Intravascular Application of Magnetic Nanoparticle for Target Thrombolysis (I)

Thrombolytic drugs, such as recombinant tissue plasminogen activator (rtPA), tend to dissolve both pathological thrombi and fibrin deposit at sites of vascular injury, resulting in hemorrhagic toxicity at therapeutic doses. We plan to resolve this problem by magnetic drug targeting using magnetic nanoparticles (MNP) as drug carriers. Polymer coating of Fe3O4 (magnetite) MNP provide water stability and functional groups for binding/adsorbing drugs; limited literature suggested that these MNP, despite of different polymer coatings, are well tolerated in the biology system. With the force from an extracorporeal magnetic field, it is anticipated that the rtPA bound to or encapsulated in MNP will be concentrated against blood stream at the site of thrombi, leading to an increase in the efficacy of drug effect and a minimized hemorrhagic side effect. Magnet may capture the MNP-rtPA in circulation, guide and concentrate the drug to the nearby of the clot, and even facilitate entering of MNP-rtPA into the clot. In a preliminary experiment, we have demonstrated the feasibility and efficacy of target thrombolysis with rtPA covalently bound to polyacrylic acid-coated magnetite (PAA-MNP) and retained to the target site in vivo by an external magnet. This approach may achieve reproducible and effective target thrombolysis with ＜20% of a regular dose of rtPA. However, in these experiments, we also demonstrated that how the MNP-rtPA was guided may eventually determine its in vivo efficacy. In the proposed study, we will test the following hypothesis: the suspension status of magnetically guided MNP-rtPA in blood vessel was crucial for its therapeutic efficacy. Strategies will be tested to facilitate MNP-rtPA suspension under magnetic field by improving the physical characteristics of MNP, moving a permanent magnet upstream and downstream of the clot, alternatively turning on-and-off between two magnets, using a stationary magnetic field with ultrasound etc. Acoustic energy of ultrasound may facilitate suspension of MNP-rtPA, lysis of the clot and release of rtPA from an encapsulated formula. These strategies will be tested with mathematical modeling, computer simulation and in vitro simulation prior to be realized in a rat iliac thromboembolic model and a rat stroke model. In addition to ischemic stroke, information we plan to acquire in the proposed study may also facilitate application of magnetic targeting in treatment of coronary embolism, restenosis after balloon injury, and angiogenesis/ tumor growth etc. Experiments are designed: Aim 1- To develop and prepare MNP-rtPA based on bindings and entrapment and determine their toxicity and in vitro thrombolysis efficacy. (Chen) Aim 2- To determine efficacy of MNP-rtPA-induced thrombolysis in the rat iliac embolic model and optimize strategy of magnet application. (Ma/Tu) Aim 3- To design a novel ultrasound-assisted magnet-guided system for improving MNP-rtPA suspension and its therapeutic effect. (Liu/Ma) Aim 4- To determine the efficacy of targeted thrombolysis in a rat cerebral embolic model. (Wu)

Project ID:PD9807-0445
External Project ID:NSC98-2120-M182-001