Development and validation of an activatable PET radiotracer reporting extracellular myeloperoxidase activity for the detection of unstable atherosclerotic plaque

Extracellular arterial activity of the pro-inflammatory enzyme myeloperoxidase (MPO) destabilizes atherosclerotic plaque and associates with future atherothrombosis. To facilitate first-in-human studies using extracellular MPO activity as a molecular imaging target to identify high-risk atherosclerotic plaque, we describe 68GaGa-IEMA, a NODAGA-based positron emission tomography (PET) radiotracer that provides an index for extracellular MPO activity. Synthesis of 68GaGa-IEMA was achieved in five steps and with high radiolabelling efficiency. 68GaGa-IEMA self-oligomerized and bound to proteins upon exposure to enzymatically active MPO, did not cross-cell membranes and was stable in human serum in vitro, while 68GaGa-IEMA had favorable blood kinetics and stability in circulation in vivo. 68GaGa-IEMA PET imaging in a mouse model of plaque instability revealed enhanced signal in unstable compared with stable plaque and plaque-free arteries. These data indicate that 68GaGa-IEMA is a promising translational candidate for the non-invasive identification of high-risk atherosclerotic plaques and the evaluation of therapies targeting arterial inflammation.