DEVELOPING NOVEL PLATELET-BASED TARGETING STRATEGIES FOR THROMBOLYTICS

Use of plasminogen activators (PAs) as thrombolytic drugs is restricted to life threatening thrombotic settings because these therapies are associated with a high risk of bleeding. We hypothesize that platelet-delivered PAs would preferentially lyse nascent, pathological clots that are actively recruiting platelets, while sparing pre-formed hemostatic clots. Two potential approaches were pursued: 1) PA-loaded platelets that release the thrombolytic from its granular stores upon activation, and 2) a thrombolytic chimeric protein that specifically binds to human platelets and activated when the platelets are incorporated into a growing thrombus. In our first approach, we desired to develop a strategy for producing platelets ex-vivo from cultured megakaryocytes that ectopically expressed urokinase-PA (uPA). No group had successfully produced sufficient ex-vivo generated platelets before, to side step this issue we infused ex-vivo generated megakaryocytes and showed that we can achieve a significant number of donor-derived platelets from these infused megakaryocytes in a murine model. The resulting platelets were normal in size, surface markers, circulating half-life, and were functional. Infused megakaryocytes localized to the pulmonary vasculature to shed platelets. We demonstrated, beginning with megakaryocytes derived from a transgenic mouse that ectopically express and store uPA in their alpha-granules that we can interfere with thrombosis by platelets generated from thes