Plasminogen activator-coated nanobubbles targeting cell-bound β2-glycoprotein I as a novel thrombus-specific thrombolytic strategy

Beta2-glycoprotein I (β2-GPI) is a serum protein widely recognized as the main target of antibodies present in patients with anti-phospholipid syndrome (APS). β2-GPI binds to activated endothelial cells, platelets and leukocytes, key players in thrombus formation. We developed a new targeted thrombolytic agent consisting of nanobubbles (NBs) coated with recombinant tissue plasminogen activator (rtPA) and recombinant antibody specific for cell-bound β2-GPI. The therapeutic efficacy of targeted nanobubbles was evaluated in vitro, using platelet-rich blood clots, and in vivo in three different animal models: 1) thrombosis developed in a rat model of APS; 2) ferric chloride-induced mesenteric thrombosis in rats, and 3) thrombotic microangiopathy in a mouse model of atypical hemolytic uremic syndrome (C3-gain-of-function mice). Targeted nanobubbles bound preferentially to platelets and leukocytes within thrombi and to endothelial cells through β2-GPI expressed on activated cells. In vitro, rtPA-targeted NBs (rtPA-tNBs) induced greater lysis of platelet-rich blood clots than untargeted NBs. In a rat model of APS, administration of rtPA-tNBs caused rapid dissolution of thrombi and, unlike soluble rtPA that induced transient thrombolysis, prevented new thrombus formation. In a rat model of ferric chloride triggered thrombosis, rtPA-tNBs, but not untargeted NBs and free rtPA, induced rapid and persistent recanalization of occluded vessels. Finally, treatment of C3-gain-of-function mice with rtPA-tNBs, that target β2-GPI deposited in kidney glomeruli, decreased fibrin deposition, and improved urinalysis data with a greater efficiency than untargeted NBs. Our findings suggest that targeting cell-bound β2-GPI may represent an efficient and thrombus-specific thrombolytic strategy in both APS-related and APSunrelated thrombotic conditions.