Investigation of sandwiched gadolinium (III) complexes with tungstosilicates as potential MRI contrast agents

Two gadolinium-sandwiched complexes with tungstosilicates, K13[Gd(SiW11O39)2] (Gd(SiW11)2) and K11H6[Gd3O3(SiW9O34)2] (Gd3(SiW9)2), have been investigated by in vitro and in vivo experiments as potential contrast agents for magnetic resonance imaging (MRI). T1-relaxivity of Gd(SiW11)2was 6.59 mM−1 · s−1 in aqueous solution and 6.85 mM−1 · s−1 in 0.725 mmol · L−1 bovine serum albumin solution at 25°C and 9.39 T, respectively. The corresponding T1-relaxivity of Gd3(SiW9)2 was 12.6 and 19.3 mM−1 · s−1 per Gd, respectively. MRI for Sprague–Dawley rats showed longer and more remarkable enhancement in rat liver after i.v. injection of these two complexes: 39.4 ± 3.9% and 57.4 ± 11.6% within the first 30 min after injection, 31.2 ± 2.6% and 39.9 ± 7.6% in the next 60 min for Gd(SiW11)2 and Gd3(SiW9)2 at doses of 0.081 and 0.084 mmol Gd/kg, respectively. Our preliminary in vitro and in vivo study indicates that Gd(SiW11)2 and Gd3(SiW9)2 are favorable candidates for hepatic contrast agents for MRI. However, the two complexes exhibit higher acute toxicity and need to be modified and studied further before clinical use.