Evaluation in mice of some iodinated melanoma imaging agents using cryosectioning and multi-wire proportional counting.

AMBIS 4000, a multi-wire proportional counter, was calibrated for iodine-125 measurements. The detector displayed a linear response over a wide dynamic range. Using whole-body mice cryosections, a linear relationship could be established between count rate per area (cpm/mm2) measured with the AMBIS 4000 detector and the count rate per gram (dpm/g) determined with an NaI(Tl) scintillation detector. A calibration curve could, thus be constructed. This new method allowed direct visual and quantitative evaluation of the biodistribution of a short series of 125I-labelled benzamides in melanoma-bearing mice. All the compounds studied showed good tumoral targeting ability. For one of them, ortho-N-(2-diethylaminoethyl)-4-iodobenzamide, liver and lung uptake decreased rapidly after dosing, making it a suitable tracer for scintigraphic detection of malignant melanoma.