Angiogenesis and tumor metastasis

Angiogenesis, the recruitment of new blood vessels, is an essential component of the metastatic pathway. These vessels provide the principal route by which tumor cells exit the primary tumor site and enter the circulation. For many tumors, the vascular density can provide a prognostic indicator of metastatic potential, with the highly vascular primary tumors having a higher incidence of metastasis than poorly vascular tumors. Tumor angiogenesis is regulated by the production of angiogenic stimulators including members of the fibroblast growth factor and vascular endothelial growth factor families. In addition, tumors may activate angiogenic inhibitors such as angiostatin and endostatin that can modulate angiogenesis both at the primary site and at downstream sites of metastasis. The potential use of these and other natural and synthetic angiogenic inhibitors as anticancer drugs is currently under intense investigation. Such agents may have reduced toxicity and be less likely to generate drug resistance than conventional cytotoxic drugs. Clinical trials are now underway to develop optimum treatment strategies for antiangiogenic agents.

Human angiostatin inhibits murine hemangioendothelioma tumor growth in vivo

Angiostatin inhibits angiogenesis and metastatic tumor growth; however, its usefulness in treating primary nonmetastasizing tumors is less well understood. We now report the effectiveness of human angiostatin administration in a mouse hemangioendothelioma model. Human angiostatin was administered to mice with s.c. hemangioendothelioma and associated disseminated intravascular coagulopathy (Kasabach-Merritt syndrome). Angiostatin significantly reduced tumor volume in comparison to nontreated controls, increased survival, and prevented the profound thrombocytopenia and anemia of Kasabach-Merritt syndrome. Apoptosis of tumor cells was induced by angiostatin, but tumor cell proliferation was not inhibited. These data suggest angiostatin as a novel treatment for nonmetastasizing vascular tumors and for Kasabach-Merritt syndrome.

Studies on the effect of human lys-plasminogen in a rat model of global cerebral ischemia

Human lys-plasminogen and the corresponding formulation buffer were tested in a rat model of global cerebral ischemia (clamping of both carotid arteries, withdrawal of 5 ml blood for 30 min). The two main parameters, tested in different experimental set-ups, were 1. brain edema (water content) 23.5 h after reperfusion and 2. assessment of neurological deficits 24, 48 and 72 h after reperfusion. In some groups of animals of the first set-up, brains were examined histologically for microvascular fibrin deposits. In a separate group of animals the fibrinolytic plasma activity of rats treated with 500 CU/kg lys-plasminogen was studied. Concerning brain water content lys-plasminogen completely antagonized the formation of brain edema when given with 500 caseolytic Units (CU)/kg i.v. with blood reperfusion and was still effective when given 30 min later. 200 CU/kg i.v. given with blood reperfusion as well as 500 CU/kg i.v. given 60 min after blood reperfusion proved ineffective. In none of the brains investigated microvascular fibrin deposits were found. In experiments with assessment of neurological deficits, animals treated with 500 CU/kg lys-plasminogen i.v. showed almost no disabilities (like sham operated animals) when compared to ischemic (positive) controls which were rather severely handicapped. The formulation buffer of lys-plasminogen, tested in an equivalent volume, was without any effect in both set-ups. No fibrinolytic activity was found in plasma samples of rats up to 240 min after treatment with 500 CU/kg lys-plasminogen i.v. It is concluded from these experiments that human lys-plasminogen has a protective effect in rats against the sequelae of global cerebral ischemia which is not related to the well-known fibrinolytic potential but might be a separate quality.

Fibrinogen heterogeneity in homozygous plasminogen deficiency type I: further evidence that plasmin is not involved in formation of LMW- and LMW'-fibrinogen

