Prourokinase mutant that induces highly effective clot lysis without interfering with hemostasis

In silico study of combination thrombolytic therapy with alteplase and mutant pro-urokinase for fibrinolysis in ischemic stroke

The synergistic advantage of combining tissue plasminogen activator (tPA) with pro-urokinase (proUK) for thrombolysis has been demonstrated in several in vitro experiments, and a single site proUK mutant (m-proUK) has been developed for better stability in plasma. Based on these studies, combination thrombolytic therapy with intravenous tPA and m-proUK has been suggested as a promising treatment for patients with ischemic stroke. This paper evaluates the efficacy and safety of the dual therapy by computational simulations of pharmacokinetics and pharmacodynamics coupled with a local fibrinolysis model. Seven dose regimens are simulated and compared with the standard intravenous tPA monotherapy. Our simulation results provide more insights into the complementary reaction mechanisms of tPA and m-proUK during clot lysis and demonstrate that the dual therapy can achieve a similar recanalization time (about 50 min) to tPA monotherapy, while keeping the circulating fibrinogen level within a normal range. Specifically, our results show that for all dual therapies with a 5 mg tPA bolus, the plasma concentration of fibrinogen remains stable at around 7.5 μM after a slow depletion over 50 min, whereas a rapid depletion of circulating fibrinogen (to 5 μM) is observed with the standard tPA therapy, indicating the potential advantage of dual therapy in reducing the risk of intracranial hemorrhage. Through simulations of varying dose combinations, it has been found that increasing tPA bolus can significantly affect fibrinogen level but only moderately improves recanalization time. Conversely, m-proUK doses and infusion duration exhibit a mild impact on fibrinogen level but significantly affect recanalization time. Therefore, future optimization of dose regimen should focus on limiting the tPA bolus while adjusting m-proUK dosage and infusion rate. Such adjustments could potentially maximize the therapeutic advantages of this combination therapy for ischemic stroke treatment.

Thrombolysis with Recombinant Human Prourokinase 4.5-6 h After Acute Ischemic Stroke: A Phase IIa, Randomized, and Open-Label Multicenter Clinical Trial

BACKGROUND

Ischemic stroke is a major cause of disability and death worldwide. A narrow therapeutic window profoundly constrained the utilization of alteplase.

OBJECTIVES

To investigate therapeutic effects and safety of intravenous recombinant human prourokinase (rhPro-UK) in patients with acute ischemic stroke (AIS) in the 4.5-6 h therapeutic time windows.

METHODS

We conducted a phase IIa, randomized, and open-label multicenter clinical trial. Between 4.5 and 6 h after the onset of AIS, patients were randomly administrated to receive intravenous rhPro-UK at a 50 mg or 35 mg dose. The primary endpoint was excellent functional outcome defined as modified Rankin scale (mRS) score of 1 or less at 90 days. The secondary outcome was the treatment response, which was based on an at least 4-point improvement from baseline National Institutes of Health stroke scale (NIHSS) score at 24 h after drug administration. Safety endpoints included death, symptomatic intracerebral hemorrhage (sICH), and other serious adverse events.

RESULTS

We enrolled 80 patients in the 4.5-6 h therapeutic time windows at 17 medical centers in China from December 2016 to November 2017. A total of 39 patients were treated with 50 mg rhPro-UK, and 39 were treated with 35 mg rhPro-UK. Compared with the baseline, the NIHSS score at 24 h and days 7, 14, 30, and 90 was decreased significantly among patients treated with either rhPro-UK 50 mg or 35 mg. The mean reduction in the NIHSS from baseline to 90 days after the onset was 3.56 and 5.79 in the rhPro-UK 50 mg group and the rhPro-UK 35 mg group, respectively. The rates of functional independence at 90 days of rhPro-UK 50 mg and 35 mg were 61.54% and 69.23%, respectively (P = 0.475), and the proportion of patients with functional response to treatment at 24 h were 28.21% and 33.33% (P = 0.624). No sICH occurred in the two groups, and death occurred in only one patient in the rhPro-UK 50 mg group. There was no significant difference in mortality at 90 days and the rate of other serious adverse events between two groups.

CONCLUSION

In the 4.5-6 h time window, more than 60% of patients at either dose of rhPro-UK (50 mg or 35 mg) achieved functional independence at 90 days without increased mortality and sICH risk. Thus, intravenous rhPro-UK was effective and safe for patients with AIS within 4.5-6 h after stroke onset. While no significant differences were identified between different dosages of rhPro-UK regarding clinical outcomes, it is a logical step to further test the safety and efficacy of the low dose of rhPro-UK in a well-powered phase III study.

