During ischemic stroke, diminished blood supply initiates a series of events (called ischemic cascade) that results in damage to brain tissue and eventually death of brain tissue. Brain-tissue death occurs in areas of no blood flow within minutes of stroke onset. Around such areas, there could be regions of reversible injured tissue, called the ischemic penumbra. The ischemic penumbra will finally die if no change in blood supply occurs, and hence saving the penumbra is the goal of all acute stroke therapies.
To date, intravenous tissue plasminogen activator (IV t-PA) is the only approved treatment for acute ischemic stroke. It is focused on reperfusion, i.e. aiming to restore artery patency and brain perfusion in order to reduce the volume of cerebral infarction which thereby reduces functional deficits. However, there is a high risk in reperfusion after several hours have passed from stroke onset, as the chances of inducing a cerebral hemorrhage dramatically increase. As a result, the use of this treatment is limited to 3-4.5 hours from stroke onset. In the US, only about 4% of ischemic stroke patients are treated with IV t-PA.
Neurothrombectomy is another treatment modality which was approved for extracting blood clots. It is approved in the US to be used in a time window of 8 hours from stroke onset, and requires the availbility of an experienced invasive neurologist. The efficacy of neurothrombectomy for acute ischemic stroke patients is currently being tested after previous studies failed to demonstrate a clinical effect.
An unmet need exists for developing additional therapies for the treatment of acute ischemic stroke at a wider therapeutic window as well as for an improvement in outcome during the rehabilitation phase.
For more information about stroke see the Heart Disease and Stroke Statistics, 2009 update by the American Heart Associateion