Enzymatically Shifting Nitroxides for EPR Spectroscopy and Overhauser‐Enhanced Magnetic Resonance Imaging

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Abstract
In vivo investigations of enzymatic processes using non‐invasive approaches are a long‐lasting challenge. Recently, we showed that Overhauser‐enhanced MRI is suitable to such a purpose. A β‐phosphorylated nitroxide substrate prototype exhibiting keto–enol equilibrium upon enzymatic activity has been prepared. Upon enzymatic hydrolysis, a large variation of the phosphorus hyperfine coupling constant (ΔaP=4 G) was observed. The enzymatic activities of several enzymes were conveniently monitored by electronic paramagnetic resonance (EPR). Using a 0.2 T MRI machine, in vitro and in vivo OMRI experiments were successfully performed, affording a 1200 % enhanced MRI signal in vitro, and a 600 % enhanced signal in vivo. These results highlight the enhanced imaging potential of these nitroxides upon specific enzymatic substrate‐to‐product conversion.
Funding Information
  • CNRS (ANR-11-IDEX-0001-02)
  • Investissements d′Avenir French Government program
  • French National Research Agency
  • Labex TRAIL grant (ANR-10-LABX-57, ANR-11-JS07-002-01, ANR-09-BLA-0017-01)

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