TRIAL REGISTRATION

http://www.chictr.org.cn . Identifier: ChiCTR1800016519. Date of registration: 6 June 2018.

Dual thrombolytic therapy with mutant pro-urokinase and small bolus alteplase for ischemic stroke (DUMAS): study protocol for a multicenter randomized controlled phase II trial

Background

The effectiveness of alteplase for ischemic stroke treatment is limited, partly due to the occurrence of intracranial and extracranial hemorrhage. Mutant pro-urokinase (m-proUK) does not deplete fibrinogen and lyses fibrin only after induction with alteplase. Therefore, this treatment has the potential to be safer and more efficacious than treatment with alteplase alone. The aim of this study is to assess the safety and efficacy of thrombolytic treatment consisting of a small bolus alteplase followed by m-proUK compared with standard thrombolytic treatment with alteplase in patients presenting with ischemic stroke.

Methods

DUMAS is a multicenter, phase II trial with a prospective randomized open-label blinded end-point (PROBE) design, and an adaptive design for dose optimization. Patients with ischemic stroke, who meet the criteria for treatment with intravenous (IV) alteplase can be included. Patients eligible for endovascular thrombectomy are excluded. Patients are randomly assigned (1:1) to receive a bolus of IV alteplase (5mg) followed by a continuous IV infusion of m-proUK (40 mg/h during 60 min) or usual care with alteplase (0.9 mg/kg). Depending on the results of interim analyses, the dose of m-proUK may be revised to a lower dose (30 mg/h during 60 min) or a higher dose (50 mg/h during 60 min). We aim to include 200 patients with a final diagnosis of ischemic stroke. The primary outcome is any post-intervention intracranial hemorrhage (ICH) on neuroimaging at 24 h according to the Heidelberg Bleeding Classification, analyzed with binary logistic regression. Efficacy outcomes include stroke severity measured with the National Institutes of Health Stroke Scale (NIHSS) at 24 h and 5–7 days, score on the modified Rankin scale (mRS) assessed at 30 days, change (pre-treatment vs. post-treatment) in abnormal perfusion volume, and blood biomarkers of thrombolysis at 24 h. Secondary safety endpoints include symptomatic intracranial hemorrhage, death, and major extracranial hemorrhage. This trial will use a deferred consent procedure.

Discussion

When dual thrombolytic therapy with a small bolus alteplase and m-proUK shows the anticipated effect on the outcome, this will lead to a 13% absolute reduction in the occurrence of ICH in patients with ischemic stroke.

Trial registration

NL7409 (November 26, 2018)/NCT04256473 (February 5, 2020)

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06596-z.

Efficacy and Safety of Recombinant Human Prourokinase in Acute Ischemic Stroke: A Phase IIa Randomized Clinical Trial

Recombinant human prourokinase (rhPro-UK) is a novel thrombolytic that has been approved to treat patients with acute myocardial infarction. However, the safety and efficacy of intravenous rhPro-UK in patients with acute ischemic stroke (AIS) has not been well established. We aimed to investigate the safety and preliminary efficacy of rhPro-UK in patients with AIS in a multi-center phase IIa trial setting. One hundred nineteen patients within 4.5 h of AIS onset were enrolled in this randomized, open-label, 23-center phase IIa clinical trial. Patients were randomly assigned to 35 mg (n = 40) or 50 mg (n = 39) intravenous rhPro-UK or 0.9 mg/kg recombinant tissue plasminogen activator (r-tPA; n = 40). The primary endpoint was functional independence defined as a modified Rankin scale (mRS) score of 0 or 1 at 90 days. The secondary outcome was early neurological improvement defined as a reduction of ≥ 4 points on the National Institutes of Health Stroke Scale (NIHSS) score from baseline to 24 h after drug administration. Safety endpoints included death due to any cause, symptomatic intracerebral hemorrhage (sICH), and other serious adverse events (SAEs). The proportion of patients with an mRS score of ≤ 1 at 90 days did not differ significantly among three groups (35 mg rhPro-UK: 55.56% vs. 50 mg rhPro-UK: 57.89% vs. vs. r-tPA: 52.63%; P = 0.92). The rates of treatment response, referring to early neurological improvement, were similar among these three groups (36.11% vs. 31.58% vs. 28.95%, respectively; P = 0.85). There was no difference in mortality at 90 days or in the rate of other SAEs among the three groups. One patient in the 50 mg rhPro-UK group suffered sICH. While neither the primary efficacy outcomes nor safety profile differed significantly among the low, high rhPro-UK and control groups, it is a logical step to further test the low-dose rhPro-UK group versus the control group in a well-powered phase III study.Trial Registration: http://www.chictr.org.cn . Identifier: ChiCTR1800016519. Date of registration: June 6 2018.

