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

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

^*Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, M.S.-60, P.O. Box 1892, Houston, TX 77251-1892; ^†Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6229; and ^‡TDA Research, 12345 West 52nd Avenue, Wheat Ridge, CO 80033

Communicated by Robert Floyd Curl, Jr., Rice University, Houston, TX (received for review June 24, 1998)

Abstract

Biodistribution studies of a water-soluble radioactive metallofullerene compound have been conducted using BALB/c mice. To this end, a sample containing Ho_x@C₈₂ (x = 1, 2) was purified and derivatized to prepare the water-soluble metallofullerol, Ho_x@C₈₂(OH)_y. This metallofullerol was then neutron-activated (¹⁶⁵Ho[n,γ]¹⁶⁶Ho) to prepare the ¹⁶⁶Ho_x@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 ¹⁶⁶Ho_x@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 ¹⁶⁶Ho_x@C₈₂(OH)_y in Fischer rats. Results indicated 20% excretion of intact ¹⁶⁶Ho_x@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.

Footnotes

↵ § To whom reprint requests should be addressed. e-mail: durango{at}ruf.rice.edu.
↵ ¶ Based on the LD-TOF MS of HPLC-purified holmium fullerenes used in this study (Fig. 2), it can be seen that the sample contained both mono- and diholmium metallofullerene. Therefore, the molecular formula for these compounds has been noted with an “x” subscript where x = 1 or 2.
↵ ‖ As a result of recent work concerning the number hydroxyl groups present for C₆₀(OH)_y, the number of hydroxyl groups on holmium metallofullerol is currently assigned as 16 (see ref. 52), although it may well be different for a metallofullerene with a C₈₂ cage. Exhaustive attempts to obtain mass spectrometry data for Ho_x@C₈₂(OH)_y by using the same techniques as in ref. 52 were unsuccessful.
ABBREVIATIONS:

LD-TOF,

laser desorption–time-of-flight;

ICP,

inductively coupled plasma;

AE,

atomic emission;

NAA,

neutron-activation analysis;

DTPA,

diethylenetriaminepentaacetate;

ID,

injected dose