Development of a kit-form analog of metaiodobenzylguanidine

The synthesis and evaluation of two radiopharmaceutical analogs of metaiodobenzylguanidine (MIBG) are described. Unlike MIBG, these analogs are rapidly and conveniently radioiodinated at room temperature in clinically applicable kit form. Radioiodinated 4-amino-3-iodobenzylguanidine (AIBG) for injection is synthesized in 20 min using IODO-GEN as the radioiodide oxidant and an anion exchange filter for purification. AIBG shows an affinity for the heart and adrenal medullae of dog and monkey similar to that of MIBG. In addition, AIBG shows improved selectivity for the adrenergic nerves of the heart as demonstrated by chemical sympathectomy studies. Tomographic images of the dog heart and planar images of the dog adrenal medullae were obtained using [123I]AIBG and [131I]AIBG, respectively. Planar images of the monkey heart using [131I]AIBG were similar in quality to those reported previously with [131I]MIBG. In view of the facile radiosynthesis of AIBG, a clinical evaluation of this new agent is warranted.