Thrombolytic efficacy of echogenic liposomes that co-encapsulate rt-PA and octafluoropropane gas

Abstract

Echogenic liposomes loaded with recombinant tissue-type plasminogen activator, rt-PA (tELIP), are under development for treatment of thrombo-occlusive disease. However, tELIP filled with air nucleate low stable cavitation activity when exposed to 120-kHz ultrasound, which limits the thrombolytic efficacy. We hypothesize that encapsulating octafluoropropane (OFP) gas in ELIP (OFP-tELIP) will enhance ultrasound-mediated stable cavitation activity and thrombolytic efficacy. A spectrophotometric method was used to assess the enzymatic activity of the rt-PA associated with OFP-tELIP. An in vitro flow model equipped with a time-lapse microscopy system was employed to observe human whole blood clots exposed to fresh-frozen plasma, rt-PA (0, 0.32, 1.58, and 3.15 μg/mL), and OFP-tELIP with and without ultrasound (120 kHz, 0.44 MPa peak-to-peak pressure). Ultraharmonic emissions indicating stable cavitation were measured using a passive cavitation detector. Sustained ultraharmonic activity was nucleated from OFP-tELIP when exposed to ultrasound, resulting in enhanced thrombolytic efficacy at an rt-PA concentration of 1.58 μg/mL. The results of this study demonstrate the advantages of encapsulating OFP within tELIP for use as a sonothrombolysis agent.