[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Nuclear Medicine 03/1986; 27(2):256-67. · 6.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fourteen 125I-labeled aralkylguanidines were synthesized and evaluated as potential imaging agents for the adrenal medullae and tumors of adrenomedullary origin. These guanidines are radiotracer analogues of guanethidine, an antihypertensive agent thought to mediate neuron blockade by uptake into adrenergic nerves. Dog adrenal medullae were used as a model to test radiotracer affinity for catecholamine storage tissue. Tissue distribution studies revealed that a number of radioiodinated guanidines showed pronounced localization in the adrenal medullae following intravenous injection, in certain cases exceeding that of either (-)-[3H]norepinephrine or [14C]guanethidine. (m-[125I]Iodobenzyl)guanidine (m-IBG, 2b) gave the best combination of high concentration and selectivity. The low adrenomedullary affinity observed with [14C]guanidine and m-[125I]iodobenzylamine demonstrates the uniqueness of the aralkylguanidine structure. Preliminary evidence suggests that 2b is a storage analogue of norepinephrine. [125I]2a is now being used clinically in imaging and radiotherapy of catecholamine tumors, such as pheochromocytoma.
[Show abstract][Hide abstract] ABSTRACT: [α-14C]-benzylguanidine (1) having a specific activity of 14 mCi/mmol was synthesized in 55% yield (isolated) by reacting [α-14C]-benzylamine hydrochloride and cyanamide in 1-butanol.