Tracers for imaging melanin with positron emission tomography

The melanin binding properties of six radioligands were determined in vivo in the eyes of pigmented mice. Binding in the eyes of nonpigmented mice was used to assess nonmelanin binding characteristics. Of these radioligands, ³H-N-methylspiperone showed the best uptake and gave the best signal-to- noise ratio at all time points examined. Its binding appeared essentially irreversible. A PET study with ¹¹C-N-methylspiperone was therefore carried out in a patient with a small ocular melanoma. Increased uptake of ¹¹C-N- methylspiperone was observed in the melanoma. Our studies indicate that PET and radiolabeled NMSP might be used for imaging melanin and for the detection of pigmented melanoma. These results suggest that with a high resolution PET camera it may be feasible to image the melanin-containing cells (dopaminergic neurons) of the substantia nigra in the central nervous system, which could be of interest for the study of Parkinson's disease.