Warfarin inhibits both procoagulant activity and metastatic capacity of Lewis lung carcinoma cells. Role of vitamin K deficiency

Towards an emerging role for anticoagulants in cancer therapy: a systematic review and meta-analysis

Background

Anticoagulants, renowned for their role in preventing blood clot formation, have captivated researchers' attention for the exploitation of their potential to inhibit cancer in pre-clinical models.

Objectives

To undertake a systematic review and meta-analysis of the effects of anticoagulants in murine cancer research models. Further, to present a reference tool for anticoagulant therapeutic modalities relating to future animal pre-clinical models of cancer and their translation into the clinic.

Methods

Four databases were utilized including Medline (Ovid), Embase (Ovid), Web of science, and Scopus databases. We included studies relating to any cancer conducted in murine models that assessed the effect of traditional anticoagulants (heparin and its derivatives and warfarin) and newer oral anticoagulants on cancer.

Results

A total of 6,158 articles were identified in an initial multi-database search. A total of 157 records were finally included for data extraction. Studies on heparin species and warfarin demonstrated statistically significant results in favour of tumour growth and metastasis inhibition.

Conclusion

Our findings constitute a valuable reference guide for the application of anticoagulants in cancer research and explore the promising utilization of non-anticoagulants heparin in preclinical cancer research.

Systematic Review Registration

PROSPERO [CRD42024555603].

Use of Warfarin or Direct Oral Anticoagulants and Risk of Prostate Cancer in PCBaSe: A Nationwide Case-Control Study

Existing literature examining warfarin's association with prostate cancer (PCa) risk provides conflicting results, while the association with direct oral anticoagulants (DOACs) has not yet been studied. We investigated the association of warfarin and DOAC use on PCa risk among men within the population-based Prostate Cancer database Sweden (PCBaSe), using a case-control design. The study population included PCa cases diagnosed 2014–2016 and five age-matched PCa-free controls. Conditional logistic regression was used to estimate odds ratios (ORs) with 95% confidence intervals (CI) for PCa associated with warfarin and DOAC use, adjusted for marital status, education level, other drug use, and comorbidities. Among 31,591 cases and 156,802 controls, there were 18,522 (9.8%) warfarin and 4,455 (2.4%) DOAC users. Warfarin ever-use was associated with reduced risk of PCa overall (OR 0.92 95% CI 0.88–0.96) as were both past and current use. DOAC use was not associated with PCa risk. For some warfarin exposures, decreased risk was observed for unfavorable PCa (high risk/locally advanced/distant metastatic) but not with favorable PCa (low/intermediate risk). Increased risk of favorable PCa was observed for men whose initial warfarin exposure occurred in the 12 month period before diagnosis (OR 1.39; 95% CI 1.13–1.70). Our findings are consistent with previous publications reporting decreased PCa risk with warfarin exposure. Increased risk of favorable PCa suggests detection bias due to increased prostate specific antigen testing when starting on warfarin. Decreased overall PCa risk could reflect bias due to reduced biopsy rates among long-term warfarin users.

Direct analysis reveals an absence of gamma-carboxyglutamic acid in cancer procoagulant from human tissues

Additional carboxylation of glutamic acid by vitamin K-dependent gamma-carboxylase is a common posttranslational modification of many proteins, including some of blood clotting factors. Vitamin K-antagonists, such as warfarin, are often included in the therapy of malignant disease, decreasing the blood coagulation potential. Cancer procoagulant, a direct blood coagulation factor X activator from malignant tissue, is considered as a vitamin K-dependent protein, so it could serve as one of possible targets for the therapy with warfarin. However, there is still no experimental data demonstrating directly the presence of gamma-carboxyglutamic acid (Gla) in a cancer procoagulant molecule. The presence of Gla in cancer procoagulant isolated from human amnion-chorion membranes and from human malignant melanoma WM 115 cell line was analyzed directly, using specific anti-Gla monoclonal antibodies. There was no detectable amount of Gla in cancer procoagulant isolated from fetal or malignant tissue. Cancer procoagulant from human tissues does not contain Gla-rich domain. The finding indicates that cancer procoagulant is rather a poor target for warfarin therapy of malignant disease.

