The gadolinium complexes with polyoxometalates as potential MRI contrast agents

The two gadolinium (Gd) polyoxometalates, K15[Gd(BW11O39)2] [Gd(BW11)2] and K17[Gd(CuW11O39)2] [Gd(CuW11)2] have been evaluated by in vivo and in vitro experiments as the candidates of potential tissue-specific magnetic resonance imaging (MRI) contrast agents. T1 relaxivities of 17.12 mM−1·s−1 for Gd(BW11)2 and 19.95 mM−1·s−1 for Gd(CuW11)2 (400 MHz, 25 °C) were much higher than that of the commercial MRI contrast agent (GdDTPA). Their relaxivities in bovine serum albumin and human serum transferrin solutions were also reported. After administration of Gd(BW11)2 and Gd(CuW11)2 to Wistar rats, MRI showed longer and remarkable enhancement in rat liver and favorable renal excretion capability. The signal intensity increased by 37.63±3.45% for the liver during the whole imaging period (100 min) and by 61.47±10.03% for kidney within 5–40 min after injection at 40±1-μmol·kg−1 dose for Gd(CuW11)2, and Gd(BW11)2 induced 50.44±3.51% enhancement in the liver in 5–50-min range and 61.47±10.03% enhancement for kidney within 5–40 min after injection at 39±4 μmol·kg−1 dose. In vitro and in vivo study showed that Gd(BW11)2 and Gd(CuW11)2 are favorable candidates as tissue-specific contrast agents for MRI.