Fibrin targeting of tissue plasminogen activator-loaded echogenic liposomes

Abstract

We recently reported entrapment of tissue-plasminogen activator (tPA) into echogenic liposomes (ELIP) with retention of echogenicity and thrombolytic effect. Integral to the potential of this agent for ultrasound-detectable local drug delivery is the specific binding of tPA-ELIP to clots. tPA contains fibrin-binding sites; we hypothesized that tPA when associated with ELIP, will maintain fibrin binding properties, rendering further manipulation for targeting of the tPA-ELIP unnecessary. We demonstrated strong fibrin binding of the ELIP-associated tPA. Fibrin binding for ELIP-associated tPA was twice that of free tPA. This strong affinity for fibrin was confirmed using echogenicity analysis of porcine clots in vitro. Both objective (mean gray scale analysis) and subjective (visual estimation by two experienced echocardiographers) evaluation of the clots showed enhanced highlighting of clots treated with tPA-ELIP when compared to control. The findings in this study represent new approaches for fibrin-targeted, ultrasound-directed and enhanced local delivery of a thrombolytic agent.

Targeted Molecular Imaging to Detect Vascular Disease

“…Recently, our laboratory has utilized the intrinsic fibrin-binding capacity of tissue plasminogen activator in the preparation of a dual function ELIP formulation that effectively targeted thrombus in vivo as well as facilitated ultrasound-enhanced thrombolysis in vivo [60,61]. The delivery of large amounts of acoustically active agents at the site of thrombus may provide added opportunities for mechanical disruption of thrombus by ultrasound and chemical clot lysis by high local concentration of thrombolytics.…”

Thrombin-Activatable Microbubbles as Potential Ultrasound Contrast Agents for the Detection of Acute Thrombosis

“…25 We are using the enzymatic activity of thrombin as the trigger to activate our contrast agent for molecular-based US recognition of active thrombosis. Our approach holds the advantage of binding specifically to active thrombus compared to other US contrast agents that target individual components of thrombi 26 such as platelets 27–29 or fibrin 30–32 and are not specific to active thrombosis.…”

Nanotechnology Development and Utilization: A Primer for Diagnostic and Interventional Radiologists

“…For instance, nanoparticles that contain streptokinase and that are targeted to fibrin have been described as yielding the same degree of thrombolysis as a 1000-fold-greater dose of free enzyme (37). Liposomes both with and without encapsulated thrombolytics have been used for clot lysis in applying US energy to rupture the liposomes and disrupt the clot (38,39).…”