Thrombosis and cancer: Trousseau syndrome revisited

In this introductory chapter a story has been reviewed concerning the evolution of the concept of "cancer and thrombosis", since its first description by Armand Trousseau in 1865. From scattered reports on experimental material (tumor extracts) or on animal models of tumor/metastasis growth, through the progress of cell biology and experimental pharmacology, during the last 20 years interest has moved to clinical questions, such as: how to prevent and treat thrombosis, a frequent complication of both solid and hematologic malignancies? Has an occult cancer to be suspected in the majority of cases of idiopathic deep vein thrombosis? Do we need to prevent pharmacologically the occurrence of chemotherapy-associated thrombosis? Do anticoagulants have an impact on the natural history of some tumors? Why antiangiogenetic agents may be associated to a thrombotic risk? Presently, a continuous cross-talk between clinical results and experimental data is required to provide answers to these questions, taking advantage of a multidisciplinary approach to this old but still partially mysterious issue.

Effect of anticoagulant drugs in cancer

PURPOSE OF REVIEW

The aim of this review is to perform a critical analysis of all completed studies evaluating the role of anticoagulant agents in improving survival in patients with cancer. Furthermore, the rationale for testing anticoagulant drugs in this setting, and the recent basic research studies providing new evidence for a link between tissue malignant transformation of tissues and hemostatic proteins, are also briefly reviewed.

RECENT FINDINGS

Four prospective randomized clinical studies to test the impact of low-molecular-weight heparin on mortality in cancer patients have been published. The results suggest a benefit from treatment, particularly in patients with nonadvanced disease. Inhibition of specific clotting pathways by anticoagulants may be hypothesized, particularly those involved in the malignant behavior of tissues. In the same vein, a direct action of anticoagulants on mechanisms of tumor growth and progression can be considered.

SUMMARY

An antineoplastic effect of anticoagulant agents has often been suggested. Heparin and vitamin K antagonists have both been tested in this context. Heparin has been more extensively studied. Data from clinical trials of thromboprophylaxis in cancer patients have suggested that heparin may have beneficial effects on survival in these patients, with a major role for low-molecular-weight heparin compared with unfractionated heparin. Recently, the results of new prospective randomized clinical trials to evaluate the effect of low-molecular-weight heparin on cancer survival have become available. The published data look promising and provide an important step forward in the research knowledge in this field.

Biological and clinical aspects of anticancer effects of antithrombotics

Hemostatic mechanisms play a role not only in cancer associated thrombotic diathesis, but also in tumor growth and dissemination. Hence, inhibition of fibrin formation has been considered a possible tool against the progression of malignant disease. An antineoplastic effect of antithrombotic agents in various experimental models (i.e. tumor cell in culture, experimental animals, and cancer patients) has often been suggested. Anticoagulant drugs such as heparins and vitamin K antagonists have been repeatedly tested in this context. However, heparins have been more extensively studied. Several reports in animal models demonstrate that heparin can reduce the primary tumor growth or its metastatic spread. Clinical studies of thrombosis in cancer patients show that, besides their role as antithrombotics, heparins may have beneficial effects on survival in these patients, with a major role for low molecular-weight heparin (LMWHs) compared to unfractionated heparin (UFH). More recently a number of prospective randomized clinical trials of LMWH for survival as a primary end-point in cancer patients have been conducted, showing favourable results.

Coagulation facilitates tumor cell spreading in the pulmonary vasculature during early metastatic colony formation

Coagulation has long been known to facilitate metastasis. To pinpoint the steps where coagulation might play a role in the metastasis, we used three-dimensional visualization of direct infusion of fluorescence labeled antibody to observe the interaction of tumor cells with platelets and fibrinogen in isolated lung preparations. Tumor cells arrested in the pulmonary vasculature were associated with a clot composed of both platelets and fibrin(ogen). Initially, the cells attached to the pulmonary vessels were rounded. Over the next 2 to 6 hours, they spread on the vessel surface. The associated clot was lysed coincident with tumor cell spreading. To assess the importance of clot formation, we inhibited coagulation with hirudin, a potent inhibitor of thrombin. The number of tumor cells initially arrested in the lung of hirudin-treated mice was essentially the same as in control mice. However, tumor cell spreading and subsequent retention of the tumor cells in the lung was markedly inhibited in the anticoagulated mice. These associations of the tumor cells with platelets were independent of tumor cell expression of P-selectin ligands. This work identifies tumor cell spreading onto the vascular surface as an important component of the metastatic cascade and implicates coagulation in this process.

