Zwitterionic Mn(III)-Tetraphenyl Porphyrins: Water-Soluble MRI Contrast Agents with High Relaxivity

Area of Science:

• Materials Science
• Biomedical Imaging
• Inorganic Chemistry

Background:

• Gadolinium-based contrast agents (GBCAs) are widely used in MRI but have safety concerns.
• Manganese-based contrast agents (MBCAs) offer a potential gadolinium-free alternative.
• Development of stable and effective MBCAs is crucial for advancing MRI technology.

Purpose of the Study:

• To synthesize and characterize novel zwitterionic Mn(III) porphyrin chelates (Mn-8 and Mn-9).
• To evaluate their physicochemical properties, including stability and relaxivity.
• To assess their potential as next-generation MRI contrast agents.

Main Methods:

• Synthesis of zwitterionic Mn(III) porphyrin chelates using copper-catalyzed azide-alkyne cycloaddition (CuAAC).
• Assessment of water solubility, stability under acidic conditions, and resistance to transmetallation.
• Measurement of T1-relaxivity and in vivo contrast enhancement.

Main Results:

• Both Mn-8 and Mn-9 are water-soluble, stable zwitterionic compounds.
• The complexes exhibit high T1-relaxivity, comparable to clinical GBCAs.
• Superior relaxivity and stability were observed compared to Mn-DPDP.
• Chelation significantly reduced singlet oxygen generation.
• Mn-8 demonstrated effective in vivo contrast enhancement.

Conclusions:

• Zwitterionic Mn(III) porphyrin chelates (Mn-8 and Mn-9) possess favorable properties for MRI contrast agents.
• These compounds represent promising candidates for next-generation, gadolinium-free MRI contrast agents.
• The design incorporating sulfobetaines or N-oxides contributes to their enhanced performance and safety profile.