Fibrin-targeted thrombolytic therapy using acoustically reflective perfluorocarbon nanoparticles

Thrombolytic agents, i.e. "clot-busters" such as tPA, have been shown to be effective therapeutics for acute ischemic stroke. However, systemic administration of such powerful agents may be complicated by increased risk of cerebral hemorrhage and expanding stroke. Targeting of clot-dissolving therapeutics has the potential to decrease the incidence of these complications while simultaneously increasing effectiveness of treatment, by concentrating the available drug at the desired site and permitting a lower overall systemic dose. We have previously demonstrated targeting of liquid perfluorocarbon nanoparticles to thrombi in vitro and in vivo, with concomitant enhancement of acoustic reflectivity from the targeted clot surfaces. In the current study, a traditional thrombolytic enzyme (streptokinase) was incorporated into fibrin-targeted nanoparticles and targeted to plasma clots in vitro to demonstrate use of the nanoparticles as both an acoustic contrast agent and an adjunctive targeted therapeutic delivery system. Human plasma clot samples targeted with streptokinase-loaded liquid perfluorocarbon nanoparticles and immersed in plasminogen/saline solution exhibited 7% loss of volume after 3 hrs exposure, as well as marked time-dependent variation in surface topography and acoustic reflectivity. Control samples exposed to either 1) targeted, streptokinase-loaded nanoparticles in the presence of saline only, or 2) targeted nanoparticles without streptokinase in the presence of plasminogen/saline solution exhibited no significant changes over time. These results suggest the potential utility of targeted nanoparticles for combined diagnosis and treatment of thrombus-initiated ischemic stroke.