Potential radiopharmaceuticals for the detection of ocular melanoma. Part III. A study with 14C and 11C labelled tyrosine and dihydroxyphenylalanine

In order to investigate the possibility of using [1-11C] labelled 3,4-dihydroxyphenylalanine (DOPA) and tyrosine as radiopharmaceuticals for the detection of eye melanoma, the biodistributions of the same 1- and 3-14C-labelled compounds were investigated in Syrian golden hamsters with Greene melanoma. The results of these investigations were compared with positron emission tomography (PET) images of 11C labelled DOPA and tyrosine. The synthesis of these 11C labelled compounds procures of DL mixture, from which D and L forms can be separated. One h after intravenous injection, both 14C labelled DL-, L- and D-DOPA showed a high uptake in tumour tissue, that of DL- and D-DOPA being the highest. These high uptakes, together with relatively low uptake in bone, skin and eye resulted in high tumour/non tumour ratio (for DL-DOPA 5.9, 4.5 and 6.6 respectively). Extraction of the tumour tissue with trichloroacetic acid showed that L-DOPA was mainly incorporated into melanin, whereas D-DOPA was not. Also, the uptake 1 h after intravenous injection of 1-14C-L- and DL-tyrosine into the tumour were high, but L- and DL- were less different; tumour/non tumour ratios were favorable. PET images of the tumour obtained 40-80 min after injection of the [1-11C] labelled DOPA and tyrosine confirmed that melanoma detection was promising and that D-DOPA produced a better melanoma image than L-DOPA.