Selective 2-[18F]fluorodopa uptake for melanogenesis in murine metastatic melanomas

The relationship between 3,4-dihydroxy-2-[18F]fluoro-L-phenylalanine (2-[18F]FDOPA) uptake and melanogenesis was studied using mice bearing two B16 melanomas: B16-F1 has a higher melanin synthesis ability and a slower growing rate than the higher metastatic B16-F10. A significantly higher 2-[18F]FDOPA uptake by B16-F1 than by B16-F10 and a reverse relationship for the uptake of [14C] 2-deoxy-2-fluoro-D-glucose and [3H]thymidine were observed 1 hr postinjection. F1-to-F10 ratios of both the 2-[18F]FDOPA uptake and the acid-insoluble radioactivity increased to about 5 at 6 hr, which paralleled the melanin content. FM3A mammary carcinoma showed a 2-[18F]FDOPA uptake similar to the B16-F10 but without the acid-insoluble radioactivity. With D,L-DOPA loading, a 55% decreased uptake by FM3A 1 hr postinjection was significantly greater than the 20% reduction in both melanomas. O-Methylated 2-[18F]FDOPA was a predominant acid-soluble metabolite in all tumors. Whole-body autoradiography discriminated the two melanomas clearly. 2-[18F]FDOPA may be a promising tracer for the selective imaging of melanogenesis.