Pathogenetic mechanisms of thrombosis in malignancy

The interactions between components of the hemostatic system and cancer cells are multifaceted. Strong clinical evidence is accumulating on the prothrombotic tendency of cancer patients, which is enhanced by anticancer therapy, such as surgery and chemotherapy. The mechanisms of thrombus promotion in malignancy include some general responses of the host to the tumor (acute phase, inflammation, angiogenesis) and specific interactions of tumor cells with the clotting/fibrinolysis systems and with blood (leukocytes, platelets) or vascular cells. It is at present difficult to rank the relative weight of these multiple interactions on the basis of the well-recognized clinical evidence of enhanced thrombotic episodes in tumor patients. In any case, the mechanisms explored so far offer a sound experimental basis for prevention/treatment of thrombosis in tumor patients and leave open the possibility that some antithrombotic strategies may also affect the processes of tumor growth and dissemination.

Fibrinogen is an important determinant of the metastatic potential of circulating tumor cells

Detailed studies of tumor cell–associated procoagulants and fibrinolytic factors have implied that local thrombin generation and fibrin deposition and dissolution may be important in tumor growth and dissemination. To directly determine whether fibrin(ogen) or plasmin(ogen) are determinants of the metastatic potential of circulating tumor cells, this study examined the impact of genetic deficits in each of these key hemostatic factors on the hematogenous pulmonary metastasis of 2 established murine tumors, Lewis lung carcinoma and the B16-BL6 melanoma. In both tumor models, fibrinogen deficiency strongly diminished, but did not prevent, the development of lung metastasis. The quantitative reduction in metastasis in fibrinogen-deficient mice was not due to any appreciable difference in tumor stroma formation or tumor growth. Rather, tumor cell fate studies indicated an important role for fibrin(ogen) in sustained adhesion and survival of tumor cells within the lung. The specific thrombin inhibitor, hirudin, further diminished the metastatic potential of circulating tumor cells in fibrinogen-deficient mice, although the inhibitor had no apparent effect on tumor cell proliferation in vitro. The absence of plasminogen and plasmin-mediated fibrinolysis had no significant impact on hematogenous metastasis. The authors concluded that fibrin(ogen) is a critical determinant of the metastatic potential of circulating tumor cells. Furthermore, thrombin appears to facilitate tumor dissemination through at least one fibrin(ogen)-independent mechanism. These findings suggest that therapeutic strategies focusing on multiple distinct hemostatic factors might be beneficial in the containment of tumor metastasis.

Fibrinogen is an important determinant of the metastatic potential of circulating tumor cells

Detailed studies of tumor cell–associated procoagulants and fibrinolytic factors have implied that local thrombin generation and fibrin deposition and dissolution may be important in tumor growth and dissemination. To directly determine whether fibrin(ogen) or plasmin(ogen) are determinants of the metastatic potential of circulating tumor cells, this study examined the impact of genetic deficits in each of these key hemostatic factors on the hematogenous pulmonary metastasis of 2 established murine tumors, Lewis lung carcinoma and the B16-BL6 melanoma. In both tumor models, fibrinogen deficiency strongly diminished, but did not prevent, the development of lung metastasis. The quantitative reduction in metastasis in fibrinogen-deficient mice was not due to any appreciable difference in tumor stroma formation or tumor growth. Rather, tumor cell fate studies indicated an important role for fibrin(ogen) in sustained adhesion and survival of tumor cells within the lung. The specific thrombin inhibitor, hirudin, further diminished the metastatic potential of circulating tumor cells in fibrinogen-deficient mice, although the inhibitor had no apparent effect on tumor cell proliferation in vitro. The absence of plasminogen and plasmin-mediated fibrinolysis had no significant impact on hematogenous metastasis. The authors concluded that fibrin(ogen) is a critical determinant of the metastatic potential of circulating tumor cells. Furthermore, thrombin appears to facilitate tumor dissemination through at least one fibrin(ogen)-independent mechanism. These findings suggest that therapeutic strategies focusing on multiple distinct hemostatic factors might be beneficial in the containment of tumor metastasis.

