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Mol Imaging Biol. 2005 Nov-Dec;7(6):403-10.

Myeloperoxidase activity imaging using (67)Ga labeled substrate.

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  • 1Department of Radiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655, USA.



The aim of the study is to assess the feasibility of imaging specific activity of myeloperoxidase (MPO), a leukocyte enzyme with important roles in inflammation and atherosclerosis, by single photon emission computed tomography (SPECT) using a novel (67)Ga-labeled radiotracer obtained by conjugating desferrioxamine (DF) and hydroxyindolyl acetic acid in vivo.


A reducing substrate of MPO (I) was synthesized by reacting commercially available DF with 2-(5-hydroxy-1H-indol-3-yl) acetic acid in the presence of a coupling agent [dicyclohexyl carbodiimide (DCC)]. The chelating unit was labeled with (67)Ga, and its interaction with MPO was characterized using MALDI-TOF and UV-vis. Mice with Matrigel implants containing human MPO were used to model diseased tissues rich in MPO. Three hours after the injection of (67)Ga-I, SPECT/computed tomography (CT) imaging was performed on a high-resolution Gamma Medica X-SPECT system. Biodistribution studies were performed six hours after the injection of the radiotracer.


The feasibility of compound I oligomerization in the presence of MPO and MPO-mediated cross-linking with proteins was initially confirmed in vitro. In vivo, a 2.7-fold increase in target-to-muscle ratio could be measured in MPO-containing Matrigel implants in mice. Biodistribution experiments demonstrated a 60% increase of radioactivity in MPO-containing vs. control (contralateral) Matrigel implants.


(67)Ga-I can be used to image MPO activity in a model system. The accumulation mechanism is based on a differential pharmacokinetics because of the size increase resulting from (67)Ga-I interaction with the target enzyme.

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