Human plasma fibrinogen is heterogeneous in SDS-polyacrylamide gel electrophoresis and other methods for separation of proteins by molecular size. A high molecular weight fraction (HMW-fibrinogen, 340 kD) contributes approximately 50% of total fibrinogen antigen. Low molecular weight fibrinogen (LMW-fibrinogen, 300 kD) adds another 40%. The residual amount is LMW'-fibrinogen with a molecular weight of 280 kD, and a small amount of very high molecular weight fibrinogen (Fib420), the product of alternative splicing of the A alpha-chain genetic information, resulting in an extended A alpha-chain C-terminus. Fibrinogen was detected by specific immunostaining of nonreduced SDS-PAGE gel immunoblots with antibodies against fibrinopeptide A. Using densitometric scans of the immunoblots we found a ratio of HMW-, LMW- and LMW'-fibrinogen in a patient with homozygous plasminogen deficiency that was similar to the ratio found in immunoblots of plasma from healthy blood donors. Treatment with plasminogen concentrate resulted in a slight decrease of the proportion of HMW-fibrinogen, followed by an increase to 78%. The LMW'-fibrinogen band gained intensity initially, increasing to 11.9% of fibrinogen antigen 6 h after starting plasminogen infusion, but then dropped to levels below detection limit of the immunoblotting assay. LMW-fibrinogen remained constant during the initial 72 h of plasminogen treatment, then dropping to values in the range of 22-25% afterwards. The proportion of HMW-, LMW-, and LMW'-fibrinogen again reached the initial levels two weeks after starting treatment with plasminogen concentrate. We conclude that plasminogen is not involved in the limited proteolysis leading to formation of LMW-fibrinogen and LMW'-fibrinogen in the absence of a generalized fibrinolytic condition. Fibrinolytic activation may lead to the formation of fibrinogen degradation product X, which appears in a similar position as LMW'-fibrinogen in SDS-PAGE.

Molecular and functional properties of fetal plasminogen and its possible influence on clot lysis in the neonatal period

The blood fibrinolytic system essentially consists of proteolytic enzyme activation processes leading to the formation of the fibrin-degrading enzyme plasmin. It is thus the counterpart of the blood coagulation system. It differs physiologically in newborns compared with adults. In newborns, the plasma levels of plasminogen, the inactive plasmin precursor, are relatively low, and a correlation between maturity and plasminogen levels is observed. Newborn plasminogen has been purified, characterized, and compared with adult plasminogen and does exist in a fetal form with an increased concentration of sialic acid, similar to fetal fibrinogen. We review the molecular and functional properties of fetal plasminogen and its possible influence on clot lysis and thrombolytic therapy in the neonatal period.

Differential effects of Lys- and mini-plasminogen on clot lysis induced by recombinant urokinase and recombinant pro-urokinase in a canine thrombosis model

These studies were conducted to examine the lytic efficacy of recombinant urokinase (r-UK) and pro-urokinase (r-proUK) in the presence and absence of truncated forms of plasminogen. Due to differences in their structures, these modified proteins are more readily activated to plasmin than the circulating form of plasminogen. Use of such modified substrates for plasminogen activators may improve the clinical outcome in patients treated for a variety of thrombotic diseases. Lys-plasminogen (46 units) or mini-plasminogen (in units of equivalent chromogenic activity), in conjunction with r-UK (7,500 units), were administered in the absence of heparin to dogs (9-11 kg) in which a radiolabelled thrombus was formed in a femoral artery. Fibrinolysis was measured as a loss of radioactivity from the clot. After intra-arterial administration of the agents, clot lysis was 48 +/- 8%, 50 +/- 9% and 75 +/- 2% in the presence of r-UK + vehicle, r-UK + lys-plasminogen, and r-UK + mini-plasminogen, respectively. When these treatment groups were examined in the presence of heparin (500 units + 350 units/hour) in a second study, r-UK (2,000 units) produced clot lysis of 54 +/- 3%; addition of lys- or mini-plasminogen to the regimen resulted in lysis of 62 +/- 9% and 46 +/- 10%, respectively. A third phase of the study examined r-proUK (1,000 units) with heparin; in this case, lysis was 51 +/- 9% in the presence of vehicle, but 55 +/- 17% and 10 +/- 5% when lys- and mini-plasminogen were administered, respectively. Flow restoration, measured in the femoral artery in each experiment, generally paralleled the lytic profile. The results indicate that supplementation with mini-plasminogen is only useful when added to a lytic regimen in the absence of heparin, and that lys-plasminogen, in conjunction with either of the lytic agents, does not improve clot lysis in this canine model.

Restoration of thrombolytic potential in plasminogen-deficient mice by bolus administration of plasminogen

