Bleeding complications produced by thrombolytic drugs is a major challenge to therapeutic interventions for thrombotic disorders such as heart attacks (MI). Thrombolytic drugs produce their action by converting plasminogen to plasmin. However, since this biochemical conversion occurs both at the thrombus site and in general circulation, thrombolytic drugs deplete critical clotting factors that leads our body to a lytic state. To address such limitations, we propose to develop a stealth heparin-triggered delivery system for tenecteplase (TNK), a third generation plasminogen activator (PA). TNK has a longer half-life, more resistance to PA inhibitors and enhanced fibrin affinity. However, like the other PAs, TNK exhibits bleeding risks that offset its potential benefits. We seek to prepare a reversible multimolecular complex of TNK with human serum albumin (HSA) and protamine. The surface of the proposed construct will be decorated with a targeting peptide, C-terminal gamma-chain sequence of fibrinogen. Upon intravenous administration, TNK will remain enzymatically inactive because of the shield produced by bulky HSA molecule. The targeting peptide will direct the camouflaged TNK to accumulate on thrombus surface by binding with an integrin, GP IIb/IIIa. The drug will then be freed from the construct to produce its thrombolytic effect by subsequent administration of heparin. Heparin will be used as a triggering agent because of its affinity for positively charged protamine and its use in the management of MI. We will test the efficacy of the proposed construct in a series of in vitro and in vivo experiments. The activity of the chemically modified TNK will be determined by fibrinolytic and chromogenic assays. The HSA-protamine-peptide conjugate will be characterized for biocompatibility and clot-binding efficiency. The prodrug features of the camouflaged TNK and the controlled regeneration by heparin will be tested both in vitro and in vivo in a rat thrombosis model. Systemic levels of the clotting factors will be monitored to investigate construct's efficacy in reducing bleeding risk. Overall, this is a highly innovative project that attempts to address the limitations of current thrombolytic therapy by development of a novel construct that will mask the activity of TNK in the systemic circulation, preferentially accumulate on thrombus surface and subsequently release upon intravenous administration of heparin, a widely used drug in the management of MI.
|Program type||Predoctoral Fellowship|
|Effective start/end date||07/01/2013 → 01/11/2014|