Chiral Pyclen-Based Heptadentate Chelates as Highly Stable MRI Contrast Agents

Inorg Chem. 2024 May 6;63(18):8462-8475. doi: 10.1021/acs.inorgchem.4c01028. Epub 2024 Apr 20.

Abstract

In recent years, pyclen-based complexes have attracted a great deal of interest as magnetic resonance imaging (MRI) contrast agents (CAs) and luminescent materials, as well as radiopharmaceuticals. Remarkably, gadopiclenol, a Gd(III) bishydrated complex featuring a pyclen-based heptadentate ligand, received approval as a novel contrast agent for clinical MRI application in 2022. To maximize stability and efficiency, two novel chiral pyclen-based chelators and their complexes were developed in this study. Gd-X-PCTA-2 showed significant enhancements in both thermodynamic and kinetic stabilities compared to those of the achiral parent derivative Gd-PCTA. 1H NMRD profiles reveal that both chiral gadolinium complexes (Gd-X-PCTA-1 and Gd-X-PCTA-2) have a higher relaxivity than Gd-PCTA, while variable-temperature 17O NMR studies show that the two inner-sphere water molecules have distinct residence times τMa and τMb. Furthermore, in vivo imaging demonstrates that Gd-X-PCTA-2 enhances the signal in the heart and kidneys of the mice, and the chiral Gd complexes exhibit the ability to distinguish between tumors and normal tissues in a 4T1 mouse model more efficiently than that of the clinical agent gadobutrol. Biodistribution studies show that Gd-PCTA and Gd-X-PCTA-2 are primarily cleared by a renal pathway, with 24 h residues of Gd-X-PCTA-2 in the liver and kidney being lower than those of Gd-PCTA.

MeSH terms

  • Animals
  • Azabicyclo Compounds*
  • Chelating Agents* / chemical synthesis
  • Chelating Agents* / chemistry
  • Contrast Media* / chemistry
  • Coordination Complexes / chemical synthesis
  • Coordination Complexes / chemistry
  • Female
  • Gadolinium* / chemistry
  • Humans
  • Magnetic Resonance Imaging*
  • Mice
  • Molecular Structure
  • Stereoisomerism

Substances

  • Contrast Media
  • Chelating Agents
  • Gadolinium
  • pyclen
  • Coordination Complexes
  • Azabicyclo Compounds