Fibrin-specific and effective clot lysis requires both plasminogen activators and for them to be in a sequential rather than simultaneous combination

Thrombolysis with tissue plasminogen activator (tPA) has been a disappointment and has now been replaced by an endovascular procedure whenever possible. Nevertheless, thrombolysis remains the only means by which circulation in a thrombosed artery can be restored rapidly. In contrast to tPA monotherapy, endogenous fibrinolysis uses both tPA and urokinase plasminogen activator (uPA), whose native form is a proenzyme, prouPA. This combination is remarkably effective as evidenced by the fibrin degradation product, D-dimer, which is invariably present in plasma. The two activators have complementary mechanisms of plasminogen activation and are synergistic in combination. Since tPA initiates fibrinolysis when released from the vessel wall and prouPA is in the blood, they induce fibrinolysis sequentially. It was postulated that this may be more effective and fibrin-specific. The hypothesis was tested in a model of clot lysis in plasma in which a clot was first exposed to tPA for 5 min, washed and incubated with prouPA. Lysis was compared with that of clots incubated with both activators simultaneously. The sequential combination was almost twice as effective and caused less fibrinogenolysis than the simultaneous combination (p < 0.0001) despite having significantly less tPA, as a result of the wash. A mechanism is described by which this phenomenon can be explained. The findings are believed to have significant therapeutic implications.

A randomized study of prourokinase during primary percutaneous coronary intervention in acute ST-segment elevation myocardial infarction

OBJECTIVES

To evaluate the efficacy and safety of intracoronary administration of prourokinase via balloon catheter during primary percutaneous coronary interventions (PCI) in patients with acute ST-segment elevation myocardial infarction (STEMI).

METHODS

Acute STEMI patients underwent primary PCI were randomly divided into two groups: intracoronary prourokinase (IP) group (n = 118) and control group (n = 112). During primary PCI, prourokinase or saline were injected to the distal end of the culprit lesion via balloon catheter after balloon catheter dilatation. Demographic and clinical characteristics, infarct size, myocardial reperfusion, and cardiac functions were evaluated and compared between two groups. Hemorrhagic complications and MACE occurred in the 6-months follow up were recorded.

RESULTS

No significant differences were observed between two groups with respect to baseline demographic, clinical, and angiographic characteristics (P > 0.05). In IP group, more patients had complete ST segment resolution (>70%) compared with control group (P < 0.05). Patients in IP group showed lower levels of serum CK, CK-MB and TnI, and a much higher myocardial blood flow (MBF) than those in control group (P < 0.05). No significant differences of TIMI major or minor bleeding complications were observed between the two groups (P > 0.05). At 6-months follow-up, there was a trend that patients in the IP group had a less chance to have MACE, though it was not statistically different (8.5% vs 12.5%, P > 0.05).

CONCLUSIONS

Intracoronary administration of prourokinase via balloon catheter during primary PCI effectively improved myocardial perfusion in STEMI patients.

Recent advances in targeted delivery of tissue plasminogen activator for enhanced thrombolysis in ischaemic stroke

Tissue plasminogen activator (tPA) is the only FDA approved medical treatment for the ischaemic stroke. However, it associates with some inevitable limitations, including: short therapeutic window, extremely short half-life and low penetration in large clots. Systemic administration may lead to complications such as haemorrhagic conversion in the brain and relapse in the form of re-occlusion. Furthermore, ultrasound has been utilised in combination with contrast agents, echogenic liposome, microspheres or nanoparticles (NPs) carrying tPA for improving thrombolysis - an approach that has resulted in slight improvement of tPA delivery and facilitated thrombolysis. Most of these delivery systems are able to extend the circulating half-life and clot penetration of tPA. Various technologies employed for ameliorated thrombolytic therapy are in different phases, some are in final steps for clinical applications while some others are under investigations for their safety and efficacy in human cases. Here, recent progresses on the thrombolytic therapy using novel nano- and micro-systems incorporating tPA are articulated. Of these, liposomes and microspheres, polymeric NPs and magnetic nanoparticles (MNPs) are discussed. Key technologies implemented for efficient delivery of tPA and advanced thrombolytic therapy and their advantages/disadvantages are further expressed.

