Efficacy and Safety of an Early Phase Single Bolus r-SAK for Acute Myocardial Infarction: a Multi-center Randomized Clinical Trial (OPTIMA-5)

Acute myocardial infarction (AMI) is one of the leading causes of death all over the world. Even if patients with AMI survive the acute period without death, some ones would inevitably develop into chronic heart failure due to myocardial ischemia caused by segmental ventricular wall dyskinesia, myocardial remodeling, etc., which would seriously affect the prognosis of these patients. Early intensive treatment is the decisive factor to reduce the death of patients with AMI. However, the primary hospitals where patients firstly visit do not have the ability of Primary Percutaneous Transluminal Coronary Intervention (PCI) the guidelines recommend. They have to transport patients to a center that has the conditions for emergency interventional treatment. But this transportation will delay a lot of time, resulting in the extension of MI area. More importantly, the thrombus load in coronary arteries would increase with time, and the implantation of stents in vessels with a large thrombus load will often lead to slow flow or no flow, which is a relative contraindication for interventional therapy.

At present, the guidelines recommend loading dose antiplatelet therapy and transport to the superior hospital for prime PCI within 2 hours if the first hospital for acute myocardial infarction does not have the conditions for emergency interventional therapy. Current guidelines recommend that thrombolytic therapy should be performed first and then transported when delivery is expected to be >2 hours to a hospital where PCI can be performed. And thrombolytic therapy is not recommended for patients who can perform PCI within <2 hours. There is a lack of clinical evidence for thrombolysis within 2 hours of first medical contact to Primary PCI. Compared with Primary PCI, early thrombolytic therapy can undoubtedly shorten the implementation time of reperfusion strategy to the maximum. For highly effective thrombolytic drugs, reperfusion time should be shortened, thrombus load should be reduced, and the size of myocardial infarction may be reduced and the prognosis of patients improved. There is a lack of clinical evidence for this. China is a developing country, whose grassroots and rural health resources are still poor. Early thrombolysis treatment plus subsequent reperfusion of interventional therapy not only conform to the Chinese characteristic, but also accord with the international research and the development direction in this field, which is worth further study.

Staphylokinase (SAK) is produced by Staphylococcus aureus and it is a protein containing 136 amino acid residues. Its ability for dissolving blood clots was first discovered in 1948. Studies have shown that SAK is not directly convert plasminogen (PLG) into plasminogen (PLi), but first combines with PLG in a 1:1 ratio to form a complex. The complex can lead to the exposure of PLG active site, from single chain to double chain PLi, resulting to form an active SAK-PLI complex, which subsequently activates PLG molecules. Then PLG transforms into PLi and further dissolve the thrombus.

Recombinant SAK (r-SAK) was developed in 1990 by Shanghai Institute of Plant and Biological Physiology. It is a gene recombinant drug prepared by molecular cloning of SAK gene in Escherichia coli. Its biological characteristics are very similar to natural SAK, and r-SAK is a highly fibrin-specific fibrinolysis agent. R-SAK is considered to be one of the most promising thrombolytic drugs due to its high thrombolysis activity (especially in platelet-rich arterial thrombosis), inactivation of system fibrinolysis, and few side effects. Clinical studies have shown that the efficacy of r-SAK in the treatment of AMI is better than urokinase, comparable to RT-PA, and it does not increase serious bleeding complications such as intracranial hemorrhage.

In terms of pharmacokinetics, r-SAK has a fast distribution and a long action time in human body. Half-lives of distribution term is 13.30±2.06min and elimination term is 67.94±21.39min when intravenous injection 10 mg r-SAK in 30min. A single bolus of r-SAK as early as possible during the first medical contact (such as prehospital care or primary hospitals or medical centers with conditional PCI) can maximize the time window for reperfusion therapy. R-SAK, a highly effective thrombolytic drug, may shorten the reperfusion time, reduce the size of myocardial infarction and improve the prognosis of the AMI patients.