Polydisulfide manganese(II) complexes as non-gadolinium biodegradable macromolecular MRI contrast agents

Purpose: To develop safe and effective manganese(II) -based biodegradable macromolecular MRI contrast agents. Materials and Methods: In this study, we synthesized and characterized two polydisulfide manganese(II) complexes, Mn-DTPA cystamine copolymers and Mn-EDTA cystamine copolymers, as new biodegradable macromolecular MRI contrast agents. The contrast enhancement of the two manganese-based contrast agents were evaluated in mice bearing MDA-MB-231 human breast carcinoma xenografts, in comparison with MnCl2. Results: The T-1 and T-2 relaxivities were 4.74 and 10.38 mM(-1)s(-1) per manganese at 3T for Mn-DTPA cystamine copolymers (M-n = 30.50 kDa) and 6.41 and 9.72 mM(-1)s(-1) for Mn-EDTA cystamine copolymers (Mn = 61.80 kDa). Both polydisulfide Mn(II) complexes showed significant liver, myocardium and tumor enhancement. Conclusion: The manganese-based polydisulfide contrast agents have a potential to be developed as alternative non-gadolinium contrast agents for MR cancer and myocardium imaging.