Application of chemical immunomodulators to the treatment of cancer and AIDS

A number of potential advantages, development of promising new agents, and the discovery of synergy with cytokines or cell products continue to spur research into the application of chemical immunomodulators for the treatment of cancer and AIDS. In preclinical in vitro and in vivo systems, chemical immunomodulators definitely modulate the immune system and have therapeutic efficacy. Although clinical trials have shown the ability of these agents to modulate the human immune system, thus far chemical immunomodulators have generally not fulfilled the therapeutic promise generated in animal models for the treatment of human diseases. While the discrepancy in results between animal models and human trials is obvious, the basis is not apparent. Species differences in elimination kinetics, presentation of active drug at the site of action, and the development of tachyphylaxis have been postulated as reasons for the minimal activity of these agents in humans. In addition, the use of investigational techniques established for cytotoxic agents may not be appropriate for immunomodulators. As with any immunomodulator, determining an optimal immunostimulatory dose and schedule and applying the therapy to patients with minimal tumor burden would perhaps be more appropriate than use of a maximally tolerated dose in patients with advanced disease. A dose-immunological effect relationship has recently been demonstrated for levamisole at doses higher than those used for many years in levamisole trials (99). While research and clinical investigation have identified several potentially useful chemical immunomodulators, the elementary understanding of the biochemical mechanisms involved in immunoregulation remains basic. Future research must elucidate these mechanisms, particularly in humans, to maximize the benefits of chemical immunomodulators as single agents or combined with cytotoxic chemotherapeutic agents, surgery, radiation therapy, other immunomodulators, and antiviral agents.

Procoagulant activity of the MC28 fibrosarcoma cell line in vitro and in vivo

Experimental evidence suggests that many tumours can activate blood coagulation and that such interaction is part of the pathology of metastatic tumour growth. This study aimed to study the procoagulant activity of the methylcholanthrene-induced (MC28) fibrosarcoma to determine whether coagulation activation by these cells could explain the previously reported effects of oral anticoagulants on lung seeding in this model. MC28 cells shortened the recalcification times of normal and factor VII-deficient plasma and directly activated factor X in a chromogenic assay, but did not aggregate platelets in vitro in either whole blood or platelet-rich plasma. Cellular coagulant activity was calcium-dependent, blocked by DFP and concanavalin A but not inhibited by iodoacetamide, E-64 or antibodies to human tissue factor or factor VII. Injection of viable MC28 cells into hooded Lister rats induced a decrease in platelet count (P < 0.001), plasma factor X (P < 0.001) and fibrinogen (P < 0.05) and a marked increase in plasma haemoglobin (P < 0.001). These effects were either not observed or were considerably less marked in heparinized or warfarinized animals. Injection of MC28 cells treated with concanavalin A in vitro completely abolished the clotting changes observed with untreated cells. In conclusion, MC28 cells possessed a potent factor X-activating serine proteinase procoagulant in vitro, which had some of the characteristics of a tissue factor/factor VIIa complex. In vivo, MC28 cells caused clotting activation and intravascular fibrin generation. Since thrombocytopenia was abolished by heparin and the cells lacked platelet aggregating activity in vitro, thrombocytopenia was probably secondary to intravascular coagulation and thrombin generation. The trigger for intravascular clotting activation appeared to be the cellular procoagulant activity since it was abolished by prior in vitro blockade of the latter with concanavalin A.

Tissue procoagulant activity may be important in sustaining metastatic tumour growth

There is strong evidence for an association between the haemostatic system and malignancy. Thus, cancer may adversely affect the host coagulation system while the haemostatic system may play a role in the development of both primary and metastatic tumours. Metastatic growth is not dependent simply on haemodynamic factors, and properties of both the tumour cell and host organ are important determinants of the site of metastatic growth. Previous studies have demonstrated that some organs are preferred sites for metastasis while others are less preferred or resistant. We have measured the procoagulant activity (PCA) of normal rat and human tissues and correlated the results with the previously reported ability of these organs to support metastatic tumour growth. In addition, we determined changes in PCA in rat tissues during oral anticoagulant therapy, and following colonic anastomosis and partial hepatectomy, procedures which are known to affect experimental metastasis. In both rat and human studies, organs which are preferred sites for metastasis had significantly higher PCA than non-preferred organs (P less than 0.001). The PCA of adrenal, lung and colon was significantly reduced by administration of warfarin (P less than 0.001). PCA was significantly (P less than 0.001) increased in both colonic anastomoses and regenerating liver and followed a time course similar to that of the enhanced tumour growth usually seen in these situations. Although the exact source of the procoagulant activity remains to be determined, the results suggest that there is a broad correlation between tissue PCA and the ability of a tissue to support metastatic tumour growth.

