Paramagnetic water-soluble metallofullerenes having the highest relaxivityfor MRI contrast agents

Water-soluble gadolinium (Gd) endohedral metallofullerenes have been synthe sized as polyhydroxyl forms (Gd@C-82(OH)(n), Gd-fullerenols) and their para magnetic properties were evaluated by in vivo as well as in vitro for the n ovel magnetic resonance imaging (MRI) contrast agents for next generation. The in vitro water proton relaxivity, R-1 (the effect on 1/T-1), of Gd-full erenols is significantly higher (20-folds) than that of the commercial MRI contrast agent, Magnevist (gadolinium-diethylenetri-aminepentaacetic acid, Gd-DTPA) at 1.0 T close to the common field of clinical MRI. This unusually high proton relaxivity of Gd-fullerenols leads to the highest signal enhan cement at extremely lower Gd concentration in MRI studies. The strong signa l was confirmed in vivo MRI at lung, liver, spleen, and kidney of CDF1 mice after i.v. administration of Gd-fullerenols at a dose of 5 mu mol Gd/kg, w hich was 1/20 of the typical clinical dose (100 mu mol Gd/kg) of Gd-DTPA.