Preparation, analysis and biodistribution in mice of iodine-123 labelled derivatives of hypericin

The synthesis of iodine-123 labelled mono- and di-iodo derivatives of hypericin, an hydroxylated phenanthroperylenequinone which is used for photodynamic therapy and has been shown to accumulate in several tumour types, is reported. Labelling was performed by electrophilic substitution on hypericin or iodohypericin with [I-123]iodide in the presence of peracetic acid and provided both mono-[I-123]iodohypericin and di-[I-123]iodohypericin in good radiochemical yields (> 80%). Mono-[I-123]iodohypericin was obtained with a high specific activity (925 GBq/mumol) whereas di-[I-123]iodohypericin was obtained in low specific activity (4 GBq/mumol) due to deiodination and subsequent iodination of iodohypericin which occurred during the labelling reaction. Biodistribution studies in mice showed a slow blood clearance and extensive hepatobiliary clearance as well as faecal excretion for both compounds. They will be further evaluated with regard to their tumor seeking properties. Copyright (C) 2004 John Wiley Sons, Ltd.