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.