Monteplase reduces infarct volume and hemorrhagic transformation in rat model of embolic stroke

The evolution of recombinant thrombolytics: Current status and future directions

Cardiovascular disorders are on the rise worldwide due to alcohol abuse, obesity, hypertension, raised blood lipids, diabetes and age-related risks. The use of classical antiplatelet and anticoagulant therapies combined with surgical intervention helped to clear blood clots during the inceptive years. However, the discovery of streptokinase and urokinase ushered the way of using these enzymes as thrombolytic agents to degrade the fibrin network with an issue of systemic hemorrhage. The development of second generation plasminogen activators like anistreplase and tissue plasminogen activator partially controlled this problem. The third generation molecules, majorly t-PA variants, showed desirable properties of improved stability, safety and efficacy with enhanced fibrin specificity. Plasmin variants are produced as direct fibrinolytic agents as a futuristic approach with targeted delivery of these drugs using liposome technlogy. The novel molecules from microbial, plant and animal origin present the future of direct thrombolytics due to their safety and ease of administration.

The novel antioxidant edaravone: from bench to bedside

Over the last decade, important advances have been made to support the fact that reactive oxygen species (ROS) are generated and play a harmful role during the acute and late stages of cerebral ischemia. Several drugs, such as radical scavengers and antioxidants, have been evaluated in preclinical and clinical studies. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one; Radicut, Mitsubishi Tanabe Pharma Corporation) is a novel antioxidant that is currently used in Japan for the treatment of patients in the acute stage of cerebral infarction. Edaravone scavenges ROS and inhibits proinflammatory responses after brain ischemia in animals and humans. In particular, postischemic inflammation, leading to brain edema and infarction due to neuronal damage and endothelial cell death, can be ameliorated by edaravone. In addition to these antistroke effects, edaravone has also been shown to prevent oxidative damage to various extracerebral organs. Therefore, in addition to its usefulness in the treatment of stroke, edaravone is expected to play an integral role in the treatment of many oxidative stress-related diseases.

FK-506 extended the therapeutic time window for thrombolysis without increasing the risk of hemorrhagic transformation in an embolic rat stroke model

FK-506 confers a neuroprotective effect and is thought to extend the time window for thrombolytic treatment of cerebral ischemia. These effects have not been assessed in an embolic stroke model. In addition, clinical studies have raised concern that FK-506 may increase the risk of hemorrhagic transformation by damaging vascular endothelial cells. We investigated whether combined administration of recombinant tissue plasminogen activator (rt-PA) and FK-506 would extend the therapeutic time window without increasing the hemorrhagic transformation in a rat embolic stroke model. Male Sprague-Dawley rats (n=66) were subjected to embolic infarction and assigned into eight groups. Six of the groups were treated with or without FK-506 (0.3 mg/kg) administration at 60 min after embolization, together with and all six groups received systemic rt-PA administration (10 mg/kg) at 60, 90, or 120 min. Two permanent ischemia groups were administered saline either with or without FK-506. Infarct and hemorrhagic volume were assessed at 24 h after embolization. Diffusion-weighted and perfusion-weighted magnetic resonance imaging (MRI) were performed in the groups administered rt-PA at 90 min and a vehicle control group to assess whether FK-506 influenced the effectiveness of MRI in revealing ischemic lesion. FK-506 extended the therapeutic time window for systemic thrombolysis compared to rt-PA alone without increasing the risk for hemorrhage. Combined therapy with FK-506 salvaged some of the MRI, revealing ischemic lesions destined to infarction in the animals treated by rt-PA alone. Single low dose of FK-506 alone did not ameliorate the embolic infarction, but it did prove effective in extending the therapeutic time windows for thrombolysis without increasing the risk of hemorrhagic transformation.

Advances in ischemic stroke treatment: neuroprotective and combination therapies

Thrombolysis with intravenous alteplase (recombinant tissue-type plasminogen activator) continues to be the sole recourse for acute ischemic stroke therapy, provided that patients seek treatment preferably within 3 h of stroke onset. The narrow window of efficacy, coupled with the significant risk of hemorrhage and the high mortality rate, preclude the use of alteplase beyond this time frame. Moreover, in part because of safety concerns, only a small percentage (6-15%) of eligible patients is treated with alteplase. Clearly, safer and more effective treatments that focus on improving the shortcomings of the present thrombolysis for stroke need to be identified. Therefore, newer thrombolytics are being developed with the goal of minimizing side effects, while also shortening the time of cerebral reperfusion and extending the therapeutic window of efficacy. Besides thrombolytics, new and potentially useful drugs and devices are also being studied either as monotherapeutic agents or for use in conjunction with alteplase. In animal models of stroke, neuroprotective agents that affect various components of the ischemic injury cascade that results in neurodegeneration have shown promise for the latter. Examples of such agents include spin traps that block oxidative stress, metalloprotease inhibitors that prevent vascular damage, anti-inflammatory drugs that suppress inflammation and transcranial infrared laser irradiation, which promotes recovery of function. Ideally, a successful combination of neuroprotectant (drug or device) and thrombolytic therapy for stroke would minimize the side effects of thrombolysis followed by supplementary neuroprotection thereafter.

Development of thrombolytic therapy for stroke: a perspective

Thrombolysis with tissue plasminogen activator (alteplase, Activase trade mark, rtPA; Genentech Inc) has proven beneficial for acute stroke management, even though only 1 - 2% of stroke patients in the US are treated with the drug [1]. Part of the reason for the under utilisation of alteplase may be the narrow therapeutic window and frequent occurrence of serious side effects, such as increased haemorrhage incidence [2,3]. It is because of these shortcomings, that recent efforts have attempted to identify new thrombolytics that might improve the benefit/risk ratio in treating stroke. Second generation derivatives of alteplase have attempted to counteract the side effects of the drug by increasing fibrin specificity (tenecteplase, TNK-tPA; Genentech Inc) or half-life (lanoteplase, SUN-9216; Genetics Institute Inc.). New recombinant DNA methodology has led to the revival of plasmin or a truncated form of plasmin (microplasmin; ThromboGenics Ltd), a direct-acting thrombolytic with non-thrombolytic related neuroprotective activities, as a therapeutic. Other promising approaches for the treatment of stroke include the development of novel plasminogen activators, such as recombinant desmodus rotundus salivary plasminogen activator (rDSPA) alpha-1 (Schering/Teijin Pharmaceuticals) and a mutant fibrin-activated human plasminogen (BB10153; British Biotech Inc.). These important areas of drug discovery and development will be reviewed.