F. Tranquart 1, B. Petit 1,2, E. Bihel 1, Y. Bohren 1, F. Yan 1, E. Allemann 2, M. Arditi 1, J. M. Hyvelin 1
1 BRACCO SUISSE SA – Plan Les Ouates, Switzerland, 
2 School of Pharmaceutical Sciences, University of Geneva, University of Lausanne – Geneva, Switzerland

Rapid restoration of vascular flow is the primary goal of acute stroke treatment, while improvement in patient’s outcome is the ultimate benefit of such treatments. Among different treatment schemes, sonothrombolysis has been used in in vitro tests, in preclinical trials and to a lesser extent in clinical trials, even though the exact underlying mechanism has not been fully clarified.

From a regulatory standpoint, any new therapeutic treatment must be proven safe before it can be widely used, especially in critical health conditions. In that objective, we have investigated in details some specific aspects of sonothrombolysis, such as the kinetics of the clot lysis in vitro.
In contrast to many authors who have used clot weight changes to characterize the effects of insonation, we have used a visual assessment with a camera allowing continuous monitoring over the treatment time. This allowed us to get more reproducible values and important information related to the rate of lysis, which can help in characterizing the effects of different pulsing sequences at various acoustic pressures. More specifically, we have studied the respective roles of fibrinolysis and haemolysis in the observed clot lysis. In essence, our results indicate an absence of fibrinolysis at acoustic pressure levels up to 1.3 MPa per se but a pure haemolysis in the absence of rtPA. Conversely, at this acoustic pressure level, the presence of 3 μg/ml rtPA led to a significant fibrinolysis when combined with US and microbubbles. These results will be further detailed with a translation in vivo to confirm the validity of the proposed approach of using moderate and acceptable US acoustic pressure levels in a clinical setting. Even though sonothrombolysis has been studied for more than 10 years, some key points remained unexplained, leading to a long delay in getting an approval for this treatment.

Key words: fibrinolysis, haemolysis, in vitro, sonothrombolysis.