Biodistribution of free 211At and 125I- in nude mice bearing tumors derived from anaplastic thyroid carcinoma cell lines

Free At-211 has been proposed for therapy of anaplastic thyroid carcinoma (ATC). However, no extensive biodistribution study comparing tumor-bearing and nontumor-bearing mice has previously been performed. The aim of this study was to perform a complete evaluation of the biodistribution of At-211, both for normal and ATC-bearing mice. For comparison, the biodistribution of I-125(-) was simultaneously studied. Dosimetric evaluations were performed to investigate if At-211 can be used for therapy of ATC. Methods: Athymic nude mice were subcutaneously injected with either of two human ATC cell lines, HTh83 and KAT-4. Tumor-bearing and nontumor-bearing mice were injected intravenously with 0.3 MBq At-211 and 0.3 MBq I-125(-) simultaneously. The mice were sacrificed 4-24 hours after injection, and the activity concentrations in tissues were determined. Results: Except for the thyroid, the concentration of At-211 was higher than that of I-125(-) in the tissues. The uptake of At-211 was primarily high in NIS-expressing organs. Furthermore, the absorbed doses to these organs were higher than both tumor types. Conclusions: The biodistribution of At-211 and I-125(-) differed in this animal model. The higher mean absorbed dose from At-211 in several organs than in tumor tissue restricts the possibility of using free At-211 for therapy of ATC.