Thrombolysis: A Critical First-Line Therapy with an Unfulfilled Potential

A blood clot or thrombus triggers the onset of most vascular diseases, like stroke or heart attack. Thrombolysis is the only treatment that can restore blood flow rapidly and easily. Unfortunately, the standard thrombolytic, tissue plasminogen activator (tPA), has proven inadequate and is being replaced by invasive endovascular procedures, which are time consuming and limited in their availability in relation to the scope of the problem. Historically, when tPA clinical trials began, it was not recognized sufficiently that without the other natural plasminogen activator, prourokinase (proUK), thrombolysis by tPA was seriously compromised. The reason is that the 2 activators have complementary mechanisms of action in fibrinolysis, making their combination a requirement for optimal efficacy and synergy. Biological fibrinolysis also uses both activators, explaining why such low endogenous concentrations are sufficient. A low-dose sequential combination of tPA and proUK was tested in acute myocardial infarction, where it was exceptionally effective and safe. Because native proUK at pharmacological doses was vulnerable to spontaneous conversion to urokinase, jeopardizing safety, a site-directed mutant was developed that improved proUK's plasma stability fivefold without interfering with its mode of action. Mini-bolus tPA followed by low-dose proUK infusion is a simple, safe, effective, and promising first-line treatment of acute thrombotic disorders.

Highly effective fibrinolysis by a sequential synergistic combination of mini-dose tPA plus low-dose mutant proUK

Results of thrombolysis by monotherapy with either tPA or proUK have not lived up to expectations. Since these natural activators are inherently complementary, this property can be utilized to a synergistic advantage; and yet, this has undergone little evaluation. ProUK is no longer available because at pharmacological concentrations it converts to UK in plasma. Therefore, a single site proUK mutant, M5, was developed to address this problem and was used in this study. Fibrinolysis was measured using preformed fluoresceinated 24 h old clots in a plasma milieu rather than by the standard automated method, because proUK/M5 is sensitive to inactivation by thrombin and activation by plasmin. The shortest 50% clot lysis time that could be achieved by tPA or M5 alone was determined: mean times were 55 and 48 minutes respectively. These bench marks were matched by 6% of the tPA monotherapy dose combined with 40% that of M5: mean lysis time 47 minutes with less associated fibrinogenolysis. Results showed that the tPA effect was limited to initiating fibrinolysis which was completed by M5 and then tcM5. Plasma C1-inhibitor inhibited fibrinogenolysis by M5, providing protection from side effects not available for proUK. In conclusion, by utilizing the complementary properties and sequential modes of action of each activator, more efficient fibrinolysis with less non-specific effects can be achieved than with traditional monotherapy. In vivo validation is needed, but in a previous clinical trial using a similar combination of tPA and proUK (5% and 50% monotherapy doses) very promising results have already been obtained.

Mutant prourokinase with adjunctive C1-inhibitor is an effective and safer alternative to tPA in rat stroke

A single-site mutant (M5) of native urokinase plasminogen activator (prouPA) induces effective thrombolysis in dogs with venous or arterial thrombosis with a reduction in bleeding complications compared to tPA. This effect, related to inhibition of two-chain M5 (tcM5) by plasma C1-inhibitor (C1I), thereby preventing non-specific plasmin generation, was augmented by the addition of exogenous C1I to plasma in vitro. In the present study, tPA, M5 or placebo +/- C1I were administered in two rat stroke models. In Part-I, permanent MCA occlusion was used to evaluate intracranial hemorrhage (ICH) by the thrombolytic regimens. In Part II, thromboembolic occlusion was used with thrombolysis administered 2 h later. Infarct and edema volumes, and ICH were determined at 24 h, and neuroscore pre (2 h) and post (24 h) treatment. In Part I, fatal ICH occurred in 57% of tPA and 75% of M5 rats. Adjunctive C1I reduced this to 25% and 17% respectively. Similarly, semiquantitation of ICH by neuropathological examination showed significantly less ICH in rats given adjunctive C1I compared with tPA or M5 alone. In Part-II, tPA, M5, and M5+C1I induced comparable ischemic volume reductions (>55%) compared with the saline or C1I controls, indicating the three treatments had a similar fibrinolytic effect. ICH was seen in 40% of tPA and 50% of M5 rats, with 1 death in the latter. Only 17% of the M5+C1I rats showed ICH, and the bleeding score in this group was significantly less than that in either the tPA or M5 group. The M5+C1I group had the best Benefit Index, calculated by dividing percent brain salvaged by the ICH visual score in each group. In conclusion, adjunctive C1I inhibited bleeding by M5, induced significant neuroscore improvement and had the best Benefit Index. The C1I did not compromise fibrinolysis by M5 in contrast with tPA, consistent with previous in vitro findings.

