Radiolabeling of thioguanine with I-125 for diagnosis and therapy: in vitro and in vivo evaluation

Labeling was carried out by direct iodination of thioguanine (100 mu g) with radioiodine in a fast single step at 60 A degrees C, to produce iodo-6-thioguanine (I-125-S6G). Chloramine-T (200 mu g) was used as oxidizing agent to oxidize the iodide ion to the iodonium ion, at pH 7 and the reaction time was 30 min. A high radiochemical yield of 96.4\% was obtained. The labeled compound was quantitatively separated and purified by means of high pressure liquid chromatography (HPLC) with a radiochemical purity greater than 98\%, which facilitates its clinical use for human application. The biodistribution of I-125-6-thioguanine was studied by injection of the tracer in both normal and tumor bearing mice. The uptake in ascetic fluid was 35.4 and 23.9\% at 1 and 24 h post intravenous injection (h.p.i.), respectively, indicating the suitability of this labeled compound for use as a radiopharmaceutical agent.