A novel Gd³⁺ DTPA-bisamide complex with high relaxivity as an MRI contrast agent

A novel Gd(III) complex-based magnetic resonance imaging (MRI) contrast agent GdL has been designed and synthesized, which exhibited a much higher relaxivity (7.8 mM^-1 s^-1) than the commercially used Magnevist® (3.5 mM^-1 s^-1), good water solubility (>100 mg mL^-1), excellent thermodynamic stability (log KGdL = 17.21 ± 0.27), high biosafety and biocompatibility. In particular, the relaxivity of GdL increased to 26.7 mM^-1 s^-1 in a 4.5% bovine serum albumin (BSA) solution at 1.5 T, which was not significant in other commercial MRI contrast agents. The interaction sites and interaction types of GdL and BSA were further demonstrated by molecular docking simulations. Furthermore, the in vivo MRI behaviour was evaluated by using a 4T1 tumour-bearing mouse model. These results suggested that GdL is an excellent T₁-weighted MRI contrast agent and has the potential to be applied in clinical diagnosis.