Preparation of 125IUdR and its evaluation in animal tumour model as a potential therapeutic agent

5-Iodo-2'-deoxyuridine or iodoxyuridine (IUdR), an analogue of thymidine, is taken up by the proliferating cells during DNA synthesis. Radioiodinated IUdR is a potential therapeutic agent since radiohalogenated thymidine analogues are used for in-vivo tumour targeting and Auger electrons from radionuclides such as 123I and 125I are very effective in cell destruction when internalised. 125IUdR was prepared and studied for its suitability as an in-vivo tumour therapy agent. 125IUdR was prepared both by direct iodination of 2'-deoxyuridine and iododemercuration of 5-chloromercury-2'-deoxyuridine. Radioiodination yields were between 60-80% at pH 7. Iododemercuration was preferred since with direct iodination poor yields were observed when high specific activity product was desired and also the purification procedure was lengthier. The identity of 125IUdR was established by comparison of TLC and HPLC patterns with those of authentic IUdR. The purified 125IUdR had radiochemical purity >95% and was stable for 20 days at 4 deg. C and for a week at 23 deg. C and 37 deg. C. Bio-uptake of 125IUdR was studied by injecting the tracer in tumour bearing mice (Sarcoma S-180). The uptake in tumour cells was 4.28 +- 2.7% per gram at 3 h and 1.48 +- 0.19% at 24 h post injection. In-vivo deiodination of the product was observed as seen by the uptake of the activity in the thyroid. About 40% the activity from all other organs was excreted in 70 h. The optimum time for injection of the tracer for therapy was studied by observing the delay in tumour growth and survival rate in mice injected at 0,3,9 and 12 days after tumour induction. Injection of the tracer on the third day was found to be the most beneficial for retardation of tumour growth, while injection of the activity on the zeroth and ninth day had no effect. (author)