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Structure Distribution Relationship of Iodine-123-Iodobenzamides as Tracers for the Detection of Melanotic Melanoma

Clinic for Nuclear Medicine, Westfälische Wilhelms-Universität Münster, Germany
Nuclear Chemistry and Radiopharmacy, Clinic for Nuclear Medicine, University of Essen, Germany

Correspondence: For correspondence or reprints contact: Wolfgang Brandau, PhD, Clinic for Nuclear Medicine, Westfälische Wilhelms-Universität Münster, Albert-Schweitzer-Straße 33, D-48129 Münster, Germany

ABSTRACT

The influence of systematic structure variations on the biodistribution of positional isomers of N-(N'-dialkylaminoethylene)-[¹²³I]iodobenzamide (ABA) derivatives in melanoma-bearing animals was investigated. Methods: Radioiodination of six bromo benzamide precursors was achieved by Cu(I)-assisted nonisotopic halogen exchange. Organ distribution, scintigraphic and metabolic studies were performed in nude mice bearing a human melanotic MM (SK-MEL 25). A patient suffering from melanotic melanoma underwent scintigraphy with a [¹²³I]iodobenzamide. Results: High radiochemical yields of 80%–95% and specific activities of >5 TBq/µmole were obtained. Animal studies revealed specific tumor uptake of all compounds with longest retention of the most lipophilic derivative p-[¹²³I]ABA 2–2. At shorter times, however, o-[¹²³I]ABA 2–2 exhibited the highest tumor uptake (8.9% ID/g, 1 hr p.i., 10.9% ID/g, 4 hr p.i.). Metabolization of o-[¹²³I]ABA 2–2, mainly to o-[¹²³I]iodohippuric acid (OIH), followed by fast renal excretion of the metabolites lead to tumor/nontumor ratios (T/NT) of >400 for tumor/blood, and >70 for tumor/liver at 48 h p.i. Unknown metastases could be localized in a patient using o-[¹²³I]ABA 2–2. Conclusion: The effects of the structure variation of iodobenzamides on their lipophilicity, metabolism and thus pharmacokinetics lead to the suggestion of o-[¹²³I]ABA 2–2 as a favorable melanoma imaging agent.

Key Words: melanoma • tumor imaging • iodine-123-iodobenzamides • nonisotopic exchange

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