In vivo studies of fullerene-based materials using endohedral metallofullerene radiotracers.

Biodistribution studies of a water-soluble radioactive metallofullerene compound have been conducted using BALB/c mice. To this end, a sample containing Hox@C82 (x = 1, 2) was purified and derivatized to prepare the water-soluble metallofullerol, Hox@C82(OH)y. This metallofullerol was then neutron-activated (165Ho[n,gamma]166Ho) to prepare the 166Hox@C82(OH)y analog as a radiotracer, which was monitored, after intravenous administration, for up to 48 hours by using dissection radioanalysis, and its biodistribution was compared with a control compound, Na2[166Ho(DTPA)(H2O)]. Results showed selective localization of the 166Hox@C82(OH)y tracer in the liver but with slow clearance, as well as uptake by bone without clearance. In contrast, excretion of the control compound was nearly quantitative after 1 hour. The fate of 166Ho was also explored by a metabolism study of 166Hox@C82(OH)y in Fischer rats. Results indicated 20% excretion of intact 166Hox@C82(OH)y within 5 days. The present findings demonstrate the feasibility of using water-solubilized metallofullerene radiotracers to monitor the fate of fullerene-based materials in animals, and suggest that water-solubilized fullerene materials, in general, may be useful components in drug design.