Radioiodine‐labelled alpha‐methyl‐tyrosine in malignant melanoma:cell culture studies and results in patients

Summary Tyrosine is a precursor of melanin synthesis and might thus present a valuable marker for melanoma. The aim of this study was to evaluate the uptake of alpha‐methyl‐tyrosine(AMT) in melanoma cell cultures and to assess its usefulness as a radiopharmaceutical for staging melanoma patients with whole‐body scintigraphy. Melanoma (M19‐cell lines) and fibroblast (negative control) cell cultures were incubated with 125 I‐AMT and the radioactive uptake in the cell lines was measured in a gamma‐counter over 24h. For in vivo studies, planar whole‐body scintigraphy and single photon emission computed tomography (SPECT) of the tumour region was performed following injection of 250–350 MBq 123 I‐AMT in six patients with known melanoma metastases. Findings were compared with results of whole‐body positron emission tomography using 18F‐fluorodeoxyglucose (FDG‐PET) as a standard of reference. Fibroblasts showed an unchanged uptake of (mean±SD)0.56±0.09% 15min and 0.066±0.09% 24h, respectively, after incubation of 125 I‐AMT, whereas there was an increased uptake in melanoma cell cultures over time from 0.9±0.05% to 7.5±1.6%. In staging melanoma patients, the sensitivity of whole‐body AMT‐scintigraphy compared with FDG‐PET was 37%(10 of 27 metastases). AMT is transported and metabolized to a high extent in melanoma cells and 123 I‐AMT is accumulated in melanoma metastases. Owing to its low sensitivity, however, the clinical use of whole‐body AMT scintigraphy cannot be recommended.