The effect of Warfarin and factor VII on tissue procoagulant activity and pulmonary seeding

Peri-tumour fibrin is a consistent feature of tumour stroma and is deposited shortly after tumour cell inoculation. Since there are several ways in which fibrin may be beneficial to tumour growth, it is possible that the ability of normal or malignant tissue to generate fibrin may influence metastasis. Many normal tissues and tumour cells possess a procoagulant activity that is due to a complex of tissue factor and factor VII. We have measured this tissue procoagulant activity in normal rats, rats stabilised on Warfarin and similarly anticoagulated animals injected with factor VII. The effect of Warfarin and factor VII administration on pulmonary seeding following injection of MC28 fibrosarcoma cells was also assessed. Procoagulant activity in adrenal, lung and colon was significantly reduced by Warfarin (P less than 0.001). Administration of factor VII significantly increased lung and adrenal tissue procoagulant activity in anticoagulated rats (P less than 0.02). Warfarinised rats had significantly slower primary tumour growth (P less than 0.001) and fewer lung deposits than control animals (P less than 0.001). Injection of factor VII restored pulmonary seeding to control levels (P less than 0.001). Warfarin did not affect the ability of the cells to adhere in vitro and did not reduce the number of tumour cells physically trapped in the lungs after intravenous injection. It is concluded that the procoagulant activity of normal tissues may influence their ability to support tumour growth and that the antimetastatic effect of Warfarin may be at least partly due to a reduction in the availability of the factor VII required for this activity.

Factor X-activating procoagulant in normal and malignant breast tissue

Factor X-activating activity (FXAA) was determined by a chromogenic assay in normal and malignant breast tissue. FXAA was found in all tissue (n = 38) irrespective of pathology, and the activity of normal tissue was similar to that of tumours. FXAA correlated with tissue hemoglobin in normal breast (p less than 0.02) but not in tumours. FXAA was markedly reduced by aluminium hydroxide, barium citrate, anti-human factor VII, DFP, PMSF and phospholipase C, but was unaffected by iodoacetamide and mercuric chloride. It is concluded that FXAA is a serine protease with the properties of a tissue factor-factor VII complex. FXAA occurs in normal and malignant breast tissue, although the 'normal' activity may be an artefact of the homogenization process.

Reduction of metastasis in a murine mammary tumour model by heparin and polyinosinic-polycytidylic acid

A murine mammary tumour model has been used to test the efficacy of a combination of heparin and the interferon inducer, poly I:C on spontaneous metastasis from a s.c. primary tumour and on experimental metastasis following i.v. injection of tumour cells. This treatment has no effect on the growth of primary tumours, but lung metastases arising from these tumours were reduced. When tumour cells were injected i.v. the number of lung colonies was significantly reduced and survival time extended. Short-term treatment did not prevent the subsequent growth of extravasated, but dormant tumour cells, although mice treated for 8 or 12 weeks survived at least 6 months without any sign of lung colonies. Several mechanisms may contribute to the overall effect of this treatment; a reduction in the mitotic indices of lung colonies (observed in poly I:C treated mice) and also NK cells appeared to be important for the effectiveness of poly I:C since the reduction in experimental metastasis was abrogated by concomitant treatment with anti-asialo GM1 serum.

Warfarin inhibits metastasis of Mtln3 rat mammary carcinoma without affecting primary tumour growth

Coumarin anticoagulants inhibit metastasis in several animal models, but the mechanism of this effect is uncertain. In order to determine the role of cytotoxic and/or cytostatic actions of coumarins on the tumour cells, we have studied the effects of warfarin on tumour cell growth in a model in which tumour metastasis is inhibited by this drug. Clonogenic assay, growth curve analysis and thymidine labelling index revealed that warfarin had no effects on Mtln3 mammary carcinoma cell growth in vitro at concentrations below 1 mM. The growth rate of subcutaneously implanted Mtln3 tumour deposits in female F344 rats, assessed by weight and by stathmokinetic analysis of the tumour tissue, was identical in warfarin-treated and control animals. Spontaneous metastasis from such tumours to the lungs was, however, significantly reduced in warfarin-treated animals (median 0 pulmonary tumours per animal in warfarin treated, eight tumours per animal in control animals; P less than 0.05, Mann-Whitney). The mean plasma warfarin concentration in warfarin treated rats was 1.63 microM. These results suggest that warfarin treatment of the host animal can inhibit tumour metastasis without having any direct or indirect effect on the growth rate of the tumour cells.

