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 [(68)Ga]Ga-IEMA, a NODAGA-based positron emission tomography (PET) radiotracer that provides an index for extracellular MPO activity. Synthesis of [(68)Ga]Ga-IEMA was achieved in five steps and with high radiolabelling efficiency. [(68)Ga]Ga-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 [(68)Ga]Ga-IEMA had favorable blood kinetics and stability in circulation in vivo. [(68)Ga]Ga-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 [(68)Ga]Ga-IEMA is a promising translational candidate for the non-invasive identification of high-risk atherosclerotic plaques and the evaluation of therapies targeting arterial inflammation.