Synthesis, photophysical characterization, relaxometric studies and molecular docking studies of gadolinium-free contrast agents for dual modal imaging

Mn-Based MRI Contrast Agents: An Overview

MRI contrast agents are required in the clinic to detect some pathologies, such as cancers. Nevertheless, at the moment, only small extracellular and non-specific gadolinium complexes are available for clinicians. Moreover, safety issues have recently emerged concerning the use of gadolinium complexes; hence, alternatives are urgently needed. Manganese-based MRI contrast agents could be one of these alternatives and increasing numbers of studies are available in the literature. This review aims at synthesizing all the research, from small Mn complexes to nanoparticular agents, including theranostic agents, to highlight all the efforts already made by the scientific community to obtain highly efficient agents but also evidence of the weaknesses of the developed systems.

Current advancement in the development of manganese complexes as magnetic resonance imaging probes

Emerging non-invasive molecular imaging modalities can detect a pathophysiological state at the molecular level before any anatomic changes are observed. Magnetic resonance imaging (MRI) is preferred over other nuclear imaging techniques owing to its radiation-free approach. Conventionally, most MRI contrast agents employed predominantly involve lanthanide metal: Gadolinium (Gd) until the discovery of associated severe nephrogenic toxicity issues. This limitation led a way to the development of manganese-based contrast agents which offer similar positive contrast enhancement capability. A vast quantity of experimental data has been accumulated over the last decade to define the physicochemical characteristics of manganese chelates with various ligand scaffolds. One can now observe how the ligand configurations, rigidity, and donor-acceptor characteristics impact the stability of the complex. This review covers the current trends in the development of manganese-based MRI contrast agents, the mechanisms they are based on and design considerations for newer manganese-based contrast agents with higher diagnostic strength along with better safety profiles.