Fibrin degradation by rtPA enhances the delivery of nanotherapeutics to A549 tumors in nude mice

Effective drug delivery to a tumor depends on favorable blood perfusion within the tumor. As an important component of tumor extracellular matrix, fibrin is abundant near tumor vessels. Inspired by the distinct distribution pattern and vessel-dependent production of fibrin, we hypothesized that fibrin depletion in tumors decompresses tumor vessels to improve tumor blood perfusion and accordingly enhance drug delivery to tumors rich in vessels. In the present study, we attempted to employ a clinically used thrombolytic drug, recombinant tissue plasminogen activator (rtPA), to modulate fibrin deposition in tumors. We then combined this drug with a nanoparticle drug delivery system for tumor therapy. RtPA treatment (25 mg/kg/d i. p. administration for two weeks) successfully depleted fibrin deposition and enhanced blood perfusion within A549 tumor xenografts. Furthermore, rtPA treatment also improved the in vivo delivery of 115-nm nanoparticles to tumor tissues. Finally, rtPA combined with therapeutic agent-loaded nanoparticles resulted in the most effective shrinkage of A549 tumor xenografts compared with the control groups. Overall, the present study provides a new strategy to enhance the delivery of nanotherapeutics to tumors rich in vessels.