Factor X-activating activity in normal and malignant colorectal tissue

The factor X-activating activity (FXAA) of homogenates from human colorectal tumours and corresponding normal colonic mucosa from the same patients was assessed with a specific chromogenic substrate technique. FXAA was detected in all normal and tumour tissue tested, but was significantly higher in tumour tissue. The procoagulant activity was inhibited by DFP, but was unaffected by iodoacetamide and mercuric chloride. FXAA was largely abolished by prior incubation of both normal and tumour tissue homogenates with a rabbit anti-human factor VII serum, but was greatly enhanced by the addition of purified factor VII. FXAA was partially adsorbed on to aluminium hydroxide and almost completely abolished by treatment with barium citrate. It is concluded that the FXAA of both normal and malignant colorectal tissue is the result of tissue factor-factor VII interaction.

Promotion of metastasis by a specific complex of coagulation factors may be independent of fibrin formation

Coumarins inhibit metastasis in a number of animal models, but the mechanism of this effect remains unclear. We have investigated the relationship between the coagulation system and metastasis using a new model system, involving i.v. injection of Mtln3 rat mammary carcinoma cells into Fischer 344 rats, and subsequent estimation of pulmonary seeding. Injection of factors II, VII, IX and X elevated the median number of surface pulmonary seedlings per animal to 182, and injection of factors II, IX and X to 181, compared with a median for control animals of 12 (P less than 0.001). Injection of factor VII alone, or of bovine serum albumin did not significantly affect pulmonary seeding. In a second experiment, arvin defibrination reduced the mean plasma fibrinogen concentration to 76.8 mg dl-1 from a control value of 228 mg dl-1. This degree of defibrination had no significant effects on pulmonary seeding, nor on the enhancing effects of factor complex injection (median numbers of seedlings per animal; control 15, arvin 21, arvin plus factors II, VII, IX and X 170, factors II, VII, IX and X only, 157). Factor complex injections did not detectably shorten thrombotest clotting times. In vitro testing suggested that Mtln3 cells contain little or no conventional factor X activating cancer procoagulant. The complex of coagulation factors II, IX and X appears to contain a component which greatly enhances metastasis in this model. This may explain the previously reported antimetastatic effect of coumarin anticoagulants, which suppress factors II, VII, IX and X. The enhancing effect of the factor complex does not appear to be altered by significant reductions in fibrin forming capacity, and defibrination itself has no effect on metastasis. These findings suggest the possibility that the effect of this factor complex on metastasis may be mediated via mechanisms other than the formation of a fibrin clot.

Initiation of coagulation by tissue factor

Tissue factor (TF) is an integral membrane glycoprotein which functions as an initiator of coagulation. Furthermore, it is probably the principal biological initiator of this essential hemostatic process. This article reviews the studies which form the basis for these assertions. The work on TF is traced from the 19th century discovery of the thromboplastic activity of tissues to the recent purification of the protein from bovine and human tissues and the isolation cDNA clones coding from human TF. The features of TF structure and function which tailor it to the role of initiator of the coagulation cascade are considered. For example, cell-surface TF and factor VII, the plasma serine proteases zymogen, form a proteolytic complex without prior proteolysis of either component. In addition, a kinetic model for the molecular mechanism of TF-initiated clotting is reviewed. The factors which control the expression of TF procoagulant activity by cultured cells are examined in light of the hypothesized role of TF in normal hemostasis. Also, the potential pathological consequences of aberrant TF expression, i.e., thrombosis and hemorrhage, are explored.

Coagulation abnormalities associated with neoplasia

Subclinical abnormalities in hemostasis occur commonly in small animal patients with cancer, but the incidence of clinical thrombosis or hemorrhage is unknown. Malignancy can lead to abnormalities in both primary and secondary hemostasis, which in turn can lead to either thrombotic or hemorrhagic tendencies. These coagulation abnormalities can be associated with the tumor itself, with anticancer chemotherapy, or with secondary organ dysfunction. Thrombocytopenia and DIC are probably the most common defects associated with clinical bleeding in small animal patients.

Warfarin inhibition of metastasis: the role of anticoagulation

Warfarin inhibits metastasis in animal models by mechanisms that remain unclear. A better understanding of this phenomenon may clarify processes underlying metastasis in human cancer. We have studied the effects of warfarin on metastasis in a rat model by intravenous injection of Mtln3 mammary carcinoma cells and subsequent counting of pulmonary seedlings. To determine whether warfarin acts principally on the tumour cells or the host, we pretreated either cells or animals with warfarin before intravenous injection of 10(4) Mtln3 cells. Pretreatment of tumour cells had no effect, whilst pretreatment of the host reduced median seedlings from 67 to 4.5 per animal (P less than 0.005). To determine whether warfarin was acting via its anticoagulant action, we reversed warfarin anticoagulation by intravenous injection of coagulation factors II, VII, IX and X. Restoration of coagulation for 12 h immediately after injection of cells completely reversed the warfarin effect (P less than 0.001), but if the injection of factors was delayed for 12 h it had no effect (P = 0.1753). We conclude that warfarin acts principally on the host, not the tumour cell, and that it acts via its effect on coagulation. The restriction of the effect to the first 12 h after tumour cell injection suggests a mechanism involving intravascular processes such as tumour cell survival or endothelial adhesion.