C1-inhibitor prevents non-specific plasminogen activation by a prourokinase mutant without impeding fibrin-specific fibrinolysis

BACKGROUND

Prourokinase (prouPA) is unstable in plasma at therapeutic concentrations. A mutant form, M5, made more stable by reducing its intrinsic activity was therefore developed. Activation to two-chain M5 (tcM5) induced a higher catalytic activity than two-chain urokinase plasminogen activator (tcuPA), implicating an active site functional difference. Consistent with this, an unusual tcM5 complex with plasma C1-inhibitor was recently described in dog and human plasma. The effect of C1-inhibitor on fibrinolysis and fibrinogenolysis by M5 is the subject of this study.

METHODS AND RESULTS

Zymograms of tcM5 and tcuPA incubated in plasma revealed prominent tcM5-C1-inhibitor complexes, which formed within 5 min. The inhibition rate by purified human C1-inhibitor (250 microg mL(-1)) was about 7-fold faster for tcM5 than it was for tcuPA (10 microg mL(-1)). The effect of the inhibitor on the stability of M5 and prouPA was determined by incubating them in plasma at high concentrations (10-20 microg mL(-1)) +/- C1-inhibitor supplementation. Above 10 microg mL(-1), depletion of all plasma plasminogen occurred, indicating plasmin generation and tcM5/tcuPA formation. With supplemental C1-inhibitor, M5 stability was restored but not prouPA stability. Clot lysis by M5 +/- supplemental C1-inhibitor showed no attenuation of the rate of fibrinolysis, whereas fibrinogenolysis was prevented by C1-inhibitor. Moreover, because of higher dose-tolerance, the rate of fibrin-specific lysis reached that achievable by non-specific fibrinolysis without inhibitor.

CONCLUSIONS

Plasma C1-inhibitor stabilized M5 in its proenzyme configuration in plasma by inhibiting tcM5 and thereby non-specific plasminogen activation. At the same time, fibrin-specific plasminogen activation remained unimpaired. This unusual dissociation of effects has significant implications for improving the safety and efficacy of fibrinolysis.

Thrombolysis vs. bleeding from hemostatic sites by a prourokinase mutant compared with tissue plasminogen activator

BACKGROUND

A single site mutant (M5) of prourokinase (proUK) was developed to make proUK less vulnerable to spontaneous activation in plasma. This was a problem that seriously compromised proUK in clinical trials, as it precluded proUK-mediated fibrinolysis at therapeutic concentrations.

METHODS AND RESULTS

After completing dose-finding studies, 12 anesthetized dogs with femoral artery thrombosis were given either M5 (2.0 mg kg(-1)) or tissue plasminogen activator (t-PA) (1.4 mg kg(-1)) by i.v. infusion over 60 min (20% administered as a bolus). Two pairs of standardized injuries were inflicted at which hemostasis was completed prior to drug administration. Blood loss was quantified by measuring the hemoglobin in blood absorbed from these sites. Thrombolysis was evaluated at 90 min and was comparably effective by both activators. Rethrombosis developed in one t-PA dog. The principal difference found was that blood loss was 10-fold higher with t-PA (mean approximately 40 mL) than with M5 (mean approximately 4 mL) (P = 0.026) and occurred at more multiple sites (mean 2.7 vs. 1.2). This effect was postulated to be related to differences in the mechanism of plasminogen activation by t-PA and M5 in which the latter is promoted by degraded rather than intact (hemostatic) fibrin. In addition, two-chain M5 was efficiently inactivated by plasma C1 inactivator, an exceptional property which helped contain its non-specific proteolytic effect.

CONCLUSIONS

Intravascular thrombolysis by M5 was accompanied by significantly less bleeding from hemostatic sites than by t-PA. This was attributed to the proUK paradigm of fibrinolysis being retained at therapeutic concentrations by the mutation.

Soluble expression of a strong thrombolytic pro-urokinase mutant in Escherichia coli

A recombinant pro-urokinase mutant GZ5-sPA was successfully constructed by fusion of a high fibrin-affinity fragment GZ5 to the N-terminus of the serine protease domain of pro-urokinase (sPA). The fragment GZ5 contains a tetrapeptide GPRP and a tripeptide RGD, and was synthesized in bacterial preferred expressing codons. The mutant was then fused to the C-terminus of maltose binding protein (MBP) carried by pMAL-C2x vector, and expressed in Escherichia coli strain Origami (DE3). The produced fusion protein was highly soluble in the cytoplasm of the bacteria. After being cleaved with PreScission Protease to remove MBP tag, GZ5-sPA showed a molecular weight of 31 kDa on SDS-PAGE. GZ5-sPA maintained the same epitope as wild-type pro-urokinase and possessed a thrombolytic activity three times higher than standard urokinase did after being activated as two-chain form. The results could be a clue to other complicated heterogenous proteins similar to pro-urokinase.