Ultrasound-enhanced drug delivery in a perfused ex vivo artery model

Acoustically driven stable cavitation may improve treatments of diseases in which passive penetration of drug into the target tissue is poor. Examples include atherosclerosis, in which the endothelium can prevent penetration of therapeutics into the plaque, and ischemic stroke, in which pathologically low flow of blood impedes the delivery of intravenous drugs to the clot. Understanding the way in which ultrasound cavitation agents nucleate cavitation in flowing blood-mimicking solutions is an important step in optimizing ultrasound-enhanced drug delivery. The use of a perfused, living ex vivo artery model permitted study of this phenomenon while still providing information on arterial bioeffects. Cavitation-enhanced delivery of anti-ICAM-1-targeted echogenic liposomes into and beyond the ex vivo murine aortic endothelium was demonstrated using 1-MHz continuous wave ultrasound. Acoustic cavitation had no apparent effect on the health of the murine arterial tissue. A method of maximizing the energy of stable cavitation through the use of intermittent 120-kHz ultrasound with quiescent periods to allow contrast agent inflow was developed. Using this insonificaiton method, sonothrombolysis was studied in ex vivo porcine carotid arteries using a 120-kHz center frequency and 0.44 MPa peak-to-peak pressure amplitude. Clot mass loss was used as a metric of thrombolytic efficacy. Clots exposed to recombinant tissue plasminogen activator and the ultrasound contrast agent, DefinityRTM in flowing porcine plasma without ultrasound experienced 34% mass loss. When robust stable cavitation was induced via 120-kHz insonation, the mean clot mass loss rose to 83%, which constituted a significant improvement (n = 6, p<0.0001). Without DefinityRTM there was no thrombolytic enhancement by ultrasound exposure alone at the same insonation pressure (n = 6, p<0.0001). Significant loss of endothelium occurred in 64% of the porcine carotid arteries, possibly due to poor oxygen delivery by the low flow of plasma. However, no correlation was observed between arterial tissue damage and treatment type. In this perfused ex vivo artery model, acoustic stable cavitation was shown to enhance both the delivery of endothelium-targeted therapeutics into the arterial wall and the lysis of whole blood clots in the presence of rt-PA.