A triple fusion tissue-type plasminogen activator (TriF-ΔtPA) enhanced thrombolysis in carotid embolism-induced stroke model

Recombinant tissue-type plasminogen activator (rtPA, or Alteplase) is the first approved thrombolytic drug for acute ischemic stroke, but suffers from a short half-life and poor resistance to plasminogen activator inhibitor (PAI-1), limiting its clinical use. The development of novel thrombolytic agents with improved benefit/risk balance has always been of great significance. In this study, we identified a mutant of serine protease domain of tPA (named ΔtPAA146V) capable of escaping the inhibition by endogenous PAI-1 with 66-fold increased resistance compared to the wild type tPA. Based on this mutant, we generated a triple fusion ΔtPA (TriF-ΔtPA) containing albumin and fibrin binding peptide(FBP). The fusion with albumin effectively prolonged the plasma half-life of ΔtPA in mice to 144 min, which is much longer than ΔtPA and did not affect its thrombolytic activity. Furthermore, FBP rendered fibrin specificity of the fusion protein, giving a dissociation constant of ∼ 25 ± 0.9 μM. In a novel murine carotid embolism-induced stroke (CES) model, i.v. administration of TriF-ΔtPA promoted vascular recanalization, reduced infarct volume, and mitigated neurobehavioral deficits more significantly compared to ΔtPA-HSA or Alteplase, showing little bleeding risk. Together, this long-acting PAI-1-resistant thrombolytic agent holds great potential for clinical applications.