Evidence for a warfarin-sensitive serum factor that participates in factor X activation by Lewis lung tumor cells

Mouse Lewis lung (LL) carcinoma cells possess a factor X activator (procoagulant) that is inhibited in vivo by warfarin treatment or diet-induced vitamin K deficiency. This inhibition suggests that vitamin-K-dependent proteins are involved in LL cell activation of factor X. A LL primary tumor clone (LL13) was isolated which contained a warfarin-sensitive vitamin-K cycle of metabolism and expressed factor X procoagulant activity. LL13 cells exposed to media containing warfarin or deficient in vitamin K grew as well as cells in normal media, and activated factor X to similar extents. In contrast, administration of warfarin to mice bearing LL13 cells inhibited factor X procoagulant activity as well as the vitamin K cycle of metabolism in the primary tumors. In relation to LL13 cells grown in media containing fetal bovine serum, those incubated for 20 hr in media containing mouse serum or the sera from LL13-bearing mice exhibited 9- to 10-times higher levels of factor X procoagulant activity. However, LL13 cells exposed to media containing the sera of warfarin-treated LL-13-bearing mice or to barium-sulfate-adsorbed normal mouse serum activated factor X much less efficiently. Collectively, these data suggest that inhibition of vitamin K function in LL cells does not affect the extent of factor X activation and thus the intrinsic factor X procoagulant is not a vitamin-K-dependent protein. They further suggest that both a warfarin-sensitive (vitamin-K-dependent) protein present in normal mouse serum and a LL13 cell component participate in factor X procoagulant activity.

Murine tumor-induced platelet aggregation and coagulation: mechanisms, inhibitors, and species differences

This study examined the platelet-aggregating and procoagulant activities of two hematogenously disseminating tumors, a mouse lymphoblastic leukemia (L5178Y) and a mouse renal adenocarcinoma (RAG). Tumor-induced human platelet aggregation was inhibited by addition of the following agents to platelet-rich plasma (PRP): a calcium channel blocker (verapamil), a chelator of divalent cations (EDTA), stimulators of adenylate cyclase (2-fluoroadenosine and forskolin), and inhibitors of cAMP phosphodiesterase (oxagrelate and papaverine). The platelet-aggregating activities of both cell lines were completely blocked by treatment of the cells with heat, sonication, phospholipase A2, and Triton X-100. These data suggest that L5178Y and RAG cell-induced human platelet aggregation are dependent on a heat-labile phospholipid component of the tumor cell membrane. L5178Y cells had greater platelet-aggregating activity in human plasma than in rat or mouse plasma, whereas RAG cells had greater procoagulant activity in rat or mouse plasma than in human plasma. The procoagulant activity of RAG cells in rat and mouse plasma was demonstrated by three lines of evidence: RAG cells induced heparinized PRP to clot; the thrombin inhibitor DAPA lengthened of the clotting time and the lag time before aggregation; and RAG cells shortened of the recalcification time of the plasma. The above data indicate that RAG cell-induced murine platelet aggregation and coagulation is dependent on thrombin generation.

Vitamin-K-dependent proteins in microsomes of primary Lewis lung tumors

Microsomes isolated from Lewis lung (LL) primary tumors raised in C57BL/6 mice have been shown to (i) contain a 4-hydroxycoumarin (warfarin)-sensitive cycle of vitamin K metabolism which is at least qualitatively similar to that of liver, and (ii) catalyze the incorporation of NaH14 CO3 into endogenous protein in a vitamin-K hydroquinone-dependent reaction to produce gamma-carboxyglutamate. As in liver microsomes, LL microsomal reduction of vitamin K 2,3-epoxide to vitamin K was greatly enhanced by exogenous dithiols such as dithiothreitol, but under identical conditions the former was 10-fold faster. The R(+) and S(-) warfarin enantiomers were highly and equally effective inhibitors of both the liver and tumor vitamin K 2,3-epoxide reductases-the average I50 against the tumor enzyme was 0.25 microM. Partially purified reductases isolated by centrifugation of sodium-cholate-treated liver and LL tumor microsomes over a discontinuous sucrose gradient were also inhibited by the sulfhydryl reagent N-ethylmaleimide following their reduction by dithiothreitol. Like the activity of the epoxide reductase, that of the gamma-carboxylase was much lower in tumor than in liver microsomes and was only detectable in microsomes isolated from tumor-bearing mice previously administered S(-) warfarin. In view of the reported inhibition of LL tumor metastasis by warfarin and diet-induced vitamin-K deficiency, vitamin-K-dependent proteins may play a role in the spread and/or subsequent growth of LL cells.

