Synthesis and Characterization of a Hypoxia-Sensitive MRI Probe

Authors

  • Dr. Federico A. Rojas-Quijano,

    1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA), Fax: (+1) 214-645-2744
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  • Dr. Gyula Tircsó,

    Corresponding author
    1. Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4010 (Hungary), Fax: (+36) 52-518-660
    • Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4010 (Hungary), Fax: (+36) 52-518-660
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  • Enikő Tircsóné Benyó,

    1. Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4010 (Hungary), Fax: (+36) 52-518-660
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  • Dr. Zsolt Baranyai,

    1. Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4010 (Hungary), Fax: (+36) 52-518-660
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  • Huan Tran Hoang,

    1. Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4010 (Hungary), Fax: (+36) 52-518-660
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  • Dr. Ferenc K. Kálmán,

    1. Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetem tér 1, Debrecen, H-4010 (Hungary), Fax: (+36) 52-518-660
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  • Dr. Praveen K. Gulaka,

    1. Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA)
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  • Prof. Vikram D. Kodibagkar,

    1. Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA)
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  • Prof. Silvio Aime,

    1. Department of Chemistry IFM & Molecular Imaging Center, Università degli Studi di Torino, Via P. Giuria 7, 10125 Torino (Italy)
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  • Prof. Zoltán Kovács,

    1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA), Fax: (+1) 214-645-2744
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  • Prof. A. Dean Sherry

    Corresponding author
    1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA), Fax: (+1) 214-645-2744
    2. Chemistry Department, University of Texas at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA), Fax: (+1) 972-883-2925
    • Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (USA), Fax: (+1) 214-645-2744
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Abstract

Tissue hypoxia occurs in pathologic conditions, such as cancer, ischemic heart disease and stroke when oxygen demand is greater than oxygen supply. An imaging method that can differentiate hypoxic versus normoxic tissue could have an immediate impact on therapy choices. In this work, the gadolinium(III) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with a 2-nitroimidazole attached to one carboxyl group via an amide linkage was prepared, characterized and tested as a hypoxia-sensitive MRI agent. A control complex, Gd(DO3A-monobutylamide), was also prepared in order to test whether the nitroimidazole side-chain alters either the water proton T1 relaxivity or the thermodynamic stability of the complex. The stabilities of these complexes were lower than that of Gd(DOTA) as expected for mono-amide derivatives. The water proton T1 relaxivity (r1), bound water residence lifetime (τM) and rotational correlation time (τR) of both complexes was determined by relaxivity measurements, variable temperature 17O NMR spectroscopy and proton nuclear magnetic relaxation dispersion (NMRD) studies. The resulting parameters (r1=6.38 mM−1 s−1 at 20 MHz, τM=0.71 μs, τR=141 ps) determined for the nitroimidazole derivative closely parallel to those of other Gd(DO3A-monoamide) complexes of similar molecular size. In vitro MR imaging experiments with 9L rat glioma cells maintained under nitrogen (hypoxic) versus oxygen (normoxic) gas showed that both agents enter cells but only the nitroimidazole derivative was trapped in cells maintained under N2 as evidenced by an approximately twofold decrease in T1 measured for hypoxic cells versus normoxic cells exposed to this agent. These results suggest that the nitroimidazole derivative might serve as a molecular reporter for discriminating hypoxic versus normoxic tissues by MRI.

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