Evaluation of radioiodination of meta-iodobenzylguanidine (MIBG) catalysed by in situ generated Cu(I) and directly added Cu(II)

A reliable method of labelling MIBG with 131I is reported. Radioiodination involved nucleophilic exchange reaction (160°C, 30 min) catalysed by directly added Cu(II) or by Cu(I) generated in situ by addition of Na2S2O5 to CuSO4. An additional step of purification of the radiolabelled MIBG by anion exchange chromatography is recommended. The radiochemical (RC) yield was over 90%, while the typical RC purity of 131I-MIBG was not less than 98%. Higher labelling yield was achieved with Cu(I) than when using Cu(II), and with 125I (commercial product) than with 131I obtained by wet radiochemical processing method in-house. The purity and stability of MIBG-131I was confirmed by biodistribution studies in monkeys with 0.03% and 0.8% uptake in adrenals and myocardium, respectively. It is concluded that Cu(I) or Cu(II) catalysed radioiodination method is well suited for production of MIBG-131I.