In Vivo Evaluation of a Radiogallium-Labeled Bifunctional Radiopharmaceutical, Ga-DOTA-MN2, for Hypoxic Tumor Imaging

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  • Sano Kohei
    Department of Biomolecular Recognition Chemistry, Graduate School of Pharmaceutical Sciences, Kyushu University
  • Okada Mayumi
    Department of Biomolecular Recognition Chemistry, Graduate School of Pharmaceutical Sciences, Kyushu University
  • Hisada Hayato
    Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University
  • Shimokawa Kenta
    Department of Biomolecular Recognition Chemistry, Graduate School of Pharmaceutical Sciences, Kyushu University
  • Saji Hideo
    Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University
  • Maeda Minoru
    Department of Biomolecular Recognition Chemistry, Graduate School of Pharmaceutical Sciences, Kyushu University
  • Mukai Takahiro
    Department of Biomolecular Recognition Chemistry, Graduate School of Pharmaceutical Sciences, Kyushu University Department of Biophysical Chemistry, Kobe Pharmaceutical University

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On the basis of the findings obtained by X-ray crystallography of Ga-DOTA chelates and the drug design concept of bifunctional radiopharmaceuticals, we previously designed and synthesized a radiogallium-labeled DOTA chelate containing two metronidazole moieties, 67Ga-DOTA-MN2, for hypoxic tumor imaging. As expected, 67Ga-DOTA-MN2 exhibited high in vivo stability, although two carboxyl groups in the DOTA skeleton were conjugated with metronidazole moieties. In this study, we evaluated 67/68Ga-DOTA-MN2 as a nuclear imaging agent for hypoxic tumors. 67Ga-labeling of DOTA-MN2 with 67GaCl3 was achieved with high radiochemical yield (>85%) by 1-min of microwave irradiation (50 W). The pharmacokinetics of 67Ga-DOTA-MN2 were examined in FM3A tumor-bearing mice, and compared with those of 67Ga-DOTA-MN1 containing one metronidazole unit and 67Ga-DOTA. Upon administration, 67Ga-DOTA-MN2 exhibited higher accumulation in the implanted tumors than 67Ga-DOTA. Tumor-to-blood ratios of 67Ga-DOTA-MN2 were about two-fold higher than those of 67Ga-DOTA-MN1. Autoradiographic analysis showed the heterogeneous localization of 67Ga-DOTA-MN2 in the tumors, which corresponds to hypoxic regions suggested by well-established hypoxia marker drug, pimonidazole. Furthermore, in positron emission tomography (PET) study, the tumors of mice administered 68Ga-labeled DOTA-MN2 were clearly imaged by small-animal PET at 1 h after administration. This study demonstrates the potential usefulness of 67/68Ga-DOTA-MN2 as a nuclear imaging agent for hypoxic tumors and suggests that two functional moieties, such as metronidazole, can be conjugated to radiogallium-DOTA chelate without reducing the complex stability. The present findings provide useful information about the chemical design of radiogallium-labeled radiopharmaceuticals for PET and single photon emission computed tomography (SPECT) studies.

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