Relaxivity Modulation of Gd-HPDO3A-like Complexes by Introducing Polar and Protic Peripheral Groups

Area of Science:

• Medical Imaging
• Radiochemistry
• Materials Science

Background:

• High-relaxivity Magnetic Resonance Imaging (MRI) contrast agents (CAs) are crucial for reducing injected doses while maintaining diagnostic information.
• Current CAs face limitations in achieving optimal relaxivity and safety profiles.

Purpose of the Study:

• To design and synthesize novel Gd(III) complexes with enhanced relaxivity.
• To investigate the impact of specific functional groups on CA relaxivity.
• To explore potential for reduced CA dosage in clinical MRI.

Main Methods:

• Synthesis of four new Gd(III) complexes based on a modified HP-DO3A macrocyclic structure.
• Introduction of polar and protic functional groups (amides, phosphonates, diols) adjacent to the metal-coordinated hydroxyl group.
• Detailed 1H NMR relaxometric analysis to evaluate relaxivity.

Main Results:

• The newly synthesized Gd(III) complexes exhibited a 20-60% increase in relaxivity compared to clinically approved CAs.
• Relaxivity enhancement was observed at standard conditions (0.5 T, 298 K, pH 7.4).
• The study evaluated the contribution of water molecules H-bonded to peripheral functional groups to the observed relaxivity.

Conclusions:

• The modified HP-DO3A based Gd(III) complexes demonstrate significantly improved relaxivity.
• These findings suggest potential for developing safer and more effective MRI contrast agents.
• The introduced functional groups play a key role in enhancing the relaxivity through second sphere effects and prototropic exchange.