Homozygous plasminogen-deficient (Plg-/-) mice had a significantly reduced thrombolytic capacity toward intravenously injected 125I-fibrin labeled plasma clots prepared from Plg-/- murine plasma (9% +/- 3% lysis after 8 hours; (mean +/- SEM, n = 6), as compared with 82% +/- 8% in wild-type mice; P < .0001). Bolus injection of 1 mg purified murine plasminogen in 10- to 17-week-old Plg-/- mice increased the plasminogen antigen and activity levels at 8 hours to normal levels (130 +/- 5 micrograms/mL). Plasminogen administration was associated with significant restoration of thrombolytic potential (64% +/- 7% spontaneous clot lysis; P < .0001 versus lysis without plasminogen injection). Bolus injection of 1 mg plasminogen in homozygous tissue-type plasminogen activator-deficient (t-PA-/-) mice doubled the plasminogen antigen and activity levels after 8 hours and increased 125I-fibrin clot lysis at 8 hours from 13% +/- 3% to 34% +/- 5% (P = .008). Fibrinogen, t-PA antigen and alpha 2-antiplasmin activity levels after 8 hours were not significantly different in the groups with or without plasminogen injection. Injection of plasminogen induced a variable increase (on average 7- to 10-fold) of PAI-1, but no correlation with the extent of spontaneous clot lysis was observed. Histopathologic examination at the end of the experiments revealed that fibrin deposition in the liver of Plg-/- mice was slightly reduced 8 hours after bolus plasminogen injection (P = .007) and markedly reduced after 24 hours (P < .0001). Plasminogen antigen levels in liver extracts were comparable with those found in wild-type mice at 8 hours (130 +/- 20 versus 110 +/- 15 ng/mg protein) and decreased to 25 +/- 3.2 ng/mg protein at 24 hours. Thus, restoration of normal plasminogen levels in Plg-/- mice normalized the thrombolytic potential toward experimentally induced pulmonary emboli, and resulted in removal of endogenous fibrin deposits within 24 hours.

Recombinant lys-plasminogen, but not glu-plasminogen, improves recombinant tissue-type plasminogen activator-induced coronary thrombolysis in dogs

OBJECTIVES

This study examined the modification of recombinant tissue-type plasminogen activator (rt-PA)-induced thrombolysis by recombinant lys-plasminogen.

BACKGROUND

Recombinant tissue-type plasminogen activator restores flow in the thrombosed coronary artery, but the artery often reoccludes. The rt-PA-induced thrombolysis is a result of activation of plasminogen bound to fibrin in the thrombus and results in generation of the fibrinolytic enzyme plasmin. Small amounts of lys-plasminogen are formed when rt-PA is used. Lys-plasminogen binds to fibrin with a 10-fold greater affinity than the predominant native glu-plasminogen, leading to a loose fibrin structure.

METHODS

Dogs with electrically induced occlusive intracoronary thrombus were treated with saline solution (n = 9), glu-plasminogen (2 mg/kg body weight, n = 5) or lys-plasminogen (2 mg/kg, n = 5), followed by infusion of rt-PA (1 mg/kg over 20 min) 10 min later.

RESULTS

Reperfusion rates were similar in all groups of dogs, but the time to reflow was lowest in dogs given lys-plasminogen compared with those given saline solution or glu-plasminogen before rt-PA (mean [+/- SE] 14 +/- 2 vs. 22 +/- 2 and 23 +/- 3 min, respectively, p < 0.05). None of the reperfused coronary arteries reoccluded in the lys-plasminogen plus rt-PA group, whereas 75% reoccluded in dogs given saline solution plus rt-PA, and 50% reoccluded in those given glu-plasminogen plus rt-PA. Accordingly, duration of reflow was greater in the lys-plasminogen plus rt-PA group (> 120 vs. 39 +/- 7 and 82 +/- 21 min, respectively, p < 0.05). Plasminogen activator inhibitor-1 activity decreased during rt-PA infusion and thereafter increased in all dogs, but less so in dogs given lys-plasminogen (p < 0.05 vs. those given saline solution before rt-PA).

CONCLUSIONS

Treatment with recombinant lys-plasminogen before rt-PA reduces time to reflow and sustains reflow after thrombolysis, whereas glu-plasminogen has no such effect.

Cancer therapy. Less blood means more sanguinity

Angiostatin, a recently discovered anti-angiogenic factor, offers the hope of long-term control of metastatic cancers following surgery.

Angiogenesis in cancer, vascular, rheumatoid and other disease

Recent discoveries of endogenous negative regulators of angiogenesis, thrombospondin, angiostatin and glioma-derived angiogenesis inhibitory factor, all associated with neovascularized tumours, suggest a new paradigm of tumorigenesis. It is now helpful to think of the switch to the angiogenic phenotype as a net balance of positive and negative regulators of blood vessel growth. The extent to which the negative regulators are decreased during this switch may dictate whether a primary tumour grows rapidly or slowly and whether metastases grow at all.

[Thrombolytic therapy in thrombosis of prosthesis]

PURPOSE

To relate our experience with thrombolytic therapy in 8 patients with cardiac metal prosthesis complicated with thrombosis.

