Platelet-inspired Delivery System for Targeted Thrombolytic Therapy

Case Western Reserve University, Cleveland OH

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Abstract

? DESCRIPTION: In occlusive vascular diseases, dissolution of thrombus and rapid restoration of blood flow is critical in preventing tissue morbidity and mortality. To this end, current clinicl `clot-busting' strategies using intravascular systemic administration of thrombolytic drugs like tPA present issues of plasma-induced drug deactivation, short plasma half-life of drugs, rapid drug washout, reduced drug availability at target site, and systemic hemorrhagic side effects. These issues can be potentially resolved by controlled release of the drugs from injectable delivery vehicles that can selectively accumulate at the clot site under hemodynamic flow. For this, it is necessary for the vehicles to (i) actively bind to the clot site, (ii) stay retained uner flow, and (iii) allow localized drug release for site-selective action. For designing such a vehicl, natural platelets provide an excellent paradigm, since platelets have the innate capability to marginate towards the vascular wall, bind actively to clot via specific ligand-receptor interactions, and release cytoplasmic contents to modulate clot activities. The margination of platelets towards the vascular wall is facilitated by their discoid shape, ~2 µ diameter size and ~25-50 kPa modulus, while their active binding at the thrombus site is mediated via ligands fibrinogen (Fg) and PSGL-1 binding to platelet surface integrin GPIIb-IIIa and P-selectin respectively. Inspired by these physico-mechanical and biointeractive cues of natural platelets, we propose to engineer vehicles that will have (i) platelet-mimetic shape, size and modulus to facilitate enhanced margination towards the vascular wall, and (ii) heteromultivalent surface-decoration with GPIIb-IIIa- and P-selectin-binding peptide ligands to enable thrombus-selective anchorage and retention under hemodynamic flow. Our central hypothesis is that controlled release of thrombolytic drugs from such platelet-inspired vehicles anchoring at the thrombus site will enhance the site-specific therapeutic efficacy, while minimizing systemic drug distribution and side-effects. To test this, we will fabricate albumin-based platelet-inspired discoid flexible vehicles, modify their surface heteromultivalently with the active platelet-targeting ligands and evaluate their thrombus anchoring capability in vitro and in vivo (Aim1). In parallel, we will cationically modify tPA (mtPA) to facilitate its loading into the albumin particles since albumin i negatively charged at physiological pH, and characterize the loading and release of mtPA from these particles in vitro (Aim 2). After optimizing the platelet-inspired thrombus- anchoring mechanisms and the mtPA loading/release kinetics via these two synergistic yet independent aims, we will integrate them to create mtPA-loaded platelet-inspired vehicles which will be evaluated for targeted thrombolysis efficacy in vitro and in vivo (Aim 3). Our principal innovation is the design of a delivery vehicle that combines key physico-mechanical and biointeractive parameters inspired by platelets for enhanced thrombus-anchoring ability. The current application will test this technology for targeted thrombolytic therapy. The technology also holds the promise to become a platform for other targeted therapies in vascular diseases.