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Molecules 2018, 23(5), 1034;

Synthesis, Stability and Relaxivity of TEEPO-Met: An Organic Radical as a Potential Tumour Targeting Contrast Agent for Magnetic Resonance Imaging

Department of Chemistry, University of Helsinki, P.O. Box 55, 00014 Helsinki, Finland
Department of Clinical Neuroscience, Karolinska Institutet, S-17176 Stockholm, Sweden
Department of Chemistry, Nanoscience Centre, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland
HUS Helsinki Medical Imaging Center, Radiology, University of Helsinki and Helsinki University Hospital, P.O. Box 340, 00029 HUS, Helsinki, Finland
Stora Enso, Innovation Centre for Biomaterials, Fannys väg 1, S-13154 Nacka, Sweden
Author to whom correspondence should be addressed.
Academic Editor: Diego Muñoz-Torrero
Received: 9 March 2018 / Revised: 6 April 2018 / Accepted: 25 April 2018 / Published: 27 April 2018
(This article belongs to the Special Issue Molecular Imaging and Treatment Monitoring of Cancer)
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Cancer is a widespread and life-threatening disease and its early-stage diagnosis is vital. One of the most effective, non-invasive tools in medical diagnostics is magnetic resonance imaging (MRI) with the aid of contrast agents. Contrast agents that are currently in clinical use contain metals, causing some restrictions in their use. Also, these contrast agents are mainly non-specific without any tissue targeting capabilities. Subsequently, the interest has notably increased in the research of organic, metal-free contrast agents. This study presents a new, stable organic radical, TEEPO-Met, where a radical moiety 2,2,6,6-tetraethylpiperidinoxide (TEEPO) is attached to an amino acid, methionine (Met), as a potentially tumour-targeting moiety. We describe the synthesis, stability assessment with electron paramagnetic resonance (EPR) spectroscopy and relaxation enhancement abilities by an in vitro nuclear magnetic resonance (NMR) and phantom MRI studies of TEEPO-Met. The new compound proved to be stable notably longer than the average imaging time in conditions mimicking a biological matrix. Also, it significantly reduced the relaxation times of water, making it a promising candidate as a novel tumour targeting contrast agent for MRI. View Full-Text
Keywords: nitroxides; radicals; methionine; contrast agents; MRI; NMR; EPR nitroxides; radicals; methionine; contrast agents; MRI; NMR; EPR

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Soikkeli, M.; Horkka, K.; Moilanen, J.O.; Timonen, M.; Kavakka, J.; Heikkinen, S. Synthesis, Stability and Relaxivity of TEEPO-Met: An Organic Radical as a Potential Tumour Targeting Contrast Agent for Magnetic Resonance Imaging. Molecules 2018, 23, 1034.

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