Towards Metabolic Organic Radical Contrast Agents (mORCAs) for Magnetic Resonance Imaging
We report two conjugates of <i>gem</i>-diethyl pyrroline nitroxide radicals with D-mannosamine as potential metabolic organic radical contrast agents, mORCAs, circumventing the need for biorthogonal reactions. In-cell EPR spectroscopy, using Jurkat cells and analogous conjugate, based on...
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| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-04-01
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| Series: | Molecules |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1420-3049/30/7/1581 |
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| Summary: | We report two conjugates of <i>gem</i>-diethyl pyrroline nitroxide radicals with D-mannosamine as potential metabolic organic radical contrast agents, mORCAs, circumventing the need for biorthogonal reactions. In-cell EPR spectroscopy, using Jurkat cells and analogous conjugate, based on a pyrrolidine nitroxide radical, shows an efficient incorporation of highly immobilized nitroxides, with a correlation time of <i>τ</i><sub>cor</sub> = 20 ns. In vivo MRI experiments in mice show that the paramagnetic nitroxide radical shortens the <i>T</i><sub>1</sub> and <i>T</i><sub>2</sub> relaxation times of protons in water located in the kidney and brain by only up to ~10% after 3 d. Ex vivo EPR spectroscopic analyses indicate that the contrast agents in mouse tissues are primarily localized in the kidney, lung, liver, heart, and blood, which primarily contain immobilized nitroxide radicals with <i>τ</i><sub>cor</sub> = 4–9 ns. The spin concentrations in tissues remain low (1–3 nmol g⁻<sup>1</sup>) at 24 h after the third mORCA injection, approximately one to two orders of magnitude lower than those of ORCAFluor and BASP-ORCA (measured at ~24 h post-injection). These low spin concentrations explain the small proton <i>T</i><sub>1</sub> and <i>T</i><sub>2</sub> relaxation changes observed in in vivo MRI. |
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| ISSN: | 1420-3049 |