PROJECT SUMMARY / ABSTRACT Vascular thrombosis is a major underlying factor in many cardiovascular, neurovascular, and related disorders, and is a significant post-surgical complication. Current imaging modalities used to assess thrombotic events present challenges because they primarily visualize the lack of blood flow rather than detailed information about a thrombus directly, and they cannot distinguish between newly formed and aged blood clots. Our team has previously demonstrated that high affinity and high specificity RNA aptamers can be generated against a number of coagulation proteins including thrombin and factor IXa. In addition, our team has demonstrated that aptamer-antidote pairs can be used as rapid binding-rapid reversal probes for real time detection of thrombi. The studies proposed in this application integrate aptamer-antidote pairs with sensitive total-body positron emission tomography (PET) imaging to develop a new approach in the way patients with thrombotic events can be stratified and subsequently treated. This proposal represents the convergence of multidisciplinary domains of expertise to explore a new team direction that will have a major impact on the field through the following Specific Aims: (1) Develop and evaluate aptamer-antidote pairs to perform rapid imaging of thrombi in mouse models for molecular thrombus profiling in vivo, and (2) Assess efficiency of radiolabeled aptamers for total-body PET in nonhuman primates. Preliminary results have demonstrated that aptamers can rapidly bind thrombin on active thrombi in vivo and that the antidotes can reverse such binding in under 5 minutes. In Specific Aim 1, we will further develop this technology by conducting studies in mice with aptamer-antidote pairs generated to thrombin, von Willebrand Factor, and platelet protein GPIIb/IIIa individually and combined. Findings will be adapted in Specific Aim 2 to the translational rhesus monkey model system using total-body PET that has demonstrated outstanding sensitivity. These investigations propose a new strategy to address characterization of thrombi in vivo and include a multidisciplinary translational team with expertise in nucleic acid biochemistry, combinatorial chemistry, antithrombotic agents, novel diagnostic imaging tools and methods, and a nonhuman primate model system of profound translational importance.