METHODS

Eight patients with clinical and echocardiographic diagnosis of cardiac valvar prosthesis thrombosis were treated.

RESULTS

The treatment efficacy was evaluated by clinical and echocardiographic improvement. The authors recognized improvement in all 8 patients. One case of hemorrhage was observed (coxo-femoral articulation). Late death were observed twice: 24 months after, sudden death and 30 months later by hemorrhagic stroke.

CONCLUSION

The results indicated that thrombolytic therapy is best way to treat patients with cardiac valve thrombosis, instead of surgical treatment.

Plasminogen acceleration of urokinase thrombolysis

PURPOSE

A relative deficiency of plasminogen within the thrombus may be the rate limiting factor in clot lysis.

METHODS

To investigate this hypothesis, we used an in vitro perfusion system and expanded polytetrafluoroethylene graft segments filled with radiolabeled human thrombus. Three groups of five perfusions were compared: (1) urokinase infusion (333 IU/min) into clots laced with buffer, (2) urokinase infusion (333 IU/min) into clots laced with plasminogen (44 CU), and (3) control, D5W infusion into clots laced with buffer. Two end points were measured over time: the amount of lysed thrombus and the flow through the graft.

RESULTS

Urokinase infusion resulted in augmented flow through the graft when compared with control (p < 0.05). Lacing with plasminogen resulted in more rapid restoration of flow when compared with urokinase infusion alone (p < 0.05). Similarly, the rate of clot dissolution was significantly greater in plasminogen-laced thrombi (p < 0.05) when compared with the control and urokinase groups. Embolization of particles of thrombus was uniformly observed in the urokinase group, resulting in a temporary decrease in flow through the thrombosed graft. This event characteristically occurred after 60 minutes of infusion but was never seen in the urokinase/plasminogen treatment group.

CONCLUSIONS

These results suggest that plasminogen supplementation of urokinase thrombolysis may result in significant clinical benefits with respect to the rate of clot lysis and the uniformity of clot dissolution with a lower likelihood of secondary embolization.

Enhancement of the thrombolytic efficacy of prourokinase by lys-plasminogen in a dog model of arterial thrombosis

Current findings suggest that the efficacy of thrombolytic therapy may be limited by the availability of active forms of plasminogen at the thrombus site. The purpose of this study was to determine if the systemic administration of 0.5 mg kg-1 glu-plasminogen (glu-plg) or 0.5 mg kg-1 lys-plasminogen (lys-plg) could safely increase the efficacy of a single intravenous bolus injection of 50,000 U kg-1 prourokinase (proUK) in a dog model of arterial thrombosis. Thrombolysis was measured by monitoring the continuous decrement of 125I-gamma emissions from a radiolabeled thrombus. Reflow was evaluated by direct visual examination. Forty dogs (mean wt 10.3 +/- 2 kg) were randomly sorted into 4 groups of 10 each. The dogs in each group were given either saline plus saline, saline plus proUK, glu-plg plus proUK, or lys-plg plus proUK 60 minutes after formation of an occlusive arterial thrombus. Ninety minutes after drug administration the dogs receiving saline plus proUK, glu-plg plus proUK, and the lys-plg plus proUK showed greater thrombolysis (41%, 43%, and 66%, respectively) than the control (saline plus saline) group (15%, P less than 0.01). The lys-plg plus proUK treatment caused greater lysis than the saline plus proUK or the glu-plg plus proUK treatment (P less than 0.05). All of the dogs (10/10) receiving lys-plg plus proUK had patent vessels at the end of the 90 minute monitoring period, whereas only 4/10 and 5/10 vessels were patent in the saline plus proUK and glu-plg plus proUK groups, respectively. None of the dogs in the saline plus saline group had patent vessels. No significant changes were observed in the various coagulation parameters tested for any of the 4 treatment groups. The results show that lys-plg can safely increase the thrombolytic efficacy of proUK.

