MRI Contrasting Agent Based on Mn-MOF-74 Nanoparticles with Coordinatively Unsaturated Sites

Nobuhiko Iki, Ryuta Nakane, Atsuko Masuya-Suzuki, Yoshikazu Ozawa, Takako Maruoka, Megumi Iiyama, Akira Sumiyoshi, Ichio Aoki

Research output: Contribution to journalArticlepeer-review


Purpose: The development of magnetic resonance imaging (MRI) contrasting agents (CAs) that are safer and have a higher relaxivity than Gd(III)-based agents is a significant research topic. Herein, we propose the use of a Mn-based metal organic framework (MOF), Mn-MOF-74, characterized by a safe paramagnetic center, a coordinatively unsaturated site (CUS) for aquation, and a long rotational correlation time, endowing high relaxivity. Furthermore, biocompatibility and delivery to the tumor are generally expected for MOFs that are obtainable in the nanometer size range. Procedure: Drop-wise mixing of 2,5-dihydroxyterephthalic acid (DHTP) and Mn(II) acetate yielded Mn-MOF-74 with a diameter of < 150 nm, which was then modified with 1–fivefold higher amounts of poly(ethylene glycol) (M.W. = 5000) to afford MOFs stably dispersed in water for at least 24 h. Results: The longitudinal and transverse relaxivity of the PEG-modified MOF was in the range of r1 = 8.08–13.5 and r2 = 32.7–46.8 mM–1 s–1, respectively (1.0 T, 23.7–23.9 °C), being larger than those of typical Gd(III)- and Mn(II)-based CAs of single-nuclear metal complexes. The in vivo imaging of a tumor-bearing mouse clearly showed that the tumor could be readily recognized due to signal enhancement (117%) in T1-weighted images, whereas other tissues showed small signal changes. Conclusions: These results suggest that PEG-Mn-MOF-74 can be passively delivered to tumors and can act as a high-relaxivity T1 agent.

Original languageEnglish
JournalMolecular Imaging and Biology
Publication statusAccepted/In press - 2023


  • Contrast agents
  • Metal organic framework
  • Mn(II)
  • MRI

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research


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