Abstract TP350: Extension of tPA Treatment Window With Granulocyte-colony Stimulating Factor in a Thromboembolic Rat Model of Stroke

Background: When given beyond 4.5 hours of stroke onset, tissue plasminogen activator (tPA) produces deleterious side effects in the ischemic brain, notably, hemorrhagic transformation (HT). Extending the narrow time window of tPA will benefit a significant number of stroke patients. We previously showed that granulocyte-colony stimulating factor (G-CSF) attenuated delayed tPA (6 h post stroke)-induced HT in rats subjected to stroke via intraluminal filament occlusion of the middle cerebral artery. Here, we examined whether the drug reduces delayed tPA induced-HT, cerebral infarction and neurological deficits in rats subjected to a thromboembolic (TE) stroke, and whether efficacy of G-CSF treatment extends at longer periods of recovery. Stroke Therapy Academic Industry Roundtable (STAIR) guidelines indicate necessity of testing effects of a drug candidate in multiple ischemia models before it progresses to clinical development. Methods and Results: After stroke induction through the TE method, rats were given intravenous saline (control), tPA (10 mg/kg), or G-CSF (300 μg/kg) and tPA at 6 h post-stroke. Treatment with G-CSF decreased delayed tPA-associated HT in stroked rats as measured by the spectrophotometric hemoglobin assay. Reduction in HT was accompanied by a decrease in infarct volume and improvement in stroke-induced motor and neurological deficits at 7 days after stroke. Moreover, G-CSF treatment also reduced the mortality rate due to delayed tPA therapy by almost 50%. Flow cytometry showed significant increase in the population of CD34+/VEGFR2+ bone marrow stem cells in the blood of stroked rats subjected to the combination treatment compared with rats given saline alone or tPA. Double labeling of CD34+ and VEGFR2 revealed enrichment of CD34+/VEGFR2 expression in the ischemic cortex and striatum of rats subjected to G-CSF treatment, indicating involvement of endothelial progenitor cells in the therapeutic effects of G-CSF. Conclusion: These results further corroborate efficacy of G-CSF to reduce delayed tPA-induced HT and neurological deficits in experimental stroke models, and suggest potentiality of the drug to extend the therapeutic time window of tPA therapy for stroke.