The beneficial effect of lys-plasminogen upon the thrombolytic efficacy of urokinase in a dog model of peripheral arterial thrombosis

The efficacy of thrombolytic therapy may be limited by local availability of plasminogen near a poorly perfused thrombus. The purpose of this study was to determine if the local (i.e., clot site) administration of 0.5 mg glu-plasminogen (glu-plg) or 0.5 mg lysplasminogen (lys-plg) could safely increase the thrombolytic efficacy of a 30-min intraarterial injection of 3,500 U kg-1 of two-chain urokinase plasminogen activator (UK) in a dog model of arterial thrombosis. Thrombolysis was measured by monitoring the continuous decrement of 125I-gamma emissions from a radiolabeled thrombus. Reflow was evaluated by a distally placed flowmeter and by direct visual examination. Forty-two dogs (mean weight 10.1 +/- 1.9 kg) were randomly sorted into six groups of 7 each. The dogs in each group were given either saline plus saline (group 1), saline plus UK (group 2), glu-plg plus saline (group 3), glu-plg plus UK (group 4), lys-plg plus saline (group 5), or lys-plg plus UK (group 6) by selective arterial catheterization 60 min after formation of an occlusive thrombus. Ninety minutes following drug administration, all groups which received UK (groups 2, 4, and 6) showed greater lysis (p less than 0.05) than the groups which received only saline or either glu- or lys-plg plus saline. Group 6, which received lys-plg plus UK, showed significantly greater lysis (34 +/- 4%) than both group 2 (23 +/- 2%), which received saline plus UK, and group 4 (19 +/- 3%), which received glu-plg plus UK (p less than 0.05). All dogs (7/7) in group 6 had reflow at 90 min whereas only 3/7 dogs had reflow in both groups 2 and 4.(ABSTRACT TRUNCATED AT 250 WORDS)

[Thrombolytic efficacy of a Lys-plasminogen-urokinase combination: studies in experimental animals and humans]

During animal experimental phase, lis-pg combined with UK produced a thrombolysis of about a 62.5%. This effect is accompanied by an important fibrinolytic system activation, a decrease in fibrinogen levels (0.37 +/- 0.2 gr/l) and an increase PDF/Fg (120.5 +/- 30 ng/ml). Such thrombolytic stage produced diverse hemorrhagic complications in experimental animals. During human clinical trial stage, then patients with Deep Venous Thrombosis (DVT) at proximal lower limbs level were submitted to diverse treatment protocols with Lis-Plasminogen (Lis-plg) and Urokinase (UK). After preliminary outcomes we can conclude that administration of Lis-plg followed by UK increases the fibrinolytic activity but also increases the risk of hemorrhagic complications. This second effect is not probably caused by an specific absorption on the thrombo surface, but by an increase of circulating plasminogen levels Lis-plg exogenous-induced.

[Systemic fibrinolysis following resuscitation or temporary electrostimulation]

Short-term systemic thrombolytic treatment with 1.5 million I.U. streptokinase or 1.8 million I.U. urokinase or APSAC was carried out in 13 patients with acute myocardial infarction (11 men, 2 women, mean age 61 [44-73] years) after cardiopulmonary resuscitation (n = 11) or transvenous electrostimulation (n = 2). In seven of the patients the infarct vessel was found to be patent after the course of thrombolytic therapy. No haemorrhagic complications occurred. Two patients died: one of a reinfarct at 3 months and the other suddenly at home at 6 months. These results show that short-term high dosage systemic thrombolytic treatment can be successfully performed in individual cases even after resuscitation or central venous catheterization, provided that any serious traumatic lesions or inadvertent arterial punctures have been avoided.

Reocclusion three months after successful thrombolytic treatment of acute myocardial infarction with anisoylated plasminogen streptokinase activating complex

Thirty consecutive patients with acute myocardial infarction (AMI) were treated with anisoylated plasminogen streptokinase activating complex (APSAC) within 4 hours after onset of symptoms. After 1.5 and 48 hours, patency of the infarct-related vessel and the quantitative degree of residual diameter stenosis were studied by selective coronary angiography. Ventriculograms were made to determine the global left ventricular ejection fraction. Patients showing patency at 48 hours were reevaluated angiographically after 3 months. At 1.5 and 48 hours after APSAC administration patent vessels were demonstrated in 65 and 69% of patients, respectively. Mean residual stenosis decreased significantly from 56 +/- 11% at 1.5 hours to 46 +/- 13% at 48 hours (p less than 0.01). Patients not responding to thrombolytic therapy showed significant deterioration of the left ventricular function during the first 48 hours after AMI. Side effects were minor and mainly associated with invasive procedures. Despite adequate oral anticoagulation, angiographically documented reocclusion at 3 months amounted to 28%. Reocclusion, however, was neither associated with clinically documented reinfarction, nor with a decrease in the left ventricular ejection fraction. Our study shows that APSAC is an effective thrombolytic agent in AMI but that late reocclusion may occur. Oral anticoagulants appear to be less effective in the prevention of reocclusion in the treatment regimen after thrombolysis.