNPs) known to decrease the estimated glomerular filtration rate (eGFR), a surrogate marker for renal dysfunction, are associated with increased risk of venous thrombosis.

APPROACH AND RESULTS

Fifty-one polymorphisms selected from the literature to robustly associate with eGFR were first tested for association with venous thrombosis in a French case-control collection of 1953 patients and 2338 healthy individuals. This led to the identification of a genetic risk score based on 9 polymorphisms that strongly associated with increased risk (odds ratio (OR)=1.09 [1.06-1.15], p=1.44·10^-7). This genetic score association replicated (OR=1.18 [1.11-1.26], p=8.86·10^-8) in an independent sample of 1289 patients and 1049 healthy controls part of the Dutch MEGA study. We then categorized the genetic score distribution observed in the combined samples into quintiles. Compared with the lowest quintile, the OR for increased risk of disease associated with the second, third, fourth and fifth quintiles were 1.13 [0.94-1.16], 1.47 [1.22-1.77], 1.52 [1.26-1.82] and 1.70 [1.41-2.05], respectively.

CONCLUSIONS

Using a genetic risk score analysis, our study provides new elements supporting the association between impaired renal function and the risk of venous thrombosis.

Factor XIIa as a Novel Target for Thrombosis: Target Engagement Requirement and Efficacy in a Rabbit Model of Microembolic Signals

Coagulation Factor XII (FXII) plays a critical role in thrombosis. What is unclear is the level of enzyme occupancy of FXIIa that is needed for efficacy and the impact of FXIIa inhibition on cerebral embolism. A selective activated FXII (FXIIa) inhibitor, recombinant human albumin-tagged mutant Infestin-4 (rHA-Mut-inf), was generated to address these questions. rHA-Mut-inf displayed potency comparable to the original wild-type HA-Infestin-4 (human FXIIa inhibition constant = 0.07 and 0.12 nM, respectively), with markedly improved selectivity against Factor Xa (FXa) and plasmin. rHA-Mut-inf binds FXIIa, but not FXII zymogen, and competitively inhibits FXIIa protease activity. Its mode of action is hence akin to typical small-molecule inhibitors. Plasma shift and aPTT studies with rHA-Mut-inf demonstrated that calculated enzyme occupancy for FXIIa in achieving a putative aPTT doubling target in human, nonhuman primate, and rabbit is more than 99.0%. The effects of rHA-Mut-inf in carotid arterial thrombosis and microembolic signal (MES) in middle cerebral artery were assessed simultaneously in rabbits. Dose-dependent inhibition was observed for both arterial thrombosis and MES. The ED₅₀ of thrombus formation was 0.17 mg/kg i.v. rHA-Mut-inf for the integrated blood flow and 0.16 mg/kg for thrombus weight; the ED₅₀ for MES was 0.06 mg/kg. Ex vivo aPTT tracked with efficacy. In summary, our findings demonstrated that very high enzyme occupancy will be required for FXIIa active site inhibitors, highlighting the high potency and exquisite selectivity necessary for achieving efficacy in humans. Our MES studies suggest that targeting FXIIa may offer a promising strategy for stroke prevention associated with thromboembolic events.