Detection of melanoma lesions using ¹³¹I-IMBA obtained by electrophilic substitution of ¹³¹I for metal organic substituent - a preliminary communication.

Background: Compounds of N-alkylated benzamide derivatives have been the subject of investigations in the last few decades from the standpoint of their possible application for scintigraphic detection of melanoma. Positive results have been observed in studies on biodistribution when using animal models and the compound IMBA (N-(2-diethylaminoethyl)-3-iodo-4-metoxybenzamide). The present study presents preliminary results of scintigraphic studies in patients with documented melanoma metastases, who were administered ¹³¹I-IMBA synthesized by modified labelling procedure (electrophilic substitution of radioactive ¹³¹I to metal organic substituent).

Material And Methods: The study was made in three patients with diagnosed melanoma metastases to tissues and organs. To each patient 111 MBq of ¹³¹I-IMBA was intravenously administered and whole body scintigraphy was performed 4 and 24 hours post injection of the radiopharmaceutical. Additionally, after 24 hours, SPECT/CT of selected regions of the body was performed.

Results: In 3 patients a total of 20 lesions of increased activity were found (15 were detected previously by other methods, 5 in the head, 4 in thorax, 2 in liver and spleen, 3 in abdomen and 6 in extremities). In the scintigrams performed 4 hours after ¹³¹I-IMBA administration, there were found 12 lesions of enhanced accumulation of the radiopharmaceutical. After 24 hours, due to reduction of background activity, there were 8 additional hot lesions detected. The mean activity tumour/background ratio for 20 lesions 4 hours post injection amounted to 1.51 ± 0.64, and the ratio increased to 2.94 ± 2.32 24 hours after administration of a radiopharmaceutical.

Conclusions: ¹³¹I-IMBA preparation, obtained by a modified labelling procedure, enabled detection of metastatic lesions in the patients. This may indicate that there is a possibility of using radioiodinated IMBA (with ¹²³I or ¹³¹I) for diagnosis of melanoma in humans. From our results it follows that scintigraphy should be performed 24 hours post injection. Further studies on diagnostic efficacy (sensitivity and specificity) of the method are necessary.