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Modifying LnHPDO3A Chelates for Improved T1 and CEST MRI Applications
Giuseppe Ferrauto1, Daniela Delli Castelli1, Loredana Leone2
1Department of Molecular Biotechnology and Health Sciences, Molecular Imaging Centre, University of Torino, via Nizza 52, 10125, Torino, Italy.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|January 9, 2019
Summary
A new ligand, HPDO3MA, enhances MRI contrast agents by improving relaxivity and kinetic inertness. This novel macrocyclic ligand offers increased sensitivity and stability for lanthanide complexes in medical imaging applications.
Area of Science:
- Coordination Chemistry
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Medical Imaging Agents
Background:
- Macrocyclic ligands are crucial for developing stable lanthanide complexes used as contrast agents in Magnetic Resonance Imaging (MRI).
- Optimizing ligand structure is key to enhancing the performance and stability of these agents.
- Existing ligands like HPDO3A and DOTMA have limitations that newer designs aim to overcome.
Purpose of the Study:
- To design and synthesize a novel macrocyclic ligand, HPDO3MA, by combining and optimizing properties of HPDO3A and DOTMA.
- To evaluate the structural, relaxometric, and kinetic properties of lanthanide complexes with HPDO3MA.
- To assess the potential of HPDO3MA-based complexes as improved MRI contrast agents.
Main Methods:
- Synthesis of the new ligand HPDO3MA.
- Characterization of Eu(HPDO3MA) using 1H NMR spectroscopy to determine isomeric distribution.
- Relaxometric NMR studies (1H and 17O) of Gd(HPDO3MA) to assess relaxivity and water exchange.
- Chemical Exchange Saturation Transfer (CEST) experiments with Yb(HPDO3MA) for sensitivity evaluation.
- Determination of kinetic inertness and dissociation half-life of Yb(HPDO3MA) at physiological pH.
Main Results:
- Eu(HPDO3MA) formed two diastereoisomers: square antiprismatic (SAP) and twisted square antiprismatic (TSAP) in a 56:44 ratio.
- Gd(HPDO3MA) exhibited a ~10% increase in relaxivity and faster water exchange compared to Gd(HPDO3A).
- Yb(HPDO3MA) showed approximately double the sensitivity in CEST imaging and twice the kinetic inertness of Yb(HPDO3A), with a dissociation half-life of ~2500 years.
Conclusions:
- The methyl groups on HPDO3MA's pendant arms enhance ligand rigidity and kinetic inertness of lanthanide complexes.
- HPDO3MA-based complexes offer improved relaxivity, water exchange, CEST sensitivity, and remarkable kinetic stability.
- HPDO3MA represents a promising scaffold for developing next-generation, highly stable, and sensitive MRI contrast agents.
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