Biodistribution of two (131)I-IMBA preparations, differently labelled, in mice with experimental B16 melanoma tumours

Numerous reports indicate that some iodinated compounds of benzamide derivatives display a strong affinity to the cells of melanoma. In the present report, a compound [N-(2-diethylaminoethyl)-3-iodo-4metyoxybenzamide ((131)I-IMBA)] has been prepared by two different labelling methods. Biodistribution of the injected compound was followed in mice with experimentally induced B16 melanoma tumours, and tumour/ tissue ratios were studied as a function of time post administration.

The iodinated (131)I-IMBA was obtained by means of (131)I exchange for nonradioactive iodine atoms (method I) and by means of (131)I substitution for a metalorganic group (method II). The last preparation was purified by chloroform extraction. The chemical purity was assessed by means of ascending thin layer chromatography (TLC). The biodistribution of (131)I-IMBA in C57 Black mice was studied in animals with experimentally induced B16 mice melanoma tumours.

The mean labelling efficiency exceeded 95 and 80 % for methods I and II, respectively, at radiochemical purity > 95% in both cases. (131)I-IMBA was vividly cumulated by melanoma tumours in mice. At 24-hours post (131)I-IMBA administration the values of tumour /non-tumour ratios for the compound labelled by method II reached the following values: tumour/liver 10 +/- 3, tumour/lung 15 +/- 12, tumour/blood 153 +/- 39, tumour/intestines 176 +/- 26, tumour/kidneys 270 +/- 107, and tumour/muscle 448 +/- 82. These values exceeded, by an order of magnitude, the corresponding ratios for the same compound labelled by method I.

High values of tumour/non-tumour ratios indicate that (131)I-IMBA could be a promising radiopharmaceutical for clinical diagnosis (staging) of melanomas in humans.