Basic mechanisms of metastasis

Metastatic disease is responsible for the majority of deaths caused by cancer. The process of metastasis is an orderly, stepwise process that results in the selection of cells that possess the capability to establish viable metastases. These cells must be locally invasive and be able to survive the physical traumas of dissemination and normal host defenses. Once metastatic cells have been arrested in a capillary bed, they must be able to invade the host organ parenchyma and survive in that milieu. Studies in a number of model systems have documented the phenotypic alterations in cells that have "metastatic potential." These differences may stem from normal tumor cell heterogeneity and surprisingly reflect only minor differences in gene expression. The role of activated oncogenes in metastasis is unclear, but a number of laboratories have documented that transfection with activated Ha-Ras results in increased metastatic potential. An increased understanding of the genetic basis of metastatic potential may suggest new directions for intervening in this deadly process.

Increased susceptibility to the anticoagulant effect of warfarin in mice bearing the Lewis lung carcinoma. Role of vitamin K deficiency

This study reports an increased susceptibility to warfarin anticoagulation in mice bearing an experimental tumour, the Lewis lung carcinoma. In these animals, following a single i.v. injection of warfarin, the prothrombin complex activity decreased normally but recovered far slower than in controls, while the rate of degradation of the clotting factors was not modified. At the level of the vitamin K-dependent liver carboxylase, it was possible to demonstrate an increase in the endogenous substrate (reflecting an impairment of the carboxylase vitamin K dependent system). This abnormality was reversed by vitamin K administration and can be reasonably ascribed to a vitamin K deficiency in association with tumour growth.

Inhibitory effect of warfarin on the metastasis of the PAIII prostatic adenocarcinoma in the rat

The PAIII rodent metastatic prostatic adenocarcinoma model was employed to evaluate the effects of dietary warfarin, a prototypic antagonist of thrombin generation on the lymphatic and pulmonary metastases of the tumor from the tail site of subcutaneous transplantation in male Lobund Wistar (LW) rats. In addition, the anticoagulant effects of warfarin were determined in the same animals. Warfarin, administered in the diet at concentrations equivalent to 0.063, 0.125 or 0.250 mg./kg. b.w. for 30 days had no effect on final body weight, gluteal or iliac lymph node weights. Significant (p less than 0.05) dose-dependent extensions of whole blood prothrombin (WBPT), activated partial thromboplastin (WBAPTT) and clotting times (WBCT) over control values were observed with warfarin treatment. Preliminary studies demonstrated that the 0.500 mg./kg. dose produced 50 per cent mortality at +14 days. Warfarin produced significant (p less than 0.05) dose-dependent decreases in the number of PAIII pulmonary metastases as indicated by reductions in dry lung weights and lung colony numbers when compared to untreated tumor-bearing controls. While the therapeutic index of warfarin is a limiting factor in clinical use as an antimetastatic agent, these results suggest that compounds capable of altering hemostatic mechanisms may be potential inhibitors of tumor metastasis. The PAIII prostatic adenocarcinoma model may be a useful system to quantitatively evaluate potential antimetastatic and cytotoxic agents.

Anti-oxidant/pro-oxidant reactions of vitamin K

Experiments were designed to measure O2 consumption caused by the oxidation of linoleic acid. These experiments show that vitamin K has antioxidant activity and that the reduction in linoleic acid oxidation is directly dependent upon vitamin K concentration. Conversely, vitamin K hydroquinone enhances linoleic acid oxidation in the absence of iron catalyst, again in a concentration dependent manner. At equilmolar concentrations vitamin K is about 80% as effective as vitamin E as an antioxidant. Vitamin E inhibits the oxidation of linoleic acid catalyzed by vitamin K hydroquinone. Vitamin E also strongly inhibits vitamin K dependent formation of both vitamin K epoxide and gamma-carboxyglutamic acid (gla). The significance of these observations to vitamin K action in vivo is discussed.